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

Peripheral Intravenous Waveform Analysis Responsiveness to Subclinical Hemorrhage in a Rat Model

BACKGROUND

Early detection and quantification of perioperative hemorrhage remains challenging. Peripheral intravenous waveform analysis (PIVA) is a novel method that uses a standard intravenous catheter to detect interval hemorrhage. We hypothesize that subclinical blood loss of 2% of the estimated blood volume (EBV) in a rat model of hemorrhage is associated with significant changes in PIVA. Secondarily, we will compare PIVA association with volume loss to other static, invasive, and dynamic markers.

METHODS

Eleven male Sprague Dawley rats were anesthetized and mechanically ventilated. A total of 20% of the EBV was removed over ten 5 minute-intervals. The peripheral intravenous pressure waveform was continuously transduced via a 22-G angiocatheter in the saphenous vein and analyzed using MATLAB. Mean arterial pressure (MAP) and central venous pressure (CVP) were continuously monitored. Cardiac output (CO), right ventricular diameter (RVd), and left ventricular end-diastolic area (LVEDA) were evaluated via transthoracic echocardiogram using the short axis left ventricular view. Dynamic markers such as pulse pressure variation (PPV) were calculated from the arterial waveform. The primary outcome was change in the first fundamental frequency (F1) of the venous waveform, which was assessed using analysis of variance (ANOVA). Mean F1 at each blood loss interval was compared to the mean at the subsequent interval. Additionally, the strength of the association between blood loss and F1 and each other marker was quantified using the marginal R2 in a linear mixed-effects model.

RESULTS

PIVA derived mean F1 decreased significantly after hemorrhage of only 2% of the EBV, from 0.17 to 0.11 mm Hg, P = .001, 95% confidence interval (CI) of difference in means 0.02 to 0.10, and decreased significantly from the prior hemorrhage interval at 4%, 6%, 8%, 10%, and 12%. Log F1 demonstrated a marginal R2 value of 0.57 (95% CI 0.40-0.73), followed by PPV 0.41 (0.28-0.56) and CO 0.39 (0.26-0.58). MAP, LVEDA, and systolic pressure variation displayed R2 values of 0.31, and the remaining predictors had R2 values ≤0.2. The difference in log F1 R2 was not significant when compared to PPV 0.16 (95% CI -0.07 to 0.38), CO 0.18 (-0.06 to 0.04), or MAP 0.25 (-0.01 to 0.49) but was significant for the remaining markers.

CONCLUSIONS

The mean F1 amplitude of PIVA was significantly associated with subclinical blood loss and most strongly associated with blood volume among the markers considered. This study demonstrates feasibility of a minimally invasive, low-cost method for monitoring perioperative blood loss.

Safety and performance of a novel implantable sensor in the inferior vena cava under acute and chronic intravascular volume modulation

AIMS

The management of congestion is one of the key treatment targets in heart failure. Assessing congestion is, however, difficult. The purpose of this study was to investigate the safety and dynamic response of a novel, passive, inferior vena cava (IVC) sensor in a chronic ovine model.

METHODS AND RESULTS

A total of 20 sheep divided into three groups were studied in acute and chronic in vivo settings. Group I and Group II included 14 sheep in total with 12 sheep receiving the sensor and two sheep receiving a control device (IVC filter). Group III included an additional six animals for studying responses to volume challenges via infusion of blood and saline solutions. Deployment was 100% successful with all devices implanted; performing as expected with no device-related complications and signals were received at all observations. At similar volume states no significant differences in IVC area normalized to absolute area range were measured (55 ± 17% on day 0 and 62 ± 12% on day 120, p = 0.51). Chronically, the sensors were completely integrated with a thin, reendothelialized neointima with no loss of sensitivity to infused volume. Normalized IVC area changed significantly from 25 ± 17% to 43 ± 11% (p = 0.007) with 300 ml infused. In contrast, right atrial pressure required 1200 ml of infused volume prior to a statistically significant change from 3.1 ± 2.6 mmHg to 7.5 ± 2.0 mmHg (p = 0.02).

CONCLUSION

In conclusion, IVC area can be measured remotely in real-time using a safe, accurate, wireless, and chronic implantable sensor promising to detect congestion with higher sensitivity than filling pressures.

Changes in inferior vena cava area represent a more sensitive metric than change in filling pressures during experimental manipulation of intravascular volume and tone

Aims

Remote monitoring of pulmonary artery pressure has reduced heart failure (HF) hospitalizations in chronic HF as elevation of pulmonary artery pressure provides information that can guide treatment. The venous system is characterized by high capacitance, thus substantial increases in intravascular volume can occur before filling pressures increase. The inferior vena cava (IVC) is a highly compliant venous conduit and thus a candidate for early detection of change in intravascular volume. We aimed to compare IVC cross‐sectional area using a novel sensor with cardiac filling pressures during experimental manipulation of volume status, vascular tone, and cardiac function.

Methods and results

Experiments were conducted in sheep to manipulate volume status (colloid infusion), vascular tone (nitroglycerin infusion) and cardiac function (rapid cardiac pacing). A wireless implantable IVC sensor was validated ex‐vivo and in‐vivo, and then used to measure the cross‐sectional area of the IVC. Right‐ and left‐sided cardiac filling pressures were obtained via right heart catheterization. The IVC sensor provided highly accurate and precise measurements of cross‐sectional area in ex‐vivo and in‐vivo validation. IVC area changes were more sensitive than the corresponding changes in cardiac filling pressures during colloid infusion (p < 0.001), vasodilatation (p < 0.001) and cardiac dysfunction induced by rapid pacing (p ≤ 0.02).

Conclusions

Inferior vena cava area can be remotely and accurately measured in real time with a wireless implantable sensor. Changes in IVC area are more sensitive than corresponding changes in filling pressures following experimental volume loading and fluid redistribution. Additional research is warranted to understand if remote monitoring of the IVC may have advantages over pressure‐based monitors in HF.

High Central Venous Pressure and Right Ventricle Size Are Related to Non-decreased Left Ventricle Stroke Volume After Negative Fluid Balance in Critically Ill Patients: A Single Prospective Observational Study

Background: Optimal adjustment of cardiac preload is essential for improving left ventricle stroke volume (LVSV) and tissue perfusion. Changes in LVSV caused by central venous pressure (CVP) are the most important concerns in the treatment of critically ill patients. Objectives: This study aimed to clarify the changes in LVSV after negative fluid balance in patients with elevated CVP, and to elucidate the relationship between the parameters of right ventricle (RV) filling state and LVSV changes. Methods: This prospective cohort study included patients with high central venous pressure (CVP) (≥8 mmHg) within 24 h of ICU admission in the Critical Medicine Department of Peking Union Medical College Hospital. Patients were classified into two groups based on the LVSV changes after negative fluid balance. The cutoff value was 10%. The hemodynamic and echo parameters of the two groups were recorded at baseline and after negative fluid balance. Results: A total of 71 patients included in this study. Forty in VI Group (LVOT VTI increased ≥10%) and 31 in VNI Group (LVOT VTI increased <10%). Of all patients, 56.3% showed increased LVSV after negative fluid balance. In terms of hemodynamic parameters at T0, patients in VI Group had a higher CVP (p < 0.001) and P(v-a)CO₂ (p < 0.001) and lower ScVO₂ (p < 0.001) relative to VNI Group, regarding the echo parameters at T0, the RV_D/LV_D ratio (p < 0.001), DIVC _{end-expiratory} (p < 0.001), and ΔLVOT VTI (p < 0.001) were higher, while T0 LVOT VTI (p < 0.001) was lower, in VI Group patients. The multifactor logistic regression analysis suggested that a high CVP and RV_D/LV_D ratio ≥0.6 were significant associated with LVSV increase after negative fluid balance in critically patients. The AUC of CVP was 0.894. A CVP >10.5 mmHg provided a sensitivity of 87.5% and a specificity of 77.4%. The AUC of CVP combined with the RV_D/LV_D ratio ≥0.6 was 0.926, which provided a sensitivity of 92.6% and a specificity of 80.4%. Conclusion: High CVP and RV_D/LV_D ratio ≥0.6 were significant associated with RV stressed in critically patients. Negative fluid balance will not always lead to a decrease, even an increase, in LVSV in these patients.

Effect of microplastics on aquatic biota: A hormetic perspective

As emerging pollutants, microplastics (MPs) have been found globally in various freshwater and marine matrices. This study recompiled 270 endpoints of 3765 individuals from 43 publications, reporting the onset of enhanced biological performance and reduced oxidative stress biomarkers induced by MPs in aquatic organisms at environmentally relevant concentrations (≤1 mg/L, median = 0.1 mg/L). The stimulatory responses of consumption, growth, reproduction and survival ranged from 131% to 144% of the control, with a combined response of 136%. The overall inhibitory response of 9 oxidative stress biomarkers was 71% of the control, and commonly below 75%. The random-effects meta-regression indicated that the extents of MPs-induced responses were independent of habitat, MP composition, morphology, particle size and exposure duration. The results implied that the exposure to MPs at low and high concentrations might induce opposite/non-monotonic responses in aquatic biota. Correspondingly, the hormetic dose response relationships were found at various endpoints, such as reproduction, genotoxicity, immunotoxicity, neurotoxicity and behavioral alteration. Hormesis offers a novel perspective for understanding the dose response mode of aquatic organisms exposed to low and high concentrations of MPs, highlighting the necessity to incorporate the hormetic dose response model into the ecological/environmental risk assessment of MPs.

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.

Preload dependence of pulmonary haemodynamics and right ventricular performance

AIMS

Systolic pulmonary artery pressure (SPAP) and right heart adaptation in relation to pre-existing preload are often disregarded. To determine volume-related changes in the pulmonary-right ventricle (RV) unit and the preload dependence of its components, we analysed pulmonary haemodynamics and right ventricular performance, taking advantage of the plasma volume removal associated to haemodialysis (HD).

METHODS AND RESULTS

Fifty-three stable patients on chronic HD with LVEF > 50% and without heart failure were recruited (mean age 63.0 ± 12.4 years; 31.2% women; hypertension in 89% and diabetes in 53%) and evaluated just before and after HD (mean ultrafiltration volume 2.4 ± 0.7 l). SPAP from both times were available in 39 patients. After HD, SPAP decreased (42.2 ± 12.6 to 33.7 ± 11.6 mmHg, p < 0.001) without modification of non-invasive pulmonary vascular resistance (1.75 ± 0.44 to 1.75 ± 0.40 eWU, p = 0.94). Age and drop in the E/e' ratio were the variables associated with greater reduction in PASP (p = 0.022 and p = 0.049, respectively). A significant reduction of right chamber sizes was observed, along with a diminution in measures of RV contractility, excluding RV longitudinal strain. Functional tricuspid regurgitation (FTR) diminution was observed in 26% of patients, occurring in every case with more than mild FTR. On multivariate analyses, left atrial size was the only predictor of pulmonary hypertension (defined as SPAP > 40 mmHg) (OR 1.29 (1.07-1.56), p = 0.006).

CONCLUSION

Rapid volemic changes may affect FTR grading, RV size and contractility, with RV longitudinal strain being less variable than conventional parameters. SPAP decreases after HD, and this reduction is related to age and greater diminution of the E/e' ratio.

What is the impact of the fluid challenge technique on diagnosis of fluid responsiveness? A systematic review and meta-analysis

Background

The fluid challenge is considered the gold standard for diagnosis of fluid responsiveness. The objective of this study was to describe the fluid challenge techniques reported in fluid responsiveness studies and to assess the difference in the proportion of ‘responders,’ (PR) depending on the type of fluid, volume, duration of infusion and timing of assessment.

Methods

Searches of MEDLINE and Embase were performed for studies using the fluid challenge as a test of cardiac preload with a description of the technique, a reported definition of fluid responsiveness and PR. The primary outcome was the mean PR, depending on volume of fluid, type of fluids, rate of infusion and time of assessment.

Results

A total of 85 studies (3601 patients) were included in the analysis. The PR were 54.4% (95% CI 46.9–62.7) where <500 ml was administered, 57.2% (95% CI 52.9–61.0) where 500 ml was administered and 60.5% (95% CI 35.9–79.2) where >500 ml was administered (p = 0.71). The PR was not affected by type of fluid. The PR was similar among patients administered a fluid challenge for <15 minutes (59.2%, 95% CI 54.2–64.1) and for 15–30 minutes (57.7%, 95% CI 52.4–62.4, p = 1). Where the infusion time was ≥30 minutes, there was a lower PR of 49.9% (95% CI 45.6–54, p = 0.04). Response was assessed at the end of fluid challenge, between 1 and 10 minutes, and >10 minutes after the fluid challenge. The proportions of responders were 53.9%, 57.7% and 52.3%, respectively (p = 0.47).

Conclusions

The PR decreases with a long infusion time. A standard technique for fluid challenge is desirable.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-017-1796-9) contains supplementary material, which is available to authorized users.

Global end-diastolic volume an emerging preload marker vis-a-vis other markers - Have we reached our goal?

A reliable estimation of cardiac preload is helpful in the management of severe circulatory dysfunction. The estimation of cardiac preload has evolved from nuclear angiography, pulmonary artery catheterization to echocardiography, and transpulmonary thermodilution (TPTD). Global end-diastolic volume (GEDV) is the combined end-diastolic volumes of all the four cardiac chambers. GEDV has been demonstrated to be a reliable preload marker in comparison with traditionally used pulmonary artery catheter-derived pressure preload parameters. Recently, a new TPTD system called EV1000™ has been developed and introduced into the expanding field of advanced hemodynamic monitoring. GEDV has emerged as a better preload marker than its previous conventional counterparts. The advantage of it being measured by minimum invasive methods such as PiCCO™ and newly developed EV1000™ system makes it a promising bedside advanced hemodynamic parameter.

Stroke volume response to liver graft reperfusion stress in cirrhotic patients

INTRODUCTION

In patients with advanced cirrhosis, stressful stimuli may reveal a silent reduced cardiac performance. During liver transplantation (LT), graft reperfusion strongly stresses the heart and may unmask latent myocardial dysfunction.

AIM

The objective of this study was to assess heart response to acutely increased preload after liver graft reperfusion and correlate this response with preoperative data and outcome.

METHODS

Preoperative clinical, echocardiographic, and hemodynamic data, and patient outcome were retrospectively recorded for 235 liver recipients who had no known cardiac disease. Myocardial dysfunction was defined as less than 10 % increase of stroke volume after graft reperfusion (non-responder).

RESULTS

We found 84 (35.7 %) non-responder patients. The non-responders showed higher Model for end-stage liver disease scores (p = 0.046), left atrial diameter (LAD) (p = 0.040), hepatic vein pressure gradient (p = 0.055), and hyperdynamic state than responders. The percentages of patients with hyponatremia (p = 0.048) and alcohol etiology (p = 0.025) were also higher among non-responders. Independent predictors of inadequate cardiac response in the multivariate analysis were low preoperative systemic vascular resistance (SVRI) [odds ratio (OR) 3.09, 95 % CI 1.15-4.82; p = 0.027] and enlargement of LAD (OR 2.08, 95 % CI 1.49-2.74; p = 0.044). Non-response was associated with higher rates of early cardiovascular events [hazard ratio (HR) 2.84, 95 % CI 1.09-4.22; p = 0.039] and higher length of intensive care unit stay (p = 0.038). No differences were found in 1-year survival rates.

CONCLUSIONS

Latent cardiac dysfunction among LT recipients, considered to be abnormal stroke volume response to unclamping of portal vein, is very prevalent. SVRI and LAD were independent predictors of inadequate responses. This condition deserves special attention since it may aggravate the early postoperative course of LT.

Fluid responsiveness predicted by elevation of PEEP in patients with septic shock

BACKGROUND

The assessment of whether a patient is fluid responsive can be difficult in clinical practice. Invasive filling pressures are inadequate indicators of preload and fluid responsiveness in critically ill patients. Dynamic indices may be unreliable in clinical practice because of arrhythmias or spontaneous breathing efforts. Elevation of positive end-expiratory pressure (PEEP) causes cardiorespiratory interactions, which may produce signs of hypovolaemia. Our aim was to assess whether haemodynamic changes during a short elevation of PEEP would predict fluid responsiveness in patients with septic shock.

METHODS

We performed a prospective observational study in 20 patients with septic shock on mechanical ventilation. We assessed the following changes in haemodynamic variables during a temporary elevation of PEEP from 10 cm H2O to 20 cm H2O during an end-expiratory pause: mean arterial pressure (MAP), systolic arterial pressure, pulse pressure, central venous pressure, pulmonary artery occlusion pressure, left ventricular end diastolic area and aortic velocity-time integral. We defined fluid responsiveness as an increase in cardiac output of 15% to a subsequent fluid challenge.

RESULTS

Decrease in MAP related to elevation of PEEP predicted fluid responsiveness (P = 0.003). The best cut-off value of ΔMAP for clinical use was -8%, with a negative predictive value for fluid responsiveness of 100%.

CONCLUSION

In patients with septic shock, the absence of decrease in MAP during an elevation of PEEP may be used to identify patients who will not increase their cardiac output in response to fluid challenge.

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 derived by arterial pulse contour analysis is a good indicator for preload estimation during liver transplantation

BACKGROUND

Accurate determination of preload during liver transplantation is essential. Continuous right ventricular end diastolic volume index (RVEDVI) has been shown to be a better preload indicator during liver transplantation than the filling pressures. However, recent evidence has shown that dynamic variables, in this case stroke volume variation (SVV), are also good indicators of preload responsiveness. In this study, we evaluated the correlation between SVV, which we derived from arterial pulse contour analysis and RVEDVI.

METHODS

In this study, we looked for possible relationships between SVV obtained through FloTrac/Vigileo monitor, central venous pressure (CVP), pulmonary arterial occlusion pressure (PAOP), and RVEDVI in 30 patients undergoing liver transplantation. Measurements were taken at 11 defined points during different phases across liver transplantation. Each set of measurement was taken during a steady state, which means at least 15 minutes elpased after any changes occured in either the infusion rate of catecholamines or ventilator settings. Pearson's test was used for correlation estimation.

RESULTS

There was a statistically significant (P<.01) relationship between SVV and RVEDVI with a correlation coefficient of -0.87. The correlations between CVP (r=0.42), PAOA (r=0.46), and RVEDVI were less strong.

CONCLUSION

We conclude that SVV is a good indicator for preload estimation during liver transplantation. A higher SVV value is associated with a more hypovolemic fluid status.

Goal-directed therapy in small animal critical illness

Monitoring critically ill patients can be a daunting task even for experienced clinicians. Goal-directed therapy is a technique involving intensive monitoring and aggressive management of hemodynamics in patients with high risk of morbidity and mortality. The aim of goal-directed therapy is to ensure adequate tissue oxygenation and survival. This article reviews commonly used diagnostics in critical care medicine and what the information gathered signifies and discusses clinical decision making on the basis of diagnostic test results. One example is early goal-directed therapy for severe sepsis and septic shock. The components and application of goals in early goal-directed therapy are discussed.

Continuous and less invasive central hemodynamic monitoring by blood pressure waveform analysis

Blood pressure waveform analysis may permit continuous (i.e., automated) and less invasive (i.e., safer and simpler) central hemodynamic monitoring in the intensive care unit and other clinical settings without requiring any instrumentation beyond what is already in use or available. This practical approach has been a topic of intense investigation for decades and may garner even more interest henceforth due to the evolving demographics as well as recent trends in clinical hemodynamic monitoring. Here, we review techniques that have appeared in the literature for mathematically estimating clinically significant central hemodynamic variables, such as cardiac output, from different blood pressure waveforms. We begin by providing the rationale for pursuing such techniques. We then summarize earlier techniques and thereafter overview recent techniques by our collaborators and us in greater depth while pinpointing both their strengths and weaknesses. We conclude with suggestions for future research directions in the field and a description of some potential clinical applications of the techniques.

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.

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.

Non-invasive method for the rapid assessment of central venous pressure: description and validation by a single examiner

OBJECTIVES

This study describes a means of assessing the external jugular venous pressure (JVP) as an indicator of normal or elevated central venous pressure (CVP).

METHODS

Intensive care unit patients having CVP monitoring were examined. With patients in bed, the external jugular vein (EJV) was occluded at the base of the neck and observed to distend. The occlusion was then removed and the vein observed for collapse. Complete collapse was hypothesized to indicate a non-elevated CVP (</=8cm of water). In those patients whose EJV collapsed incompletely, the vein was then occluded with the finger near the angle of the jaw. With the occlusion maintained, the vein was milked downwards with the other hand to cause its emptying and was then observed for filling from below. Filling from below was hypothesized to indicate an elevated CVP (>8cm of water).

RESULTS

In 12 of the 40 patients examined, the EJV could not be assessed (EJV not seen at all: 5, and difficult to visualize: 7). For the remaining 28 patients 11 had a CVP > 8 cm, while 17 had a CVP patients, of </= 8. EJV assessment was 100% accurate (95% Confidence Interval 88-100) in predicting whether or not a patient's CVP was greater or less than 8 cm of water.

CONCLUSION

EJV assessment, when visible, is accurate to clinically assess a patient's CVP in the hands of the author. Further studies are needed to see if they are reproducible by other observer.

Xenon alters right ventricular function

BACKGROUND

In contrast to other volatile anesthetics, xenon produces less cardiovascular depression with fewer fluctuations of various hemodynamic parameters, but reduces cardiac output (CO) in vivo. Besides an increase in left ventricular afterload and reduction of heart rate, an impairment of the right ventricular function might be an additional pathophysiological mechanism for the reduction of CO. Therefore, we used an animal model to study the effects of xenon as a supplemental anesthetic on right ventricular function, especially right ventricular afterload.

METHODS

Right ventricular function was monitored with a volumetric pulmonary artery catheter in 11 pigs during general anesthesia with thiopental. Six animals received additional 70% (volume) xenon (equivalent to 0.55 MAC minimum alveolar concentration). Parameters for systolic function, afterload, and preload were calculated at baseline and during 50 min of xenon application, and in a corresponding control group. Significant differences were detected by multivariate analyses of variance for repeated measures.

RESULTS

Xenon reduced CO on average by 30% and increased pulmonary arterial elastance by 60%, which led to a reduction of the right ventricular ejection fraction by 25%. Whereas right ventricular preload remained stable, maximal slope of pulmonary artery pressure and the right ventricular elastance increased. No effect on the ratio of stroke work and end-diastolic volume was found.

CONCLUSION

The reduction in CO during xenon anesthesia was partly due to an impairment of the right ventricular function, mainly caused by an increased afterload, without an impairment of systolic ventricular function.

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.

A clinician's guide to predicting fluid responsiveness in critical illness: applied physiology and research methodology

Intravenous fluid administration is often used in critical care with the goal of improving haemodynamics and consequently tissue perfusion and oxygen delivery. While inotropic and vasoactive drugs are often necessary to correct haemodynamic instability, resuscitation usually begins with fluid therapy. As fluid challenge can result in clinical deterioration, the ability to predict haemodynamic response is desirable. In this way it might be possible to avoid unnecessary volume replacement in critically ill patients. Cardiac preload is a concept that accounts for the relationship between ventricular filling and stroke volume. It has been challenging to apply this concept to clinical practice. For this reason, the study of fluid responsiveness is of increasing research and clinical interest. The clinical application of predicting fluid responsiveness requires an understanding of relevant physiological principles. Furthermore, an improved understanding of these principles should assist the clinician in appraising published data, which has been characterised by significant methodological differences. This review aims to assist the clinician by detailing the physiological principles that underlie the prediction of fluid responsiveness in the critically ill. In addition, the potential importance of methodological differences in the cutrent literature will be considered.

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.

Comparison of two methods for enhanced continuous circulatory monitoring in patients with septic shock

OBJECTIVE

To compare a modified pulmonary artery catheter (PAC) and pulse-contour analysis by the PiCCO (Pulsion Medical Systems, Munich, Germany) system for continuous assessment of cardiac output in patients with septic shock. In addition, to assess the relationships between an index of global end-diastolic volume (GEDV) derived by the PiCCO system with traditional PAC-derived indicators of filling: central venous pressure; pulmonary artery occlusion pressure; and right ventricular end-diastolic volume (RVEDV).

DESIGN

Prospective cohort study.

SETTING

Surgical intensive care unit of a university hospital.

PATIENTS AND PARTICIPANTS

14 patients with septic shock.

INTERVENTIONS

None.

MEASUREMENTS AND RESULTS

A significant correlation was found between continuous cardiac output by PAC (CCO(PAC)) and by pulse-contour analysis (r (2) = 0.714, p < 0.0001), accompanied by a bias of 0.1 l min(-1) and a precision of 2.7 l min(-1). The correlation between CCO(PAC) and cardiac output measured by transcardiopulmonary thermodilution was also significant (r (2) = 0.781, p < 0.0001). There was a bias for the two methods of 0.2 l min(-1), and a precision of 2.2 lmin(-1). The GEDV showed no correlation with central venous pressure, pulmonary artery occlusion pressure, or RVEDV.

CONCLUSION

In patients with septic shock, the averaged bias in continuous measurement of cardiac output by both a modified pulmonary artery catheter and pulse-contour analysis was small, but variability was large. No correlation was found between GEDV and RVEDV. The clinical importance of different cardiac filling parameters needs further investigation.

Right atrial effects on right ventricular ejection fraction derived from thermodilution measurements

OBJECTIVE

The thermodilution technique provides a convenient means to monitor cardiac output, right ventricular (RV) ejection fraction (EF), and volumes at the bedside. To calculate RVEF from the pulmonary artery temperature curve, the bolus thermodilution technique assumes that right atrial (RA) temperature returns to baseline value within 1 beat following the cold saline injection. The authors hypothesized that this assumption is the reason why the thermodilution technique consistently underestimates RVEF.

DESIGN

A theoretical analysis and animal study.

SETTING

Laboratory, university, multi-institutional.

PARTICIPANTS

Animals.

INTERVENTIONS

Cold saline injections.

MEASUREMENTS AND MAIN RESULTS

In 2 porcine experiments, after a rapid injection of cold saline into right atrium, RA temperature took several heartbeats to return to baseline. In a theoretical analysis, if after the cold saline injection RA temperature returned to baseline in 1 beat (RAEF = 1), then thermodilution-derived RVEF(T) = actual RVEF(A). In contrast, if RA temperature took several beats to return to baseline (RAEF = RVEF), then RVEF(T) consistently underestimated RVEF(A). A least square fit of RVEF(A) versus RVEF(T) resulted in RVEF(A) = 1.0 x RVEF(T) + 0.11. Applying this correction (adding 0.11 to RVEF(T)) to the data gave relatively small errors in estimating RVEF over a wide EF range.

CONCLUSIONS

After injecting cold saline into the right atrium, RA temperature takes several heart beats to return to baseline temperature, leading to underestimating RVEF and overestimating RV volumes. The pulsed thermal energy approach by injecting heat into the RV avoids these problems, but the impact of its small temperature signal on RVEF measurements needs to be determined.

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.

Heterogeneity and prediction of hemodynamic responses to dobutamine in patients with septic shock

OBJECTIVE

To establish the heterogeneity of hemodynamic responses to dobutamine in patients with septic shock and to identify the predictive factors of these hemodynamic responses.

DESIGN

Prospective study.

SETTING AND PATIENTS

A total of 12 patients with septic shock in a tertiary medical intensive care unit.

INTERVENTIONS

A 20-min dobutamine infusion at 5 microg.kg(-1).min(-1) with subsequent increments to 8, 12.6, and 20 microg.kg(-1).min(-1), on two consecutive days. Responses were dichotomized into changes in heart rate (HR) or stroke volume index (SVI) of >10% and < or =10% at the maximal dobutamine infusion.

MEASUREMENTS AND MAIN RESULTS

No differences were found in survival, Acute Physiology and Chronic Health Evaluation II score, maximal dobutamine doses, or pharmacokinetics of dobutamine between HR and SVI groups. In DeltaHR > 10% vs. DeltaHR < or = 10%, baseline HR was lower, and baseline mixed venous oxygen tension and saturation were higher. During dobutamine infusion, mean arterial pressure decreased in DeltaHR > 10%. Cardiac index and the systemic oxygen delivery index increased and the systemic vascular resistance index decreased at unchanged SVI. Pressure work index increased and the ratio of the diastolic to systolic aortic pressure time indices decreased but not to <0.6. In DeltaHR < or = 10%, systemic vascular resistance index and the ratio of the diastolic to systolic aortic pressure time indices decreased (but remained >0.6) without changes in SVI or cardiac index. Baseline hemodynamic and metabolic variables did not differ between SVI groups. In DeltaSVI > 10%, cardiac index increased with dobutamine, but Pao2 and the systemic oxygen delivery index decreased. In DeltaSVI < or = 10%, HR and the systemic oxygen delivery index increased; mean arterial pressure, left ventricular stroke work index, systemic vascular resistance index, and the ratio of the diastolic to systolic aortic pressure time indices decreased.

CONCLUSIONS

Patients with a positive chronotropic response to dobutamine had lower baseline HR values, and a chronotropic rather than inotropic response predicted an increase in cardiac index and systemic oxygen delivery index. Incremental dosages of dobutamine did not compromise indirectly measured myocardial oxygen balance.

Arterial pressure-based technologies: a new trend in cardiac output monitoring

New trends in cardiovascular monitoring use the arterial pulse as a less invasive means of assessing cardiac output. When adopting a new technology into practice, three questions need to be answered: (1) is the method technologically sound?, (2) is it based on physiologic principles?, and (3) are the applications clinically important? This article provides a clinical review on the technology, physiology, and applications of a new arterial pressure-based method of determining cardiac output and stroke volume variation as an additional parameter for fluid status assessment.

Selective pulmonary vasodilation with inhaled aerosolized milrinone in heart transplant candidates

PURPOSE

Selective pulmonary vasodilation is an advantageous method for testing the responsiveness of the pulmonary vasculature of heart transplant candidates. A pilot study was under-taken to test the hypothesis that inhaled aerosolized milrinone may cause selective pulmonary vasodilation.

METHODS

18 consecutive male heart transplant candidates with either dilated or ischemic cardiomyopathy were included in this open clinical study. Nine of the patients had significant pulmonary hypertension with a mean pulmonary arterial pressure > 30 mmHg. After baseline measurements, 2 mg of milrinone was administered by ultrasonic nebulization. Pulmonary and systemic hemodynamics were measured ten, 30, and 60 min after inhalation.

RESULTS

After inhalation for ten minutes, milrinone induced a significant reduction of mean pulmonary arterial pressure (32.7 +/- 9.1 vs 37.7 +/- 7.5 mmHg, P = 0.01), pulmonary vascular resistance index (296 +/- 150 vs 396 +/- 151 dyn.sec(-1).cm(-5).m(2), P = 0.02) and transpulmonary gradient (10.6 +/- 5.5 vs 15 +/- 4.9, P = 0.01) only in patients with significant pulmonary hypertension. There was no significant effect on mean arterial pressure or systemic vascular resistance at any time after inhalation in either group. Furthermore, there was no influence on extravascular lung water or intrathoracic blood volume.

CONCLUSIONS

We conclude that inhaled aerosolized milrinone for a short period selectively dilates the pulmonary vasculature in heart transplant candidates with elevated pulmonary arterial pressure, without producing systemic side effects. Further comparative studies are necessary to evaluate possible advantages of milrinone compared to other inhaled vasodilators.

Inhaled aerosolized iloprost in the evaluation of heart transplant candidates—experiences with 45 cases

PURPOSE

Pulmonary hypertension represents a significant predictor of postoperative right heart insufficiency and increased mortality in patients undergoing orthotopic heart transplantation. As the use of intravenous vasodilators is limited by their systemic effects, we evaluated the pulmonary and systemic hemodynamic effects of inhaled aerosolized iloprost in heart transplant candidates with elevated pulmonary vascular resistance.

METHODS

Forty-five male heart transplant candidates with dilated or ischemic cardiomyopathy were included in the study. After assessing baseline hemodynamics, 20 microg of aerosolized iloprost was administered by ultrasonic inhalation. All patients were breathing spontaneously.

RESULTS

Inhalation of iloprost reduced pulmonary vascular resistance index (395 +/- 205 vs 327 +/- 222 dyne.s.cm(-5).m(-2); P < 0.05) and mean pulmonary arterial pressure (28.7 +/- 10 vs 24.3 +/- 10 mm Hg; P < 0.05). An additional improvement of ventricular performance with an increase of cardiac index (2.7 +/- 0.7 vs 3.0 +/- 0.8 L.min(-1).m(-2); P < 0.05) and a decrease of pulmonary capillary wedge pressure (16.6 +/- 7.7 vs 13.4 +/- 7.3 mm Hg; P < 0.05) was accompanied by a slight decrease of systemic vascular resistance (1280 +/- 396 vs 1172 +/- 380 dyne.s.cm(-5); P < 0.05). However, the mean arterial pressure remained uninfluenced.

CONCLUSIONS

Inhaled aerosolized iloprost effectively reduces mean pulmonary arterial pressure and also induces an increase in cardiac index. Further advantages of iloprost inhalation are the lack of adverse reactions and ease of administration. Iloprost represents a useful drug to screen for vascular reactivity in cardiac transplantation patients.