Applicability of pulse pressure variation: how many shades of grey?

Intra-operative haemodynamic monitoring and management of adults having noncardiac surgery: A statement from the European Society of Anaesthesiology and Intensive Care

This article was developed by a diverse group of 25 international experts from the European Society of Anaesthesiology and Intensive Care (ESAIC), who formulated recommendations on intra-operative haemodynamic monitoring and management of adults having noncardiac surgery based on a review of the current evidence. We recommend basing intra-operative arterial pressure management on mean arterial pressure and keeping intra-operative mean arterial pressure above 60 mmHg. We further recommend identifying the underlying causes of intra-operative hypotension and addressing them appropriately. We suggest pragmatically treating bradycardia or tachycardia when it leads to profound hypotension or likely results in reduced cardiac output, oxygen delivery or organ perfusion. We suggest monitoring stroke volume or cardiac output in patients with high baseline risk for complications or in patients having high-risk surgery to assess the haemodynamic status and the haemodynamic response to therapeutic interventions. However, we recommend not routinely maximising stroke volume or cardiac output in patients having noncardiac surgery. Instead, we suggest defining stroke volume and cardiac output targets individually for each patient considering the clinical situation and clinical and metabolic signs of tissue perfusion and oxygenation. We recommend not giving fluids simply because a patient is fluid responsive but only if there are clinical or metabolic signs of hypovolaemia or tissue hypoperfusion. We suggest monitoring and optimising the depth of anaesthesia to titrate doses of anaesthetic drugs and reduce their side effects.

Context-specific clinical applicability of the end-expiratory occlusion test to predict fluid responsiveness in mechanically ventilated patients: A systematic review and meta-analysis

BACKGROUND

The emergence of context-specific clinical evidence from the end-expiratory occlusion test (EEOT) may change the perception of its operative performance to predict fluid responsiveness.

OBJECTIVES

Assessment of predictive performance of the EEOT in the intensive care unit (ICU) and operating room.

DESIGN

Systematic review of observational diagnostic test accuracy studies with meta-analysis.

DATA SOURCES

MEDLINE, Embase and Scopus were used as data sources for relevant publications until February 2024.

ELIGIBILITY CRITERIA

Prospective clinical studies in which the EEOT was used to predict fluid responsiveness in mechanically ventilated adults, regardless of the clinical care context. The operative performance characteristics must also have been reported.

RESULTS

Twenty-four studies involving 1073 adult patients (588 receiving intensive care and 485 in the operating room) were systematically reviewed, and 22 studies comprising 1049 volume expansions were meta-analysed. The pooled sensitivity [95% confidence interval (CI)] of the EEOT was 0.87 (0.81 to 0.92), and the pooled specificity was 0.90 (0.85 to 0.94); the median [interquartile range] cardiac index (CI) threshold for a positive test was a 5.0 [3.3 to 5.3] increase. The clinical context, the method used for haemodynamic monitoring, the ratio of the averaging time of the monitoring method to the occlusion time and the levels of positive end-expiratory pressure were identified as significant sources of heterogeneity. However, the occlusion duration, choice of cardiac output marker and tidal volume did not significantly affect its performance. A novel insight is that performance was notably lower in the operating room setting. The likelihood ratios were 14 (positive) and 0.12 (negative) for the ICU, both better than 3.1 and 0.21 for the operating room. The overall quality of the evidence was assessed to be very low, mainly due to high heterogeneity and risk of bias; however, no publication bias was detected.

CONCLUSION

The EEOT for predicting fluid responsiveness in critical care performs acceptably well overall and is a confirmative test. In the operating room and/or with specific technical settings, its performance and clinical utility are reduced, driving the need for more context-specific and patient-specific fluid responsiveness assessments.

Changes in pulse pressure variation induced by passive leg raising test to predict preload responsiveness in mechanically ventilated patients with low tidal volume in ICU: a systematic review and meta-analysis

BACKGROUND

Pulse pressure variation (PPV) is limited in low tidal volume mechanical ventilation. We conducted this systematic review and meta-analysis to evaluate whether passive leg raising (PLR)-induced changes in PPV can reliably predict preload/fluid responsiveness in mechanically ventilated patients with low tidal volume in the intensive care unit.

METHODS

PubMed, Embase, and Cochrane databases were screened for diagnostic research relevant to the predictability of PPV change after PLR in low-tidal volume mechanically ventilated patients. The QUADAS-2 scale was used to assess the risk of bias of the included studies. In-between study heterogeneity was assessed through the I2 indicator. Publication bias was assessed by the Deeks' funnel plot asymmetry test. Summary receiving operating characteristic curve (SROC), pooled sensitivity, and specificity were calculated.

RESULTS

Five studies with a total of 474 patients were included in this meta-analysis. The SROC of the absolute PPV change resulted in an area under the curve of 0.91 (95% CI 0.88-0.93), with overall pooled sensitivity and specificity of 0.88 (95% CI 0.82-0.91) and 0.83 (95% CI 0.76-0.89), respectively. The diagnostic odds ratio was 35 (95% CI 19-67). The mean and median cutoff values of PLR-induced absolute change in absolute PPV were both -2 points and ranged from -2.5 to -1 points. Overall, there was no significant heterogeneity with I2 = 0%. There was no significant publication bias. Fagan's nomogram showed that with a pre-test probability of 50%, the post-test probability reached 84% and 17% for the positive and negative tests, respectively.

CONCLUSIONS

PLR-induced change in absolute PPV has good diagnostic performance in predicting preload/fluid responsiveness in ICU patients on mechanical ventilation with low tidal volume. Trial registration PROSPERO (CRD42024496901). Registered on 15 January 2024.

Management of adult sepsis in resource-limited settings: global expert consensus statements using a Delphi method

PURPOSE

To generate consensus and provide expert clinical practice statements for the management of adult sepsis in resource-limited settings.

METHODS

An international multidisciplinary Steering Committee with expertise in sepsis management and including a Delphi methodologist was convened by the Asia Pacific Sepsis Alliance (APSA). The committee selected an international panel of clinicians and researchers with expertise in sepsis management. A Delphi process based on an iterative approach was used to obtain the final consensus statements.

RESULTS

A stable consensus was achieved for 30 (94%) of the statements by 41 experts after four survey rounds. These include consensus on managing patients with sepsis outside a designated critical care area, triggers for escalating clinical management and criteria for safe transfer to another facility. The experts agreed on the following: in the absence of serum lactate, clinical parameters such as altered mental status, capillary refill time and urine output may be used to guide resuscitation; special considerations regarding the volume of fluid used for resuscitation, especially in tropical infections, including the use of simple tests to assess fluid responsiveness when facilities for advanced hemodynamic monitoring are limited; use of Ringer's lactate or Hartmann's solution as balanced salt solutions; epinephrine when norepinephrine or vasopressin are unavailable; and the administration of vasopressors via a peripheral vein if central venous access is unavailable or not feasible. Similarly, where facilities for investigation are unavailable, there was consensus for empirical antimicrobial administration without delay when sepsis was strongly suspected, as was the empirical use of antiparasitic agents in patients with suspicion of parasitic infections.

CONCLUSION

Using a Delphi method, international experts reached consensus to generate expert clinical practice statements providing guidance to clinicians worldwide on the management of sepsis in resource-limited settings. These statements complement existing guidelines where evidence is lacking and add relevant aspects of sepsis management that are not addressed by current international guidelines. Future studies are needed to assess the effects of these practice statements and address remaining uncertainties.

Predictive value of trendelenburg position and carotid ultrasound for fluid responsiveness in patients on VV-ECMO with acute respiratory distress syndrome in the prone position

Fluid administration is widely used to treat hypotension in patients undergoing veno-venous extracorporeal membrane oxygenation (VV-ECMO). However, excessive fluid administration may lead to fluid overload can aggravate acute respiratory distress syndrome (ARDS) and increase patient mortality, predicting fluid responsiveness is of great significance for VV-ECMO patients. This prospective single-center study was conducted in a medical intensive care unit (ICU) and finally included 51 VV-ECMO patients with ARDS in the prone position (PP). Stroke volume index variation (ΔSVI), pulse pressure variation (PPV), stroke volume variation (SVV), baseline carotid corrected flow time (FTcBaseline), and respirophasic variation in carotid artery blood flow peak velocity (ΔVpeakCA) were taken before and after the Trendelenburg position or volume expansion. Fluid responsiveness was defined as a 15% or more increase in stroke volume index as assessed by transthoracic echocardiography after the volume expansion (VE). In our study, 33 patients (64.7%) were identified as fluid responders. Stroke volume index variation induced by the Trendelenburg position (ΔSVITrend), FTcBaseline, and ΔVpeakCA demonstrated superior predictive performance of fluid responsiveness. ΔSVITrend had an AUC of 0.89 (95% CI, 0.80-0.98) with an optimal threshold of 14.5% (95% CI, 12.5-21.5%), with the sensitivity and specificity were 82% (95% CI, 66-91%) and 83% (95% CI, 61-94%). FTcBaseline had an AUC of 0.87 (95% CI, 0.76-0.98) with an optimal threshold of 332ms (95% CI, 318-335ms), the sensitivity and specificity were 85% (95% CI, 69-93%) and 83% (95% CI, 61-94%), respectively. ΔVpeakCA showed an AUC of 0.83 (95% CI, 72-95), with a 10% optimal threshold (95% CI, 9-13%), sensitivity was 82% (95% CI, 66-91%) and specificity 78% (95% CI, 55-91%). ΔSVITrend, FTcBaseline and ΔVpeakCA could effectively predict fluid responsiveness in VV-ECMO patients with ARDS in the PP. Compared to ΔSVITrend and ΔVpeakCA, FTcBaseline is easier and more direct to acquire, and it does not require Trendelenburg position or VE, making it a more accessible and efficient option for assessing fluid responsiveness.

Restrictive versus Decision Support Guided Fluid Therapy during Major Hepatic Resection Surgery: A Randomized Controlled Trial

BACKGROUND

Fluid therapy during major hepatic resection aims at minimizing fluids during the dissection phase to reduce central venous pressure, retrograde liver blood flow, and venous bleeding. This strategy, however, may lead to hyperlactatemia. The Acumen assisted fluid management system uses novel decision support software, the algorithm of which helps clinicians optimize fluid therapy. The study tested the hypothesis that using this decision support system could decrease arterial lactate at the end of major hepatic resection when compared to a more restrictive fluid strategy.

METHODS

This two-arm, prospective, randomized controlled, assessor- and patient-blinded superiority study included consecutive patients undergoing major liver surgery equipped with an arterial catheter linked to an uncalibrated stroke volume monitor. In the decision support group, fluid therapy was guided throughout the entire procedure using the assisted fluid management software. In the restrictive fluid group, clinicians were recommended to restrict fluid infusion to 1 to 2 ml · kg-1 · h-1 until the completion of hepatectomy. They then administered fluids based on advanced hemodynamic variables. Noradrenaline was titrated in all patients to maintain a mean arterial pressure greater than 65 mmHg. The primary outcome was arterial lactate level upon completion of surgery (i.e., skin closure).

RESULTS

A total of 90 patients were enrolled over a 7-month period. The primary outcome was lower in the decision support group than in the restrictive group (median [quartile 1 to quartile 3], 2.5 [1.9 to 3.7] mmol · l-1vs. 4.6 [3.1 to 5.4] mmol · l-1; median difference, -2.1; 95% CI, -2.7 to -1.2; P < 0.001). Among secondary exploratory outcomes, there was no difference in blood loss (median [quartile 1 to quartile 3], 450 [300 to 600] ml vs. 500 [300 to 800] ml; P = 0.727), although central venous pressure was higher in the decision support group (mean ± SD of 7.7 ± 2.0 mmHg vs. 6.6 ± 1.1 mmHg; P < 0.002).

CONCLUSIONS

Patients managed using a clinical decision support system to guide fluid administration during major hepatic resection had a lower arterial lactate concentration at the end of surgery when compared to a more restrictive fluid strategy. Future trials are necessary to make conclusive recommendations that will change clinical practice.

EDITOR’S PERSPECTIVE

Mistaken Identity: Misidentification of Other Vascular Structures as the Inferior Vena Cava and How to Avoid It

While point-of-care ultrasound (POCUS) of the inferior vena cava (IVC) is broadly perceived as having value in intravascular volume status assessment, this has not been borne out in large-scale meta-analyses containing heterogenous populations of acutely ill patients. While the limitations of IVC POCUS could be largely due to the complexity of the relationship between IVC appearance and volume status, another confounder not widely appreciated is the ease with which the aorta or right hepatic vein (RHV) can be mistaken for the IVC. While misidentification of the aorta as the IVC has been recognized elsewhere, misidentification of the RHV for the IVC has not and, in our experience, occurs frequently, even in the hands of experienced sonographers. We demonstrate how these errors occur and provide guidance on how to systematically avoid them.

Intraoperative haemodynamic monitoring and management of adults having non-cardiac surgery: Guidelines of the German Society of Anaesthesiology and Intensive Care Medicine in collaboration with the German Association of the Scientific Medical Societies

Haemodynamic monitoring and management are cornerstones of perioperative care. The goal of haemodynamic management is to maintain organ function by ensuring adequate perfusion pressure, blood flow, and oxygen delivery. We here present guidelines on "Intraoperative haemodynamic monitoring and management of adults having non-cardiac surgery" that were prepared by 18 experts on behalf of the German Society of Anaesthesiology and Intensive Care Medicine (Deutsche Gesellschaft für Anästhesiologie und lntensivmedizin; DGAI).

Heart-Lungs interactions: the basics and clinical implications

Heart-lungs interactions are related to the interplay between the cardiovascular and the respiratory system. They result from the respiratory-induced changes in intrathoracic pressure, which are transmitted to the cardiac cavities and to the changes in alveolar pressure, which may impact the lung microvessels. In spontaneously breathing patients, consequences of heart-lungs interactions are during inspiration an increase in right ventricular preload and afterload, a decrease in left ventricular preload and an increase in left ventricular afterload. In mechanically ventilated patients, consequences of heart-lungs interactions are during mechanical insufflation a decrease in right ventricular preload, an increase in right ventricular afterload, an increase in left ventricular preload and a decrease in left ventricular afterload. Physiologically and during normal breathing, heart-lungs interactions do not lead to significant hemodynamic consequences. Nevertheless, in some clinical settings such as acute exacerbation of chronic obstructive pulmonary disease, acute left heart failure or acute respiratory distress syndrome, heart-lungs interactions may lead to significant hemodynamic consequences. These are linked to complex pathophysiological mechanisms, including a marked inspiratory negativity of intrathoracic pressure, a marked inspiratory increase in transpulmonary pressure and an increase in intra-abdominal pressure. The most recent application of heart-lungs interactions is the prediction of fluid responsiveness in mechanically ventilated patients. The first test to be developed using heart-lungs interactions was the respiratory variation of pulse pressure. Subsequently, many other dynamic fluid responsiveness tests using heart-lungs interactions have been developed, such as the respiratory variations of pulse contour-based stroke volume or the respiratory variations of the inferior or superior vena cava diameters. All these tests share the same limitations, the most frequent being low tidal volume ventilation, persistent spontaneous breathing activity and cardiac arrhythmia. Nevertheless, when their main limitations are properly addressed, all these tests can help intensivists in the decision-making process regarding fluid administration and fluid removal in critically ill patients.

Cardiac index-guided therapy to maintain optimised postinduction cardiac index in high-risk patients having major open abdominal surgery: the multicentre randomised iPEGASUS trial

BACKGROUND

It is unclear whether optimising intraoperative cardiac index can reduce postoperative complications. We tested the hypothesis that maintaining optimised postinduction cardiac index during and for the first 8 h after surgery reduces the incidence of a composite outcome of complications within 28 days after surgery compared with routine care in high-risk patients having elective major open abdominal surgery.

METHODS

In three German and two Spanish centres, high-risk patients having elective major open abdominal surgery were randomised to cardiac index-guided therapy to maintain optimised postinduction cardiac index (cardiac index at which pulse pressure variation was <12%) during and for the first 8 h after surgery using intravenous fluids and dobutamine or to routine care. The primary outcome was the incidence of a composite outcome of moderate or severe complications within 28 days after surgery.

RESULTS

We analysed 318 of 380 enrolled subjects. The composite primary outcome occurred in 84 of 152 subjects (55%) assigned to cardiac index-guided therapy and in 77 of 166 subjects (46%) assigned to routine care (odds ratio: 1.87, 95% confidence interval: 1.03-3.39, P=0.038). Per-protocol analyses confirmed the results of the primary outcome analysis.

CONCLUSIONS

Maintaining optimised postinduction cardiac index during and for the first 8 h after surgery did not reduce, and possibly increased, the incidence of a composite outcome of complications within 28 days after surgery compared with routine care in high-risk patients having elective major open abdominal surgery. Clinicians should not strive to maintain optimised postinduction cardiac index during and after surgery in expectation of reducing complications.

CLINICAL TRIAL REGISTRATION

NCT03021525.

Dynamic parameters of fluid responsiveness in the operating room : An analysis of intraoperative ventilation framework conditions

BACKGROUND

Reliable assessment of fluid responsiveness with pulse pressure variation (PPV) depends on certain ventilation-related preconditions; however, some of these requirements are in contrast with recommendations for protective ventilation.

OBJECTIVE

The aim of this study was to evaluate the applicability of PPV in patients undergoing non-cardiac surgery by retrospectively analyzing intraoperative ventilation data.

MATERIAL AND METHODS

Intraoperative ventilation data from three large medical centers in Germany and Switzerland from January to December 2018 were extracted from electronic patient records and pseudonymized; 10,334 complete data sets were analyzed with respect to the ventilation parameters set as well as demographic and medical data.

RESULTS

In 6.3% of the 3398 included anesthesia records, patients were ventilated with mean tidal volumes (mTV) > 8 ml/kg predicted body weight (PBW). These would qualify for PPV-based hemodynamic assessment, but the majority were ventilated with lower mTVs. In patients who underwent abdominal surgery (75.5% of analyzed cases), mTVs > 8 ml/kg PBW were used in 5.5% of cases, which did not differ between laparoscopic (44.9%) and open (55.1%) approaches. Other obstacles to the use of PPV, such as elevated positive end-expiratory pressure (PEEP) or increased respiratory rate, were also identified. Of all the cases 6.0% were ventilated with a mTV of > 8 ml/kg PBW and a PEEP of 5-10 cmH2O and 0.3% were ventilated with a mTV > 8 ml/kg PBW and a PEEP of > 10 cmH2O.

CONCLUSION

The data suggest that only few patients meet the currently defined TV (of > 8 ml/kg PBW) for assessment of fluid responsiveness using PPV during surgery.

Major liver resections, perioperative issues and posthepatectomy liver failure: A comprehensive update for the anesthesiologist

Significant advances in surgical techniques and relevant medium- and long-term outcomes over the past two decades have led to a substantial expansion in the indications for major liver resections. To support these outstanding results and to reduce perioperative complications, anesthesiologists must address and master key perioperative issues (preoperative assessment, proactive intraoperative anesthesia strategies, and implementation of the Enhanced Recovery After Surgery approach). Intensive care unit monitoring immediately following liver surgery remains a subject of active and often unresolved debate. Among postoperative complications, posthepatectomy liver failure (PHLF) occurs in different grades of severity (A-C) and frequency (9%-30%), and it is the main cause of 90-d postoperative mortality. PHLF, recently redefined with pragmatic clinical criteria and perioperative scores, can be predicted, prevented, or anticipated. This review highlights: (1) The systemic consequences of surgical manipulations anesthesiologists must respond to or prevent, to positively impact PHLF (a proactive approach); and (2) the maximal intensive treatment of PHLF, including artificial options, mainly based, so far, on Acute Liver Failure treatment(s), to buy time waiting for the recovery of the native liver or, when appropriate and in very selected cases, toward liver transplant. Such a clinical context requires a strong commitment to surgeons, anesthesiologists, and intensivists to work together, for a fruitful collaboration in a mandatory clinical continuum.

Haemodynamic monitoring during noncardiac surgery: past, present, and future

During surgery, various haemodynamic variables are monitored and optimised to maintain organ perfusion pressure and oxygen delivery - and to eventually improve outcomes. Important haemodynamic variables that provide an understanding of most pathophysiologic haemodynamic conditions during surgery include heart rate, arterial pressure, central venous pressure, pulse pressure variation/stroke volume variation, stroke volume, and cardiac output. A basic physiologic and pathophysiologic understanding of these haemodynamic variables and the corresponding monitoring methods is essential. We therefore revisit the pathophysiologic rationale for intraoperative monitoring of haemodynamic variables, describe the history, current use, and future technological developments of monitoring methods, and finally briefly summarise the evidence that haemodynamic management can improve patient-centred outcomes.

Use of stepwise lung recruitment maneuver to predict fluid responsiveness under lung protective ventilation in the operating room

Recent research has revealed that hemodynamic changes caused by lung recruitment maneuvers (LRM) with continuous positive airway pressure can be used to identify fluid responders. We investigated the usefulness of stepwise LRM with increasing positive end-expiratory pressure and constant driving pressure for predicting fluid responsiveness in patients under lung protective ventilation (LPV). Forty-one patients under LPV were enrolled when PPV values were in a priori considered gray zone (4% to 17%). The FloTrac-Vigileo device measured stroke volume variation (SVV) and stroke volume (SV), while the patient monitor measured pulse pressure variation (PPV) before and at the end of stepwise LRM and before and 5 min after fluid challenge (6 ml/kg). Fluid responsiveness was defined as a ≥ 15% increase in the SV or SV index. Seventeen were fluid responders. The areas under the curve for the augmented values of PPV and SVV, as well as the decrease in SV by stepwise LRM to identify fluid responders, were 0.76 (95% confidence interval, 0.61-0.88), 0.78 (0.62-0.89), and 0.69 (0.53-0.82), respectively. The optimal cut-offs for the augmented values of PPV and SVV were > 18% and > 13%, respectively. Stepwise LRM -generated augmented PPV and SVV predicted fluid responsiveness under LPV.

Recent advances in cardiorespiratory monitoring in acute respiratory distress syndrome patients

BACKGROUND

Recent advances on cardiorespiratory monitoring applied in ARDS patients undergoing invasive mechanical ventilation and noninvasive ventilatory support are available in the literature and may have potential prognostic implication in ARDS treatment.

MAIN BODY

The measurement of oxygen saturation by pulse oximetry is a valid, low-cost, noninvasive alternative for assessing arterial oxygenation. Caution must be taken in patients with darker skin pigmentation, who may experience a greater incidence of occult hypoxemia. Dead space surrogates, which are easy to calculate, have important prognostic implications. The mechanical power, which can be automatically computed by intensive care ventilators, is an important parameter correlated with ventilator-induced lung injury and outcome. In patients undergoing noninvasive ventilatory support, the use of esophageal pressure can measure inspiratory effort, avoiding possible delays in endotracheal intubation. Fluid responsiveness can also be evaluated using dynamic indices in patients ventilated at low tidal volumes (< 8 mL/kg). In patients ventilated at high levels of positive end expiratory pressure (PEEP), the PEEP test represents a valid alternative to passive leg raising. There is growing evidence on alternative parameters for evaluating fluid responsiveness, such as central venous oxygen saturation variations, inferior vena cava diameter variations and capillary refill time.

CONCLUSION

Careful cardiorespiratory monitoring in patients affected by ARDS is crucial to improve prognosis and to tailor treatment via mechanical ventilatory support.

Closed-loop anesthesia: foundations and applications in contemporary perioperative medicine

A closed-loop automatically controls a variable using the principle of feedback. Automation within anesthesia typically aims to improve the stability of a controlled variable and reduce workload associated with simple repetitive tasks. This approach attempts to limit errors due to distractions or fatigue while simultaneously increasing compliance to evidence based perioperative protocols. The ultimate goal is to use these advantages over manual care to improve patient outcome. For more than twenty years, clinical studies in anesthesia have demonstrated the superiority of closed-loop systems compared to manual control for stabilizing a single variable, reducing practitioner workload, and safely administering therapies. This research has focused on various closed-loops that coupled inputs and outputs such as the processed electroencephalogram with propofol, blood pressure with vasopressors, and dynamic predictors of fluid responsiveness with fluid therapy. Recently, multiple simultaneous independent closed-loop systems have been tested in practice and one study has demonstrated a clinical benefit on postoperative cognitive dysfunction. Despite their advantages, these tools still require that a well-trained practitioner maintains situation awareness, understands how closed-loop systems react to each variable, and is ready to retake control if the closed-loop systems fail. In the future, multiple input multiple output closed-loop systems will control anesthetic, fluid and vasopressor titration and may perhaps integrate other key systems, such as the anesthesia machine. Human supervision will nonetheless always be indispensable as situation awareness, communication, and prediction of events remain irreplaceable human factors.

Measurement error of pulse pressure variation

Dynamic preload parameters are used to guide perioperative fluid management. However, reported cut-off values vary and the presence of a gray zone complicates clinical decision making. Measurement error, intrinsic to the calculation of pulse pressure variation (PPV) has not been studied but could contribute to this level of uncertainty. The purpose of this study was to quantify and compare measurement errors associated with PPV calculations. Hemodynamic data of patients undergoing liver transplantation were extracted from the open-access VitalDatabase. Three algorithms were applied to calculate PPV based on 1 min observation periods. For each method, different durations of sampling periods were assessed. Best Linear Unbiased Prediction was determined as the reference PPV-value for each observation period. A Bayesian model was used to determine bias and precision of each method and to simulate the uncertainty of measured PPV-values. All methods were associated with measurement error. The range of differential and proportional bias were [- 0.04%, 1.64%] and [0.92%, 1.17%] respectively. Heteroscedasticity influenced by sampling period was detected in all methods. This resulted in a predicted range of reference PPV-values for a measured PPV of 12% of [10.2%, 13.9%] and [10.3%, 15.1%] for two selected methods. The predicted range in reference PPV-value changes for a measured absolute change of 1% was [- 1.3%, 3.3%] and [- 1.9%, 4%] for these two methods. We showed that all methods that calculate PPV come with varying degrees of uncertainty. Accounting for bias and precision may have important implications for the interpretation of measured PPV-values or PPV-changes.

CAROTID ARTERY ULTRASOUND FOR ASSESSING FLUID RESPONSIVENESS IN PATIENTS UNDERGOING MECHANICAL VENTILATION WITH LOW TIDAL VOLUME AND PRESERVED SPONTANEOUS BREATHING

ABSTRACT

Objective : This study aimed to investigate whether changes in carotid artery corrected flow time (ΔFTc bolus ) and carotid artery peak flow velocity respiratory variation (Δ V peak bolus ) induced by the fluid challenge could reliably predict fluid responsiveness in mechanically ventilated patients with a tidal volume < 8 mL/kg Predicted Body Weight while preserving spontaneous breathing. Methods : Carotid artery corrected flow time, Δ V peak, and hemodynamic data were measured before and after administration of 250 mL crystalloids. Fluid responsiveness was defined as a 10% or more increase in stroke volume index as assessed by noninvasive cardiac output monitoring after the fluid challenge. Results : A total of 43 patients with acute circulatory failure were enrolled in this study. Forty-three patients underwent a total of 60 fluid challenges. The ΔFTc bolus and Δ V peak bolus showed a significant difference between the fluid responsiveness positive group (n = 35) and the fluid responsiveness negative group (n = 25). Spearman correlation test showed that ΔFTc bolus and Δ V peak bolus with the relative increase in stroke volume index after fluid expansion ( r = 0.5296, P < 0.0001; r = 0.3175, P = 0.0135). Multiple logistic regression analysis demonstrated that ΔFTc bolus and Δ V peak bolus were significantly correlated with fluid responsiveness in patients with acute circulatory failure. The areas under the receiver operating characteristic curves of ΔFTc bolus and Δ V peak bolus for predicting fluid responsiveness were 0.935 and 0.750, respectively. The optimal cutoff values of ΔFTc bolus and Δ V peak bolus were 0.725 (sensitivity = 97.1%, specificity = 84%) and 4.21% (sensitivity = 65.7%, specificity = 80%), respectively. Conclusion : In mechanically ventilated patients with a tidal volume < 8 mL/kg while preserving spontaneous breathing, ΔFTc bolus and Δ V peak bolus could predict fluid responsiveness. The predictive performance of ΔFTc bolus was superior to Δ V peak bolus .

Improving perioperative care in low-resource settings with goal-directed therapy: a narrative review

Perioperative Goal-Directed Therapy (PGDT) has significantly showed to decrease complications and risk of death in high-risk patients according to numerous meta-analyses. The main goal of PGDT is to individualize the therapy with fluids, inotropes, and vasopressors, during and after surgery, according to patients' needs in order to prevent organic dysfunction development. In this opinion paper we aimed to focus a discussion on possible alternatives to invasive hemodynamic monitoring in low resource settings.

The effects of respiratory rate and tidal volume on pulse pressure variation in healthy lungs-a generalized additive model approach may help overcome limitations

Pulse pressure variation (PPV) is a well-established method for predicting fluid responsiveness in mechanically ventilated patients. The predictive accuracy is, however, disputed for ventilation with low tidal volume (VT) or low heart-rate-to-respiratory-rate ratio (HR/RR). We investigated the effects of VT and RR on PPV and on PPV's ability to predict fluid responsiveness. We included patients scheduled for open abdominal surgery. Prior to a 250 ml fluid bolus, we ventilated patients with combinations of VT from 4 to 10 ml kg-1 and RR from 10 to 31 min-1. For each of 10 RR-VT combinations, PPV was derived using both a classic approach and a generalized additive model (GAM) approach. The stroke volume (SV) response to fluid was evaluated using uncalibrated pulse contour analysis. An SV increase > 10% defined fluid responsiveness. Fifty of 52 included patients received a fluid bolus. Ten were fluid responders. For all ventilator settings, fluid responsiveness prediction with PPV was inconclusive with point estimates for the area under the receiver operating characteristics curve between 0.62 and 0.82. Both PPV measures were nearly proportional to VT. Higher RR was associated with lower PPV. Classically derived PPV was affected more by RR than GAM-derived PPV. Correcting PPV for VT could improve PPV's predictive utility. Low HR/RR has limited effect on GAM-derived PPV, indicating that the low HR/RR limitation is related to how PPV is calculated. We did not demonstrate any benefit of GAM-derived PPV in predicting fluid responsiveness.Trial registration: ClinicalTrials.gov, reg. March 6, 2020, NCT04298931.

Correlation coefficient between plethysmographic variability index and Systolic Pressure Variation as an indicator for fluid responsiveness in hypotensive patients in the ICU/OT

Background

Prediction of fluid responsiveness in hypotensive patients is a challenge. The correlation between a novel noninvasive dynamic indicator, Pleth Variability Index (PVI ®), and a gold-standard Systolic Pressure Variation (SPV) as a measure of fluid responsiveness was assessed in the Intensive Care Unit (ICU) or Operation Theatre (OT) in a tertiary care hospital.

Methods

A prospective experimental study was conducted over a span of one year on 100 mechanically ventilated patients with hypotension. Vital parameters along with SPV and PVI ® were recorded before and after a standard volume expansion protocol. A 10% SPV threshold was used to define fluid responders and nonresponders.

Results

Pearson's correlation graph at baseline showed positive correlation between PVI ® and SPV (r = 0.59, p-value = 0.001). Strength of correlation was comparatively less but still showed positive correlation at 15 (r = 0.39, p-value = 0.009) and 30 (r = 0.404, p-value = 0.004) minutes of fluid bolus. The Bland Altman analysis of baseline values of PVI ® and SPV showed good agreement with a mean bias of 9.05. Percentage change of PVI ® and SPV over 30 min showed a statistically significant positive correlation in the responder group (r = 0.53, p < 0.05). A threshold value of PVI ® more than 18% before volume expansion differentiated fluid responders and nonresponders with a sensitivity of 75% and specificity of 67%, with an area under Receiver Operating Characteristic (ROC) of 0.78.

Conclusion

A positive correlation exists between SPV and PVI ®, justifying the use of noninvasive PVI ® in a clinical setting of hypotension.

Stroke volume variation and dynamic arterial elastance predict fluid responsiveness even in thoracoscopic esophagectomy: a prospective observational study

PURPOSE

It remains unknown whether stroke volume variation (SVV), pulse pressure variation (PPV), and dynamic arterial elastance (Eadyn) are suitable for monitoring fluid management during thoracoscopic esophagectomy (TE) in the prone position with one-lung ventilation and artificial pneumothorax. Our study aimed to evaluate the accuracy of SVV, PVV, and Eadyn in predicting the fluid responsiveness in these patients.

METHODS

We recruited 24 patients who had undergone TE. Patients with a mean arterial blood pressure ≤ 65 mmHg received a 200-ml bolus of 6% hydroxyethyl starch over 10 min. Fluid responders showed the stroke volume index ≥ 15% 5 min after the fluid bolus. Receiver operating characteristic (ROC) curves were generated and area under the ROC curve (AUROC) was calculated.

RESULTS

We obtained 61 fluid bolus data points, of which 20 were responders and 41 were non-responders. The median SVV before the fluid bolus in responders was significantly higher than that in non-responders (18% [interquartile range (IQR) 13-21] vs. 12% [IQR 8-15], P = 0.001). Eadyn was significantly lower in responders than in non-responders (0.55 [IQR 0.45-0.78] vs. 0.91 [IQR 0.67-1.00], P < 0.001). There was no difference in the PPV between the groups. The AUROC was 0.76 for SVV (95% confidence interval [CI] 0.62-0.89, P = 0.001), 0.56 for PPV (95% CI 0.41-0.71, P = 0.44), and 0.82 for Eadyn (95% CI 0.69-0.95, P < 0.001).

CONCLUSIONS

SVV and Eadyn are reliable parameters for predicting fluid responsiveness in patients undergoing TE.

Respiratory variation in the internal jugular vein does not predict fluid responsiveness in the prone position during adolescent idiopathic scoliosis surgery: a prospective cohort study

BACKGROUND

Respiratory variation in the internal jugular vein (IJVV) has not shown promising results in predicting volume responsiveness in ventilated patients with low tidal volume (Vt) in prone position. We aimed to determine whether the baseline respiratory variation in the IJVV value measured by ultrasound might predict fluid responsiveness in patients with adolescent idiopathic scoliosis (AIS) undergoing posterior spinal fusion (PSF) with low Vt.

METHODS

According to the fluid responsiveness results, the included patients were divided into two groups: those who responded to volume expansion, denoted the responder group, and those who did not respond, denoted the non-responder group. The primary outcome was determination of the value of baseline IJVV in predicting fluid responsiveness (≥15% increases in stroke volume index (SVI) after 7 ml·kg-1 colloid administration) in patients with AIS undergoing PSF during low Vt ventilation. Secondary outcomes were estimation of the diagnostic performance of pulse pressure variation (PPV), stroke volume variation (SVV), and the combination of IJVV and PPV in predicting fluid responsiveness in this surgical setting. The ability of each parameter to predict fluid responsiveness was assessed using a receiver operating characteristic curve.

RESULTS

Fifty-six patients were included, 36 (64.29%) of whom were deemed fluid responsive. No significant difference in baseline IJVV was found between responders and non-responders (25.89% vs. 23.66%, p = 0.73), and no correlation was detected between baseline IJVV and the increase in SVI after volume expansion (r = 0.14, p = 0.40). A baseline IJVV greater than 32.00%, SVV greater than 14.30%, PPV greater than 11.00%, and a combination of IJVV and PPV greater than 64.00% had utility in identifying fluid responsiveness, with a sensitivity of 33.33%, 77.78%, 55.56%, and 55.56%, respectively, and a specificity of 80.00%, 50.00%, 65.00%, and 65.00%, respectively. The area under the receiver operating characteristic curve for the baseline values of IJVV, SVV, PPV, and the combination of IJVV and PPV was 0.52 (95% CI, 0.38-0.65, p=0.83), 0.54 (95% CI, 0.40-0.67, p=0.67), 0.58 (95% CI, 0.45-0.71, p=0.31), and 0.57 (95% CI, 0.43-0.71, p=0.37), respectively.

CONCLUSIONS

Ultrasonic-derived IJVV lacked accuracy in predicting fluid responsiveness in patients with AIS undergoing PSF during low Vt ventilation. In addition, the baseline values of PPV, SVV, and the combination of IJVV and PPV did not predict fluid responsiveness in this surgical setting.

TRAIL REGISTRATION

This trial was registered at www.chictr.org (ChiCTR2200064947) on 24/10/2022. All data were collected through chart review.

Goal-directed therapy in cardiovascular surgery: A case series study

Hemodynamic and intravascular volume monitoring has been utilized and significantly improved thanks to the technology revolution. Goal-Directed Therapy (GDT) derived from this advanced monitoring is beneficial for complex surgeries, and it shifted the medical approaches from static therapy to more personalized functional treatments. Conventional monitoring methods such as blood pressure, heart rate, urinary output, and central venous pressure are commonly used. However, studies have shown these routine parameters often cannot precisely estimate the quality of tissue perfusion. Tissue hypoperfusion and hypoxia play a crucial role in initiating a systemic inflammatory response after prolonged surgeries, resulting in unstable hemodynamic condition of the patients. Several studies reported the importance of GDT in non-cardiac surgeries and there are few reports on cardiac surgeries. However, tissue perfusion and fluid management are more critical in complex and prolonged cardiovascular surgeries to avoid complications such as low cardiac output syndrome and renal or pulmonary dysfunction. Different advanced hemodynamic monitorings have been utilized perioperatively in cardiac surgery to help decision-making on inotrope and fluid management. In this article we present 5 cases of usefulness hemodynamic monitoring in patients who underwent cardiovascular surgeries.

Pressure- vs. volume-controlled ventilation and their respective impact on dynamic parameters of fluid responsiveness: a cross-over animal study

BACKGROUND AND GOAL OF STUDY

Pulse pressure variation (PPV) and stroke volume variation (SVV), which are based on the forces caused by controlled mechanical ventilation, are commonly used to predict fluid responsiveness. When PPV and SVV were introduced into clinical practice, volume-controlled ventilation (VCV) with tidal volumes (VT) ≥ 10 ml kg- 1 was most commonly used. Nowadays, lower VT and the use of pressure-controlled ventilation (PCV) has widely become the preferred type of ventilation. Due to their specific flow characteristics, VCV and PCV result in different airway pressures at comparable tidal volumes. We hypothesised that higher inspiratory pressures would result in higher PPVs and aimed to determine the impact of VCV and PCV on PPV and SVV.

METHODS

In this self-controlled animal study, sixteen anaesthetised, paralysed, and mechanically ventilated (goal: VT 8 ml kg- 1) pigs were instrumented with catheters for continuous arterial blood pressure measurement and transpulmonary thermodilution. At four different intravascular fluid states (IVFS; baseline, hypovolaemia, resuscitation I and II), ventilatory and hemodynamic data including PPV and SVV were assessed during VCV and PCV. Statistical analysis was performed using U-test and RM ANOVA on ranks as well as descriptive LDA and GEE analysis.

RESULTS

Complete data sets were available of eight pigs. VT and respiratory rates were similar in both forms. Heart rate, central venous, systolic, diastolic, and mean arterial pressures were not different between VCV and PCV at any IVFS. Peak inspiratory pressure was significantly higher in VCV, while plateau, airway and transpulmonary driving pressures were significantly higher in PCV. However, these higher pressures did not result in different PPVs nor SVVs at any IVFS.

CONCLUSION

VCV and PCV at similar tidal volumes and respiratory rates produced PPVs and SVVs without clinically meaningful differences in this experimental setting. Further research is needed to transfer these results to humans.

Performance of four cardiac output monitoring techniques vs. intermittent pulmonary artery thermodilution during a modified passive leg raise maneuver in isoflurane-anesthetized dogs

Objective

This study investigated the performance among four cardiac output (CO) monitoring techniques in comparison with the reference method intermittent pulmonary artery thermodilution (iPATD) and their ability to diagnose fluid responsiveness (FR) during a modified passive leg raise (PLRM) maneuver in isoflurane-anesthetized dogs undergoing acute blood volume manipulations. The study also examined the simultaneous effect of performing the PLRM on dynamic variables such as stroke distance variation (SDV), peak velocity variation (PVV), and stroke volume variation (SVV).

Study design

Prospective, nonrandomized, crossover design.

Study animals

Six healthy male Beagle dogs.

Methods

The dogs were anesthetized with propofol and isoflurane and mechanically ventilated under neuromuscular blockade. After instrumentation, they underwent a series of sequential, nonrandomized steps: Step 1: baseline data collection; Step 2: removal of 33 mL kg-1 of circulating blood volume; Step 3: blood re-transfusion; and Step 4: infusion of 20 mL kg-1 colloid solution. Following a 10-min stabilization period after each step, CO measurements were recorded using esophageal Doppler (EDCO), transesophageal echocardiography (TEECO), arterial pressure waveform analysis (APWACO), and electrical cardiometry (ECCO). Additionally, SDV, PVV, and SVV were recorded. Intermittent pulmonary artery thermodilution (iPATDCO) measurements were also recorded before, during, and after the PLRM maneuver. A successful FR diagnosis made using a specific test indicated that CO increased by more than 15% during the PLRM maneuver. Statistical analysis was performed using one-way analysis of variance for repeated measures with post hoc Tukey test, linear regression, Lin's concordance correlation coefficient (ρc), and Bland-Altman analysis. Statistical significance was set at p < 0.05.

Results

All techniques detected a reduction in CO (p < 0.001) during hemorrhage and an increase in CO after blood re-transfusion and colloid infusion (p < 0.001) compared with baseline. During hemorrhage, CO increases with the PLRM maneuver were as follows: 33% for iPATD (p < 0.001), 19% for EC (p = 0.03), 7% for APWA (p = 0.97), 39% for TEE (p < 0.001), and 17% for ED (p = 0.02). Concurrently, decreases in SVV, SDV, and PVV values (p < 0.001) were also observed. The percentage error for TEE, ED, and EC was less than 30% but exceeded 55% for APWA. While TEECO and ECCO slightly underestimated iPATDCO values, EDCO and APWACO significantly overestimated iPATDCO values. TEE and EC exhibited good and acceptable agreement with iPATD. However, CO measurements using all four techniques and iPATD did not differ before, during, and after PLRM at baseline, blood re-transfusion, and colloid infusion.

Conclusion and clinical relevance

iPATD, EC, TEE, and ED effectively assessed FR in hypovolemic dogs during the PLRM maneuver, while the performance of APWA was unacceptable and not recommended. SVV, SDV, and PVV could be used to monitor CO changes during PLRM and acute blood volume manipulations, suggesting their potential clinical utility.

Inspiratory effort impacts the accuracy of pulse pressure variations for fluid responsiveness prediction in mechanically ventilated patients with spontaneous breathing activity: a prospective cohort study

BACKGROUND

Pulse pressure variation (PPV) is unreliable in predicting fluid responsiveness (FR) in patients receiving mechanical ventilation with spontaneous breathing activity. Whether PPV can be valuable for predicting FR in patients with low inspiratory effort is unknown. We aimed to investigate whether PPV can be valuable in patients with low inspiratory effort.

METHODS

This prospective study was conducted in an intensive care unit at a university hospital and included acute circulatory failure patients receiving volume-controlled ventilation with spontaneous breathing activity. Hemodynamic measurements were collected before and after a fluid challenge. The degree of inspiratory effort was assessed using airway occlusion pressure (P0.1) and airway pressure swing during a whole breath occlusion (ΔPocc) before fluid challenge. Patients were classified as fluid responders if their cardiac output increased by ≥ 10%. Areas under receiver operating characteristic (AUROC) curves and gray zone approach were used to assess the predictive performance of PPV.

RESULTS

Among the 189 included patients, 53 (28.0%) were defined as responders. A PPV > 9.5% enabled to predict FR with an AUROC of 0.79 (0.67-0.83) in the whole population. The predictive performance of PPV differed significantly in groups stratified by the median value of P0.1 (P0.1 < 1.5 cmH2O and P0.1 ≥ 1.5 cmH2O), but not in groups stratified by the median value of ΔPocc (ΔPocc < - 9.8 cmH2O and ΔPocc ≥ - 9.8 cmH2O). Specifically, in patients with P0.1 < 1.5 cmH2O, PPV was associated with an AUROC of 0.90 (0.82-0.99) compared with 0.68 (0.57-0.79) otherwise (p = 0.0016). The cut-off values of PPV were 10.5% and 9.5%, respectively. Besides, patients with P0.1 < 1.5 cmH2O had a narrow gray zone (10.5-11.5%) compared to patients with P0.1 ≥ 1.5 cmH2O (8.5-16.5%).

CONCLUSIONS

PPV is reliable in predicting FR in patients who received controlled ventilation with low spontaneous effort, defined as P0.1 < 1.5 cmH2O. Trial registration NCT04802668. Registered 6 February 2021, https://clinicaltrials.gov/ct2/show/record/NCT04802668.

How to integrate hemodynamic variables during resuscitation of septic shock?

Resuscitation of septic shock is a complex issue because the cardiovascular disturbances that characterize septic shock vary from one patient to another and can also change over time in the same patient. Therefore, different therapies (fluids, vasopressors, and inotropes) should be individually and carefully adapted to provide personalized and adequate treatment. Implementation of this scenario requires the collection and collation of all feasible information, including multiple hemodynamic variables. In this review article, we propose a logical stepwise approach to integrate relevant hemodynamic variables and provide the most appropriate treatment for septic shock.

The increase in cardiac output induced by a decrease in positive end-expiratory pressure reliably detects volume responsiveness: the PEEP-test study

BACKGROUND

In patients on mechanical ventilation, positive end-expiratory pressure (PEEP) can decrease cardiac output through a decrease in cardiac preload and/or an increase in right ventricular afterload. Increase in central blood volume by fluid administration or passive leg raising (PLR) may reverse these phenomena through an increase in cardiac preload and/or a reopening of closed lung microvessels. We hypothesized that a transient decrease in PEEP (PEEP-test) may be used as a test to detect volume responsiveness.

METHODS

Mechanically ventilated patients with PEEP ≥ 10 cmH₂O ("high level") and without spontaneous breathing were prospectively included. Volume responsiveness was assessed by a positive PLR-test, defined as an increase in pulse-contour-derived cardiac index (CI) during PLR ≥ 10%. The PEEP-test consisted in reducing PEEP from the high level to 5 cmH₂O for one minute. Pulse-contour-derived CI (PiCCO2) was monitored during PLR and the PEEP-test.

RESULTS

We enrolled 64 patients among whom 31 were volume responsive. The median increase in CI during PLR was 14% (11-16%). The median PEEP at baseline was 12 (10-15) cmH₂O and the PEEP-test resulted in a median decrease in PEEP of 7 (5-10) cmH₂O, without difference between volume responsive and unresponsive patients. Among volume responsive patients, the PEEP-test induced a significant increase in CI of 16% (12-20%) (from 2.4 ± 0.7 to 2.9 ± 0.9 L/min/m², p < 0.0001) in comparison with volume unresponsive patients. In volume unresponsive patients, PLR and the PEEP-test increased CI by 2% (1-5%) and 6% (3-8%), respectively. Volume responsiveness was predicted by an increase in CI > 8.6% during the PEEP-test with a sensitivity of 96.8% (95% confidence interval (95%CI): 83.3-99.9%) and a specificity of 84.9% (95%CI 68.1-94.9%). The area under the receiver operating characteristic curve of the PEEP-test for detecting volume responsiveness was 0.94 (95%CI 0.85-0.98) (p < 0.0001 vs. 0.5). Spearman's correlation coefficient between the changes in CI induced by PLR and the PEEP-test was 0.76 (95%CI 0.63-0.85, p < 0.0001).

CONCLUSIONS

A CI increase > 8.6% during a PEEP-test, which consists in reducing PEEP to 5 cmH₂O, reliably detects volume responsiveness in mechanically ventilated patients with a PEEP ≥ 10 cmH₂O. Trial registration ClinicalTrial.gov (NCT 04,023,786). Registered July 18, 2019. Ethics Committee approval CPP Est III (N° 2018-A01599-46).

Noninvasive Assessment of Arterial Pulse-Pressure Variation During General Anesthesia: Clinical Evaluation of a New High-Fidelity Upper Arm Cuff

OBJECTIVES

To compare noninvasive pulse-pressure variation (PPV) measurements obtained from a new high-fidelity upper arm cuff using a hydraulic coupling technique to corresponding intraarterial PPV measurements.

DESIGN

The authors used prospective multicenter comparison and development studies for the new high-fidelity upper arm cuff.

SETTING

The study was performed in the departments of Anesthesiology at the Ludwig-Maximilians-Universität München Hospital, the University Hospital of Bonn, and the RoMed Hospital in Rosenheim (all Germany).

PARTICIPANTS

A total of 153 patients were enrolled, undergoing major abdominal surgery or neurosurgery with mechanical ventilation. For the evaluation of PPV, 1,467 paired measurements in 107 patients were available after exclusion due to predefined quality criteria.

INTERVENTIONS

Simultaneous measurements of PPV were performed from a reference femoral arterial catheter (PPV_ref) and the high-fidelity upper arm cuff (PPV_cuff). The new device uses a semirigid conical shell. It incorporates a hydraulic sensor pad with a pressure transducer, leading to a tissue pressure-pulse contour with all characteristics of an arterial- pulse contour.

MEASUREMENTS AND MAIN RESULTS

The comparative analysis of the included measurements showed that PPV_ref and PPV_cuff were closely correlated (r = 0.92). The mean of the differences between PPV_ref and PPV_cuff was 0.1 ± 2.0%, with 95% limits of agreement between -4.1% and 3.9%. To track absolute changes in PPV >2%, the concordance rate between the 2 methods was 93%.

CONCLUSIONS

The new high-fidelity upper arm cuff method provided a clinically reliable estimate of PPV.

Individualizing Fluid Management in Patients with Acute Respiratory Distress Syndrome and with Reduced Lung Tissue Due to Surgery—A Narrative Review

Fluids are the cornerstone of therapy in all critically ill patients. During the last decades, we have made many steps to get fluid therapy personalized and based on individual needs. In patients with lung involvement—acute respiratory distress syndrome—finding the right amount of fluids after lung surgery may be extremely important because lung tissue is one of the most vulnerable to fluid accumulation. In the current narrative review, we focus on the actual perspectives of fluid therapy with the aim of showing the possibilities to tailor the treatment to a patient’s individual needs using fluid responsiveness parameters and other therapeutic modalities.

New Hemodynamic Parameters in Peri-Operative and Critical Care-Challenges in Translation

Hemodynamic monitoring technologies are evolving continuously-a large number of bedside monitoring options are becoming available in the clinic. Methods such as echocardiography, electrical bioimpedance, and calibrated/uncalibrated analysis of pulse contours are becoming increasingly common. This is leading to a decline in the use of highly invasive monitoring and allowing for safer, more accurate, and continuous measurements. The new devices mainly aim to monitor the well-known hemodynamic variables (e.g., novel pulse contour, bioreactance methods are aimed at measuring widely-used variables such as blood pressure, cardiac output). Even though hemodynamic monitoring is now safer and more accurate, a number of issues remain due to the limited amount of information available for diagnosis and treatment. Extensive work is being carried out in order to allow for more hemodynamic parameters to be measured in the clinic. In this review, we identify and discuss the main sensing strategies aimed at obtaining a more complete picture of the hemodynamic status of a patient, namely: (i) measurement of the circulatory system response to a defined stimulus; (ii) measurement of the microcirculation; (iii) technologies for assessing dynamic vascular mechanisms; and (iv) machine learning methods. By analyzing these four main research strategies, we aim to convey the key aspects, challenges, and clinical value of measuring novel hemodynamic parameters in critical care.

Haemodynamic monitoring and management in patients having noncardiac surgery: A survey among members of the European Society of Anaesthesiology and Intensive Care

BACKGROUND

Haemodynamic monitoring and management is a mainstay of peri-operative anaesthetic care.

OBJECTIVE

To determine how anaesthesiologists measure and manage blood pressure and cardiac output, and how they guide fluid administration and assess fluid responsiveness in patients having noncardiac surgery.

DESIGN

Web-based survey.

SETTING

Survey among members of the European Society of Anaesthesiology and Intensive Care (ESAIC) in October and November 2021.

PARTICIPANTS

ESAIC members responding to the survey.

MAIN OUTCOME MEASURES

Respondents' answers to 30 questions on haemodynamic monitoring and management, and fluid therapy.

RESULTS

A total of 615 fully completed surveys were analysed. Arterial catheters are usually not placed before induction of general anaesthesia (378/615; 61%) even when invasive blood pressure monitoring is planned. Mean arterial pressure (532/615; 87%) with lower intervention thresholds of 65 mmHg (183/531; 34%) or 20% below pre-operative baseline (166/531; 31%) is primarily used to guide blood pressure management. Cardiac output is most frequently measured using pulse wave analysis (548/597; 92%). However, only one-third of respondents (almost) always use cardiac output to guide haemodynamic management in high-risk patients (225/582; 39%). Dynamic cardiac preload variables are more frequently used to guide haemodynamic management than cardiac output [pulse pressure variation (almost) always: 318/589; 54%]. Standardised treatment protocols are rarely used for haemodynamic management (139/614; 23%). For fluid therapy, crystalloids are primarily used as maintenance fluids, to treat hypovolaemia, and for fluid challenges. The use of 0.9% saline and hydroxyethyl starch has declined over the last decade. The preferred methods to assess fluid responsiveness are dynamic preload variables and fluid challenges, most commonly with 250 ml of fluid (319/613; 52%).

CONCLUSION

This survey provides important information how anaesthesiologists currently measure and manage blood pressure and cardiac output, and how they guide fluid administration in patients having noncardiac surgery.

Using generalized additive models to decompose time series and waveforms, and dissect heart-lung interaction physiology

Common physiological time series and waveforms are composed of repeating cardiac and respiratory cycles. Often, the cardiac effect is the primary interest, but for, e.g., fluid responsiveness prediction, the respiratory effect on arterial blood pressure also convey important information. In either case, it is relevant to disentangle the two effects. Generalized additive models (GAMs) allow estimating the effect of predictors as nonlinear, smooth functions. These smooth functions can represent the cardiac and respiratory cycles' effects on a physiological signal. We demonstrate how GAMs allow a decomposition of physiological signals from mechanically ventilated subjects into separate effects of the cardiac and respiratory cycles. Two examples are presented. The first is a model of the respiratory variation in pulse pressure. The second demonstrates how a central venous pressure waveform can be decomposed into a cardiac effect, a respiratory effect and the interaction between the two cycles. Generalized additive models provide an intuitive and flexible approach to modelling the repeating, smooth, patterns common in medical monitoring data.

Volumetric evaluation of fluid responsiveness using a modified passive leg raise maneuver during experimental induction and correction of hypovolemia in anesthetized dogs

OBJECTIVE

To demonstrate if modified passive leg raise (PLR_M) maneuver can be used for volumetric evaluation of fluid responsiveness (FR) by inducing cardiac output (CO) changes during experimental induction and correction of hypovolemia in healthy anesthetized dogs. The effects of PLR_M on plethysmographic variability index (PVI) and pulse pressure variation (PPV) were also investigated.

STUDY DESIGN

Prospective, crossover study.

ANIMALS

A total of six healthy anesthetized Beagle dogs.

METHODS

Dogs were anesthetized with propofol and isoflurane. They were mechanically ventilated under neuromuscular blockade, and normothermia was maintained. After instrumentation, all dogs were subjected to four stages: 1, baseline; 2, removal of 27 mL kg^-1 circulating blood volume; 3, after blood re-transfusion; and 4, after 20 mL kg^-1 hetastarch infusion over 20 minutes. A 10 minute stabilization period was allowed after induction of each stage and before data collection. At each stage, CO via pulmonary artery thermodilution, PVI, PPV and cardiopulmonary variables were measured before, during and after the PLR_M maneuver. Stages were sequential, not randomized. Statistical analysis included repeated measures anova and Tukey's post hoc test, considering p < 0.05 as significant.

RESULTS

During stage 2, PLR_M at a 30° angle significantly increased CO (mean ± standard deviation, 1.0 ± 0.1 to 1.3 ± 0.1 L minute^-1; p < 0.001), with a simultaneous significant reduction in PVI (38 ± 4% to 21 ± 4%; p < 0.001) and PPV (27 ± 2% to 18 ± 2%; p < 0.001). The PLR_M did not affect CO, PPV and PVI during stages 1, 3 and 4.

CONCLUSIONS AND CLINICAL RELEVANCE

In anesthetized dogs, PLR_M at a 30° angle successfully detected FR during hypovolemia, and identified fluid nonresponsiveness during normovolemia and hypervolemia. Also, in hypovolemic dogs, significant decreases in PVI and PPV occurred in response to PLR_M maneuver.

Tidal volume challenge to predict preload responsiveness in patients with acute respiratory distress syndrome under prone position

Background

Prone position is frequently used in patients with acute respiratory distress syndrome (ARDS), especially during the Coronavirus disease 2019 pandemic. Our study investigated the ability of pulse pressure variation (PPV) and its changes during a tidal volume challenge (TVC) to assess preload responsiveness in ARDS patients under prone position.

Methods

This was a prospective study conducted in a 25-bed intensive care unit at a university hospital. We included patients with ARDS under prone position, ventilated with 6 mL/kg tidal volume and monitored by a transpulmonary thermodilution device. We measured PPV and its changes during a TVC (ΔPPV TVC6–8) after increasing the tidal volume from 6 to 8 mL/kg for one minute. Changes in cardiac index (CI) during a Trendelenburg maneuver (ΔCITREND) and during end-expiratory occlusion (EEO) at 8 mL/kg tidal volume (ΔCI EEO8) were recorded. Preload responsiveness was defined by both ΔCITREND ≥ 8% and ΔCI EEO8 ≥ 5%. Preload unresponsiveness was defined by both ΔCITREND < 8% and ΔCI EEO8 < 5%.

Results

Eighty-four sets of measurements were analyzed in 58 patients. Before prone positioning, the ratio of partial pressure of arterial oxygen to fraction of inspired oxygen was 104 ± 27 mmHg. At the inclusion time, patients were under prone position for 11 (2–14) hours. Norepinephrine was administered in 83% of cases with a dose of 0.25 (0.15–0.42) µg/kg/min. The positive end-expiratory pressure was 14 (11–16) cmH2O. The driving pressure was 12 (10–17) cmH2O, and the respiratory system compliance was 32 (22–40) mL/cmH2O. Preload responsiveness was detected in 42 cases. An absolute change in PPV ≥ 3.5% during a TVC assessed preload responsiveness with an area under the receiver operating characteristics (AUROC) curve of 0.94 ± 0.03 (sensitivity: 98%, specificity: 86%) better than that of baseline PPV (0.85 ± 0.05; p = 0.047). In the 56 cases where baseline PPV was inconclusive (≥ 4% and < 11%), ΔPPV TVC6–8 ≥ 3.5% still enabled to reliably assess preload responsiveness (AUROC: 0.91 ± 0.05, sensitivity: 97%, specificity: 81%; p < 0.01 vs. baseline PPV).

Conclusion

In patients with ARDS under low tidal volume ventilation during prone position, the changes in PPV during a TVC can reliably assess preload responsiveness without the need for cardiac output measurements.

Trial registration: ClinicalTrials.gov (NCT04457739). Registered 30 June 2020 —Retrospectively registered, https://clinicaltrials.gov/ct2/show/record/NCT04457739

Dynamic changes of pulse pressure but not of pulse pressure variation during passive leg raising predict preload responsiveness in critically ill patients with spontaneous breathing activity

PURPOSE

To evaluate whether the changes in arterial pulse pressure (PP) and/or pulse pressure variation (PPV) during passive leg raising (PLR) can be used to evaluate preload responsiveness in patients with spontaneous breathing activity.

MATERIALS AND METHODS

Patients ventilated with pressure support mode or totally spontaneously breathing were prospectively included. The values of PP and PPV were recorded before and at the end of PLR. The changes in cardiac index (CI) or the velocity-time integral (VTI) of the left ventricular outflow tract during PLR were tracked by the pulse contour analysis or transthoracic echocardiography. Patients exhibiting an increase in CI ≥ 10% or VTI ≥ 12% during PLR were defined as preload responders.

RESULTS

Among 33 patients included, 28 (80%) received norepinephrine and 14 were preload responders. The increase in PP > 2 mmHg in absolute value (4% in percentage) during PLR (PLR_PP) predicted preload responsiveness with an area under the receiver operating characteristic (AUROC) of 0.76 ± 0.09 (p = 0.003 vs. AUROC of 0.5). The changes in PPV during PLR, however, failed to predict preload responsiveness (p = 0.82 vs. AUROC of 0.5).

CONCLUSION

In patients with full spontaneous breathing activity, PLR-induced changes in PP had a fair ability to assess preload responsiveness even when norepinephrine was administered.

REGISTRATION NUMBER

ClinicalTrials.gov (NCT04369027).

Passive leg raising-induced changes in pulse pressure variation to assess fluid responsiveness in mechanically ventilated patients: a multicentre prospective observational study

BACKGROUND

Passive leg raising-induced changes in cardiac index can be used to predict fluid responsiveness. We investigated whether passive leg raising-induced changes in pulse pressure variation (ΔPPVPLR) can also predict fluid responsiveness in mechanically ventilated patients.

METHODS

In this multicentre prospective observational study, we included 270 critically ill patients on mechanical ventilation in whom volume expansion was indicated because of acute circulatory failure. We did not include patients with cardiac arrythmias. Cardiac index and PPV were measured before/during a passive leg raising test and before/after volume expansion. A volume expansion-induced increase in cardiac index of >15% defined fluid responsiveness. To investigate whether ΔPPVPLR can predict fluid responsiveness, we determined areas under the receiver operating characteristic curves (AUROCs) and grey zones for relative and absolute ΔPPVPLR.

RESULTS

Of the 270 patients, 238 (88%) were on controlled mechanical ventilation with no spontaneous breathing activity and 32 (12%) were on pressure support ventilation. The median tidal volume was 7.1 (inter-quartile range [IQR], 6.6-7.6) ml kg-1 ideal body weight. One hundred sixty-four patients (61%) were fluid responders. Relative and absolute ΔPPVPLR predicted fluid responsiveness with an AUROC of 0.92 (95% confidence interval [95% CI], 0.88-0.95; P<0.001) each. The grey zone for relative and absolute ΔPPVPLR included 4.8% and 22.6% of patients, respectively. These results were not affected by ventilatory mode and baseline characteristics (type of shock, centre, vasoactive treatment).

CONCLUSIONS

Passive leg raising-induced changes in pulse pressure variation accurately predict fluid responsiveness with a small grey zone in critically ill patients on mechanical ventilation.

CLINICAL TRIAL REGISTRATION

NCT03225378.

Prediction of fluid responsiveness. What’s new?

Although the administration of fluid is the first treatment considered in almost all cases of circulatory failure, this therapeutic option poses two essential problems: the increase in cardiac output induced by a bolus of fluid is inconstant, and the deleterious effects of fluid overload are now clearly demonstrated. This is why many tests and indices have been developed to detect preload dependence and predict fluid responsiveness. In this review, we take stock of the data published in the field over the past three years. Regarding the passive leg raising test, we detail the different stroke volume surrogates that have recently been described to measure its effects using minimally invasive and easily accessible methods. We review the limits of the test, especially in patients with intra-abdominal hypertension. Regarding the end-expiratory occlusion test, we also present recent investigations that have sought to measure its effects without an invasive measurement of cardiac output. Although the limits of interpretation of the respiratory variation of pulse pressure and of the diameter of the vena cava during mechanical ventilation are now well known, several recent studies have shown how changes in pulse pressure variation itself during other tests reflect simultaneous changes in cardiac output, allowing these tests to be carried out without its direct measurement. This is particularly the case during the tidal volume challenge, a relatively recent test whose reliability is increasingly well established. The mini-fluid challenge has the advantage of being easy to perform, but it requires direct measurement of cardiac output, like the classic fluid challenge. Initially described with echocardiography, recent studies have investigated other means of judging its effects. We highlight the problem of their precision, which is necessary to evidence small changes in cardiac output. Finally, we point out other tests that have appeared more recently, such as the Trendelenburg manoeuvre, a potentially interesting alternative for patients in the prone position.

Slope analysis for the prediction of fluid responsiveness by a stepwise PEEP elevation recruitment maneuver in mechanically ventilated patients

Objective

Assessment of fluid responsiveness is problematic in intensive care unit patients. Lung recruitment maneuvers (LRM) can be used as a functional test to predict fluid responsiveness. We propose a new test to predict fluid responsiveness in mechanically ventilated patients by analyzing the variations in central venous pressure (CVP) and systemic arterial parameters during a prolonged sigh breath LRM without the use of a cardiac output measuring device.

Design

Prospective observational cohort study.

Setting

Intensive Care Unit, Saint-Etienne University Central Hospital.

Patients

Patients under mechanical ventilation, equipped with invasive arterial blood pressure, CVP, pulse contour analysis (PICCO™), requiring volume expansion, with no right ventricular dysfunction.

Interventions.

None.

Measurements and main results

CVP, systemic arterial parameters and stroke volume (SV) were recorded during prolonged LRM followed by a 500 mL fluid expansion to asses fluid responsiveness. 25 patients were screened and 18 patients analyzed. 9 patients were responders to volume expansion and 9 were not. Evaluation of hemodynamic parameters suggested the use of a linear regression model. Slopes for systolic arterial pressure, pulse pressure (PP), CVP and SV were all significantly different between responders and non-responders during the pressure increase phase of LRM (STEP-UP) (p = 0.022, p = 0.014, p = 0.006 and p = 0.038, respectively). PP and CVP slopes during STEP-UP were strongly predictive of fluid responsiveness with an AUC of 0.926 (95% CI, 0.78 to 1.00), sensitivity = 100%, specificity = 89% and an AUC = 0.901 (95% CI, 0.76 to 1.00), sensibility = 78%, specificity = 100%, respectively. Combining sensitivity of PP and specificity of CVP, prediction of fluid responsiveness can be achieved with 100% sensitivity and 100% specificity (AUC = 0.96; 95% CI, 0.90 to 1.00). One patient showed inconclusive values using the grey zone approach (5.5%).

Conclusions

In patients under mechanical ventilation with no right heart dysfunction, the association of PP and CVP slope analysis during a prolonged sigh breath LRM seems to offer a very promising method for prediction of fluid responsiveness without the use and associated cost of a cardiac output measurement device.

Trial registration

NCT04304521, IRBN902018/CHUSTE. Registered 11 March 2020, Fluid responsiveness predicted by a stepwise PEEP elevation recruitment maneuver in mechanically ventilated patients (STEP-PEEP)

The Use of the Hypotension Prediction Index Integrated in an Algorithm of Goal Directed Hemodynamic Treatment during Moderate and High-Risk Surgery

(1) Background: The Hypotension Prediction Index (HPI) is an algorithm that predicts hypotension, defined as mean arterial pressure (MAP) less than 65 mmHg for at least 1 min, based on arterial waveform features. We tested the hypothesis that the use of this index reduces the duration and severity of hypotension during noncardiac surgery. (2) Methods: We enrolled adults having moderate- or high-risk noncardiac surgery with invasive arterial pressure monitoring. Participating patients were randomized 1:1 to standard of care or hemodynamic management with HPI guidance with a goal directed hemodynamic treatment protocol. The trigger to initiate treatment (with fluids, vasopressors, or inotropes) was a value of HPI of 85 (range, 0–100) or higher in the intervention group. Primary outcome was the amount of hypotension, defined as time-weighted average (TWA) MAP less than 65 mmHg. Secondary outcomes were time spent in hypertension defined as MAP more than 100 mmHg for at least 1 min; medication and fluids administered and postoperative complications. (3) Results: We obtained data from 99 patients. The median (IQR) TWA of hypotension was 0.16 mmHg (IQR, 0.01–0.32 mmHg) in the intervention group versus 0.50 mmHg (IQR, 0.11–0.97 mmHg) in the control group, for a median difference of −0.28 (95% CI, −0.48 to −0.09 mmHg; p = 0.0003). We also observed an increase in hypertension in the intervention group as well as a higher weight-adjusted administration of phenylephrine in the intervention group. (4) Conclusions: In this single-center prospective study of patients undergoing elective noncardiac surgery, the use of this prediction model resulted in less intraoperative hypotension compared with standard care. An increase in the time spent in hypertension in the treatment group was also observed, probably as a result of overtreatment. This should provide an insight for refining the use of this prediction index in future studies to avoid excessive correction of blood pressure.

Clinical Application of the Fluid Challenge Approach in Goal-Directed Fluid Therapy: What Can We Learn From Human Studies?

Resuscitative fluid therapy aims to increase stroke volume (SV) and cardiac output (CO) and restore/improve tissue oxygen delivery in patients with circulatory failure. In individualized goal-directed fluid therapy (GDFT), fluids are titrated based on the assessment of responsiveness status (i.e., the ability of an individual to increase SV and CO in response to volume expansion). Fluid administration may increase venous return, SV and CO, but these effects may not be predictable in the clinical setting. The fluid challenge (FC) approach, which consists on the intravenous administration of small aliquots of fluids, over a relatively short period of time, to test if a patient has a preload reserve (i.e., the relative position on the Frank-Starling curve), has been used to guide fluid administration in critically ill humans. In responders to volume expansion (defined as individuals where SV or CO increases ≥10–15% from pre FC values), FC administration is repeated until the individual no longer presents a preload reserve (i.e., until increases in SV or CO are <10–15% from values preceding each FC) or until other signs of shock are resolved (e.g., hypotension). Even with the most recent technological developments, reliable and practical measurement of the response variable (SV or CO changes induced by a FC) has posed a challenge in GDFT. Among the methods used to evaluate fluid responsiveness in the human medical field, measurement of aortic flow velocity time integral by point-of-care echocardiography has been implemented as a surrogate of SV changes induced by a FC and seems a promising non-invasive tool to guide FC administration in animals with signs of circulatory failure. This narrative review discusses the development of GDFT based on the FC approach and the response variables used to assess fluid responsiveness status in humans and animals, aiming to open new perspectives on the application of this concept to the veterinary field.

Perioperative Hemodynamic Monitoring: An Overview of Current Methods

Perioperative hemodynamic monitoring is an essential part of anesthetic care. In this review, we aim to give an overview of methods currently used in the clinical routine and experimental methods under development. The technical aspects of the mentioned methods are discussed briefly. This review includes methods to monitor blood pressures, for example, arterial pressure, mean systemic filling pressure and central venous pressure, and volumes, for example, global end-diastolic volume (GEDV) and extravascular lung water. In addition, monitoring blood flow (cardiac output) and fluid responsiveness (preload) will be discussed.

Perioperative hemodynamic optimization: from guidelines to implementation-an experts' opinion paper

Despite a large body of evidence, the implementation of guidelines on hemodynamic optimization and goal-directed therapy remains limited in daily routine practice. To facilitate/accelerate this implementation, a panel of experts in the field proposes an approach based on six relevant questions/answers that are frequently mentioned by clinicians, using a critical appraisal of the literature and a modified Delphi process. The mean arterial pressure is a major determinant of organ perfusion, so that the authors unanimously recommend not to tolerate absolute values below 65 mmHg during surgery to reduce the risk of postoperative organ dysfunction. Despite well-identified limitations, the authors unanimously propose the use of dynamic indices to rationalize fluid therapy in a large number of patients undergoing non-cardiac surgery, pending the implementation of a "validity criteria checklist" before applying volume expansion. The authors recommend with a good agreement mini- or non-invasive stroke volume/cardiac output monitoring in moderate to high-risk surgical patients to optimize fluid therapy on an individual basis and avoid volume overload. The authors propose to use fluids and vasoconstrictors in combination to achieve optimal blood flow and maintain perfusion pressure above the thresholds considered at risk. Although purchase of disposable sensors and stand-alone monitors will result in additional costs, the authors unanimously acknowledge that there are data strongly suggesting this may be counterbalanced by a sustained reduction in postoperative morbidity and hospital lengths of stay. Beside existing guidelines, knowledge and explicit clinical reasoning tools followed by decision algorithms are mandatory to implement individualized hemodynamic optimization strategies and reduce postoperative morbidity and duration of hospital stay in high-risk surgical patients.

Comparison between pulse pressure variation and systolic pressure variation measured from a peripheral artery for accurately predicting fluid responsiveness in mechanically ventilated dogs

OBJECTIVE

To compare pulse pressure variation (PPV) and systolic pressure variation (SPV) measured from a peripheral artery to predict fluid responsiveness in anesthetized healthy dogs.

STUDY DESIGN

Prospective study.

ANIMALS

A total of 39 dogs (13.8-26.8 kg) anesthetized with isoflurane for elective ovariohysterectomy.

METHODS

Ventilation was controlled (tidal volume 12 mL kg^-1; 40% inspiratory pause). PPV and SPV were recorded from a dorsal pedal artery catheter using an automated algorithm. A fluid challenge (FC) with lactated Ringer's solution (20 mL kg^-1 over 15 minutes) was administered once (21 animals) or twice (18 animals) before surgery. Increases in transpulmonary thermodilution stroke volume index > 15% from values recorded before each FC defined responders to volume expansion. Final fluid responsiveness status was based on the response to single FC or second FC. Predictive ability of PPV and SPV was compared by receiver operating characteristic (ROC) curve analysis and by the range of cut-off values associated with uncertain results (gray zone).

RESULTS

All animals after the single FC were responders; all animals administered two FCs were nonresponders after the second FC. The area under the ROC curve (AUROC) of PPV (0.968) did not differ from that of SPV (0.937) (p = 0.45). Best cut-off thresholds to discriminate responders from nonresponders were >11.7% (PPV) and >7.4 mmHg (SPV). The gray zone of PPV and SPV was 8.2-14.6% and 7.0-7.4 mmHg, respectively. The percentage of animals with PPV and SPV values within the gray zone was less for SPV (10.2%) than for PPV (30.8%).

CONCLUSIONS AND CLINICAL RELEVANCE

PPV and SPV obtained from the dorsal pedal artery are useful predictors of fluid responsiveness in dogs. Using an automated algorithm, SPV may more accurately predict fluid responsiveness than PPV, with responders identifiable by PPV > 14.6% and SPV > 7.4 mmHg.

Effect of prone position without volume expansion on pulse pressure variation in spinal surgery : a prospective observational study

Background : Pulse pressure variation (PPV) is a predictor of fluid responsiveness in supine patients under mechanical ventilation. Its use has also been validated in the prone position. The aim of this study was to assess changes in PPV induced by prone position in patients undergoing spinal surgery. Methods : Ninety-six patients aged 12 to 75 years, scheduled for elective spinal surgery were included. Patients were excluded if they had clinical signs related to any organ failure, or if they required vasoactive drugs and/or volume expansion during the early stages of anesthesia. Patients received a standardized anesthesia protocol. Fluid expansion was not allowed from induction until 10 minutes after positioning. Hemodynamic measurements recorded before the induction of anesthesia (T0) included : arterial pressure (systolic (SAP) diastolic (DAP) and mean (MAP)) and heart rate (HR). Radial artery was cannulated after intubation and measurements, as well as PPV, were noted in supine position (T1). Patients were then placed in prone position hemodynamics and PPV measurements were repeated (T2). Results : Forty-eight patients completed the study. Anesthesia induction induced a significant decrease in SAP, DAP, and MAP with no effect on HR. Prone position did not induce any significant changes in SAP, MAP, DAP, and HR. A significant difference was found between PPV values in supine (Mean=10.5, SD=4.5) and prone positions (Mean=15.2, SD=7.1) ; t=-4.15 (p<0.001). The mean increase in PPV was 4.7%. Conclusion : Prone position without prior volume expansion induces a significant increase in PPV prior to any modification in arterial blood pressure and heart rate.