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Abstract & Commentary
By Richard H. Kallet, MS, RRT, FAARC, FCCM
Director of Quality Assurance, Respiratory Care Services, San Francisco General Hospital
Mr. Kallet reports no financial relationships relevant to this field of study.
SYNOPSIS: This multicenter, retrospective, observational study of 344 patients with acute spinal cord injury examined ventilator weaning, extubation, and tracheostomy practices. Patients undergoing tracheostomy had lower weaning success rates and fewer ventilator-free days, along with a higher incidence of both ventilator-associated pneumonia and acute lung injury, compared to those managed with an endotracheal tube.
This study reviewed outcomes among patients with acute spinal cord injury (SCI) who initially required mechanical ventilation to determine the effect of receiving a tracheostomy as compared to being managed exclusively via endotracheal tube. Study patients had radiologically confirmed cervical (65%), thoracic (26%), and lumbar (9%) SCI that was consistent with clinical presentation. Blunt injury was the predominant mechanism (86%). A diagnosis of complete SCI was made in 50% of cases, and 20% of the patients also had traumatic brain injury (TBI). Attempts at extubation occurred in only 54% of patients, but increased as the level of SCI decreased from cervical (36%), to thoracic (67%), to lumbar (88%). However, extubation was surprisingly successful in all three groups: 84%, 92%, and 96%, respectively.
At hospital discharge, 63% of cervical, 87% of thoracic, and 94% of lumbar SCI patients had achieved unassisted breathing. The use of tracheostomy (82% vs 16%) and the incidence of ventilator-associated pneumonia (VAP; 45% vs 32%) were higher in cervical vs thoracic SCI, while ventilator-free days (in the first 28 days) were lower (10 vs 21, respectively). There was a marked increased incidence in VAP among patients who had a tracheostomy (61% vs 21%) as well as a higher incidence of acute lung injury (ALI; 13% vs 4%). However, patients treated with tracheostomy also had a significantly higher incidence of complete injury, TBI, and other injuries. In the multivariate logistic regression, tracheostomy was the most salient variable associated with ventilator dependence (adjusted odds ratio of 14.11, P = 0.001).
Impaired pulmonary function is the primary cause of morbidity and mortality in SCI.1 The constellation of problems includes respiratory muscle weakness or paralysis, chest wall instability, ineffective sigh and cough, and autonomic dysfunction resulting in bronchospasm, increased secretions, and pulmonary edema. Moreover, sudden death from either a catastrophic loss of airway or "delayed apnea" is not uncommon in the early stages of cervical SCI without an artificial airway.2,3
Early tracheostomy is considered essential to SCI management and is perceived both to facilitate pulmonary care and to expedite discharge from the ICU, particularly in patients diagnosed with complete cervical injury and having an Injury Severity Score (ISS) > 32.1 Not surprisingly, the tracheostomy cohort in the current study had a mean ISS of 34, and those who remained on mechanical ventilation at hospital discharge, 94% of whom had complete injury, had a mean ISS of 36.
The current study is provocative as it demonstrates that > 60% of cervical SCI patients do not require mechanical ventilation at discharge from an acute care facility. This suggests that clinicians may prematurely judge these patients as "unweanable," thus placing them at increased risk for VAP. Another retrospective study examined ventilator dependence in cervical SCI based on higher vs lower, and complete vs incomplete injury.4 In that study, only 35% of incomplete cervical SCI patients actually required intubation, while only 7% ultimately required tracheostomy. Of those with complete injury at C6 or below, only 15% of survivors were ventilator-dependent on hospital discharge.4
Aggressive, early weaning of SCI patients is hindered partly by the phenomenon of ascending cord injury from worsening inflammation and/or bleeding.4 However, inflammation also can subside with unanticipated early improvement in pulmonary status. Thus, determination of the need for tracheostomy and the timing of weaning should be made empirically on objective measures of pulmonary function. Probably the most pertinent variables informing successful weaning and extubation in SCI (i.e., spontaneous tidal volume, vital capacity, and maximal expiratory pressure) were not reported in this study, but need to be incorporated in any prospective trial. As the authors argue, a prospective trial aimed at identifying which SCI patients should be targeted for early weaning and extubation is urgently needed. Of paramount importance will be identifying threshold values of respiratory muscle function and pulmonary hygiene that allow the safe, early termination of mechanical ventilation.
1. Vazquez RG, et al. Respiratory management in the patient with spinal cord injury. BioMed Res Int 2013;168:757.
2. Hassid VJ, et al. Definitive establishment of airway control is critical for optimal outcome in lower cervical spinal cord injury. J Trauma 2008;65:1328-1332.
3. Lu K, et al. Delayed apnea in patients with mid- to lower cervical spinal cord injury. Spine 2000;25:1332-1338.
4. Como JJ, et al. Characterizing the need for mechanical ventilation following cervical spinal cord injury with neurologic deficit. J Trauma 2005;59:912-916.