Effects of blood volume and discontinuance of ventilation on pulmonary vascular pressures and blood gases in patients with low levels of positive end-expiratory pressure.

Abstract

Hypervolemic, normovolemic and hypovolemic patients with PEEP values less than 10 cm H2O were studied during brief discontinuance of mechanical ventilation to determine whether blood volume status would affect on-off ventilator pulmonary artery pressure (PAP) readings. There were no appreciable hemodynamic effects in patients with blood volume deficits less than one liter. Discontinuance for 1 min decreased PaO2 from 121 +/- 8 (SD) to 77 +/- 7 torr (p less than .001) and increased PaCO2 from 32 +/- 1 to 35 +/- 1 torr (p less than .01). The decreased PaO2 persisted up to one hour after return to mechanical ventilation. Our data reveal that brief discontinuance of ventilation in the normovolemic or hypervolemic patient with physiologic levels of PEEP does not increase the accuracy of PAP measurements. However, with severe hypovolemia, marked reductions in PAP may occur with discontinuance of mechanical ventilation. The practice of recording PAP off the ventilator and frequent suctioning of patients should be abandoned when interruption of mechanical ventilation has little utility and can result in persistent hypoxemia.