Assist-control vs. pressure support ventilation: sleep patterns and sedation

No comparisons between pressure support ventilation (PSV) and assist-control ventilation (ACV) during noninvasive ventilation (NIV) are actually available in critically ill patients (awake or asleep). Only physiological studies have described the reciprocal influences of sleep with the delivered ventilation during ACV or PSV. Whatever the mode used, sleep is known to induce a glottic narrowing that reduces the amount of ventilation that can reach the lungs. Moreover, due to glottic interferences, NIV using PSV (in its controlled mode) appears less predictable and less stable than NIV with ACV. PSV used in spontaneous mode does not appear more efficient due to respiratory rhythm instability despite absence of any glottic interference with the delivered ventilation. In intubated critically ill patients, sedation with or without neuro-muscular blockade is generally required, at least during the beginning of the resuscitation. If sedation induces an 'unnatural sleep', it does not seem to account for sleep deprivation. For invasive mechanical ventilation, PSV or ACV is actually favoured to full controlled modes which are known to induce diaphragmatic muscle injury. In its spontaneous mode, PSV may induce central apnoeas during sleep that may be associated with deep oxygen desaturation and, thus, must always be used with a back-up frequency. Increasing the ventilatory support with ACV (and probably PSV) overnight improves sleep quality, especially in patients with decreased respiratory capacity at baseline. Whether the respiratory muscles of ICU patients undergoing weaning procedure should be rested during the night remains to be explored