Independence from ventilation is a primary goal for patients with SCI, but the ability to wean from the ventilator is primarily determined by the level of injury. A C1 or C2 level injury results in lifetime ventilator dependency because there is loss of function of the diaphragm, abdomen, and accessory muscles that control breathing. A C3-C4 injury is more variable in whether independent breathing will be achieved, with approximately 40% of these patients managing successful weaning (Berney et al. 2011). Patients with an injury at C5 or lower often need ventilation only in the earliest stages of the injury and during spine fixation surgery but are able to wean from the ventilator soon after. Although this review focuses on ventilator weaning, extubation and decannulation during the first weeks and months of SCI, this process can span much longer in some cases (Galeiras Vázquez et al. 2013). For more information on long-term ventilator weaning, refer to the section “Mechanical Ventilation and Weaning Protocols” in the Respiratory Management chapter in SCIRE version 6.0. Before a patient initiates the weaning process, extubation or decannulation, a vital capacity of 1500 mL, clear lung radiographs, stable blood gases, stable heart rate and respiratory rate, and stable excretion levels must be achieved (Chiodo et al. 2008; Peterson et al. 1999).
To begin weaning, a patient is removed from the ventilator for short periods of time that progress to longer and more frequent intervals of independent breathing. There are several protocols for this process; progressive ventilator-free breathing (PVFB), intermittent mandatory ventilation (IMV), and pressure support are the most common protocols (Weinberger & Weiss, 1995). Newer studies are also examining the safety of higher tidal volumes for ventilator weaning (Fenton et al., 2016). PVFB is the process whereby a patient experiences intervals of ventilator-free time that increases in length throughout the day to build muscle tone (Galeiras Vázquez et al. 2013). If PVFB is the chosen method for weaning, a patient can be weaned using either low tidal volume or high tidal volume. Using larger ventilator volumes (greater than 20 mL/kg) is thought to be more effective than low tidal volume and can resolve atelectasis and increase surfactant production; however, this method is also associated with more pulmonary complications in certain patient cohorts (Peterson et al. 1999; Wallbom et al. 2005). IMV is the process whereby the ventilator provides a predetermined number of breaths within a certain time frame and the patient is encouraged to spontaneously breathe in between them when they can. The number of breaths decreases as patients gain pulmonary independence. Lastly, pressure support ventilation is the technique whereby the patient must initiate every breath and the ventilator assists with the rest of the breathing process. Biphasic positive airway pressure (BiPAP) and continuous positive airway pressure (CPAP) are two systems designed for non-invasive respiratory pressure support (Tromans et al. 1998). In addition to these ventilation procedures, transition from intubation to a tracheostomy, immediate extubation, and the use of diaphragmatic pacemakers are alternatives to patients requiring full time ventilation.