Efficacy of an alveolar recruitment maneuver for improving gas exchange and pulmonary mechanics in anesthetized horses ventilated with oxygen or a helium-oxygen mixture.

This research article studies how an alveolar recruitment maneuver (ARM) improves lung function in horses under anesthesia, and compares the efficacy of using oxygen alone versus using a mixture of helium and oxygen (heliox) for ventilation. An alveolar recruitment maneuver is shown to significantly improve pulmonary oxygen exchange and respiratory mechanics in anesthetized horses, with heliox outperforming pure oxygen.

Research Methods

• The study involved six healthy adult horses and followed a randomized crossover format.
• The horses were anesthetized and positioned on their backs for the experiment.
• Volume-controlled ventilation was performed either with pure oxygen or heliox (a combination of 70% helium and 30% oxygen) with the fraction of inspired oxygen (Fio) being more than 90%.
• The experiment started with mechanical ventilation using either of the gases. An hour in, an alveolar recruitment maneuver (ARM) was performed, entailing increased positive end-expiratory pressures (PEEPs), ratcheting up from 0 to 30 cm HO in steps of 5 cm HO every 5 minutes.

Parameters Measured

• A range of data was collected during each step of the ARM, including the peak inspiratory pressure, dynamic lung compliance (C), and arterial oxygen pressure (Pao).
• Indices of pulmonary oxygen exchange (how efficiently the lungs were exchanging gases) and alveolar dead space (regions in the lung where gas exchange could not take place) were calculated.
• The measurements were then compared with the baseline values (when PEEP was at 0 cm HO) and between the two types of ventilation gases, oxygen and heliox.

Key Results

• The ARM effectively increased pulmonary oxygen exchange indices and overall lung compliance under both ventilation gases.
• When using the heliox mixture, both dynamic lung compliance and the Pao-to-Fio ratio were significantly higher, and the alveolar-arterial difference in Pao was significantly lower, indicating more efficient gas exchange.
• This infers that heliox outperformed treatment with pure oxygen, leading to better pulmonary oxygen exchange and respiratory mechanics.

Conclusions

• The study concluded that an alveolar recruitment maneuver in horses under isoflurane-induced anesthesia and ventilated with heliox significantly improved their pulmonary oxygen exchange and respiratory mechanics.
• This improvement was possible due to reduced resistance in the respiratory system and diminished turbulent gas flow in the small airways.