Protective intraoperative ventilation with higher versus lower levels of positive end-expiratory pressure in obese patients (PROBESE): study protocol for a randomized controlled trial

Table 3 Z-statistic boundaries and boundary-crossing probabilities

Look	Information fraction	N	Cumulative α spent	Cumulative β spent	Z-efficacy	Z-futility	Boundary-crossing probabilities under H1
Look	Information fraction	N	Cumulative α spent	Cumulative β spent	Z-efficacy	Z-futility	Efficacy	Futility
1	0.5	956	0.006	0.024	≥2.75	<0.225	0.234	0.024
2	0.75	1434	0.018	0.071	≥2.432	<0.929	0.296	0.047
3	1	1912	0.05	0.2	≥2.012	<2.012	0.271	0.129

Look Interim analysis, N Number of patients, H1 Hypothesis 1 (group difference exists)
Values were calculated using power = 0.80, α = 0.05, γ spending functions (γ = −4), and expected incidence of postoperative pulmonary complications of 20% (p1) and 15% (p2) in the lower and higher positive end-expiratory pressure groups, respectively

ISSN: 1745-6215