T-piece Trial Unnecessary Following Pressure Support Weaning
December 1, 2000 4 minutes read
T-piece Trial Unnecessary Following Pressure Support Weaning
Abstract & Commentary
Various tests of the adequacy of ventilation have been used in an attempt to predict successful extubation following prolonged intubation. The failure rates of all of these indices are significant. The advent of pressure support ventilation (PSV) has permitted controlled and easy weaning of mechanical support. A low level of PSV is often maintained to overcome the imposed work of breathing of the endotracheal tube and ventilator circuit. The appropriate end point for extubation from PSV is not clear. It has been suggested that a period of spontaneous ventilation on a T-piece may be a sensitive measure of limited respiratory reserve, and should be used following pressure support weaning and ventilatory support continued if the patient fails the trial. Whether this approach would reduce the reintubation rate was tested in a group of patients undergoing prolonged intubation and ventilation.
Koh and colleagues studied 42 weaning trials in 36 patients with respiratory failure requiring at least three days of mechanical ventilation in a medical ICU. All patients were intubated with an 8-mm endotracheal tube and managed using pressure controlled ventilation. When the primary disease process was judged to be improved and oxygenation was adequate on FiO2 = 0.5, PEEP less than 6 cm H2O, patients were switched to 15 cm H2O PSV and weaned to minimal pressure support (PSmin) as quickly as possible (3-5 cm H2O per hour). PSmin was determined as peak flow rate (during spontaneous ventilation) x total respiratory system resistance on the ventilator without positive pressure. Total resistance was determined during a controlled breath. When patients were weaned to this level, they were randomized to be either extubated immediately or placed on an additional hour of T-piece breathing. If they showed signs of respiratory distress or decline in gas exchange, weaning failure was diagnosed. If this was following T-piece trial, extubation was delayed until they successfully completed the trial.
Weaning failure occurred 16 times in 14 patients out of the 42 trials performed. Therefore, 70% of the immediate extubation group remained extubated while only 55% of the T-piece group was able to complete the trial and remain extubated. This difference, however, was not statistically different. Patients who failed one method were crossed over for weaning and about half were successfully weaned using the other method. Two patients failed by both methods. Reintubation rates in the initially successful patients were identical in the two groups, 18% in the T-piece and 20% in the PSV group; noninvasive ventilation was used in four patients to avoid reintubation. Prior to weaning, respiratory indices were not different, including: tidal volume, respiratory rate, minute ventilation, rapid shallow breathing index (spontaneous respiratory rate divided by average tidal volume), work of breathing, respiratory drive, and duration of ventilation (> 10 days). Patients were older (65 vs 55 years) in the T-piece group, had slightly higher albumin level (3.0 vs 2.7 mg%), and lower APACHE II scores (33 vs 38). However, none of these differences were reported as statistically significant. (Koh Y, et al. J Crit Care 2000;15:41-45.)
Comment by Charles G. Durbin, Jr., MD, FCCM
This study is useful for several reasons. Koh et al have detailed a simple way of calculating the minimum level of PSV needed to overcome most of the work of breathing imposed by the ventilator, endotracheal tube, and circuit. They then demonstrated that if patients could tolerate this minimum level, they could be extubated without a period of T-piece breathing at a higher work of breathing. In fact, a T-piece trial delayed extubation in some patients who were then successfully extubated immediately. When extubation was delayed until the patient was able to pass the T-piece trial, the chance of remaining extubated was not greater than if the trial was avoided altogether.
The mechanics of this study are important. Seimens 300 and 900 series ventilators were used. These ventilators use pressure-triggered systems with moderately high work of breathing. All patients in the study, including the women, were intubated with an 8-mm endotracheal tube. Patients who failed either method were different from those who succeeded by either method, showing signs of poor respiratory performance prior to weaning, but not longer duration of intubation.
There are several concerns about this study. The small number of patients is limiting. One or two more successful patients in either group would have made a statistical difference in outcome. The additional 10 years average age difference in the T-piece group, which was reported as "not significant," is concerning. The small number and unequal distribution of sick patients may have led to finding no differences in duration of intubation. Also, since noninvasive ventilation, which is as expensive as invasive ventilation and requires as many or more personnel, was used to rescue extubation failures, the effect of this intervention on outcome needs to be included. This study is a good start comparing T-piece to PSV weaning but many more patients need to be included before a difference can be totally ruled out.
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