Respiratory complications occur in 36-83% of patients with acute SCI, the exact nature of which is dependent on the level of injury as this determines which respiratory muscles are affected due to loss of innervation (Warren et al. 2014). Impaired respiratory muscle function leads to complications such as improper bronchial secretion clearance, pneumonia, atelectasis, septicemia, pulmonary embolism, and reduced vital and inspiratory capacity (Warren et al. 2014). It has been suggested that the key to their prevention is intense secretion management (Claxton et al. 1998). Hygienic behaviours, such as changing the patient’s body position to promote postural draining, performing manual assisted coughing or chest percussion, and clearing bronchial secretions, are effective in reducing death from pulmonary complications (Mansel & Norman, 1990). Large volumes of mucus, or mucus harbouring inside the lung for extensive periods of time, encourage the growth of bacteria and subsequent development of pneumonia. With respect to pneumonia, Raab et al. (2016) found that maximal inspiratory pressure was significantly associated with pneumonia risk. Those with maximal inspiratory pressure at 115% above their lesion-specific reference values had significantly fewer instances of pneumonia (Raab et al., 2016). In addition to pneumonia, atelectasis and respiratory failure are the most common pulmonary complications following acute SCI (Berlly & Shem, 2007) which often require mechanical ventilation to manage (Galeiras Vázquez et al. 2013). To confound this problem, mechanical ventilation puts patients at an increased risk for ventilator-assisted pneumonia, demonstrating how these complications can be difficult to control. Individuals with ventilator-assisted pneumonia have a death rate of 20-30% and an extended hospital stay (Call et al. 2011; Cook, 2000). Other conditions such as aspiration, acute lung injury, acute respiratory distress syndrome, and complications related to tracheostomy and intubation, such as tracheal stenosis or stomal cellulitis, also have negative respiratory implications but are less well studied.
The main conclusion drawn from these studies is that respiratory complications are prevalent among patients with acute SCI, and the likelihood of their development depends on a number of factors related to the initial injury on admission. Overall, pneumonia is the most studied associated complication with a greater incidence in patients with a higher level of injury (Cotton et al. 2005; Fishburn et al. 1990), a more severe injury (Hassid et al. 2008; Huang & Ou, 2014), larger lesions (Aarabi et al. 2012), additional fractures (Chen et al. 2013; Harrop et al. 2001), no return of deep tendon reflexes after one day (Lemons & Wagner, 1994), and who received surgical instead of percutaneous tracheostomy (Romero-Ganuza et al. 2011). With regard to tracheostomies, there is conflicting evidence regarding their contribution to respiratory complications. Some studies have found that patients who had tracheostomies experienced reduced respiratory complications compared to patients who did not have a tracheostomy (Leelapattana et al. 2012), whereas other studies reported the opposite (Harrop et al. 2004; Kornblith et al. 2014).
The development of respiratory complications is also dependent on several other factors including the completeness of the injury (Lemons & Wagner, 1994), the timing of the tracheostomy (Romero-Ganuza et al. 2011; Romero et al. 2009) and the cause of injury (Aarabi et al. 2012). Age may play a role in the development of complications (Aarabi et al. 2012), although this finding is not always supported (Lemons & Wagner, 1994). Likewise, some studies reported that receiving an early tracheostomy lowered the risk of problems (Kornblith et al. 2014; Romero-Ganuza et al. 2011; Romero et al. 2009), but other studies found it did not matter (Choi et al. 2013). Additional data on the timing of tracheostomies can be found in Section 4.4. Pulmonary complications cause a significant burden to the individual and health care system, as it increases time on ventilation, hospital stay, and costs (Aarabi et al. 2012; Chen et al. 2013; Kornblith et al. 2014; Winslow et al. 2002). Furthermore, if complications cannot be managed initially, they may accumulate and put a patient at risk for more respiratory problems. For example, Huang and Ou (2014) found that the presence of respiratory failure led to a higher likelihood of developing pneumonia. It is therefore important that prophylactic measures be taken to prevent pulmonary complications, and that they are managed intensely should they arise.
Other factors that have been less studied but still shown to be associated with higher rates of respiratory complications include a history of smoking, electrolyte imbalances, and hypoalbuminemia (Chen et al., 2013). The etiology of the SCI is also a factor, specifically sports-related SCIs (Aarabi et al., 2012). There are a variety of factors, both pre-existing and related to the injury, which determine the risk of having a respiratory complication in the acute phase. Overall, the current literature indicates that all individuals with SCI should be screened and monitored for respiratory complications in the acute phase of SCI given their frequency as well as multifaceted origins.