Effect of sleep on patient/ventilator asynchrony in patients undergoing chronic non-invasive mechanical ventilation

Patients who require home non-invasive ventilation (NIV) during sleep normally have the ventilation settings adjusted empirically during daytime wakefulness. However, patient-ventilator asynchrony may occur during sleep. To detect the incidence of ineffective efforts (IE) during the sleep compared to wakefulness, we studied 48 patients already enrolled in a long-term home NIV programme.

We evaluated arterial blood gases, breathing pattern during spontaneous breathing (SB) and ventilation during wakefulness. In addition, we assessed the breathing pattern and oxygen gas exchange during night-time NIV.

Daytime NIV significantly improved blood gases compared to SB (PaO2 NIV 10.2 +/- 1.95 kPa vs PaO2 SB 8 +/- 1.37, p < 0.001; PaCO2 NIV 5.75 +/- 1.08 kPa, vs PaCO2 SB 6.5 +/- 1.25, p < 0.001). The IE index was higher during sleep compared to wakefulness (48 +/- 39.5 events/h versus 0 +/- 0). The IE index was correlated with the time spent with SaO2 < 90% (r = 0.39, p < 0.01), but not with ventilator parameters, underlying disease, ventilation mode or type of mask. Eight patients had an IE index >100 events/h; these patients had a faster respiratory rate, required a higher level of inspiratory assistance and had poor gas exchange during sleep.

We conclude that IE to breath are common during nocturnal NIV and that they may be associated with desaturations even in patients who are considered compliant and effectively treated.