Effect of the initiation of noninvasive bi-level positive airway pressure on haemodynamic stability.

Noninvasive ventilation using noninvasive bilevel positive airway pressure (Bi-PAP) has been shown to be an effective means of improving oxygenation and respiratory status in patients with obstructive pulmonary disease (COPD) and acute congestive heart failure (CHF). However, it is uncertain what effects this positive airway pressure has on the haemodynamic condition of these patients. This study examines the acute changes in basic circulatory parameters with the initiation of Bi-PAP. Noninvasive measurements of the heart rate, systolic and diastolic arterial pressure, cardiac index, total peripheral resistance, ventricular ejection time, and total diastolic time were determined by impedance cardiography before and after the institution of Bi-PAP (pressures 15/5) in a group of healthy volunteers. In a collateral study, the same measurements were made in COPD patients in whom Bi-PAP was initiated for therapeutic reasons. Changes in the haemodynamic parameters were analysed using a paired t-test (p < 0.05). In the 12 healthy volunteers studied there were no significant differences in any of the haemodynamic parameters measured (average cardiac index: 2.75 +/- 0.78) over a period of 15 minutes after the placement of Bi-PAP. Similar results for most haemodynamic parameters were found in the 7 COPD patients with imminent respiratory failure (average respiratory rate 24.8 +/- 3.2) when Bi-PAP was utilized with the exception of significant but small increases in the cardiac index, stroke volume and oxygen saturation (p<0.05). While Bi-PAP is frequently used in the treatment of patients with acute respiratory failure, little is known about its effect on haemodynamics. This study suggests that the effects of the initiation of Bi-PAP on the general circulation and cardiac output may be of minor relevance.