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Study Clarifies Link between Obesity and Surgical Complications

Jim McCartney

October 11, 2023

The largest multicenter retrospective analysis to date linking obesity and surgical outcomes is shedding new light on complications and the opportunities for preoperative patient management.

The study, an analysis using 7 years of data from the 鶹ýNational Surgical Quality Improvement Program® (NSQIP®), was published in the May 2023 issue of Surgery. It included 2012–2018 data from approximately 5.6 million patients and 64 studies within nine surgical specialties (general, gynecology, neurosurgery, orthopaedics, otolaryngology, plastics, thoracic, urology, and vascular).1

“Most studies have been about the impact on specific operations, disease states, and patient populations,” said senior author Robert A. Meguid, MD, MPH, FACS, a professor of cardiothoracic surgery at the University of Colorado Department of Surgery in Aurora. “We wanted to harness the power of the 鶹ýNSQIP database to examine outcomes in obese class II and III populations, which were largely underpowered in prior studies.”

Obese class II patients have a body mass index (BMI) of 35.0 to 39.9 kg/m2; obese class III patients have a BMI of at least 40.0 kg/m2.

More than two in five adults in the US are obese (BMI of at least 30.0 kg/m2), and the number of obese surgical patients continues to grow. Obesity is associated with cardiovascular disease, stroke, type 2 diabetes, certain types of cancer, and other comorbidities.2-3

Study Results

Grouping patients by BMI class, the researchers examined 12 postoperative adverse outcomes: 30-day mortality, overall morbidity, pulmonary, infection, urinary tract infection, venous thromboembolism (VTE), cardiac, bleeding/transfusion, renal, stroke, unplanned readmission, and nonhome discharge.

“Our team thought we’d see an increased rate across the board of the different complications but that wasn’t the case,” said Dr. Meguid.

They did not find elevated odds of postoperative complications such as mortality, overall morbidity, pulmonary issues, and urinary tract infection among obese patients. What they did find was an association between obesity and higher rates of infection, VTE, and renal failure.

The researchers offered the following explanations:

  • Infection may be higher because of an impaired immune system response due to immune cell interactions with adipocytes, increased wound tension after closure, trauma due to retractor use to improve surgical visibility, and poor microcirculation among obese patients. Infections are also associated with longer operations, possibly due to intraoperative hypothermia.
  • VTE may be due to a prothrombotic state of chronic inflammation and impaired fibrinolysis caused by the release of proinflammatory cytokines and plasminogen-activator inhibitor-1 by adipocytes. Obesity also is associated with a chronic inflammatory state, decreased perioperative mobility for obese patients, underdosing of subcutaneous heparin, and challenges with using standard sequential compression devices.
  • Renal failure may be due to volume shifts associated with a larger volume of distribution, increased intra-abdominal pressure associated with possible renal hypoperfusion, and chronic inflammation among obese patients.

A big takeaway from the study was that more effort needs to be made preoperatively on preventing complications, especially VTE. “Even in this really diverse population, VTE events were statistically more common,” explained Anthony T. Petrick, MD, FACS, a general surgeon specializing in esophageal and bariatric surgery at Geisinger Health in Danville, Pennsylvania, and Chair of the 鶹ýMetabolic and Bariatric Surgery Accreditation and Quality Improvement Program (MBSAQIP) Data and Quality Committee.

In addition to specific complications, the researchers examined how long an operation took, the rate of complications from complex operations, and challenges to patient recovery.


Dr. Robert Meguid

Longer Operations

Although the study showed that it takes longer to operate on overweight and obese patients than on normal-weight patients, the difference was marginal (89 minutes vs. 83 minutes), possibly due to the wide variety of operations included, as well as advances in technology such as minimally invasive procedures.

Nevertheless, the small difference in operating time was a surprise to Dr. Meguid, who—as a cardiothoracic surgeon performing foregut surgery—said he experiences longer and more complicated procedures when patients have extra intra-abdominal fat tissue because it decreases visibility and complicates access to the organs.

“There’s also an increase in what we call dead space where the wound is being closed, due to the fat tissue,” Dr. Meguid said.

Longer operation times in the study were associated with obese patients undergoing plastic reconstructive surgery, neurologic surgery, and gynecologic surgery.

More Complications in Complex Operations

The researchers found that the more complex the operation, the greater the likelihood of a wide variety of complications.

For higher-complexity operations such as pancreaticoduodenectomy, however, obese patients also faced increased risk of mortality, overall morbidity, pulmonary complications, unplanned readmissions, and nonhome discharge.

In lower-complexity operations such as cholecystectomy, obese patients had an increased risk of infection, VTE, and renal complications, similar to the overall outcomes.

Harder Recovery

In his practice, Dr. Meguid said he often sees a correlation between high BMI and difficulty in walking after the operation, as nurses, physical therapists, and assistants often have a hard time getting obese patients out of bed. This reality can prolong recovery and increase complications, since perioperative ambulation decreases the risk of pulmonary and VTE complications. In addition, obese patients are more likely to face wound complications than normal-weight patients, which can lengthen their recovery.

Limitations of the Study

Although the broad, sweeping approach of the study is one of its strengths, it also is the source of some of its limitations because it groups many different operations and surgical specialties into one analysis.

“You’re looking at a very diverse group of procedures, some of which are associated with very low complication rates across the board, so the impact of obesity on these outcomes is diminished,” Dr. Petrick said.

There can be significant differences between procedures that occur at the skin level compared to those within body cavities, especially when it comes to infection, but the impact of these various types of infections were not differentiated in the study.


Dr. Anthony Petrick repairs a hiatal hernia and revises the gastric pouch in a patient with a previous laparoscopic gastric bypass.

Need for Longer-Term Outcomes

“Many complications for surgical patients in general, and obese patients in particular, occur more than 30 days after an operation, and therefore, aren’t captured in the 鶹ýNSQIP patient data,” explained Dr. Meguid. “The 鶹ýhas made an effort to start looking at longer-term outcomes and measure patient-reported outcomes, which are, to me, the heart of how patients are doing.”

There are challenges, however, in gathering long-term patient data, said Dr. Petrick, a participant in MBSAQIP.

Getting this long-term patient data often requires multiple telephone calls, and obtaining this information is a particular challenge for national patient databases. For example, MBSAQIP incorporates data on patients a year out from their bariatric surgery, such as weight loss, he said. But it has been difficult to register even 10% of these patients—a reality that is compounded by the fact that people move frequently, and their contact information often changes.

It may be more strategic for specific institutions to focus on gathering longer follow-up information from patients, according to Dr. Petrick.

Better Metric for Obesity

Although the ease and simplicity of the BMI measurement makes it a convenient tool, it has several inherent limitations. BMI assessments do not consider cardiorespiratory fitness or metabolic health; some individuals may have higher BMIs due to higher muscle mass and bone density rather than higher levels of fat. In addition, not all types of obesity are considered equal; for example, visceral fat is associated with increased mortality risk.

Some possibilities for better measures include waist circumference or body fat percentage. “A lot of our medical programs that manage patients long term use these measures,” Dr. Petrick said. However, these alternative measures typically require more time, effort, and money. BMI, on the other hand, is simple and easy to compute from regularly collected patient information.

“It’s a question of ‘Is good better than perfect?’” Dr. Petrick said. “BMI is universally available, and it’s pretty good, so it’s an important step forward for medicine. But clearly it isn’t perfect.”

obesityfigure1b1023.jpg (1)

Reducing Surgical Risks for Obese Patients

To help better mitigate potential obesity-related surgical risks, Dr. Meguid recommends using a risk-assessment tool to create a preoperative plan for the patient, their families, and the surgical team.

This individualized patient care plan would complement the standard of care regarding VTE prophylaxis, intraoperative normothermia, and appropriate perioperative antibiotic administration and glucose control.

“For instance, surgeons can take extra precautions to minimize renal failure by monitoring postoperative renal function,” he said. “For wound infections, we would use meticulous tissue handling and wound closure techniques, and early and more frequent perioperative follow-up to identify and treat infections early.”

Several national quality improvement programs through MBSAQIP have demonstrated successful strategies to improve surgical outcomes in obese patients. They include Decreasing Readmissions through Opportunities Provided (DROP), Employing New Enhanced Recovery Goals for Bariatric Surgery (ENERGY),4 and Bariatric Surgery Targeting Opioids Postoperatively (BSTOP).5

The goal of DROP was to decrease all-cause 30-day readmissions for primary bariatric surgery at comprehensive centers by 20% in 1 year using interventions that include an educational video, a discharge checklist, follow-up phone calls by an RN, distribution of key clinical phone numbers, and multiple visits with the nutritionist.6 ENERGY focused on reducing postoperative surgical infections through measures like antibiotic delivery and prepping patients to ensure they’re appropriately nourished and their blood glucose levels are under control,7 while BSTOP created a multimodal perioperative pain management regimen that helped to minimize opioid use.5

From the recent Surgery study, other suggestions to reduce risk for obese surgical patients include:

  • Performing minimally invasive procedures versus open procedures, when possible
  • Using weight-based dosing for anesthetics, muscle relaxants, neuromuscular reversal agents, analgesics, antibiotics, and anticoagulants
  • Ensuring appropriate perioperative care such as early ambulation is available
  • Conducting early and more frequent perioperative follow-up to guide intervention and minimize postoperative complications
  • Recommending patients follow specific infection protocols such as a multidisciplinary wound-management approach, daily bathing, and/or negative pressure wound therapy
  • Stratifying patients using a risk score such as the Caprini score to help prevent VTE; high-risk patients should receive mechanical and pharmacological prophylaxis, in some cases, even after hospital discharge
  • Maintaining adequate hemodynamics and sufficient fluid resuscitation and avoiding nephrotoxic agents to help preventing acute kidney injury
  • Optimizing preoperative hemoglobin levels to avoid excessive transfusions

鶹ýStrong for Surgery Program

For obese patients preparing for elective procedures, losing weight should be part of the equation.
Many institutions have enhanced recovery after surgery protocols, and the 鶹ýStrong for Surgery program provides guidance and strategies—such as checklists to assess nutrition, blood sugar control, smoking cessation, and medications—to optimize the health of patients before surgery. The Strong for Surgery program also includes a patient toolkit.

More information about the program is available at facs.org/quality-programs/strong-for-surgery.

Jim McCartney is a freelance writer.

  1. Madsen HJ, Gillette RA, Colborn KL, et al. The association between obesity and postoperative outcomes in a broad surgical population: A 7-year ACS-NSQIP analysis. Surgery. 2023;173(5):1213-1219.
  2. Centers for Disease Control and Prevention. Adult Obesity Facts. Available at: . Accessed September 7, 2023.
  3. National Institute of Diabetes and Digestive and Kidney Diseases. Overweight & Obesity Statistics. Available at: . Accessed September 9, 2023.
  4. Brethauer SA, Grieco A, Fraker T, et al. Employing Enhanced Recovery Goals in Bariatric Surgery (ENERGY): A national quality improvement project using the Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program. Surg Obes Relat Dis. 2019;15(11):1977-1989.
  5. Seu R, Pereira X, Goriacko P, et al. Effectiveness of Bariatric Surgery Targeting Opioid Prescriptions (BSTOP) protocol on postoperative pain control. Surg Endosc. 2023;37(6):4902-4909.
  6. Gadaleta D, Petrick AT. Raising the standard: DROP—The first national MBSAQIP quality improvement project: Decreasing Readmissions through Opportunities Provided. Bariatric Times. Available at: . Accessed September 14, 2023.
  7. Brethauer SA, Grieco A, Fraker T, et al. Employing Enhanced Recovery Goals in Bariatric Surgery (ENERGY): A national quality improvement project using the Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program. Surg Obes Relat Dis. 2019;15(11):1977-1989.