Joris Lemson

Dynamic indices do not predict volume responsiveness in routine clinical practice

BACKGROUND Dynamic indices, including pulse pressure, systolic pressure, and stroke volume variation (PPV, SPV, and SVV), are accurate predictors of fluid responsiveness under strict conditions, for example, controlled mechanical ventilation using conventional tidal volumes (TVs) in the absence of cardiac arrhythmias. However, in routine clinical practice, these prerequisites are not always met. We evaluated the effect of regularly used ventilator settings, different calculation methods, and the presence of cardiac arrhythmias on the ability of dynamic indices to predict fluid responsiveness in sedated, mechanically ventilated patients. METHODS We prospectively evaluated 47 fluid challenges in 29 consecutive cardiac surgery patients. Patients were divided into different groups based on TV. Dynamic indices were calculated in various ways: calculation over 30 s, breath-by-breath (with and without excluding arrhythmias), and with correction for TV. RESULTS The predictive value was optimal in the group ventilated with TVs >7 ml kg(-1) with correction for TV, calculated breath-by-breath, and with exclusion of arrhythmias [area under the curve (AUC)=0.95, 0.93, and 0.90 for PPV, SPV, and SVV, respectively]. Including patients ventilated with lower TVs decreased the predictive value of all dynamic indices, while calculating dynamic indices over 30 s and not excluding cardiac arrhythmias further reduced the AUC to 0.51, 0.63, and 0.51 for PPV, SPV, and SVV, respectively. CONCLUSIONS PPV, SPV, and SVV are the only reliable predictors of fluid responsiveness under strict conditions. In routine clinical practice, factors including low TV, cardiac arrhythmias, and the calculation method can substantially reduce their predictive value.

Validation of transpulmonary thermodilution cardiac output measurement in a pediatric animal model

Objective: This study was undertaken to validate the transpulmonary thermodilution cardiac output measurement (COTPTD) in a controlled newborn animal model under various hemodynamic conditions with special emphasis on low cardiac output. Design: Prospective, experimental, pediatric animal study. Setting: Animal laboratory of a university hospital. Subjects: Twelve lambs. Interventions: We studied 12 lambs under various hemodynamic conditions. Cardiac output was measured using the transpulmonary thermodilution technique with central venous injections of ice-cold saline. An ultrasound transit time perivascular flow probe around the main pulmonary artery served as the standard reference measurement (COUFP). During the experiment, animals were resuscitated from hemodynamic shock using fluid boluses. Cardiac output measurements were performed throughout the experiment. Measurements and Main Results: The correlation coefficient between COTPTD and COUFP was .97 (95% confidence interval .94–.98, p < .0001). Bland-Altman analysis showed a mean bias of 0.19 L/min with limits of agreement of −0.04 and 0.43 L/min (12.0% and ±14.7%, respectively). The correlation coefficient between changes in COTPTD and COUFP during volume loading was .95 (95% confidence interval .91–.96, p < .0001). There was a significant correlation between changes in global end-diastolic volume and changes in stroke volume (r = .59) but not between changes in central venous pressure and changes in stroke volume (r = .03). Conclusions: The transpulmonary thermodilution technique is a reliable method of measuring cardiac output in newborn animals. It is also capable of tracking changes in cardiac output.

Non-invasive measurement of pulse pressure variation and systolic pressure variation using a finger cuff corresponds with intra-arterial measurement

BACKGROUND Pulse pressure variation (PPV) and systolic pressure variation (SPV) are reliable predictors of fluid responsiveness in patients undergoing controlled mechanical ventilation. Currently, PPV and SPV are measured invasively and it is unknown if an arterial pressure (AP) signal obtained with a finger cuff can be used as an alternative. The aim of this study was to validate PPV and SPV measured using a finger cuff. METHODS Patients receiving mechanical ventilation under sedation after cardiac artery bypass graft (CABG) surgery were included after arrival on the intensive care unit. AP was measured invasively in the radial artery and non-invasively using the finger cuff of the Nexfin™ monitor. I.V. fluid challenges were administered according to clinical need. The mean value of PPV and SVV was calculated before and after administration of a fluid challenge. Agreement of the calculated PPV and SPV from both methods was assessed using the Bland-Altman analysis. RESULTS Nineteen patients were included and 28 volume challenges were analysed. Correlation between the two methods for PPV and SPV [mean (sd)=6.9 (4.3)% and 5.3 (2.6)%, respectively] was r=0.96 (P<0.0001) and r=0.95 (P<0.0001), respectively. The mean bias was -0.95% for PPV and -0.22% for SPV. Limits of agreement were -4.3% and 2.4% for PPV and -2.2% and 1.7% for SPV. The correlation between changes in PPV and SPV as a result of volume expansion measured by the two different methods was r=0.88 (P<0.0001) and r=0.87 (P<0.0001), respectively. CONCLUSIONS In patients receiving controlled mechanical ventilation after CABG, PPV and SPV can be measured reliably non-invasively using the inflatable finger cuff of the Nexfin™ monitor.

Cardiac output monitoring in pediatric patients

Cardiac output (CO) measurement is becoming increasingly important in the field of pediatric intensive care medicine and pediatric anesthesia. In the past few decades, various new technologies have been developed for the measurement of CO. Some of these methods are applicable to pediatric patients and some are already being used in children. The devices and methods have their advantages and limitations and, therefore, it is difficult for the clinician to decide which technique should be used. This article focuses on the currently available minimally invasive and noninvasive monitoring devices for CO measurement in children. A brief explanation of the technical aspects of each method and clinical use will be followed by the knowledge gained from infant animal and clinical pediatric studies. The goal of this article is to give an update of the various CO measurement technologies in children.

Advanced Hemodynamic Monitoring in Critically Ill Children

Circulatory shock is an important cause of pediatric morbidity and mortality and requires early recognition and prompt institution of adequate treatment protocols. Unfortunately, the hemodynamic status of the critically ill child is poorly reflected by physical examination, heart rate, blood pressure, or laboratory blood tests. Advanced hemodynamic monitoring consists, among others, of measuring cardiac output, predicting fluid responsiveness, calculating systemic oxygen delivery in relation to oxygen demand, and quantifying (pulmonary) edema. We discuss here the potential value of these hemodynamic monitoring technologies in relation to pediatric physiology.

Extravascular lung water index measurement in critically ill children does not correlate with a chest x-ray score of pulmonary edema

IntroductionExtravascular lung water index (EVLWI) can be measured at the bedside using the transpulmonary thermodilution technique (TPTD). The goal of this study was to compare EVLWI values with a chest x-ray score of pulmonary edema and markers of oxygenation in critically ill children.MethodsThis was a prospective observational study in a pediatric intensive care unit of a university hospital. We included 27 critically ill children with an indication for advanced invasive hemodynamic monitoring. No specific interventions for the purpose of the study were carried out. Measurements included EVLWI and other relevant hemodynamic variables. Blood gas analysis, ventilator parameters, chest x-ray and TPTD measurements were obtained within a three-hour time frame. Two radiologists assessed the chest x-ray and determined a score for pulmonary edema.ResultsA total of 103 measurements from 24 patients were eligible for final analysis. Mean age was two years (range: two months to eight years). Median cardiac index was 4.00 (range: 1.65 to 10.85) l/min/m2. Median EVLWI was 16 (range: 6 to 31) ml/kg. The weighted kappa between the chest x-ray scores of the two radiologists was 0.53. There was no significant correlation between EVLWI or chest x-ray score and the number of ventilator days, severity of illness or markers of oxygenation. There was no correlation between EVLWI and the chest x-ray score. EVLWI was significantly correlated with age and length (r2 of 0.47 and 0.67 respectively).ConclusionsThe extravascular lung water index in critically ill children does not correlate with a chest x-ray score of pulmonary edema, nor with markers of oxygenation.

The reliability of continuous noninvasive finger blood pressure measurement in critically ill children.

INTRODUCTION: Continuous noninvasive arterial blood pressure can be measured in finger arteries using an inflatable finger cuff (FINAP) with a special device and has proven to be feasible and reliable in adults. We studied prototype pediatric finger cuffs and pediatric software to compare this blood pressure measurement with intraarterially measured blood pressure (IAP) in critically ill children. METHODS: We included sedated and mechanically ventilated children admitted to our pediatric intensive care unit. We performed simultaneous arterial blood pressure measurements during a relatively stable hemodynamic period and compared FINAP, IAP, and the noninvasive blood pressure oscillometric technique. We also compared IAP to a reconstruction of brachial pressure from finger pressure. RESULTS: Thirty-five children between 2 and 22 kg body weight were included. In total, 152 attempts to record a FINAP pressure were performed of which 4.6% were unsuccessful. When comparing FINAP to IAP, bias was −16.2, −7.7, and −10.2 mm Hg for systolic arterial blood pressure, diastolic arterial blood pressure, and mean arterial blood pressure. Limits of agreement (LOA) were respectively 26.1%, 30.1%, and 22.6%. When reconstruction of brachial pressure from finger pressure was compared to IAP, these results were −11.8, 0.6, and −0.9 mm Hg for bias and 21.7%, 8.9%, and 8.9% for LOA. When noninvasive blood pressure oscillometric technique was compared to IAP, the results were: −6.8, −0.9, and −3.8 mm Hg for bias and 18.2%, 38.6%, and 22.1% for LOA. CONCLUSION: Beta type continuous noninvasive arterial blood pressure monitoring using a finger cuff with brachial arterial waveform reconstruction seems reliable in hemodynamically stable critically ill children.

The “cross-talk phenomenon” in transpulmonary thermodilution is flow dependent.

Sir: Transpulmonary thermodilution (TPTD) is a reliable technique for measuring cardiac output in adults [1]. With the use of a thermistor-tipped arterial catheter and a monitoring device (PiCCOplus; Pulsion Medical Systems Munich, Germany) a temperature–dilution curve can be registered when an ice-cold solution is injected into a central venous line. Cardiac output is calculated according to the Stewart Hamilton equation. This method is also valid in children [2]. With the use of TPTD it is also possible to detect a right-to-left intra cardiac shunt because the TPTD curve becomes biphasic [3]. However, a biphasic curve can also occur if the injection port of the central venous line and the thermistor tipped arterial line are in close position. This is described as the “cross-talk phenomenon” [4]. We report that this “cross-talk phenomenon” is blood flow depen-

Extravascular lung water index and global end-diastolic volume index should be corrected in children.

PURPOSE The aim of the present study was to explain why extravascular lung water index (EVLWI) is higher and why global end-diastolic blood volume index (GEDVI) is lower in young children when measured with the PiCCO system (Pulsion, Munich, Germany). MATERIALS AND METHODS We pooled available data from literature from children concerning organ weight derived from autopsy studies and computed tomographic lung measurements. These data include age, height, body weight, body surface area (BSA), and lung and heart weights. For standard, age-dependent weight and height, we used published data from the World Health Organization. From the available data, we calculated the lung weight-to-body weight ratio, the heart weight-to-BSA ratio, and the end-diastolic volume-to-BSA ratio. We compared these ratios to body growth and development. RESULTS Lung weight develops more slowly and with less magnitude than does body weight. In addition, the (relatively) greater lung weight in younger children results in a higher amount of pulmonary blood volume. This explains the higher EVLWI in young children. End-diastolic blood volume and heart weight increase faster and are more pronounced compared with BSA. This explains the lower GEDVI in young children. We propose correction factors for comparing EVLWI and GEDVI with adult reference values. CONCLUSIONS Extravascular lung water index is higher and GEDVI is lower in young children because of changing organ-to-body weight relationships during growth.

Cardiac output can be measured with the transpulmonary thermodilution method in a paediatric animal model with a left-to-right shunt

BACKGROUND The transpulmonary thermodilution (TPTD) technique for measuring cardiac output (CO) has never been validated in the presence of a left-to-right shunt. METHODS In this experimental, paediatric animal model, nine lambs with a surgically constructed aorta-pulmonary left-to-right shunt were studied under various haemodynamic conditions. CO was measured with closed and open shunt using the TPTD technique (CO(TPTD)) with central venous injections of ice-cold saline. An ultrasound transit time perivascular flow probe around the main pulmonary artery served as the standard reference measurement (CO(MPA)). RESULTS Seven lambs were eligible for further analysis. Mean (sd) weight was 6.6 (1.6) kg. The mean CO(MPA) was 1.21 litre min(-1) (range 0.61-2.06 l min(-1)) with closed shunt and 0.93 litre min(-1) (range 0.48-1.45 litre min(-1)) with open shunt. The open shunt resulted in a mean Q(p)/Q(s) ratio of 1.8 (range 1.6-2.4). The bias between the two CO methods was 0.17 litre min(-1) [limits of agreement (LOA) of 0.27 litre min(-1)] with closed shunt and 0.14 litre min(-1) (LOA of 0.32 litre min(-1)) with open shunt. The percentage errors were 22% with closed shunt and 34% with open shunt. The correlation (r) between the two methods was 0.93 (P<0.001) with closed shunt and 0.86 (P<0.001) with open shunt. The correlation (r) between the two methods in tracking changes in CO (ΔCO) during the whole experiment was 0.94 (P<0.0001). CONCLUSIONS The TPTD technique is a feasible method of measuring CO in paediatric animals with a left-to-right shunt.