We found that patients requiring PMV (≥14 days) who did not undergo tracheostomy had significantly higher ICU and in-hospital mortality, and were less likely to be successfully weaned, after carefully controlling for potential demographic and clinical confounders. Interestingly, translaryngeal intubated patients had significantly shorter durations of MV and ICU and hospital stays than patients who underwent a tracheostomy. To the best of our knowledge, this is the first report to have compared the short-term outcomes of patients who received MV for at least 14 days and either underwent tracheostomy or remained intubated by the translaryngeal route for a prolonged period.
We also found that the ICU type, a DNR order, undergoing NIV after extubation, brain disorders and trauma as the cause of ICU admission, renal function, CCI score and comorbidities such as chronic heart, liver and connective tissue diseases were associated with the rate and timing of tracheostomy, findings that are consistent with a previous report . Our finding that tracheostomy was independently associated with reduced ICU and in-hospital mortality rates is also consistent with some previous reports [17, 18], but not others [19, 20]. Clec'h et al.  reported that tracheostomy had no positive influence on survival when performed in unselected mechanically ventilated patients. Their cohort included patients requiring MV for at least 2 days but nearly half received MV for <15 days, and therefore their findings may have been biased by the presence of a subgroup more likely to have been weaned from MV without the need for tracheostomy . In contrast, our study included only those patients receiving MV for ≥14 days, a cohort in which failed extubation and severe comorbidities were more common; a greater proportion would be expected to require long-term ventilatory support and would be more likely to benefit from tracheostomy . Similarly, Trouillet and colleagues  compared patients undergoing tracheostomy after 5 days of ventilatory support with those intubated by the translaryngeal route for a prolonged period, and found that tracheostomy did not affect mortality; however, they included patients ventilated after cardiac surgery who had failed weaning trials at day 4 of MV and 27 % of the patients in the prolonged translaryngeal intubation group eventually underwent a tracheostomy.
In our study, the substantially reduced risk of death (aHR 0.26) in the tracheostomy group could in part be explained by the fact that tracheostomy is associated with a decreased risk for VAP in patients requiring PMV . In tracheostomized patients, tracheostomy allows the vocal cords to close, reduces aspiration of oropharyngeal secretions, reduces bacterial biofilm formation along the inside of the tracheotomy cannula and facilitates weaning from MV. All these factors probably result in a reduced risk for VAP . Another potential explanation is that ICU physicians may be adept at selecting candidates for tracheostomy based on the highest probability of survival, and therefore may provide more aggressive treatment for these patients while being more likely to offer conservative or palliative treatment to those intubated by the translaryngeal route for a prolonged period. In a retrospective study, it is also possible that we might have missed some important confounding factors associated with the decision to undertake tracheostomy that might also affect outcomes, even when sophisticated adjustment methods such as multivariable analyses or propensity score-based nested case–control studies are used.
Aside from tracheostomy, we identified a DNR order, NIV after extubation, malignancy and a PaO2/FiO2 ratio (w2) as the factors independently associated with in-hospital mortality in patients receiving MV for ≥14 days. There is a body of evidence that using NIV after extubation improves survival rate in high-risk patients [13–16]; NIV is commonly employed in our clinical practice to prevent post-extubation respiratory failure. Malignancy is recognized as a predictor of poor outcome in patients requiring PMV . Increased PaO2/FiO2 ratio in week 2 might simply reflect a favorable response to treatment, leading to better outcomes. Furthermore, we found that tracheostomy was associated with increased successful weaning rates. In contrast, Wu et al.  reported that tracheostomy has no effect on successful weaning. This discrepancy might be explained by a difference in study setting (ours was conducted in an ICU while theirs took place in a specialist respiratory care center). Moreover, tracheostomy has been reported to contribute to facilitation of weaning from MV by decreasing airflow resistance and the associated work of breathing, allowing clinicians to be more aggressive in their weaning strategies and reducing their concerns about sedation and reintubation . In addition, we found that a DNR order, sepsis, chronic lung disease, APACHE II score, PaO2/FiO2 ratio (w2) and platelet count (w2) were independently associated with weaning success. These findings are similar to that of previous studies regarding the prediction of weaning or extubation failure . Platelet count has also been reported to be associated with successful weaning in patients requiring PMV after cardiac surgery . The relationship between existence of a current DNR order and poor outcomes can be explained by the presence of irreversible and terminal diseases.
There have been reports that early tracheostomy was not associated with a reduced length of ICU stay, hospital stay or duration of MV [9, 10]. Indeed, consistent with previous studies [17–19], we found that tracheostomy increased the duration of MV and length of ICU and hospital stays compared with translaryngeal intubation. These observations may be partially explained by the relatively long median time before tracheostomy (18 days) in the tracheostomy group. The shorter duration of MV, and shorter length of ICU and hospital stays in the translaryngeal intubation group probably reflect these patients’ higher mortality rate and earlier death (30 days compared with 61 days) or transition to lower-level regional hospitals.
Our study had some limitations. First, we did not record data regarding the effects of inadvertent extubation on the outcomes of the translaryngeal intubated group, tracheostomy complications, the incidence of extubation failure or the rate of VAP. All these factors may be associated with patient morbidity, mortality and successful weaning. We did not record serial ICU scores (such as the daily Sequential Organ Failure Assessment), which may have more accurately reflected the severity of illness at the time of tracheostomy (after a median of 18 days of MV) than the APACHE II score in the first 24 h of ICU admission . Second, our study was undertaken retrospectively; this may have caused us to miss important confounders relevant to the results, while accounting for the significant heterogeneity between the translaryngeal intubation group and the tracheostomy group. Consequently, we cannot completely rule out the possibility that clinical practice on the ICU tends to select patients with the highest likelihood of survival for tracheostomy, although we matched for propensity scores, adjusted for potential confounders and performed a sensitivity analysis in which even more stringent propensity score matching was employed that yielded the same results. Third, we did not assess the long-term outcomes after hospital discharge. Further study is needed to determine whether there are long-term benefits of tracheostomy on outcomes compared with translaryngeal intubation. A prospective, randomized controlled study will be needed to eliminate the biases described above.