Early and relatively nonselective use of tracheostomy in patients with severe acute respiratory failure has been proposed by a number of investigators [4, 5]. However, this approach will commit a number of patients to the risks of a surgical procedure from which many will not benefit. Alternatively, limiting tracheostomy to the most difficult to wean patients may contribute to unnecessarily prolonged weaning, to more days of MV and to complications such as pneumonia and laryngeal injury, and possibly death . The authors advocating ET only compared patients who underwent tracheostomy early with patients who underwent later tracheostomy, and did not consider patients who were extubated after the arbitrary definition of ET [4, 5]. This leads to an important bias against late tracheostomy. In light of the difficulties presented by the existing literature, our objective was to define a reasonable, physiologically based and clinically relevant time point at which tracheostomy should be considered in critically ill patients requiring MV.
Before considering the implications of our observations, it is important to address the limitations of this study. First, this was a retrospective analysis of a dataset that, while prospectively collected, was used to address a separate research question. We were therefore cognizant of the potential pitfalls of overinterpreting our observations. In part, we selected a limited number of end-points in order to minimize falsely positive associations with tracheostomy. We were primarily interested in the potential influence of tracheostomy on the duration of weaning and of MV, as these periods are distinguished by a relatively clear onset (by criteria detailed in Patients and methods) and end (liberation from MV). The other end-points we examined, pneumonia and fatigue, were of secondary interest in this study, but nonetheless provided interesting and important observations. Fatigue, potentially the most subjective end-point, was assigned prospectively according to a predefined set of criteria, minimizing the bias in its assignment .
The outcomes we examined are arguably few of many end-points that a study such as this may address. There are, no doubt, other outcomes that are of equal relevance, such as mortality and the costs of care associated with tracheostomy. Relatively few patients in this series died (5/75 patients; 7%), and all were in the ST group. This low case-fatality rate will make it difficult to test the effect of tracheostomy on mortality in a clinical trial. Other complications of tracheostomy exist and it is possible that they would nullify any benefit of a more liberal use of tracheostomy. Although complication rates for surgical and percutaneous tracheostomy are low, it will be important to consider how this should influence the decision to perform these procedures [8, 12]. Nevertheless, it reasonable to consider tracheostomy safe. When performed in patients who are hemodynamically stable and require minimal ventilator support (positive end-expiratory pressure ≤ 5 cmH2O, FiO2 ≤ 0.4, etc.), the perioperative complication rate has been reported to be 0–46% and the attributable mortality rate is not higher than 2% [8, 13]. In our study, the majority of tracheostomies were performed by the open surgical technique in the operating room and there were no deaths attributable to the procedure. It is not clear whether the safety of the percutaneous approach should alter the decision regarding when to perform the procedure [12, 14].
Perhaps the greatest limitation of our study is the inclusion of heterogeneous patients with regard to the presence of a TBI. Nevertheless, because all patients were cared for by the same critical care team and according to the same respiratory care protocols, we chose to include all patients rather than an arbitrary subgroup based upon the presence or absence of TBI. We have attempted to address this issue in our analyses, but recognize that our conclusions must be tempered by the baseline differences between the two groups.
In some patients who are otherwise able to breathe spontaneously, liberation from MV may be prevented by concerns over the ability to protect against pharyngeotracheal aspiration and to clear pulmonary secretions. Tracheostomy may facilitate liberation in such circumstances, although the benefits here are not clear. It is often difficult to objectively determine which patients will be able to protect their airway after extubation. For example, neurosurgical patients with GCS score < 8 are more likely to require reintubation than patients with GCS score ≥ 8 . However, extubation is often possible in patients with GCS score < 8 . A number of patients in our study had TBI and many were in the ET group (14/30 patients with TBI had an ET). It is probable that concerns over the ability of patients with depressed consciousness to protect their airway contributed to the decision to perform tracheostomy earlier in patients with TBI. Nevertheless, the frequency of altered mental status at the time readiness-to-wean criteria were met was similar in the ET group (14/21 patients with GCS score ≤ 8) and in the ST group (41/53 patients with GCS ≤ 8), suggesting that differences in mental status were not the primary factor in deciding for tracheostomy.
In addition, calculation of the propensity score is meant to address unmeasured bias and confounding that may exist in the decision to perform tracheostomy. We observed that after this adjustment the association between ET and a shorter duration or weaning remained unchanged, suggesting no important residual confounding or bias. However, in order to further explore the potential role of altered mental status and TBI in the process of liberation from MV, we re-examined the relationship between ET and the duration of weaning separately for patients with and without TBI, controlling for the same factors in each analysis. We observed that the association between ET and a shorter period of weaning was similar in patients with and without TBI. Thus, while the inclusion of patients with TBI did not appear to bias our results, it will be necessary to consider the importance of a depressed level of consciousness and to determine other objective measures of a patient's ability to protect their airway in our decisions about tracheostomy and weaning and in future studies of the role of tracheostomy. It will be important to consider the observations of Coplin and colleagues, which indicate that a reduced level of consciousness should not be the primary factor in deciding for or against tracheostomy .
It is not clear from previous reports what the correct reference time point should be for defining ET. This was a primary objective of the present report. A threshold based upon an arbitrary number of days after intubation is problematic, given that many patients may not safely undergo tracheostomy due to hemodynamic, neurological or respiratory instability for a number of days. In our study, 20% of patients did not meet readiness-to-wean criteria until after more than 8 days of MV. For many of these patients it may have been unsafe to perform a tracheostomy at a point that has been defined by other investigators as 'early'. Nonetheless, the findings of our study provide the basis for re-examining whether the timing of tracheostomy may impact clinical outcomes. In patients with resolving respiratory failure, most studies have found that tracheostomy results in small changes in dead space ventilation, work of breathing or other objective parameters that may aid in liberation from MV [17, 18]. These small changes probably benefit the few patients with borderline respiratory muscle function or relatively large percentage of alveolar dead space. Both circumstances are not typically encountered in postoperative or patients or trauma victims [17, 18]. Therefore, potential benefits would be related to less easily quantifiable measures, such as improvements in patient comfort, reductions in anxiety, changes in physician behavior or the minimization of aspiration related to translaryngeal intubation. These may translate into a measurable decrease in the duration of weaning.
Prolonged translaryngeal intubation is associated with a number of complications potentially leading to permanent damage to the laryngeal complex. While the incidence of vocal cord injury is associated with increased length of intubation and certain medical conditions such as diabetes mellitus, conversion from a translaryngeal airway to a tracheostomy may not reduce anatomical airway complications . In general, long-term airway complications such as laryngeal stenosis are uncommon enough to be considered reportable events, and often occur in the presence of additional airway insults, such as inhalation injury . Because laryngeal stenosis is uncommon (2–6%) it would be necessary to study over 1000 patients with adequate follow-up in order to demonstrate a 50% reduction in laryngeal stenosis . However, while most of the acute laryngeal changes (inflammation, ulceration, and edema) resolve without long-term sequelae, translaryngeal intubation leads to transient vocal cord dysfunction that may cause microaspiration and pneumonia . We observed a higher incidence of pneumonia in the ST group, and the majority were diagnosed after weaning criteria were met (15/20 patients; 75%). Given that the assignment of pneumonia is potentially biased in this nonblinded observational study, it is impossible to attribute the increased pneumonia risk to prolonged translaryngeal intubation. Nevertheless, this possibility should be addressed as an important end-point in future clinical trials of the effects of ET.