Effects of continuous positive airway pressure/positive end-expiratory pressure and pressure-support ventilation on work of breathing, using an animal model.

OBJECTIVE Evaluate the effects of continuous positive airway pressure (CPAP)/positive end-expiratory pressure (PEEP) and pressure support ventilation (PSV) on work of breathing (WOB). METHODS With 13 anesthetized lambs we measured WOB with an esophageal balloon and flow signals. All the animals were sedated, intubated, and ventilated, using 2 pediatric ventilators (Servo 300 and VIP Bird). Ventilator settings were CPAP of 0, 5, and 10 cm H(2)O and PSV of 5 and 10 cm H(2)O with PEEP of 0, 5, and 10 cm H(2)O. Data were analyzed with 2-way analysis of variance. RESULTS With the Servo 300 the total WOB (WOB(T)) increased between CPAP/PEEP of 0 and 10 cm H(2)O (p </= 0.0001) and between CPAP/PEEP of 5 and 10 cm H(2)O (p </= 0.0002). With the Servo 300 the addition of PSV decreased WOB(T) (p </= 0.003). With the VIP Bird the WOB(T) significantly increased between CPAP/PEEP of 0 and 10 cm H(2)O (p </= 0.02) and between CPAP/PEEP of 5 and 10 cm H(2)O (p </= 0.03). With PSV the WOB(T) was lower only at PSV 10 cm H(2)O (p </= 0.0001). CONCLUSIONS WOB(T) increased as CPAP/PEEP was increased, and PSV lowered WOB(T.) We hypothesize that in a healthy animal model increased CPAP/PEEP may cause alveolar overdistention.