Normalization of blood carbon dioxide levels by transition from conventional ventilatory support to noninvasive inspiratory aids

Abstract

Chronic hypocapnia seems to be common in long-term ventilator assisted individuals (VAIs) with paralytic/restrictive respiratory conditions. It has predominantly been reported for VAIs using intermittent positive pressure ventilation (IPPV) delivered via tracheostomy tubes. Chronic hypocapnia decreases ventilator-free breathing time (VFBT) and may be associated with increased bone resorption. Attempts to reverse chronic hypocapnia by decreasing minute ventilation and providing supplemental carbon dioxide have failed because of air hunger and patient resistance. We maintained normocapnia in 22 24-hour-a-day VAIs by using noninvasive IPPV. Chronic hypocapnia was corrected in three VAIs and hypercapnia in two VAIs by switching from conventional ventilatory support to the use of noninvasive inspiratory muscle aids. The other 17 VAIs remained normocapneic by being managed by noninvasive ventilatory support from onset of ventilatory failure. Eleven of these VAIs had been intubated or tracheostomized for brief periods but were successfully returned to noninvasive support. We conclude that alveolar ventilation can be maintained within normal range for VAIs who use noninvasive IPPV and can be normalized by transition from conventional tracheostomy IPPV to noninvasive IPPV.