Is there an increased risk of anesthesia complications in pregnant patients with a Body Mass Index (BMI) over 40?

From the Guidelines

Pregnant patients with a BMI over 40 are at a significantly increased risk of anesthesia complications, and early anesthesia consultation is crucial to mitigate these risks. The increased risks include difficult airways, failed neuraxial anesthesia attempts, altered drug distribution and metabolism, and increased risks of aspiration, hypoxemia, and postoperative respiratory complications 1.

Key Considerations

• Difficult airways due to excess soft tissue, reduced functional residual capacity, and increased oxygen consumption
• Higher rates of failed neuraxial anesthesia attempts, requiring more insertion attempts and increasing the risk of accidental dural puncture
• Altered drug distribution and metabolism, potentially leading to unpredictable responses to anesthetic medications
• Increased risks of aspiration, hypoxemia, and postoperative respiratory complications
• Cardiovascular challenges, including difficult blood pressure monitoring, venous access problems, and increased strain on the heart

Management Recommendations

• Early anesthesia consultation is essential for pregnant patients with a BMI over 40 1
• Consideration for early epidural placement, appropriate equipment preparation including difficult airway tools, and positioning aids
• Dosing adjustments may be necessary for some medications, and extended postoperative monitoring is recommended due to increased risks of respiratory depression and obstructive sleep apnea complications
• Antenatal patient referral to an anaesthesiologist is recommended, particularly for women with BMI greater than 40 kg/m2, to discuss the limitations and risks of anaesthesia during delivery 1

Additional Risks and Considerations

• Obese patients are particularly vulnerable to aorto-caval compression and vascular access may be more difficult, requiring early establishment of vascular access in labour 1
• The provision of general anaesthesia and central neuraxial blockade is associated with increased difficulties, leading to an increased decision-to-delivery interval in women who require a category-1 or -2 caesarean section 1
• Pregnant patients with a BMI over 40 are also at increased risk of venous thromboembolism (VTE) and postpartum haemorrhage, and may require higher doses of anticoagulants and closer monitoring 1

From the Research

Anesthesia Risks for Pregnant Patients with a BMI over 40

• Pregnant patients with a Body Mass Index (BMI) over 40 are considered to be at a higher risk for anesthesia complications due to their increased weight and associated comorbidities 2, 3, 4.
• Studies have shown that morbidly obese parturients (BMI 40-49.9) and super-obese parturients (BMI >50) are at a higher risk for anesthesia-related complications, including difficult intubation, hypotension, and respiratory complications 3, 5, 4.
• A retrospective analysis of 494 patients with a BMI exceeding 40 kg/m2 at delivery found that super-obese patients had significantly greater volumes of ephedrine and norepinephrine consumption, intravenous fluids, and bleeding during surgery, as well as more hypotensive episodes 5.
• Another study found that pregestational BMI ≥ 25 kg/m2 was a risk factor for hypotension after spinal anesthesia in patients undergoing cesarean section, and that obese patients required higher doses of vasopressors 6.

Anesthetic Management for Pregnant Patients with a BMI over 40

• Neuraxial techniques, such as epidural or spinal anesthesia, are preferred for cesarean delivery in obese parturients, but can be technically challenging due to poor anatomical landmarks and increased risk of complications 2, 3.
• General anesthesia may be necessary in some cases, particularly if neuraxial anesthesia is contraindicated or fails 2, 3.
• A thorough preoperative evaluation and multidisciplinary planning are essential to minimize the risks associated with anesthesia in pregnant patients with a BMI over 40 2, 3, 4.
• Close monitoring of ventilation, hemodynamic status, and postoperative care are crucial to prevent complications and ensure a successful outcome 3, 5.