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How to inform a morbidly obese patient on the specific risk to develop postoperative pulmonary complications using evidence-based methodology

Flier, S.*; Knape, J. T. A.*

European Journal of Anaesthesiology (EJA): February 2006 - Volume 23 - Issue 2 - p 154–159
doi: 10.1017/S0265021505002073
Original Article

Background and objective: Patients have the right to be informed about the expected benefits and risks of medical and surgical procedures. Ideally this information should be scientifically based and presented to the patient in time. In morbidly obese patient undergoing general anaesthesia, postoperative pulmonary complications are an important cause of postoperative morbidity and mortality. A 46-yr-old female with a body mass index of 89.8 kg m−2 was scheduled to undergo radical abdominal surgery for cervix carcinoma. In order to inform her accurately on the risk of developing postoperative pulmonary complications, we undertook to answer the following question: What is the risk to develop postoperative pulmonary complications in a morbidly obese patient about to undergo abdominal surgery under general anaesthesia?

Methods: A Medline search was conducted from 1966 to 2004 with respect to postoperative pulmonary complications in abdominal surgery of morbidly obese patients. Altogether, 213 articles were found, of which seven were selected. Additionally, seven cross-references and or related articles were used.

Results: For obese patients who undergo abdominal surgery under general anaesthesia, the likelihood to develop atelectasis is 10.4 ± 4.8% (P < 0.001) with a correlation coefficient of 0.28-0.34 (P < 0.05). The likelihood to develop atelectasis and pneumonia taken together is 29.3% with an adjusted odds ratio of 2.82 (95% confidence interval 1.66-4.78; P = 0.0001).

Conclusion: Considering the positive correlation coefficient and the high body mass index of this patient she has a risk of at least 29.3% to develop pneumonia and/or atelectasis, which should affect the anaesthetic strategy in this patient.

*University Medical Centre Utrecht, Department of Perioperative Care and Emergency Medicine, Utrecht, The Netherlands

Correspondence to: Suzanne Flier, Department P&S, Hp Q04.2.313, UMC Utrecht, P.O. Box 85500, 3508 GA Utrecht, The Netherlands. E-mail:; Tel: +31 302509678; Fax: +31 302541828

Accepted for publication September 2005

First published online January 2006

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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 [1].

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.

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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 [2] 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.

Table 1

Table 1

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Critical appraisal

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 [3] and Pasulka and colleagues [4]; follow-up of less than 80%: Forrest and colleagues [5] and Mason and colleagues [6]; abdominal surgical procedures <80% or surgical procedures not specified: Rose and colleagues [7] and Garibaldi and colleagues [8]).

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 2

Table 2

Table 3 shows the validity of the selected studies by using the checklists for appraising studies of the Dutch Cochrane Centre [17] and the Oxford Centre for Evidence Based Medicine [18]. 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.

Table 3

Table 3

Table 4

Table 4

The requisite score was set on a minimum of +/−. Consequently, the studies by Ogunnaike and colleagues [11], Flancbaum and colleagues [12] and Dominguez-Cherit and colleagues [13] were excluded from further analysis. The study by Blouw and colleagues [10] 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].

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Coussa and colleagues [9] 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 [14] 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 [15] 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 [16] 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.

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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 [9] put an upper limit for weight of 160 kg on his study population, whereas Brooks-Brunn [14] used a lower limit for BMI only and Strandberg and colleagues [16] 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.

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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.

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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.

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© 2006 European Society of Anaesthesiology