A Nusmeier

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.

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.

Validation of extravascular lung water measurement by transpulmonary thermodilution in a pediatric animal model

Objective: The measurement of extravascular lung water using the transpulmonary thermodilution technique enables the bedside quantification of the amount of pulmonary edema. Children have higher indexed to body weight values of extravascular lung water compared with adults. Transpulmonary thermodilution measurements of extravascular lung water in children have not yet been validated. The purpose of this study was to validate the extravascular lung water measurements with the transpulmonary thermodilution method over a wide range of lung water values in a pediatric animal model. Design: Experimental animal intervention study. Setting: Animal laboratory at the Radboud University Nijmegen, The Netherlands. Subjects: Eleven lambs. Intervention: Pulmonary edema was induced using a surfactant washout model. Measurements and Main Results: Between the lavages, extravascular lung water index was estimated using transpulmonary single and double indicator dilution. Two additional lambs were used to estimate extravascular lung water index in lungs without pulmonary edema. The final extravascular lung water index results were compared with the extravascular lung water index estimations by postmortem gravimetry (EVLWIG). The results were analyzed using both correlation and Bland-Altman statistics. Extravascular lung water index by transpulmonary thermodilution (EVLWITPTD) correlated significantly with either EVLWIG (r2 = 0.88) or with extravascular lung water index by transpulmonary double indicator dilution (EVLWITPDD) (r2 = 0.98). The mean bias with EVLWIG was 12.2 mL/kg (limits of agreement ± 10.9 mL/kg) and with EVLWITPDD 2.4 mL/kg (limits of agreement ± 3.8 mL/kg). The percentage errors were 41% and 14%, respectively. The bias became more positive when the mean of EVLWITPTD and EVLWIG increased (r2 = 0.72; p = 0.003). Conclusions: EVLWITPTD was significantly correlated to the postmortem gravimetric gold standard, although a significant overestimation was demonstrated with increasing pulmonary edema.

Gold standard must be solid gold

Dear Editor, In search of an optimal haemodynamic treatment strategy, much interest has risen in advanced haemodynamic monitoring in paediatric patients. Therefore, it was with great interest that we read the article by Floh and colleagues [1]. However, we do have concerns about their validation study of the transpulmonary ultrasound dilution (TPUD) technology in paediatric patients after biventricular repair. In this study, TUPD is validated against the oxygen-Fick (O2F) method, that can be regarded as the gold standard of cardiac output (CO) measurement in a clinical setting. Prerequisites for the O2F method are: accurate measurements of oxygen consumption, arterial oxygen content and mixed venous content (CmvO2). Any error in measurement in these vital parameters will directly result in an inaccurate calculation of CO. CmvO2 calculation demands sampling of blood via a pulmonary artery catheter. In this study, central venous blood was sampled from the internal jugular vein (86 %), subclavian vein (6 %), femoral vein (6 %) and right atrium (3 %). It is known that central venous oxygen saturation (ScvO2) does not reflect mixed venous oxygen saturation (SmvO2) and that the difference between these parameters is influenced by the venous sampling site, presence of left-to-right shunt, redistribution of blood flow, level of consciousness (anaesthesia) and myocardial oxygen consumption. Limits of agreement (LOA) between SmvO2 and ScvO2 range from ± 15 to ± 25 % (see Table. 1). Use of erroneous venous oxygen saturation in this order to calculate venous oxygen content, which is used in the Fick equation, may overestimate cardiac output up to sixfold (see Fig. 1) Hence, the O2F method is not applied as should be and therefore, cannot be regarded as gold standard under these conditions.

Transpulmonary thermodilution cardiac output measurement is not affected by severe pulmonary oedema: a newborn animal study

BACKGROUND The transpulmonary thermodilution (TPTD) technique is widely used in clinical practice for measuring cardiac output (CO). This study was designed to investigate the influence of various levels of pulmonary oedema on the reliability of CO measurements by the TPTD method. METHODS In 11 newborn lambs pulmonary oedema was induced using a surfactant washout technique. Serial CO measurements using TPTD (CO(TPTD)) were performed at various amounts of lung water. Simultaneously, CO was measured by an ultrasound flow probe around the main pulmonary artery (CO(MPA)) and used as the standard reference. CO was divided by the body surface area to calculate cardiac index (CI). Data were analysed using correlational statistics and Bland-Altman analysis. RESULTS One lamb died prematurely. A total of 56 measurements in 10 lambs were analysed with a median CI(MPA) of 2.95 (IQR 1.04) litre min(-1) m(-2). Mean percentage increase in extravascular lung water (EVLW) between the start and the end of the study was 126.4% (SD 40.4). Comparison of the two CO methods showed a mean bias CI of -0.16 litre min(-1) m(-2) (limits of agreement ±0.73 litre min(-1) m(-2)) and a percentage error of 23.8%. Intraclass correlation coefficients were 0.91 (95% CI 0.81-0.95) for absolute agreement and 0.92 (95% CI 0.87-0.95) for consistency. Acceptable agreement was confirmed by a tolerability-agreement ratio of 0.39. The within-subject correlation between the amount of EVLWI and the bias between the two methods was not significant (-0.02; P=0.91). CONCLUSIONS CO measurements by the transpulmonary thermodilution technique over a wide range of CI values are not affected by the presence of high EVLWI. The slight underestimation of the CO is independent of the amount of pulmonary oedema.

209 Cardiac Output Measurement in Juvenile Animals with a Surgically Constructed Extra Cardiac Left-To-Right Shunt Using the Transpulmonary Thermodilution Technique

209 Cardiac Output Measurement in Juvenile Animals with a Surgically Constructed Extra Cardiac Left-To-Right Shunt Using the Transpulmonary Thermodilution Technique