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.

Effectiveness of albumin versus normal saline as a test of volume responsiveness in post-cardiac surgery patients.

PURPOSE: A volume challenge is useful for determining whether cardiac output will respond to further volume loading by the Frank-Starling mechanism. To properly test this mechanism, there must be an increase in right atrial pressure (Pra) but this requires variable amounts of normal saline. The purpose of this study was to determine if 100 mL of 25% albumin would reliably provide a predictable increase in Pra and to compare this with a volume challenge with normal saline. As in a previous study, we also examined the potential for the pattern of respiratory variation of Pra to predict the response to a fluid challenge. MATERIALS AND METHODS: Twenty-eight stable patients following cardiopulmonary bypass surgery were studied in a randomized, nonblinded interventional study in an intensive care unit. All patients had pulmonary artery flotation catheter as part of their routine management and were breathing spontaneously. They were randomized to receive sufficient normal saline to increase Pra by 2 mm Hg (n = 15) or 100 mL of 25% albumin (n = 13). We also tested the ability of the respiratory variation in Pra to predict the response to a fluid challenge. They had to have an inspiratory fall in the pulmonary capillary wedge pressure of more than 2 mm Hg as an indication that they had an adequate inspiratory effort. They were classified as either having or not having an inspiratory fall in Pra. We predicted that patients without an inspiratory fall in Pra should not respond to volume loading. RESULTS: In contrast to our prediction, the increase in Pra with albumin was less than the increase with normal saline. However, the cardiac output increased more with albumin, which suggests that there was an increase in cardiac function with the hypertonic, hyperosmolar albumin solution. In the saline group, a lack of inspiratory fall in Pra successfully predicted that cardiac output would fail to increase with an increase in Pra in 8 out of 10 patients given saline, and 5 of 6 patients given albumin. CONCLUSION: A hyperoncotic albumin solution appears to have an inotropic effect in patients following cardiopulmonary bypass procedures. We also again show that the pattern of respiratory variation in right atrial pressure is a useful guide to predict response to volume loading.