Nutritional requirements and gas-exchange: is it possible to perform indicrect calorimetry in children undergoing nasal CPAP?

Introduction. Nutrition plays a pivotal role in critically ill children and personalized nutritional therapy requires the measurement of resting energy expenditure (REE) [1-2]. Indirect calorimetry (IC) is the gold standard for REE assessment and is based on VO2 and VCO2 measurements. Furthermore, IC provides information on carbohydrates/lipids consumption by defining the respiratory quotient (RQ). In spontaneously breathing patients, IC is performed using a transparent helmet (Canopy mode). The helmet is placed on patients’ head and is connected to the calorimeter through a tube. An aspiration flow generated by the calorimeter allows gas collection and analysis. In mechanically ventilated patients, the measurements are performed connecting IC analyzers to the ventilator circuit. However, while IC is validated for spontaneously breathing and mechanically ventilated patients, it is not for patients undergoing CPAP (continuous positive airway pressure) [3]. This limitation is of great clinical relevance, as the use of CPAP and other non-invasive modes of ventilation is increasing in the pediatric intensive care units (PICUs). The aim of the present study is therefore to validate IC in children undergoing nasal CPAP (n-CPAP) by comparing IC results obtained during spontaneous breathing with data gathered during n-CPAP. Methods. Patients (age <6 years) admitted to our PICU from February to May 2019 and treated with n-CPAP were enrolled. Patients were studied during the weaning phase, i.e., once they were able to maintain spontaneous breathing in room air. In order to test the validity of IC during n-CPAP, two measurements were performed in Canopy mode for 20 minutes, in randomized order with the following settings: 1) Spontaneous breathing (SB), 2) n-CPAP of 4 cmH2O. A turbine-driven ventilator with a single-limb circuit and a vented nasal mask was used to deliver n-CPAP. Of note, in this way, both intentional and non-intentional leaks remained in the canopy helmet. Total minute flow delivered by the ventilator was measured by a Fleisch pneumotachograph connected to the respiratory circuit, in order to personalize the aspiration flow setting [4]. Average values for VCO2, VO2, RQ and REE were obtained in these two conditions. Comparison between groups was performed via paired t-test. Agreement was assessed via Bland-Altman analysis. Statistical significance was defined as p<0.05. Results. Five patients (median age 16 months, IQR 9 months, median weight 8.5 kg, IQR 0.6 kg) were enrolled. All patients were in resting state during both measurements, thus allowing for standardized conditions. VCO2, VO2, RQ and REE did not differ significantly between groups. Bias and Limits of Agreement (LOA) indicate a good agreement between the two measures (Table 1). Conclusions. Our preliminary data suggest that IC can be accurately performed in children undergoing n-CPAP using a single limb circuit with intentional leaks. These results need to be confirmed on a broader cohort of critically ill children. References 1. De Cosmi V et al. Nutrients. 2017 2. Mehta NM et al. Pediatr Crit Care Med. 2017 3. Taku Oshima et al. Clinical Nutr. 2017 4. Smallwood CD et al. J Parenter Enteral Nutr. 2014