The use of respiratory variations in right atrial pressure to predict the cardiac output response to PEEP.

PURPOSE

The purpose of this study was to determine whether the pattern of respiratory variation in right atrial pressure (Pra) predicts the cardiac output response to positive end-expiratory pressure (PEEP).

MATERIALS AND METHODS

We studied 18 patients with a variety of cardiac and pulmonary disorders requiring ventilatory support. A pulmonary artery flotation catheter was in place as part of their routine management. Changes in PEEP were made from 0 to 14 cm H2O to determine the level of PEEP, which increased PO(2) without decreasing cardiac output (ie, assessment of best PEEP). Static lung compliance and auto-PEEP were obtained from the pressure signal on the ventilator. The change in Pra with a spontaneous inspiratory effort (ie, triggered breath) was used to determine whether patients had a restrictive (ie, operating on the flat part of the Starling curve), or nonrestrictive pattern (acting on the ascending part of the Starling curve) as previously described.

RESULTS

Cardiac output decreased 0.7 +/- 0.8 L/min (change from baseline P <.05) in the group with an inspiratory decrease in Pra and -0.04 +/- 1.50 L/min (P = NS) in the group without an inspiratory decrease in Pra. The groups were not significantly different. However, the variance in cardiac output was large and, in contrast to our hypothesis, two patients in the group with an inspiratory decrease in Pra did not have a decrease in cardiac output. Pra and pulmonary artery occlusion pressure after the PEEP trial were greater than before, indicating that reflex circulatory adjustments occurred in response to the PEEP.

CONCLUSIONS

The inspiratory pattern in Pra does not predict the response to cardiac output to PEEP in individual patients. This is most likely because of reflex adaptations in the circuit that occur with the application of PEEP. The response of a patient to PEEP is affected by the patient's volume reserves, filling status of the right atrium, and neurosympathetic activity.