Comparison of pulmonary vascular pressures based on blood volume and ventilator status

Pulmonary artery pressures (PAP), hemodynamic and oxygen transport variables, arterial blood gases (ABG), and blood volume (BV) were measured in 30 hypervolemic, normovolemic, and hypovolemic critically ill adults receiving physiologic levels of positive and expiratory pressure (PEEP). The measurements were taken while patients remained on the ventilator and during brief discontinuance of mechanical ventilation. The purposes of the study were to determine whether BV status could affect PAP and to quantify the effect of temporary discontinuance of ventilation on ABG. No differences were seen in PAP, mean arterial pressure, cardiac index, oxygen delivery, oxygen extraction, or oxygen consumption regardless of ventilator or BV status. Arterial oxygen tension dropped significantly, p less than .001, in less than 1 minute off ventilation and the decrease persisted for 1 hour after mechanical ventilation was resumed. These results suggest that recording PAP off the ventilator should be abandoned, as this technique contributes little to increased validity of PAP and may result in persistent hypoxemia.