Tidal Volume during Assisted Ventilation after Double-Lung Transplantation.

The rate of lung transplants is increasing, and these patients frequently develop respiratory complications necessitating mechanical ventilation (1). When treating these patients, the risks of mechanical ventilation constitute an important concern, and clinicians aim to simultaneously protect the lung while avoiding ventilator-induced diaphragm dysfunction by maintaining spontaneous breathing. Targeting the ideal VT for each patient is challenging. According to the underlying lung disease of the recipient and his or her previous total lung capacity (TLC), the size of the transplanted lungs may differ from the theoretical TLC based on height. Actual TLC can vary considerably from one transplanted patient to the next and is poorly correlated with height (2). Furthermore, bipulmonary transplanted patients have denervated lungs without vagal afferent fibers. As a consequence, some feedback mechanisms necessary for control of breathing may be lacking, which can result in large VT, as shown in animals (3) and during exercise in lung-transplanted patients (4). Neurally adjusted ventilatory assist (NAVA) is a mode of ventilation that delivers support in proportion to diaphragmatic electrical activity, the latter being a direct expression of neural inspiratory activity (5). Over a certain range of assist, the patient is able to fully control his or her VT, which is not the case with traditional modes of assist. We analyzed VT in patients ventilated with NAVA after bilateral lung transplantation. We compared these volumes with nontransplanted patients at a similar stage of difficult weaning, using the same approach to titrate NAVA. In addition, we examined the relationship between the patient’s VT under NAVA and their most recent TLC.