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(Chest. 2006;130:517-525.)
© 2006 American College of Chest Physicians

Cardiorespiratory Fitness and Short-term Complications After Bariatric Surgery*

Peter A. McCullough, MD, MPH; Michael J. Gallagher, MD; Adam T. deJong, MA; Keisha R. Sandberg, MPH; Justin E. Trivax, MD; Daniel Alexander, DO; Gopi Kasturi, MD; Syed M. A. Jafri; Kevin R. Krause, MD; David L. Chengelis, MD; Jason Moy, MD and Barry A. Franklin, PhD

* From the Department of Medicine, Divisions of Cardiology, Nutrition and Preventive Medicine (Drs. McCullough, Gallagher, Trivax, Alexander, Kasturi, and Franklin, Mr. deJong, Ms. Sandberg, and Mr. Jafri), and the Department of Surgery (Drs. Krause, Chengelis, and Moy), William Beaumont Hospital, Royal Oak, MI.

Correspondence to: Peter A. McCullough, MD, MPH, Divisions of Cardiology, Nutrition, and Preventive Medicine, William Beaumont Hospital, 4949 Coolidge Hwy, Royal Oak, MI 48073; e-mail: pmc975{at}yahoo.com

Abstract

Background: Morbid obesity is associated with reduced functional capacity, multiple comorbidities, and higher overall mortality. The relationship between complications after bariatric surgery and preoperative cardiorespiratory fitness has not been previously studied.

Methods: We evaluated cardiorespiratory fitness in 109 patients with morbid obesity prior to laparoscopic Roux-en-Y gastric bypass surgery. Charts were abstracted using a case report form by reviewers blinded to the cardiorespiratory evaluation results.

Results: The mean age (± SD) was 46.0 ± 10.4 years, and 82 patients (75.2%) were female. The mean body mass index (BMI) was 48.7 ± 7.2 (range, 36.0 to 90.0 kg/m2). The composite complication rate, defined as death, unstable angina, myocardial infarction, venous thromboembolism, renal failure, or stroke, occurred in 6 of 37 patients (16.6%) and 2 of 72 patients (2.8%) with peak oxygen consumption (VO2) levels < 15.8 mL/kg/min or > 15.8 mL/kg/min (lowest tertile), respectively (p = 0.02). Hospital lengths of stay and 30-day readmission rates were highest in the lowest tertile of peak VO2 (p = 0.005). There were no complications in those with BMI < 45 kg/m2 or peak VO2 ≥ 15.8 mL/kg/min. Multivariate analysis adjusting for age and gender found peak VO2 was a significant predictor of complications: odds ratio, 1.61 (per unit decrease); 95% confidence interval, 1.19 to 2.18 (p = 0.002).

Conclusions: Reduced cardiorespiratory fitness levels were associated with increased, short-term complications after bariatric surgery. Cardiorespiratory fitness should be optimized prior to bariatric surgery to potentially reduce postoperative complications.

Key Words: bariatric surgery • exercise testing • gastric bypass surgery • obesity • oxygen consumption • preoperative evaluation • surgical complications

In recent years, there has been a rapid increase in the prevalence of obesity. Data from the National Health and Nutrition Examination Survey1 demonstrate that nearly one out of three US residents are obese. Data from the Coronary Artery Risk Development in Young Adults study2 indicate that in subjects aged 25 to 40 years, only 18.1% maintain a stable weight, while 81.9% of the subjects had an increase in body mass index (BMI) > 2 kg/m2. We have reported that for those with morbid obesity, mean BMI increases rapidly from approximately 29 kg/m2 to approximately 50 kg/m2 from 18 to 44 years of age.3 The obesity epidemic is having a major adverse public health impact in the United States by elevating risks of cardiovascular disease (CVD), hypertension, dysmetabolic syndrome, type 2 diabetes mellitus, sleep apnea syndrome, hyperlipidemia, osteoarthritis, certain cancers, and death from all causes.45678910111213

Decreased peak oxygen consumption (VO2) or aerobic capacity, as a measure of cardiorespiratory fitness, is associated with increased CVD and all-cause mortality.1415 Low cardiorespiratory fitness increases the relative risk of death to a similar level as tobacco abuse, hypertension, and/or diabetes.16171819 Previous studies2021 have shown that obesity is associated with disproportionate increases in the rate-pressure product and reduced work tolerance, resulting in reduced oxygen delivery to muscles during activity. We have reported that cardiorespiratory fitness levels in the morbidly obese were similar to patients with advanced heart failure (HF).22 Furthermore, there was a graded inverse relationship between BMI > 25 kg/m2 and peak VO2.22

In recent years, bariatric surgery has become an increasingly utilized therapeutic option for those with morbid obesity.23 Surgery for obesity results in sustained weight reduction and improvement or often resolution of comorbid conditions, including type 2 diabetes mellitus, hypertension, sleep apnea, lower-extremity venous stasis, gastroesophageal reflux disease, degenerative joint disease, and nonalcoholic steatohepatitis.2425 In 2003, it is estimated that > 100,000 bariatric operations were performed, with > 80% of cases being gastric bypass surgery.26 The reported in-hospital mortality rate ranges from 0.1 to 0.2%.26 The rate of unexpected reoperations for surgical complications ranges from 6 to 9%, and pulmonary complications range from 4 to 7%.26 There are no uniform standards for the medical preoperative evaluation for a patient who is undergoing bariatric surgery. The current American Heart Association/American College of Cardiology guidelines2728 state that an assessment of functional capacity is the first step in the evaluation process for noncardiac surgery but do not address the specific issues of bariatric patients. Patients with morbid obesity have reduced functional capacity as measured by peak VO2 expressed as milliliters per kilogram per minute or metabolic equivalents (METs) [1 MET = 3.5 mL/kg/min]. Thus, we sought to evaluate the relationship, if any, between measures of cardiorespiratory fitness, including peak VO2, other clinical variables, and postoperative complications after bariatric surgery.

Materials and Methods

Study Population
The study sample included 109 consecutive, morbidly obese patients evaluated at the William Beaumont Hospital Weight Control Center (Royal Oak, MI) from November 2001 to December 2003, and undergoing laparoscopic Roux-en-Y gastric bypass surgery. Inclusion criteria were as follows: (1) BMI > 35 kg/m2 and > 40 kg/m2 in patients with and without diabetes, respectively; (2) absence of limiting cardiopulmonary disease (Canadian Cardiovascular Society class 4 angina, or functional class 4 dyspnea); and (3) ability to perform cardiopulmonary exercise testing (CPX) to exhaustion. Patients with severe lung disease requiring long-term oxygen therapy were also excluded.

Baseline Evaluation
All patients underwent a comprehensive medical evaluation with history, physical examination, 12-lead ECG, and blood and urine testing. Estimated glomerular filtration rates (eGFR) [milliliters per minute per 1.73 m2] were calculated using the Levey-modified Modification of Diet in Renal Disease formula: (186.3 x [serum creatinine-1.154]x [age-0.203]); calculated values were multiplied by 0.742 for women and by 1.21 for African Americans.29 The presence of hypertension, diabetes, tobacco abuse, and medications, including ß-blocker therapy, was recorded for all subjects. Habitual physical activity was assessed via questionnaire during the initial evaluation; regular exercise was defined as structured or formal exercise three or more times per week. All subjects underwent standardized psychological testing and a face-to-face interview with a licensed psychologist. Patients must have been approved from a multidisciplinary perspective before undergoing bariatric surgery.

CPX
Morbidly obese patients underwent peak or symptom-limited CPX using Bruce or modified Bruce treadmill protocols that increased workload by approximately 2 METs every 3 min.30 One patient who was unable to negotiate the treadmill walking underwent dual-action arm-leg ergometry via a commercially available ergometer (Schwinn Airdyne; Nautilus; Vancouver, WA), using the levers and pedals simultaneously. Heart rate (HR) and BP (standard cuff method) were measured at rest in supine and standing positions during each 3-min stage of exercise and throughout a 6-min recovery. Test termination criteria included the following: patient request, volitional fatigue, increasing chest or leg pain, ECG abnormalities (≥ 2 mm ST-segment depression and/or threatening ventricular arrhythmias), and a hypertensive or hypotensive BP response.

ECG was monitored continuously by oscilloscope (Q-stress II; Quinton; Seattle, WA), with three-channel (V1, V5, and aVF) recordings obtained throughout the exercise test, and 12-lead ECGs (1 millivolt/10 mm) recorded at the end of each stage and during maximal exercise. Perception of the intensity of physical effort at submaximal and maximal exercise was obtained using the Borg category scale (6 to 20).31

Metabolic data were obtained using a gas exchange system (CPX/D Systems; Medical Graphics; Minneapolis, MN). This system includes a computer assembly for breath-by-breath and on-line 15-s calculations of VO2 (milliliters per kilogram per minute or METs), minute ventilation (VE), carbon dioxide production (VCO2), and respiratory exchange ratio (RER; VCO2/VO2). Before each test, the pneumotachometer was referenced according to manufacturer specifications with a 3-L syringe, and the gas analyzers were calibrated with a certified air mixture representing room air (21% oxygen and balance nitrogen) and certified oxygen/carbon dioxide concentrations (12% oxygen and 5% carbon dioxide). The pneumotach was a bi-directional differential pressure preVent model (Medical Graphics) that utilized a standard, Kraton mouthpiece and saliva trap.

The V-slope method was used to determine the ventilatory-derived anaerobic threshold (V-AT; ie, the break point in linearity when VCO2 was plotted as a function of VO2), expressed as a percentage of the peak VO2. This method has been reported to be a sensitive, reliable, and noninvasive technique for detection of the onset of metabolic acidosis.3233 We also computed the slopes of the relation between VE and VO2, and between VE and VCO2, as markers of breathing economy and functional limitations, respectively.

Bariatric Surgery and In-hospital Care
All patients underwent planned laparoscopic Roux-en-Y gastric bypass surgery. After receiving general endotracheal anesthesia, the abdomen was prepped and draped, and accessed using laparoscopic techniques. Gastric bypass using the Roux-en-Y anastomosis restricting the size of the stomach by division of 90% of the lower stomach from the residual gastric pouch was performed. The jejunum was anastomosed to the gastric pouch. The abdomen and viscera were checked for bleeding and leaks. Thereafter, the abdomen was evacuated of air, and subcutaneous drains were placed only for excess serosanginous drainage. Patients underwent planned extubation in the postoperative recovery room. Supplemental oxygen was administered to keep the oxygen saturation > 92%. Ambulation was encouraged later the same day. Routine postoperative care included pneumatic external compression stockings and 5,000 U of subcutaneous unfractionated heparin every 12 h. Discharge was targeted for the third day after surgery.

Chart Abstraction and Definitions of Postoperative Complications
Charts were abstracted using a case report form by physician reviewers (J.E.T., D.A., G.K.) blinded to CPX results. Data were collected on a case report form for the index hospitalization during which the bariatric surgery occurred, and all subsequent hospitalizations over a 30-day period after discharge. Operative times were determined from the anesthesia record. Outcomes were organized a priori into intermediate (operative and reversible), primary (permanent or potential organ damage), and secondary (length of stay and readmission). The primary composite complication rate was defined as death, unstable angina, myocardial infarction, deep venous thrombosis (DVT), pulmonary embolism (PE), renal failure, or stroke. Unstable angina was defined as chest discomfort consistent with myocardial ischemia (with or without characteristic ECG changes) but without an elevation of markers of myonecrosis. Myocardial infarction was defined as an elevation of cardiac troponin I above the normal laboratory range with one or more corroborators including associated chest discomfort, ischemic ST-segment elevation or depression, new pathologic Q-waves, or an occluded culprit coronary artery on angiography. DVT was classified as a thrombus identified in the superficial femoral or deeper veins detected by ultrasonography or venography, and pulmonary embolism (PE) was defined as characteristic symptoms supported by findings on a ventilation/perfusion scan or chest CT. Renal failure was defined as a rise in baseline serum creatinine level > 25% from baseline or an absolute rise of 0.5 mg/dL at any time during the hospital stay after surgery. Stroke was defined as a sudden neurologic deficit lasting > 24 h associated with a new anatomic lesion on brain axial imaging. Exacerbation of existing or new HF required characteristic HF symptoms requiring the use of unscheduled IV diuretics, vasodilators, or inotropic agents. Infection was described as suspected bacterial infection requiring the use of IV antibiotics. GI bleeding was classified as any endoluminal bleeding event causing a > 2 g/dL drop in hemoglobin or requiring blood transfusion.

Statistical Analysis
Baseline characteristics were expressed as mean ± SD or counts with proportions as appropriate. Univariate comparisons were made with Student t test, Fisher exact test, {chi}2, and {chi}2 for trend as appropriate. All hypothesis testing was two tailed. Tertile of peak VO2 was used as the main predictor variable to explore the data for linear and nonlinear relationships among predictors and outcomes. Stepwise, multiple logistic regression was performed for the primary composite outcome using tertile of peak VO2 and the baseline variables of age, gender, BMI, and eGFR. In order to achieve the most parsimonious model given the sparse end point frequency, BMI and eGFR were not included in the final model since their p values were > 0.10. Smoking was not entered into this model since the second tertile contained no smokers; therefore, unstable point estimates would have been generated. A second model was generated using peak VO2 as a continuous variable, again adjusting for age and gender. Receiver operating characteristic curve analysis was used to derive the area under the curve for selected CPX variables with respect to the primary outcome. A p value < 0.05 was considered statistically significant. This study and analysis was approved by the Human Investigations Committee at William Beaumont Hospital.

Results

The study sample had a mean age of 46.0 ± 10.4 years (82 women [75.2%] and 27 men [24.8%]). Mean BMI was 48.7 ± 7.2 (range, 36.0 to 90.0 kg/m2). Mean BMI was 48.1 ± 7.5 kg/m2 and 50.4 ± 6.0 kg/m2 for women and men, respectively (p = 0 0.17). Table 1 shows the baseline characteristics of patients stratified by tertile of peak VO2. Peak VO2 values were as follows: first tertile: mean, 13.7 mL/kg/min; median, 14.2 mL/kg/min; range 6.8 to 15.8 mL/kg/min; second tertile: mean, 17.1 mL/kg/min; median, 17.1 mL/kg/min; range, 15.9 to 18.4 mL/kg/min; and third tertile: mean, 21.2 mL/kg/min; median, 20.8 mL/kg/min; range, 18.5 to 27.7 mL/kg/min. Patients in the first tertile were more likely to be female, older, and nonwhite, and had a higher BMI, diabetes, and hypertension. Rates of coronary artery disease (CAD), pulmonary diseases, and arthritis were similar among the tertiles of peak VO2. Of note, 6 of 37 subjects (16.2%) in the first tertile were cigarette smokers, compared with 3 of 72 patients (4.2%) of the second and third tertiles combined (p = 0.07). The correlation between BMI and peak VO2 was 0.50 (p < 0.0001).


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  		Table 1.. Baseline Characteristics by Tertile of Peak VO2*

 
Baseline and maximal exercise responses, including hemodynamic and cardiopulmonary data, are listed in Table 2 . Of note, all cardiopulmonary variables measured with exercise differed across the tertiles with the exception of VE/VCO2 slope. Patients in the first tertile achieved lower HRs, lower percentage of predicted maximum HR, and lower RERs, suggesting less voluntary effort during exercise. However, perceived exertion ratings were uniformly high, with an overall mean of 16.7 ± 1.1, which was similar across the tertiles.


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  		Table 2.. Resting and Cardiopulmonary Stress Testing Data by Tertile*

 
Table 3 gives detailed surgical outcome data according to peak VO2 tertile. Operative times were longer by 24.8 min for the first tertile compared with the third tertile. Likewise, intubation duration and estimated blood losses were both numerically higher in the first tertile. Intermediate, primary, and secondary complications were infrequent in the second and third tertiles. There were no cases of reoperation. The primary composite complication rate defined as death, unstable angina, myocardial infarction, venous thromboembolism (DVT or PE), renal failure, or stroke occurred in 6 of 37 patients (16.6%) and 2 of 72 patients (2.8%) with peak VO2 > 15.8 mL/kg/min and < 15.8 mL/kg/min (lowest tertile) [p = 0.02, Fisher exact test, two tailed; Fig 1 ]: univariate odds ratio (OR), 6.77; 95% confidence interval (CI), 1.14 to 51.76. Figure 2 shows a scatterplot of peak VO2 vs BMI among patients with and without complications represented by the closed and open circles, respectively. There were no complications in the lower right and left quadrants in patients with BMI < 45 kg/m2 or peak VO2 ≥ 15.8 mL/min. Complications occurred in one of nine patients (11.1%; p = 0.51) of those who currently smoked. Acute renal failure occurred as a singular primary end point in two patients and was associated with at least one other primary outcome in five patients. The fatality occurred in a 60-year-old woman with BMI of 52 kg/m2, history of diabetes but no CAD, and a peak VO2 of 10.7 mL/kg/min. This patient had upper GI bleeding with aspiration, respiratory and renal failure, and death due to cerebral anoxia.


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  		Table 3.. Surgical Outcome Data by Tertile of Peak VO2*

 

Figure 1
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  		Figure 1.. Composite primary complication rate by baseline peak VO2.

 

Figure 2
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  		Figure 2.. Scattergram of patients with (solid circles) and without (open circles) complications with bariatric surgery according to BMI and peak VO2.

 
Multivariate analysis found the first tertile of peak VO2 had an OR of 12.89 (vs all others) [95% CI, 1.14 to 146.21; p = 0.04] and male gender had an OR of 10.65 (95% CI, 1.91 to 59.21; p = 0.007) for the prediction of postoperative complications. Age was not found to be a significant predictor of complications (p = 0.63). Figure 3 displays the independent OR for each tertile of peak VO2 compared to the highest tertile as the referent. The second multivariate model, which used peak VO2 as a continuous variable and included smoking status confirmed peak VO2 (OR, 1.61, per unit decrease; 95% CI, 1.19 to 2.18; p = 0.002) and male gender (OR, 22.82; 95% CI, 3.02 to 172.41; p = 0.002) were the only significant predictors of complications. Hospital length of stay and 30-day readmission rates (assessed in all patients) were highest in the lowest tertile of peak VO2: 3.8 days, vs 2.8 days for all others (p = 0.002).


Figure 3
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  		Figure 3.. Independent ORs for tertile of peak VO2 and the primary composite outcome of perioperative complications after adjusting for age and gender. Variables excluded from the final model (p > 0.10) were BMI and eGFR. When analyzed as a continuous variable, peak VO2 retained significance: OR, 1.61 (per unit decrease); 95% CI, 1.19 to 2.18 (p = 0.002).

 
The area under the receiver operating characteristic curve (AUC) for the following variables was as follows: peak VO2 (milliliters per kilogram per minute) AUC, 0.77; V-AT (milliliters per kilogram per minute) AUC, 0.69; maximum VO2 (milliliters per minute) AUC, 0.58; maximum VCO2 (milliliters per minute) AUC, 0.58; RER AUC, 0.54; VE (liters per minute) AUC, 0.38; and exercise duration (minutes) AUC, 0.74. At a cut point of 15.8 mL/kg/min (upper boundary for first tertile) for peak VO2, there was a sensitivity of 75.0% and a specificity of 73.3%. Conversely, a cut point of 18.5 mL/kg/min (lower boundary of third tertile) had 87.5% sensitivity and 34.7% specificity for the composite outcome of postoperative complications.

The overall readmission rate was 11 per 109 patients (10.1%). The most common reason for readmission was vomiting due to the limiting size of the gastric pouch,3 gastrojejunal stenosis requiring dilation,3 and GI bleeding.1 Two patients were admitted due to acute cholecystitis related to rapid weight loss. There were two, late serious complications including one case of pancreatitis (peak VO2, 15.7 mL/kg/min) and one PE(peak VO2, 12.5 mL/kg/min).

Discussion

We found a critical, inverse relationship between cardiopulmonary fitness and complications after bariatric surgery that has not been previously reported. Low peak VO2 and associated higher BMI were related to longer operative times and minor complications from the outset of surgery. The composite of death, unstable angina, myocardial infarction, DVT, PE, renal failure, or stroke was more frequent in those with the lowest peak VO2. These complications appeared to have a cumulative effect ultimately causing longer lengths of stay. One explanation for these findings may be that postoperative complications occur in a stochastic manner and only those with a critically low peak VO2 manifest an observable complication or have a reduced ability to withstand the event compared with those with a sufficient level of cardiopulmonary reserve. Another explanation is that the combination of morbid obesity and low peak VO2 identifies a patient subset who are more difficult to operate on, require longer operative and intubation times and, thus, have opportunities for additional complications. Another possible explanation is that both the low peak VO2 and BMI are surrogate markers for a high-risk, proinflammatory state with elevations of cytokines, adipokines, and other factors that could be related to the development of postoperative complications.

Variables measured with expired gas analysis during exercise testing, whether expressed as absolute (liters per minute) or relative to body weight, were related to the risk of complications developing with bariatric surgery. The measured peak VO2, expressed as milliliters per kilogram per minute, appeared to be the best single measured predictor of complications. However, integrating BMI and peak VO2 in a grid allowed identification of a group of patients with BMI < 45 kg/m2 or peak VO2 ≥ 15.8 mL/kg/min who had no observed complications (lower right and left quadrants of Fig 2). The independent relation between peak VO2 was confirmed with multivariate testing, which included BMI in the model. Male gender was the only other independent predictor of complications.

Our data are consistent with the observation that among the nonobese, functional capacity is a reliable index for perioperative and long-term prediction of CVD events.34353637383940 In the nonobese, functional status may be estimated from the ability to perform activities of daily living.39 Functional capacity can be expressed as MET levels; for example, the VO2 of a 70-kg, 40-year-old man in a resting state is 3.5 mL/kg/min or 1 MET. For this purpose, in young and middle-age adults, functional capacity has been classified as excellent (> 10 METs), good (7 to 10 METs), moderate (4 to 7 METs), and poor (< 4 METs). By this framework, 98.2% of our subjects would have been classified as moderate/poor and 16.5% with poor functional capacity. Hence, our data suggest the need for measured peak VO2 as a more precise indicator of functional capacity and prediction of risk in the morbidly obese.

Prior studies3637 have shown that perioperative cardiac and long-term risks are increased in patients unable to achieve a 4-MET (VO2 of 14.0 mL/kg/min) capacity during peak or symptom-limited exercise testing. In a study37 of 600 consecutive patients undergoing major noncardiac procedures, perioperative myocardial ischemia and CVD events were more common in patients reporting poor exercise tolerance (inability to walk four blocks or climb two flights of stairs) even after adjustment for baseline predictors. The likelihood of a serious complication occurring was inversely related to the number of blocks that could be walked (p = 0.006) or flights of stairs that could be climbed (p = 0.01), analogous to the graded relationship between risk and peak VO2 we observed in our study. Reduced aerobic fitness (milliliters per kilogram per minute) in our morbidly obese patients is undoubtedly attributed, at least in part, to their low rate of regular exercise participation and increased adiposity. However, other potential mechanisms for this observation should be considered. A recent report41 found that young obese females, despite normal left ventricular ejection fraction, commonly have subtle changes in left ventricular size and geometry with concordant changes in diastolic filling patterns. This suggests that adiposity itself may directly impair cardiopulmonary function and create the substrate for postoperative complications.42 We have previously reported that the peak VO2 in the morbidly obese is comparable to patients with class III and IV HF.22 The use of peak VO2 as a measure of exercise tolerance and a predictor of CVD and all-cause mortality in patients with chronic HF is well established.434445 Our data suggest that this variable also provides an important indicator of postoperative outcomes in the morbidly obese and may be a sufficient stratification test for those with a BMI < 45 kg/m2 or a peak VO2 ≥ 15.8 mL/kg/min, reducing or eliminating the need for other cardiac testing including myocardial perfusion imaging.

Our findings present a clinical opportunity to potentially reduce complications with bariatric surgery. Peak VO2 can be increased by weight loss, aerobic endurance training, or both.4046 Collectively, our data suggest that occupational or leisure-time activities corresponding to ≥ 3 METs are likely to induce somatic fatigue, since they may exceed the V-AT, and thus represent an upper limit for exercise training in patients prior to bariatric surgery.22 For our morbidly obese cohort, this would suggest an aerobic requirement of 2 to 3 METs, which approximates walking speeds of only 1 to 2.5 miles per hour. These estimates would need to be confirmed given the known differences in HR response and VO2 in the obese as compared with normal-weight subjects on which the American College of Sports Medicine based its recommendations.47 Nevertheless, even slow walking in this highly unfit cohort, at least during the initial weeks of training, may serve to improve aerobic capacity and reduce complications with bariatric surgery. A randomized trial in those with low peak VO2 designed to augment this measure of cardiorespiratory fitness, vs usual care, would be needed to conclude that selected patients should undergo preoperative weight loss and exercise training to reduce complications with bariatric surgery. In the meantime, the present findings suggest that it would be prudent to directly measure peak VO2 and provide this prognostic information to the patient and the surgical team.

We recognize several limitations in our study. Exercise testing was effort dependent, and there may have been decreased efforts in the morbidly obese due to a lack of confidence in their physical abilities. However, somatic perceived exertion was similar across the peak VO2 tertiles, suggesting patients gave an equal voluntary effort. In addition, we did not have echocardiographic or spirometry data; hence, we relied on the clinical history confirming the absence of heart or pulmonary failure in these groups. The greatest limitation to this analysis, however, is the small sample size, with a total of 8 composite and 16 individual primary outcome events. Although, we do not yet have longer-term outcomes that are expected to include many favorable changes in comorbidities, our focus was the immediate risks of bariatric surgery. It is in this clinical sphere where understanding the prognostic significance of measured peak VO2 appears to be an advance and is worthy of replication by others.

Conclusions

Reduced cardiorespiratory fitness levels were associated with increased short-term complications after bariatric surgery. Cardiorespiratory fitness should be optimized prior to bariatric surgery to potentially reduce postoperative complications.

Footnotes

Abbreviations: AUC = area under the receiver operating characteristic curve; BMI = body mass index; CAD = coronary artery disease; CI = confidence interval; CPX = cardiopulmonary exercise testing; CVD = cardiovascular disease; DVT = deep venous thrombosis; eGFR = estimated glomerular filtration rate; HF = heart failure; HR = heart rate; MET = metabolic equivalent; OR = odds ratio; PE = pulmonary embolism; RER = respiratory exchange ratio; V-AT = ventilatory-derived anaerobic threshold; VCO2 = carbon dioxide production; VE = minute ventilation; VO2 = oxygen consumption

Presented in part at CHEST 2005, the Annual Scientific Sessions of the American College of Chest Physicians, October 29 to November 3, 2005, Montréal, PQ, Canada.

The authors disclose that they have no conflicts of interest related to this topic.

Received for publication January 3, 2006. Accepted for publication February 8, 2006.

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