In general anaesthesia, postoperative pulmonary complications (PPC) remain an important cause of postoperative morbidity and mortality. The many advances of modern surgical care over the last 30 yr have not appreciably altered the incidence of these complications. Various factors have been shown to contribute to this problem, with obesity being a major contributor. The number of morbidly obese patients undergoing anaesthesia and surgery is increasing, as obesity has reached epidemic proportions globally, with more than 1 billion adults overweight and at least 300 million of them clinically obese .
In deciding on a surgical and anaesthetic treatment strategy, patients must be informed about the associated risks. Patients require information specific to their case in order to make a fully informed decision. Our patient was a 46-yr-old female with a body mass index (BMI) of 89.8 kg m−2 (height 160 cm and weight 230 kg). She was diagnosed with cervix carcinoma and scheduled for hysterectomy. A combined general and regional anaesthetic technique was first considered, but rejected for anatomical reasons and only a general anaesthesia technique was decided upon.
The patient insisted upon being informed of the anticipated pulmonary risk. In order to be able to inform her accurately, we searched the literature for relevant information on the pulmonary risk in morbidly obese patients undergoing abdominal surgery.
Searching the literature
The first step was to formulate a relevant clinical question. This was the likelihood of a morbidly obese patient developing a PPC after abdominal surgery under general anaesthesia.
Our favourite textbook, Textbook of Anaesthesia  claimed that obesity is indeed associated with a high incidence of pulmonary complications, due to low functional residual capacity and increased work of breathing postoperatively. Unfortunately, exact data were not available. Moreover, the references dated from 1990 to 2000. Hence, we performed a search in the Medline database to retrieve more recent data.
The domain was set as anesthe*, anaesthe* or surg*, and for the determinant we used obes* in the title or abstract. For the outcome we used a combination of ventilat*, or pulmon*, or pneumo*, or respir*, or atelectas* together with perioperat* or postoperat*, and risk*, or complicat* and added the field tag [Text Word].
These three searches were combined with the Boolean operator AND. Thirdly; we limited the resulting hits by language (English). This left us with 213 results. The titles and/or abstracts were scanned manually for the domain, determinant and outcome of our research question, type of study, type of anaesthesia used, and whether the full text could be retrieved from the Internet or the local medical library. We excluded studies that handled specific types of surgery such as laparoscopic, orthopaedic, cardiac, or transplantation surgery as well as studies dealing with regional anaesthesia and studies performed in day case surgery. This yielded seven hits. We identified seven additional studies, by using the PubMed function related articles for the seven hits, and by manually searching the reference lists of those studies for cross-references. Altogether we found 14 articles [3-16] eligible for critical appraisal, as depicted in Table 1.
Our search strategy resulted in 14 hits, as shown in Table 1. After carefully reading the full articles we found six of them not applicable to our question (criterion for obesity not specified: Øberg and colleagues  and Pasulka and colleagues ; follow-up of less than 80%: Forrest and colleagues  and Mason and colleagues ; abdominal surgical procedures <80% or surgical procedures not specified: Rose and colleagues  and Garibaldi and colleagues ).
In Table 2 we show the baseline characteristics of the remaining articles. To determine their potential relevance we selected the following criteria: (a) domain: should match the baseline criteria of our patient, combined anaesthesia or mode of anaesthesia unknown scored −; (b) determinant: should be specified in kg m−2; (c) outcome and results: PPC should be properly defined and should have statistic significance and (d) follow-up: admission until discharge scored +, intraoperative or unknown scored −.
Table 3 shows the validity of the selected studies by using the checklists for appraising studies of the Dutch Cochrane Centre  and the Oxford Centre for Evidence Based Medicine . The following methodological criteria were scored: (a) type of study: systematic review or prospective cohort study scored +; follow-up of untreated controls in randomized controlled trials and prospective model building study scored +/−; outcomes research and case-control study scored −; (b) number: number of subjects <100 scored −, number of studies in systematic review <3 scored −; (c) blinding: no blinding or unknown scored −; (d) loss to follow-up: unknown scored −; (e) level of evidence: ≥2 scored +, <2 scored − and (f) grades of recommendation: A scored +, B scored +/−, <B scored −. Table 4 shows how the studies were graded with respect to relevance and validity.
The requisite score was set on a minimum of +/−. Consequently, the studies by Ogunnaike and colleagues , Flancbaum and colleagues  and Dominguez-Cherit and colleagues  were excluded from further analysis. The study by Blouw and colleagues  was not considered to be a cohort study with acceptable methodology as described above, but its figures were extracted from outcomes research - work that studies a single cohort of patients with the same diagnosis (obesity) and relates their clinical and health outcomes to the care that they received (abdominal surgery). This could only tell us whether the outcomes we expected to observe (based on cohort studies) could be observed in real-world clinical care. Hence, we could not attribute efficacy to any of the analyses, and could not use their statistical calculations on PPC for our case. This left us with four golden hits that we could use to answer our research question [9,14-16].
Coussa and colleagues  found a significant increase in atelectasis before and after intubation (incidence 0.8 ± 1.2% vs. 10.4 ± 4.8% after intubation; P < 0.001). Brooks-Brunn  collectively assessed the incidence and risk of postoperative atelectasis and pneumonia and found obesity to be a significant risk factor (incidence 29.3%; adjusted odds ratio (OR) 2.82; 95% confidence interval (CI) 1.66-4.78; P = 0.0001). Delgado-Rodriguez and colleagues  found an incidence of postoperative pneumonia in obese patients of 4.2%. In the univariate analysis there was indeed a significant relative risk (RR 5.3; 95% CI 2.0-14.2). However, in a multivariate analysis this significance was lost (OR 2.9; 95% CI 0.9-9.4). Thus, we could not take these results into account. Strandberg and colleagues  demonstrated a significant correlation coefficient between postoperative atelectasis and obesity, i.e. for weight (kg) 0.28, and for Broca's index (kg cm−1) 0.34; P < 0.05.
After searching, scanning and appraising the studies found in Medline, there were only three studies left that particularly fitted our research question [9,14,16]. The authors agreed that obesity was a relevant risk factor for developing atelectasis or pneumonia after abdominal surgery under general anaesthesia. Unfortunately, these studies comprised figures on atelectasis and pneumonia only, and not on other postoperative complications, such as prolonged intubation, or reintubation, which prevents us to completely answer the purpose of our study.
The results mentioned above show some variation. This can in part be explained by the difference in domains. Coussa and colleagues  put an upper limit for weight of 160 kg on his study population, whereas Brooks-Brunn  used a lower limit for BMI only and Strandberg and colleagues  did not use any limit.
With respect to our search strategy, we admit that we might have missed relevant articles. Moreover, we excluded all hits that were not available with full text on the Internet or in the Medical Library of the Utrecht University, which can be a negative contributor as well.
When applying the results to our patient mentioned above, we have to consider that her BMI exceeded that of the study patients of all studies listed above. Therefore, we cannot extrapolate the incidence figures uncritically. However, since one study showed a direct correlation between the risk of developing atelectasis and body weight, we expected that the risk of our patient developing PPC would be similar to or even exceed those presented above. We were obliged to inform her that she would bear a substantial risk to develop atelectasis or pneumonia of at least 29.3%. Compared to non-obese patients the OR was at least 2.82. Obviously, she was prepared to accept this risk, because of the severity of the diagnosis ‘cervix carcinoma’ and the expected benefit of the surgical procedure. Therefore, we ascertained that she was carefully monitored in the postoperative care unit for early recognition and early treatment in case of early signs and symptoms of pneumonia.
We have shown that individual clinical questions by patients can be answered fairly accurately using relatively simple evidence-based methodology although sufficient evidence is lacking in many fields of medicine. For further research we recommend to propose high-quality prospective cohort studies with sufficient power, in order to fill in the blanks of today's knowledge on the incidence and risks of PPC in obesity.
The patient underwent general anaesthesia without sequelae. The surgical procedure had to be aborted peroperatively since the hysterectomy could not be carried out due to technical reasons related to the extreme obesity. Postoperatively the patient was weaned from the ventilator successfully after ventilatory support for 20 h. She resumed normal breathing on day 2 following surgery and anaesthesia. Fortunately, she did not develop pneumonia, but the postoperative course was complicated by serious wound healing disturbances lasting 152 days.
The authors wish to thank J. C. van den Berg for his secretarial assistance and Dr G. J. M. G. van der Heijden, Julius Centre for Health Sciences and Primary Care, University Medical Centre Utrecht, who facilitated the production of this evidence based case report.
2. Aitkenhead AR, Rowbotham DJ, Smith G. Textbook of Anaesthesia
. London, Great Britain: Churchill Livingstone, 2001: 445, 532.
3. Øberg B, Poulsen TD. Obesity: an anaesthetic challenge. Acta Anaesthesiol Scand
4. Pasulka PS, Bistrian BR, Benotti PN, Blackburn GL. The risks of surgery
in obese patients. Ann Intern Med
5. Forrest JB, Rehder K, Cahalan MK, Goldsmith CH. Multicenter study of general anaesthesia. III. Predictors of severe perioperative adverse outcomes. Anesthesiology
6. Mason EE, Renquist KE, Jiang D. Perioperative risks and safety of surgery
for severe obesity. Am J Clin Nutr
1992; 55 (Suppl 2)
7. Rose DK, Cohen MM, Wigglesworth DF, DeBoer DP. Critical respiratory events in the postanesthesia care unit. Patient, surgical, and anesthetic factors. Anesthesiology
8. Garibaldi RA, Britt MR, Coleman ML, Reading JC, Pace NL. Risk factors for postoperative pneumonia. Am J Med
9. Coussa M, Proietti S, Schnyder P et al
. Prevention of atelectasis formation during the induction of general anesthesia in morbidly obese patients. Anesth Analg
10. Blouw EL, Rudolph AD, Narr BJ, Sarr MG. The frequency of respiratory failure in patients with morbid obesity undergoing gastric bypass. AANA J
11. Ogunnaike BO, Jones SB, Jones DB, Provost D, Whitten CW. Anesthetic considerations for bariatric surgery
. Anesth Analg
12. Flancbaum L, Choban PS. Surgical implications of obesity. Annu Rev Med
13. Dominguez-Cherit G, Gonzalez R, Borunda D, Pedroza J, Gonzalez-Barranco J, Herrera MF. Anesthesia for morbidly obese patients. World J Surg
14. Brooks-Brunn JA. Predictors of postoperative pulmonary complications following abdominal surgery
15. Delgado-Rodriguez M, Medina-Cuadros M, Martinez-Gallego G, Sillero-Arenas M. Usefulness of intrinsic surgical wound infection risk indices as predictors of postoperative pneumonia risk. J Hosp Infect
16. Strandberg A, Tokics L, Brismar B, Lundquist H, Hedenstierna G. Constitutional factors promoting development of atelectasis during anaesthesia. Acta Anaesthesiol Scand
18. Philips B, Ball C, Sackett D et al
. Levels of evidence and grades of recommendation. Oxford Centre for Evidence Based Medicine, 2001; available from URL http://www.cebm.net/levels_of_evidence.asp
on July 20, 2005.
19. Seymour DG, Pringle R. Post-operative complications in the elderly surgical patient. Gerontology
Keywords:© 2006 European Society of Anaesthesiology
ANAESTHESIA GENERAL; OBESITY MORBID; SURGERY; POSTOPERATIVE COMPLICATIONS