Effects of sighs and different tidal volumes on compliance, functional residual capacity and arterial oxygen tension in normal and hypoxemic dogs.

In order to assess the usefulness of sighs in preventing deterioration of arterial PO2 (PaO2), functional residual capacity (FRC), and compliance in hypoxemic patients, the authors studied 20 anesthetized and paralyzed dogs. The dogs were ventilated with either normal (11.5 ml/kg) or large (23 ml/kg) tidal volumes and their lungs were either normal or made edematous with oleic acid injection. Sighs (46 ml/kg) were administered periodically and PaO2, FRC, and compliance were measured at intervals between sighs. In dogs with normal lungs, regardless of tidal volume, sighs produced a transient increase in compliance and FRC but PaO2 was not significantly affected. In dogs with pulmonary edema, sighs produced inconsistent effects on FRC and compliance and, interestingly, PaO2 decreased after the sighs may be unnecessary in patients with pulmonary edema, especially when they are already receiving large tidal volumes.