Mechanical ventilators optimized for pediatric use decrease work of breathing and oxygen consumption during pressure-support ventilation

Objectives: a) To investigate whether the patient work of breathing needed to trigger inspiration is affected by the type of ventilator delivering pressure-support ventilation for mechanically ventilated pediatric patients. b) To determine whether changes in oxygen consumption (V̇O₂) trend with changes in work of breathing and would thus be helpful in tracking work of breathing. Design: Prospective study. Setting: Pediatric intensive care unit at a university hospital. Patients: Nine mechanically ventilated patients (2 to 75 months of age). Interventions: While maintaining a constant pressure- support ventilation level, patients were alternately supported with the Siemens Servo 900C, the Bird VIP, and the Newport Wave E200 ventilators in random order. Measurements and Main Results: Work of breathing, defined as the integral of the pressure-volume curve corresponding to negative pressure, was calculated with a pulmonary monitoring system. V̇O₂ was measured with a metabolic cart. Patient distress levels were assessed using the COMFORT scale, a behavioral scoring system. Mean values (20 breaths/patient) for measured variables with each ventilator were compared using analysis of variance and Scheffe tests, with p < .05 indicating statistical significance. The lowest V̇O₂ (103 ± 35 mL/min/m²) and work of breathing (24 ± 15 g · cm/m²) were achieved with the Bird VIP ventilator and were significantly (p < .05) lower than those values obtained with either the Siemens Servo 900C (V̇O₂ 147 ± 33 mL/min/m²; work of breathing 49 ± 18 g · cm/m²) or the Newport Wave E200 (V̇O₂ 122 ± 33 mL/min/m²; work of breathing 35 ± 15 g · cm/m²). Also, the values of work of breathing and V̇O₂ obtained using the Newport Wave E200 were significantly (p < .05) lower than those values obtained using the Servo 900C. No change in behavioral distress occurred when the ventilators were changed. In all patients, there was a clear similarity in the trends of V̇O₂ and work of breathing. Conclusions: We conclude that V̇O₂ and work of breathing may be reduced significantly using the latest generation of mechanical ventilators optimized for infant and pediatric use. Because work of breathing is less with the Bird VIP than the other two ventilators tested, leading to a corresponding decrease in V̇O₂, we suggest that the Bird VIP better adapts the patient to the ventilator and may facilitate weaning from ventilatory support. We also suggest that changes in V̇O₂ might be helpful in tracking changes in work of breathing.