Low body mass index and anesthetic-surgical risks

The Non-Hospital Medical and Surgical Facilities Accreditation Program Patient Safety Incident Review Panel recently reviewed two incidents involving underweight patients.

While elevated body mass index (BMI) is now well known to increase surgical and anesthetic risks such as surgical site infection and difficult intubation, patients with low BMI (<20.5) may not be appreciated as having increased perioperative risk. 

The BMI-surgical risk curve is U-shaped, and recent studies have shown increased 30-day mortality and malnutrition with those who have low BMI. Intraoperative hypothermia is also more difficult to manage in those with low BMI. The conditions associated with low BMI include old age, cancer, malnutrition, and eating disorders. These comorbidities are also associated with additional anesthetic considerations including hypoglycemia, hypoalbuminemia, intraoperative hypothermia, and possible sensitivity to neuromuscular blocking drugs due to low muscle mass. 

Patients with low BMI scheduled for surgery should be seen in anesthetic consultation prior to the day of surgery to ensure appropriate work-up and assessment is completed and to confirm the patient is appropriate for surgery in the non-hospital setting.

The following information and recommendations are being shared with all facilities in the spirit of learning and improving patient safety. Medical directors are encouraged to discuss these articles with their clinical teams. 

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