General Anaesthesia Management & Obesity

Obesity brings about a variety of anatomical and physiological changes that pose specific risks during medical procedures.¹ To mitigate these risks, appropriate pre-operative assessment is essential. When considering the patient's cardio-respiratory function, it's worth noting that they may not display any symptoms initially due to limited mobility. However, further assessment may reveal significant dysfunction.¹ Therefore, it is crucial to evaluate for signs and symptoms of respiratory and cardiac failure. The specific exams and investigations conducted should be tailored to the individual patient's comorbidity, as well as the type and urgency of the surgery being performed.¹

Obesity is linked to a 30% greater chance of difficult or failed intubation, highlighting the need for a thorough airway assessment during the pre-operative phase.³ Factors such as mouth opening, Mallampati score, neck extension, and collar size (greater than 17.5 inches) should be noted as they can predict a potentially challenging airway.¹ Once the assessment is complete, a robust airway strategy should be developed and discussed to prevent rapid desaturation and increased morbidity. It is also important to consider sleep-disordered breathing in obese patients and use the STOP-BANG questionnaire to assess it. ³

Effective intra-operative management of patients with obesity requires special attention to anaesthetic considerations, beginning with the necessity for experienced anaesthesiologists and surgical staff.³ According to multiple authors, regional anaesthesia should be taken into account as it can mitigate the dangers of difficult intubation and acid aspiration, while also offering safer and more effective postoperative analgesia.^2,3

 In situations where regional anaesthesia is not feasible due to surgical or patient-related restrictions, administering general anaesthesia requires specific care. Some patients may not tolerate the conventional supine position for induction and intubation of general anaesthesia due to oxygen desaturation, airway obstruction, or respiratory compromise.¹ As such, awake intubation in a sitting position is often better tolerated and should be considered as an alternative.¹

It is advisable to select easily reversible drugs with fast onset and offset for general anaesthesia because the pharmacokinetics of most general anaesthetic drugs are influenced by the amount of adipose tissue present, resulting in a longer and less predictable effect.¹ Drug dosing should be determined based on lean body weight and titrated to achieve the desired effect. Caution must be exercised when using long-acting opioids and sedatives.³ Total Intravenous Anaesthesia (TIVA) using propofol provides several potential benefits compared to volatile anaesthesia for obese patients, such as quick offset of action, clear-headed emergence, lower risk of laryngospasm, reliable clearance of hypnotic agents, reduced incidence of postoperative nausea and vomiting, and sustained anaesthesia during prolonged airway manipulation.⁷ It is recommended to use local anaesthetics as a means of reducing opioid usage.³

Adequate monitoring throughout anaesthesia is crucial. Invasive arterial pressure monitoring has been advocated for all but the most minor procedures in the morbidly obese.⁵ Pulse oximetry, electrocardiography, capnography and monitoring of neuromuscular block are all mandatory.⁵ In addition, the use of a depth of anaesthesia monitor can help guide the anaesthesiologist to administer accurate and individualised drug to obese patients, which helps to avoid awareness or drug overdose.^3,7,8  

Techniques to limit anaesthetic load, particularly when neuromuscular blocking drugs and/or a total intravenous anaesthetic technique should be utilised.³

Use of central venous and pulmonary artery flotation catheters should be considered in patients undergoing extensive surgery or those with serious cardiorespiratory disease.⁵

Obese patients who receive general anaesthesia may experience reduced lung volumes in the postoperative period.¹ To mitigate this risk, extubation should be performed in the sitting position while the patient is fully awake, and they should be transferred to a suitable postoperative environment as soon as possible. ³ Maintaining a head-up position during recovery and monitoring oxygen saturation levels until the patient is able to move independently are also recommended measures.³

Many anaesthetists consider perioperative epidural anaesthesia an important part of a multimodal approach to improving patient outcome and analgesia rather than relying solely on systemic opioid administration for pain management.¹

Appropriate prophylaxis against venous thromboembolism and early mobilisation are recommended taking into consideration the increased incidence of venous thromboembolism in obese patients.³

Managing the risks of obesity and anaesthesia requires trained and experienced professionals, adequate patient assessment, preparedness of environment, careful choice of drugs, and intra and post-operative monitoring until full recovery has been achieved.

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