Evaluation of Work of Breathing in Spontaneously Breathing Animals during Partial Liquid Ventilation

Abstract

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 (WOBT), elastic work of breathing (WOBE), and resistive work of breathing (WOBR), were obtained using pressure-controlled synchronized intermittent mandatory ventilation with positive end-expiratory pressure of 5 cm H2O at PSV levels of 0, 5, and 10 cm H2O. 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 WOBT, WOBR, or WOBE between the gas-filled lung and the lung filled to functional residual capacity with perflubron. However, compared to the gas-filled lung, WOBT and WOBR 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 H2O. 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.