Right atrial pressure predicts hemodynamic response to apneic positive airway pressure

Objective: To evaluate if the preexistant filling state, assessed by right atrial pressure (RAP), pulmonary artery occlusion pressure (PAOP), and righ t ventricular end-diastolic volume index (EDVI), would define the subsequen t hemodynamic effects of increases in airway pressure (Paw). Design: Prospective open clinical study. Setting: Postoperative intensive care unit, university hospital. Patients: Twenty-two consecutive ventilator-dependent patients with mild to severe acute lung injury with Murray scores (scoring infiltrates an chest radiograph, oxygenation index, lung compliance, and the level of positive e nd-expiratory pressure) ranging from 0.5 to 3.0 without history of preexist ing cardiopulmonary disease. Interventions: Paw varied during apnea from 0 to 10, 20, and 30 cm H2O usin g inspiratory hold maneuvers of 15 sees. Measurements and Main Results: Cardiac index and right ventricular ejection fraction were measured by the thermodilution technique. We made measuremen ts in triplicate using manual injection of iced saline. Right ventricular v olumes were calculated. Increasing Paw induced variable changes in cardiac index among subjects (+6 % to -43% change from baseline 0 cm H2O Paw values), which correlated with percentage changes in both stroke index (r(2) = .89) and right ventricular EDVI (r(2) = .75), whereas heart rate and right ventricular ejection fracti on did not change. The change in cardiac index from 0 to 30 cm H2O Paw corr elated with baseline values for RAP, PAOP, and right ventricular EDVI (r(2) = .68, .43, and .34, respectively, p < 0.01). Increases in RAP correlated with lung compliance if baseline RAP was >10 mm Hg but did not if it was le ss than or equal to 10 mm Hg. Similarly, patients with baseline RAP less th an or equal to 10 mm Hg had a greater decrease in cardiac index than patien ts with a RAP >10 mm Hg (for 30 cm H2O Paw: -30% +/- 9% vs. -8% +/- 7%, p < .01). Conclusions: Apneic positive Paw decreased cardiac output mainly by reducin g venous return. From the investigated filling variables, RAP was most sens itive in predicting the hemodynamic response, followed by PAOP and right ve ntricular EDVI. Patients with RAP less than or equal to 10 mm Hg, if subjec ted to aggressive positive pressure ventilation, are at risk of hemodynamic deterioration and organ hypoperfusion.