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

Evaluation of work of breathing in spontaneously breathing animals during partial liquid ventilation.

BACKGROUND: Partial liquid ventilation improves lung mechanics and gas exchange in paralyzed mechanically ventilated animals. OBJECTIVE: Examine the work of breathing (WOB) in a spontaneously breathing animal model during partial liquid ventilation with and without the use of pressure-support ventilation (PSV). METHODS: This was a prospective study including 6 lambs (mean weight 10.9 +/- 1.3 kg). Baseline measurements, including total work of breathing (WOB(T)), elastic work of breathing (WOB(E)), and resistive work of breathing (WOB(R)), were obtained using pressure-controlled synchronized intermittent mandatory ventilation with positive end-expiratory pressure of 5 cm H(2)O at PSV levels of 0, 5, and 10 cm H(2)O. The animals' lungs were filled with perflubron through an endotracheal tube, in 10-20 mL aliquots, until filled, approximately 30 mL/kg or functional residual capacity. Repeat measurements were obtained at 10 mL/kg, 20 mL/kg, and full. Perflubron was then allowed to evaporate from the lungs and repeat measurements were obtained 3 additional times, with at least a 1 hour separation between phases, for up to 7 hours after the lungs were filled. RESULTS: No differences were detected in WOB(T), WOB(R), or WOB(E) between the gas-filled lung and the lung filled to functional residual capacity with perflubron. However, compared to the gas-filled lung, WOB(T) and WOB(R) were higher during the filling (p < 0.05) and evaporative phases (p < 0.05). The PSV level affected WOB. Work of breathing was least at PSV 10 cm H(2)O. CONCLUSION: In this pilot study of healthy animals breathing spontaneously with perflubron-filled lungs, there was an acceptable amount of WOB, which decreased with the addition of PSV. However, WOB increased when the perflubron level was not maintained at functional residual capacity.