Right ventricular end-diastolic volume as a measure of preload

Alterations of biaxial viscoelastic properties of the right ventricle in pulmonary hypertension development in rest and acute stress conditions

Introduction: The right ventricle (RV) mechanical property is an important determinant of its function. However, compared to its elasticity, RV viscoelasticity is much less studied, and it remains unclear how pulmonary hypertension (PH) alters RV viscoelasticity. Our goal was to characterize the changes in RV free wall (RVFW) anisotropic viscoelastic properties with PH development and at varied heart rates. Methods: PH was induced in rats by monocrotaline treatment, and the RV function was quantified by echocardiography. After euthanasia, equibiaxial stress relaxation tests were performed on RVFWs from healthy and PH rats at various strain-rates and strain levels, which recapitulate physiological deformations at varied heart rates (at rest and under acute stress) and diastole phases (at early and late filling), respectively. Results and Discussion: We observed that PH increased RVFW viscoelasticity in both longitudinal (outflow tract) and circumferential directions. The tissue anisotropy was pronounced for the diseased RVs, not healthy RVs. We also examined the relative change of viscosity to elasticity by the damping capacity (ratio of dissipated energy to total energy), and we found that PH decreased RVFW damping capacity in both directions. The RV viscoelasticity was also differently altered from resting to acute stress conditions between the groups-the damping capacity was decreased only in the circumferential direction for healthy RVs, but it was reduced in both directions for diseased RVs. Lastly, we found some correlations between the damping capacity and RV function indices and there was no correlation between elasticity or viscosity and RV function. Thus, the RV damping capacity may be a better indicator of RV function than elasticity or viscosity alone. These novel findings on RV dynamic mechanical properties offer deeper insights into the role of RV biomechanics in the adaptation of RV to chronic pressure overload and acute stress.

The contemporary pulmonary artery catheter. Part 2: measurements, limitations, and clinical applications

Nowadays, the classical pulmonary artery catheter (PAC) has an almost 50-year-old history of its clinical use for hemodynamic monitoring. In recent years, the PAC evolved from a device that enabled intermittent cardiac output measurements in combination with static pressures to a monitoring tool that provides continuous data on cardiac output, oxygen supply and-demand balance, as well as right ventricular performance. In this review, which consists of two parts, we will introduce the difference between intermittent pulmonary artery thermodilution using bolus injections, and the contemporary PAC enabling continuous measurements by using a thermal filament which heats up the blood. In this second part, we will discuss in detail the measurements of the contemporary PAC, including continuous cardiac output measurement, right ventricular ejection fraction, end-diastolic volume index, and mixed venous oxygen saturation. Limitations of all of these measurements are highlighted as well. We conclude that thorough understanding of measurements obtained from the PAC is the first step in successful application of the PAC in daily clinical practice.

Fluid and Volume Monitoring

Background

Fluid resuscitation is not only used to prevent acute kidney injury (AKI) but fluid management is also a cornerstone of treatment for patients with established AKI and renal failure. Ultrafiltration removes volume initially from the intravascular compartment inducing a relative degree of hypovolemia. Normal reflex mechanisms attempt to sustain blood pressure constant despite marked changes in blood volume and cardiac output. Thus, compensated shock with a normal blood pressure is a major cause of AKI or exacerbations of AKI during ultrafiltration.

Methods

We undertook a systematic review of the literature using MEDLINE, Google Scholar and PubMed searches. We determined a list of key questions and convened a 2-day consensus conference to develop summary statements via a series of alternating breakout and plenary sessions. In these sessions, we identified supporting evidence and generated clinical practice recommendations and/or directions for future research.

Results

We defined three aspects of fluid monitoring: i) normal and pathophysiological cardiovascular mechanisms; ii) measures of volume responsiveness and impending cardiovascular collapse during volume removal, and; iii) measured indices of each using non-invasive and minimally invasive continuous and intermittent monitoring techniques. The evidence documents that AKI can occur in the setting of normotensive hypovolemia and that under-resuscitation represents a major cause of both AKI and mortality ion critically ill patients. Traditional measures of intravascular volume and ventricular filling do not predict volume responsiveness whereas dynamic functional hemodynamic markers, such as pulse pressure or stroke volume variation during positive pressure breathing or mean flow changes with passive leg raising are highly predictive of volume responsiveness. Numerous commercially-available devices exist that can acquire these signals.

Conclusions

Prospective clinical trials using functional hemodynamic markers in the diagnosis and management of AKI and volume status during ultrafiltration need to be performed. More traditional measure of preload be abandoned as marked of volume responsiveness though still useful to assess overall volume status.

Effect of hydration status on atrial and ventricular volumes and function in healthy adult volunteers

BACKGROUND

Assessment of cardiac chamber volumes is a fundamental part of cardiac magnetic resonance (CMR) imaging. While the effects of inter- and intraobserver variability have been studied and have a recognized effect on the comparability of serial cardiac MR imaging studies, the effect of differences in hydration status has not been evaluated.

OBJECTIVE

To evaluate the effects of volume administration on cardiac chamber volumes.

MATERIALS AND METHODS

Thirteen healthy adults underwent a baseline cardiac MR to evaluate cardiac chamber volumes after an overnight fast. They were then given two saline boluses of 10 ml/kg of body weight and the cardiac MR was repeated immediately after each bolus.

RESULTS

From the baseline scan to the final scan there was a significant increase in all four cardiac chamber end-diastolic volumes. Right atrial volumes increased 8.0%, from 61.1 to 66.0 ml/m2 (P<0.001), and left atrial volumes increased 10.0%, from 50.0 to 55.0 ml/m2 (P<0.001). Right ventricular volumes increased 6.0%, from 91.1 to 96.5 ml/m2 (P<0.001), and left ventricular volumes increased 3.2%, from 87.0 to 89.8 ml/m2 (P<0.001).

CONCLUSION

Hydration status has a significant effect on the end-diastolic volumes of all cardiac chambers assessed by cardiac MR. Thus, hydration represents a "variable" that should be taken into account when assessing cardiac chamber volumes, especially when performing serial imaging studies in a patient.

Induced Hypothermia Does Not Harm Hemodynamics after Polytrauma: A Porcine Model

BACKGROUND

The deterioration of hemodynamics instantly endangers the patients' life after polytrauma. As accidental hypothermia frequently occurs in polytrauma, therapeutic hypothermia still displays an ambivalent role as the impact on the cardiopulmonary function is not yet fully understood.

METHODS

We have previously established a porcine polytrauma model including blunt chest trauma, penetrating abdominal trauma, and hemorrhagic shock. Therapeutic hypothermia (34°C) was induced for 3 hours. We documented cardiovascular parameters and basic respiratory parameters. Pigs were euthanized after 15.5 hours.

RESULTS

Our polytrauma porcine model displayed sufficient trauma impact. Resuscitation showed adequate restoration of hemodynamics. Induced hypothermia had neither harmful nor major positive effects on the animals' hemodynamics. Though heart rate significantly decreased and mixed venous oxygen saturation significantly increased during therapeutic hypothermia. Mean arterial blood pressure, central venous pressure, pulmonary arterial pressure, and wedge pressure showed no significant differences comparing normothermic trauma and hypothermic trauma pigs during hypothermia.

CONCLUSIONS

Induced hypothermia after polytrauma is feasible. No major harmful effects on hemodynamics were observed. Therapeutic hypothermia revealed hints for tissue protective impact. But the chosen length for therapeutic hypothermia was too short. Nevertheless, therapeutic hypothermia might be a useful tool for intensive care after polytrauma. Future studies should extend therapeutic hypothermia.

Cardiovascular implications of abdominal compartment syndrome

Cardiovascular dysfunction and failure are commonly encountered in the patient with intra-abdominal hypertension or abdominal compartment syndrome. Accurate assessment and optimization of preload, contractility, and afterload, in conjunction with appropriate goal-directed resuscitation and abdominal decompression when indicated, are essential to restoring end-organ perfusion and maximizing patient survival. The validity of traditional hemodynamic resuscitation endpoints, such as pulmonary artery occlusion pressure and central venous pressure, must be reconsidered in the patient with intra-abdominal hypertension as these pressure-based estimates of intravascular volume have significant limitations in patients with elevated intra-abdominal pressure. If such limitations are not recognized, misinterpretation of the patient's cardiac status is likely, resulting in inappropriate and potentially detrimental therapy. Appropriate fluid administration is mandatory as under-resuscitation leads to organ failure and over-resuscitation the development of secondary abdominal compartment syndrome, both of which are associated with increased morbidity and mortality. Volumetric monitoring techniques have been proven to be superior to traditional intra-cardiac filling pressures in directing the appropriate resuscitation of this patient population. Calculation of the "abdominal perfusion pressure", defined as mean arterial pressure minus intra-abdominal pressure, has been shown to be a beneficial resuscitation endpoint as it assesses not only the severity of the patient's intra-abdominal hypertension, but also the adequacy of abdominal blood flow. Application of a goal-directed resuscitation strategy, including abdominal decompression when indicated, improves cardiac function, reverses end-organ failure, and minimizes intra-abdominal hypertension-related patient morbidity and mortality.

Hemodynamic monitoring in the intensive care unit

Patients in the intensive care unit are often critically ill with inadequate tissue perfusion and oxygenation. This inadequate delivery of substrates at the cellular level is a common definition of shock. Hemodynamic monitoring is the observation of cardiovascular physiology. The purpose of hemodynamic monitoring is to identify abnormal physiology and intervene before complications, including organ failure and death, occur. The most common types of invasive hemodynamic monitors are central venous catheters, pulmonary artery catheters, and arterial pulse-wave analysis. Ultrasonography is a noninvasive alternative being used in intensive care units for hemodynamic measurements and assessments.

Clinical pathology of the shock syndromes

The clinical aspects of shock syndromes are described from their inception as compensated physiology to a stage of decompensation. The clinical significance of hypotension, fluid-responsive and non fluid-responsive hypotension, is discussed. Untimely or inadequate treatment leads to persistent subclinical shock despite adjustments of the macrohemodynamic variables, which evolves in a second hit of physiological deterioration if not aggressively managed. Irreversible shock ensues as consequence of direct hit or as result of inadequate or delayed treatment and is characterized by drug-resistant hypotension.

Modeling and simulation of right ventricular volume measurement system during right heart catheterization

Haemodynamic monitoring is necessary for the effective management of critically ill cardiac patients. Pulmonary artery catheterization has been used for monitoring the circulation, for measurement of intracardiac pressures and to estimate preload and afterload. However, pressures may not be accurate reflection of the circulation and simultaneous measurement of volumes would improve patient treatment. However, measurement of cardiac volumes especially of the right ventricle is difficult in everyday clinical practice In this work we propose the use of pulmonary artery catheter (PAC) with ultrasonic sensors built on it, to calculate the right ventricular end-diastolic (RVEDV) and end-systolic volume (RVESV). This is achieved by using the Ultrasonic (US) beam, to measure the distances between the transducers on the catheter and the RV walls. These distances, will be used as an input to a Volume calculating algorithm, which finally provides the RVEDV and RVESV, using a Neural Network (NN). For that reason, we have used cardiac Magnetic Resonance Imaging (MRI) and have modeled the catheter and the US transducers, to get as input the distances to the surface of the cavity. With these distances, and the known cardiac volumes (calculated using MR images) we trained and validated a NN for volume calculation. The results show that the algorithm accurately calculates the RVEDV. For the RVESV, greater deviations are observed between values calculated with our algorithm and cardiac MRI.

Static measures of preload assessment

This article focuses on static methods for determining preload, specifically pressure and volumetric indices measured at the bedside. The underlying ventricular function will determine where the patient is located on Frank-Starling ventricular function curve and the patient's response to a fluid challenge. The proper interpretation and use of such measures, coupled with an understanding of their limitations and knowledge of alternative methods, is necessary to guide properly volume resuscitation in the critically ill.

Perioperative considerations in patients with cirrhotic cardiomyopathy

PURPOSE OF REVIEW

This review aims to identify specific criteria for cirrhotic cardiomyopathy, examine the correlation with perioperative adverse outcomes and explore options for hemodynamic monitoring.

RECENT FINDINGS

Cirrhotic cardiomyopathy is characterized by an increase in cardiac output, blunted systolic contractile response to stress, diastolic dysfunction and electrophysiological abnormalities. Adverse events due to cirrhotic cardiomyopathy are not as well characterized, but evidence suggests that some cardiovascular complications during surgery and in the postoperative period are caused by an impaired response to physiological stress. New developments in hemodynamic monitoring using not only thermodilution technology provide more reliable information about cardiac performance than pressure-derived measures. Transesophogeal echocardiography also offers the physician new information including the ability to visualize heart structures, shape, and function.

SUMMARY

To detect cirrhotic cardiomyopathy, physicians must conduct a systematic examination of the patient. Overt manifestations of cirrhotic cardiomyopathy often only become evident after a patient is exposed to physiological or drug-induced stress. Appropriate hemodynamic monitoring is a cornerstone in the perioperative management of cirrhotic patients.

A comparison between pulse pressure variation and right end diastolic volume index as guides to resuscitation in a model of hemorrhagic shock in pigs

BACKGROUND

Different hemodynamic parameters including static indicators of cardiac preload as right ventricular end-diastolic volume index (RVEDVI) and dynamic parameters as pulse pressure variation (PPV) have been used in the decision-making process regarding volume expansion in critically ill patients. The objective of this study was to compare fluid resuscitation guided by either PPV or RVEDVI after experimentally induced hemorrhagic shock.

METHODS

Twenty-six anesthetized and mechanically ventilated pigs were allocated into control (group I), PPV (group II), or RVEDVI (group III) group. Hemorrhagic shock was induced by blood withdrawal to target mean arterial pressure of 40 mm Hg, maintained for 60 minutes. Parameters were measured at baseline, time of shock, 60 minutes after shock, immediately after resuscitation with hydroxyethyl starch 6% (130/0.4), 1 hour and 2 hours thereafter. The endpoint of fluid resuscitation was determined as the baseline values of PPV and RVEDVI. Statistical analysis of data was based on analysis of variance for repeated measures followed by the Bonferroni test (p < 0.05).

RESULTS

Volume and time to resuscitation were higher in group III than in group II (group III = 1,305 +/- 331 mL and group II = 965 +/- 245 mL, p < 0.05; and group III = 24.8 +/- 4.7 minutes and group II = 8.8 +/- 1.3 minutes, p < 0.05, respectively). All static and dynamic parameters and biomarkers of tissue oxygenation were affected by hemorrhagic shock and nearly all parameters were restored after resuscitation in both groups.

CONCLUSION

In the proposed model of hemorrhagic shock, resuscitation to the established endpoints was achieved within a smaller amount of time and with less volume when guided by PPV than when guided by pulmonary artery catheter-derived RVEDVI.

Continuous right ventricular end-diastolic volume in comparison with left ventricular end-diastolic area

BACKGROUND AND OBJECTIVE

Intraoperative management of patients with end-stage liver disease undergoing liver transplantation requires fluid administration to increase cardiac output and oxygen delivery to the tissues. Filling pressures have been widely shown to correlate poorly with changes in cardiac output in the critically ill patient. Continuous right ventricular end-diastolic volume index (cRVEDVI) and left ventricular end-diastolic area index (LVEDAI) monitoring have been increasingly used for preload assessment. The aim of this study was to compare cRVEDVI, LVEDAI, central venous pressure and pulmonary artery occlusion pressure with respect to stroke volume index (SVI) during liver transplantation.

METHODS

Measurements were made in 20 patients at four predefined steps during liver transplantation. Univariate and multivariate panel-data fixed effect regression models (across phases of the surgical procedure) were fitted to assess associations between SVI and cRVEDVI, pulmonary artery occlusion pressure, central venous pressure and LVEDAI after adjusting for ejection fraction (categorized as <or=30, 31-40, >40).

RESULTS

SVI was associated with continuous right ventricular ejection fraction. The model showing the best fit to the data was that including cRVEDVI: even after adjusting for continuous right ventricular ejection fraction and phase, the regression coefficient of cRVEDVI in predicting SVI was statistically significant and indicated an increase in SVI of 0.21 ml m(-2) for each increase of 1 ml m(-2). At the multivariate analysis, an increase in LVEDAI of 1 cm m(-2) led to an increase in SVI of 1.47 ml m(-2) (P = 0.054).

CONCLUSION

cRVEDVI and LVEDAI gave a better reflection of preload than filling pressure, even if only cRVEDVI reached statistical significance.

Intraoperative hemodynamic monitoring during organ transplantation: what is new?

PURPOSE OF REVIEW

To highlight the recent developments in hemodynamic monitoring during liver and lung transplantation.

RECENT FINDINGS

Even though a consensus on intraoperative hemodynamic monitoring is still lacking, the most frequently monitoring tool used is the pulmonary artery catheter (PAC). The filling pressures are widely accepted as not being able to accurately define cardiac preload. On the contrary, the use of transesophageal echocardiography (TEE), although it is operator dependent and requires a prolonged training, is increasing during the intraoperative period to directly evaluate the cardiovascular function. New frontiers have been opened by the transpulmonary thermodilution: intrathoracic blood volume has been shown to have a better correlation with preload than the filling pressures. The advanced modified PAC permits evaluation of the right heart function and preload. Recently, right ventricular end diastolic volume has been shown to correlate better with preload than the filling pressures and also the left ventricular end diastolic area.

SUMMARY

The PAC still represents the most used intraoperative hemodynamic monitoring technique. TEE is increasing in popularity. Recent studies demonstrate that volumetric monitoring conducted with transpulmonary thermodilution and advanced volumetric PAC give good definition of preload and should be implemented in clinical practice.

Continuous right ventricular end diastolic volume and right ventricular ejection fraction during liver transplantation: a multicenter study

Cardiac preload is traditionally considered to be represented by its filling pressures, but more recently, estimations of end diastolic volume of the left or right ventricle have been shown to better reflect preload. One method of determining volumes is the evaluation of the continuous right ventricular end diastolic volume index (cRVEDVI) on the basis of the cardiac output thermodilution technique. Because preload and myocardial contractility are the main factors determining cardiac output during liver transplantation (LTx), accurate determination of preload is important. Thus, monitoring of cRVEDVI and cRVEF should help with fluid management and with the assessment of the need for inotropic and vasoactive agents. In this multicenter study, we looked for possible relationships between the stroke volume index (SVI) and cRVEDVI, cRVEF, and filling pressures at 4 predefined steps in 244 patients undergoing LTx. Univariate and multivariate autoregression models (across phases of the surgical procedure) were fitted to assess the possible association between SVI and cRVEDVI, pulmonary artery occlusion pressure (PAOP), and central venous pressure (CVP) after adjustment for cRVEF (categorized as < or =30, 31-40, and >40%). SVI was strongly associated with both cRVEDVI and cRVEF. The model showing the best fit to the data was that including cRVEDVI. Even after adjustment for cRVEF, there was a statistically significant (P < 0.05) relationship between SVI and cRVEDVI with a regression coefficient (slope of the regression line) of 0.25; this meant that an increase in cRVEDVI of 1 mL m(-2) resulted in an increase in SVI of 0.25 mL m(-2). The correlations between SVI and CVP and PAOP were less strong. We conclude that cRVEDVI reflected preload better than CVP and PAOP.

Clinical relevance of data from the pulmonary artery catheter

The usefulness of parameters measured using the pulmonary artery catheter has been challenged because no benefit in patient outcome has been observed in clinical trials. However, technological advances have been made, including continuous measurement of cardiac output (CO), mixed venous saturation (SvO₂), and right ventricle end-diastolic volume (CEDV) have been made. Pulmonary artery occlusion pressure (PAOP), CEDV and right atrial pressure (RAP) are not good predictors of fluid load responsiveness except when very low. Despite this methodological limitation, variation of these parameters during fluid loading remains a good indicator of fluid challenge tolerance. Accuracy of continuous thermodilution and SvO₂ measurement has been demonstrated in vitro and at bedside. A decrease in SvO₂ is a global index of an inadequate oxygen delivery (DO₂)/oxygen requirement relationship. In this setting, a therapeutic decision to improve determinants of SvO₂ should be considered with the help of all other PAC parameters. Technological improvement transforms PAC in a real time integrated physiological device and allows one to observe the impact of therapeutic intervention. What we need now is a clinical trial with a PAC-guided treatment algorithm taking into account the above integrated PAC parameters.

Year in review 2005: critical care--cardiology

This review summarizes key research papers published in the fields of cardiology and intensive care during 2005 in Critical Care. The papers have been grouped into categories: haemodynamic monitoring; goal-directed therapy; cardiac enzymes and critical care; metabolic considerations in cardiovascular performance; thrombosis prevention; physiology; and procedures and techniques.

Clinical review: Positive end-expiratory pressure and cardiac output

In patients with acute lung injury, high levels of positive end-expiratory pressure (PEEP) may be necessary to maintain or restore oxygenation, despite the fact that 'aggressive' mechanical ventilation can markedly affect cardiac function in a complex and often unpredictable fashion. As heart rate usually does not change with PEEP, the entire fall in cardiac output is a consequence of a reduction in left ventricular stroke volume (SV). PEEP-induced changes in cardiac output are analyzed, therefore, in terms of changes in SV and its determinants (preload, afterload, contractility and ventricular compliance). Mechanical ventilation with PEEP, like any other active or passive ventilatory maneuver, primarily affects cardiac function by changing lung volume and intrathoracic pressure. In order to describe the direct cardiocirculatory consequences of respiratory failure necessitating mechanical ventilation and PEEP, this review will focus on the effects of changes in lung volume, factors controlling venous return, the diastolic interactions between the ventricles and the effects of intrathoracic pressure on cardiac function, specifically left ventricular function. Finally, the hemodynamic consequences of PEEP in patients with heart failure, chronic obstructive pulmonary disease and acute respiratory distress syndrome are discussed.

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.

Volumetric preload measurement by thermodilution: a comparison with transoesophageal echocardiography

BACKGROUND

End-diastolic volume indices determined by transpulmonary thermodilution and pulmonary artery thermodilution may give a better estimate of left ventricular preload than pulmonary capillary wedge pressure monitoring. The aim of this study was to compare volume preload monitoring using the two different thermodilution techniques with left ventricular preload assessment by transoesophageal echocardiography (TOE).

METHODS

Twenty patients undergoing elective cardiac surgery with preserved left-right ventricular function were studied after induction of anaesthesia. Conventional haemodynamic variables, global end-diastolic volume index using the pulse contour cardiac output (PiCCO) system (GEDVI(PiCCO)), continuous end-diastolic volume index (CEDVI(PAC)) measured by a modified pulmonary artery catheter (PAC), left ventricular end-diastolic area index (LVEDAI) using TOE and stroke volume indices (SVI) were recorded before and 20 and 40 min after fluid replacement therapy. Analysis of variance (Bonferroni-Dunn), Bland-Altman analysis and linear regression were performed.

RESULTS

GEDVI(PiCCO), CEDVI(PAC), LVEDAI and SVI(PiCCO/PAC) increased significantly after fluid load (P<0.05). An increase >10% for GEDVI(PiCCO) and LVEDAI was observed in 85% and 90% of the patients compared with 45% for CEDVI(PAC). Mean bias (2 SD) between percentage changes (delta) in GEDVI(PiCCO) and deltaLVEDAI was -3.2 (17.6)% and between deltaCEDVI(PAC) and deltaLVEDAI -8.7 (30.0)%. The correlation coefficient (r2) for deltaGEDVI(PiCCO) vs deltaLVEDAI was 0.658 and for deltaCEDVI(PAC) vs deltaLVEDAI 0.161. The relationship between deltaGEDVI(PiCCO) and deltaSVI(PiCCO) was stronger (r2=0.576) than that between deltaCEDVI(PAC) and deltaSVI(PAC) (r2=0.267).

CONCLUSION

GEDVI assessed by the PiCCO system gives a better reflection of echocardiographic changes in left ventricular preload, in response to fluid replacement therapy, than CEDVI measured by a modified PAC.

Advances and New Insights in Monitoring

It cannot be overemphasized that a piece of electrical equipment is not capable of replacing a vigilant, well-trained clinician. As monitoring devices become more sophisticated, the potential for artifact or misinterpretation increases. When applied appropriately, operated properly, and interpreted correctly, however, the monitors afford the patient the best possible outcome.

Continuous assessment of right ventricular ejection fraction: new pulmonary artery catheter versus transoesophageal echocardiography

In 25 cardiac surgical patients, right ventricular ejection fraction was continuously measured with a new pulmonary artery catheter and transoesophageal echocardiography, scanning the 'fractional area change' in a standardised transatrial cross section area. Measurements were recorded at three predefined time points (pre-, intra-, and postoperatively). Both methods were compared using the Bland-Altman analysis. Comparing right ventricular ejection fraction values obtained from the pulmonary artery catheter with those assessed by transoesophageal echocardiography, bias was -3.7%, with a precision of 30.9%. Bias and precision significantly improved when the heart rate was less than 100 beats.min(-1), pulmonary artery pressures were low and cardiac performance adequate. In conclusion, the new continuous pulmonary artery catheter system appears to be a valid and useful bedside monitoring device in the haemodynamic management of critically ill patients.

Assessment of cardiac preload and left ventricular function under increasing levels of positive end-expiratory pressure

OBJECTIVE

(1) To assess the impact of high intrathoracic pressure on left ventricular volume and function. (2) To test the hypothesis that right ventricular end-diastolic volume (RVEDV) and intrathoracic blood volume (ITBV) represent cardiac preload and are superior to central venous pressure (CVP) or pulmonary capillary wedge pressure (PCWP). The validity of these parameters was tested by means of correlation with left ventricular end-diastolic volume (LVEDV), the true cardiac preload.

DESIGN

Prospective animal study.

SUBJECTS

Fifteen adult sheep.

INTERVENTIONS

All animals were studied before and after saline washout-induced lung injury, undergoing volume-controlled ventilation with increasing levels of PEEP (0, 7, 14 and 21 cmH2O, respectively).

MEASUREMENTS AND MAIN RESULTS

Left ventricular ejection fraction (LVEF), stroke volume (LVSV) and LVEDV were measured using computed tomography. ITBV and RVEDV were obtained by the thermal dye dilution technique. At PEEP 21 cmH2O, LVSV significantly decreased compared to baseline, PEEP 0 and PEEP 7 cmH2O. LVEDV was maintained except for the highest level of PEEP, while LVEF remained unchanged. RVEDV and RVEF also remained unchanged. The overall correlation of RVEDV and ITBV with LVEDV was satisfactory ( r=0.56 and r=0.62, respectively) and clearly superior to cardiac filling pressures.

CONCLUSION

In the present study, (1) ventilation with increasing levels of PEEP did not alter RV function, while LV function was impaired at the highest level of PEEP; (2) unlike cardiac filling pressures, ITBV and RVEDV both provide valid estimates of cardiac preload even at high intrathoracic pressures.

The esophageal Doppler monitor in mechanically ventilated surgical patients: does it work?

BACKGROUND

Assessment of cardiac volumes and cardiac output (CO) using a pulmonary artery catheter (PAC) in mechanically ventilated patients can be inconsistent and difficult. The esophageal Doppler monitor (EDM) is emerging as a potential alternative to the PAC. This prospective study evaluated the comparative accuracy between the PAC and EDM for preload assessment and CO in mechanically ventilated surgical patients. METHODS The EDM was placed in 15 patients with PACs in place. A total of 187 simultaneously measured EDM and PAC comparative data sets were obtained. The Pearson correlation (r) was used to compare measurements, with significance defined as a value of p < 0.05.

RESULTS

CO measured by EDM and PAC correlated closely (r = 0.97, p < 0.0001). Corrected flow time (FTc), a measure of left ventricular filling, correlated with PAC CO to the same degree as pulmonary capillary wedge pressure (PCWP) when positive end-expiratory pressure (PEEP) was < 10 cm H2O (FTc, r = 0.51; PCWP, r = 0.56). When PEEP was > or = 10 cm H2O, FTc correlated with PAC CO better than PCWP (FTc, r = 0.85; PCWP, r = 0.29).

CONCLUSION

FTc correlates with EDM and PAC CO better than PCWP. On the basis of the current study, it is reasonable to conclude that the EDM is a valuable adjunct technology for CO and preload assessment in surgical patients on mechanical ventilation, regardless of the level of mechanical ventilatory support.

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.

Critical care hemodynamic parameters and pharmacologic interventions

Hemodynamics are a critical component in treatment of serious illness in the ICU setting. Understanding hemodynamic parameters and their implications for care is a cornerstone of critical care nursing. Appropriate interventions for hemodynamic instability and a thorough understanding of the rationale for the intervention make the difference for the critically ill patient.

Mathematical coupling does not explain the relationship between right ventricular end-diastolic volume and cardiac output

OBJECTIVE

To evaluate the clinical significance of mathematical coupling on the correlation between cardiac output and right ventricular end-diastolic volume (RVEDV) through measurement of cardiac output by two independent techniques.

DESIGN

Prospective, observational study.

SETTING

Surgical intensive care unit in a level 1 trauma center.

PATIENTS

Twenty-eight critically ill surgical patients who received mechanical ventilation and hemodynamic monitoring with a pulmonary artery catheter.

INTERVENTIONS

A pulmonary artery catheter designed to measure right ventricular ejection fraction (RVEF) and cardiac output by the intermittent bolus thermodilution (TDCO) method and continuous cardiac output by the pulsed thermal energy technique was placed. A computerized data logger was used to collect data simultaneously from the RVEF/TDCO system and the continuous cardiac output system.

MEASUREMENTS AND MAIN RESULTS

Two hundred forty-nine data sets from 28 patients were compared. There is statistical correlation between TDCO and continuous cardiac output measurements (r = 0.95, p < 0.0001) with an acceptable bias (-0.11 L/min) and precision (+/-0.74 L/min). The correlation was maintained over a wide range of cardiac outputs (2.3-17.8 L/min). There is a high degree of correlation between RVEDV and both TDCO (r = 0.72, p < 0.0001) and independently measured continuous cardiac output (r = 0.68, p < 0.0001). These correlation coefficients are not statistically different (p = 0.15).

CONCLUSIONS

The continuous cardiac output technique accurately approximates cardiac output measured by the TDCO method. RVEDV calculated from TDCO correlates well with both TDCO and independently measured continuous cardiac output. Because random measurement errors of the two techniques differ, mathematical coupling alone does not explain the correlation between RVEDV estimates of preload and cardiac output.

The future of bedside monitoring

Today's intensivists are provided with more information than ever before, yet current monitors present data from multiple sources in a relatively raw form with virtually no intelligent data integration and processing. In the next century, technological advances in miniaturization, biosensors and computer processing, coupled with an improved understanding of critical illnesses at the molecular level, will lead to the development of a new generation of monitors. Monitoring will move from the traditional macroscopic invasive approach to a noninvasive, molecular analysis of evolving critical disease processes. It is likely that disturbances in homeostasis will become known immediately or before they would otherwise be manifest clinically. Nanotechnology will permit monitoring of critical changes in the intracellular environment or the by-products of cellular metabolism and signal messaging. This article discusses monitoring technologies that hold promise for further development in the next century and point out techniques likely to be abandoned.

A critical assessment of endpoints of shock resuscitation

Modern hemodynamic therapy is not only the recognition and treatment of hypotension but also the avoidance and treatment of shock in its broadest sense. The major issues include the recognition of hypoperfusion of the body as a whole or its individual tissues and organ systems and the determination of the best endpoints for the treatment of shock. Even if all of the commonly used clinical indicators of shock are "normal," shock on a cellular, tissue, or organ basis may still be present. Whether "organ-specific" assessments, such as gastric tonometry or tissue oxygen tension measurement, are the ultimate answer to this problem remains to be seen. The determination of adequate intravascular volume (preload) continues to present major difficulties in the care of critically ill or injured patients. Although PCWP is frequently helpful, it is not a gold standard. A bedside ultrasonic technique, such as esophageal Doppler sonography, may replace the Swan-Ganz catheter technique in many patients.

Abdominal compartment syndrome

Intra-abdominal hypertension (IAH) associated with organ dysfunction defines the abdominal compartment syndrome (ACS). Elevated intra-abdominal pressure (IAP) adversely impacts pulmonary, cardiovascular, renal, splanchnic, musculoskeletal/integumentary, and central nervous system physiology. The combination of IAH and disordered physiology results in a clinical syndrome with significant morbidity and mortality. The onset of the ACS requires prompt recognition and appropriately timed and staged intervention in order to optimize outcome. The history, pathophysiology, clinical presentation, and management of this disorder is outlined.

Pulmonary artery catheterization and esophageal doppler monitoring in the ICU

The clinical assessment of cardiac performance and ventricular preload is notoriously unreliable in critically ill patients. Consequently, a number of technologies have been developed to provide the clinician with indexes of cardiovascular function to assist in therapeutic decision making. Foremost among these is the pulmonary artery catheter (PAC). Indeed, the PAC has largely shaped the practice of modern critical care. Yet, the information provided by the PAC is largely misunderstood, and its efficacy is never proven. Recently, continuous esophageal Doppler monitoring has emerged as an alternative to pulmonary artery catheterization. This paper evaluates the clinical utility of the PAC and esophageal Doppler monitoring in assessing the hemodynamic status of ICU patients.

Esophageal Doppler ultrasound monitor versus pulmonary artery catheter in the hemodynamic management of critically ill surgical patients

BACKGROUND

The pulmonary artery (PA) catheter has been used to determine hemodynamic indices; however, it has recently been criticized. This study was undertaken to evaluate an esophageal Doppler monitor (EDM) as a possible replacement for PA catheter in critically ill, mechanically ventilated patients.

METHODS

EDM and PA catheters were placed in patients in the surgical intensive care units (n = 14, 118 matched sets of data). PA catheter and EDM measurements, including corrected flow time (FTc,) a measure of preload, were obtained. Pearson correlation (r) was analyzed to compare PA catheter and EDM measurements, and a nonlinear regression model was used to describe Starling Relationships.

RESULTS

Cardiac output correlated between EDM and PA catheter (r = 0.6; p < 0.001). FTc correlated more strongly with cardiac output than did pulmonary capillary wedge pressure. (FTc: r2 = 0.27; p < 0.001; cardiac output: r2 = 0.04; p = 0.06).

CONCLUSION

Corrected flow time is a better indicator of preload than pulmonary capillary wedge pressures. EDM seems to be at least as useful as PA catheter in managing the hemodynamic status of critically ill surgical patients.

Preload assessment in patients with an open abdomen

BACKGROUND

Intra-abdominal hypertension and abdominal compartment syndrome cause significant morbidity and mortality in surgical and trauma patients. Maintenance of intravascular preload and use of open abdomen techniques are essential. The accuracy of pulmonary artery occlusion pressure (PAOP) and central venous pressure (CVP) in patients with intra-abdominal hypertension has been questioned.

METHODS

Twenty surgical and trauma patients with intra-abdominal hypertension requiring open abdominal decompression were monitored using volumetric thermodilution pulmonary artery catheters. Hemodynamic, oxygenation, inspiratory, and intravesicular pressure measurements were collected prospectively. PAOP, CVP, and right ventricular end-diastolic volume index (RVEDVI) were compared as estimates of preload status.

RESULTS

Multiple regression analysis demonstrated that cardiac index correlated significantly better with RVEDVI (r = 0.69) than with PAOP (r = -0.27) or CVP (r = -0.28) during resuscitation after open abdominal decompression (p < 0.0001).

CONCLUSION

RVEDVI is superior to PAOP and CVP as an estimate of preload status in patients with an open abdomen.

Right ventricular end-diastolic volume index as a predictor of preload status in patients on positive end-expiratory pressure

OBJECTIVE

To evaluate the clinical utility of right ventricular end-diastolic volume index (RVEDVI) and pulmonary artery occlusion pressure (PAOP) as measures of preload status in patients with acute respiratory failure receiving treatment with positive end-expiratory pressure.

DESIGN

Prospective, cohort study.

SETTING

Surgical intensive care unit in a Level I trauma center/university hospital.

PATIENTS

Sixty-four critically ill surgical patients with acute respiratory failure.

INTERVENTIONS

All patients were treated for acute respiratory failure with titrated levels of positive end-expiratory pressure (PEEP) with the goal of increasing arterial oxygen saturation to > or =0.92, reducing FIO2 to <0.5, and reducing intrapulmonary shunt to < or =0.2. Serial determinations of RVEDVI, PAOP, and cardiac index (CI) were recorded.

MEASUREMENTS AND MAIN RESULTS

Two hundred-fifty sets of hemodynamic variables were measured in 64 patients. The level of PEEP ranged from 5 to 50 cm H2O (mean 12+/-9 [SD] cm H2O). At all levels of PEEP, CI correlated significantly better with RVEDVI than with PAOP. At levels of PEEP > or =15 cm H2O, CI was inversely correlated with PAOP, but remained positively correlated with RVEDVI.

CONCLUSIONS

CI correlates significantly better with RVEDVI than PAOP at all levels of PEEP up to 50 cm H2O. RVEDVI is a more reliable predictor of volume depletion and preload recruitable increases in CI, especially in patients receiving higher levels of PEEP where PAOP is difficult to interpret.

Intra-abdominal hypertension and the abdominal compartment syndrome

IAH causes multiple and profound physiologic abnormalities both within and outside the abdomen. IAP monitoring is easily performed by bladder measurements. Careful monitoring and prompt recognition and treatment of IAP are critical in patients after damage control surgery because IAH is extremely common in these patients. Use of mesh fascial prostheses at the initial celiotomy in high-risk patients may prevent the deleterious effects of IAH. IAH should be considered an earlier manifestation of ACS. Surgical intervention should be indicated by IAH and not delayed until ACS is clinically apparent.

Right ventricular volumes overestimate left ventricular preload in critically ill patients

BACKGROUND

Studies have shown right ventricular end-diastolic volume (RVEDV) to be a more accurate estimate of left ventricular preload than pulmonary artery wedge pressure. We prospectively evaluated the ability of RVEDV to predict left ventricular end-diastolic volume (LVEDV) in critically ill patients.

METHODS

Thirty critically ill patients in the surgical intensive care unit underwent concurrent measurement of RVEDV and LVEDV. RVEDV was measured using a residual fraction Swan-Ganz catheter (RF Swan). LVEDV was measured using transesophageal echocardiography with acoustic quantification. Intracardiac, intra-abdominal, and ventilatory pressures were also measured.

RESULTS

RVEDV as measured by the RF Swan was significantly larger (by a factor of 2) than LVEDV (p < 0.0001 analysis of variance). However, the RVEDV and LVEDV were strongly correlated (r = 0.71, p < 0.0001, Pearson's correlation).

CONCLUSIONS

RVEDV from the RF Swan markedly overestimated left ventricular preload. If RVEDV is used as an absolute value for determining preload, patients may be underresuscitated. Transesophageal echocardiography in conjunction with RF Swan can be used to more accurately determine preload and cardiac performance than RF Swan alone in critically ill patients.

Effects of increasing airway pressure and PEEP on the assessment of cardiac preload

BACKGROUND

Cardiac preload is most commonly assessed by pulmonary artery wedge pressure. It was postulated that the right ventricular end-diastolic volume index (RVEDVI) derived by thermodilution would be a better predictor of preload in trauma patients with high airway pressures associated with positive pressure ventilation and positive end-expiratory pressure.

METHODS

Volumetric thermodilution catheters were placed in 52 mechanically ventilated trauma patients. Regression analysis was performed on 986 sets of hemodynamic data comparing pulmonary artery wedge pressure and RVEDVI to cardiac index (CI) at various airway pressures.

RESULTS

There was much better correlation between RVEDVI and CI (r = 0.41) than with pulmonary artery wedge pressure and CI (r = -0.06). This was true of all levels of airway pressure tested. When analyzed by the degree of right ventricular dysfunction, as indexed by right ventricular ejection fraction, the strongest correlation between RVEDVI and CI was noted when right ventricular ejection fraction was > 30%.

CONCLUSIONS

Unlike the pulmonary artery wedge pressure, RVEDVI is as reliable indicator of preload in the mechanically ventilated trauma patient. This is especially true when the right ventricular ejection fraction is not severely depressed.

High-level positive end expiratory pressure management in the surgical patient with acute respiratory distress syndrome

Although the exact incidence of ARDS is not know, it is frequently reported that there are 150,000 cases in the United States each year. Despite major advances in medical and respiratory intensive care, the mortality for patients with ARDS remains exceedingly high and has not changed appreciably from the 50% to 75% reported during the last 25 years. Currently there is no widespread, acceptable, specific therapeutic approach or agent available for the prevention or treatment of ARDS. Clinical management remains entirely supportive in nature. Although most practitioners agree that patients with severe ARDS require mechanical ventilation to maintain adequate gas exchange, controversies center on the amount of supplemental oxygen, level of positive end expiratory pressure (PEEP), and mode of ventilation needed to increase patient survival but reduce ventilator-associated complications. This review provides supportive evidence for the use of high-level PEEP (more than 15 cm H20) in the care of the surgical patient with severe ARDS.

The new pulmonary arterial catheters. Right ventricular ejection fraction and continuous cardiac output

The flow-directed pulmonary artery catheter is the mainstay of hemodynamic monitoring in critically ill and injured patients. During its 25-year history, the catheter has been modified to measure mixed venous oxygen saturation, right ventricular ejection fraction, and recently, continual thermodilution cardiac output. The clinical application of the new generations of pulmonary artery catheters is reviewed in this article.