To the Editor:—
In the May 2008 issue of Anesthesiology, Chung et al
. published an article where they describe the validation of the Berlin questionnaire and the American Society of Anesthesiologist checklist as screening tools for obstructive sleep apnea in surgical patients, and compare them with the STOP questionnaire.1
The authors conclude that both the STOP and American Society of Anesthesiologists checklist were able to identify patients who were likely to develop postoperative complications. However, after taking a look at the results, I believe that it would have been more accurate to mention respiratory complications in particular. Moreover, when reviewing the odds ratios for effectors on the incidence of postoperative complications, I am concerned to find that the confidence intervals for both the STOP and American Society of Anesthesiologists checklists include the null value.2
In contrast, the odds ratio for the STOP-Bang questionnaire presents a confidence interval that does not comprise the null value.
With reference to the potential limitations for this study described by the authors, I agree with them about the possible bias associated with self-selection of patients. Only 416 (17%) of 2,467 patients gave consent to participate in a polysomnographic study, whereas finally 211 (8.6% of the total population) showed up to undergo it. Another issue is, when reading the analysis of those 211 patients, there is little valuable information left about their preexisting conditions, such as number of smokers, type of surgery and anesthesia technique given,3
or patients suffering from asthma or other pulmonary diseases, which could have been desirable to discuss when comparing the higher incidence of respiratory complications among patients with higher scores in the questionnaires. Knowing more about preexisting morbidities might have allowed classifying patients to make comparisons between them in further multivariate analyses.
At the same time, following the requirement in one hospital to closely monitor patients with an apnea-hypopnea index greater than 30, the authors did not find this variable to be a risk factor for postoperative complications. I would want to know what result would have been obtained had those patients been excluded from the analysis.
To sum up, I believe that this study presents some unsatisfactory points that hamper the conclusions given and deserve to be addressed in more detail.
Jose Ramon Perez Valdivieso, Ph.D., M.D.,*
Maira Bes-Rastrollo, Pharm.D., Ph.D.
*Clinica Universitaria, University of Navarra, Spain. firstname.lastname@example.org
1. Chung F, Yegneswaran B, Liao P, Chung SA, Vairavanathan S, Islam S, Khajehdehi A, Shapiro CM: Validation of the Berlin questionnaire and American Society of Anesthesiologists checklist as screening tools for obstructive sleep apnea in surgical patients. Anesthesiology 2008; 108:822–30
2. Bland JM, Altman DG: Statistics notes. The odds ratio. BMJ 2000; 320:1468
3. Tziavrangos E, Schung SA: Regional anaesthesia and perioperative outcome. Curr Op Anaesthesiol 2006; 19:521–25
© 2009 American Society of Anesthesiologists, Inc.