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.