There are several predictors (factors/injury level) of respiratory function in patients with SCI which should be considered:
- A lower lesion level positively predicts lung function and respiratory muscle strength in people with motor complete SCI (Mueller et al. 2012; N=440). Mueller et al (2008; N=109) reported a significantly lower lung function in patients with SCI and high tetraplegia (C3-C5), compared with low tetraplegia (C6-C8), and low tetraplegia compared with low paraplegia patients (T7-T12).
- Younger age, being male, heavier, and tall were also significant positive predictors of lung function parameters (Mueller et al. 2012; N=440). Inspiratory muscle strength (PImax) was positively predicted by younger age, being male, and being heavier, while expiratory muscle strength (PEmax) was positively predicted from younger age, being male, and a greater time since injury.
- Wheezing significantly predicted (after adjusting for age) mortality in patients with chronic SCI, with a relative risk of 2.38 (Garshick et al. 2005; N=361). A persistent wheeze (after adjusting for age) marginally predicted mortality, with a relative risk of 1.87 (Garshick et al. 2005; N=361).
- Garshick et al. (2005; N=361) reported a 3% decrease in mortality rate with every increase in percent-predicted FEV1 and FVC.
- Patients with SCI with a higher lesion level (C1-C5) and injury severity (ASIA A) are at greater risk of mortality (odds ratio of 2.3, p = 0.0002) than ventilator-dependent patients with SCI with a lower level and severity (Shavelle et al. 2006; n=319).
- Shavelle et al. (2006; N=1986) also suggested that following discharge, patients with SCI and with lower-level injuries (C6 below) are more likely to wean off ventilator dependency, compared to higher and more severe SCI injuries (i.e., C1-C5 ASIA A).
- A Swedish retrospective study found the risk of mortality (relative risk) to be 2.1 times greater in patients with SCI who experienced respiratory complications during their first rehabilitation visit, compared with those who had no respiratory complications (Josefson et al. 2021; N=136).
- The risk of pulmonary complications was 10 times more likely in AIS A patients and 1.7 times more likely in AIS C patients compared with AIS D (Aarabi et al. 2012, n=109).
The effects of respiratory function on functional outcomes are listed below:
- Patients with SCI and dyspnea during physical activity and rest (p < 0.001), weak cough strength (p = 0.02), and a reduced FVC (p = 0.04) reported significantly greater restrictions in social functioning (Postma et al. 2016; N=147).
- Phrenic nerve stimulation (PNS), in comparison with mechanical ventilation (MV), is suggested to significantly (p < 0.001) improve quality of speech in respiratory device-dependent patients with SCI (Hirschfeld et al. 2008; N=64). Although a small sample size, patients with SCI on PNS were more likely to return to work or school, compared with the MV group (Work, PNS 7 vs. MV 2; School, PNS 2 vs. MV 0) (Hirschfeld et al. 2008; N=64).
- In the presence of respiratory complications, patients with SCI are less likely to participate in 18 of 26 different daily activities (Cobb et al. 2014; N=1137). Specifically, there was a 20% to 139% increased probability that patients with SCI would be less likely to participate as much as they wanted in a specific daily activity. The relative risk of not participating in traveling and holidays was 1.20, while the relative risk of not communicating by electronic means was 2.39 (Cobb et al. 2014; N=1137).
- Patients with SCI who did not require ventilator use at discharge report a better quality of life (QOL) and health status 1 year following injury, compared to those who required assisted ventilation (Charlifue et al. 2011; N=1635). In the 1635 patients with SCI assessed, the non-ventilator group reported a better health status than the previous year (odds ratio 1.2, p = 0.012), and a reduced depression incidence (OR 1.7, p = 0.045) compared with the ventilator group (Charlifue et al. 2011; N=1635). Satisfaction with life was reported to be 1.7 times greater in the non-ventilator group compared with the ventilation group (p = 0.015). Although social integration had a reported odds ratio of 1.65, it was not a significant predictor in the model (Charlifue et al. 2011; N=1635).
- A multicenter study of 14 trauma centers in the USA found approximately 72% of people with SCI at discharge did not require MV (Kornblith et al. 2013; N=360). In the cervical SCI subgroup analysis, approximately 84% had successful extubation, and 62% were discharged not requiring MV.
- Kornblith et al. (2013; N=360) also reported that participants with SCI and with a cervical injury were 14 times more likely to continue with MV following tracheostomy (TOT) (p < 0.05).
- Sports injuries, a higher AIS admission score, lesion length, younger age, and a greater neurological level were associated with pulmonary complications (Aarabi et al. 2012; n = 109).