- Email: [email protected]
Obesity in general elective surgery
CORRESPONDENCE
by surgeons. Despite the prevalence of obstructive sleep apnoea syndrome in obese people, Sabers and colleagues3 noted that this syndrome is not an independent risk factor for perioperative complications in patients undergoing outpatient surgical procedures. This finding complements that of Dindo and colleagues. Egbert Pravinkumar Academic Unit of Anaesthesia and Intensive Care, Department of Medicine and Therapeutics, Institute of Medical Sciences, Foresterhill, Aberdeen AB25 2ZD, UK (e-mail: [email protected]) 1
2
3
Dindo D, Muller MK, Weber M, Clavien P-A. Obesity in general elective surgery. Lancet 2003; 361: 2032–35. Association for the study of obesity. Obesity: the scale of the problem. http://aso.org.uk/apps/oric/oric_frames.asp (accessed July 22, 2003). Sabers C, Plevak DJ, Schroeder DR, Warner DO. The diagnosis of obstructive sleep apnoea as a risk factor for unanticipated admissions in outpatient surgery. Anesth Analg 2003; 96: 1328–35.
Sir—Daniel Dindo and colleagues1 should be congratulated because they tried to answer a daily question in general surgery. Their prospective study deserves, however, some statistical and methodological comments. Beyond the unavoidable imbalance between the two groups (obese versus non-obese patients), our main criticism is that the groups were not comparable in terms of major independent risk factors for postoperative complications. Since there were significantly more open procedures in the non-obese group, the lack of difference between the two groups could be artificially related to the high rate of open procedures in the non-obese group. Another flaw of the study is the statistical power. We calculated that to show a reduction of 20% in the morbidity rate, more than 1500 patients would be needed in each group, whereas the number of nonobese patients did not exceed 808. Thus, the finding of the study may be a false negative one. We also have two methodological concerns about the study. First, what about the operating surgeons as a confounding factor? The effect of surgeon’s volume and expertise is now well established for most of the procedures included in this study.2,3 What about distribution of surgeons in the two groups? Dindo and colleagues did not state whether they included this factor in their analyses. Did more experienced surgeons operate on the obese patients? This may be one explanation of the good postoperative
results of surgery. Finally, instead of studying the crude results, an alternative and valid approach is to compare expected with observed morbidity in each group or subgroup, which can be done with validated scoring systems, such as POSSUM.4 This approach limits the biases related to the aforementioned confounding factors. Without answers to these questions, the study by Dindo and colleagues cannot unequivocally overturn “the regressive attitude” in referring obese patients for general surgery. Although the risks associated with obesity are probably overestimated, this assumption needs to be further confirmed by more rigorous studies. *Karem Slim, Fabrice Kwiatkowski, Jacques Chipponi *Department of Digestive Surgery, Hotel-Dieu Clermont-Ferrand, France (KS, JC); and Department of Statistics, Centre Jean Perrin, Clermont-Ferrand (FK) (e-mail: [email protected]) 1
2
3
4
Dindo D, Muller MK, Weber M, Clavien P-A. Obesity in general elective surgery. Lancet 2003; 361: 2032–35. Meagher AP. Colorectal cancer: is the surgeon a prognostic factor? A systematic review. Med J Aust 1999; 171: 308–10. Slim K, Flamein R, Chipponi J. Relation between activity volume and surgeon’s results: myth or reality? Ann Chir 2002; 126: 502–11. Copeland GP. The POSSUM system of surgical audit. Arch Surg 2002; 137: 15–19.
Sir—We believe that there are some fundamental flaws in the study by Daniel Dindo and colleagues1 that account for their somewhat surprising conclusion that obesity is not a risk factor for elective general surgery. The study is a non-randomised, observational, cohort-based assessment of surgical practice in one institution. There is, therefore, an unacceptable selection bias, and the two groups are not comparable in terms of sex, comorbidity, American Society of Anesthesiologists grade, or type of surgery. Of particular note is the exclusion of local anaesthesia—a technique often used in high-risk patients—and the larger proportion of obese than non-obese patients who received minimally invasive or intermediate grade surgery. In view of these biases, it would have been informative for Dindo and colleagues to use a comparative audit tool, such as POSSUM,2 to assess the predicted effect of comorbidity and surgery on outcome. We are especially puzzled by the fact that although diabetes and cardiac disease are more common in obese than non-obese patients (and are independent risk factors for poor
outcome), Dindo and colleagues recorded no statistical relation between obesity and outcome in the univariate and multivariate analyses. Dindo and colleagues use a graded complication score, but do not explain who assessed patients for severity of complications and what internal validation was used to ensure objectivity. The follow-up period of about 8–9 days will at best detect some of the acute and early complications, but will miss important late problems, such as readmissions, incisional herniae, and some venous thromboembolism. This short follow-up will bias against nonobese patients who are having major surgery associated with longer hospital stay and a higher rate of inpatient complications.3 Although we do not deny patients surgery on grounds of their weight, obesity is a risk factor for general health, and we believe it is part of a surgeon’s duty to try and modify all risk factors through lifestyle assessment and, where appropriate, therapeutic means. We will not stop encouraging patients to lose weight before surgery. R McCarthy, T Leslie, *D J Williams Department of Vascular Surgery, Bristol Royal Infirmary, Bristol BS2 8HW, UK (e-mail: [email protected]) 1
2
3
Dindo D, Muller MK, Weber M, Clavien P-A. Obesity in general surgery. Lancet 2003; 361: 2032–35. Copeland GP, Jones D, Walters M. POSSUM: a scoring system for surgical audit. Br J Surg 1991; 78: 355–60. Doty JR, Salazar JD, Forestiere AA, Heath EI, Kleinberg L, Heitmiller RF. Postoesophagectomy morbidity, mortality, and length of hospital stay after preoperative chemoradiation therapy. Ann Thorac Surg 2002; 74: 227–31.
Authors’ reply Sir—Egbert Pravinkumar requests additional data on the prevalence of comorbid conditions. We included details of diabetes, hypertension, and cardiac diseases in the study participants. Cardiac disorders are difficult to assess in obese patients. Most obese patients present with dyspnoea related to being overweight rather than to a cardiac disease. Furthermore, appropriate preoperative work-up—for example, exercise stress testing—is often unsuccessful because of fatigue, and non-exercise stress testing or myocardial perfusion imaging are not done routinely at our centre. Therefore, we used American Society of Anesthesiologists status, available in each patient, to assess the preoperative risk. Karem Slim and colleagues point out some imbalance between the obese and
THE LANCET • Vol 362 • August 16, 2003 • www.thelancet.com
For personal use. Only reproduce with permission from The Lancet.
577
by surgeons. Despite the prevalence of obstructive sleep apnoea syndrome in obese people, Sabers and colleagues3 noted that this syndrome is not an independent risk factor for perioperative complications in patients undergoing outpatient surgical procedures. This finding complements that of Dindo and colleagues. Egbert Pravinkumar Academic Unit of Anaesthesia and Intensive Care, Department of Medicine and Therapeutics, Institute of Medical Sciences, Foresterhill, Aberdeen AB25 2ZD, UK (e-mail: [email protected]) 1
2
3
Dindo D, Muller MK, Weber M, Clavien P-A. Obesity in general elective surgery. Lancet 2003; 361: 2032–35. Association for the study of obesity. Obesity: the scale of the problem. http://aso.org.uk/apps/oric/oric_frames.asp (accessed July 22, 2003). Sabers C, Plevak DJ, Schroeder DR, Warner DO. The diagnosis of obstructive sleep apnoea as a risk factor for unanticipated admissions in outpatient surgery. Anesth Analg 2003; 96: 1328–35.
Sir—Daniel Dindo and colleagues1 should be congratulated because they tried to answer a daily question in general surgery. Their prospective study deserves, however, some statistical and methodological comments. Beyond the unavoidable imbalance between the two groups (obese versus non-obese patients), our main criticism is that the groups were not comparable in terms of major independent risk factors for postoperative complications. Since there were significantly more open procedures in the non-obese group, the lack of difference between the two groups could be artificially related to the high rate of open procedures in the non-obese group. Another flaw of the study is the statistical power. We calculated that to show a reduction of 20% in the morbidity rate, more than 1500 patients would be needed in each group, whereas the number of nonobese patients did not exceed 808. Thus, the finding of the study may be a false negative one. We also have two methodological concerns about the study. First, what about the operating surgeons as a confounding factor? The effect of surgeon’s volume and expertise is now well established for most of the procedures included in this study.2,3 What about distribution of surgeons in the two groups? Dindo and colleagues did not state whether they included this factor in their analyses. Did more experienced surgeons operate on the obese patients? This may be one explanation of the good postoperative
results of surgery. Finally, instead of studying the crude results, an alternative and valid approach is to compare expected with observed morbidity in each group or subgroup, which can be done with validated scoring systems, such as POSSUM.4 This approach limits the biases related to the aforementioned confounding factors. Without answers to these questions, the study by Dindo and colleagues cannot unequivocally overturn “the regressive attitude” in referring obese patients for general surgery. Although the risks associated with obesity are probably overestimated, this assumption needs to be further confirmed by more rigorous studies. *Karem Slim, Fabrice Kwiatkowski, Jacques Chipponi *Department of Digestive Surgery, Hotel-Dieu Clermont-Ferrand, France (KS, JC); and Department of Statistics, Centre Jean Perrin, Clermont-Ferrand (FK) (e-mail: [email protected]) 1
2
3
4
Dindo D, Muller MK, Weber M, Clavien P-A. Obesity in general elective surgery. Lancet 2003; 361: 2032–35. Meagher AP. Colorectal cancer: is the surgeon a prognostic factor? A systematic review. Med J Aust 1999; 171: 308–10. Slim K, Flamein R, Chipponi J. Relation between activity volume and surgeon’s results: myth or reality? Ann Chir 2002; 126: 502–11. Copeland GP. The POSSUM system of surgical audit. Arch Surg 2002; 137: 15–19.
Sir—We believe that there are some fundamental flaws in the study by Daniel Dindo and colleagues1 that account for their somewhat surprising conclusion that obesity is not a risk factor for elective general surgery. The study is a non-randomised, observational, cohort-based assessment of surgical practice in one institution. There is, therefore, an unacceptable selection bias, and the two groups are not comparable in terms of sex, comorbidity, American Society of Anesthesiologists grade, or type of surgery. Of particular note is the exclusion of local anaesthesia—a technique often used in high-risk patients—and the larger proportion of obese than non-obese patients who received minimally invasive or intermediate grade surgery. In view of these biases, it would have been informative for Dindo and colleagues to use a comparative audit tool, such as POSSUM,2 to assess the predicted effect of comorbidity and surgery on outcome. We are especially puzzled by the fact that although diabetes and cardiac disease are more common in obese than non-obese patients (and are independent risk factors for poor
outcome), Dindo and colleagues recorded no statistical relation between obesity and outcome in the univariate and multivariate analyses. Dindo and colleagues use a graded complication score, but do not explain who assessed patients for severity of complications and what internal validation was used to ensure objectivity. The follow-up period of about 8–9 days will at best detect some of the acute and early complications, but will miss important late problems, such as readmissions, incisional herniae, and some venous thromboembolism. This short follow-up will bias against nonobese patients who are having major surgery associated with longer hospital stay and a higher rate of inpatient complications.3 Although we do not deny patients surgery on grounds of their weight, obesity is a risk factor for general health, and we believe it is part of a surgeon’s duty to try and modify all risk factors through lifestyle assessment and, where appropriate, therapeutic means. We will not stop encouraging patients to lose weight before surgery. R McCarthy, T Leslie, *D J Williams Department of Vascular Surgery, Bristol Royal Infirmary, Bristol BS2 8HW, UK (e-mail: [email protected]) 1
2
3
Dindo D, Muller MK, Weber M, Clavien P-A. Obesity in general surgery. Lancet 2003; 361: 2032–35. Copeland GP, Jones D, Walters M. POSSUM: a scoring system for surgical audit. Br J Surg 1991; 78: 355–60. Doty JR, Salazar JD, Forestiere AA, Heath EI, Kleinberg L, Heitmiller RF. Postoesophagectomy morbidity, mortality, and length of hospital stay after preoperative chemoradiation therapy. Ann Thorac Surg 2002; 74: 227–31.
Authors’ reply Sir—Egbert Pravinkumar requests additional data on the prevalence of comorbid conditions. We included details of diabetes, hypertension, and cardiac diseases in the study participants. Cardiac disorders are difficult to assess in obese patients. Most obese patients present with dyspnoea related to being overweight rather than to a cardiac disease. Furthermore, appropriate preoperative work-up—for example, exercise stress testing—is often unsuccessful because of fatigue, and non-exercise stress testing or myocardial perfusion imaging are not done routinely at our centre. Therefore, we used American Society of Anesthesiologists status, available in each patient, to assess the preoperative risk. Karem Slim and colleagues point out some imbalance between the obese and
THE LANCET • Vol 362 • August 16, 2003 • www.thelancet.com
For personal use. Only reproduce with permission from The Lancet.
577