We thank Xue et al . for their interest in our subgroup analysis of obese patients1randomized to 80% or 30% oxygen in the PROXI Trial.2 

We agree that it would have been interesting to screen all patients for obstructive sleep apnea, but that was not done. Patients were nursed after surgery in the semirecumbent position in all departments participating in the trial. Chest physiotherapy may be beneficial, but the evidence is not very convincing, and the effect depends on the patient's ability to cooperate.3 

We do not agree that every possible risk factor has to be standardized in a randomized clinical study. We sought to optimize and standardize care as much as possible,4but we realized that minor differences would still be present among centers. In our pragmatic and randomized trial, we stratified for study center, diabetes mellitus, and acute or elective surgery, and this will most likely reduce the probability of intergroup differences in known as well as unknown risk factors of postoperative complications. The aim was to enable us to detect a clinically relevant difference according to inspiratory oxygen fraction, if present. Pragmatic trials should inform decision-makers about the effectiveness of treatments in the settings in which they are to be implemented.5Tight control over every anesthetic and surgical variable may not be possible in large multicenter trials.6Actually, tightly controlled explanatory trials will have little generalizability.7,8 

Staehr AK, Meyhoff CS, Rasmussen LS; PROXI Trial Group: Inspiratory oxygen fraction and postoperative complications in obese patients: A subgroup analysis of the PROXI trial. ANESTHESIOLOGY 2011; 114:1313–9
Meyhoff CS, Wetterslev J, Jorgensen LN, Henneberg SW, Høgdall C, Lundvall L, Svendsen PE, Mollerup H, Lunn TH, Simonsen I, Martinsen KR, Pulawska T, Bundgaard L, Bugge L, Hansen EG, Riber C, Gocht-Jensen P, Walker LR, Bendtsen A, Johansson G, Skovgaard N, Heltø K, Poukinski A, Korshin A, Walli A, Bulut M, Carlsson PS, Rodt SA, Lundbech LB, Rask H, Buch N, Perdawid SK, Reza J, Jensen KV, Carlsen CG, Jensen FS, Rasmussen LS; PROXI Trial Group: Effect of high perioperative oxygen fraction on surgical site infection and pulmonary complications after abdominal surgery: The PROXI randomized clinical trial. JAMA 2009; 302:1543–50
Orman J, Westerdahl E: Chest physiotherapy with positive expiratory pressure breathing after abdominal and thoracic surgery: A systematic review. Acta Anaesthesiol Scand 2010; 54:261–7
Meyhoff CS, Wetterslev J, Jorgensen LN, Henneberg SW, Simonsen I, Pulawska T, Walker LR, Skovgaard N, Heltø K, Gocht-Jensen P, Carlsson PS, Rask H, Karim S, Carlsen CG, Jensen FS, Rasmussen LS; PROXI Trial Group: Perioperative oxygen fraction – effect on surgical site infection and pulmonary complications after abdominal surgery: A randomized clinical trial. Rationale and design of the PROXI-Trial. Trials 2008; 9:58
Zwarenstein M, Treweek S, Gagnier JJ, Altman DG, Tunis S, Haynes B, Oxman AD, Moher D: Improving the reporting of pragmatic trials: An extension of the CONSORT statement. BMJ 2008; 337:a2390
Yusuf S, Collins R, Peto R: Why do we need some large, simple randomized trials? Stat Med 1984; 3:409–22
McMahon AD: Study control, violators, inclusion criteria and defining explanatory and pragmatic trials. Stat Med 2002; 21:1365–76
Tunis SR, Stryer DB, Clancy CM: Practical clinical trials: Increasing the value of clinical research for decision making in clinical and health policy. JAMA 2003; 290:1624–32