Cardiopulmonary effects of non-invasive positive pressure ventilation (NPPV) - a controlled, prospective study

Background: This study was undertaken to investigate the haemodynamic effect of non-invasive positive pressure ventilation (NPPV) in patients after cardiac surgery. NPPV has recently become popular as method for treating acute respiratory failure. Its influence on cardiopulmonary haemodynamics is still unknown. Methods: 30 extubated low-risk patients were included in four study intervals after cardiac surgery. During the first and the third interval, the patients breathed spontaneously and received oxygen via face mask for 45 min. Both intervals were followed by 45 min on NPPV. Results: Cardiac index increased significantly from 2.8 to 3.1 ml/min/m(2) during NPPV (p < 0.001) and from 2.7 to 3.2 ml/ min/m(2) (p < 0.001). Mixed venous saturation rose significantly from 72.4 to 74.8 % (p < 0.001) and from 72.1 75.4% (p < 0.001) during NPPV while the oxygen extraction ratio decreased from 25.5 and 26.1% to 23.0 (p < 0.001) and 22.6% (p < 0.001) during NPPV. At the same time, urine production increased significantly from 182 to 328 ml/h and from 186 to 285 ml/h (p < 0.001). Heart rate and mean arterial blood pressure rose significantly during NPPV. There were no significant changes in systemic and pulmonary haemodynamics, oxygenation or CO2 elimination. Conclusions: NPPV improves Cl significantly in stable cardiac surgery patients. Factors other than blood pressure, vascular resistance or blood gases must exert an additional influence on Cl. They are still not identified. Changes in transmural pressure during NPPV may play an important role.