Limitations of continuous long-term ventilation in the prone position

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The effects of body position on hemodynamics during hypoxic mechanical ventilation in rabbits in vivo, and on the degree of lung damage caused by hypoxia in vitro (isolated perfused lung) were investigated. Values for heart rates and rate pressure products were high in the prone group, whereas those for cardiac output, oxygen consumption, oxygen delivery and arteriovenous oxygen difference were high in the supine group. The changes in pressure in the prone group and in flow in the supine group were thought to result from a response to hypoxia. The wet to dry weight ratio of the perfused lung was significantly higher, and the capillary filtration coefficient of lung water after hypoxic loading was significantly increased in the prone group. Long-term ventilation in a hypoxic state was apparently problematic for the prone group, as a large volume of blood pooled in the lungs.