Anaesthesia for Bariatric Surgery

This is not intended to restrict clinical freedom but to give guidance from educational reviews to produce the best possible outcome for the patient.

An overview of the process

The first is respiratory. Functional residual capacity is reduced, desaturation is rapid, difficult mask ventilation is more common, and obstructive sleep apnoea is frequent. Every element of the induction sequence exists to buy time.

The second is drug dosing. Total body weight overdoses and ideal body weight underdoses; the correct scalar differs by drug.

Pre-op assessment

Screen for obstructive sleep apnoea and obesity hypoventilation syndrome. The thresholds below follow the SOBA single sheet guideline. Red flags are poor functional capacity, an abnormal ECG, uncontrolled hypertension, cardiac failure or ischaemic heart disease, SpO₂ below 94% on air, previous venous thromboembolism, STOP-BANG 5 or more, OS-MRS above 3, metabolic syndrome and a high NSQIP risk score.
A bicarbonate above 27 mmol/L suggests obesity hypoventilation syndrome. It is the cheapest available screening test.
Where red flags are present, consider preoperative CPAP, blood gases or sleep studies, cardiorespiratory referral, an experienced anaesthetist and booking an HDU bed.
Central obesity, defined as a waist greater than half the height, predicts difficult airway and ventilation, greater cardiovascular and thrombotic risk, and metabolic syndrome. Peripheral obesity carries lower risk.
Record the STOP-BANG score, CPAP use, previous anaesthetics and functional capacity.
Smoking cessation at least 4 weeks before surgery. Where there is alcohol misuse, abstinence should be maintained, and the risk of relapse after bariatric surgery acknowledged.
Preoperative weight loss with a low or very low calorie diet is recommended. Patients taking glucose-lowering drugs should monitor treatment effects and be aware of the risk of hypoglycaemia.
Fasting 6 hours for solids and 2 hours for clear fluids, in the absence of gastroparesis or bowel obstruction. Patients with diabetes follow the same recommendations.
Dexamethasone intravenously, for PONV and the inflammatory response.
Statins may be safely continued. Beta blockade may be safely continued in patients at high cardiovascular risk.
Consent covers general anaesthesia, the airway plan, postoperative monitoring and opioid-sparing analgesia.

Equipment

A suitable bed, trolley and operating table. Gel padding, wide strapping and table extensions or arm boards.
A forearm cuff or large blood pressure cuff.
Equipment for ramping, and a step for the anaesthetist.
Difficult airway equipment including a videolaryngoscope.
A ventilator capable of PEEP and pressure modes.
A hover mattress or equivalent, and sufficient staff to move the patient.
Long spinal, regional and vascular needles, and ultrasound.
Appropriately sized calf compression devices.
Depth of anaesthesia monitoring and neuromuscular monitoring.

Induction and airway management

Let the patient position themselves on the operating table.
Pre-oxygenate and intubate in the ramped or sitting position, with the tragus level with the sternum. This reduces the risk of difficult laryngoscopy and improves ventilation and pre-oxygenation.
Consider CPAP and high-flow nasal oxygen during pre-oxygenation.
Minimise the interval between induction and ventilation, and commence maintenance promptly.
Tracheal intubation is the main technique for intraoperative airway management. Use caution with a supraglottic airway where BMI exceeds 40 kg/m².
Avoid spontaneous ventilation; use PEEP.
Consider an antacid premedication.

Drug dosing

Lean body weight — propofol induction, thiopentone, fentanyl and alfentanil, morphine, and non-depolarising neuromuscular blocking drugs. Maximum 100 kg in males and 70 kg in females.
Adjusted body weight — ideal body weight plus 40% of the excess.
Total body weight — as set out on the SOBA single-sheet guideline, which should be available in the anaesthetic room.

Anaesthetic technique and ventilation

No specific anaesthetic agent or technique can be recommended. Short-acting inhalational agents or TIVA are both used.
using a multimodal approach including local anaesthetics should be used.
Regional techniques should be used where possible to reduce opioid requirement. Thoracic epidural should be considered for laparotomy.
Depth of anaesthesia monitoring should be considered where end-tidal agent monitoring is not used, which includes TIVA.
Lung protective ventilation for all patients, avoiding high PEEP values. Avoid increases in driving pressure resulting from adjustments to PEEP.
Pressure-controlled or volume-controlled ventilation may be used.
Reverse Trendelenburg, flexed hips or beach chair positioning improves pulmonary mechanics and gas exchange, particularly with pneumoperitoneum.
Deep neuromuscular blockade improves surgical conditions. Confirm full reversal with objective monitoring.
Nasogastric tubes and abdominal drains are not to be used routinely.
Careful glucose control.

Emergence and recovery

Ensure full reversal of neuromuscular blockade. Extubate and recover the patient sitting up.
Patients without obstructive sleep apnoea, or with uncomplicated obstructive sleep apnoea, should receive prophylactic oxygen in a head-elevated or semi-sitting position, and may be safely monitored on a surgical ward after the initial recovery stay. Maintain a low threshold for non-invasive positive pressure ventilation where there are signs of respiratory distress.
Patients on home CPAP should use their own equipment in the immediate postoperative period. Allow additional time in recovery until free of apnoeas without stimulation.
Patients with obesity hypoventilation syndrome are at higher risk of respiratory adverse events. Consider non-invasive ventilation liberally, particularly where there is hypoxaemia.
Where a patient is untreated, intolerant of CPAP or ineffectively treated, avoid intravenous opioids. Where they are necessary, provide continuous SpO₂ monitoring and consider level 2 care.
Recovery discharge requires the usual criteria to be met, SpO₂ maintained at preoperative levels with minimal oxygen therapy, and no evidence of hypoventilation.

Post-operative care

Multimodal analgesia. Use caution with long-acting opioids and sedatives.
NSAIDs. They may be used where renal function is adequate, the patient is euvolaemic and there is no specific contraindication.
Early mobilisation and a robust thromboprophylaxis regimen. Thromboprophylaxis should combine mechanical and pharmacological measures, with doses and duration individualised.
A clear liquid regimen can usually begin several hours after surgery. All patients require comprehensive dietetic assessment.
Be aware of the risk of thiamine deficiency, particularly in the early postoperative period.
Lifelong vitamin and mineral supplementation with biochemical monitoring is required.
Proton pump inhibitor prophylaxis for at least 30 days after Roux-en-Y gastric bypass. It may be considered after sleeve gastrectomy given the high rate of reflux.
Sustained tachycardia is the most important early sign of a staple line leak and is often the only one. A heart rate persistently above 120 should be treated as a leak until disproven. Fever, abdominal or shoulder-tip pain and anxiety may accompany it.
Rhabdomyolysis may follow a prolonged operation with pressure on dependent tissue. Consider it where there is buttock or back pain with dark urine.
Other complications to anticipate are respiratory failure and hypoventilation, venous thromboembolism and staple line bleeding.

References

Stenberg E, Dos Reis Falcão LF, O'Kane M, et al. Guidelines for Perioperative Care in Bariatric Surgery: Enhanced Recovery After Surgery (ERAS) Society Recommendations: A 2021 Update. World Journal of Surgery, 2022.
Society for Obesity and Bariatric Anaesthesia. Anaesthesia for the Obese Patient — single sheet guideline, 2020.
Members of the Working Party, Nightingale CE, Margarson MP, et al. Peri-operative management of the obese surgical patient 2015. Association of Anaesthetists of Great Britain and Ireland and Society for Obesity and Bariatric Anaesthesia. Anaesthesia, 2015.
Centre for Perioperative Care. Guideline for Perioperative Care for People with Diabetes Mellitus Undergoing Elective and Emergency Surgery, 2021, updated 2023.