Physiological changes during low- and high-intensity noninvasive ventilation

Abstract

In a physiological randomised cross-over study performed in stable hypercapnic chronic obstructive disease patients, we assessed the short-term effects of two settings of noninvasive ventilation. One setting was aimed at maximally reducing arterial carbon dioxide tension (Pa,CO2) (high-intensity (Hi) noninvasive positive pressure ventilation (NPPV)): mean±SD 27.6±2.1 cmH2O of inspiratory positive airway pressure, 4±0 cmH2O of expiratory positive airway pressure and respiratory rate of 22 breaths·min-1. The other was performed according to the usual parameters used in earlier studies (low-intensity (Li)-NPPV): 17.7±1.6 cmH2O of inspiratory positive airway pressure, 4±0 cmH2O of expiratory positive airway pressure and respiratory rate of 12 breaths·min-1. Both modes of ventilation significantly improved gas exchange compared with spontaneous breathing (SB), but to a greater extent using Hi-NPPV (Pa,CO2 59.3±7.5, 55.2±6.9 and 49.4±7.8 mmHg for SB, Li-NPPV and Hi-NPPV, respectively). Similarly, Hi-NPPV induced a greater reduction in the pressure-time product of the diaphragm per minute from 323±149 cmH2O·s·min-1 during SB to 132±139 cmH2O·s· min-1 during Li-NPPV and 40±69 cmH2O·s·min-1 during Hi-NPPV, while in nine out of 15 patients, it completely abolished SB activity. Hi-NPPV also induced a marked reduction in cardiac output (CO) measured noninvasively with a Finometer PRO (Finapres Medical Systems BV, Amsterdam, the Netherlands) compared with Li-NPPV. We conclude that while Hi-NPPV is more effective than Li-NPPV in improving gas exchange and in reducing inspiratory effort, it induces a marked reduction in CO, which needs to be considered when Hi-NPPV is applied to patients with pre-existing cardiac disease. Copyright©ERS 2012.