Discussion
Mechanical ventilation is perhaps the most important advancement in the care of critically ill patients of the 20th century, as the severe pulmonary dysfunction that is common to sepsis, severe trauma, and primary cardiopulmonary disease is essentially non-survivable in the absence of mechanical support. It is well recognized, however, that with mechanical ventilation comes risks, including lung injury, pneumonia, and laryngeal injury from indwelling endotracheal tubes. Recognition of the time-dependent nature of these risks has led to clinical vigilance with respect to discontinuing ventilator support and extubating patients as soon as the clinical condition allows. Whether or not the patient is in fact ready for extubation is a clinical assessment, and naturally, sometimes this assessment will be incorrect in retrospect, and a patient will require reintubation.
Unfortunately, extubation failure is associated with deleterious outcomes including increased duration of mechanical ventilation and mortality.2 The results of this study further confirm these associations. The mechanisms of the relationship between extubation failure and mortality, however, remain unclear. It is possible that extubation failure is simply a marker of severity of illness—sicker patients are more likely to fail extubation and more likely to die in hospital. However, the contribution of the period of distress between extubation and reintubation, along with the act of reintubation in a distressed patient, likely causes subsequent patient deterioration as well.
A number of causes of extubation failure have been identified, including upper airway obstruction, excessive secretions, cardiac comorbidity, and encephalopathy.2 The majority of studies that examine this issue have originated from cohorts of primarily medical or mixed cohorts of ICU patients. Patients with trauma represent a unique group, given that the indications for mechanical ventilation are often heterogeneous and multifactorial, including severe brain injury, hemorrhagic shock and the sequelae of resuscitation, thoracic injury, and delirium often associated with recreational drugs and/or alcohol. Relatively few studies have addressed extubation failure in cohorts of patients with trauma. Brown et al5 performed a study of extubation failure among patients with trauma, and observed a failure rate of 6%, similar to the failure rate reported in the present study. In contrast to this study, Brown et al identified that spine fracture, initial intubation for airway compromise (present or impending), GCS at extubation, and delirium tremens were independent risk factors for extubation failure. Bilello et al6 performed a similar study at a level I trauma center, focusing specifically on patients with blunt trauma with pulmonary contusion. They observed that PaO2/FiO2 ratio <290 and alveolar-arterial oxygen difference ≥100 mm Hg at time of extubation were predictive of extubation failure.
In both of these studies and in the present study, it is notable that the large majority of patients had successfully completed an SBT. Evidence for the superiority of SBT over other weaning strategies originated in the 1990s, and since that time the SBT has become the foundation for institutional extubation protocols, including our own. It is instructive, however, that successful completions of SBT does not predict extubation success. As discussed by Brown et al,5 it is important to remember that several factors need to be considered in a patient who has passed an SBT prior to committing to extubation. SBT does not account precisely for a patient's level of cognition, ability to clear secretions, or participate in pulmonary toilet following extubation.
A relatively distinctive observation in the present study was the association between extubation failure and non-surgical intensivist consultation. Over the period of time during which the study was conducted, the trauma service call panel was staffed by surgeons with and without board certification in surgical critical care. However, all trauma surgeons were credentialed to provide surgical critical care by the hospital. The hospital's intensive care units were of the ‘open’ model, whereby any physician could place a patient in the ICU and intensivist consultation was not mandated. The available intensivist consult service was composed of non-surgeons (primarily certified in critical care via internal medicine pathway), and it was the practice of the trauma service to selectively consult this group for assistance with patient care. However, no specific criteria or guideline for consultation was in place during the study period. Approximately 60% of the patients studied received non-surgical intensivist consultation prior to extubation, including 59 of the 63 extubation failures. In contrast, over one-quarter of the patients in the study were admitted to a trauma surgeon who was board-certified in surgical critical care, and this had no significant bearing on extubation failure versus success.
The explanation for the association between non-surgeon intensivist consultation and extubation failure is not clear. It is possible that patients with intensivist consultation were more likely to fail extubation as a result of underlying comorbidities, severity of illness, and/or time on the ventilator. However, these variables were evaluated and accounted for in bivariate comparison and multivariate regression analysis, and demographic and/or clinical characteristic differences between groups are not apparent. It remains plausible, however, that patients with relatively more complicated clinical issues were more likely to have received intensivist consultation and, in turn, were more likely to have higher risk for extubation failure. This confounding by indication (ie, intensivist consultation) may be present despite the apparent similarities between groups according to the variables that were compared.
It is also possible that the trauma surgeon, privy to an inherent understanding of a patient's injury burden, may be at an advantage with respect to the decision to extubate. Klein et al8 compared the outcomes of patients managed at a regional trauma center before and after the implementation of a surgical critical care service. Prior to the implementation of the service, the ICU care at their center was provided by a pulmonary medicine intensivist group. The authors identified that following implementation of a surgical critical care service, whereby their patients with trauma received ICU care solely from trauma surgeons on a rotating basis, there were improvements in pulmonary complications (3% vs 6%, p<0.001) and fewer ventilator days (3 vs 4, p=0.002). Notably, there was also an observed decrease in the rate of failed extubation (4% vs 9%, p<0.001). The American College of Surgeons' Committee on Trauma (ACSCOT) has advocated for trauma surgeon-led care of trauma surgeons in the ICU, and in the most recent version of the Resources for Optimal Care of the Injured Patient (the ACSCOT published guidelines for trauma center verification), a surgically directed ICU physician team led by a surgeon boarded in surgical critical care is mandated for level I accreditation/verification.9 In accordance, we have recently reconfigured our care model to satisfy this requirement, whereby surgeons who are board-certified in surgical critical care provide all intensivist consultation to our trauma service. Whether or not our experience will be similar to that reported by Klein et al remains to be determined, but ultimately will help to determine whether the relationship between non-surgeon intensivist and extubation failure was relatively more attributable to provider or patient.
The remaining significant observation of this study was the association between fever and extubation failure. In bivariate analysis, fever and pneumonia were significantly associated with extubation failure. These variables were noted to be collinear; however, including both in the regression proved to provide the best fit, and ultimately fever was observed to be the independent predictor of extubation failure. The presence of fever may or may not have been associated with a pulmonary source. Nonetheless, its presence should signal to the provider that an active infectious or inflammatory process is present, and attempting to extubate the patient in the midst of this process may be ill advised, whether or not the patient had successfully completed SBT.
Limitations of this study include the issue of confounding by indication as described above. The reason for intensivist consultation was not tracked, but indications for consultation likely included the presence of chronic pulmonary comorbid disease, acute pulmonary dysfunction beyond the comfort level of the trauma surgeon, and individual trauma surgeon's interest and comfort with the critical care issues for each patient. Although underlying comorbidities, severity of illness, and/or time on the ventilator were similar between groups, it is possible that there is residual confounding between intensivist consultation and extubation failure explained by additional patient disparities. In addition, the attribution of the decision to extubate to a specific physician was not explicitly captured. In general, the decision to extubate was made by the intensivist if following the patient in consultation, or the trauma surgeon if no intensivist was involved. However, it is possible that in some cases, the trauma surgeon made the decision to extubate despite non-surgeon intensivist consultation. Our center is a teaching institution with surgery and medicine residency programmes, and although decision to extubate is generally an attending-level decision in our facility, it is also possible that some events could have been attributable to resident physician decisions.