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 endexpiratory 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 H₂O and PSV of 5 and 10 cm H₂O with PEEP of 0, 5, and 10 cm H₂O. 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 H₂O (p ≤ 0.0001) and between CPAP/PEEP of 5 and 10 cm H₂O (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 H₂O (p ≤ 0.02) and between CPAP/PEEP of 5 and 10 cm H₂O (p ≤ 0.03). With PSV the WOB_T was lower only at PSV 10 cm H₂O (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.