J. Lemson

Hemodynamic monitoring by transpulmonary thermodilution and pulse contour analysis in critically ill children

Objectives: To summarize the physiologic principles underlying the hemodynamic monitoring using the PiCCO device (Pulsion, Munich, Germany) incorporating the transpulmonary thermodilution technique, the pulse contour cardiac output, and estimation of the arterial pressure variation method. Analysis and review of the current literature. Design: A MEDLINE-based literature search using the key words transpulmonary thermodilution, pulse contour analysis, cardiac output, animal models, and child. Measurements and Main Results: The bias and precision of cardiac output measured by transpulmonary thermodilution are reliable. The reproducibility for repeated measurements is approximately 5% and the percentage error is approximately 15%. Transpulmonary thermodilution may adequately track changes in cardiac output in animals submitted to hypovolemic conditions and during volume loading. Conversely, data from experimental and clinical studies suggest that continuous monitoring of cardiac output using pulse contour analysis requires careful interpretation because periodic recalibration with transpulmonary thermodilution is necessary. Transpulmonary thermodilution-derived static indicator of cardiac preload (global end-diastolic volume, intrathoracic blood volume) may be more sensitive than conventional measurements of vascular filling pressure. However, the value of stroke volume variation or pulse pressure variation have not been evaluated in pediatric patients. Further studies are needed to determine whether theoretical assumptions underlying the measurement of extravascular lung water are valid in children. Conclusions: The PiCCO device may be a useful adjunct for hemodynamic monitoring in critically ill children. Further studies are needed to clarify the reliability and clinical value of pulse contour method and extravascular lung water measurement.

Continuous non-invasive finger arterial pressure monitoring reflects intra-arterial pressure changes in children undergoing cardiac surgery

BACKGROUNDnContinuous non-invasive measurement of finger arterial pressure (FAP) is a reliable technology in adults. FAP is measured with an inflatable cuff around the finger and simultaneously converted to a reconstructed brachial artery pressure waveform (reBAP) by the Nexfin™ device. We assessed the adequacy of a prototype device (Nexfin-paediatric), designed for a paediatric population, for detecting rapid arterial pressure changes in children during cardiac surgery.nnnMETHODSnThirteen anaesthetized children with a median age of 11 months (2 months-7 yr) undergoing congenital cardiac surgery were included in the study. reBAP and intra-arterial pressure (IAP) were recorded simultaneously during the surgical procedure. To assess the accuracy of reBAP in tracking arterial pressure changes, the four largest IAP variations within a 5 min time interval were identified from each procedure. These variations were compared offline with reBAP during a 10 s control period before and a 10 s period after an arterial pressure change had occurred.nnnRESULTSnIn 10 out of 13 children, a non-invasive arterial pressure recording could be obtained. Therefore, recordings from these 10 children were eligible for further analysis, resulting in 40 data points. The correlation coefficient between reBAP and IAP in tracking mean arterial pressure (MAP) changes was 0.98. reBAP followed changes in IAP with a mean bias for systolic, diastolic arterial pressure, and MAP of 0.0 mm Hg (sd 5.8), 0.1 (sd 2.8), and 0.19 (sd 2.7), respectively.nnnCONCLUSIONSnThe prototype device closely follows arterial pressure changes in children. However, in a considerable number of attempts, obtaining a signal was time-consuming or unsuccessful. This technique seems promising but requires further technical development.

Mechanical ventilation-induced intrathoracic pressure distribution and heart-lung interactions*

Objective:Mechanical ventilation causes cyclic changes in the heart’s preload and afterload, thereby influencing the circulation. However, our understanding of the exact physiology of this cardiopulmonary interaction is limited. We aimed to thoroughly determine airway pressure distribution, how this is influenced by tidal volume and chest compliance, and its interaction with the circulation in humans during mechanical ventilation. Design:Intervention study. Setting:ICU of a university hospital. Patients:Twenty mechanically ventilated patients following coronary artery bypass grafting surgery. Intervention:Patients were monitored during controlled mechanical ventilation at tidal volumes of 4, 6, 8, and 10 mL/kg with normal and decreased chest compliance (by elastic binding of the thorax). Measurements and Main Results:Central venous pressure, airway pressure, pericardial pressure, and pleural pressure; pulse pressure variations, systolic pressure variations, and stroke volume variations; and cardiac output were obtained during controlled mechanical ventilation at tidal volume of 4, 6, 8, and 10u2009mL/kg with normal and decreased chest compliance. With increasing tidal volume (4, 6, 8, and 10u2009mL/kg), the change in intrathoracic pressures increased linearly with 0.9u2009±u20090.2, 0.5u2009±u20090.3, 0.3u2009±u20090.1, and 0.3u2009±u20090.1u2009mmu2009Hg/mL/kg for airway pressure, pleural pressure, pericardial pressure, and central venous pressure, respectively. At 8u2009mL/kg, a decrease in chest compliance (from 0.12u2009±u20090.07 to 0.09u2009±u20090.03u2009L/cm H2O) resulted in an increase in change in airway pressure, change in pleural pressure, change in pericardial pressure, and change in central venous pressure of 1.1u2009±u20090.7, 1.1u2009±u20090.8, 0.7u2009±u20090.4, and 0.8u2009±u20090.4u2009mmu2009Hg, respectively. Furthermore, increased tidal volume and decreased chest compliance decreased stroke volume and increased arterial pressure variations. Transmural pressure of the superior vena cava decreased during inspiration, whereas the transmural pressure of the right atrium did not change. Conclusions:Increased tidal volume and decreased chest wall compliance both increase the change in intrathoracic pressures and the value of the dynamic indices during mechanical ventilation. Additionally, the transmural pressure of the vena cava is decreased, whereas the transmural pressure of the right atrium is not changed.

Crew Resource Management in the Intensive Care Unit: a prospective 3-year cohort study.

Human factors account for the majority of adverse events in both aviation and medicine. Human factors awareness training entitled “Crew Resource Management (CRM)” is associated with improved aviation safety. We determined whether implementation of CRM impacts outcome in critically ill patients.

Extravascular lung water measurement using transpulmonary thermodilution in children

Objective: Measurement of extravascular lung water (EVLW) may be useful in the treatment of critically ill children and can be performed at the bedside using the transpulmonary thermodilution technique (TPTD). There are currently no data to verify the accuracy of these measurements in (small) children. We compared the results of TPTD measurement with the clinical gold standard transpulmonary double indicator dilution (TPDD) measurement in young children. Design: Prospective clinical study in children. Setting: Catheterization laboratory of a university hospital. Patients and Methods: Twelve children (<2 yrs or <12 kg) under general anesthesia. Interventions: None. Measurements and Main Results: Measurements were performed using injections of ice-cold indicator (saline or dye) through a central venous catheter. Mean cardiac index was 3.91 L/min/m2, mean intrathoracic blood volume index (ITBVITPDD) was 614.9 mL/m2, and mean extravascular lung water index (EVLWITPDD) was 11.7 mL/kg. The correlation coefficient between EVLWITPDD and EVLWITPTD is 0.96 (95% confidence interval: 0.87–0.99; p < 0.0001). Bland–Altman analysis for EVLW measurements showed a mean bias of 2.34 mL/kg (18.13%) and limits of agreement ±2.97 mL/kg (19.78%). The difference between measurements via the right atrium compared with the femoral vein was 2.8% for cardiac output, 8.2% for global end-diastolic volume, and 0.1% for EVLW. Conclusion: Clinical measurement of EVLW in young children can be performed using the TPTD with the injection catheter inserted in the femoral vein. Further studies are needed to clarify the clinical value of these measurements.

Pediatric Acute Respiratory Distress Syndrome: Fluid Management in the PICU

The administration of an appropriate volume of intravenous fluids, while avoiding fluid overload, is a major challenge in the pediatric intensive care unit. Despite our efforts, fluid overload is a very common clinical observation in critically ill children, in particular in those with pediatric acute respiratory distress syndrome (PARDS). Patients with ARDS have widespread damage of the alveolar–capillary barrier, potentially making them vulnerable to fluid overload with the development of pulmonary edema leading to prolonged course of disease. Indeed, studies in adults with ARDS have shown that an increased cumulative fluid balance is associated with adverse outcome. However, age-related differences in the development and consequences of fluid overload in ARDS may exist due to disparities in immunologic response and body water distribution. This systematic review summarizes the current literature on fluid imbalance and management in PARDS, with special emphasis on potential differences with adult patients. It discusses the adverse effects associated with fluid overload and the corresponding possible pathophysiological mechanisms of its development. Our intent is to provide an incentive to develop age-specific fluid management protocols to improve PARDS outcomes.

Dynamic preload indicators decrease when the abdomen is opened

BackgroundOptimizing cardiac stroke volume during major surgery is of interest to many as a therapeutic target to decrease the incidence of postoperative complications. Because dynamic preload indicators are strongly correlated with stroke volume, it is suggested that these indices can be used for goal directed fluid therapy. However, threshold values of these indicators depend on many factors that are influenced by surgery, including opening of the abdomen. The aim of this study was therefore to assess the effect of opening the abdomen on arterial pressure variations in patients undergoing abdominal surgery.MethodsBlood pressure and bladder pressure were continuously recorded just before and after opening of the abdomen in patients undergoing elective laparotomy. Based on waveform analysis of the non-invasively derived blood pressure, the stroke volume index, pulse pressure variation (PPV) and stroke volume variation (SVV) were calculated off-line.ResultsThirteen patients were included. After opening the abdomen, PPV and SVV decreased from 11.5u2009±u20095.8% to 6.4u2009±u20092.9% (pu2009<u20090.005, a relative decrease of 40u2009±u200919%) and 12.7u2009±u20096.1% to 4.8u2009±u20091.6% (pu2009<u20090.05, a relative decrease of 53u2009±u200926%), respectively. Although mean arterial pressure and stroke volume index tended to increase (41u2009±u20096 versus 45u2009±u20094xa0ml/min/m2, pu2009=u20090.14 and 41u2009±u20096 versus 45u2009±u20094xa0ml/min/m2, pu2009=u20090.05), and heart rate tended to decrease (73u2009±u200915 versus 68u2009±u200911 1/min, pu2009=u20090.05), no significant change was found. No significant change was found in respiratory parameter (tidal volume, respiratory rate or inspiratory pressure; pu2009=u20090.36, 0.34 and 0.17, respectively) or bladder pressure (6.0u2009±u20093.7 versus 5.6u2009±u20092.7xa0mmHg, pu2009=u20090.6) either.ConclusionsOpening of the abdomen decreases PPV and SVV. During goal directed therapy, current thresholds for fluid responsiveness should be changed accordingly.

Ventilator-induced pulse pressure variation in neonates.

During positive pressure ventilation, arterial pressure variations, like the pulse pressure variation (PPV), are observed in neonates. However, the frequency of the PPV does not always correspond with the respiratory rate. It is hypothesized that PPV is caused by cardiopulmonary interaction, but that this mismatch is related to the low respiratory rate/heart rate ratio. Therefore, the goal of this study is to investigate the relation between PPV and ventilation in neonates. A prospective observational cross‐sectional study was carried out in a third‐level neonatal intensive care unit in a university hospital. Neonates on synchronized intermittent mandatory ventilation (SIMV) or high‐frequency ventilation (HFV) participated in the study. The arterial blood pressure was continuously monitored in 20 neonates on SIMV and 10 neonates on HFV. In neonates on SIMV the CO2 waveform and neonates on HFV the thorax impedance waveform were continuously monitored and defined as the respiratory signal. Correlation and coherence between the respiratory signal and pulse pressure were determined. The correlation between the respiratory signal and pulse pressure was ‐0.64 ± 0.18 and 0.55 ± 0.16 and coherence at the respiratory frequency was 0.95 ± 0.11 and 0.76 ± 0.4 for SIMV and HFV, respectively. The arterial pressure variations observed in neonates on SIMV or HFV are related to cardiopulmonary interaction. Despite this relation, it is not likely that PPV will reliably predict fluid responsiveness in neonates due to physiological aliasing.

Estimation of extravascular lung water using the transpulmonary ultrasound dilution (TPUD) method: a validation study in neonatal lambs

Increased extravascular lung water (EVLW) may contribute to respiratory failure in neonates. Accurate measurement of EVLW in these patients is limited due to the lack of bedside methods. The aim of this pilot study was to investigate the reliability of the transpulmonary ultrasound dilution (TPUD) technique as a possible method for estimating EVLW in a neonatal animal model. Pulmonary edema was induced in 11 lambs by repeated surfactant lavages. In between the lavages, EVLW indexed by bodyweight was estimated by TPUD (EVLWItpud) and transpulmonary dye dilution (EVLWItpdd) (nxa0=xa022). Final EVLWItpud measurements were also compared with EVLWI estimations by gold standard post mortem gravimetry (EVLWIgrav) (nxa0=xa06). EVLWI was also measured in two additional lambs without pulmonary edema. Bland–Altman plots showed a mean bias between EVLWItpud and EVLWItpdd of −3.4xa0mL/kg (LOAxa0±xa025.8xa0mL/kg) and between EVLWItpud and EVLWIgrav of 1.7xa0mL/kg (LOAxa0±xa08.3xa0mL/kg). The percentage errors were 109 and 43xa0% respectively. The correlation between changes in EVLW measured by TPUD and TPDD was r2xa0=xa00.22. Agreement between EVLWI measurements by TPUD and TPDD was low. Trending ability to detect changes between these two methods in EVLWI was questionable. The accuracy of EVLWItpud was good compared to the gold standard gravimetric method but the TPUD lacked precision in its current prototype. Based on these limited data, we believe that TPUD has potential for future use to estimate EVLW after adaptation of the algorithm. Larger studies are needed to support our findings.

Near-normal values of extravascular lung water in children

Objectives: To define near-normal values of extravascular lung water indexed to body weight in children. Design: Prospective multicenter observational study. Setting: Medical/surgical PICUs of 5 multinational hospitals. Patients: Fifty-eight children with a median age of 4 years (range 1 month to 17 year) with heterogeneous PICU admission diagnoses were included. Extravascular lung water measurements from these children were collected after resolution of their illness. Obtained values were indexed to actual body weight and height and subsequently related to age. Interventions: None. Measurements and Main Results: Extravascular lung water indexed to body weight correlated with age (r2 = 0.7) and could be categorized in three-age groups consisting of significantly different median extravascular lung water indexed to body weight values (5th–95th percentile): less than 1 year, 9–29 mL/kg; 1–5 years, 7–25 mL/kg; and 5–17 years, 5–13 mL/kg. Extravascular lung water indexed to height did not correlate to age and resulted in an age-independent near-normal value of less than 315 mL/m. Conclusions: Younger children have higher values of extravascular lung water indexed to actual body weight. Age categorized near-normal values of extravascular lung water indexed to body weight are presented for possible clinical use. Furthermore, we suggest to index extravascular lung water to height, which seems to be age independent.