Table 6: Examination of Mechanical Ventilator Weaning, Extubation and Decannulation during Acute SCI
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.
Discussion
In comparing methods of ventilator weaning, one case control showed that PVFB allowed patients to wean faster than IMV (Peterson et al. 1994). This finding is recommended by the Paralyzed Veterans of America Consortium for Spinal Cord Medicine (2005) and is consistent with other studies that examined non-SCI patients (Brochard et al. 1994; Esteban et al. 1995). The only study to investigate the efficacy of high versus low tidal volume on ventilator weaning found that high tidal volume resulted in faster weaning and more instances of resolved atelectasis than low tidal volume (Peterson et al. 1999). The weaning period for patients on high tidal volume ventilation was an average of three weeks sooner than those who received low tidal volume ventilation.
Successful decannulation and extubation has been found to be affected by the level and severity of injury whereby a higher rate of extubation is more likely to be achieved in patients with lower spinal cord injuries (Call et al. 2011). Decannulation is performed with a higher rate of success among patients with lower level cervical injuries compared to those with higher cervical cord injuries (Nakashima et al. 2013). The presence of a tracheostomy was found by Kornblith et al. (2014) to reduce attempts at extubation, but in cases where extubation was successful on the first attempt, patients had shorter intensive care unit and hospital stays compared to those who have failed one or more times (Call et al. 2011). Kornblith et al. (2014) also noted that among the patients included in their study, the majority of individuals did not require mechanical ventilation at the time of discharge indicating that the many SCI patients can be successfully weaned from ventilators; however, this was significantly more common in patients who did not have a tracheostomy compared to those who did require this procedure (p<0.05).
Conclusion
There is level 3 evidence (from one case control study; Kornblith et al. 2014) that acute SCI patients who do not require tracheostomies have a higher success rate of mechanical ventilation weaning compared to those who do require this procedure.
There is level 3 evidence (from two case control studies; Nakashima et al. 2013; Call et al. 2011) that higher level SCI correlates with lower rates of decannulation and extubation in acute SCI patients.
There is level 2 evidence (from one cohort study; Peterson et al. 1999) that higher ventilator tidal volumes may speed up the mechanical ventilation weaning process compared to lower ventilator tidal volumes in acute SCI patients.
There is level 3 evidence (from one case control; Peterson et al. 1994) that progressive ventilator-free breathing is a more successful method of weaning acute cervical SCI patients from mechanical ventilation than intermittent mandatory ventilation.
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Weaning from mechanical ventilation is more successful in patients who have not had a tracheostomy, and rates of decannulation and extubation are higher in patients with lower level injuries during the acute phase post SCI.
For mechanical ventilation weaning, progressive ventilator-free breathing may be more successful than intermittent mandatory ventilation, and using higher ventilator tidal volumes may speed up the weaning process compared to lower ventilator tidal volumes during the acute phase post SCI.
