New Trick for Liberation from Mechanical Ventilation?

Abstract & Commentary

By Saadia R. Akhtar, MD, MSc, Idaho Pulmonary Associates, Boise, is Associate Editor for Critical Care Alert.

Dr. Akhtar does research for Eli Lilly.

Synopsis: This prospective observational study suggests that a successful spontaneous breathing trial with pressure support immediately after a failed T-piece trial may predict and allow successful liberation from the ventilator.

Source: Ezingeard E, et al. Weaning from mechanical ventilation with pressure support in patients failing a T-tube trial of spontaneous breathing. Intensive Care Med. 2006;32:165-169.

Some studies have shown that breathing through an endotracheal tube imposes a small but measurable excess respiratory workload. Although randomized, controlled studies have found no difference between T-piece and pressure support (PS) spontaneous breathing trials (SBTs) as predictors of readiness for extubation, the authors suggest that perhaps the excess respiratory workload may be an issue for specific patients. They aimed to evaluate the utility of a PS SBT following a failed T-piece SBT. Their primary outcome was extubation failure rate within 48 hours.

A prospective observational study was performed in 2 French medical-surgical intensive care units between 2003 and 2004. Over a 17-month-period, all patients requiring mechanical ventilation for > 24 hours and ready for a SBT were eligible. Patients with tracheostomies and those with pending decisions about goals of care were excluded. Patients underwent a 30-minute T-piece SBT with extubation if successful. A successful trial was defined as absence of signs of respiratory distress (eg, retractions or agitation), oxygen saturations ≥ 90% on ≤ 50% oxygen, respiratory rate ≤ 35 per minute and absence of a 20% variation in respiratory rate or blood pressure. If patients failed a T-piece SBT, they were immediately placed on a PS of 7 cm H2O for 30 minutes. If they met the noted criteria of success, they were extubated. Standard statistical methods were used to compare groups.

A total of 118 consecutive patients were enrolled. Of these, 87 were extubated after a 30-minute T-piece SBT. Of the remaining 31 patients, 21 (68%, or 18% of the original cohort) were extubated following a PS SBT. Reintubation rates at 48 hours were not significantly different (13% for T-piece group and 19% for those undergoing PS SBT after T-piece). Patients in the 2 groups were similar in terms of age, chronic medical problems, acute diagnoses, endotracheal tube size, duration of mechanical ventilation and death. The only difference was in percentage of patients with decompensated COPD in each group: 13% of those successfully liberated from the ventilator after T-piece SBT had decompensated COPD compared to 38% of those successfully liberated after PS SBT. The authors note that they adjusted sensitivity and pressurization slope individually for each patient undergoing a PS SBT: they suggest that this allowed for improved patient-ventilator synchronization and thus a successful SBT particularly in those patients with COPD.

Commentry

Well designed, large, randomized trials have previously compared weaning strategies (time to extubation and success rates measured by reintubation at 48 hours) and found no significant difference between T-piece and PS SBTs.1 Although there may be reasons to think that respiratory failure in patients with COPD differs from respiratory failure in other settings, some studies have even compared these weaning strategies specifically in patients with COPD and found no difference.2

Ezingeard and colleagues’ work may appear to put these findings into question. However, a direct comparison is difficult since this study assesses immediately consecutive weaning trials (rather than delayed, daily weaning trials). The study is clearly limited by lack of randomization and the number of patients (total and with decompensated COPD): would immediately following up a failed PS SBT with a T-piece SBT lead to similar results? Would this study have revealed more or less striking results in a large group of patients with COPD?

Another concern is that the authors’ defined criteria for failure of a SBT may not be those used by other intensivists (a 20% variation in respiratory rate or blood pressure was used but without specific thresholds; respiratory rate > 35 per minute may be too low).3 This is an important issue as the majority of patients considered to fail their T-piece SBT did so based on only 1 of the several criteria: the results may have been greatly altered had the criteria varied or failure been defined by not meeting 2 or more of the criteria. Finally, as with many other studies of weaning, criteria for reintubation and failed extubation are not clearly defined, adding considerable potential bias to the primary outcome.

It is essential to continue to evaluate our approach to weaning and to work to avoid unnecessary days on the ventilator. I hope that despite the limitations of this study, Ezingeard et al follow up their interesting hypothesis with a larger randomized trial. Until then, we must continue to consider T-piece and PS SBTs as equals.

References

  1. Esteban A, et al. A comparison of four methods of weaning patients from mechanical ventilation. Spanish Lung Failure Collaborative Group. N Engl J Med. 1995;332:345-350.
  2. Vitacca M, et al. Comparison of two methods for weaning patients with chronic obstructive pulmonary disease requiring mechanical ventilation for more than 15 days. Am J Respir Crit Care Med. 2001;164:225-230.
  3. Meade M, et al. Predicting success in weaning from mechanical ventilation. Chest. 2001;120(6 Suppl):400S-424S.