Respiratory changes in aortic blood velocity as an indicator of fluid responsiveness in ventilated patients with septic shock

How can the response to volume expansion in patients with spontaneous respiratory movements be predicted?

INTRODUCTION

The aim of the study was to evaluate the ability of different static and dynamic measurements of preload to predict fluid responsiveness in patients with spontaneous respiratory movements.

METHODS

The subjects were 21 critically ill patients with spontaneous breathing movements receiving mechanical ventilation with pressure support mode (n = 9) or breathing through a face mask (n = 12), and who required a fluid challenge. Complete hemodynamic measurements, including pulmonary artery occluded pressure (PAOP), right atrial pressure (RAP), pulse pressure variation (DeltaPP) and inspiratory variation in RAP were obtained before and after fluid challenge. Fluid challenge consisted of boluses of either crystalloid or colloid until cardiac output reached a plateau. Receiver operating characteristics (ROC) curve analysis was used to evaluate the predictive value of the indices to the response to fluids, as defined by an increase in cardiac index of 15% or more.

RESULTS

Cardiac index increased from 3.0 (2.3 to 3.5) to 3.5 (3.0 to 3.9) l minute-1 m-2 (medians and 25th and 75th centiles), p < 0.05. At baseline, DeltaPP varied between 0% and 49%. There were no significant differences in DeltaPP, PAOP, RAP and inspiratory variation in RAP between fluid responders and non-responders. Fluid responsiveness was predicted better with static indices (ROC curve area +/- SD: 0.73 +/- 0.13 for PAOP, p < 0.05 vs DeltaPP and 0.69 +/- 0.12 for RAP, p = 0.054 compared with DeltaPP) than with dynamic indices of preload (0.40 +/- 0.13 for DeltaPP and 0.53 +/- 0.13 for inspiratory changes in RAP, p not significant compared with DeltaPP).

CONCLUSION

In patients with spontaneous respiratory movements, DeltaPP and inspiratory changes in RAP failed to predict the response to volume expansion.

Comparison of stroke volume (SV) and stroke volume respiratory variation (SVV) measured by the axillary artery pulse-contour method and by aortic Doppler echocardiography in patients undergoing aortic surgery

BACKGROUND

The goal of the study was to compare stroke volume (SV) and respiratory stroke volume variation (SVV) measured by pulse-contour analysis and aortic Doppler.

METHODS

These were measured by pulse-contour analysis and thermodilution (PiCCO) and by aortic pulsed wave Doppler with transoesophageal echocardiography in patients undergoing abdominal aortic surgery. Simultaneous measurements were done at different times of surgery. All data were recorded on PiCCOwin software and videotape and analysed off-line by a blinded investigator.

RESULTS

A total of 114 measurements were achieved in 20 patients. There was a good correlation and small bias between the PiCCO and the echo-Doppler values of the mean SV [r=0.885; bias=0.2 (8) ml], and between the minimum [r=0.842; bias=1 (9) ml] and maximum SV [r=0.840; bias=2 (10) ml] values.

CONCLUSIONS

There is a fair correlation between pulse-contour analysis and aortic Doppler for beat-by-beat measurement of SV but not for calculation of SV respiratory ventilation.

Ability of pulse contour and esophageal Doppler to estimate rapid changes in stroke volume

OBJECTIVE

Two technologies to acquire beat-to-beat stroke volume values exist, pulse contour analysis and esophageal Doppler monitoring. Pulse contour analysis assumes fixed aortic impedance. Esophageal Doppler assumes a constant proportional descending aortic flow and diameter. These assumptions may not be correct as arterial tone or myocardial contractility vary. We tested these relationships in the setting of rapidly changing stroke volumes and different cardiovascular states over a period of 10-15 cardiac cycles.

DESIGN AND SETTING

In a university research facility we compared beat-to-beat changes in stroke volume as measure by aortic root flow probe or conductance catheter to pulse contour analysis and stroke distance as measured by esophageal Doppler.

SUBJECTS

Five purpose-bred research hounds.

INTERVENTIONS

To obtain a wide range of rapidly changing stroke volumes measurements were made during transient inferior vena cava occlusion. Data were gathered under baseline conditions and during norepinephrine, nitroprusside, and dobutamine infusions.

MEASUREMENTS AND RESULTS

The pulse contour stroke volumes and esophageal Doppler stroke distance paralleled flow probe stroke volumes under all conditions (R(2)=0.89 for all measures). However, the absolute changes and proportional changes and the absolute values for both surrogate measures differed from absolute stroke volumes. Bland-Altman analysis showed no consistent bias or degree of precision across all animals under any given cardiovascular state.

CONCLUSIONS

Both pulse contour stroke volumes and esophageal Doppler derived stroke distance estimates yield significant correlations with aortic root flow probe. However, the absolute values, absolute changes, or proportional changes may not reflect actual stroke volumes as cardiovascular state varies, making their use in estimating absolute changes in stroke volume potentially inaccurate.

Echocardiographic measurement of fluid responsiveness

PURPOSE OF REVIEW

Fluid responsiveness is a relatively new concept. It enables the efficacy of volume expansion to be predicted before use, rather than assessed afterwards, thus avoiding inappropriate fluid infusion. Echocardiography is a fantastic noninvasive tool which can directly visualize the heart and assess cardiac function. Its use was long limited by the absence of accurate indices to diagnose hypovolemia and predict the effect of volume expansion. In the last few years, several French teams have used echocardiography to develop new parameters of fluid responsiveness, taking advantage of its ability to monitor cardiac function beat by beat during the respiratory cycle.

RECENT FINDINGS

In mechanically ventilated patients perfectly adapted to the respirator, respiratory variations in superior and inferior vena cava diameters and in left ventricular stroke volume have been validated as parameters of fluid responsiveness. In our opinion, the collapsibility index of the superior vena cava is the most reliable of these parameters, but does require transesophageal echocardiography.

SUMMARY

Echocardiography has been widely demonstrated to predict fluid responsiveness accurately. This is now a complete and noninvasive tool able to accurately determine hemodynamic status in circulatory failure.

Passive leg raising predicts fluid responsiveness in the critically ill

OBJECTIVE

Passive leg raising (PLR) represents a "self-volume challenge" that could predict fluid response and might be useful when the respiratory variation of stroke volume cannot be used for that purpose. We hypothesized that the hemodynamic response to PLR predicts fluid responsiveness in mechanically ventilated patients.

DESIGN

Prospective study.

SETTING

Medical intensive care unit of a university hospital.

PATIENTS

We investigated 71 mechanically ventilated patients considered for volume expansion. Thirty-one patients had spontaneous breathing activity and/or arrhythmias.

INTERVENTIONS

We assessed hemodynamic status at baseline, after PLR, and after volume expansion (500 mL NaCl 0.9% infusion over 10 mins).

MEASUREMENTS AND MAIN RESULTS

We recorded aortic blood flow using esophageal Doppler and arterial pulse pressure. We calculated the respiratory variation of pulse pressure in patients without arrhythmias. In 37 patients (responders), aortic blood flow increased by > or =15% after fluid infusion. A PLR increase of aortic blood flow > or =10% predicted fluid responsiveness with a sensitivity of 97% and a specificity of 94%. A PLR increase of pulse pressure > or =12% predicted volume responsiveness with significantly lower sensitivity (60%) and specificity (85%). In 30 patients without arrhythmias or spontaneous breathing, a respiratory variation in pulse pressure > or =12% was of similar predictive value as was PLR increases in aortic blood flow (sensitivity of 88% and specificity of 93%). In patients with spontaneous breathing activity, the specificity of respiratory variations in pulse pressure was poor (46%).

CONCLUSIONS

The changes in aortic blood flow induced by PLR predict preload responsiveness in ventilated patients, whereas with arrhythmias and spontaneous breathing activity, respiratory variations of arterial pulse pressure poorly predict preload responsiveness.

The influence of tidal volume on the dynamic variables of fluid responsiveness in critically ill patients

Respiratory-related variabilities in stroke volume and arterial pulse pressure (Delta%Pp) are proposed to predict fluid responsiveness. We investigated the influence of tidal volume (Vt) and adrenergic tone on these variables in mechanically ventilated patients. Cyclic changes in aortic velocity-time integrals (Delta%VTI(Ao), echocardiography) and Delta%Pp (catheter) were measured simultaneously before and after intravascular volume expansion, and Vt was randomly varied below and above its basal value. Intravascular volume expansion was performed by hydroxyethyl starch (100 mL, 60 s). Receiver operating characteristic curves were generated for Delta%VTI(Ao), Delta%Pp and left ventricle cross-sectional end-diastolic area (echocardiography), considering the change in stroke volume after intravascular volume expansion (> or =15%) as the response criterion. Covariance analysis was used to test the influence of Vt on Delta%VTI(Ao) and Delta%Pp. Twenty-one patients were prospectively included; 9 patients (43%) were responders to intravascular volume expansion. Delta%VTI(Ao) and Delta%Pp were higher in responders compared with nonresponders. Predictive values of Delta%VTI(Ao) and Delta%Pp were similar (threshold: 20.4% and 10.0%, respectively) and higher than that of left ventricle cross-sectional end-diastolic area at the appropriate level of Vt. Delta%Pp was slightly correlated with norepinephrine dosage. Delta%Pp increased with the increase in the level of Vt both before and after intravascular volume expansion, contrasting with an unexpected stability of Delta%VTI(Ao). In conclusion, Delta%VTI(Ao) and Delta%Pp are good predictors of intravascular fluid responsiveness but the divergent evolution of these two variables when Vt was increased needs further explanation.

Comparison of tricuspid inflow and superior vena caval Doppler velocities in acute simulated hypovolemia: new non-invasive indices for evaluating right ventricular preload

Background

Assessment of cardiac preload is important for clinical management of some emergencies related to hypovolemia. Effects of acute simulated hypovolemia on Doppler blood flow velocity indices of tricuspid valve (TV) and superior vena cava (SVC) were investigated in order to find sensitive Doppler indices for predicting right ventricular preload.

Methods

Doppler flow patterns of SVC and TV in 12 healthy young men were examined by transthoracic echocardiography (TTE) during graded lower body negative pressure (LBNP) of up to -60 mm Hg which simulated acute hypovolemia. Peak velocities of all waves and their related ratios (SVC S/D and tricuspid E/A) were measured, calculated and statistically analyzed.

Results

Except for the velocity of tricuspid A wave, velocities of all waves and their related ratios declined during volume decentralization. Of all indices measured, the peak velocities of S wave and AR wave in SVC correlated most strongly with levels of LBNP (r = -0.744 and -0.771, p < 0.001).

Conclusion

The S and AR velocities are of good values in assessing right ventricular preload. Monitoring SVC flow may provide a relatively noninvasive means to assess direct changes in right ventricular preload.

Assessment of fluid responsiveness in mechanically ventilated cardiac surgical patients

BACKGROUND AND OBJECTIVE

Accurate assessment of preload responsiveness is an important goal of the clinician to avoid deleterious volume replacement associated with increased morbidity and mortality in mechanically ventilated patients. This study was designed to evaluate the accuracy of simultaneously assessed stroke volume variation and pulse pressure variation using an improved algorithm for pulse contour analysis (PiCCO plus, V 5.2.2), compared to the respiratory changes in transoesophageal echo-derived aortic blood velocity (deltaVpeak), intrathoracic blood volume index, central venous pressure and pulmonary capillary wedge pressure to predict the response of stroke volume index to volume replacement in normoventilated cardiac surgical patients.

METHODS

We studied 20 patients undergoing elective coronary artery bypass grafting. After induction of anaesthesia, haemodynamic measurements were performed before and after volume replacement by infusion of 6% hydroxyethyl starch 200/0.5 (7 mL kg(-1) ) with a rate of 1 mL kg(-1) min(-1).

RESULTS

Baseline stroke volume variation correlated significantly with changes in stroke volume index (deltaSVI) (r2 = 0.66; P < 0.05) as did baseline pulse pressure variation (r2 = 0.65; P < 0.05), whereas baseline values of deltaVpeak, intrathoracic blood volume index, central venous pressure and pulmonary artery wedge pressure showed no correlation to deltaSVI. Pulse contour analysis underestimated the volume-induced increase in cardiac index measured by transpulmonary thermodilution (P < 0.05).

CONCLUSIONS

The results of our study suggest that stroke volume variation and its surrogate pulse pressure variation derived from pulse contour analysis using an improved algorithm can serve as indicators of fluid responsiveness in normoventilated cardiac surgical patients. Whenever changes in systemic vascular resistance are expected, the PiCCO plus system should be recalibrated.

Functional hemodynamic monitoring

Hemodynamic monitoring is a central component of intensive care. Patterns of hemodynamic variables often suggest cardiogenic, hypovolemic, obstructive, or distributive (septic) etiologies to cardiovascular insufficiency, thus defining the specific treatments required. Monitoring increases in invasiveness, as required, as the risk for cardiovascular instability-induced morbidity increases because of the need to define more accurately the diagnosis and monitor the response to therapy. Monitoring is also context specific: requirements during cardiac surgery will be different from those in the intensive care unit or emergency department. Solitary hemodynamic values are useful as threshold monitors (e.g. hypotension is always pathological, central venous pressure is only elevated in disease). Some hemodynamic values can only be interpreted relative to metabolic demand, whereas others have multiple meanings. Functional hemodynamic monitoring implies a therapeutic application, independent of diagnosis such as a therapeutic trial of fluid challenge to assess preload responsiveness. Newer methods for assessing preload responsiveness include monitoring changes in central venous pressure during spontaneous inspiration, and variations in arterial pulse pressure, systolic pressure, and aortic flow variation in response to vena caval collapse during positive pressure ventilation or passive leg raising. Defining preload responsiveness using these functional measures, coupled to treatment protocols, can improve outcome from critical illness. Potentially, as these and newer, less invasive hemodynamic measures are validated, they could be incorporated into such protocolized care in a cost-effective manner.

Pre-ejection period variations predict the fluid responsiveness of septic ventilated patients

OBJECTIVES

In septic patients with acute circulatory failure, reliable predictors of fluid responsiveness are needed at the bedside. We hypothesized that the respiratory change in pre-ejection period (DeltaPEP) would allow the prediction of changes in cardiac index following volume administration in mechanically ventilated septic patients.

DESIGN

Prospective clinical investigation.

SETTING

A ten-bed hospital intensive care unit.

PATIENTS

Patients admitted after septic shock equipped with an arterial catheter.

INTERVENTIONS

Pre-ejection period (PEP)--defined as the time interval between the beginning of the R wave on the electrocardiogram and the upstroke of the radial arterial pressure curve (PEPKT) or the pulse plethysmographic waveforms (PEPPLET)--and cardiac index (transthoracic echocardiography-Doppler) were determined before and after volume infusion of colloid (8 mL x kg). DeltaPEP (%) was defined as the difference between expiratory and inspiratory PEP divided by the mean of expiratory and inspiratory values. Respiratory changes in pulse pressure (DeltaPP) was also measured.

MEASUREMENTS AND MAIN RESULTS

: Twenty-two volume challenges were done in 20 deeply sedated patients. DeltaPEPKT, DeltaPEPPLET, and DeltaPP (measured in all patients) before volume expansion were correlated with cardiac index change after fluid challenge (r = .73, r = .67, and r = .70, respectively, p < .0001). Patients with a cardiac index increase induced by volume expansion > or = 15% and <15% were classified as responders and nonresponders, respectively. Receiver operating characteristic curves showed that the threshold DeltaPP value of 17% allowed discrimination between responder/nonresponder patients with a sensitivity of 85% and a specificity of 100%. For both DeltaPEPKT and DeltaPEPPLET, the best threshold value was 4% with a sensitivity-specificity of 92%-89% and 100%-67%, respectively.

CONCLUSIONS

The present study found DeltaPEPKT and DeltaPEPPLET to be as accurate as DeltaPP in the prediction of fluid responsiveness in mechanically ventilated septic patients.

The influence of cardiac preload and positive end-expiratory pressure on the pre-ejection period

The pre-ejection period (PEP) has recently been described as a potential parameter for monitoring cardiac preload. This study further investigated the influence of changes in intravascular volume status and the application of positive end-expiratory pressure (PEEP) on the pre-ejection period. In ten pigs, ECG, arterial pressure and stroke volume derived from an aortic flowprobe were registered. Global end-diastolic volume (GEDV) was measured by transcardiopulmonary thermodilution. Total blood volume (TBV) and intrathoracic blood volume (ITBV) were measured by the dye-dilution technique. Measurements were performed during normovolaemic conditions, after volume loading with haemodilution blood (20 ml kg(-1)) and following haemorrhage (30 ml kg(-1)) without PEEP and with PEEP (15 cm H(2)O) applied. Volume loading increased GEDV, ITBV, TBV and SV, whereas PEP remained constant. However, the changes were not significant (P > 0.05). Subsequent haemorrhage significantly decreased GEDV (from 436 to 308 ml), ITBV (from 729 to 452 ml), TBV (from 2,131 to 1,488 ml) (all P-values <0.05), and SV (from 20.7 ml to 14.3 ml, P < 0.001). However, PEP did not change significantly (from 73 to 82 ms, P > 0.05). No correlation between the changes in PEP and changes in any other variable was observed. It is concluded that PEP is not sensitive to the changes in intravascular volume status.

Non-Invasive Cardiac Output Determination by Two-Dimensional Independent Doppler During and After Cardiac Surgery

PURPOSE

This study was to compare noninvasive measurement of cardiac output (CO) using a novel Doppler technique with invasive CO measurements in the postcardiac surgical intensive care unit.

DESCRIPTION

Thirty-six patients (67.2 +/- 10 years, New York Heart Association functional class 3.1 +/- 0.3) undergoing coronary revascularization were prospectively examined postoperatively. One hundred eighty paired CO and stroke volume measurements were compared from the noninvasive USCOM device (Sydney, Australia) and the invasive Swan-Ganz catheter at varying COs. Eighteen measurements were performed intraoperatively by direct insonation of the right ventricular outflow tract.

EVALUATION

Mean noninvasive and invasive CO values were 5.15 +/- 1.98 L/min and 4.92 +/- 2.0 L/min, respectively (r = 0.870; p < 0.01). The mean difference between methods was -0.23 +/- 1.01 L/min greater than a range of CO values from 2.5 to 9.9 L/min. Mean central venous saturation percentage was 72 +/- 9%, correlating with both noninvasive and invasive CO (r = 0.474 and 0.606, respectively, p < 0.01). Intraoperatively, both direct and invasive CO were identical.

CONCLUSIONS

Using the ultrasonic cardiac output monitoring (USCOM) device it is possible to determine noninvasive beat-to-beat CO in postcardiac surgery patients without the possible complications associated with invasive right heart catheterization. The USCOM CO and stroke volume showed a very good agreement with invasive Swan-Ganz measures and correlated with central venous saturation percentage.

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

STUDY OBJECTIVES

Stroke volume variation (SVV) and pulse pressure variation (PPV) determined by the PiCCOplus system (Pulsion Medical Systems; Munich, Germany) may be useful dynamic variables in guiding fluid therapy in patients receiving mechanical ventilation. However, with respect to the prediction of volume responsiveness, conflicting results for SVV have been published in cardiac surgery patients. The goal of this study was to reevaluate SVV in predicting volume responsiveness and to compare it with PPV.

DESIGN

Prospective nonrandomized clinical investigation.

SETTING

University-based cardiac surgery.

PATIENTS

Forty patients with preserved left ventricular function undergoing elective off-pump coronary artery bypass grafting.

INTERVENTIONS

Volume replacement therapy before surgery.

MEASUREMENTS AND RESULTS

Following induction of anesthesia, before and after volume replacement (6% hydroxyethyl starch solution, 10 mL/kg ideal body weight), hemodynamic measurements of stroke volume index (SVI), SVV, PPV, global end-diastolic volume index (GEDVI), central venous pressure (CVP) and pulmonary capillary wedge pressure (PCWP) were obtained. Also, left ventricular end-diastolic area index (LVEDAI) was assessed by transesophageal echocardiography. Prediction of ventricular performance was tested by calculating the area under the receiver operating characteristic (ROC) curves and by linear regression analysis; p < 0.05 was considered significant. All measured hemodynamic variables except heart rate changed significantly after fluid loading. GEDVI, CVP, PCWP, and LVEDAI increased, whereas SVV and PPV decreased. The best area under the ROC curve (AUC) was found for SVV (AUC = 0.823) and PPV (AUC = 0.808); the AUC for other preload indexes ranged from 0.493 to 0.636. A significant correlation with changes of SVI was observed for SVV (r = 0.606, p < 0.001) and PPV (r = 0.612, p < 0.001) only. SVV and PPV were closely related (r = 0.861, p < 0.001).

CONCLUSIONS

In contrast to standard preload indexes, SVV and PPV, comparably, showed a good performance in predicting fluid responsiveness in patients before off-pump coronary artery bypass grafting.

Bedside ultrasonography in the ICU: part 1

Ultrasonography has become an invaluable tool in the management of critically ill patients. Its safety and portability allow for use at the bedside to provide rapid, detailed information regarding the cardiovascular system and the function and anatomy of certain internal organs. Echocardiography can noninvasively elucidate cardiac function and structure. This information is vital in the management hemodynamically unstable patients in the ICU. In addition, ultrasonography has particular value for the assessment and safe drainage of pleural and intra-abdominal fluid and the placement of central venous catheters. A new generation of portable, battery-powered, inexpensive, hand-carried ultrasound devices have recently become available; these devices can provide immediate diagnostic information not assessable by physical examination alone and allow for ultrasound-guided thoracocentesis, paracentesis, and central venous cannulation. This two-part article reviews the application of bedside ultrasonography in the ICU.

Stroke output variations calculated by esophageal Doppler is a reliable predictor of fluid response

OBJECTIVE

Esophageal Doppler allows continuous monitoring of stroke volume index (SVI) and corrected flow time (FTc). We hypothesized that variations in stroke output index SOI (SVI/FTc) during volume expansion can predict the hemodynamic response to subsequent fluid loading better than the static values.

DESIGN AND SETTING

Prospective study in the intensive care unit of a university hospital.

PATIENTS

Fifty-one patients with circulatory failure were monitored by esophageal Doppler.

INTERVENTIONS

Patients who responded to a first fluid challenge received a second one. Patients who responded to both were classified as responders-responders, and those who did not respond to the second as responders-nonresponders. In these two groups we compared DeltaSVI, DeltaFTc, and DeltaSOI during each fluid challenge and also static values at the end of each fluid challenge.

MEASUREMENTS AND RESULTS

After the first fluid challenge DeltaSOI and DeltaSVI were significantly higher in patients who responded to subsequent volume expansion than in patients who no longer responded. ROC curves showed that DeltaSOI was a better predictor of fluid responsiveness than DeltaSVI. During volume expansion a DeltaSOI value of 11% discriminated between responders and nonresponders to subsequent volume expansion with a sensitivity of 91% and a specificity of 97%. There was no significant difference between the two groups for FTc value at the end of first fluid challenge.

CONCLUSIONS

Analysis of DeltaSOI during fluid challenge predicts response to subsequent fluid challenge and FTc is not a reliable indicator of cardiac preload.

Esophageal Doppler monitoring predicts fluid responsiveness in critically ill ventilated patients

OBJECTIVE

To test whether fluid responsiveness can be predicted by the respiratory variation in aortic blood flow and/or the flow time corrected for heart rate monitored with esophageal Doppler.

DESIGN AND SETTING

Prospective study in a 24-bed medical intensive care unit of a university hospital.

PATIENTS

38 mechanically ventilated patients with sinus rhythm and without spontaneous breathing activity in whom volume expansion was planned.

INTERVENTIONS

The aortic blood flow was measured using an esophageal Doppler monitoring device before and after fluid infusion (500 ml NaCl 0.9% over 10 min). The variation in aortic blood flow over a respiratory cycle between its minimal and maximal values was calculated. The flow time was also measured.

MEASUREMENTS AND RESULTS

Aortic blood flow increased by at least 15% after volume expansion in 20 patients (defined as responders). Before fluid infusion the respiratory variation in aortic flow was higher in responders than in nonresponders (28+/-12% vs. 12+/-5%). It significantly decreased after volume expansion (18+/-11%) in responders only. A respiratory variation in aortic flow before volume expansion of at least 18% predicted fluid responsiveness with a sensitivity of 90% and a specificity of 94%. Flow time increased with fluid infusion in responders and nonresponders. A flow time corrected for heart rate below 277 ms predicted fluid responsiveness with a sensitivity of 55% and a specificity of 94%. The area under the ROC curve generated for variation in aortic blood flow ABF was greater than that generated for flow time.

CONCLUSIONS

The respiratory variation in aortic blood flow reliably predicts fluid responsiveness in patients with sinus rhythm and without breathing activity.

Hemodynamic assessment of critically ill patients using echocardiography Doppler

PURPOSE OF REVIEW

The evaluation of hemodynamic status in critically ill patients is a leading recommended indication of transesophageal echocardiography in the intensive care unit. Advantages and diagnostic yield of transesophageal echocardiography in this setting are particularly relevant when considering limitations and questioned prognostic impact of pulmonary artery catheterization.

RECENT FINDINGS

Recent clinical studies have been performed to validate and assess the value of transesophageal echocardiography in determining cardiac output, cardiac preload dependence, right ventricular function, and left ventricular filling pressure. In addition, diagnostic capacity and therapeutic impact of transesophageal echocardiography have been widely reported in various intensive care unit settings.

SUMMARY

Transesophageal echocardiography appears well suited for the determination of cardiac index and to track its variations after therapeutic interventions. Although repeated measurements of left ventricular end-diastolic dimension allows to accurately track preload variations, a single determination is not reliable to predict fluid responsiveness in intensive care unit patients. Identification of preload dependence in hemodynamically unstable patients currently tends to rely mainly on dynamic parameters that use cardiopulmonary interactions under mechanical ventilation. Transesophageal echocardiography also allows to adequately assess right ventricular function and left ventricular filling pressure using combined Doppler modalities. Adequate education and training of intensivists and anesthesiologists is crucial to further develop the use of transesophageal echocardiography in the intensive care unit setting. Despite the absence of randomized controlled studies documenting transesophageal echocardiography benefits on patient outcome, present evidence and experience strongly recommend a larger use of echocardiography Doppler for a comprehensive functional hemodynamic assessment of critically ill patients with circulatory failure.

Pulse pressure and stroke volume variations during severe haemorrhage in ventilated dogs

BACKGROUND

Similarly to systolic pressure variation (SPV), pulse pressure variation (PPV) and stroke volume variation (SVV) derived from arterial pulse contour analysis have been shown to reflect fluid responsiveness in ventilated patients. However, unlike the SPV, both PPV and SVV have not been validated during extreme hypovolaemia. The aim of the present study was to examine whether these newly introduced variables respond to gradual hypovolaemia like the SPV by increasing gradually with each step of the haemorrhage even during extreme hypovolaemia.

METHODS

SPV, SVV and PPV were measured in 8 dogs following initial volume loading (10% of the estimated blood volume administered as colloid solution), 5 steps of graded haemorrhage, each consisting of 10% of the estimated blood volume, followed by retransfusion of the shed blood.

RESULTS

The correlations of the SVV, SPV and PPV to the stroke volume (SV) throughout the study were -0.89, -0.91 and -0.91, respectively. Correlations of the CVP and the global end-diastolic volume (GEDV) of the heart chambers to the SV were 0.79 and 0.95, respectively. The SPV correlated significantly with both the PPV and the SVV (r=0.97 and 0.93 respectively). However, the PPV increased by more than 400% at 50% haemorrhage compared with increases of 200% and 120% for the SVV and %SPV, respectively.

CONCLUSION

This study demonstrates that the present algorithm used for the calculation of the SVV and the formula used to calculate the PPV, perform well over a wide range of preload states including severe hypovolaemia. However, the PPV changes more than the SPV and SVV. This may be due to the changing relation of the SV to the pulse pressure when the filling of the aorta is greatly decreased.

Pulse pressure variations to predict fluid responsiveness: influence of tidal volume

OBJECTIVE

To evaluate the influence of tidal volume on the capacity of pulse pressure variation (DeltaPP) to predict fluid responsiveness.

DESIGN

Prospective interventional study.

SETTING

A 31-bed university hospital medico-surgical ICU.

PATIENTS AND PARTICIPANTS

Sixty mechanically ventilated critically ill patients requiring fluid challenge, separated according to their tidal volume.

INTERVENTION

Fluid challenge with either 1,000 ml crystalloids or 500 ml colloids.

MEASUREMENTS AND RESULTS

Complete hemodynamic measurements including DeltaPP were obtained before and after fluid challenge. Tidal volume was lower than 7 ml/kg in 26 patients, between 7-8 ml/kg in 9 patients, and greater than 8 ml/kg in 27 patients. ROC curve analysis was used to evaluate the predictive value of DeltaPP at different tidal volume thresholds, and 8 ml/kg best identified different behaviors. Overall, the cardiac index increased from 2.66 (2.00-3.47) to 3.04 (2.44-3.96) l/min m(2) ( P <0.001). It increased by more than 15% in 33 patients (fluid responders). Pulmonary artery occluded pressure was lower and DeltaPP higher in responders than in non-responders, but fluid responsiveness was better predicted with DeltaPP (ROC curve area 0.76+/-0.06) than with pulmonary artery occluded pressure (0.71+/-0.07) and right atrial (0.56+/-0.08) pressures. Despite similar response to fluid challenge in low (<8 ml/kg) and high tidal volume groups, the percent of correct classification of a 12% DeltaPP was 51% in the low tidal volume group and 88% in the high tidal volume group.

CONCLUSIONS

DeltaPP is a reliable predictor of fluid responsiveness in mechanically ventilated patients only when tidal volume is at least 8 ml/kg.

Pulse Pressure Variation Predicts Fluid Responsiveness Following Coronary Artery Bypass Surgery

STUDY OBJECTIVE

To determine whether the degree of pulse pressure variation (PPV) and systolic pressure variation (SPV) predict an increase in cardiac output (CO) in response to volume challenge in postoperative patients who have undergone coronary artery bypass grafting (CABG), and to determine whether PPV is superior to SPV in this setting.

DESIGN AND SETTING

This was a prospective clinical study conducted in the cardiovascular ICU of a university hospital.

PATIENTS

Twenty-one patients were studied immediately after arrival in the ICU following CABG.

INTERVENTION

A fluid bolus was administered to all patients.

MEASUREMENTS

Hemodynamic measurements, including central venous pressure (CVP), pulmonary artery occlusion pressure (PAOP), CO (thermodilution), percentage of SPV (%SPV), and percentage of PPV (%PPV), were performed shortly after patient arrival in the ICU. Patients were given a rapid 500-mL fluid challenge, after which hemodynamic measurements were repeated. Patients whose CO increased by >/= 12% were considered to be fluid responders. The ability of different parameters to distinguish between responders and nonresponders was compared.

RESULTS

In response to the volume challenge, 6 patients were responders and 15 were nonresponders. Baseline CVP and PAOP were no different between these two groups. In contrast, the %SPV and the %PPV were significantly higher in responders than in nonresponders. Receiver operating characteristic curve analysis suggested that the %PPV was the best predictor of fluid responsiveness. The ideal %PPV threshold for distinguishing responders from nonresponders was found to be 11. A PPV value of >/= 11% predicted an increase in CO with 100% sensitivity and 93% specificity.

CONCLUSION

PPV and SPV can be used to predict whether or not volume expansion will increase CO in postoperative CABG patients. PPV was superior to SPV at predicting fluid responsiveness. Both of these measures were far superior to CVP and PAOP.

Prediction of fluid responsiveness in patients during cardiac surgery

BACKGROUND

Left ventricular stroke volume variation (SVV) has been shown to be a predictor of fluid responsiveness in various subsets of patients. However, the accuracy and reliability of SVV are unproven in patients ventilated with low tidal volumes.

METHODS

Fourteen patients were studied immediately after coronary artery bypass grafting (CABG). All patients were mechanically ventilated in pressure-controlled mode [tidal volume 7.5 (1.2) ml kg(-1)]. In addition to standard haemodynamic monitoring, SVV was assessed by arterial pulse contour analysis. Left ventricular end-diastolic area index (LVEDAI) was determined by transoesophageal echocardiography. A transpulmonary thermodilution technique was used for measurement of cardiac index (CI), stroke volume index (SVI) and intrathoracic blood volume index (ITBI). All variables were assessed before and after a volume shift induced by tilting the patients from the anti-Trendelenburg (30 degrees head up) to the Trendelenburg position (30 degrees head down).

RESULTS

After the change in the Trendelenburg position, SVV decreased significantly, while CI, SVI, ITBI, LVEDAI, central venous pressure (CVP) and pulmonary artery occlusion pressure (PAOP) increased significantly. Changes in SVI were significantly correlated to changes in SVV (r=0.70; P<0.0001) and to changes in LVEDAI, ITBI, CVP and PAOP. Only prechallenge values of SVV were predictive of changes in SVI after change from the anti-Trendelenburg to the Trendelenburg position.

CONCLUSIONS

In patients after CABG surgery who were ventilated with low tidal volumes, SVV enabled prediction of fluid responsiveness and assessment of the haemodynamic effects of volume loading.

Hand-held echocardiography with Doppler capability for the assessment of critically-ill patients: is it reliable?

OBJECTIVE

To evaluate the diagnostic capability of a hand-carried ultrasound device (HCU) in critically ill patients when using conventional transthoracic echocardiography (TTE) as a reference.

DESIGN

Prospective, descriptive study.

SETTING

Medical-surgical intensive care unit of a teaching hospital.

PATIENTS

All patients requiring a TTE study were eligible.

INTERVENTIONS

Each patient underwent an echocardiographic examination using a full-feature echocardiographic platform (Sonos 5500, Philips Medical Systems, Andover, MA) and a small battery-operated device (SonoHeart Elite, SonoSite, Bothell, WA). The operators (level III training in echocardiography) were randomized (HCU vs. TTE) and they independently interpreted the echocardiograms at the patient bedside.

RESULTS

During a 2-month period, 55 consecutive patients (age: 61+/-16 years, simplified acute physiology score 46+/-15, body mass index 26+/-7) were studied, 40 of them being mechanically ventilated (73%). The number of acoustic windows was comparable using HCU and TTE (2.3+/-0.8 vs. 2.4+/-0.8: P=0.24). The overall diagnostic accuracy of HCU was lower compared with conventional TTE (137/171 vs. 158/171 clinical questions solved: P=0.002), reaching 80% and 92%, respectively. Despite its spectral Doppler capability, HCU missed diagnoses that were adequately identified by TTE: elevated left ventricular pressure ( n=2), relevant valvulopathy ( n=2) and moderate ( n=4) or severe ( n=2) pulmonary hypertension. Acute management was altered by HCU and TTE findings in 27 patients (49%) and 28 patients (51%), respectively.

CONCLUSIONS

In this study, HCU had a lower diagnostic accuracy compared with conventional TTE, despite its spectral Doppler capability. Further studies are needed to validate these evolving diagnostic tools in critical care settings.

The respiratory variation in inferior vena cava diameter as a guide to fluid therapy

OBJECTIVE

To investigate whether the respiratory variation in inferior vena cava diameter (DeltaD(IVC)) could be related to fluid responsiveness in mechanically ventilated patients.

DESIGN

Prospective clinical study.

SETTING

Medical ICU of a non-university hospital.

PATIENTS

Mechanically ventilated patients with septic shock (n=39).

INTERVENTIONS

Volume loading with 8 mL/kg of 6% hydroxyethylstarch over 20 min.

MEASUREMENTS AND RESULTS

Cardiac output and DeltaD(IVC) were assessed by echography before and immediately after the standardized volume load. Volume loading induced an increase in cardiac output from 5.7+/-2.0 to 6.4+/-1.9 L/min (P<0.001) and a decrease in DeltaD(IVC) from 13.8+/-13.6 vs 5.2+/-5.8% (P<0.001). Sixteen patients responded to volume loading by an increase in cardiac output > or =15% (responders). Before volume loading, the DeltaD(IVC) was greater in responders than in non-responders (25+/-15 vs 6+/-4%, P<0.001), closely correlated with the increase in cardiac output (r=0.82, P<0.001), and a 12% DeltaD(IVC) cut-off value allowed identification of responders with positive and negative predictive values of 93% and 92%, respectively.

CONCLUSION

Analysis of DeltaD(IVC) is a simple and non-invasive method to detect fluid responsiveness in mechanically ventilated patients with septic shock.

Respiratory changes in inferior vena cava diameter are helpful in predicting fluid responsiveness in ventilated septic patients

OBJECTIVE

To evaluate the extent to which respiratory changes in inferior vena cava (IVC) diameter can be used to predict fluid responsiveness.

DESIGN

Prospective clinical study.

SETTING

Hospital intensive care unit.

PATIENTS

Twenty-three patients with acute circulatory failure related to sepsis and mechanically ventilated because of an acute lung injury.

MEASUREMENTS

Inferior vena cava diameter (D) at end-expiration (Dmin) and at end-inspiration (Dmax) was measured by echocardiography using a subcostal approach. The distensibility index of the IVC (dIVC) was calculated as the ratio of Dmax - Dmin / Dmin, and expressed as a percentage. The Doppler technique was applied in the pulmonary artery trunk to determine cardiac index (CI). Measurements were performed at baseline and after a 7 ml/kg volume expansion using a plasma expander. Patients were separated into responders (increase in CI > or =15%) and non-responders (increase in CI <15%).

RESULTS

Using a threshold dIVC of 18%, responders and non-responders were discriminated with 90% sensitivity and 90% specificity. A strong relation (r = 0.9) was observed between dIVC at baseline and the CI increase following blood volume expansion. Baseline central venous pressure did not accurately predict fluid responsiveness.

CONCLUSION

Our study suggests that respiratory change in IVC diameter is an accurate predictor of fluid responsiveness in septic patients.

Monitoring of respiratory variations of aortic blood flow velocity using esophageal Doppler

OBJECTIVE

The purpose of this study was to determine whether monitoring of respiratory changes in aortic blood flow velocity, recorded by esophageal Doppler, could be used to detect changes in volume depletion.

DESIGN

Animal study.

ANIMALS AND INTERVENTIONS

After general anesthesia and tracheotomy, ten New Zealand female rabbits, weighing 4-4.5 kg were studied under mechanical ventilation at a fixed tidal volume; during this time 5-ml blood samples were withdrawn (in increments up to a total of 30 ml) and then retransfused.

MEASUREMENTS AND RESULTS

At each step, systolic (SBP), diastolic (DBP), pulse (PP) pressures and maximum descending aortic blood flow (V) were recorded. Respiratory changes of V (DeltaV), SBP (DeltaSBP) and PP (DeltaPP) were calculated as the difference of maximal and minimal values divided by their respective means and expressed as a percentage. The amount of blood withdrawn correlated negatively with SBP, DBP, PP and V and positively with DeltaSBP, DeltaPP and DeltaV. Among these parameters, DeltaV correlated best with the amount of blood withdrawn ( r=0.89, p<0.001) and it was the most accurate index of volume depletion.

CONCLUSION

Monitoring of the respiratory variation in V, calculated by esophageal Doppler technique, seems to be a highly accurate index of blood volume depletion and restitution.

Hemodynamic monitoring in the intensive care unit

Hemodynamic monitoring is a diagnostic tool. Because hemodynamic monitoring often requires invasive procedures, it can be associated with an increased incidence of untoward events. Like any diagnostic tool, its ability to improve outcome will be primarily related to the survival benefit enjoyed by specific therapies that can only be given without complications based on their use. Presently, few specific treatment plans fit into this category. The diagnostic accuracy of preload responsiveness is markedly improved by the use of arterial pulse pressure or stroke volume variation, neither of which require pulmonary arterial catheterization. The field of hemodynamic monitoring is rapidly evolving and will probably continue to evolve at this rapid pace over the next 5 to 10 years as new technologies, information management systems, and our understanding of the pathophysiology of critical illness progresses.

Cyclic changes in arterial pulse during respiratory support revisited by Doppler echocardiography

It has long been known that there are cyclic changes in arterial pressure during mechanical ventilation. They are caused by cyclic changes in both the right and left ventricular stroke output, occurring in opposite phases. As a result, arterial pulse pressure is increased during inspiration and decreased during expiration. A cyclic improvement in left ventricular systolic function could thus be expected during mechanical lung inflation. We tested this hypothesis in 31 septic patients who were mechanically ventilated in controlled mode by combining left ventricular measurements by transesophageal echocardiography with invasive arterial pressure recordings and Doppler analysis of pulmonary venous flow and right and left ventricular stroke volume. Lung inflation by tidal ventilation significantly improved left ventricular stroke volume (26 +/- 0.4 cm3/m2 [mean +/- SEM] vs. 22.3 +/- 0.4 cm3/m2 at end deflation). Beat-to-beat analysis of pulmonary venous flow velocity illustrated the boosting effect of lung inflation on pulmonary venous return. The beneficial effect of inspiration thus appeared directly related to a significant increase in left ventricular diastolic volume (60.3 +/- 1.5 cm3/m2 vs. 53.3 +/- 1.4 cm3/m2 at end-expiration) and to a lesser extent to an improved left ventricular ejection fraction. We concluded that the transient beneficial hemodynamic effect of tidal ventilation on the left ventricular pump is essentially mediated by an improved left ventricular filling.

Rationale for cardiovascular monitoring

A primary aspect of cardiovascular support of the critically ill patient is the titration of cardiopulmonary therapies based on the baseline cardiopulmonary status and the subsequent physiologic response. Implicit in this paradigm is the monitoring of the processes being titrated. The degree to which a specific physiologic variable, such as mean arterial pressure or arterial oxygen saturation, needs to be assessed is a function of the therapy used, the stability of the patient, the relation among the variables defining the hemodynamic profile, and the ability of the support staff to remain in close attendance at the bedside. In an otherwise stable patient in heart failure being treated with mild afterload reduction and diuretics, periodic measures of heart rate, urine output, and daily measures of body weight are all that are reasonably needed to titrate therapy. However, in the management of a patient with cardiogenic shock with pulmonary edema and respiratory failure, continuous measures of mean arterial pressure, left ventricular filling pressure, cardiac output, arterial oxygen content, and end-organ function may be necessary as more potent and risky therapies are used. How, then, does one arrive at the correct formula to prescribe appropriate physiologic monitoring for the patient in the intensive care unit setting? To a large extent this is unknown, primarily because the utility of monitoring techniques to diagnose pathophysiologic processes and the resultant effect of therapy to reverse it is not known for most of the diseases treated in the intensive care unit. Few monitoring techniques have progressed through a logical progression of development to their present level of use. Thus, their use in the management of the critically ill patient cannot be vigorously defended, except under specific conditions.

Stroke volume variation as an indicator of fluid responsiveness using pulse contour analysis in mechanically ventilated patients

Assessment of cardiac performance and adequate fluid replacement of a critically ill patient are important goals of a clinician. We designed this study to evaluate the ability of stroke volume variation (SVV), derived from pulse contour analysis, and frequently used preload variables (central venous pressure and pulmonary capillary wedge pressure) to predict the response of stroke volume index and cardiac index to volume replacement in normoventilated cardiac surgical patients. We studied 20 patients undergoing elective coronary artery bypass grafting. After the induction of anesthesia, hemodynamic measurements were performed before (T1) and subsequent to volume replacement by infusion of 6% hydroxyethyl starch 200/0.5 (7 mL/kg) with a rate of 1 mL x kg(-1) x min(-1). Except for heart rate, all hemodynamic variables changed significantly (P < 0.01) after volume loading. Linear regression analysis between SVV at baseline (T1) and DeltaSVV after volume application showed a significant correlation (r = -0.97; P < 0.01), whereas linear regression analysis between SVV (T1) and percentage changes of stroke volume index (r = 0.19) and cardiac index (r = 0.17) did not reveal a significant relationship between variables. The results of our study suggest that SVV derived from pulse contour analysis cannot serve as an indicator of fluid responsiveness in normoventilated cardiac surgical patients.

Fluid responsiveness in mechanically ventilated patients: a review of indices used in intensive care

OBJECTIVE

In mechanically ventilated patients the indices which assess preload are used with increasing frequency to predict the hemodynamic response to volume expansion. We discuss the clinical utility and accuracy of some indices which were tested as bedside indicators of preload reserve and fluid responsiveness in hypotensive patients under positive pressure ventilation.

RESULTS AND CONCLUSIONS

Although preload assessment can be obtained with fair accuracy, the clinical utility of volume responsiveness-guided fluid therapy still needs to be demonstrated. Indeed, it is still not clear whether any form of monitoring-guided fluid therapy improves survival.

Monitoring cardiac function in intensive care

Systolic cardiac function results from the interaction of four interdependent factors: heart rate, preload, contractility, and afterload. Heart rate can be quantified easily at the bedside, while preload estimation has traditionally relied on invasive pressure measurements, both central venous and pulmonary artery wedge. These have significant clinical limitations; however, adult literature has highlighted the superiority of several novel preload measures. Measurement of contractility and afterload is difficult; thus in clinical practice the bedside assessment of cardiac function is represented by cardiac output. A variety of techniques are now available for cardiac output measurement in the paediatric patient. This review summarises cardiac function and cardiac output measurement in terms of methodology, interpretation, and their contribution to the concepts of oxygen delivery and consumption in the critically ill child.

Techniques for assessing and achieving fluid balance in acute renal failure

Fluid therapy, together with attention to oxygen supply, is the cornerstone of resuscitation in all critically ill patients. Hypovolemia results in inadequate blood flow to meet the metabolic requirements of the tissues and must be treated urgently to avoid the complication of progressive organ failure, including acute renal failure. The kidney plays a critical role in body fluid homeostasis. Renal dysfunction disturbs this homeostasis and requires special attention to issues of fluid balance and fluid overload. In addition, fluid therapy is the only treatment that has been shown to be effective in the prevention of acute renal failure. Special attention to volume status is therefore required in patients at risk for acute renal failure. Hypovolemia is also a major causal factor of morbidity during hemodialysis and may contribute to further renal insults. Although the importance of fluid management is generally recognized, the choice of fluid, the amount, and assessment of fluid status are controversial. As the choice of fluids becomes wider and monitoring devices become more sophisticated, the controversy increases. This article provides an overview of the concept of fluid management in the critically ill patient with acute renal failure.

Respiratory variations of aortic VTI: a new index of hypovolemia and fluid responsiveness

In 12 mechanically ventilated and anesthetized rabbits, we investigated whether the magnitude of respiratory changes in the aortic velocity time integral (VTI(Ao)), recorded by transthoracic echocardiography (TTE) during a stepwise blood withdrawal and restitution, could be used as a reliable indicator of volume depletion and responsiveness. At each step, left and right ventricular dimensions and the aortic diameter and VTI(Ao) were recorded to calculate stroke volume (SV) and cardiac output (CO). Respiratory changes of VTI(Ao) (maximal - minimal values divided by their respective means) were calculated. The amount of blood withdrawal correlated negatively with left and right ventricular diastolic diameters, VTI(Ao), SV, and CO and correlated directly with respiratory changes of VTI(Ao). Respiratory VTI(Ao) variations (but not other parameters) at the last blood withdrawal step was also correlated with changes in SV after blood restitution (r = 0.83, P < 0.001). In conclusion, respiratory variations in VTI(Ao) using TTE appear to be a sensitive index of blood volume depletion and restitution. This dynamic parameter predicted fluid responsiveness more reliably than static markers of cardiac preload.

Measurement of cardiac output and tissue perfusion

Recent technologic innovations have allowed a greater scope for cardiac output measurement in critically ill children. There is a move toward both less invasive and continuous methods, several of which also offer novel measures of preload. Many of the new methods are still undergoing preliminary evaluation in the pediatric population and will be summarized in this article.

Predicting fluid responsiveness in ICU patients: a critical analysis of the evidence

STUDY OBJECTIVE

To identify and critically review the published peer-reviewed, English-language studies investigating predictive factors of fluid responsiveness in ICU patients.

DESIGN

Studies were collected by doing a search in MEDLINE (from 1966) and scanning the reference lists of the articles. Studies were selected according to the following criteria: volume expansion performed in critically ill patients, patients classified in two groups (responders and nonresponders) according to the effects of volume expansion on stroke volume or on cardiac output, and comparison of responder and nonresponder patients' characteristics before volume expansion.

RESULTS

Twelve studies were analyzed in which the parameters tested were as follows: (1) static indicators of cardiac preload (right atrial pressure [RAP], pulmonary artery occlusion pressure [PAOP], right ventricular end-diastolic volume [RVEDV], and left ventricular end-diastolic area [LVEDA]); and (2) dynamic parameters (inspiratory decrease in RAP [Delta RAP], expiratory decrease in arterial systolic pressure [Delta down], respiratory changes in pulse pressure [Delta PP], and respiratory changes in aortic blood velocity [Delta Vpeak]). Before fluid infusion, RAP, PAOP, RVEDV, and LVEDA were not significantly lower in responders than in nonresponders in three of five studies, in seven of nine studies, in four of six studies, and in one of three studies, respectively. When a significant difference was found, no threshold value could discriminate responders and nonresponders. Before fluid infusion, Delta RAP, Delta down, Delta PP, and Delta Vpeak were significantly higher in responders, and a threshold value predicted fluid responsiveness with high positive (77 to 95%) and negative (81 to 100%) predictive values.

CONCLUSION

Dynamic parameters should be used preferentially to static parameters to predict fluid responsiveness in ICU patients.