The use of transesophageal echocardiography for preload assessment in critically ill patients

Should we use diastolic function parameters to determine preload responsiveness in cardiac surgery? A pilot study

BACKGROUND

Left ventricular (LV) diastolic function (DF) may play an important role in predicting fluid responsiveness. However, few studies assessed the role of diastolic function in predicting fluid responsiveness. The aim of this pilot study was to assess whether parameters of right and left diastolic function assessed with transesophageal echocardiography, including the mitral E/e' ratio, is associated with fluid responsiveness among patients undergoing elective bypass graft surgery. We also sought to compare other methods of fluid responsiveness assessment, including echocardiographic and hemodynamic parameters, pulse pressure variation, and stroke volume variation (SVV) (arterial pulse contour analysis, Flotrac/Vigileo system).

RESULTS

We prospectively studied seventy patients undergoing coronary artery bypass grafting (CABG) monitored with a radial arterial catheter, transesophageal echocardiography (TEE), and a pulmonary artery catheter (for cardiac output measurements), before and after the administration of 500 mL of crystalloid over 10 min after the anesthetic induction. Thirteen patients were excluded (total of 57 patients). Fluid responsiveness was defined as an increase in cardiac index of ≥ 15%. There were 21 responders (36.8%) and 36 non-responders (63.2%). No difference in baseline pulsed wave Doppler echocardiographic measurements of any components of the mitral, tricuspid, and pulmonary and hepatic venous flows were found between responders and non-responders. There was no difference in MV tissue Doppler measurements between responders and non-responders, including E/e' ratio (8.7 ± 4.1 vs. 8.5 ± 2.8 in responders vs. non-responders, P = 0.85). SVV was the only independent variable to predict an increase in cardiac index by multivariate analysis (P = 0.0208, OR = 1.196, 95% CI (1.028-1.393)).

CONCLUSIONS

In this pilot study, we found that no parameters of right and left ventricular diastolic function were associated with fluid responsiveness in patients undergoing CABG. SVV was the most useful parameter to predict fluid responsiveness.

TRIAL REGISTRATION

ClinicalTrials.gov , NCT02714244 . Registered 21 March 2016-retrospectively registered.

Pleth variability index may predict preload responsiveness in patients treated with nasal high flow: a physiological study

The purpose of this study was to determine whether the plethysmographic variability index ("PVi") can predict preload responsiveness in patients with nasal high flow (NHF) (≥30 L/min) with any sign of hypoperfusion. "Preload responsiveness" was defined as a ≥10% increase in stroke volume (SV), measured by transthoracic echocardiography, after passive leg raising. SV and PVi were reassessed in preload responders after receiving a 250-mL fluid challenge. Twenty patients were included and 12 patients (60%) were preload responders. Responders showed higher baseline mean PVi (24% vs. 13%; P = 0.001) and higher mean PVi variation (ΔPVi) after passive leg raising (6.8% vs. -1.7%; P < 0.001). No differences between mean ΔPVi after passive leg raising and mean ΔPVi after fluid challenge were observed (6.8% vs. 7.4%; P = 0.24); and both values were strongly correlated (r = 0.84; P < 0.001). Baseline PVi and ΔPVi after passive leg raising showed excellent diagnostic accuracy identifying preload responders (AUROC 0.92 and 1.00, respectively). Baseline PVi ≥ 16% had a sensitivity of 91.7% and a specificity of 87.5% for detecting preload responders. Similarly, ΔPVi after passive leg raising ≥2% had a 100% of both sensitivity and specificity. Thus, PVi might predict "preload responsiveness" in patients treated with NHF, suggesting that it may guide fluid administration in these patients.NEW & NOTEWORTHY This is the first study that analyzes the use of noninvasive plethysmographic variability index (PVi) for preload assessment in patients treated with nasal high flow (NHF). Its results showed that PVi might identify preload responders. Therefore, PVi may be used in the day-to-day clinical decision-making process in critically ill patients treated with NHF, helping to provide adequate resuscitation volume.

Transoesophageal echocardiography (TOE): contra-indications, complications and safety of perioperative TOE

Transoesophageal echocardiography (TOE) has, in certain clinical situations, become an almost universal monitor and diagnostic tool. In the perioperative environment, TOE is frequently used to guide anaesthetic management and assist with surgical decision making for, but not limited to, cardiothoracic, major vascular and transplant operations. The use of TOE is not limited to the theatre environment being frequently used in outpatient clinics, emergency departments and intensive care settings. Two case reports, one of oesophageal perforation and another of TOE utilization in a patient having previously undergone an oesophagectomy, introduce the need for care while using TOE and highlight the need for vigilance. The safe use of TOE, the potential complications and the suggested contra-indications are then considered together with suggestions for improving the safety of TOE in adult and paediatric patients.

Pharmacologic agents for acute hemodynamic instability: recent advances in the management of perioperative shock- a systematic review

Despite the growing body of evidence evaluating the efficacy of vasoactive agents in the management of hemodynamic instability and circulatory shock, it appears no agent is superior. This is becoming increasingly accepted as current guidelines are moving away from detailed algorithms for the management of shock, and instead succinctly state that vasoactive agents should be individualized and guided by invasive hemodynamic monitoring. This extends to the perioperative period, where vasoactive agent selection and use may still be left to the discretion of the treating physician with a goal-directed approach, consisting of close hemodynamic monitoring and administration of the lowest effective dose to achieve the hemodynamic goals. Successful therapy depends on the ability to rapidly diagnose the etiology of circulatory shock and thoroughly understand its pathophysiology as well as the pharmacology of vasoactive agents. This review focuses on the physiology and resuscitation goals in perioperative shock, as well as the pharmacology and recent advances in vasoactive agent use in its management.

Predicting and measuring fluid responsiveness with echocardiography

Echocardiography is ideally suited to guide fluid resuscitation in critically ill patients. It can be used to assess fluid responsiveness by looking at the left ventricle, aortic outflow, inferior vena cava and right ventricle. Static measurements and dynamic variables based on heart–lung interactions all combine to predict and measure fluid responsiveness and assess response to intravenous fluid resuscitation. Thorough knowledge of these variables, the physiology behind them and the pitfalls in their use allows the echocardiographer to confidently assess these patients and in combination with clinical judgement manage them appropriately.

Effect of fluid loading on left ventricular volume and stroke volume variability in patients with end-stage renal disease: a pilot study

Purpose

The aim of this study was to investigate fluid loading-induced changes in left ventricular end-diastolic volume (LVEDV) and stroke volume variability (SVV) in patients with end-stage renal disease (ESRD) using real-time three-dimensional transesophageal echocardiography and the Vigileo-FloTrac system.

Patients and methods

After obtaining ethics committee approval and informed consent, 28 patients undergoing peripheral vascular procedures were studied. Fourteen patients with ESRD on hemodialysis (HD) were assigned to the HD group and 14 patients without ESRD were assigned to the control group. Institutional standardized general anesthesia was provided in both groups. SVV was measured using the Vigileo-FloTrac system. Simultaneously, a full-volume three-dimensional transesophageal echocardiography dataset was acquired to measure LVEDV, left ventricular end-systolic volume, and left ventricular ejection fraction. Measurements were obtained before and after loading 500 mL hydroxyethyl starch over 30 minutes in both groups.

Results

In the control group, intravenous colloid infusion was associated with a significant decrease in SVV (13.8%±2.6% to 6.5%±2.6%, P<0.001) and a significant increase in LVEDV (83.6±23.4 mL to 96.1±28.8 mL, P<0.001). While SVV significantly decreased after infusion in the HD group (16.2%±6.0% to 6.2%±2.8%, P<0.001), there was no significant change in LVEDV.

Conclusion

Our preliminary data suggest that fluid responsiveness can be assessed not by LVEDV but also by SVV due to underlying cardiovascular pathophysiology in patients with ESRD.

The correlation between the Trendelenburg position and the stroke volume variation

Background

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

Methods

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

Results

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

Conclusions

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

Transesophageal echocardiography for the noncardiac surgical patient

Transesophageal echocardiography (TEE) has been established as a very valuable asset for patient monitoring during cardiac surgery. The value of perioperative TEE for patients undergoing noncardiac surgery is less clear. This article reviews the technical aspects of TEE and comments on the potential benefit of using TEE as a monitoring modality apart from cardiac surgery. Based on patient's comorbidities and/or injury pattern, TEE is a fast and minimally invasive approach to obtain important hemodynamic information, especially useful in a hemodynamically unstable patient. However, certain requirements for the use of the technique are necessary, most important the development of sufficient echocardiographic skills by the anesthesiologists. Indications, skill requirements, and possible complications of the technique are reviewed.

Goal-directed therapy in intraoperative fluid and hemodynamic management

Intraoperative fluid management is pivotal to the outcome and success of surgery, especially in high-risk procedures. Empirical formula and invasive static monitoring have been traditionally used to guide intraoperative fluid management and assess volume status. With the awareness of the potential complications of invasive procedures and the poor reliability of these methods as indicators of volume status, we present a case scenario of a patient who underwent major abdominal surgery as an example to discuss how the use of minimally invasive dynamic monitoring may guide intraoperative fluid therapy.

Corrected right ventricular end-diastolic volume and initial distribution volume of glucose correlate with cardiac output after cardiac surgery

PURPOSE

Appropriate adjustment of cardiac preload is essential to maintain cardiac output (CO), especially in patients after cardiac surgery. This study was intended to determine whether index of right ventricular end-diastolic volume (RVEDVI), corrected RVEDVI using ejection fraction (cRVEDVI), index of initial distribution volume of glucose (IDVGI), or cardiac filling pressures are correlated with cardiac index (CI) following cardiac surgery in the presence or absence of arrhythmias.

METHODS

Eighty-six consecutive cardiac surgical patients were studied. Patients were divided into two groups: the non-arrhythmia (NA) group (n = 72) and the arrhythmia (A) group (n = 14). Three sets of measurements were performed: on admission to the ICU and daily on the first 2 postoperative days. The relationship between each cardiac preload variable and cardiac index (CI) was evaluated. A p value less than 0.05 indicated statistically significant differences.

RESULTS

Each studied variable was not different between the two groups immediately after admission to the ICU. cRVEDVI had a linear correlation with CI in both group (NA group: r = 0.67, n = 216, p < 0.001; A group: r = 0.77, n = 42, p < 0.001), but RVEDVI had a poor correlation with CI (NA group: r = 0.27, n = 216, p < 0.001; A group: r = 0.19, n = 42, p = 0.036). IDVGI had a linear correlation with CI (NA group: r = 0.49, n = 216, p < 0.001; A group: r = 0.61, n = 42, p < 0.001), Cardiac filling pressures had no correlation with CI.

CONCLUSION

Our results demonstrated that cRVEDVI and IDVGI were correlated with CI in the presence or absence of arrhythmias. cRVEDVI and IDVGI have potential as indirect cardiac preload markers following cardiac surgery.

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.

Perioperative intravascular fluid assessment and monitoring: a narrative review of established and emerging techniques

Accurate assessments of intravascular fluid status are an essential part of perioperative care and necessary in the management of the hemodynamically unstable patient. Goal-directed fluid management can facilitate resuscitation of the hypovolemic patient, reduce the risk of fluid overload, reduce the risk of the injudicious use of vasopressors and inotropes, and improve clinical outcomes. In this paper, we discuss the strengths and limitations of a spectrum of noninvasive and invasive techniques for assessing and monitoring intravascular volume status and fluid responsiveness in the perioperative and critically ill patient.

Cardiac filling volumes versus pressures for predicting fluid responsiveness after cardiovascular surgery: the role of systolic cardiac function

INTRODUCTION

Static cardiac filling volumes have been suggested to better predict fluid responsiveness than filling pressures, but this may not apply to hearts with systolic dysfunction and dilatation. We evaluated the relative value of cardiac filling volume and pressures for predicting and monitoring fluid responsiveness, according to systolic cardiac function, estimated by global ejection fraction (GEF, normal 25 to 35%) from transpulmonary thermodilution.

METHODS

We studied hypovolemic, mechanically ventilated patients after coronary (n = 18) or major vascular (n = 14) surgery in the intensive care unit. We evaluated 96 colloid fluid loading events (200 to 600 mL given in three consecutive 30-minute intervals, guided by increases in filling pressures), divided into groups of responding events (fluid responsiveness) and non-responding events, in patients with low GEF (<20%) or near-normal GEF (≥ 20%). Patients were monitored by transpulmonary dilution and central venous (n = 9)/pulmonary artery (n = 23) catheters to obtain cardiac index (CI), global end-diastolic volume index (GEDVI), central venous (CVP) and pulmonary artery occlusion pressure (PAOP).

RESULTS

Fluid responsiveness occurred in 8 (≥ 15% increase in CI) and 17 (≥ 10% increase in CI) of 36 fluid loading events when GEF was <20%, and 7 (≥ 15% increase in CI) and 17 (≥ 10% increase in CI) of 60 fluid loading events when GEF was ≥ 20%. Whereas a low baseline GEDVI predicted fluid responsiveness particularly when GEF was ≥ 20% (P = 0.002 or lower), a low PAOP was of predictive value particularly when GEF was <20% (P = 0.004 or lower). The baseline CVP was lower in responding events regardless of GEF. Changes in CVP and PAOP paralleled changes in CI particularly when GEF was <20%, whereas changes in GEDVI paralleled CI regardless of GEF.

CONCLUSIONS

Regardless of GEF, CVP may be useful for predicting fluid responsiveness in patients after coronary and major vascular surgery provided that positive end-expiratory pressure is low. When GEF is low (<20%), PAOP is more useful than GEDVI for predicting fluid responsiveness, but when GEF is near-normal (≥20%) GEDVI is more useful than PAOP. This favors predicting and monitoring fluid responsiveness by pulmonary artery catheter-derived filling pressures in surgical patients with systolic left ventricular dysfunction and by transpulmonary thermodilution-derived GEDVI when systolic left ventricular function is relatively normal.

Relation of tricuspid annular displacement and tissue Doppler imaging velocities with duration of weaning in mechanically ventilated patients with acute pulmonary edema

BACKGROUND

Liberation from the ventilator is a difficult task, whereas early echocardiographic indices of weaning readiness are still lacking. The aim of this study was to test whether tricuspid annular plane systolic excursion (TAPSE) and right ventricular (RV) systolic (Sm) and diastolic (Em & Am) tissue Doppler imaging (TDI) velocities are related with duration of weaning in mechanically ventilated patients with acute respiratory failure due to acute pulmonary edema (APE).

METHODS

Detailed quantification of left and right ventricular systolic and diastolic function was performed at admission to the Intensive Care Unit by Doppler echocardiography, in a cohort of 32 mechanically ventilated patients with APE. TAPSE and RV TDI velocities were compared between patients with and without prolonged weaning (> or = or < 7 days from the first weaning trial respectively), whereas their association with duration of ventilation and left ventricular (LV) echo-derived indices was tested with multivariate linear and logistic regression analysis.

RESULTS

Patients with prolonged weaning (n = 12) had decreased TAPSE (14.59 +/- 1.56 vs 19.13 +/- 2.59 mm), Sm (8.68 +/- 0.94 vs 11.62 +/- 1.77 cm/sec) and Em/Am ratio (0.98 +/- 0.80 vs 2.62 +/- 0.67, p <0.001 for all comparisons) and increased Epsilon/e' (11.31 +/- 1.02 vs 8.98 +/- 1.70, p <0.001) compared with subjects without prolonged weaning (n = 20). Logistic regression analysis revealed that TAPSE (R2 = 0.53, beta slope = 0.76, p < 0.001), Sm (R2 = 0.52, beta = 0.75, p < 0.001) and Em/Am (R2 = 0.57, beta = 0.32, p < 0.001) can predict length of weaning > or = 7 days. The above measures were also proven to correlate significantly with Epsilon/e' (r = -0.83 for TAPSE, r = -0.87 for Sm and r = -0.79 for Em/Am, p < 0.001 for all comparisons).

CONCLUSIONS

We suggest that in mechanically ventilated patients with APE, low TAPSE and RV TDI velocities upon admission are associated with delayed liberation from mechanical ventilation, probably due to more severe LV heart failure.

Which cardiac surgical patients can benefit from placement of a pulmonary artery catheter?

The use of pulmonary artery catheters (PACs) during cardiac surgery varies considerably depending on local policy, ranging from use in 5–10% of the patient population to routine application. However, as in other clinical fields, recent years have witnessed a progressive decline in PAC use. One of the reasons for this is probably the increasing use of transoesophageal echocardiograpy, even though careful analysis of the information provided by PAC and transoesophageal echocardiograpy indicates that the two tools should be considered subsidiary rather than alternatives. The principal categories of cardiac patients who can benefit from PAC monitoring are those with present and those with possible haemodynamic instability. On this basis we can identify five groups: patients with impaired left ventricular systolic function; those with impaired right ventricular systolic function; those with left ventricular diastolic dysfunction; those with an acute ventricular septal defect; and those with a left ventricular assist device. This review highlights the specific role of PAC-derived haemodynamic data for each category.

Haemodynamic monitoring

The monitoring of cardiovascular function is an indispensable element in anaesthesia. A thorough understanding of pathophysiology in various disease states allows optimal balancing of the invasiveness and completeness of haemodynamic monitoring. The prevention of both intraoperative and postoperative complications is therefore a primary goal.

Haemodynamic monitoring in acute heart failure

Acute Heart Failure is a major cause of hospitalisation, with a rate of death and complications. New guidelines have been developed in order to diagnose and treat this disease. Despite these efforts pathophysiology and treatments options are still limited. There is agreement among the experts that increasing the cardiac output and the stroke volume without fluid overloading the patient should be the goal of every treatment. Despite this, there is no agreement on how to monitor the cardiac function and how to follow it after a therapeutic intervention. In other fields of critical care cardiovascular monitoring and application of early goal directed protocols showed benefits. This review explores the available possibilities of how to monitor the cardiac function in Acute Heart Failure. Standard and more advanced techniques are presented. Cardiac output monitors from the pulmonary artery catheter to the pulse pressure analysis and Doppler techniques are discussed, with focus on this specific clinical setting. Undoubtedly monitoring is valuable tool, but without a protocol of how to manipulate the haemodynamics, no monitor will prove alone to be beneficial. Haemodynamic driven early goal directed therapy are largely awaited in this field of medicine.

Hemodynamic monitoring in shock and implications for management. International Consensus Conference, Paris, France, 27-28 April 2006

OBJECTIVE

Shock is a severe syndrome resulting in multiple organ dysfunction and a high mortality rate. The goal of this consensus statement is to provide recommendations regarding the monitoring and management of the critically ill patient with shock.

METHODS

An international consensus conference was held in April 2006 to develop recommendations for hemodynamic monitoring and implications for management of patients with shock. Evidence-based recommendations were developed, after conferring with experts and reviewing the pertinent literature, by a jury of 11 persons representing five critical care societies.

DATA SYNTHESIS

A total of 17 recommendations were developed to provide guidance to intensive care physicians monitoring and caring for the patient with shock. Topics addressed were as follows: (1) What are the epidemiologic and pathophysiologic features of shock in the ICU? (2) Should we monitor preload and fluid responsiveness in shock? (3) How and when should we monitor stroke volume or cardiac output in shock? (4) What markers of the regional and micro-circulation can be monitored, and how can cellular function be assessed in shock? (5) What is the evidence for using hemodynamic monitoring to direct therapy in shock? One of the most important recommendations was that hypotension is not required to define shock, and as a result, importance is assigned to the presence of inadequate tissue perfusion on physical examination. Given the current evidence, the only bio-marker recommended for diagnosis or staging of shock is blood lactate. The jury also recommended against the routine use of (1) the pulmonary artery catheter in shock and (2) static preload measurements used alone to predict fluid responsiveness.

CONCLUSIONS

This consensus statement provides 17 different recommendations pertaining to the monitoring and caring of patients with shock. There were some important questions that could not be fully addressed using an evidence-based approach, and areas needing further research were identified.

Prediction of fluid responsiveness using respiratory variations in left ventricular stroke area by transoesophageal echocardiographic automated border detection in mechanically ventilated patients

Background

Left ventricular stroke area by transoesophageal echocardiographic automated border detection has been shown to be strongly correlated to left ventricular stroke volume. Respiratory variations in left ventricular stroke volume or its surrogates are good predictors of fluid responsiveness in mechanically ventilated patients. We hypothesised that respiratory variations in left ventricular stroke area (ΔSA) can predict fluid responsiveness.

Methods

Eighteen mechanically ventilated patients undergoing coronary artery bypass grafting were studied immediately after induction of anaesthesia. Stroke area was measured on a beat-to-beat basis using transoesophageal echocardiographic automated border detection. Haemodynamic and echocardiographic data were measured at baseline and after volume expansion induced by a passive leg raising manoeuvre. Responders to passive leg raising manoeuvre were defined as patients presenting a more than 15% increase in cardiac output.

Results

Cardiac output increased significantly in response to volume expansion induced by passive leg raising (from 2.16 ± 0.79 litres per minute to 2.78 ± 1.08 litres per minute; p < 0.01). ΔSA decreased significantly in response to volume expansion (from 17% ± 7% to 8% ± 6%; p < 0.01). ΔSA was higher in responders than in non-responders (20% ± 5% versus 10% ± 5%; p < 0.01). A cutoff ΔSA value of 16% allowed fluid responsiveness prediction with a sensitivity of 92% and a specificity of 83%. ΔSA at baseline was related to the percentage increase in cardiac output in response to volume expansion (r = 0.53, p < 0.01).

Conclusion

ΔSA by transoesophageal echocardiographic automated border detection is sensitive to changes in preload, can predict fluid responsiveness, and can quantify the effects of volume expansion on cardiac output. It has potential clinical applications.

Continuously assessed right ventricular end-diastolic volume as a marker of cardiac preload and fluid responsiveness in mechanically ventilated cardiac surgical patients

Introduction

Assessing cardiac preload and fluid responsiveness accurately is important when attempting to avoid unnecessary volume replacement in the critically ill patient, which is associated with increased morbidity and mortality. The present clinical trial was designed to compare the reliability of continuous right ventricular end-diastolic volume (CEDV) index assessment based on rapid response thermistor technique, cardiac filling pressures (central venous pressure [CVP] and pulmonary capillary wedge pressure [PCWP]), and transesophageal echocardiographically derived evaluation of left ventricular end-diastolic area (LVEDA) index in predicting the hemodynamic response to volume replacement.

Methods

We studied 21 patients undergoing elective coronary artery bypass grafting. After induction of anesthesia, hemodynamic parameters were measured simultaneously before (T1) and 12 min after volume replacement (T2) by infusion of 6% hydroxyethyl starch 200/0.5 (7 ml/kg) at a rate of 1 ml/kg per min.

Results

The volume-induced increase in thermodilution-derived stroke volume index (SVI_TD) was 10% or greater in 19 patients and under 10% in two. There was a significant correlation between changes in CEDV index and changes in SVI_TD (r² = 0.55; P < 0.01), but there were no significant correlations between changes in CVP, PCWP and LVEDA index, and changes in SVI_TD. The only variable apparently indicating fluid responsiveness was LVEDA index, the baseline value of which was weakly correlated with percentage change in SVI_TD (r² = 0.38; P < 0.01).

Conclusion

An increased cardiac preload is more reliably reflected by CEDV index than by CVP, PCWP, or LVEDA index in this setting of preoperative cardiac surgery, but CEDV index did not reflect fluid responsiveness. The response of SVI_TD following fluid administration was better predicted by LVEDA index than by CEDV index, CVP, or PCWP.

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.

Tissue Doppler imaging estimation of pulmonary artery occlusion pressure in ICU patients

OBJECTIVE

Earlier reports suggested that transthoracic (TTE) determination of the ratio of mitral inflow E wave velocity to early diastolic mitral annulus velocity (E/E') measured by tissue Doppler imaging (TDI) closely approximates PAOP in cardiac patients. However, the value of E/E' for PAOP assessment in ICU patients has not been evaluated. This study assessed whether the E/E' ratio provides an accurate estimation of pulmonary artery occlusion pressure (PAOP) in mechanically ventilated ICU patients.

DESIGN AND SETTING

Prospective, open, clinical study in the ICU of a university hospital.

PATIENTS

Twenty-three consecutive mechanically ventilated patients.

INTERVENTIONS

Volume expansion in 14 patients.

MEASUREMENTS AND RESULTS

Doppler TTE or TEE mitral inflow and TDI mitral annulus velocities were determined and compared with PAOP measured using a Swan-Ganz catheter. Of all the Doppler variables studied the best correlations were observed between PAOP and the lateral (r=0.84) and medial (r=0.76) annulus E/E' ratio and remained highly significant when the analysis was restricted to TEE (r=0.91 and 0.86) or TTE (r=0.73 and 0.61). The sensitivities and specificities of estimating PAOP at 15 mmHg or higher were, respectively, 86% and 81% for lateral E/E' above 7.5 and 76% and 80% for medial E/E' above 9. PAOP changes after volume expansion (700+/-230 ml) were limited and accurately assessed by repeated E/E' determinations.

CONCLUSIONS

In mechanically ventilated ICU patients TTE or TEE E/E' determinations using TDI closely approximate PAOP.

Preload indexes in thoracic anesthesia

PURPOSE OF THE REVIEW

An adequate cardiac preload is essential in the treatment of critically ill patients. During anesthesia for thoracic surgery, volume and vasoactive therapy to optimize cardiac output, oxygen delivery (tissue perfusion) and to avoid pulmonary edema is a central therapeutic aspect. Cardiac preload has been estimated with different techniques in clinical practice, even though studies performed on thoracic anesthesia are lacking.

RECENT FINDINGS

We analyze the conventional pulmonary artery catheter, transesophageal echocardiography and the transpulmonary indicator dilution technique as preload monitoring devices with their indications and limits in thoracic anesthesia.

SUMMARY

The pulmonary artery catheter is confirmed as a fundamental device particularly in patients with pulmonary hypertension. For transesophageal echocardiography monitoring, the dependency on operator experience, the low repeatability and the high costs limit its interpretation and diffusion in clinical practice. During lung transplantation, Swan Ganz catheter monitoring is recommended. The optimization of fluid balance and vasoactive drug administration based on volumetric monitoring makes the transpulmonary indicator dilution technique a new option as an effective monitoring system during anesthesia for thoracic surgery when intravascular volume management is a primary objective.

Using heart-lung interactions to assess fluid responsiveness during mechanical ventilation

According to the Frank-Starling relationship, a patient is a 'responder' to volume expansion only if both ventricles are preload dependent. Mechanical ventilation induces cyclic changes in left ventricular (LV) stroke volume, which are mainly related to the expiratory decrease in LV preload due to the inspiratory decrease in right ventricular (RV) filling and ejection. In the present review, we detail the mechanisms by which mechanical ventilation should result in greater cyclic changes in LV stroke volume when both ventricles are 'preload dependent'. We also address recent clinical data demonstrating that respiratory changes in arterial pulse (or systolic) pressure and in Doppler aortic velocity (as surrogates of respiratory changes in LV stroke volume) can be used to detect biventricular preload dependence, and hence fluid responsiveness in critically ill patients.