Objective: The detrimental effect of positive airway pressure on right ventricular (RV) performance is controversial and the aim of this study was to determine the effects of constant positive airway pressure without ventilatory fluctuation on RV performance with the aid of a pulmonary arterial catheter equipped with a rapid response thermistor for measuring RV ejection fraction (RVEF) and RV end-diastolic volume index (RVEDVI).
Design: A prospective, clinical study.
Setting: The central operating theatre of a university hospital.
Patients: Nine patients who had major surgery and required right heart catheterization for normal clinical management.
Measurements and results: Cold indicator was injected into the RV 4 or 5 times for each airway pressure (0, 10 or 20 cmH2O) which was maintained manually stable for 15 s, and 9 paired data were analyzed by repeated-measures analysis of variance. They are separated into two groups; RVEF at zero airway pressure greater (A group) or less (B group) than 0.4. In A group (7 patients), increasing airway pressures (0 vs 10 vs 20 cmH2O) did not affect RVEF (0.55 +/- 0.05 vs 0.54 +/- 0.06 vs 0.56 +/- 0.04), RVEDVI (69 +/- 36 vs 73 +/- 29 vs 58 +/- 20 ml.m-2), or stroke volume index (SVI: 38 +/- 18 vs 40 +/- 17 vs 33 +/- 13 ml.beat-1.m-2); however, in B (2 patients), RVEF (0.35 and 0.38 vs 0.31 and 0.28 vs 0.19 and 0.17) and SVI (35 and 28 vs 32 and 27 vs 27 and 23) decreased, while RVEDVI increased (99 and 73 vs 103 and 97 vs 146 and 132).
Conclusions: In most patients, the changes in RVEF, SVI, and RVEDVI did not occur under constant positive airway pressure, therefore the changes reported in mechanically ventilated patients may not attributable to the extent of positive airway pressure but rather to abrupt increases in airway pressure. These appears, however, to be patients whose RV function is so disturbed that they cannot cope with increased afterloads.