Comparison of various types of inert gas components on efficacy of an alveolar recruitment maneuver in dorsally recumbent anesthetized horses.

Objective: To assess effects of nitrogen and helium on efficacy of an alveolar recruitment maneuver (ARM) for improving pulmonary mechanics and oxygen exchange in anesthetized horses.

Animals: 6 healthy adult horses.

Procedures: Horses were anesthetized twice in a randomized crossover study. Isoflurane-anesthetized horses in dorsal recumbency were ventilated with 30% oxygen and 70% nitrogen (treatment N) or heliox (30% oxygen and 70% helium; treatment H) as carrier gas. After 60 minutes, an ARM was performed. Optimal positive end-expiratory pressure was identified and maintained for 120 minutes. Throughout the experiment, arterial blood pressures, heart rate, peak inspiratory pressure, dynamic compliance (C), and Pao were measured. Variables were compared with baseline values and between treatments by use of an ANOVA.

Results: The ARM resulted in significant increases in Pao and C and decreases in the alveolar-arterial gradient in the partial pressure of oxygen in all horses. After the ARM and during the subsequent 120-minute phase, mean values were significantly lower for treatment N than treatment H for Pao and C. Optimal positive end-expiratory pressure was consistently 15 cm HO for treatment N, but it was 10 cm HO (4 horses) and 15 cm HO (2 horses) for treatment H.

Conclusions And Clinical Relevance: An ARM in anesthetized horses might be more efficacious in improving Pao and C when animals breathe helium instead of nitrogen as the inert gas.