Avoidance of aggravated hypoxemia during measurement of mean pulmonary artery wedge pressure in ARDS.

A marked drop occurs in mixed venous oxygen saturation during temporary interruption of mechanical ventilation. To avoid this potentially dangerous problem and eliminate possible errors induced by associated hemodynamic changes, a simple electronic circuit was constructed for measurement of mean pulmonary artery wedge pressure without separation of the patient from the ventilator. Its 12-second time constant was sufficient to cover two to four respiratory cycles. In 50 ventilator-supported patients with the adult respiratory distress syndrome, it was shown that the value obtained from the circuit was not different from the instantaneous value obtained at the end of expiration during temporary cessation of mechanical ventilation, but was different from the pulmonary artery diastolic pressure. The circuit value was not affected by positive end-expiratory pressures up to 10 cm H2O. The method is sufficiently accurate for its intended purpose, improves the care of these severely-ill patients, and can be safely used without a physician being present.