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

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  • 1 1Department of Clinical Studies-New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA 19348.

Abstract

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 (Cdyn), and Pao2 were measured. Variables were compared with baseline values and between treatments by use of an ANOVA.

RESULTS

The ARM resulted in significant increases in Pao2 and Cdyn 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 Pao2 and Cdyn. Optimal positive end-expiratory pressure was consistently 15 cm H2O for treatment N, but it was 10 cm H2O (4 horses) and 15 cm H2O (2 horses) for treatment H.

CONCLUSIONS AND CLINICAL RELEVANCE

An ARM in anesthetized horses might be more efficacious in improving Pao2 and Cdyn when animals breathe helium instead of nitrogen as the inert gas.

Abstract

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 (Cdyn), and Pao2 were measured. Variables were compared with baseline values and between treatments by use of an ANOVA.

RESULTS

The ARM resulted in significant increases in Pao2 and Cdyn 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 Pao2 and Cdyn. Optimal positive end-expiratory pressure was consistently 15 cm H2O for treatment N, but it was 10 cm H2O (4 horses) and 15 cm H2O (2 horses) for treatment H.

CONCLUSIONS AND CLINICAL RELEVANCE

An ARM in anesthetized horses might be more efficacious in improving Pao2 and Cdyn when animals breathe helium instead of nitrogen as the inert gas.

Contributor Notes

Drs. Varner and Hopster contributed equally to this manuscript.

Address correspondence to Dr. Hopster (khopster@vet.upenn.edu).