Assessing fluid responsiveness in critically ill patients: False-positive pulse pressure variation is detected by Doppler echocardiographic evaluation of the right ventricle

Basic concepts of fluid responsiveness

Predicting fluid responsiveness, the response of stroke volume to fluid loading, is a relatively novel concept that aims to optimise circulation, and as such organ perfusion, while avoiding futile and potentially deleterious fluid administrations in critically ill patients. Dynamic parameters have shown to be superior in predicting the response to fluid loading compared with static cardiac filling pressures. However, in routine clinical practice the conditions necessary for dynamic parameters to predict fluid responsiveness are frequently not met. Passive leg raising as a means to alter biventricular preload in combination with subsequent measurement of the change in stroke volume can provide a fast and accurate way to guide fluid management in a broad population of critically ill patients.

Pavane for a pulse pressure variation defunct

Hemodynamic management of critically ill patients in the ICU or high-risk patients in the operating room has paradoxically shown progress in terms of outcome after the systematic application of volume responsiveness/flow optimization based on pulse pressure variation and/or stroke volume variation during controlled, positive-pressure ventilation in patients without spontaneous respiratory efforts. This assessment of circulatory optimization should ideally be based on an exhaustive, predictive and coherent physiological understanding of the cardiovascular system model. This paper sketches the extremely complex physiological background of the concept of volume responsiveness, concluding that it is not a reliable means of guiding hemodynamic optimization because it is based on a nonexhaustive, nonpredictive and incoherent physiological model.

Predicting fluid responsiveness during infrarenal aortic cross-clamping in pigs

OBJECTIVE

Infrarenal aortic cross-clamping (ACC) induces hemodynamic disturbances that may affect respiratory-induced variations in stroke volume and, therefore, affect the ability of dynamic parameters such as pulse-pressure variation (PPV) to predict fluid responsiveness. Since this issue has not been investigated yet to authors' knowledge, the hypothesis was tested that ACC may change PPV and impair its ability to predict fluid responsiveness.

DESIGN

Prospective laboratory experiment.

SETTING

A university research laboratory.

PARTICIPANTS

Nineteen anesthetized and mechanically ventilated pigs.

INTERVENTIONS

Two courses of volume expansion were performed using 500 mL of saline before and during ACC. Animals were monitored using a systemic arterial catheter, and a pulmonary arterial catheter (stroke volume, central venous pressure, pulmonary arterial occlusion pressure). Animals were defined as responders to volume expansion if stroke volume increased ≥ 15%.

RESULTS

Before ACC, 13 animals were responders. Fluid responsiveness was predicted by a PPV ≥ 14% with a sensitivity of 77% (95% CI = 46%-95%) and a specificity of 83% (95% CI = 36%-97%). The area under the receiver operating characteristic curve was 0.90(95% CI = 0.67-0.99) and was higher than those generated for central venous pressure and pulmonary arterial occlusion pressure. ACC induced an increase in PPV (p<0.0005). During ACC, 8 animals were responders. An 18% PPV threshold discriminated between responders and non-responders to volume expansion, with a sensitivity of 87% (95% CI = 47%-98%) and a specificity of 54% (95% CI = 23%-83%). The area under the receiver operating characteristic curve was 0.72 (95% CI = 0.47-0.90) and was not different from those generated for central venous pressure and pulmonary arterial occlusion pressure.

CONCLUSIONS

ACC induced a significant increase in PPV and reduced its ability to predict fluid responsiveness.

Fluid challenge: tracking changes in cardiac output with blood pressure monitoring (invasive or non-invasive)

PURPOSE

To assess whether invasive and non-invasive blood pressure (BP) monitoring allows the identification of patients who have responded to a fluid challenge, i.e., who have increased their cardiac output (CO).

METHODS

Patients with signs of circulatory failure were prospectively included. Before and after a fluid challenge, CO and the mean of four intra-arterial and oscillometric brachial cuff BP measurements were collected. Fluid responsiveness was defined by an increase in CO ≥10 or ≥15% in case of regular rhythm or arrhythmia, respectively.

RESULTS

In 130 patients, the correlation between a fluid-induced increase in pulse pressure (Δ500mlPP) and fluid-induced increase in CO was weak and was similar for invasive and non-invasive measurements of BP: r² = 0.31 and r² = 0.29, respectively (both p < 0.001). For the identification of responders, invasive Δ500mlPP was associated with an area under the receiver-operating curve (AUC) of 0.82 (0.74-0.88), similar (p = 0.80) to that of non-invasive Δ500mlPP [AUC of 0.81 (0.73-0.87)]. Outside large gray zones of inconclusive values (5-23% for invasive Δ500mlPP and 4-35% for non-invasive Δ500mlPP, involving 35 and 48% of patients, respectively), the detection of responsiveness or unresponsiveness to fluid was reliable. Cardiac arrhythmia did not impair the performance of invasive or non-invasive Δ500mlPP. Other BP-derived indices did not outperform Δ500mlPP.

CONCLUSIONS

As evidenced by large gray zones, BP-derived indices poorly reflected fluid responsiveness. However, in our deeply sedated population, a high increase in invasive pulse pressure (>23%) or even in non-invasive pulse pressure (>35%) reliably detected a response to fluid. In the absence of a marked increase in pulse pressure (<4-5%), a response to fluid was unlikely.

Noninvasive assessment of hemodynamic response to a fluid challenge using femoral Doppler in critically ill ventilated patients

PURPOSE

The purpose of the study is to determine if femoral artery blood flow Doppler parameters can assess cardiac response to a fluid challenge (FC).

MATERIALS AND METHODS

We prospectively recorded in 52 critically ill ventilated patients' velocity time integral variation (%VTIf) and maximal systolic velocity variation (%Vfmax) derived from femoral Doppler analysis and aortic velocity time integral variation registered on transthoracic echocardiography before and after an FC of 500-mL saline.

RESULTS

According to Pearson coefficient, %Vfmax and %VTIf were found to be positively correlated with aortic velocity time integral variation (r(2) = 0.46 and 0.51, respectively; P < .0001) and were significantly different between responder patients and nonresponders (11% ± 3.4% vs 5.9% ± 4.3% and 14.9% ± 4.2% vs 5.5% ± 5.5%, respectively; P < .0001). Increase of %VTIf 10% or higher and %Vfmax 7% or higher after an FC showed a sensitivity of 80% and 84%, a specificity of 85% and 73%, and an area under the curve of 0.905 and 0.851, respectively, for discriminating responder and nonresponder patients.

CONCLUSION

Variation of femoral Doppler parameters before and after FC mirrors cardiac response to fluid loading. This tool could be considered as an alternative to transthoracic echocardiography in case of poor thoracic insonation.

Cardiopulmonary interactions in acute lung injury

PURPOSE OF REVIEW

Through shared anatomy, pressures, and endothelial connections, the respiratory and cardiovascular systems affect each other in complex but clinically important ways.

RECENT FINDINGS

Lung injury has clinically important circulatory effects, especially with regards to right ventricular function. Mechanical ventilation and PEEP produce a host of circulatory consequences, some beneficial, some life-threatening. At the same time, circulatory impairments and treatments can magnify the impact of lung failure.

SUMMARY

Cardiopulmonary interactions underpin current views of fluid management and mechanical ventilation. Understanding cardiopulmonary interactions and their physiological basis has direct clinical relevance.

Sepsis-induced cardiomyopathy

Myocardial dysfunction is one of the main predictors of poor outcome in septic patients, with mortality rates next to 70%. During the sepsis-induced myocardial dysfunction, both ventricles can dilate and diminish its ejection fraction, having less response to fluid resuscitation and catecholamines, but typically is assumed to be reversible within 7-10 days. In the last 30 years, It´s being subject of substantial research; however no explanation of its etiopathogenesis or effective treatment have been proved yet. The aim of this manuscript is to review on the most relevant aspects of the sepsis-induced myocardial dysfunction, discuss its clinical presentation, pathophysiology, etiopathogenesis, diagnostic tools and therapeutic strategies proposed in recent years.

Assessment of an uncalibrated pressure waveform device's ability to track cardiac output changes due to norepinephrine dose adjustments in patients with septic shock: a comparison with Doppler echocardiography

OBJECTIVES

The FloTrac Vigileo (FTV) estimates cardiac output (CO) on the basis of an uncalibrated arterial pressure waveform. To assess the ability of the third-generation of FTV (v.3.02) to track changes in CO following norepinephrine dose adjustment in patients with septic shock, we performed a comparative study using Doppler echocardiography (DE).

STUDY DESIGN

Prospective observational study.

PATIENTS

We prospectively included 20 mechanically ventilated patients receiving norepinephrine and monitored with the FTV. Five minutes after each change in norepinephrine dose (decided by the attending physician), CO was measured simultaneously with the FTV (CO(FTV)) and DE (CO(DE)). The changes in CO were compared. ROC curves were built to assess the ability of FTV to detect significant changes in CO(DE) of at least 15%.

RESULTS

Ninety pairs of CO variations measurements were made. The intertechnique correlation coefficient for changes in CO of at least 15% was r=0.59; P=0.0009. The AUC of a ROC curve built to test the FTV's ability to detect a CO(DE) increase of 15% or more was 0.783 (±0.083) (P=0.005). A CO(FTV) threshold value of 15% had a sensitivity of 54% (25-81) and a specificity of 87% (77-94). For a CO(DE) decrease of 15% or more, the ROC curve had an AUC of 0.616 (±0.075) (P=0.12) and a CO(FTV) threshold value of 13% yielded a sensitivity of 53% (27-79) and a specificity of 72% (60-82).

CONCLUSIONS

The FTV was unable to accurately track changes in CO following norepinephrine dose adjustments in critically ill patients with septic shock.

Optimization of preload in severe sepsis and septic shock

In sepsis both under- and overresuscitation are associated with increased morbidity and mortality. Moreover, sepsis can be complicated by myocardial dysfunction, and only half of the critically ill patients exhibit preload responsiveness. It is of paramount importance to accurately, safely, and rapidly determine and optimize preload during resuscitation. Traditional methods of determining preload based on measurement of pressure in a heart chamber or volume of a heart chamber ("static" parameters) are inaccurate and should be abandoned in favor of determining preload responsiveness by using one of the "dynamic parameters" based on respiratory variation in the venous or arterial circulation or based on change in stroke volume in response to an endogenous or exogenous volume challenge. The recent development and validation of a number of noninvasive technologies now allow us to optimize preload in an accurate, safe, rapid and, cost-effective manner.

Pulse pressure variation and prediction of fluid responsiveness in patients ventilated with low tidal volumes

OBJECTIVE

To determine the utility of pulse pressure variation (ΔRESP PP) in predicting fluid responsiveness in patients ventilated with low tidal volumes (V T) and to investigate whether a lower ΔRESP PP cut-off value should be used when patients are ventilated with low tidal volumes.

METHOD

This cross-sectional observational study included 37 critically ill patients with acute circulatory failure who required fluid challenge. The patients were sedated and mechanically ventilated with a V T of 6-7 ml/kg ideal body weight, which was monitored with a pulmonary artery catheter and an arterial line. The mechanical ventilation and hemodynamic parameters, including ΔRESP PP, were measured before and after fluid challenge with 1,000 ml crystalloids or 500 ml colloids. Fluid responsiveness was defined as an increase in the cardiac index of at least 15%. ClinicalTrial.gov: NCT01569308.

RESULTS

A total of 17 patients were classified as responders. Analysis of the area under the ROC curve (AUC) showed that the optimal cut-off point for ΔRESP PP to predict fluid responsiveness was 10% (AUC = 0.74). Adjustment of the ΔRESP PP to account for driving pressure did not improve the accuracy (AUC = 0.76). A ΔRESP PP ≥ 10% was a better predictor of fluid responsiveness than central venous pressure (AUC = 0.57) or pulmonary wedge pressure (AUC = 051). Of the 37 patients, 25 were in septic shock. The AUC for ΔRESP PP ≥ 10% to predict responsiveness in patients with septic shock was 0.484 (sensitivity, 78%; specificity, 93%).

CONCLUSION

The parameter D RESP PP has limited value in predicting fluid responsiveness in patients who are ventilated with low tidal volumes, but a ΔRESP PP>10% is a significant improvement over static parameters. A ΔRESP PP ≥ 10% may be particularly useful for identifying responders in patients with septic shock.

Respiratory variations of R-wave amplitude in lead II are correlated with stroke volume variations evaluated by transesophageal Doppler echocardiography

OBJECTIVE

The authors hypothesized that variations in electrocardiographically derived R-wave amplitude might be correlated with mechanical ventilation-induced variations in stroke volume as determined by transesophageal echocardiography.

DESIGN

Observational prospective study.

SETTING

Single university hospital.

PARTICIPANTS

Thirty-four patients undergoing coronary artery bypass surgery.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Respiratory R-wave variations in lead II (ΔRII) were correlated with aortic velocity time integral variations (r = 0.82, p < 0.0001). Respiratory R-wave variations in leads III and aVF and pulse pressure variation also were correlated with aortic velocity time integral variations (r = 0.49, p = 0.015; r = 0.61, p = 0.0016; and r = 0.72, p < 0.0001, respectively). R-wave respiratory variations in lead V(5) were not correlated with aortic velocity time integral variations. ΔRII was correlated with pulse pressure variation (r = 0.71, p < 0.0001). A ΔRII cutoff value of 15% accurately predicted stroke volume variations >15%, with a specificity of 92%, a sensitivity of 86%, a positive likelihood ratio of 11.1, a negative likelihood ratio of 0.15, a positive predictive value of 95%, and a negative predictive value of 80%.

CONCLUSIONS

ΔRII is correlated with stroke volume variations as determined by transesophageal echocardiography in mechanically ventilated patients and can identify the stroke volume variation cutoff of 15%, previously determined to be the cutoff for volume responsiveness.

Hemodynamic consequences of auto-PEEP

Auto-positive end-expiratory pressure (PEEP) is a common but frequently unrecognized problem in critically ill patients. It has important physiologic consequences and can cause shock and cardiac arrest. Treatment consists of relieving expiratory airflow obstruction and reducing minute ventilation delivered by positive pressure ventilation. Sedation and fluid management are important adjunctive therapies. This analytic review discusses the prevalence, pathophysiology, and hemodynamic consequences of auto-PEEP and an approach to its treatment.

Evaluation of fluid responsiveness: is photoplethysmography a noninvasive alternative?

Background. Goal-directed fluid therapy reduces morbidity and mortality in various clinical settings. Respiratory variations in photoplethysmography are proposed as a noninvasive alternative to predict fluid responsiveness during mechanical ventilation. This paper aims to critically evaluate current data on the ability of photoplethysmography to predict fluid responsiveness. Method. Primary searches were performed in PubMed, Medline, and Embase on November 10, 2011. Results. 14 papers evaluating photoplethysmography and fluid responsiveness were found. Nine studies calculated areas under the receiver operating characteristic curves for ΔPOP (>0.85 in four, 0.75–0.85 in one, and <0.75 in four studies) and seven for PVI (values ranging from 0.54 to 0.98). Correlations between ΔPOP/PVI and ΔPP/other dynamic variables vary substantially. Conclusion. Although photoplethysmography is a promising technique, predictive values and correlations with other hemodynamic variables indicating fluid responsiveness vary substantially. Presently, it is not documented that photoplethysmography is adequately valid and reliable to be included in clinical practice for evaluation of fluid responsiveness.

Advanced hemodynamic monitoring: principles and practice in neurocritical care

Advanced hemodynamic monitoring is necessary for many patients with acute brain and/or spinal cord injury. Optimizing cerebral and systemic physiology requires multi-organ system function monitoring. Hemodynamic manipulations are cardinal among interventions to regulate cerebral perfusion pressure and cerebral blood flow. The pulmonary artery catheter is not any more the sole tool available; less invasive and potentially more accurate methodologies have been developed and employed in the operating room and among diverse critically ill populations. These include transpulmonary thermodilution, arterial pressure pulse contour, and waveform analysis and bedside critical care ultrasound. A thorough understanding of hemodynamics and of the available monitoring modalities is an essential skill for the neurointensivist.

Hemodynamic changes during a deep inspiration maneuver predict fluid responsiveness in spontaneously breathing patients

Objective. We hypothesized that the hemodynamic response to a deep inspiration maneuver (DIM) indicates fluid responsiveness in spontaneously breathing (SB) patients. Design. Prospective study. Setting. ICU of a general hospital. Patients. Consecutive nonintubated patients without mechanical ventilation, considered for volume expansion (VE). Intervention. We assessed hemodynamic status at baseline and after VE. Measurements and Main Results. We measured radial pulse pressure (PP) using an arterial catheter and peak velocity of femoral artery flow (VF) using continuous Doppler. Changes in PP and VF induced by a DIM (ΔPPdim and ΔVFdim) were calculated in 23 patients. ΔPPdim and ΔVFdim ≥12% predicted responders to VE with sensitivity of 90% and specificity of 100%. Conclusions. In a restricted population of SB patients with severe sepsis or acute pancreatitis, ΔPPdim and ΔVFdim are accurate indices for predicting fluid responsiveness. These results should be confirmed in a larger population before validating their use in current practice.

Year in review 2010: Critical Care--Cardiology

We review key research papers in cardiology and intensive care published during 2010 in Critical Care and quote related studies published in other journals if appropriate. Papers were grouped into the following categories: cardiovascular therapies, biomarkers, hemodynamic monitoring, cardiovascular diseases, and microcirculation.

Photoplethysmographic and pulse pressure variations during abdominal surgery

BACKGROUND

Respiratory variations in pulse pressure (ΔPP) predict fluid responsiveness during mechanical ventilation. Variations in pulse oximetry plethysmography amplitude (ΔPOP) are proposed as a non-invasive alternative. Large variations in ΔPOP and poor agreement between ΔPP and ΔPOP are found in intensive care unit patients. General anaesthesia is suggested to reduce variability of ΔPOP and improve agreement between the variables. We evaluated the variability of the agreement between and the diagnostic values of ΔPP and ΔPOP during ongoing open abdominal surgery. The variability of diagnostic methods in specific clinical conditions is important, as this reflects the stability over time during which clinical decisions are made.

METHODS

Observational study during open abdominal surgery in general anaesthesia. ΔPP and ΔPOP were calculated semi-automatically from recording periods of approximately 5 min both before and after fluid challenges. Fluid responsiveness was evaluated by changes in stroke volume (oesophageal Doppler) after 250 ml colloid.

RESULTS

Thirty-four fluid challenges were performed in 25 patients. Variance both within registration periods and between patients were significantly larger for ΔPOP than for ΔPP (54.1% vs. 22.1% and 69.6% vs. 22.6%, respectively, both P < 0.001). Limits of agreement with a regression-based correction were ± 13.9%. Areas under receiver operating characteristics curves for fluid responsiveness were 0.67 for ΔPP and 0.72 for ΔPOP.

CONCLUSIONS

Analysis of raw signals during open abdominal surgery documents that the variance of ΔPOP is larger than of ΔPP, with wide limits of agreement between ΔPP and ΔPOP. The diagnostic values of ΔPP and ΔPOP are relatively poor.

Passive leg raising can predict fluid responsiveness in patients placed on venovenous extracorporeal membrane oxygenation

Introduction

In ICUs, fluid administration is frequently used to treat hypovolaemia. Because volume expansion (VE) can worsen acute respiratory distress syndrome (ARDS) and volume overload must be avoided, predictive indicators of fluid responsiveness are needed. The purpose of this study was to determine whether passive leg raising (PLR) can be used to predict fluid responsiveness in patients with ARDS treated with venovenous extracorporeal membrane oxygenation (ECMO).

Methods

We carried out a prospective study in a university hospital surgical ICU. All patients with ARDS treated with venovenous ECMO and exhibiting clinical and laboratory signs of hypovolaemia were enrolled. We measured PLR-induced changes in stroke volume (ΔPLRSV) and cardiac output (ΔPLRCO) using transthoracic echocardiography. We also assessed PLR-induced changes in ECMO pump flow (ΔPLRPO) and PLR-induced changes in ECMO pulse pressure (ΔPLRPP) as predictors of fluid responsiveness. Responders were defined by an increase in stroke volume (SV) > 15% after VE.

Results

Twenty-five measurements were obtained from seventeen patients. In 52% of the measurements (n = 13), SV increased by > 15% after VE (responders). The patients' clinical characteristics appeared to be similar between responders and nonresponders. In the responder group, PLR significantly increased SV, cardiac output and pump flow (P < 0.001). ΔPLRSV values were correlated with VE-induced SV variations (r² = 0.72, P = 0.0001). A 10% increased ΔPLRSV predicted fluid responsiveness with an area under the receiver operating characteristic curve (AUC) of 0.88 ± 0.07 (95% confidence interval (CI₉₅): 0.69 to 0.97; P < 0.0001), 62% sensitivity and 92% specificity. On the basis of AUCs of 0.62 ± 0.11 (CI₉₅: 0.4 to 0.8; P = 0.31) and 0.53 ± 0.12 (CI₉₅: 0.32 to 0.73, P = 0.79), respectively, ΔPLRPP and ΔPLRPO did not predict fluid responsiveness.

Conclusions

In patients treated with venovenous ECMO, a > 10% ΔPLRSV may predict fluid responsiveness. ΔPLRPP and ΔPLRPO cannot predict fluid responsiveness.

Detection of right ventricular insufficiency and guidance of volume therapy are facilitated by simultaneous monitoring of static and functional preload parameters

OBJECTIVE

Acute right ventricular failure (RVF) is a life-threatening condition. This study investigated whether the combination of central venous pressure (CVP) and left ventricular functional preload parameters, such as stroke volume variation (SVV) and pulse pressure variation (PPV), can be used for the detection of acute RVF and for guidance of volume therapy.

DESIGN AND SETTING

Experimental study in a university laboratory.

PARTICIPANTS

Fifteen anesthetized and ventilated pigs.

MEASUREMENTS AND MAIN RESULTS

For the induction of RVF, mean pulmonary artery pressure (MPAP) was increased by 50% with a continuous infusion of a thromboxane-A(2) analog (U46619). Then, blood removal (300 mL) and retransfusion (blood 200 mL + colloid solution 200 mL) were performed. An analysis of volume responders and nonresponders was implemented. Increasing MPAP (25.1 to 37.4 mmHg) led to decreases in mean arterial pressure (72.2 to 60.1 mmHg) and cardiac output (2.8 to 2.3 L/min, p < 0.05). CVP (11.3 to 12.6 mmHg), PPV (13% to 17%), and SVV (11 to 14%) increased significantly (p < 0.05). During volume removal, MPAP (37.4 to 34.1 mmHg), mean arterial pressure (60.1 to 53.2 mmHg), and cardiac output (2.3 to 2.1 L/min) decreased (p < 0.05), whereas PPV and SVV remained unchanged. During volume loading, CVP increased in volume responders and nonresponders; however, PPV decreased in responders only.

CONCLUSIONS

Increases of CVP and SVV or PPV are suspicious for RVF. However, SVV and PPV fail to predict volume responsiveness in RVF. Changes in SVV and PPV during a volume-loading maneuver can be used to assess volume responsiveness.

Physiologic and Clinical Principles behind Noninvasive Resuscitation Techniques and Cardiac Output Monitoring

Clinical assessment and vital signs are poor predictors of the overall hemodynamic state. Optimal measurement of the response to fluid resuscitation and hemodynamics has previously required invasive measurement with radial and pulmonary artery catheterization. Newer noninvasive resuscitation technology offers the hope of more accurately and safely monitoring a broader range of critically ill patients while using fewer resources. Fluid responsiveness, the cardiac response to volume loading, represents a dynamic method of improving upon the assessment of preload when compared to static measures like central venous pressure. Multiple new hemodynamic monitors now exist that can noninvasively report cardiac output and oxygen delivery in a continuous manner. Proper assessment of the potential future role of these techniques in resuscitation requires understanding the underlying physiologic and clinical principles, reviewing the most recent literature examining their clinical validity, and evaluating their respective advantages and limitations.

Impact of norepinephrine on the relationship between pleth variability index and pulse pressure variations in ICU adult patients

INTRODUCTION

Pleth Variability Index (PVI) is an automated and continuous calculation of respiratory variations in the perfusion index. PVI correlates well with respiratory variations in pulse pressure (ΔPP) and is able to predict fluid responsiveness in the operating room. ICU patients may receive vasopressive drugs, which modify vascular tone and could affect PVI assessment. We hypothesized that the correlation between PVI and ΔPP and the ability of PVI to identify patients with ΔPP > 13% is dependent on norepinephrine (NE) use.

METHODS

67 consecutive mechanically ventilated patients in the ICU were prospectively included. Three were excluded. The administration and dosage of NE, heart rate, mean arterial pressure, PVI and ΔPP were measured simultaneously.

RESULTS

In all patients, the correlation between PVI and ΔPP was weak (r2 = 0.21; p = 0.001). 23 patients exhibited a ΔPP > 13%. A PVI > 11% was able to identify patients with a ΔPP > 13% with a sensitivity of 70% (95% confidence interval: 47%-87%) and a specificity of 71% (95% confidence interval: 54%-84%). The area under the curve was 0.80 ± 0.06. 35 patients (53%) received norepinephrine (NE(+)). In NE(+) patients, PVI and ΔPP were not correlated (r2 = 0.04, p > 0.05) and a PVI > 10% was able to identify patients with a ΔPP > 13% with a sensitivity of 58% (95% confidence interval: 28%-85%) and a specificity of 61% (95% confidence interval:39%-80%). The area under the ROC (receiver operating characteristics) curve was 0.69 ± 0.01. In contrast, NE(-) patients exhibited a correlation between PVI and ΔPP (r2 = 0.52; p < 0.001) and a PVI > 10% was able to identify patients with a ΔPP > 13% with a sensitivity of 100% (95% confidence interval: 71%-100%) and a specificity of 72% (95% confidence interval: 49%-90%). The area under the ROC curve was 0.93 ± 0.06 for NE(-) patients and was significantly higher than the area under the ROC curve for NE(+) patients (p = 0.02).

CONCLUSIONS

Our results suggest that in mechanically ventilated adult patients, NE alters the correlation between PVI and ΔPP and the ability of PVI to predict ΔPP > 13% in ICU patients.

Monitoring in pediatric cardiac critical care: a worldwide perspective

Our ability to directly monitor the mechanisms that govern cellular function, oxygen use, and survival is minimal. Therefore, in critically ill children, surrogate markers are used to try to detect evolving or established hypoxia. These surrogate markers are best used in combination and are complementary to clinical examination. Regardless of resource limitations, we propose that the availability of certain monitoring tools form a standard of care without which pediatric cardiac critical care cannot be safely or optimally provided. These tools include standard invasive hemodynamic monitoring with electrocardiography, lactate measurement, central venous oxygen saturation, and echocardiography. Ultimately, monitoring is only useful when the clinician observes a specific value or trend and has the expertise to act appropriately.

The ability of pulse pressure variations obtained with CNAP™ device to predict fluid responsiveness in the operating room

BACKGROUND

Respiratory-induced pulse pressure variations obtained with an arterial line (ΔPP(ART)) indicate fluid responsiveness in mechanically ventilated patients. The Infinity® CNAP™ SmartPod® (Dräger Medical AG & Co. KG, Lübeck, Germany) provides noninvasive continuous beat-to-beat arterial blood pressure measurements and a near real-time pressure waveform. We hypothesized that respiratory-induced pulse pressure variations obtained with the CNAP system (ΔPP(CNAP)) predict fluid responsiveness as well as ΔPP(ART) predicts fluid responsiveness in mechanically ventilated patients during general anesthesia.

METHODS

Thirty-five patients undergoing vascular surgery were studied after induction of general anesthesia. Stroke volume (SV) measured with the Vigileo™/FloTrac™ (Edwards Lifesciences, Irvine, CA), ΔPP(ART), and ΔPP(CNAP) were recorded before and after intravascular volume expansion (VE) (500 mL of 6% hydroxyethyl starch 130/0.4). Subjects were defined as responders if SV increased by ≥15% after VE.

RESULTS

Twenty patients responded to VE and 15 did not. The correlation coefficient between ΔPP(ART) and ΔPP(CNAP) before VE was r = 0.90 (95% confidence interval [CI] = 0.84-0.96; P < 0.0001). Before VE, ΔPP(ART) and ΔPP(CNAP) were significantly higher in responders than in nonresponders (P < 0.0001). The values of ΔPP(ART) and ΔPP(CNAP) before VE were significantly correlated with the percent increase in SV induced by VE (respectively, r(2) = 0.50; P < 0.0001 and r(2) = 0.57; P < 0.0001). Before VE, a ΔPP(ART) >10% discriminated between responders and nonresponders with a sensitivity of 90% (95% CI = 69%-99%) and a specificity of 87% (95% CI = 60%-98%). The area under the receiver operating characteristic (ROC) curve was 0.957 ± 0.035 for ΔPP(ART). Before VE, a ΔPP(CNAP) >11% discriminated between responders and nonresponders with a sensitivity of 85% (95% CI = 62%-97%) and a specificity of 100% (95% CI = 78%-100%). The area under the ROC curve was 0.942 ± 0.040 for ΔPP(CNAP). There was no significant difference between the area under the ROC curve for ΔPP(ART) and ΔPP(CNAP).

CONCLUSIONS

A value of ΔPP(CNAP) >11% has a sensitivity of at least 62% in predicting preload-dependent responders to VE in mechanically ventilated patients during general anesthesia.

Echocardiography in the sepsis syndromes

Purpose of the review

Non-invasiveness and instantaneous diagnostic capability are prominent features of the use of echocardiography in critical care. Sepsis and septic shock represent complex situations where early hemodynamic assessment and support are among the keys to therapeutic success. In this review, we discuss the range of applications of echocardiography in the management of the septic patient, and propose an echocardiography-based goal-oriented hemodynamic approach to septic shock.

Recent findings

Echocardiography can play a key role in the critical septic patient management, by excluding cardiac causes for sepsis, and mostly by guiding hemodynamic management of those patients in whom sepsis reaches such a severity to jeopardize cardiovascular function. In recent years, there have been both increasing evidence and diffusion of the use of echocardiography as monitoring tool in the patients with hemodynamic compromise. Also thanks to echocardiography, the features of the well-known sepsis-related myocardial dysfunction have been better characterized. Furthermore, many of the recent echocardiographic indices of volume responsiveness have been validated in populations of septic shock patients.

Conclusion

Although not proven yet in terms of patient outcome, echocardiography can be regarded as an ideal monitoring tool in the septic patient, as it allows (a) first line differential diagnosis of shock and early recognition of sepsis-related myocardial dysfunction; (b) detection of pre-existing cardiac pathology, that yields precious information in septic shock management; (c) comprehensive hemodynamic monitoring through a systematic approach based on repeated bedside assessment; (d) integration with other monitoring devices; and (e) screening for cardiac source of sepsis.

Respiratory pulse pressure variation fails to predict fluid responsiveness in acute respiratory distress syndrome

INTRODUCTION

Fluid responsiveness prediction is of utmost interest during acute respiratory distress syndrome (ARDS), but the performance of respiratory pulse pressure variation (ΔRESPPP) has scarcely been reported. In patients with ARDS, the pathophysiology of ΔRESPPP may differ from that of healthy lungs because of low tidal volume (Vt), high respiratory rate, decreased lung and sometimes chest wall compliance, which increase alveolar and/or pleural pressure. We aimed to assess ΔRESPPP in a large ARDS population.

METHODS

Our study population of nonarrhythmic ARDS patients without inspiratory effort were considered responders if their cardiac output increased by >10% after 500-ml volume expansion.

RESULTS

Among the 65 included patients (26 responders), the area under the receiver-operating curve (AUC) for ΔRESPPP was 0.75 (95% confidence interval (CI95): 0.62 to 0.85), and a best cutoff of 5% yielded positive and negative likelihood ratios of 4.8 (CI95: 3.6 to 6.2) and 0.32 (CI95: 0.1 to 0.8), respectively. Adjusting ΔRESPPP for Vt, airway driving pressure or respiratory variations in pulmonary artery occlusion pressure (ΔPAOP), a surrogate for pleural pressure variations, in 33 Swan-Ganz catheter carriers did not markedly improve its predictive performance. In patients with ΔPAOP above its median value (4 mmHg), AUC for ΔRESPPP was 1 (CI95: 0.73 to 1) as compared with 0.79 (CI95: 0.52 to 0.94) otherwise (P = 0.07). A 300-ml volume expansion induced a ≥ 2 mmHg increase of central venous pressure, suggesting a change in cardiac preload, in 40 patients, but none of the 28 of 40 nonresponders responded to an additional 200-ml volume expansion.

CONCLUSIONS

During protective mechanical ventilation for early ARDS, partly because of insufficient changes in pleural pressure, ΔRESPPP performance was poor. Careful fluid challenges may be a safe alternative.

Pulse pressure variation and stroke volume variation during increased intra-abdominal pressure: an experimental study

INTRODUCTION

The aim of this study was to evaluate dynamic indices of fluid responsiveness in a model of intra-abdominal hypertension.

METHODS

Nine mechanically-ventilated pigs underwent increased intra-abdominal pressure (IAP) by abdominal banding up to 30 mmHg and then fluid loading (FL) at this IAP. The same protocol was carried out in the same animals made hypovolemic by blood withdrawal. In both volemic conditions, dynamic indices of preload dependence were measured at baseline IAP, at 30 mmHg of IAP, and after FL. Dynamic indices involved respiratory variations in stroke volume (SVV), pulse pressure (PPV), and systolic pressure (SPV, %SPV and Δdown). Stroke volume (SV) was measured using an ultrasound transit-time flow probe placed around the aortic root. Pigs were considered to be fluid responders if their SV increased by 15% or more with FL. Indices of fluid responsiveness were compared with a Mann-Whitney U test. Then, receiver operating characteristic (ROC) curves were generated for these parameters, allowing determination of the cut-off values by using Youden's method.

RESULTS

Five animals before blood withdrawal and all animals after blood withdrawal were fluid responders. Before FL, SVV (78 ± 19 vs 42 ± 17%), PPV (64 ± 18 vs 37 ± 15%), SPV (24 ± 5 vs 18 ± 3 mmHg), %SPV (24 ± 4 vs 17 ± 3%) and Δdown (13 ± 5 vs 6 ± 4 mmHg) were higher in responders than in non-responders (P < 0.05). Areas under ROC curves were 0.93 (95% confidence interval: 0.80 to 1.06), 0.89 (0.70 to 1.07), 0.90 (0.74 to 1.05), 0.92 (0.78 to 1.06), and 0.86 (0.67 to 1.06), respectively. Threshold values discriminating responders and non-responders were 67% for SVV and 41% for PPV.

CONCLUSIONS

In intra-abdominal hypertension, respiratory variations in stroke volume and arterial pressure remain indicative of fluid responsiveness, even if threshold values identifying responders and non-responders might be higher than during normal intra-abdominal pressure. Further studies are required in humans to determine these thresholds in intra-abdominal hypertension.

The passive leg-raising maneuver cannot accurately predict fluid responsiveness in patients with intra-abdominal hypertension

OBJECTIVES

The passive leg-raising maneuver is a reversible fluid-loading procedure used to predict fluid responsiveness in mechanically ventilated patients. The aim of the present study was to determine whether intra-abdominal hypertension (which impairs venous return) reduces the ability of passive leg raising to detect fluid responsiveness in critically ill ventilated patients.

DESIGN

A prospective study.

SETTING

The medical and surgical intensive care unit of a university medical center.

PATIENTS

Forty-one mechanically ventilated patients with a pulse pressure variation of >12%.

INTERVENTIONS

Stroke volume was continuously monitored by esophageal Doppler. Intra-abdominal pressure was measured via bladder pressure. After a passive leg-raising maneuver and a return to baseline, fluid loading with 500 mL of saline was performed. Hemodynamic parameters were recorded at each step. Nonresponders to volume loading were not analyzed (10 patients). Thirty-one patients were classified into two groups according to their response to passive leg raising: responders to passive leg raising (at least a 12% increase in stroke volume) and nonresponders to passive leg raising.

MEASUREMENTS AND MAIN RESULTS

Sixteen patients (52%) were responders to passive leg raising, and 15 (48%) were nonresponders to passive leg raising (i.e., false negatives). At baseline, the median intra-abdominal pressure was significantly higher in the nonresponders to passive leg raising than in the responders to passive leg raising (20 [6.5] vs. 11.5 [5.5], respectively; p < .0001). The area under the receiver-operating characteristic curve was 0.969 +/- 0.033. An intra-abdominal pressure cutoff value of 16 mm Hg discriminated between responders to passive leg raising and nonresponders to passive leg raising with a sensitivity of 100% (confidence interval, 78-100) and a specificity of 87.5% (confidence interval, 61.6-98.1). An intra-abdominal pressure of > or =16 mm Hg was the only independent predictor of nonresponse to passive leg raising in a multivariate analysis (odds ratio, 2.6 [confidence interval, 1.1-6.6]; p = .04).

CONCLUSIONS

An intra-abdominal pressure of > or =16 mm Hg seems to be responsible for false negatives to passive leg raising. Hence, the intra-abdominal pressure should be measured in critically ill ventilated patients, especially before performing passive leg raising.

Pulse pressure variation and volume responsiveness during acutely increased pulmonary artery pressure: an experimental study

Introduction

We found that pulse pressure variation (PPV) did not predict volume responsiveness in patients with increased pulmonary artery pressure. This study tests the hypothesis that PPV does not predict fluid responsiveness during an endotoxin-induced acute increase in pulmonary artery pressure and right ventricular loading.

Methods

Pigs were subjected to endotoxemia (0.4 μg/kg/hour lipopolysaccharide), followed by volume expansion, subsequent hemorrhage (20% of estimated blood volume), retransfusion, and additional stepwise volume loading until cardiac output did not increase further (n = 5). A separate control group (n = 7) was subjected to bleeding, retransfusion, and volume expansion without endotoxemia. Systemic hemodynamics were measured at baseline and after each intervention, and PPV was calculated offline. Prediction of fluid-challenge-induced stroke volume increase by PPV was analyzed using receiver operating characteristic (ROC) curves.

Results

Sixty-eight volume challenges were performed in endotoxemic animals (22 before and 46 after hemorrhage), and 51 volume challenges in the controls. Endotoxin infusion resulted in an acute increase in pulmonary artery and central venous pressure and a decrease in stroke volume (all P < 0.05). In endotoxemia, 68% of volume challenges before hemorrhage increased the stroke volume by > 10%, but PPV did not predict fluid responsiveness (area under the ROC curve = 0.604, P = 0.461). After hemorrhage in endotoxemia, stroke volume increased in 48% and the predictive value of PPV improved (area under the ROC curve for PPV = 0.699, P = 0.021). In controls after hemorrhage, stroke volume increased in 67% of volume challenges and PPV was a predictor of fluid responsiveness (area under the ROC curve = 0.790, P = 0.001).

Conclusions

Fluid responsiveness cannot be predicted with PPV during acute pulmonary hypertension in porcine endotoxemia. Even following severe hemorrhage during endotoxemia, the predictive value of PPV is marginal.

Pulse-pressure variation and hemodynamic response in patients with elevated pulmonary artery pressure: a clinical study

Introduction

Pulse-pressure variation (PPV) due to increased right ventricular afterload and dysfunction may misleadingly suggest volume responsiveness. We aimed to assess prediction of volume responsiveness with PPV in patients with increased pulmonary artery pressure.

Methods

Fifteen cardiac surgery patients with a history of increased pulmonary artery pressure (mean pressure, 27 ± 5 mm Hg (mean ± SD) before fluid challenges) and seven septic shock patients (mean pulmonary artery pressure, 33 ± 10 mm Hg) were challenged with 200 ml hydroxyethyl starch boli ordered on clinical indication. PPV, right ventricular ejection fraction (EF) and end-diastolic volume (EDV), stroke volume (SV), and intravascular pressures were measured before and after volume challenges.

Results

Of 69 fluid challenges, 19 (28%) increased SV > 10%. PPV did not predict volume responsiveness (area under the receiver operating characteristic curve, 0.555; P = 0.485). PPV was ≥13% before 46 (67%) fluid challenges, and SV increased in 13 (28%). Right ventricular EF decreased in none of the fluid challenges, resulting in increased SV, and in 44% of those in which SV did not increase (P = 0.0003). EDV increased in 28% of fluid challenges, resulting in increased SV, and in 44% of those in which SV did not increase (P = 0.272).

Conclusions

Both early after cardiac surgery and in septic shock, patients with increased pulmonary artery pressure respond poorly to fluid administration. Under these conditions, PPV cannot be used to predict fluid responsiveness. The frequent reduction in right ventricular EF when SV did not increase suggests that right ventricular dysfunction contributed to the poor response to fluids.