Monitoring fluid responsiveness

Continuous Non-Invasive Hemodynamic Monitoring in Cirrhotic Patients-Friend or Foe?

Background and Objectives: Liver cirrhosis leads to significant hemodynamic changes, particularly portal hypertension and a hyperdynamic circulatory state. Traditional invasive methods for hemodynamic monitoring, while accurate, carry risks such as infection and hemorrhage in a patient predisposed to these conditions. This study evaluates the accuracy of non-invasive continuous hemodynamic monitoring compared to a minimally invasive method in patients with decompensated liver cirrhosis. Materials and Materials and Methods: The study enrolled 51 patients with decompensated liver cirrhosis requiring continuous hemodynamic monitoring in the ICU. Patients underwent simultaneous monitoring via the minimally invasive FloTrac system and continuous non-invasive ClearSight sensor over 24 h, with measurements registered at 6 h intervals. Hemodynamic parameters measured included cardiac output (CO), cardiac index (CI), stroke volume (SV), stroke volume variation (SVV), systemic vascular resistance (SVR), and mean arterial pressure (MAP). Results: Significant discrepancies were observed between the two monitoring methods for most parameters, particularly CO, CI, and MAP, at most time intervals. However, SVV measurements showed no significant differences, indicating similar efficacy in assessing fluid responsiveness between the devices. Conclusions: The ClearSight system, although a valuable non-invasive alternative, demonstrated lower accuracy compared to the FloTrac system for hemodynamic measurements in patients with decompensated liver cirrhosis. Its effectiveness in assessing fluid responsiveness, particularly by SVV, suggests it could play a role in the monitoring of these patients, especially when invasive techniques have increased risks.

In vivo evaluation of an adaptive resuscitation controller using whole blood and crystalloid infusates for hemorrhagic shock

Introduction

Hemorrhage remains the leading cause of preventable death on the battlefield. The most effective means to increase survivability is early hemorrhage control and fluid resuscitation. Unfortunately, fluid resuscitation requires constant adjustments to ensure casualty is properly managed, which is often not feasible in the pre-hospital setting. In this study, we showed how an adaptive closed-loop controller for hemorrhage resuscitation can be used to automate hemodynamic management using a swine hemorrhagic shock injury model.

Methods

The adaptive resuscitation controller (ARC) was previously developed to track pressure-volume responsiveness in real time and adjust its infusion rate to reach the target mean arterial pressure (MAP). Swine while maintained under a surgical plane of anesthesia and analgesia underwent a splenectomy, followed by two hemorrhage and resuscitation events. For the first resuscitation event, hemorrhage was induced to reduce the MAP to 35 mmHg until arterial lactate reached 4 mmol/L. The ARC system then infused whole blood (WB) to reach the target MAP and maintained the subject using crystalloids for 120 min. For the second resuscitation event, the subjects were hemorrhaged again but resuscitated using only crystalloid infusion to reach the target MAP and 120-min maintenance.

Results

The ARC was effective at WB resuscitation, reaching the target MAP in 2.0 ± 1.0 min. The median performance error was 1.1% ± 4.6%, and target overshoot was 14.4% ± 7.0% of the target MAP. The ARC maintained all animals throughout the 120 min maintenance period. For the second crystalloid-based resuscitation, ARC required a longer time to reach the target MAP, at an average rise time of 4.3 ± 4.0 min. However, target overshoot was reduced to 8.4% ± 7.3% of the target MAP. Much higher flow rates were required to maintain the target MAP during the second resuscitation event than during the first resuscitation event.

Discussion

The ARC was able to rapidly reach and maintain the target MAP effectively. However, this sometimes required large volumes of fluid as the ARC's only goal was to reach the target MAP. Further clinical insight is needed regarding the preferred aggression level to achieve the target MAP. In conclusion, the ARC was successful in its programmed objective of reaching and maintaining the target MAP for extended periods of time in vivo, a critical next step toward improving hemorrhage treatment in the pre-hospital environment.

The Pleth Variability Index as a Guide to Fluid Therapy in Dogs Undergoing General Anesthesia: A Preliminary Study

The aim of this prospective, randomized clinical trial was to evaluate the use of the pleth variability index (PVi) to guide the rate of intraoperative fluid therapy compared to a traditional fixed-fluid-rate approach in ASA 1-2 dogs undergoing surgery. Twenty-seven dogs met the inclusion criteria and were randomly assigned to the conventional fluid management group (CFM, n = 12) or the PVi-guided group (PVi, n = 15). The CFM group received a fixed rate of 5 mL kg-1 h-1 of crystalloid solution, while in the PVi group the rate was continuously adjusted based on the PVi: PVi < 14% = 3 mL kg-1 h-1; 14% ≤ PVi ≥ 20% = 10 mL kg-1 h-1; and PVi > 20% = 15 mL kg-1 h-1. Hypotension (MAP < 65 mmHg) in the CFM was treated with a maximum of two fluid boluses (5 mL kg-1 in 10 min) and in the case of no response, dobutamine (1-3 mcg kg-1 min-1) was administered. In the PVi group, the treatment of hypotension was similar, except when the PVi > 14%, when dobutamine was started directly. Total fluid volume was significantly lower in the PVI group (0.056 ± 0.027 mL kg-1 min-1) compared to the CFM group (0.132 ± 0.115 mL kg-1 min-1), and the incidence of hypotension was lower (p = 0.023) in the PVi group (0%) compared to the CFM group (41%). The mean arterial pressure (MAP) was significantly higher in the PVi group during surgery. Dobutamine was never administered in either group. Preliminary data suggest that the PVi may be considered as a potential target to guide fluid therapy in dogs; larger studies are needed, especially in cases of cardiovascular instability.

Predicting Fluid Responsiveness Using Carotid Ultrasound in Mechanically Ventilated Patients: A Systematic Review and Meta-Analysis of Diagnostic Test Accuracy Studies

BACKGROUND

A noninvasive and accurate method of determining fluid responsiveness in ventilated patients would help to mitigate unnecessary fluid administration. Although carotid ultrasound has been previously studied for this purpose, several studies have recently been published. We performed an updated systematic review and meta-analysis to evaluate the accuracy of carotid ultrasound as a tool to predict fluid responsiveness in ventilated patients.

METHODS

Studies eligible for review investigated the accuracy of carotid ultrasound parameters in predicting fluid responsiveness in ventilated patients, using sensitivity and specificity as markers of diagnostic accuracy (International Prospective Register of Systematic Reviews [PROSPERO] CRD42022380284). All included studies had to use an independent method of determining cardiac output and exclude spontaneously ventilated patients. Six bibliographic databases and 2 trial registries were searched. Medline, Embase, Emcare, APA PsycInfo, CINAHL, and the Cochrane Library were searched on November 4, 2022. Clinicaltrials.gov and Australian New Zealand Clinical Trials Registry were searched on February 24, 2023. Results were pooled, meta-analysis was conducted where possible, and hierarchical summary receiver operating characteristic models were used to compare carotid ultrasound parameters. Bias and evidence quality were assessed using the Quality Assessment of Diagnostic Accuracy Studies (QUADAS) tool and the Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) guidelines.

RESULTS

Thirteen prospective clinical studies were included (n = 648 patients), representing 677 deliveries of volume expansion, with 378 episodes of fluid responsiveness (58.3%). A meta-analysis of change in carotid Doppler peak velocity (∆CDPV) yielded a sensitivity of 0.79 (95% confidence interval [CI], 0.74-0.84) and a specificity of 0.85 (95% CI, 0.76-0.90). Risk of bias relating to recruitment methodology, the independence of index testing to reference standards and exclusionary clinical criteria were evaluated. Overall quality of evidence was low. Study design heterogeneity, including a lack of clear parameter cutoffs, limited the generalizability of our results.

CONCLUSIONS

In this meta-analysis, we found that existing literature supports the ability of carotid ultrasound to predict fluid responsiveness in mechanically ventilated adults. ∆CDPV may be an accurate carotid parameter in certain contexts. Further high-quality studies with more homogenous designs are needed to further validate this technology.

Validation of a Suprasystolic Cuff System for Static and Dynamic Representation of the Central Pressure Waveform

BACKGROUND

Noninvasive pulse waveform analysis is valuable for central cardiovascular assessment, yet controversies persist over its validity in peripheral measurements. Our objective was to compare waveform features from a cuff system with suprasystolic blood pressure hold with an invasive aortic measurement.

METHODS AND RESULTS

This study analyzed data from 88 subjects undergoing concurrent aortic catheterization and brachial pulse waveform acquisition using a suprasystolic blood pressure cuff system. Oscillometric blood pressure (BP) was compared with invasive aortic systolic BP and diastolic BP. Association between cuff and catheter waveform features was performed on a set of 15 parameters inclusive of magnitudes, time intervals, pressure-time integrals, and slopes of the pulsations. The evaluation covered both static (subject-averaged values) and dynamic (breathing-induced fluctuations) behaviors. Peripheral BP values from the cuff device were higher than catheter values (systolic BP-residual, 6.5 mm Hg; diastolic BP-residual, 12.4 mm Hg). Physiological correction for pressure amplification in the arterial system improved systolic BP prediction (r2=0.83). Dynamic calibration generated noninvasive BP fluctuations that reflect those invasively measured (systolic BP Pearson R=0.73, P<0.001; diastolic BP Pearson R=0.53, P<0.001). Static and dynamic analyses revealed a set of parameters with strong associations between catheter and cuff (Pearson R>0.5, P<0.001), encompassing magnitudes, timings, and pressure-time integrals but not slope-based parameters.

CONCLUSIONS

This study demonstrated that the device and methods for peripheral waveform measurements presented here can be used for noninvasive estimation of central BP and a subset of aortic waveform features. These results serve as a benchmark for central cardiovascular assessment using suprasystolic BP cuff-based devices and contribute to preserving system dynamics in noninvasive measurements.

Value of carotid corrected flow time or changes value of FTc could be more useful in predicting fluid responsiveness in patients undergoing robot-assisted gynecologic surgery: a prospective observational study

Background

The aim of this study was to evaluate the ability of point-of-care Doppler ultrasound measurements of carotid corrected flow time and its changes induced by volume expansion to predict fluid responsiveness in patients undergoing robot-assisted gynecological surgery.

Methods

In this prospective study, carotid corrected flow time was measured using Doppler images of the common carotid artery before and after volume expansion. The stroke volume index at each time point was recorded using noninvasive cardiac output monitoring with MostCare. Of the 52 patients enrolled, 26 responded.

Results

The areas under the receiver operating characteristic curves of the carotid corrected flow time and changes in carotid corrected flow time induced by volume expansion were 0.82 and 0.67, respectively. Their optimal cut-off values were 357 and 19.5 ms, respectively.

Conclusion

Carotid corrected flow time was superior to changes in carotid corrected flow time induced by volume expansion for predicting fluid responsiveness in this population.

A Logical Prescription of Intravenous Fluids

This chapter guides clinicians through the assessment and management of patients requiring intravenous (IV) fluids during hospitalization in the regular ward and ICU. It aims to aid in the determination of the patient’s actual fluid or volume status and guides the prescription and management of electrolyte replacement whilst avoiding potential harm to patients from fluid mismanagement leading to electrolyte disturbances, fluid accumulation, and organ impairment (or a combination). This is referred to as IV Fluid Stewardship, and it incorporates much of the National Institute for Health and Care Excellence (NICE) guidance published.

Cardiac output monitoring in children: a review

Cardiac output monitoring enables physiology-directed management of critically ill children and aids in the early detection of clinical deterioration. Multiple invasive techniques have been developed and have demonstrated ability to improve clinical outcomes. However, all require invasive arterial or venous catheters, with associated risks of infection, thrombosis and vascular injury. Non-invasive monitoring of cardiac output and fluid responsiveness in infants and children is an active area of interest and several proven techniques are available. Novel non-invasive cardiac output monitors offer a promising alternative to echocardiography and have proven their ability to influence clinical practice. Assessment of perfusion remains a challenge; however, technologies such as near-infrared spectroscopy and photoplethysmography may prove valuable clinical adjuncts in the future.

Mock circulatory loop generated database for dynamic characterization of pressure-based cardiac output monitoring systems

Pulse contour cardiac output monitoring systems allow real-time and continuous estimation of hemodynamic variables such as cardiac output (CO) and stroke volume variation (SVV) by analysis of arterial blood pressure waveforms. However, evaluating the performance of CO monitoring systems to measure the small variations in these variables sometimes used to guide fluid therapy is a challenge due to limitations in clinical reference methods. We developed a non-clinical database as a tool for assessing the dynamic attributes of pressure-based CO monitoring systems, including CO response time and CO and SVV resolutions. We developed a mock circulation loop (MCL) that can simulate rapid changes in different parameters, such as CO and SVV. The MCL was configured to simulate three different states (normovolemic, cardiogenic shock, and hyperdynamic) representing a range of flow and pressure conditions. For each state, we simulated stepwise changes in the MCL flow and collected datasets for characterizing pressure-based CO systems. Nine datasets were generated that contain hours of peripheral pressure, central flow and pressure waveforms. The MCL-generated database is provided open access as a tool for evaluating dynamic characteristics of pressure-based CO algorithms and systems in detecting variations in CO and SVV indices. In an example application of the database, a CO response time of 10 s, CO and SVV resolutions with lower and upper limits of (-9.1%, 8.4%) and (-5.0%, 3.8%), respectively, were determined for a pressure-based CO benchtop system. This tool will support a more comprehensive assessment of pressure-based CO monitoring systems and algorithms.

Passive longitudinal weight and cardiopulmonary monitoring in the home bed

Home health monitoring has the potential to improve outpatient management of chronic cardiopulmonary diseases such as heart failure. However, it is often limited by the need for adherence to self-measurement, charging and self-application of wearables, or usage of apps. Here, we describe a non-contact, adherence-independent sensor, that when placed beneath the legs of a patient's home bed, longitudinally monitors total body weight, detailed respiratory signals, and ballistocardiograms for months, without requiring any active patient participation. Accompanying algorithms separate weight and respiratory signals when the bed is shared by a partner or a pet. Validation studies demonstrate quantitative equivalence to commercial sensors during overnight sleep studies. The feasibility of detecting obstructive and central apneas, cardiopulmonary coupling, and the hemodynamic consequences of non-sustained ventricular tachycardia is also established. Real-world durability is demonstrated by 3 months of in-home monitoring in an example patient with heart failure and ischemic cardiomyopathy as he recovers from coronary artery bypass grafting surgery. BedScales is the first sensor to measure adherence-independent total body weight as well as longitudinal cardiopulmonary physiology. As such, it has the potential to create a multidimensional picture of chronic disease, learn signatures of impending hospitalization, and enable optimization of care in the home.

Changes in stroke volume variation and cardiac index during open major bowel surgery

Background

Stroke volume variation (SVV) is a dynamic indicator of preload, which is a determinant of cardiac output. Aims: Aim of this study was to evaluate the relationship between changes in SVV and cardiac index (CI) in patients with normal left ventricular function undergoing major open abdominal surgery.

Patients and Methods

Patients undergoing major open abdominal surgery were monitored continuously with FloTrac® to measure SVV and CI along with standard monitoring. Both SVV and CI were noted at baseline and every 10 min thereafter till the end of surgery and were observed for concurrence between the measurements.

Results

1800 pairs of measurement of SVV and CI were obtained from 60 patients. Mean SVV and CI (of all patients) measured at different time points of measurement showed that as SVV increased with time, the CI dropped correspondingly. When individual readings of CI and SVV were plotted against each other, the scatter was found to be wide, reiterating the lack of agreement between the two parameters (R² = 0.035). SVV >13% suggesting hypovolemia was found at 207 time points. Of these, 175 had a CI >2.5 L/min/m² and only 32 patients had a CI <2.5 L/min/m².

Conclusion

SVV, a dynamic index of fluid responsiveness can be used to monitor patients expected to have large fluid shifts during major abdominal surgery. It is very specific and has a high negative predictive value. When SVV increases, CI is usually maintained. Since many factors affect SVV and CI, any increase in SVV >13%, must be correlated with other parameters before administration of the fluid challenge.

Perioperative Management of Complex Hepatectomy for Colorectal Liver Metastases: The Alliance between the Surgeon and the Anesthetist

Hepatic resection has been widely accepted as the first choice for the treatment of colorectal metastases. Liver surgery has been recognized as a major abdominal procedure; it exposes patients to a high risk of perioperative adverse events. Decision sharing and the multimodal approach to the patients' management are the two key items for a safe outcome, even in such a high-risk surgery. This review aims at addressing the main perioperative issues (preoperative evaluation; general anesthesia and intraoperative fluid management and hemodynamic monitoring; intraoperative metabolism; administration policy for blood-derivative products; postoperative pain control; postoperative complications), in particular, from the anesthetist's point of view; however, only an alliance with the surgery team may be successful in case of adverse events to accomplish a good final outcome.

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.

Fluid responsiveness to passive leg raising in patients with and without coronary artery disease: A prospective observational study

Introduction:

Hemodynamic stability and fluid responsiveness (FR) assume importance in perioperative management of patients undergoing major surgery. Passive leg raising (PLR) is validated in assessing FR in intensive care unit patients. Very few studies have examined FR to PLR in intraoperative scenario. We prospectively studied FR to PLR using transesophageal echocardiography (TEE), in patients with no coronary artery disease (CAD) undergoing major neurosurgery and those with CAD undergoing coronary artery bypass grafting (CABG).

Methods:

We enrolled 29 adult consenting patients undergoing major neurosurgery with TEE monitoring and 25 patients undergoing CABG. After induction of anesthesia, baseline hemodynamic parameters were obtained which was followed by PLR using automated adjustment of the operating table. Clinical and TEE-derived hemodynamic parameters were recorded at 1 and 10 min after PLR following which patients were returned to supine position.

Results:

A total of 162 TEE and clinical examinations were done across baseline, 1 and 10 min after PLR; and paired comparison was done at data intervals of baseline versus 1 min PLR, baseline versus 10 min PLR, and 1 min versus 10 min PLR. There was no significant change in hemodynamic variables at any of the paired comparison intervals in patients undergoing neurosurgery. CABG cases had significant hemodynamic improvement 1 min after PLR, partially sustained at 10 min.

Conclusion:

Patients undergoing CABG had significant hemodynamic response to PLR, whereas non-CAD patients undergoing neurosurgery did not. A blood pressure–left ventricular end-diastolic volume combination represented strong correlation in response prediction (Pearson's coefficient 0.641; P < 0.01).

Determining pediatric fluid responsiveness by stroke volume variation analysis using ICON® electrical cardiometry and ultrasonic cardiac output monitor: A cross-sectional study

Purpose:

The purpose is to determine the adequacy fluid responsiveness by the validity and cut off point of stroke volume variation (SVV) usingelectrical cardiometry, ICON® (Osypka Medical, Berlin, Germany) and ultrasonic cardiac output monitor (USCOM) and to recognize cut off point of tidal volume in shock children with mechanical ventilation.

Materials and Methods:

A cross-sectional study was conducted from March 2017 to September 2017 in a single center. The selection of subject through consecutive sampling. Measurements of SVV and stroke volume (SV) using USCOM and ICON were performed before and after fluid challenge. The tidal volume of individuals was measured and recorded.

Results:

Analysis was performed in 45 patients with median age of 14 months and 62.2% of male population. It showed that the sensitivity and specificity of ICON were 58% and 74%, respectively. The optimal cut off point of SVV using ICON was 16.5% and the area under the curve (AUC) value was 53% (95% confidence interval [CI] 35.9%–70%), P > 0.05 and cut off point of SVV using USCOM was 33.5% with the AUC value was 70% (95% CI 52.9%–87.7%), P < 0.05. The optimal cut off point of tidal volume to fluid responsivenes was 6.8 ml/kg BW and the AUC value was 44.6% (95% CI 27.4%–61.9%), P > 0.05.

Conclusion:

This study showed that electrical cardiometry (ICON) is unable to assess preload and the response of fluid resuscitation in children.

Inducing Brain Cooling Without Core Temperature Reduction in Pigs Using a Novel Nasopharyngeal Method: An Effectiveness and Safety Study

BACKGROUND

Acute brain lesions constitute an alarming public health concern. Neuroprotective therapies have been implemented to stabilize, prevent, or reduce brain lesions, thus improving neurological outcomes and survival rates. Hypothermia is the most effective approach, mainly attributed to the reduction in cellular metabolic activity. Whole-body cooling is currently implemented by healthcare professionals; however, adverse events are frequent, limiting the potential benefits of therapeutic hypothermia. Therefore, selective methods have been developed to reduce adverse events while delivering neuroprotection. Nasopharyngeal approaches are the safest and most effective methods currently considered. Our primary objective was to determine the effects of a novel nasopharyngeal catheter on the brain temperature of pigs.

METHODS

In this prospective, non-randomized, interventional experimental trial, 10 crossbred pigs underwent nasopharyngeal cooling for 60 min followed by 15 min of rewarming. Nasopharyngeal catheters were inserted into the left nostril and properly positioned at the nasopharyngeal cavity.

RESULTS

Nasopharyngeal cooling was associated with a decrease in brain temperature, which was more significant in the left cerebral hemisphere (p = 0.01). There was a reduction of 1.47 ± 0.86 °C in the first 5 min (p < 0.001), 2.45 ± 1.03 °C within 10 min (p < 0.001), and 4.45 ± 1.36 °C after 1 h (p < 0.001). The brain-core gradient was 4.57 ± 0.87 °C (p < 0.001). Rectal, esophageal, and pulmonary artery temperatures and brain and systemic hemodynamic parameters, remained stable during the procedure. Following brain cooling, values of oxygen partial pressure in brain tissue significantly decreased. No mucosal lesions were detected during nasal, pharyngeal, or oral inspection after nasopharyngeal catheter removal.

CONCLUSIONS

In this study, a novel nasopharyngeal cooling catheter effectively induced and maintained exclusive brain cooling when combined with effective counter-warming methods. Exclusive brain cooling was safe with no device-related local or systemic complications and may be desired in selected patient populations.

Rhabdomyolysis in a Morbidly Obese Patient After Oral Cavity Free Flap Reconstruction

Post-operative rhabdomyolysis is a rare but life-threatening condition. Less than ten cases have been described in the otolaryngic literature and, to our knowledge, no reports exist in the setting of oral reconstructive free tissue transfer. Case report presentation. We discuss the clinical course that lead to the diagnosis of rhabdomyolysis with special consideration to simultaneous microvascular anastomosis. Serial lab values were closely followed to prevent kidney injury while preventing flap congestion. Excessive fluid resuscitation in free flap reconstruction has been associated with increased post-operative complications and flap failure. We present a cautionary case to highlight the need for early diagnosis of rhabdomyolysis, a condition that may become more prevalent in the head and neck population as obesity, the main risk factor, continues to increase worldwide.

Use of plethysmographic variability index and perfusion index to evaluate changes in arterial blood pressure in anesthetized tigers (Panthera tigris)

OBJECTIVE To investigate use of the plethysmographic variability index (PVI) and perfusion index (PI) for evaluating changes in arterial blood pressure in anesthetized tigers (Panthera tigris). ANIMALS 8 adult tigers. PROCEDURES Each tiger was anesthetized once with a combination of ketamine, midazolam, medetomidine, and isoflurane. Anesthetic monitoring included assessment of PI, PVI, direct blood pressure measurements, anesthetic gas concentrations, esophageal temperature, and results of capnography and ECG. Mean arterial blood pressure (MAP) was maintained for at least 20 minutes at each of the following blood pressure conditions: hypotensive (MAP = 50 ± 5 mm Hg), normotensive (MAP = 70 ± 5 mm Hg), and hypertensive (MAP = 90 ± 5 mm Hg). Arterial blood gas analysis was performed at the beginning of anesthesia and at each blood pressure condition. RESULTS Mean ± SD PI values were 1.82 ± 2.38%, 1.17 ± 0.77%, and 1.71 ± 1.51% and mean PVI values were 16.00 ± 5.07%, 10.44 ± 3.55%, and 8.17 ± 3.49% for hypotensive, normotensive, and hypertensive conditions, respectively. The PI values did not differ significantly among blood pressure conditions. The PVI value for the hypotensive condition differed significantly from values for the normotensive and hypertensive conditions. The PVI values were significantly correlated with MAP (r = -0.657). The OR of hypotension to nonhypotension for PVI values ≥ 18% was 43.6. CONCLUSIONS AND CLINICAL RELEVANCE PVI was a clinically applicable variable determined by use of noninvasive methods in anesthetized tigers. Values of PVI ≥ 18% may indicate hypotension.

In-human subject-specific evaluation of a control-theoretic plasma volume regulation model

The goal of this study was to conduct a subject-specific evaluation of a control-theoretic plasma volume regulation model in humans. We employed a set of clinical data collected from nine human subjects receiving fluid bolus with and without co-administration of an inotrope agent, including fluid infusion rate, plasma volume, and urine output. Once fitted to the data associated with each subject, the model accurately reproduced the fractional plasma volume change responses in all subjects: the error between actual versus model-reproduced fractional plasma volume change responses was only 1.4 ± 1.6% and 1.2 ± 0.3% of the average fractional plasma volume change responses in the absence and presence of inotrope co-administration. In addition, the model parameters determined by the subject-specific fitting assumed physiologically plausible values: (i) initial plasma volume was estimated to be 36 ± 11 mL/kg and 37 ± 10 mL/kg in the absence and presence of inotrope infusion, respectively, which was comparable to its actual counterpart of 37 ± 4 mL/kg and 43 ± 6 mL/kg; (ii) volume distribution ratio, specifying the ratio with which the inputted fluid is distributed in the intra- and extra-vascular spaces, was estimated to be 3.5 ± 2.4 and 1.9 ± 0.5 in the absence and presence of inotrope infusion, respectively, which accorded with the experimental observation that inotrope could enhance plasma volume expansion in response to fluid infusion. We concluded that the model was equipped with the ability to reproduce plasma volume response to fluid infusion in humans with physiologically plausible model parameters, and its validity may persist even under co-administration of inotropic agents.

Arterial Pressure Variation in Elective Noncardiac Surgery: Identifying Reference Distributions and Modifying Factors

BACKGROUND

Assessment of need for intravascular volume resuscitation remains challenging for anesthesiologists. Dynamic waveform indices, including systolic and pulse pressure variation, are demonstrated as reliable measures of fluid responsiveness for mechanically ventilated patients. Despite widespread use, real-world reference distributions for systolic and pulse pressure variation values have not been established for euvolemic intraoperative patients. The authors sought to establish systolic and pulse pressure variation reference distributions and assess the impact of modifying factors.

METHODS

The authors evaluated adult patients undergoing general anesthetics for elective noncardiac surgery. Median systolic and pulse pressure variations during a 50-min postinduction period were noted for each case. Modifying factors including body mass index, age, ventilator settings, positioning, and hemodynamic management were studied via univariate and multivariable analyses. For systolic pressure variation values, effects of data entry method (manually entered vs. automated recorded) were similarly studied.

RESULTS

Among 1,791 cases, per-case median systolic and pulse pressure variation values formed nonparametric distributions. For each distribution, median values, interquartile ranges, and reference intervals (2.5th to 97.5th percentile) were, respectively, noted: these included manually entered systolic pressure variation (6.0, 5.0 to 7.0, and 3.0 to 11.0 mmHg), automated systolic pressure variation (4.7, 3.9 to 6.0, and 2.2 to 10.4 mmHg), and automated pulse pressure variation (7.0, 5.0 to 9.0, and 2.0 to 16.0%). Nonsupine positioning and preoperative β blocker were independently associated with altered systolic and pulse pressure variations, whereas ventilator tidal volume more than 8 ml/kg ideal body weight and peak inspiratory pressure more than 16 cm H2O demonstrated independent associations for systolic pressure variation only.

CONCLUSIONS

This study establishes real-world systolic and pulse pressure variation reference distributions absent in the current literature. Through a consideration of reference distributions and modifying factors, the authors' study provides further evidence for assessing intraoperative volume status and fluid management therapies.

Predicting the Need for Fluid Therapy-Does Fluid Responsiveness Work?

Fluid overdose can be harmful in critically ill patients. Since central venous pressure (CVP) is currently considered to be an inappropriate indicator of preload, much attention is being given to predicting fluid responsiveness, i.e., the response of stroke volume (SV) or cardiac output (CO) to fluid challenge. However, when fluid responsiveness was evaluated in critically ill patients, including sepsis, only 40–50% of the patients responded. Moreover, most fluid responders do not show significant hemodynamic improvement after fluid administration. In this review, we discuss why fluid responsiveness based on the Starling mechanism did not work well in the clinical setting.

According to the Starling mechanism, a patient whose SV/CO significantly increases after a fluid challenge is considered to be a fluid responder and judged to need fluid therapy. However, the currently recommended fluid challenge dose of crystalloid 250–500 mL has little effect on increasing blood volume and is not sufficient to increase the preload of the Starling curve. Especially in septic patients, due to their vascular hyperpermeability, increase in blood volume is even smaller. Furthermore, Infusion induced hemodilution is known to reduce blood viscosity and hematocrit, as a result, decreasing afterload. This indicates that the increased SV/CO after fluid challenge is caused not only by increased preload but also by decreased afterload. For these reasons, fluid responsiveness with small crystalloid challenge is questionable as a clinical indicator of fluid therapy.

Does stroke volume variation predict fluid responsiveness in children: A systematic review and meta-analysis

OBJECTIVE

Stroke volume variation (SVV) is a reliable predictor of fluid responsiveness in adult patients. However, the predictive value of SVV is uncertain in pediatric patients. We performed the first systematic meta-analysis to evaluate the diagnostic value of SVV in predicting fluid responsiveness in children.

METHODS

PUBMED, EMBASE, and Cochrane Central Register of Controlled Trials were searched up to December 2016. Original studies assessing the diagnostic accuracy of SVV in predicting fluid responsiveness in children were considered to be eligible. A random-effects model was used to calculate pooled values of sensitivity, specificity and diagnostic odds ratio with 95% CI. The summary receiver operating characteristic curve was estimated and area under the curve was calculated. Quality of the studies was assessed with the QUADAS-2 tool.

RESULTS

Six studies with a total of 279 fluid boluses in 224 children were included. The analysis demonstrated a pooled sensitivity of 0.68 (95% CI,0.59-0.76), pooled specificity of 0.65 (95% CI, 0.57-0.73), pooled diagnostic odds ratio of 8.24 (95% CI, 2.58-26.30), and the summary area under the summary receiver operating characteristic curve of 0.81. However, significant inter-study heterogeneity was found (p<0.05, I2 = 61.3%), likely due to small sample size and diverse study characteristics.

CONCLUSIONS

Current evidence suggests that SVV was of diagnostic value in predicting fluid responsiveness in children under mechanical ventilation. Given the high heterogeneity of published data, further studies are needed to confirm the diagnostic accuracy of SVV in predicting fluid responsiveness in pediatric patients.

Respiratory variation of systolic and diastolic time intervals within radial arterial waveform: a comparison with dynamic preload index

BACKGROUND

A blood pressure (BP) waveform contains various pieces of information related to respiratory variation. Systolic time interval (STI) reflects myocardial performance, and diastolic time interval (DTI) represents diastolic filling. This study examined whether respiratory variations of STI and DTI within radial arterial waveform are comparable to dynamic indices.

METHODS

During liver transplantation, digitally recorded BP waveform and stroke volume variation (SVV) were retrospectively analyzed. Beat-to-beat STI and DTI were extracted within each BP waveform, which were separated by dicrotic notch. Systolic time variation (STV) was calculated by the average of 3 consecutive respiratory cycles: [(STImax- STImin)/STImean]. Similar formula was used for diastolic time variation (DTV) and pulse pressure variation (PPV). Receiver operating characteristic analysis with area under the curve (AUC) was used to assess thresholds predictive of SVV ≥12% and PPV ≥12%.

RESULTS

STV and DTV showed significant correlations with SVV (r= 0.78 and r= 0.67, respectively) and PPV (r= 0.69 and r= 0.69, respectively). Receiver operating characteristic curves demonstrated that STV ≥11% identified to predict SVV ≥12% with 85.7% sensitivity and 89.3% specificity (AUC = 0.935; P< .001). DTV ≥11% identified to predict SVV ≥12% with 71.4% sensitivity and 85.7% specificity (AUC = 0.829; P< .001). STV ≥12% and DTV ≥11% identified to predict PPV ≥12% with an AUC of 0.881 and 0.885, respectively.

CONCLUSION

Respiratory variations of STI and DTI derived from radial arterial contour have a potential to predict hemodynamic response as a surrogate for SVV or PPV.

Fluid management in abdominal surgery: what, when, and when not to administer

The entire team (including anesthesiologists, surgeons, and intensive care physicians) must work together (before, during, and after abdominal surgery) to determine the optimal amount (quantity) and type (quality) of fluid necessary in the perioperative period. The authors present an overview of the basic principles that underlie fluid management, including evidence-based recommendations (where tenable) and a rational approach for when and what to administer.

Pulse pressure variation and stroke volume variation under different inhaled concentrations of isoflurane, sevoflurane and desflurane in pigs undergoing hemorrhage

OBJECTIVES

Inhalant anesthesia induces dose-dependent cardiovascular depression, but whether fluid responsiveness is differentially influenced by the inhalant agent and plasma volemia remains unknown. The aim of this study was to compare the effects of isoflurane, sevoflurane and desflurane on pulse pressure variation and stroke volume variation in pigs undergoing hemorrhage.

METHODS

Twenty-five pigs were randomly anesthetized with isoflurane, sevoflurane or desflurane. Hemodynamic and echocardiographic data were registered sequentially at minimum alveolar concentrations of 1.00 (M1), 1.25 (M2), and 1.00 (M3). Then, following withdrawal of 30% of the estimated blood volume, these data were registered at a minimum alveolar concentrations of 1.00 (M4) and 1.25 (M5).

RESULTS

The minimum alveolar concentration increase from 1.00 to 1.25 (M2) decreased the cardiac index and increased the central venous pressure, but only modest changes in mean arterial pressure, pulse pressure variation and stroke volume variation were observed in all groups from M1 to M2. A significant decrease in mean arterial pressure was only observed with desflurane. Following blood loss (M4), pulse pressure variation, stroke volume variation and central venous pressure increased (p < 0.001) and mean arterial pressure decreased in all groups. Under hypovolemia, the cardiac index decreased with the increase of anesthesia depth in a similar manner in all groups.

CONCLUSION

The effects of desflurane, sevoflurane and isoflurane on pulse pressure variation and stroke volume variation were not different during normovolemia or hypovolemia.

Mini-fluid challenge can predict arterial pressure response to volume expansion in spontaneously breathing patients under spinal anaesthesia

INTRODUCTION

The objective of this study was to test whether stroke volume (SV) variations in response to a fixed mini-fluid challenge (ΔSV100) measured by impedance cardiography (ICG) could predict an increase in arterial pressure with volume expansion in spontaneously breathing patients under spinal anaesthesia.

METHODS

Thirty-four patients, monitored by ICG who required intravenous fluid to expand their circulating volume during surgery under spinal anaesthesia, were studied. Haemodynamic variables and bioimpedance indices (blood pressure, SV, cardiac output [CO]) were measured before and after fluid challenge with 100mL of crystalloid, and before/after volume expansion. Responders were defined by ≥15% increase in systolic arterial pressure (SAP) after infusion of 500 mL of crystalloid solution.

RESULTS

SAP increased by ≥15% in 20 (59%) of the 34 patients. SAP, SV, and CO increased and HR decreased only in responders. SV variations in response to mini-fluid challenge and volume expansion differed between patients who showed arterial responsiveness and those in whom SAP did not increase with volume expansion (11.6% [9.1-19.3] versus 2.5% [1.3-7], P<0.001, and 22.4% [11.7-36.6] versus 0.9 [0-5.5], P<0.001, respectively). ΔSV100 predicted an increase of arterial pressure with an area under the receiver operating characteristic (AUC) curve of 0.89 (CI95%: 0.73-0.97, P<0.001). The cut-off was 5%. Baseline SAP and HR were not predictive of arterial responsiveness (P>0.05).

CONCLUSION

A ΔSV100 over 5% accurately predicted arterial pressure response to volume expansion during surgery.

Arterial Pressure Variation as a Biomarker of Preload Dependency in Spontaneously Breathing Subjects - A Proof of Principle

OBJECTIVE

Pulse (PPV) and systolic pressure variation (SPV) quantify variations in arterial pressure related to heart-lung interactions and have been introduced as biomarkers of preload dependency to guide fluid treatment in mechanically ventilated patients. However, respiratory intra-thoracic pressure changes during spontaneous breathing are considered too small to affect preload and stroke volume sufficiently for the detection by PPV and/or SPV. This study addressed the effects of paced breathing and/or an external respiratory resistance on PPV and SPV in detecting preload dependency in spontaneously breathing subjects.

METHODS

In 10 healthy subjects, hemodynamic and respiratory parameters were evaluated during progressive central hypovolemia (head-up tilt). Breathing conditions were varied by manipulating breathing frequency and respiratory resistance. Subjects responding with a reduction in stroke volume index ≥15% were classified as having developed preload dependency. The ability for PPV and SPV to predict preload dependency was expressed by the area under the ROC curve (AUC).

RESULTS

A breathing frequency at 6/min increased the PPV (16±5% vs. 10±3%, p<0.001) and SPV (9±3% vs. 5±2%, p<0.001) which was further enhanced by an expiratory resistance (PPV: 19±3%, p = 0.025 and SPV: 10±2%, p = 0.047). These respiratory modifications, compared to free breathing, enhanced the predictive value of PPV with higher accuracy (AUC: 0.92 vs. 0.46).

CONCLUSION

Under conditions of progressive central hypovolemia, the application of an external respiratory resistance at a breathing frequency of 6/min enhanced PPV and SPV and is worth further study for detection of preload dependency from arterial pressure variations in non-ventilated subjects.

Non-invasive measurements of pulse pressure variation and stroke volume variation in anesthetized patients using the Nexfin blood pressure monitor

Nexfin beat-to-beat arterial blood pressure monitoring enables continuous assessment of hemodynamic indices like cardiac index (CI), pulse pressure variation (PPV) and stroke volume variation (SVV) in the perioperative setting. In this study we investigated whether Nexfin adequately reflects alterations in these hemodynamic parameters during a provoked fluid shift in anesthetized and mechanically ventilated patients. The study included 54 patients undergoing non-thoracic surgery with positive pressure mechanical ventilation. The provoked fluid shift comprised 15° Trendelenburg positioning, and fluid responsiveness was defined as a concomitant increase in stroke volume (SV) >10 %. Nexfin blood pressure measurements were performed during supine steady state, Trendelenburg and supine repositioning. Hemodynamic parameters included arterial blood pressure (MAP), CI, PPV and SVV. Trendelenburg positioning did not affect MAP or CI, but induced a decrease in PPV and SVV by 3.3 ± 2.8 and 3.4 ± 2.7 %, respectively. PPV and SVV returned back to baseline values after repositioning of the patient to baseline. Bland–Altman analysis of SVV and PPV showed a bias of −0.3 ± 3.0 % with limits of agreement ranging from −5.6 to 6.2 %. The SVV was more superior in predicting fluid responsiveness (AUC 0.728) than the PVV (AUC 0.636), respectively. The median bias between PPV and SVV was different for patients younger [−1.5 % (−3 to 0)] or older [+2 % (0–4.75)] than 55 years (P < 0.001), while there were no gender differences in the bias between PPV and SVV. The Nexfin monitor adequately reflects alterations in PPV and SVV during a provoked fluid shift, but the level of agreement between PPV and SVV was low. The SVV tended to be superior over PPV or Ea_dyn in predicting fluid responsiveness in our population.

Respiratory variation in carotid peak systolic velocity predicts volume responsiveness in mechanically ventilated patients with septic shock: a prospective cohort study

Background

The evaluation of fluid responsiveness in patients with hemodynamic instability remains to be challenging. This investigation aimed to determine whether respiratory variation in carotid Doppler peak velocity (ΔCDPV) predicts fluid responsiveness in patients with septic shock and lung protective mechanical ventilation with a tidal volume of 6 ml/kg.

Methods

We performed a prospective cohort study at an intensive care unit, studying the effect of 59 fluid challenges on 19 mechanically ventilated patients with septic shock. Pre-fluid challenge ΔCDPV and other static or dynamic measurements were obtained. Fluid challenge responders were defined as patients whose stroke volume index increased more than 15 % on transpulmonary thermodilution. The area under the receiver operating characteristic curve (AUROC) was compared for each predictive parameter.

Results

Fluid responsiveness rate was 51 %. The ΔCDPV had an AUROC of 0.88 (95 % confidence interval (CI) 0.77–0.95); followed by stroke volume variation (0.72, 95 % CI 0.63–0.88), passive leg raising (0.69, 95 % CI 0.56–0.80), and pulse pressure variation (0.63, 95 % CI 0.49–0.75). The ΔCDPV was a statistically significant superior predictor when compared with the other parameters. Sensitivity, specificity, and positive and negative predictive values were also the highest for ΔCDPV, with an optimal cutoff at 14 %. There was good correlation between ΔCDPV and SVI increment after the fluid challenge (r = 0.84; p < 0.001).

Conclusions

ΔCDPV can be more accurate than other methods for assessing fluid responsiveness in patients with septic shock receiving lung protective mechanical ventilation. ΔCDPV also has a high correlation with SVI increase after fluid challenge.

The correlation between the Trendelenburg position and the stroke volume variation

Background

The stroke volume variation (SVV), based on lung-heart interaction during mechanical ventilation, is a useful dynamic parameter for fluid responsiveness. However, it is affected by many factors. The aim of this study was to evaluate the effects of SVV on Trendelenburg (T) and reverse Trendelenburg (RT) position and to further elaborate on the patterns of the SVV with position.

Methods

Forty-two patients undergoing elective surgery were enrolled in this study. Fifteen minutes after standardized induction of anesthesia with propofol, fentanyl, and rocuronium with volume controlled ventilation (tidal volume of 8 ml/kg of ideal body weight, inspiration : expiration ratio of 1 : 2, and respiratory rate of 10-13 breaths/min), the patients underwent posture changes as follows: supine, T position at slopes of operating table of -5°, -10°, and -15°, and RT position at slopes of operating table of 5°, 10°, and 15°. At each point, SVV, cardiac output (CO), peak airway pressure (PAP), mean blood pressure, and heart rate (HR) were recorded.

Results

The SVV was significant decreased with decreased slopes of operating table in T position, and increased with increased slopes of operating table in RT position (P = 0.000). Schematically, it was increased by 1% when the slope of operating table was increased by 5°. But, the CO and PAP were significant increased with decreased slopes of operating table in T position, and decreased with increased slopes of operating table in RT position (P = 0.045, 0.027).

Conclusions

SVV is subjected to the posture, and we should take these findings into account on reading SVV for fluid therapy.

Ultrasonographic measurement of the respiratory variation in the inferior vena cava diameter is predictive of fluid responsiveness in critically ill patients: systematic review and meta-analysis

Respiratory variation in the inferior vena cava (ΔIVC) has been extensively studied with respect to its value in predicting fluid responsiveness, but the results are conflicting. This systematic review was aimed at investigating the diagnostic accuracy of ΔIVC in predicting fluid responsiveness. Databases including Medline, Embase, Scopus and Web of Knowledge were searched from inception to May 2013. Studies exploring the diagnostic performance of ΔIVC in predicting fluid responsiveness were included. To allow for more between- and within-study variance, a hierarchical summary receiver operating characteristic model was used to pool the results. Subgroup analyses were performed for patients on mechanical ventilation, spontaneously breathing patients and those challenged with colloids and crystalloids. A total of 8 studies involving 235 patients were eligible for analysis. Cutoff values of ΔIVC varied across studies, ranging from 12% to 40%. The pooled sensitivity and specificity in the overall population were 0.76 (95% confidence interval [CI]: 0.61-0.86) and 0.86 (95% CI: 0.69-0.95), respectively. The pooled diagnostic odds ratio (DOR) was 20.2 (95% CI: 6.1-67.1). The diagnostic performance of ΔIVC appeared to be better in patients on mechanical ventilation than in spontaneously breathing patients (DOR: 30.8 vs. 13.2). The pooled area under the receiver operating characteristic curve was 0.84 (95% CI: 0.79-0.89). Our study indicates that ΔIVC measured with point-of-care ultrasonography is of great value in predicting fluid responsiveness, particularly in patients on controlled mechanical ventilation and those resuscitated with colloids.

Limitations of global end-diastolic volume index as a parameter of cardiac preload in the early phase of severe sepsis: a subgroup analysis of a multicenter, prospective observational study

Background

In patients with severe sepsis, depression of cardiac performance is common and is often associated with left ventricular (LV) dilatation to maintain stroke volume. Although it is essential to optimize cardiac preload to maintain tissue perfusion in patients with severe sepsis, the optimal preload remains unknown. This study aimed to evaluate the reliability of global end-diastolic volume index (GEDI) as a parameter of cardiac preload in the early phase of severe sepsis.

Methods

Ninety-three mechanically ventilated patients with acute lung injury/acute respiratory distress syndrome secondary to sepsis were enrolled for subgroup analysis in a multicenter, prospective, observational study. Patients were divided into two groups—with sepsis-induced myocardial dysfunction (SIMD) and without SIMD (non-SIMD)—according to a threshold LV ejection fraction (LVEF) of 50% on the day of enrollment. Both groups were further subdivided according to a threshold stroke volume variation (SVV) of 13% as a parameter of fluid responsiveness.

Results

On the day of enrollment, there was a positive correlation (r = 0.421, p = 0.045) between GEDI and SVV in the SIMD group, whereas this paradoxical correlation was not found in the non-SIMD group and both groups on day 2. To evaluate the relationship between attainment of cardiac preload optimization and GEDI value, GEDI with SVV ≤13% and SVV >13% was compared in both the SIMD and non-SIMD groups. SVV ≤13% implies the attainment of cardiac preload optimization. Among patients with SIMD, GEDI was higher in patients with SVV >13% than in patients with SVV ≤13% on the day of enrollment (872 [785–996] mL/m² vs. 640 [597–696] mL/m²; p < 0.001); this finding differed from the generally recognized relationship between GEDI and SVV. However, GEDI was not significantly different between patients with SVV ≤13% and SVV >13% in the non-SIMD group on the day of enrollment and both groups on day 2.

Conclusions

In the early phase of severe sepsis in mechanically ventilated patients, there was no constant relationship between GEDI and fluid reserve responsiveness, irrespective of the presence of SIMD. GEDI should be used as a cardiac preload parameter with awareness of its limitations.

The maintenance and monitoring of perioperative blood volume

The assessment and maintenance of perioperative blood volume is important because fluid therapy is a routine part of intraoperative care. In the past, patients undergoing major surgery were given large amounts of fluids because health-care providers were concerned about preoperative dehydration and intraoperative losses to a third space. In the last decade it has become clear that fluid therapy has to be more individualized. Because the exact determination of blood volume is not clinically possible at every timepoint, there have been different approaches to assess fluid requirements, such as goal-directed protocols guided by invasive and less invasive devices.

This article focuses on laboratory volume determination, capillary dynamics, aspects of different fluids and how to clinically assess and monitor perioperative blood volume.