Physiological changes during low and high “intensity “ noninvasive ventilation

Abstract

In a physiological randomized cross-over study, performed in stable hypercapnic COPD patients, we have assessed the short term effects of two settings of non-invasive ventilation, one aimed at maximally reducing Pa,CO2 level (Hi-NPPV:27.6±2.1 cmH2O of IPAP, 4±0 cmH2O of EPAP and respiratory rate of 22·min⁻¹) and one according to the usual parameters used in earlier studies (Li-NPPV:17.7±1.6 cmH2O of IPAP, 4±0 cmH2O of EPAP and respiratory rate of 12·min⁻¹). Both modes of ventilation significantly improved gas exchange compared to spontaneous breathing (SB), but to a greater extent using Hi-NPPV (PCO2:59.3±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*sec·min⁻¹ during SB to 132±139 cmH2O*sec·min⁻¹ during Li-NPPV and 40±69 cmH2O*sec·min⁻¹ during Hi-NPPV, while in 9/15 patients completely abolished spontaneous breathing activity. Hi-NPPV also induced a marked reduction in cardiac output measured noninvasively with a Finometer, compared to 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 cardiac output, which needs to be considered when Hi-NPPV is applied to patients with pre-existing cardiac disease.