Voies aériennes supérieures et ventilation non invasive

Abstract

Nowadays, noninvasive ventilation (NIV) is widely used for the treatment of acute respiratory failure in order to avoid endotracheal intubation. However, the glottis can influence the effective minute ventilation. Nasal intermittent positive pressure ventilation (nIPPV) using volumetric ventilators results in an adduction of the vocal cords leading to a decrease in the percentage of the delivered minute ventilation effectively reaching the lungs (VE). During NIV using a two-level positive-pressure ventilator in the controlled mode, the behaviour of the glottis and thus VE are less stable and predictable. In spontaneous mode, the glottis does not play a role in the control of VE that increases with increasing inspiratory pressures, significantly above 20 cmH 2O. During negative pressure ventilation (NPV), the increase in mechanical ventilation does not result in a narrowing of vocal cords, allowing to achieve levels of VE higher than those observed during nIPPV. Thus, the best setting are as follows: in the controlled mode with barometric ventilators: a respiratory frequency (f) around 20 breaths per minute; an I/E ratio of 1/1; 15 cmH 2O of inspiratory positive airway pressure and an expiratory positive airway pressure as low as possible; during nIPPV with volumetric ventilators: a tidal volume of 13 ml/kg; a f of 20 breaths per minute; an inspiratory flow of 0.56–0.85 l per second; during NPV: a negative inspiratory pressure of –30 cmH 2O and a f of 20 breaths per minute. Moreover, in sleeping subjects, the glottic behaviour during NIV is different from that observed in awake subjects. The best settings established during wakefulness can be not suitable during sleep as observed a glottic narrowing during NREM sleep. Thus, by contrast with endotracheal mechanical ventilation, the respiratory system does not behave like an one-compartment model during NIV.