From the Guidelines
A Body Mass Index (BMI) of 30 or greater is associated with an increased risk of complications during anesthesia and surgical procedures, with the most recent and highest quality evidence suggesting that patients with BMIs of 35 or greater face significantly higher risks 1. Patients with BMIs between 30-34.9 (Class I obesity), 35-39.9 (Class II obesity), and 40 or greater (Class III or morbid obesity) face progressively higher risks. These complications include:
- Difficult airway management
- Increased risk of aspiration
- Respiratory complications
- Cardiovascular issues
- Challenges with drug dosing Obese patients often have reduced functional residual capacity and may desaturate more quickly during intubation attempts. They frequently have comorbidities such as obstructive sleep apnea, hypertension, and diabetes that further complicate anesthesia management. Positioning can also be challenging, potentially leading to nerve injuries or pressure sores. Anesthesiologists typically need to modify their approach for these patients, including careful pre-operative assessment, potentially difficult airway preparation, adjusted medication dosing, and enhanced post-operative monitoring. The risk increases proportionally with BMI, with those having a BMI over 40 requiring the most significant modifications to anesthetic management, as supported by the 2023 American College of Rheumatology and American Association of Hip and Knee Surgeons clinical practice guideline 1. It is conditionally recommended to proceed with total joint arthroplasty (TJA) without delaying for weight reduction in patients with a BMI of 35 or greater, as the evidence supporting preoperative weight reduction is indirect and of very low quality 1. However, patients with elevated BMIs should be informed of the associated risks and encouraged to reduce weight prior to TJA, if possible, to mitigate such risk. The decision to proceed with TJA should be based on a shared decision-making process between the patient and surgeon, taking into account the patient's individual circumstances and the potential benefits and risks of the procedure.
From the Research
Body Mass Index (BMI) and Surgical Complications
- A BMI of 40 or higher has been associated with an increased risk of complications during anesthesia and surgical procedures 2, 3, 4.
- Studies have shown that patients with a BMI greater than or equal to 40 are at a higher risk for postoperative complications, such as wound infections, renal failure, and prolonged ventilation 2, 3.
- Morbidly obese patients (BMI ≥ 40) are also at a higher risk for postsurgical complications, including thromboembolism, pulmonary, septic, and urinary tract infections 3.
- A BMI of 35 or higher has been identified as a risk factor for morbidity and mortality in patients undergoing bariatric surgery 4.
- Obesity (BMI ≥ 30) has been associated with a higher rate of block failure and acute complications in regional anesthesia in the ambulatory setting 5.
Specific BMI Categories and Risks
- Normal BMI (20-30): serves as a comparison group for studies on obesity and surgical complications 2.
- Overweight (BMI 25-29): may have decreased odds of perioperative mortality, prolonged length of stay, and blood transfusion compared to normal BMI patients 3.
- Obese (BMI 30-40): may have increased length of stay and prolonged ventilation compared to non-obese patients 2.
- Morbidly obese (BMI ≥ 40): at higher risk for postoperative complications, including wound infections, renal failure, and prolonged ventilation 2, 3, 4.