PRESSURE SUPPORT VENTILATION ATTENUATES THE CARDIOPULMONARY RESPONSE TO AN ACUTE INCREASE IN OXYGEN-DEMAND

Critically ill patients undergo interventions, such as chest physical therapy, that acutely increase metabolic rate. Previous observations r evealed that chest physical therapy is accompanied by increases of 40 to 50% in oxygen consumption (V over dot O-2) and of 40% in minute ven tilation contributes to the rise in V over dot O-2 and its associated hemodynamic responses. This was done by increasing mandatory ventilato ry support during the chest physical therapy session: In phase 1 the m andatory ventilation rate was increased by 35% and in phase 2 pressure support ventilation 15 cm H2O was added. In phase 1 (n=12), the incre ase in mandatory rate did not attenuate the chest physical therapy ind uced rises in heart rate, arterial blood pressure and V over dot O-2. The increase in minute ventilation when the mandatory rate was increas ed prevented a rise in PaCO2. In phase 2 (n=15), no change in the incr ease in V over dot O-2 with chest physical therapy was observed with t he addition of pressure support. Yet the rises in heart rate and syste mic and pulmonary artery pressures were attenuated, as was the increas e in PaCO2. Respiratory rate did not increase as much with pressure su pport. There appears to be a role for pressure support ventilation in attenuating the pulmonary and hemodynamic responses to interventions t hat increase oxygen demand.