Physiological effects of posture on mask ventilation in awake stable chronic hypercapnic COPD patients

Abstract

Stable chronic hypercapnic patients are often prescribed long-term mask noninvasive pressure support ventilation (NPSV). There is a lack of information on the effects of posture on NPSV. Therefore posture induced changes in physiological effects of NPSV in awake stable chronic hypercapnic patients were evaluated. In 12 awake chronic obstructive pulmonary disease (COPD) patients breathing pattern, respiratory muscles, mechanics and dyspnoea (by visual analogue scale: VAS) were evaluated during spontaneous breathing (SB) in sitting posture and during NPSV in sitting, supine and lateral positions randomly assigned. Arterial blood gases were evaluated during SB and at the end of the last NPSV session (whatever the posture). As expected NPSV resulted in a significant improvement in carbon dioxide tension in arterial blood (Pa,CO2) (from 7.4+/-0.85 to 6.9+/-0.7 kPa). When compared with SB, sitting NPSV resulted in a significant increase in tidal volume and minute ventilation and in a significant decrease in breathing frequency. Inspiratory muscle effort as assessed by oesophageal pressure swings and pressure-time product per minute (from 14+/-4.8 to 6.2+/-3.5 cmH2O, and from 240+/-81 to 96+/-60 cmH2O x s x min(-1) respectively), intrinsic dynamic positive end expiratory pressure (from 2.7+/-2.3 to 1.4+/-1.3 cmH2O) and expiratory airway resistance (from 18+/-7 to 5+/-3 cmH2O x L x s(-1)) decreased during sitting NPSV, whereas VAS did not change. Changing posture did not significantly affect any parameter independently of the patients weight, whether obese or not. In awake stable hypercapnic chronic obstructive pulmonary disease patients changing posture does not significantly influence breathing pattern and respiratory muscles during noninvasive pressure support ventilation suggesting that mask ventilation may be performed in different positions without any relevant difference in its effectiveness.