Asian Cardiovasc Thorac Ann 2008;16:463-467
© 2008 Asia Publishing EXchange Ltd
Effect of Body Mass Index on Perioperative Complications in Thoracic Surgery
Ryuichi Suemitsu, MD,
Taro Sakoguchi, MD1,
Keiko Morikawa, MD1,
Masafumi Yamaguchi, MD,
Hiroyuki Tanaka, MD1,
Sadanori Takeo, MD
Department of Thoracic Surgery
1 Department of Anesthesiology, Clinical Research Institute, National Hospital Organization, Kyushu Medical Center Fukuoka, Japan
For reprint information contact: Ryuichi Suemitsu, MD, Tel: 81 92 852 0700, Fax: 81 92 847 8802, Email: suemitsu{at}qmed.hosp.go.jp, Department of Thoracic Surgery, National Hospital Organization, Kyushu Medical Center, Jigyohama 1-8-1, Fukuoka, Japan 810-8563.
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ABSTRACT
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Obesity is perceived as a risk factor in general thoracic surgery. We conducted a single-center retrospective evaluation of perioperative complications in 822 patients who underwent thoracic surgery between 2000 and 2005. According to body mass index, 82 were underweight (< 18.5 kg·m–2), 568 were normal (18.5–24.9 kg·m–2), 155 were overweight (25.0–29.9 kg·m–2), and 17 were obese (
30 kg·m–2). A significant increase in preoperative comorbidity (hypertension and ischemic heart disease) was observed with increasing body mass index. There was no significant difference in operation time or length of stay in the operating room, but extubation time was significantly different among the 4 groups. Of the intraoperative complications, alveolar-arterial oxygen difference increased significantly with increasing obesity, and hypoxia was least common in the normal group. Postoperatively, there was more pulmonary leakage in the underweight group and less pneumonia in the normal group. Both the underweight and the obese are at increased risk of perioperative complications and need to be carefully observed and managed intraoperatively and postoperatively.
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INTRODUCTION
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Obesity in Japan has been increasing as Japanese lifestyles have been changing during the last couple of decades. One of the indicators of obesity is body mass index (BMI). BMI = weight (kg)/[height (m)]2. Obesity is defined as BMI > 25 kg·m–2, according to the Japan Society for the Study of Obesity.1 Obese people have a higher risk of fatty liver, diabetes mellitus, hypertension, stroke and coronary artery disease.2,3 Furthermore, obese patients undergoing thoracic surgery are more likely to suffer perioperative complications.4,5 In terms of physique, more Japanese people tend to be of normal weight or slender, compared to Europeans and Americans. In 2006, 24% of Japanese adults were classified as obese.2 There have been many reports on the relationship between obesity and operative complications;5,6 however, there have been very few reports regarding perioperative complications with respect to BMI. We investigated whether BMI is an indicator of perioperative complications in Japanese patients undergoing general thoracic surgery under general anesthesia.
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PATIENTS AND METHODS
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From January 2000 to December 2005, 830 patients underwent general thoracic surgery in our department. Of these, we retrospectively analyzed data of 822 patients; in 8, we lacked data on height and/or weight. Almost all patients had an electrocardiogram and a respiratory function test, and if necessary, an echocardiogram, cardiac scintigram, and pulmonary ventilation-blood flow scintigram. Preoperative data were collected from medical records and included thoracic disease and other preexisting disease as preoperative comorbidities. Operative data were reviewed using anesthetic charts, comprising age, sex, height, surgical methods, anesthetic methods, anesthetic drugs, operation time, length of stay in the operating room, extubation time, failure to extubate, and intraoperative complications. We defined length of stay in the operating room as time from when the patient was carried into the operating room to when they were carried out. Extubation time was from closure of the incision to extubation. BMI was calculated using height and weight at the time of surgery. The patients were classified into 4 groups: underweight (BMI < 18.5 kg·m–2), normal (BMI 18.5–24.9 kg·m–2), overweight (BMI 25.0–29.9 kg·m–2), and obese (BMI 30 kg·m–2). Postoperative complications and mortality were analyzed using data from medical records. Morbidly underweight patients, such as those with more advanced disease, low albumin, or malnutrition, were excluded. Operative death was defined as death within 30 postoperative days. Hospital death was death specifically related to the operation and its complications.
All operations were performed under general anesthesia with or without epidural analgesia. Propofol was used mainly for anesthetic induction, and its concentration was controlled using a target-controlled infusion system (Diprifusor; AstraZeneca); the concentration of propofol was determined according to the patient’s age and weight.7 Anesthesia was maintained in almost all patients with sevoflurane and nitrous oxide gas if necessary. No epidural analgesia was used in 0%–2.6% of patients in the 4 groups because of the use of anticoagulants such as antiplatelet or antithrombotic agents, difficulty in inserting epidural tubing, or minimally invasive operation by video-assisted thoracic surgery, such as bullectomy.
Continuous variables are presented as mean ± standard deviation. Statistical analysis was performed using the independent Student’s t test for continuous variables, and chi-squared analysis for categorical variables. A Kruskal-Wallis test was performed to compare medians across groups. In all statistical analyses, a p value < 0.05 was held to be significant.
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RESULTS
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The patient characteristics are listed in Table 1
. Preoperative comorbidities are given in Table 2. Hypertension and ischemic heart disease were significantly more frequent with increasing BMI, but rates of emphysema and renal disorders were relatively lower in the overweight group. Operative complications and anesthetic details are shown in Table 3. The amount of propofol required increased significantly with increasing BMI, whereas patients who received sevoflurane showed no such increase. The propofol/BMI ratio was similar among the 4 groups, but the sevoflurane/BMI ratio decreased significantly with increasing BMI. Extubation time increased significantly with increasing BMI. Postoperative complications and operative mortality are shown in Table 4. Hospital stay was significantly longer in the obese group. The hospital death rate decreased with increasing BMI, but the differences were not significant. Operative deaths also showed no statistical significance among groups; the overall operative mortality in all 822 patients was 0.85% (7 patients). The primary diseases in these patients who died were lung cancer in 4, pulmonary metastasis in 2, and thymoma in 1; operations were 2 pneumonectomies, 2 lobectomies, 2 wedge resections and 1 mediastinal tumor resection; postoperative complications were 4 cases of respiratory failure and 1 case each of cerebral infarction, bronchoesophageal fistula, and bleeding.
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DISCUSSION
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The percentage of the Japanese population classified as obese is no greater than that worldwide. Obesity is known to cause metabolic syndromes such as diabetes mellitus, hypertension, cerebral infarction, and ischemic heart disease.1,4 In patients undergoing surgery, physique, especially obesity, is believed to influence both the operation and the outcome of general anesthesia.3,5,6,8–10 In Japan, the rate of male obesity is higher than that of 1 or 2 decades ago, while the rate of female obesity is lower now in women aged 20–50 years, and the number of underweight women aged 20–40 years has also decreased in the last 2 decades.2 In the past, the Japanese were less obese than Westerners, and we therefore believed Japanese people to have different perioperative complications because of their lower body weights. However, there have been few reports of complications in underweight patients. In this series, patients in the overweight and obese groups had more cardiac complications than underweight and normal patients. Overweight and obese patients are considered to be more at risk of cardiac diseases such as hypertension and ischemic heart disease.1–4 On the other hand, underweight patients were found to have more thoracic complications, mostly emphysema. A higher rate of renal disorders was detected in underweight patients: 7 of 8 underwent dialysis.
It was necessary to increase the dose of both propofol and sevoflurane with increasing BMI (Table 3
). However, underweight patients might be able to undergo anesthesia with smaller doses. Thus we revised the dosages of anesthetic drugs based on BMI (dose/BMI) to eliminate differences in individual metabolisms and to clarify whether the dosages were appropriate. Intraoperative thoracic complications were more frequent in the higher BMI groups. It might be that overweight and obese patients poorly tolerate the lateral position and single-lung ventilation. Most general thoracic surgery is performed with the patient in the lateral position, which contributes to contralateral atelectasis, especially in obese patients, leading to an increase in alveolar-arterial oxygen difference. One improvement in the treatment of intraoperative hypoxia in obese patients is the use of positive end-expiratory pressure ventilation, and this might also be made available to underweight patients with single-lung ventilation.8 Another problem associated with obesity is difficulty in intubation because of a short thick neck, anterior larynx, large tongue, and limited movement of the jaw, neck, and head.10 In this series, difficult intubation was experienced in 2.6%–5.9% of obese patients.
Postoperative thoracic complications tended to be more frequent in the underweight group. It has been reported that the risk of postoperative hypoxia in obese patients is increased by preoperative hypoxia and by thoracic incision, and lasts for 4–7 postoperative days.10,11 Although we did not investigate postoperative hypoxia in the overweight group, aggressive pulmonary care with incentive spirometry, coughing, deep breathing, and early ambulation may prevent thoracic complications in such patients. Additionally, adequate postoperative analgesia is essential to prevent diaphragmatic splinting, and the use of regional techniques, such as epidural analgesia, may reduce the incidence of respiratory complications.11 Obese patients especially have a risk of perioperative deep venous thrombosis and pulmonary embolism.3 We actively try to prevent embolism by using intermittent pneumatic compression and early ambulation, with heparinization if necessary. There has been no incidence of deep venous thrombosis or pulmonary embolism since we instituted these preventative measures.
Although we found no significant differences in mortality among the 4 groups, there tended to be more hospital deaths in underweight patients, possibly because of poor respiratory function due to preoperative emphysematous pulmonary diseases. Smith and colleagues12 found no difference in postoperative complications, mortality, or length of hospital stay after thoracic surgery in obese and non-obese patients. In contrast, we noted hospital stay in obese patients was significantly longer than that of the other groups, despite the small number of patients in this group. Life-threatening postoperative morbidity was more likely in patients with poor cardiothoracic function due to empyema and/or respiratory failure. Thus we concluded that BMI was not associated with increased mortality after general thoracic surgery, although underweight and obese patients have a higher risk of perioperative complications than those with a normal BMI. Surgeons and anesthesiologists must be aware of these differences to provide appropriate premedication, proper general anesthesia, and adequate perioperative managements for patients with an abnormal physique.
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REFERENCES
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- Japan Society for the Study of Obesity. Available at: http://wwwsoc.nii.ac.jp/jasso/index-e.html. Accessed July 10 2008.
- Organization of the Japanese Ministry of Health, Labor and Welfare. Available at: http://www.mhlw.go.jp/english/index.html. Accessed July 10 2008.
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- Wigfield CH, Lindsey JD, Muñoz A, Chopra PS, Edwards NM, Love RB. Is extreme obesity a risk factor for cardiac surgery? An analysis of patients with a BMI > or = 40. Eur J Cardiothorac Surg 2006;29:434–40.[Abstract/Free Full Text]
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- Yoshino J, Akata T, Takahashi S. Intraoperative changes in arterial oxygenation during volume-controlled mechanical ventilation in modestly obese patients undergoing laparotomies with general anesthesia. Acta Anaesthesiol Scand 2003;47:742–50.[Medline]
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ABSTRACT
INTRODUCTION
