Stroke volume and pulse pressure variation for prediction of fluid responsiveness in patients undergoing off-pump coronary artery bypass grafting

Outcomes associated with stroke volume variation versus central venous pressure guided fluid replacements during major abdominal surgery

Background and Aims:

There is limited data on the impact of perioperative fluid therapy guided by dynamic preload variables like stroke volume variation (SVV) on outcomes after abdominal surgery. We studied the effect of SVV guided versus central venous pressure (CVP) guided perioperative fluid administration on outcomes after major abdominal surgery.

Material and Methods:

Sixty patients undergoing major abdominal surgeries were randomized into two equal groups in this prospective single blind randomized study. In the standard care group, the CVP was maintained at 10-12 mmHg while in the intervention group a SVV of 10% was achieved by the administration of fluids. The primary end-points were the length of Intensive Care Unit (ICU) and hospital stay. The secondary end points were intraoperative lactate, intravenous fluid use, requirement for inotropes, postoperative ventilation and return of bowel function.

Results:

The ICU stay was significantly shorter in the intervention group as compared to the control group (2.9 ± 1.15 vs. 5.4 ± 2.71 days). The length of hospital stay was also shorter in the intervention group, (9.9 ± 2.68 vs. 11.96 ± 5.15 days) though not statistically significant. The use of intraoperative fluids was significantly lower in the intervention group than the control group (7721.5 ± 4138.9 vs. 9216.33 ± 2821.38 ml). Other secondary outcomes were comparable between the two groups.

Conclusion:

Implementation of fluid replacement guided by a dynamic preload variable (SVV) versus conventional static variables (CVP) is associated with lesser postoperative ICU stay and reduced fluid requirements in major abdominal surgery.

Intra-Operative Fluid Management in Adult Neurosurgical Patients Undergoing Intracranial Tumour Surgery: Randomised Control Trial Comparing Pulse Pressure Variance (PPV) and Central Venous Pressure (CVP)

INTRODUCTION

Fluid management in neurosurgery presents specific challenges to the anaesthesiologist. Dynamic para-meters like Pulse Pressure Variation (PPV) have been used successfully to guide fluid management.

AIM

To compare PPV against Central Venous Pressure (CVP) in neurosurgical patients to assess hemodynamic stability and perfusion status.

MATERIALS AND METHODS

This was a single centre prospective randomised control trial at a tertiary care centre. A total of 60 patients undergoing intracranial tumour excision in supine and lateral positions were randomised to two groups (Group 1, CVP n=30), (Group 2, PPV n=30). Intra-operative fluid management was titrated to maintain baseline CVP in Group 1(5-10cm of water) and in Group 2 fluids were given to maintain PPV less than 13%. Acid base status, vital signs and blood loss were monitored.

RESULTS

Although intra-operative hypotension and acid base changes were comparable between the groups, the patients in the CVP group had more episodes of hypotension requiring fluid boluses in the first 24 hours post surgery. {CVP group median (25, 75) 2400ml (1850, 3110) versus PPV group 2100ml (1350, 2200) p=0.03} The patients in the PPV group received more fluids than the CVP group which was clinically significant. {2250 ml (1500, 3000) versus 1500ml (1200, 2000) median (25, 75) (p=0.002)}. The blood loss was not significantly different between the groups The median blood loss in the CVP group was 600ml and in the PPV group was 850 ml; p value 0.09.

CONCLUSION

PPV can be used as a reliable index to guide fluid management in neurosurgical patients undergoing tumour excision surgery in supine and lateral positions and can effectively augment CVP as a guide to fluid management. Patients in PPV group had better hemodynamic stability and less post operative fluid requirement.

Ultrasonographic measurements of the inferior vena cava variation as a predictor of fluid responsiveness in patients undergoing anesthesia for surgery

BACKGROUND

Both hypovolemia and hypervolemia are connected with increased morbidity and mortality in the treatment and prognosis of patients. An accurate assessment of volume state allows the optimization of organ perfusion and oxygen supply. Recently, ultrasonography has been used to detect hypovolemia in critically ill patients and perioperative patients. The objective of our study was to assess the correlation between inferior vena cava (IVC) variation obtained with ultrasound and stroke volume variation (SVV) measured by the Vigileo/FloTrac monitor, as fluid responsiveness indicators, in patients undergoing anesthesia for surgery.

METHODS

Forty patients (American Society of Anesthesiologists grades I and II) scheduled for elective gastrointestinal surgery were enrolled in our study. After anesthesia induction, 6% hydroxyethyl starch solution was administered to patients as an intravenous (IV) fluid. The IVC diameters were measured with ultrasonography. SVV and stroke volume index (SVI) were obtained from the Vigileo monitor. All data were collected both before and after fluid challenge.

RESULTS

Forty patients underwent IVC sonographic measurements and SVV calculation. After fluid challenge, mean arterial pressure, central venous pressure, SVI, and IVC diameters increased significantly, whereas SVV decreased markedly. The correlation coefficient between the increase in SVI and the baseline of IVC variation after an IV fluid was 0.710, and receiver operating characteristic (ROC) curve was 0.85. The correlation coefficient between the increase in SVI and the baseline of SVV was 0.803 with an ROC curve of 0.93. Central venous pressure had no significant correlation with SVI.

CONCLUSIONS

Our data show that IVC variation and SVV proved to be reliable predictors of fluid responsiveness in patients undergoing anesthesia for surgery with mechanical ventilation.

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.

The impact of inspiratory pressure on stroke volume variation and the evaluation of indexing stroke volume variation to inspiratory pressure under various preload conditions in experimental animals

PURPOSE

Stroke volume variation (SVV) measures fluid responsiveness, enabling optimal fluid management under positive pressure ventilation. We aimed to investigate the effect of peak inspiratory pressure (PIP) on SVV under various preload conditions in experimental animals and to ascertain whether SVV indexed to PIP decreases the effect.

METHODS

Mild and moderate hemorrhage models were created in nine anesthetized, mechanically ventilated beagle dogs by sequentially removing 10 and then an additional 10 ml/kg of blood, respectively. In all the animals, PIP was incrementally increased by 4 cmH2O, from 5 to 21 cmH2O. SVV was measured by arterial pulse contour analysis. Stroke volume was derived using a thermodilution method, and central venous pressure and mean arterial pressure were also measured.

RESULTS

SVV increased according to PIP with significant correlation at baseline, with mild hemorrhage and moderate hemorrhage. PIP regression coefficients at baseline and in the mild and moderate hemorrhage models were 0.59, 0.86, and 1.4, respectively. Two-way repeated-measures analysis of variance showed that PIP and the degree of hemorrhage had a significant interaction effect on SVV (p = 0.0016). SVV indexed to PIP reflected the hemorrhage status regardless of PIP changes ≥9 cmH2O.

CONCLUSIONS

PIP is significantly correlated with SVV, even under hypovolemia, and the effect is enhanced with decreasing preload volumes. Compared with SVV, the indexed SVV was less susceptible to higher inspiratory pressures.

Minimally invasive monitoring

Although use of the classic pulmonary artery catheter has declined, several techniques have emerged to estimate cardiac output. Arterial pressure waveform analysis computes cardiac output from the arterial pressure curve. The method of estimating cardiac output for these devices depends on whether they need to be calibrated by an independent measure of cardiac output. Some newer devices have been developed to estimate cardiac output from an arterial curve obtained noninvasively with photoplethysmography, allowing a noninvasive beat-by-beat estimation of cardiac output. This article describes the different devices that perform pressure waveform analysis.

Prediction of fluid responsiveness using a non-invasive cardiac output monitor in children undergoing cardiac surgery

BACKGROUND

This study evaluated the ability of a non-invasive cardiac output monitoring device (NICOM) to predict fluid responsiveness in paediatric patients undergoing cardiac surgery.

METHODS

Children aged <5 yr undergoing congenital heart surgery were included. Once the sternum had been closed after repair of the congenital heart defect, 10 ml kg(-1) colloid solution was administered for volume expansion. Transoesophageal echocardiography (TOE) was performed to measure stroke volume (SV) and respiratory variation in aortic blood flow peak velocity (ΔV(peak)) before and after volume expansion. Haemodynamic and NICOM variables, including SV(NICOM), stroke volume variance (SVV(NICOM)), cardiac index (CI(NICOM)), and percentage change in thoracic fluid content compared with baseline (TFCd0%), were also recorded. Patients in whom the stroke volume index (SVI), measured using TOE, increased by >15% were defined as fluid responders.

RESULTS

Twenty-nine patients were included (13 responders and 16 non-responders). Before volume expansion, only ΔV(peak) differed between groups (P=0.036). The SVV(NICOM), HR, and central venous pressure did not predict fluid responsiveness, but ΔV(peak) did. The CI(NICOM) was not correlated with CI(TOE) (r=0.107, P=0.43). Using Bland-Altman analysis, the mean bias between CI(TOE) and CI(NICOM) was 0.89 litre min(-1) m(-2), with a precision of 1.14 litre min(-1) m(-2). Trending ability of NICOM for SVI and CI was poor when TOE was a reference method.

CONCLUSIONS

The SVV(NICOM) did not predict fluid responsiveness in paediatric patients during cardiac surgery. In addition, there was no correlation between CI(TOE) and CI(NICOM). Fluid management guided by NICOM should be performed carefully.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov NCT01996956.

Perioperative fluid therapy: a statement from the international Fluid Optimization Group

BACKGROUND

Perioperative fluid therapy remains a highly debated topic. Its purpose is to maintain or restore effective circulating blood volume during the immediate perioperative period. Maintaining effective circulating blood volume and pressure are key components of assuring adequate organ perfusion while avoiding the risks associated with either organ hypo- or hyperperfusion. Relative to perioperative fluid therapy, three inescapable conclusions exist: overhydration is bad, underhydration is bad, and what we assume about the fluid status of our patients may be incorrect. There is wide variability of practice, both between individuals and institutions. The aims of this paper are to clearly define the risks and benefits of fluid choices within the perioperative space, to describe current evidence-based methodologies for their administration, and ultimately to reduce the variability with which perioperative fluids are administered.

METHODS

Based on the abovementioned acknowledgements, a group of 72 researchers, well known within the field of fluid resuscitation, were invited, via email, to attend a meeting that was held in Chicago in 2011 to discuss perioperative fluid therapy. From the 72 invitees, 14 researchers representing 7 countries attended, and thus, the international Fluid Optimization Group (FOG) came into existence. These researches, working collaboratively, have reviewed the data from 162 different fluid resuscitation papers including both operative and intensive care unit populations. This manuscript is the result of 3 years of evidence-based, discussions, analysis, and synthesis of the currently known risks and benefits of individual fluids and the best methods for administering them.

RESULTS

The results of this review paper provide an overview of the components of an effective perioperative fluid administration plan and address both the physiologic principles and outcomes of fluid administration.

CONCLUSIONS

We recommend that both perioperative fluid choice and therapy be individualized. Patients should receive fluid therapy guided by predefined physiologic targets. Specifically, fluids should be administered when patients require augmentation of their perfusion and are also volume responsive. This paper provides a general approach to fluid therapy and practical recommendations.

Arterial waveform analysis

The bedside measurement of continuous arterial pressure values from waveform analysis has been routinely available via indwelling arterial catheterization for >50 years. Invasive blood pressure monitoring has been utilized in critically ill patients, in both the operating room and critical care units, to facilitate rapid diagnoses of cardiovascular insufficiency and monitor response to treatments aimed at correcting abnormalities before the consequences of either hypo- or hypertension are seen. Minimally invasive techniques to estimate cardiac output (CO) have gained increased appeal. This has led to the increased interest in arterial waveform analysis to provide this important information, as it is measured continuously in many operating rooms and intensive care units. Arterial waveform analysis also allows for the calculation of many so-called derived parameters intrinsically created by this pulse pressure profile. These include estimates of left ventricular stroke volume (SV), CO, vascular resistance, and during positive-pressure breathing, SV variation, and pulse pressure variation. This article focuses on the principles of arterial waveform analysis and their determinants, components of the arterial system, and arterial pulse contour. It will also address the advantage of measuring real-time CO by the arterial waveform and the benefits to measuring SV variation. Arterial waveform analysis has gained a large interest in the overall assessment and management of the critically ill and those at a risk of hemodynamic deterioration.

Pulse pressure variation does not reflect stroke volume variation in mechanically ventilated rats with lipopolysaccharide-induced pneumonia

1. The present study examined the relationship between centrally measured stroke volume variation (SVV) and peripherally derived pulse pressure variation (PPV) in the setting of increased total arterial compliance (CA rt ). 2. Ten male Wistar rats were anaesthetized, paralysed and mechanically ventilated before being randomized to receive intrapulmonary lipopolysaccharide (LPS) or no LPS. Pulse pressure (PP) was derived from the left carotid artery, whereas stroke volume (SV) was measured directly in the left ventricle. Values of SVV and PPV were calculated over three breaths. Balloon inflation of a catheter positioned in the inferior vena cava was used, for a maximum of 30 s, to decrease preload while the SVV and PPV measurements were repeated. Values of CA rt were calculated as SV/PP. 3. Intrapulmonary LPS increased CA rt and SV. Values of SVV and PPV increased in both LPS-treated and untreated rats during balloon inflation. There was a correlation between SVV and PPV in untreated rats before (r = 0.55; P = 0.005) and during (r = 0.69; P < 0.001) occlusion of the vena cava. There was no such correlation in LPS-treated rats either before (r = -0.08; P = 0.70) or during (r = 0.36; P = 0.08) vena cava occlusion. 4. In conclusion, under normovolaemic and hypovolaemic conditions, PPV does not reflect SVV during an increase in CA rt following LPS-induced pneumonia in mechanically ventilated rats. Our data caution against their interchangeability in human sepsis.

Haemodynamic-guided fluid administration for the prevention of contrast-induced acute kidney injury: the POSEIDON randomised controlled trial

BACKGROUND

The administration of intravenous fluid remains the cornerstone treatment for the prevention of contrast-induced acute kidney injury. However, no well-defined protocols exist to guide fluid administration in this treatment. We aimed to establish the efficacy of a new fluid protocol to prevent contrast-induced acute kidney injury.

METHODS

In this randomised, parallel-group, comparator-controlled, single-blind phase 3 trial, we assessed the efficacy of a new fluid protocol based on the left ventricular end-diastolic pressure for the prevention of contrast-induced acute kidney injury in patients undergoing cardiac catheterisation. The primary outcome was the occurrence of contrast-induced acute kidney injury, which was defined as a greater than 25% or greater than 0·5 mg/dL increase in serum creatinine concentration. Between Oct 10, 2010, and July 17, 2012, 396 patients aged 18 years or older undergoing cardiac catheterisation with an estimated glomerular filtration rate of 60 mL/min per 1·73 m(2) or less and one or more of several risk factors (diabetes mellitus, history of congestive heart failure, hypertension, or age older than 75 years) were randomly allocated in a 1:1 ratio to left ventricular end-diastolic pressure-guided volume expansion (n=196) or the control group (n=200) who received a standard fluid administration protocol. Four computer-generated concealed randomisation schedules, each with permuted block sizes of 4, were used for randomisation, and participants were allocated to the next sequential randomisation number by sealed opaque envelopes. Patients and laboratory personnel were masked to treatment assignment, but the physicians who did the procedures were not masked. Both groups received intravenous 0·9% sodium chloride at 3 mL/kg for 1 h before cardiac catheterisation. Analyses were by intention to treat. Adverse events were assessed at 30 days and 6 months and all such events were classified by staff who were masked to treatment assignment. This trial is registered with ClinicalTrials.gov, number NCT01218828.

FINDINGS

Contrast-induced acute kidney injury occurred less frequently in patients in the left ventricular end-diastolic pressure-guided group (6·7% [12/178]) than in the control group (16·3% [28/172]; relative risk 0·41, 95% CI 0·22-0·79; p=0·005). Hydration treatment was terminated prematurely because of shortness of breath in three patients in each group.

INTERPRETATION

Left ventricular end-diastolic pressure-guided fluid administration seems to be safe and effective in preventing contrast-induced acute kidney injury in patients undergoing cardiac catheterisation.

FUNDING

Kaiser Permanente Southern California regional research committee grant.

Arterial pressure variations as parameters of brain perfusion in response to central blood volume depletion and repletion

Rationale: A critical reduction in central blood volume (CBV) is often characterized by hemodynamic instability. Restoration of a volume deficit may be established by goal-directed fluid therapy guided by respiration-related variation in systolic- and pulse pressure (SPV and PPV). Stroke volume index (SVI) serves as a surrogate end-point of a fluid challenge but tissue perfusion itself has not been addressed.

Objective: To delineate the relationship between arterial pressure variations, SVI and regional brain perfusion during CBV depletion and repletion in spontaneously breathing volunteers.

Methods: This study quantified in 14 healthy subjects (11 male) the effects of CBV depletion [by 30 and 70 degrees passive head-up tilt (HUT)] and a fluid challenge (by tilt back) on CBV (thoracic admittance), mean middle cerebral artery (MCA) blood flow velocity (V_mean), SVI, cardiac index (CI), PPV, and SPV.

Results: PPV (103 ± 89%, p < 0.05) and SPV (136 ± 117%, p < 0.05) increased with progression of central hypovolemia manifested by a reduction in thoracic admittance (11 ± 5%, p < 0.001), SVI (28 ± 6%, p < 0.001), CI (6 ± 8%, p < 0.001), and MCAV_mean (17 ± 7%, p < 0.05) but not in arterial pressure. The reduction in MCAV_mean correlated to the fall in SVI (R² = 0.52, p < 0.0001) and inversely to PPV and SPV [R² = 0.46 (p < 0.0001) and R² = 0.45 (p < 0.0001), respectively]. PPV and SPV predicted a ≥15% reduction in MCAV_mean and SVI with comparable sensitivity (67/67% vs. 63/68%, respectively) and specificity (89/94 vs. 89/94%, respectively). A rapid fluid challenge by tilt-back restored all parameters to baseline values within 1 min.

Conclusion: In spontaneously breathing subjects, a reduction in MCAV_mean was related to an increase in PPV and SPV during graded CBV depletion and repletion. Specifically, PPV and SPV predicted changes in both SVI and MCAV_mean with comparable sensitivity and specificity, however the predictive value is limited in spontaneously breathing subjects.

Individually optimized hemodynamic therapy reduces complications and length of stay in the intensive care unit: a prospective, randomized controlled trial

BACKGROUND

The authors hypothesized that goal-directed hemodynamic therapy, based on the combination of functional and volumetric hemodynamic parameters, improves outcome in patients with cardiac surgery. Therefore, a therapy guided by stroke volume variation, individually optimized global end-diastolic volume index, cardiac index, and mean arterial pressure was compared with an algorithm based on mean arterial pressure and central venous pressure.

METHODS

This prospective, controlled, parallel-arm, open-label trial randomized 100 coronary artery bypass grafting and/or aortic valve replacement patients to a study group (SG; n = 50) or a control group (CG; n = 50). In the SG, hemodynamic therapy was guided by stroke volume variation, optimized global end-diastolic volume index, mean arterial pressure, and cardiac index. Optimized global end-diastolic volume index was defined before and after weaning from cardiopulmonary bypass and at intensive care unit (ICU) admission. Mean arterial pressure and central venous pressure served as hemodynamic goals in the CG. Therapy was started immediately after induction of anesthesia and continued until ICU discharge criteria, serving as primary outcome parameter, were fulfilled.

RESULTS

Intraoperative need for norepinephrine was decreased in the SG with a mean (±SD) of 9.0 ± 7.6 versus 14.9 ± 11.1 µg/kg (P = 0.002). Postoperative complications (SG, 40 vs. CG, 63; P = 0.004), time to reach ICU discharge criteria (SG, 15 ± 6 h; CG, 24 ± 29 h; P < 0.001), and length of ICU stay (SG, 42 ± 19 h; CG, 62 ± 58 h; P = 0.018) were reduced in the SG.

CONCLUSION

Early goal-directed hemodynamic therapy based on cardiac index, stroke volume variation, and optimized global end-diastolic volume index reduces complications and length of ICU stay after cardiac surgery.

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.

A comparison of noninvasive bioreactance with oesophageal Doppler estimation of stroke volume during open abdominal surgery: an observational study

CONTEXT

The anaesthetist must maintain tissue perfusion by ensuring optimal perioperative fluid balance. This can be achieved using less invasive cardiac output monitors such as oesophageal Doppler monitoring (ODM). Other less invasive cardiac output monitors using bio-impedence technology (noninvasive cardiac output monitoring, NICOM) may have a role in monitoring the circulation and informing fluid management decisions.

OBJECTIVE

To compare estimates of stroke volume from ODM with those from NICOM, a noninvasive monitor using bioreactance, a modification of transthoracic bio-impedence.

DESIGN

An observational study.

SETTING

Manchester Royal Infirmary, UK. Data collected in 2011 and 2012.

PARTICIPANTS

Twenty-two patients scheduled for major, open abdominal surgery. Reasons for noninclusion: atrial fibrillation; heart failure; oesophageal disease; lack of capacity; and known sensitivity to colloid.

INTERVENTION

All patients had oesophageal Doppler cardiac output monitoring as a standard element of anaesthesia care. We placed NICOM Bioreactance electrodes and recorded stroke volume estimates from both devices. Fluid challenges were given by the anaesthetist and the haemodynamic responses were recorded.

MAIN OUTCOME MEASURE

Stroke volume during surgery. The Bland-Altman method was used to compare bias and limits of agreement for stroke volume and cardiac output. Fluid responders were defined as patients who increased stroke volume by at least 10% after fluid loading. The precision of each device was calculated during periods of haemodynamic stability.

RESULTS

We made 788 acceptable measurements of cardiac output. The bias was -6.9 ml and the limits of agreement were -22.9 to 36.8 ml. The percentage error was 57%. Average precision for both the ODM and NICOM were similar, 8.5% (SD 5.4%) and 8.7% (SD 3.2%). The concordance for the stroke volume change following fluid challenge was 90.5%. Both devices produced unacceptable readings with electrical diathermy.

CONCLUSION

Simultaneous stroke volume estimations made by noninvasive Bioreactance (NICOM) and oesophageal Doppler showed bias and limits of agreement that are not clinically acceptable. The measurements made by these two devices cannot be regarded as interchangeable.

Perioperative hemodynamic monitoring

Hemodynamic monitoring is the cornerstone of perioperative anesthetic monitoring. In the unconscious patient, hemodynamic monitoring not only provides information relating to cardiac output, volume status and ultimately tissue perfusion, but also indicates depth of anesthesia and adequacy of pain control. In the 21st century the anesthesiologist has an array of devices to choose from. No single device provides a complete assessment of hemodynamic status, and the use of all devices in every situation is neither practical nor appropriate. This article aims to provide the reader with an overview of the devices currently available, and the information they provide, to assist anesthesiologists in the selection of the most appropriate devices for any given situation.

Does the central venous pressure predict fluid responsiveness? An updated meta-analysis and a plea for some common sense

BACKGROUND

Despite a previous meta-analysis that concluded that central venous pressure should not be used to make clinical decisions regarding fluid management, central venous pressure continues to be recommended for this purpose.

AIM

To perform an updated meta-analysis incorporating recent studies that investigated indices predictive of fluid responsiveness. A priori subgroup analysis was planned according to the location where the study was performed (ICU or operating room).

DATA SOURCES

MEDLINE, EMBASE, Cochrane Register of Controlled Trials, and citation review of relevant primary and review articles.

STUDY SELECTION

Clinical trials that reported the correlation coefficient or area under the receiver operating characteristic curve (AUC) between the central venous pressure and change in cardiac performance following an intervention that altered cardiac preload. From 191 articles screened, 43 studies met our inclusion criteria and were included for data extraction. The studies included human adult subjects, and included healthy controls (n = 1) and ICU (n = 22) and operating room (n = 20) patients.

DATA EXTRACTION

Data were abstracted on study characteristics, patient population, baseline central venous pressure, the correlation coefficient, and/or the AUC between central venous pressure and change in stroke volume index/cardiac index and the percentage of fluid responders. Meta-analytic techniques were used to summarize the data.

DATA SYNTHESIS

Overall 57% ± 13% of patients were fluid responders. The summary AUC was 0.56 (95% CI, 0.54-0.58) with no heterogenicity between studies. The summary AUC was 0.56 (95% CI, 0.52-0.60) for those studies done in the ICU and 0.56 (95% CI, 0.54-0.58) for those done in the operating room. The summary correlation coefficient between the baseline central venous pressure and change in stroke volume index/cardiac index was 0.18 (95% CI, 0.1-0.25), being 0.28 (95% CI, 0.16-0.40) in the ICU patients, and 0.11 (95% CI, 0.02-0.21) in the operating room patients.

CONCLUSIONS

There are no data to support the widespread practice of using central venous pressure to guide fluid therapy. This approach to fluid resuscitation should be abandoned.

[Influence of pressure- and volume-controlled ventilation on pulse pressure variations: randomized study]

OBJECTIVE

Pulse pressure variation (ΔPP) has been demonstrated to be an accurate dynamic parameter to predict fluid responsiveness. However, the impact of different ventilator modes on this parameter is unknown. We compared ΔPP values calculated alternatively during pressure- and volume-controlled ventilation.

STUDY DESIGN

Double-blind randomized study, cross-over design.

PATIENTS

Patients in intensive care unit after a cardiac surgery.

METHOD

Patients were ventilated alternatively in both ventilator modes (according to the randomization): volume-controlled ventilation (VVC) and pressure-controlled ventilation (VPC). Other parameters of ventilation were identical. ΔPP values were calculated for each patient in both ventilator modes.

RESULTS

Among the 26 patients analyzed, mean ΔPP value was de 14.0±7.3% in VVC and 11.8±6.2% in VPC (P<0,0001). On Bland-Altman representation, mean bias was +2.2±2.3% and inferior and superior limits of agreement were respectively -2.3 and 6.7%. Arterial blood pressure and central venous pressure were not modified.

CONCLUSION

ΔPP values obtained with both ventilator modes were not interchangeable. On average, ΔPP decreases by more than two points in the passage VVC to VPC for a given patient, all others things being equal.

Comparison of stroke volume and fluid responsiveness measurements in commonly used technologies for goal-directed therapy

STUDY OBJECTIVE

To compare stroke volume (SV) and preload responsiveness measurements from different technologies with the esophageal Doppler monitor (EDM).

DESIGN

Prospective measurement study.

SETTING

Operating room.

PATIENTS

20 ASA physical status 3 patients undergoing vascular, major urological, and bariatric surgery.

INTERVENTIONS

Subjects received fluids using a standard Doppler protocol of 250 mL of colloid administered until SV no longer increased by >10%, and again when the measured SV decreased by 10%.

MEASUREMENTS

Simultaneous readings of SV, stroke volume variation (SVV) and pulse pressure variation (PPV) from the LiDCOrapid, and SVV from the FloTrac/Vigileo were compared with EDM measurements. The pleth variability index (PVI) also was recorded.

MAIN RESULTS

No correlation was seen in percentage SV change as measured by either the LiDCOrapid (r=0.05, P=0.616) or FloTrac (r=0.09, P= 0.363) systems compared with the EDM. Correlation was present between the LiDCOrapid and FloTrac (r=0.515, P<0.0001). Percentage error compared with the EDM was 81% for the FloTrac and 90% for the LiDCOrapid. SVV as measured by LiDCOrapid differed for fluid responders and nonresponders (10% vs 7%; P=0.021). Receiver operator curve analysis to predict a 10% increase in SV from the measured variables showed an area under the curve of 0.57 (95% CI 0.43-0.72) for SVV(FloTrac), 0.64 (95% CI 0.52-0.78) for SVV(LiDCO), 0.61 (95% CI 0.46 -0.76) for PPV, and 0.59 (95% CI 0.46 -0.71) for PVI.

CONCLUSIONS

Stroke volume as measured by the FloTrac and LiDCOrapid systems does not correlate with the esphageal Doppler, has poor concordance, and a clinically unacceptable percentage error. The predictive value of the fluid responsiveness parameters is low, with only SVV measured by the LiDCOrapid having clinical utility.

[Fluid therapy in cardiac surgery. An update]

The anesthetist has 2 major tools for optimizing haemodynamics in cardiac surgery: Vasoactive drugs and the intravascular volume. It is necessary to identify which patients would benefit from one or the other therapies for a suitable response to treatment. Hemodynamic monitoring with the different existing parameters (pressure, volumetric static, volumetric functional and echocardiography) allows the management of these patients to be optimized. In this article a review is presented on the most recent and relevant publications, and the different tools available to control the management of the fluid therapy in this context, and to suggest a few guidelines for the haemodynamics monitoring of patients submitted to cardiac surgery. A systematic search has been made in PubMed, limiting the results to the publications over the last five years up to February 2012.

Neither dynamic, static, nor volumetric variables can accurately predict fluid responsiveness early after abdominothoracic esophagectomy

Background

Hypotension is common in the early postoperative stages after abdominothoracic esophagectomy for esophageal cancer. We examined the ability of stroke volume variation (SVV), pulse pressure variation (PPV), central venous pressure (CVP), intrathoracic blood volume (ITBV), and initial distribution volume of glucose (IDVG) to predict fluid responsiveness soon after esophagectomy under mechanical ventilation (tidal volume >8 mL/kg) without spontaneous respiratory activity.

Methods

Forty-three consecutive non-arrhythmic patients undergoing abdominothoracic esophagectomy were studied. SVV, PPV, cardiac index (CI), and indexed ITBV (ITBVI) were postoperatively measured by single transpulmonary thermodilution (PiCCO system) after patient admission to the intensive care unit (ICU) on the operative day. Indexed IDVG (IDVGI) was then determined using the incremental plasma glucose concentration 3 min after the intravenous administration of 5 g glucose. Fluid responsiveness was defined by an increase in CI >15% compared with pre-loading CI following fluid volume loading with 250 mL of 10% low molecular weight dextran.

Results

Twenty-three patients were responsive to fluids while 20 were not. The area under the receiver-operating characteristic (ROC) curve was the highest for CVP (0.690) and the lowest for ITBVI (0.584), but there was no statistical difference between tested variables. Pre-loading IDVGI (r = −0.523, P <0.001), SVV (r = 0.348, P = 0.026) and CVP (r = −0.307, P = 0.046), but not PPV or ITBVI, were correlated with a percentage increase in CI after fluid volume loading.

Conclusions

These results suggest that none of the tested variables can accurately predict fluid responsiveness early after abdominothoracic esophagectomy.

Effect of rapid plasma volume expansion during anesthesia induction on haemodynamics and oxygen balance in patients undergoing gastrointestinal surgery

AIMS

To investigate the reasonable dose of Voluven for rapid plasma volume expansion during the anaesthesia induction patients receiving gastrointestinal surgery.

METHODS

Sixty patients were randomly divided into three groups (n=20): Group A (5 ml/kg), Group B (7 ml/kg) and Group C (9 ml/kg). HES 130/0.4 was intravenously transfused at a rate of 0.3 ml/kg/min) at 30 min before anaesthesia induction. Besides standard haemodynamic monitoring, cardiac index (CI), systemic vascular resistance index (SVRI) and stroke volume variation (SVV) was continuously detected with the FloTrac/Vigileo system. Haemodynamic variables were recorded immediately before fluid transfusion (T0), immediately before induction (T1), immediately before intubation (T2), immediately after intubation (T3) and 5 min, 10 min, 20 min and 60 min after intubation (T4-T7). Arterial and venous blood was collected for blood gas analysis, Hb and Hct before volume expansion (t0), immediately after volume expansion (t1) and at 1 h after volume expansion (t2). Oxygen delivery (DO2), oxygen extraction ratio (ERO2) and volume expansion rate were calculated.

RESULTS

1) MAP and CI decreased in Group A in T2~T7 and remained changed in Group B and C. 2) CVP increased in three groups after fluid infusion without significant difference. 3) The decrease in SVRI was more obvious in Group B and C than that in Group A after induction and more obvious in Group C than in Group B in T2-T4 and T6~T7. 4) SVV was lower in Group B and C than that in Group A after intubation, and lower in Group C than that in Group B in T3-T6. 5) Hb and Hct decreased after fluid infusion, and the decrease in Hb and Hct was in the order of C>B>A. 6) Volume expansion rate was in the order of C>B>A. 7) ScvO2, PaO2 and DO2 increased in three groups after fluid infusion and the increase in DO2 was in the order of C>B>A.

CONCLUSIONS

Rapid plasma volume expansion with Voluven at 7-9 ml/kg can prevent haemodynamic fluctuation during anaesthesia induction, maintain the balance between oxygen supply and oxygen consumption during gastrointestinal surgery, and Voluven at 9 ml/kg can improve the oxygen delivery.

Stroke Volume Variation for Prediction of Fluid Responsiveness in Patients Undergoing Gastrointestinal Surgery

Background: Stroke volume variation (SVV) has been shown to be a reliable predictor of fluid responsiveness. However, the predictive role of SVV measured by FloTrac/Vigileo system in prediction of fluid responsiveness was unproven in patients undergoing ventilation with low tidal volume. Methods: Fifty patients undergoing elective gastrointestinal surgery were randomly divided into two groups: Group C [n1=20, tidal volume (Vt) = 8 ml/kg, frequency (F) = 12/min] and Group L [n2=30, Vt= 6 ml/kg, F=16/min]. After anesthesia induction, 6% hydroxyethyl starch130/0.4 solution (7 ml/kg) was intravenously transfused. Besides standard haemodynamic monitoring, SVV, cardiac output, cardiac index (CI), stroke volume (SV), stroke volume index (SVI), systemic vascular resistance (SVR) and systemic vascular resistance index (SVRI) were determined with the FloTrac/Vigileo system before and after fluid loading. Results: After fluid loading, the MAP, CVP, SVI and CI increased significantly, whereas the SVV and SVR decreased markedly in both groups. SVI was significantly correlated to the SVV, CVP but not the HR, MAP and SVR. SVI was significantly correlated to the SVV before fluid loading (Group C: r = 0.909; Group L: r = 0.758) but not the HR, MAP, CVP and SVR before fluid loading. The largest area under the ROC curve (AUC) was found for SVV (Group C, 0.852; Group L, 0.814), and the AUC for other preloading indices in two groups ranged from 0.324 to 0.460. Conclusion: SVV measured by FloTrac/Vigileo system can predict fluid responsiveness in patients undergoing ventilation with low tidal volumes during gastrointestinal surgery.

Alternative methods to central venous pressure for assessing volume status in critically ill patients

INTRODUCTION

Early goal-directed therapy increases survival in persons with sepsis but requires placement of a central line. We evaluate alternative methods to measuring central venous pressure (CVP) to assess volume status, including peripheral venous pressure (PVP) and stroke volume variation (SVV), which may facilitate nurse-driven resuscitation protocols.

METHODS

Patients were enrolled in the emergency department or ICU of an academic medical center. Measurements of CVP, PVP, SVV, shoulder and elbow position, and dichotomous variables Awake, Movement, and Vented were measured and recorded 7 times during a 1-hour period. Regression analysis was used to predict CVP from PVP and/or SVV, shoulder/elbow position, and dichotomous variables.

RESULTS

Twenty patients were enrolled, of which 20 had PVP measurements and 11 also had SVV measurements. Multiple regression analysis demonstrated significant predictive relationships for CVP using PVP (CVP = 6.7701 + 0.2312 × PVP - 0.1288 × Shoulder + 12.127 × Movement - 4.4805 × Neck line), SVV (CVP = 14.578 - 0.3951 × SVV + 18.113 × Movement), and SVV and PVP (CVP = 4.2997 - 1.1675 × SVV + 0.3866 × PVP + 18.246 × Awake + 0.1467 × Shoulder = 0.4525 × Elbow + 15.472 × Foot line + 10.202 × Arm line).

DISCUSSION

PVP and SVV are moderately good predictors of CVP. Combining PVP and SVV and adding variables related to body position, movement, ventilation, and sleep/wake state further improves the predictive value of the model. The models illustrate the importance of standardizing patient position, minimizing movement, and placing intravenous lines proximally in the upper extremity or neck.

Extravascular lung water does not increase in hypovolemic patients after a fluid-loading protocol guided by the stroke volume variation

Introduction. Circulatory failure secondary to hypovolemia is a common situation in critical care patients. Volume replacement is the first option for the treatment of hypovolemia. A possible complication of volume loading is pulmonary edema, quantified at the bedside by the measurement of extravascular lung water index (ELWI). ELWI predicts progression to acute lung injury (ALI) in patients with risk factors for developing it. The aim of this study was to assess whether fluid loading guided by the stroke volume variation (SVV), in patients presumed to be hypovolemic, increased ELWI or not. Methods. Prospective study of 17 consecutive postoperative, fully mechanically ventilated patients diagnosed with circulatory failure secondary to presumed hypovolemia were included. Cardiac index (CI), ELWI, SVV, and global end-diastolic volume index (GEDI) were determined using the transpulmonary thermodilution technique during the first 12 hours after fluid loading. Volume replacement was done with a strict hemodynamic protocol. Results. Fluid loading produced a significant increase in CI and a decrease in SVV. ELWI did not increase. No correlation was found between the amount of fluids administered and the change in ELWI. Conclusion. Fluid loading guided by SVV in hypovolemic and fully mechanically ventilated patients in sinus rhythm does not increase ELWI.

Noninvasive monitoring by photoplethysmography

The photoplethysmogram (PPG) is a noninvasive circulatory signal related to the pulsatile volume in tissue and is displayed by many pulse oximeters. The PPG is similar in appearance to the invasive arterial waveform, but is noninvasive and ubiquitous in hospitals. There is increasing interest in seeking circulatory information from the PPG and developing techniques for a wide variety of novel applications. This article addresses the basic physics of photoplethysmography, physiologic principles behind pulse oximetry operation, and recent technological advances in the usefulness of the PPG waveform to assess microcirculation and intravascular fluid volume monitoring during intensive care.

Anaesthetic and cardiorespiratory effects of a constant-rate infusion of alfaxalone in desflurane-anaesthetised sheep

A prospective, randomised, blinded controlled study was performed to determine the anaesthetic and cardiorespiratory effects of a constant-rate infusion (CRI) of alfaxalone in 12 sheep anaesthetised with desflurane, and undergoing experimental orthopaedic surgery. Sheep were sedated with dexmedetomidine (4 μg/kg, intravenously) and butorphanol (0.3 mg/kg, intravenously). Anaesthesia was induced with alfaxalone (1 mg/kg/minute to effect, intravenously) and maintained with desflurane in oxygen and alfaxalone 0.07 mg/kg/minute or saline for 150 minutes (range 150-166 minutes). The anaesthetic induction dose of alfaxalone, the desflurane expiratory fraction required for anaesthetic maintenance, cardiorespiratory measurements and blood-gases were recorded at predetermined intervals. Quality of sedation, anaesthetic induction and recovery were assessed. The alfaxalone induction dose was 1.7 mg/kg (1.2 to 2.6 mg/kg). The desflurane expiratory fraction was lower (22 per cent) in sheep receiving alfaxalone CRI (P=0). Also, heart rate (P=0), cardiac index (P=0.002), stroke index (P=0) and contractility (P=0) were higher, and systemic vascular resistance (P=0.002) was lower. Although respiratory rate tended to be higher with alfaxalone, there was no difference in PCO2 between the groups. Recovery times were significantly longer in sheep given alfaxalone (25.4 v 9.5 minutes) but recovery quality was similar. Alfaxalone reduced requirements of desflurane and maintained similar cardiorespiratory function, but recovery time was more prolonged.

Prediction of fluid responsiveness by a continuous non-invasive assessment of arterial pressure in critically ill patients: comparison with four other dynamic indices

BACKGROUND

We evaluated the ability of an infrared photoplethysmography arterial waveform (continuous non-invasive arterial pressure, CNAP) to estimate arterial pulse pressure variation (PPV). We compared the ability of non-invasive PPV to predict fluid responsiveness with invasive PPV, respiratory variation of pulse contour-derived stroke volume, and changes in cardiac index induced by passive leg raising (PLR) and end-expiratory occlusion (EEO) tests.

METHODS

We measured the responses of cardiac index (PiCCO) to 500 ml of saline in 47 critically ill patients with haemodynamic failure. Before fluid administration, we recorded non-invasive and invasive PPVs, stroke volume variation, and changes in cardiac index induced by PLR and by 15 s EEO. Logistic regressions were performed to investigate the advantage of combining invasive PPV, stroke volume variation, PLR, and EEO when predicting fluid responsiveness.

RESULTS

In eight patients, CNAP could not record arterial pressure. In the 39 remaining patients, fluid increased cardiac index by ≥15% in 17 'responders'. Considering the 195 pairs of measurements, the bias (sd) between invasive and non-invasive PPVs was -0.6 (2.3)%. The areas under the receiver operating characteristic (ROC) curves for predicting fluid responsiveness were 0.89 (95% confidence interval, 0.78-1.01) for non-invasive PPV compared with 0.89 (0.77-1.01), 0.84 (0.70-0.96), 0.95 (0.88-1.03), and 0.97 (0.91-1.03) for invasive pulse pressure, stroke volume variations, PLR, and EEO tests (no significant difference). Combining multiple tests did not significantly improve the area under the ROC curves.

CONCLUSIONS

Non-invasive assessment of PPV seems valuable in predicting fluid responsiveness.

Evaluation of Stroke Volume Variation Obtained by the FloTrac™/Vigileo™ System to Guide Preoperative Fluid Therapy in Patients Undergoing Brain Surgery

OBJECTIVE: The accuracy of stroke volume variation (SVV) obtained by the FloTrac™/Vigileo™ system in otherwise healthy patients undergoing brain surgery was assessed. METHODS: Anaesthesia was induced in 48 patients with minimal fluid infusion. Before surgery, fluid volume loading was performed by infusion with Ringer's lactate solution in 200 ml steps over 3 min, repeated successively if the patient responded with an increase in stroke volume of ≥ 10%, until the increase was < 10% (nonresponsive). RESULTS: A total of 157 volume loading steps were performed in the 48 patients. Responsive and nonresponsive steps differed significantly in baseline values of blood pressure, heart rate and SVV. Significant correlations were found between the change in stroke volume after fluid loading and values of blood pressure, heart rate and SVV before fluid loading, with SVV the most sensitive variable. CONCLUSION: Stroke volume variation obtained using the FloTrac™/Vigileo™ system is a sensitive predictor of fluid responsiveness in healthy patients before brain surgery.

Influence of pressure control levels on the pulse pressure variations: an animal study using healthy piglets

Pulse pressure variation (PPV) is a promising predictor for volume responsiveness. However, recent studies have criticized its validity during small tidal volume (TV) ventilation. The present study evaluated the influence of pressure control level (PCL) on PPV. Six anesthetized healthy piglets simulating hemorrhagic shock underwent five stages of intravascular volume status change. Each stage comprised four cycles of PCL manipulation. In each cycle, five different PCLs were applied in random order. Among 600 arterial pressure tracings obtained during PCL manipulations, 26 tracings were excluded because of signal artifact or ectopic beats. For the remaining 574 tracings, the percentage of normal beats among total recorded beats in each tracing was 99.80% ± 0.85%. When manipulating PCL causing an abrupt change within -16 ∼ +8 cmH(2)O, the PPV responded rapidly and stabilized within 60 s after manipulation. With higher increment in PCL (+12 ∼ +16 cmH(2)O), it required 90 s for PPV to stabilize. Under each cycle of PCL manipulation, the PPVs are linearly correlated to the PCL (r = 0.84 ± 0.21) and TV (r = 0.83 ± 0.22). The PPV as well as the slopes of the trend lines decreased from hypovolemic stages toward hypervolemic stages. Pulse pressure variation responds rapidly to change in ventilator setting and is linearly correlated with the PCL and TV. These characteristics may have important applications in critical care to improve the interpretation of PPV in accord to different ventilator settings.

Evaluation of stroke volume variations obtained with the pressure recording analytic method

OBJECTIVE

To investigate whether stroke volume variations obtained with the pressure recording analytic method can predict fluid responsiveness in mechanically ventilated patients with circulatory failure.

DESIGN

Prospective study.

SETTING

Surgical intensive care unit of a university hospital.

PATIENTS

Thirty-five mechanically ventilated patients with circulatory failure for whom the decision to give fluid was taken by the physician were included. Exclusion criteria were: Arrhythmia, tidal volume <8 mL/kg, left ventricular ejection fraction<50%, right ventricular dysfunction, and heart rate/respiratory rate ratio <3.6.

INTERVENTIONS

Fluid challenge with 500 mL of saline over 15 mins.

MEASUREMENTS AND MAIN RESULTS

Stroke volume variations and cardiac output obtained with a pressure recording analytic method, pulse pressure variations, and cardiac output estimated by echocardiography were recorded before and after volume expansion. Patients were defined as responders if stroke volume obtained using echocardiography increased by ≥15% after volume expansion. Nineteen patients responded to the fluid challenge. Median [interquartile range, 25% to 75%] stroke volume variation values at baseline were not different in responders and nonresponders (10% [8-16] vs. 14% [12-16]), whereas pulse pressure variations were significantly higher in responders (17% [13-19] vs. 7% [5-10]; p < .0001). A 12.6% stroke volume variations threshold discriminated between responders and nonresponders with a sensitivity of 63% (95% confidence interval 38% to 84%) and a specificity of 69% (95% confidence interval 41% to 89%). A 10% pulse pressure variation threshold discriminated between responders and nonresponders with a sensitivity of 89% (95% confidence interval 67% to 99%) and a specificity of 88% (95% confidence interval 62% to 98%). The area under the receiver operating characteristic curves was different between pulse pressure variations (0.95; 95% confidence interval 0.82-0.99) and stroke volume variations (0.60; 95% confidence interval 0.43-0.76); p < .0001). Volume expansion-induced changes in cardiac output measured using echocardiography or pressure recording analytic method were not correlated (r = 0.14; p > .05) and the concordance rate of the direction of change in cardiac output was 60%.

CONCLUSION

Stroke volume variations obtained with a pressure recording analytic method cannot predict fluid responsiveness in intensive care unit patients under mechanical ventilation. Cardiac output measured by this device is not able to track changes in cardiac output induced by volume expansion.

Novel anaesthetic approach for surgical access and haemodynamic management during off-pump coronary artery bypass through a left thoracotomy

For myocardial revascularization on a beating heart through a thoracotomy, a properly deployed endobronchial blocker (EBB) provides ideal conditions for surgical access. In addition, adequate volume replacement to achieve optimal cardiac performance is a primary goal of haemodynamic management in patients undergoing off-pump coronary artery bypass grafting. To achieve both these ends, this case report describes the combined use of a left-sided EBB along with a volumetric pulmonary artery catheter in a patient who underwent a successful off-pump coronary artery bypass surgery through an anterolateral thoracotomy.

Using arterial pressure waveform analysis for the assessment of fluid responsiveness

Predicting the effects of volume expansion on cardiac output and oxygen delivery is of major importance in different clinical scenarios. Functional hemodynamic parameters based on pulse waveform analysis, which are relying on the effects of mechanical ventilation on stroke volume and its surrogates, have been shown to be reliable predictors of fluid responsiveness during anesthesia and intensive care unit treatment, as demonstrated by several clinical studies and meta-analyses. However, different limitations of these parameters have to be considered when they are used in clinical practice. Today, they can be continuously and automatically monitored by a variety of commercially available devices. These parameters have been introduced into the concept of perioperative fluid management and hemodynamic optimization - an approach that may positively impact postoperative patients' outcomes. In this article, technical aspects of the assessment of the functional hemodynamic parameters derived from pulse waveform analysis are summarized, emphasizing their advantages, limitations and potential applications, primarily in a perioperative setting in order to improve patient outcome.

Hemodynamic monitoring in the critically ill: spanning the range of kidney function

Critically ill patients often have deranged hemodynamics. Physical examination, central venous pressure, and pulmonary artery occlusion pressure ("wedge") have been shown to be unreliable at assessing volume status, volume responsiveness, and adequacy of cardiac output in critically ill patients. Thus, invasive and noninvasive cardiac output monitoring is a core feature of evaluating and managing a hemodynamically unstable patient. In this review, we discuss the various techniques and options of cardiac output assessment available to clinicians for hemodynamic monitoring in the intensive care unit. Issues related to patients with kidney disease, such as timing and location of arterial and central venous catheters and the approach to hemodynamics in patients treated by long-term dialysis also are discussed.

Arm occlusion pressure is a useful predictor of an increase in cardiac output after fluid loading following cardiac surgery

BACKGROUND AND OBJECTIVE

In pharmacological research, arm occlusion pressure is used to study haemodynamic effects of drugs. However, arm occlusion pressure might be an indicator of static filling pressure of the arm. We hypothesised that arm occlusion pressure can be used to predict fluid loading responsiveness.

METHODS

Twenty-four patients who underwent cardiac surgery were studied during their first 2 h in the ICU. The lungs were ventilated mechanically and left ventricular function was supported as necessary. Arm occlusion pressure was defined as the radial artery pressure after occluding arterial flow for 35 s by a blood pressure cuff inflated to 50 mmHg above SBP. The cuff was positioned around the arm in which a radial artery catheter had been inserted. Measurements were performed before (baseline) and after fluid loading (500 ml hydroxyethyl starch 6%). Patients whose cardiac output increased by at least 10% were defined as responders.

RESULTS

In responders (n = 17), arm occlusion pressure, mean arterial pressure and central venous pressure increased and stroke volume variation and pulse pressure variation decreased. In non-responders (n = 7), arm occlusion pressure and central venous pressure increased, and pulse pressure variation decreased. Mean arterial pressure, stroke volume variation and heart rate did not change significantly. The area under the curve to predict fluid loading responsiveness for arm occlusion pressure was 0.786 (95% confidence interval 0.567-1.000), at a cut-off of 21.9 mmHg, with sensitivity of 71% and specificity of 88% in predicting fluid loading responsiveness. Prediction of responders with baseline arm occlusion pressure was as good as baseline stroke volume variation and pulse pressure variation.

CONCLUSION

Arm occlusion pressure was a good predictor of fluid loading responsiveness in our group of cardiac surgery patients and offers clinical advantages over stroke volume variation and pulse pressure variation.