Alveolar target ventilation and dead space in children under anaesthesia: The proventiped cohort study.

INTRODUCTION: Ventilator settings in children under anaesthesia remain difficult because of the changes in the physiology and the high dead space. OBJECTIVE: To determine the alveolar minute-volume to sustain normocapnia in children under mechanical ventilation. DESIGN: A prospective observational study. SETTINGS: This study was performed between May and October 2019 in a tertiary care children's hospital. PATIENTS: Children between 2 months and 12 years, weighing between 5 and 40 kg, admitted for general anaesthesia. INTERVENTION: Volumetric capnography was used to estimate the alveolar and dead space volume (Vd). MAIN OUTCOME MEASURES: Total and alveolar minute ventilation in (ml kg -1  min -1 ) over 100 breaths. RESULTS: Sixty patients were included comprising 20 per group: 5 to 10 kg (group 1), 10 to 20 kg (group 2), 20 to 40 kg (group 3). Seven patients were excluded for aberrant capnographic curves. After normalisation to weight, the median [IQR] tidal volume per kilogram was similar between the three groups: 6.5 ml kg -1 [6.0 to 7.5 ml kg -1 ], 6.4  ml kg -1 [5.7 to 7.3  ml kg -1 ], 6.4  ml kg -1 [5.3 to 6.8  ml kg -1 ]; P  = 0.3. Total Vd (in ml kg -1 ) was negatively correlated to weight ( r  = -0.62, 95% confidence interval -0.41 to -0.76, P  < 0.001). The total normalised minute ventilation (ml kg -1  min -1 ) to obtain normocapnia was higher in group 1 than in group 2 and in group 3; 203  ml kg -1  min -1 [175 to 219 ml kg -1  min -1 ], 150  ml kg -1  min -1 [139 to 181  ml kg -1  min -1 ] and 128  ml kg -1  min -1 [107 to 157  ml kg -1  min -1 ]; P  < 0.001 (mean ± SD), but (mean ± SD) alveolar minute ventilation was similar between the three groups; 68 ±â€Š21  ml kg -1  min -1 . CONCLUSION: Total dead space volume (including apparatus dead space) represents a major component of tidal volume in children less than 30 kg, when using large heat and moisture exchanger filters. The total minute ventilation necessary to achieve normocapnia decreased with increasing weight, while the alveolar minute ventilation remained constant. TRIAL REGISTRATION: ClinicalTrials.gov, identifier: NCT03901599.

Preload Dependence Fails to Predict Hemodynamic Instability During a Fluid Removal Challenge in Children.

OBJECTIVES: Fluid overload increases morbidity and mortality in PICU patients. Active fluid removal improves the prognosis but may worsen organ dysfunction. Preload dependence in adults does predict hemodynamic instability induced by a fluid removal challenge (FRC). We sought to investigate the diagnostic accuracy of dynamic and static markers of preload in predicting hemodynamic instability and reduction of stroke volume during an FRC in children. We followed the Standards for Reporting of Diagnostic Accuracy statement to design conduct and report this study. DESIGN: Prospective noninterventional cohort study. SETTINGS: From June 2017 to April 2019 in a pediatric cardiac ICU in a tertiary hospital. PATIENTS: Patients 8 years old or younger, with symptoms of fluid overload after cardiac surgery, were studied. INTERVENTIONS: We confirmed preload dependence by echocardiography before and during a calibrated abdominal compression test. We then performed a challenge to remove 10-mL/kg fluid in less than 120 minutes with an infusion of diuretics. Hemodynamic instability was defined as a decrease of 10% of mean arterial pressure. MEASUREMENT AND MAIN RESULTS: We compared patients showing hemodynamic instability with patients remaining stable, and we built receiver operative characteristic (ROC) curves. Among 58 patients studied, 10 showed hemodynamic instability. The area under the ROC curve was 0.55 for the preload dependence test (95% CI, 0.34-0.75). Using a threshold of 10% increase in stroke volume index (SVi) during calibrated abdominal compression, the specificity was 0.30 (95% CI, 0.00-0.60) and the sensitivity was 0.77 (95% CI, 0.65-0.88). Mean arterial pressure variation and SVi variation were not correlated during fluid removal; r = 0.19; 95% CI -0.07 to 0.43; p = 0.139. CONCLUSIONS: Preload dependence is not accurate to predict hemodynamic instability during an FRC. Our data do not support a reduction in intravascular volume being mainly responsible for the reduction in arterial pressure during an FRC in children.