In vitro validation and clinical testing of an indirect calorimetry systemfor ventilated preterm infants that is unaffected by endotracheal tube leaks and can be used during nasal continuous positive airway pressure

Energy expenditure measurements in ventilated preterm infants are difficult because indirect calorimetry underestimates energy expenditure during gas leaks around uncuffed endotracheal tubes routinely used in preterm infants or during nasal continuous positive airway pressure (CPAP). We, therefore, developed a breath collector that simultaneously sampled expired air expell ed at the ventilator outlet and escaping via the tube leak from the infant' s mouth and nose. Our breath collector was combined with a proprietary calo rimeter (Deltatrac II). In vitro validation was done by methanol burning (V o(2), 13.8 mL/min; Vco(2), 9.2 mL/min) during intermittent positive pressur e ventilation (IPPV) with two commonly used ventilators (Sechrist IV-100B a nd Infant Star). Measurement error was determined at different ventilator f lows, peak inspiratory pressures of 12-24 cm H2O, and during a complete tub e leak. The mean measurement error with both ventilators was low (Vo(2) +/- 3%, Vco(2) +/- 2%) even during a complete tube leak and did not increase w ith peak inspiratory pressure. The system response time was 2 min. In vivo measurements at the bedside were performed in 25 preterm infants (body weig ht, 537-1402 g). Energy expenditure during IPPV was 40 +/- 9 kcal/kg per da y and 46 +/- 15 kcal/kg per day during nasal CPAP. The tube leak in the pre term infants studied during IPPV was 0 to 47%, and during nasal CPAP 84 to 97%. In conclusion, indirect calorimetry performed with our breath collecto r was accurate during IPPV and nasal CPAP and was unaffected by tube leaks.