T-piece trials

Vallverdu I, Calaf N, Subrrana M, et al. Clinical characteristics, respiratory functional parameters, and outcome of a two-hour T-piece trial in patients weaning from mechanical ventilation. Am J Respir Crit Care Med 1998 158(6) 1855-1862. 

Weaning can be assisted with stable support techniques, which include multiple daily T-piece trials alternating with periods of ventilatory support, and techniques of progressively reducing ventilatory support such as synchronized intermittent mandatory ventilation (SIMV) and PSV. Prospective randomized trials of daily T-piece trials, PSV, or SIMV among intubated patients (39) favor T-piece and PSV approaches over SIMV. There is no evidence that more recent modes of ventilation further improve weaning outcomes (40). 

This is a surprisingly widespread piece of nonsense which has even made its way into one book on drug industry trials. Consider, for example, the case of a two parallel group trial to compare an experimental treatment with a placebo. Conventionally we would use a two-sided test to examine the efficacy of the treatment. (See Chapter 12 for a discussion. The essence of the argument which follows, however, is unaffected by whether one-sided or two-sided tests are used.) Let t be the true difference (experimental treatment-placebo). We then write the two hypotheses. 

---