FRCA Notes

Bariatric Surgery

This topic features in the curriculum as 'Recalls/describes the anaesthetic implications of bariatric surgery'.

Resources

  • Obesity is initially treated with lifestyle modification, including education, dietary change and exercise
  • If that fails then medical management, as part of specialist-led weight management programmes, can be used as an adjunct in those with BMI >30kg/m2
    • E.g. orlistat (lipase inhibitor) or liraglutide (GLP-1 receptor agonist)
  • If that too fails, surgery may be indicated
  • Referral for NHS-funded bariatric surgery follows assessment by a specialist weight management surgery
  • It is an option if the patient fulfils all the following criteria:
    1. BMI
      • >40kg/m2
      • 35 - 40kg/m2 + other significant diseases e.g. HTN, T2DM
      • 30 - 35kg/m2 or Asian family origin + recent onset T2DM
    2. All appropriate non-surgical measures have failed to achieve or maintain clinically beneficial weight loss
    3. Patient will receive intensive management in a Tier 3 service
    4. Generally fit for anaesthesia and surgery
    5. Commits to need for long-term follow-up

  • Can be classified as either:
    • Restrictive e.g. gastric banding, intra-gastric balloon
    • Malabsorptive e.g. sleeve gastrectomy, Roux-en-Y bypass or biliopancreatic diversion with duodenal switch

Gastric banding

  • Adjustable gastric band placed around proximal stomach via a laparoscopic approach
  • A subcutaneous injection port is placed over the xiphisternum to allow alteration of the size of the restriction
  • The aim is to induce early satiety by reducing gastric volume
  • It is generally not a painful procedure, although the band can slip and cause pain

Intra-gastric balloon

  • Endoscopically placed inflatable silicon balloon to reduce gastric volume and cause early satiety

Sleeve gastrectomy

  • Laparoscopic, permanent reduction in stomach volume by approximately 80%
  • A 34Fr bougie/OGT is placed per-orally and placed against the lesser curvature of the stomach
  • It is used as a guide to staple the stomach into a banana shape

  • It provides effective weight loss similar to Roux-en-Y bypass, but is simpler and with lower morbidity & mortality rates
  • The most serious complication is a gastric leak, which typically occurs at the GOJ

Roux-en-Y gastric bypass

  • Complex laparoscopic procedure involving:
    • A 'Roux' loop of small bowel anastomosed to a small stomach pouch, which bypasses the distal stomach, duodenum and jejunum
    • A bilio-pancreatic limb, end-to-side small bowel anastomosed to deliver digestive fluid to the bowel
  • The most painful of the bariatric procedures
  • Various post-operative risks including:
    • Anastamotic leak
    • Vitamin- and mineral-deficiencies
    • Weight (re)gain

Biliopancreatic diversion with duodenal switch (BPD/DS)

  • A small tubular stomach pouch with intact pylorus is created and plumbed into the ileum to create a 'digestive loop'
  • A separate 'biliopancreatic loop' is created from the duodenum and jejunum and anastamosed to the digestive loop distally
  • This rearranges the small intestine to separate the flow of food from the flow of bile and pancreatic juices, creating relative malabsortion and fewer calories absorbed
  • Typically a two-stage procedure
  • Associated with:
    • Less risk of GI ulceration
    • Less hunger
    • More normal eating as the gastric pouch is bigger than in other malabsorptive procedures
    • Lower risk of 'dumping syndrome'
    • Rapid weight loss which may be better sustained than in other surgeries

Perioperative management of the patient undergoing bariatric surgery


  • Patients should be managed by an MDT including bariatric-experienced staff, ideally in a bariatric centre
  • Median age is 43yrs, with a median BMI of 44kg/m2 and an overall female preponderance of 77%

History and examination

  • Pre-operative assessment should evaluate common coalescing diseases:
  • Bariatric surgery is an elective procedure and these comorbidities should be optimised prior to surgery

  • Thorough airway assessment as higher incidence of difficult intubation

Investigations

  • Bloods inc. FBC, U&E, LFT, coagulation, group and save
  • ECG
  • Consider TTE if history indicative of cardiac dysfunction or prior ischaemic heart disease
  • ± CPET

Risk assessment

  • Risk prediction can be facilitated with the Obesity Surgery Mortality Risk Score (OS-MRS)
  • It is only validated in bariatric surgery but may be used in non-bariatric surgery

  • The score can be used to plan the need for postoperative care
    • A score of 4-5 indicates a high-risk patient and should prompt consideration of post-operative admission to critical care
Risk Factor Score
BMI >50kg/m2 1
Male gender 1
Hypertension 1
Age >45yrs 1
Any risk factor for PE:
OSA/OHS
Previous VTE
Right heart failure
Pulmonary hypertension
IVC filter inserted per-operatively		 Max 1

Liver diet

  • Patients undergo a pre-operative weight loss regimen for 2 - 4 weeks before surgery
  • Regimen involves 800kcal/day
  • Reduces liver volume by 16 - 20%, improving surgical access
  • Reduces post-operative complications

General equipment

  • Suitable gowns and theatre-wear of appropriate size
  • Appropriate transfer equipment should be available:
    • Patient should maintain their own mobility as much as possible
    • Equipment such as chairs, trolleys and beds should be safe to use at patient’s weight
    • May require use of hover mattresses or similar devices
    • Adequate staff members present to facilitate safe transfer

  • Oxford HELP pillow or other mode of ramping
  • Large IPC's or TEDS (10x increased risk DVT)
  • Sufficient staff to move the patient
  • Once on the operating table require:
    • Extra-wide extensions or arm gutters
    • Gel pads to protect pressure points

Anaesthetic equipment

  • Large NIBP cuff
    • May need to use forearm for NIBP monitoring
    • Do not routinely require intra-arterial BP monitoring
  • Predict difficult intubation therefore VL and associated difficult airway kit
  • Ultrasound machine in case of difficult vascular access
  • Long spinal/epidural and regional needles
  • Ventilator capable of delivering suitable driving pressure and PEEP
  • Neuromuscular monitoring as higher potential for incomplete reversal of NMBA

Induction and airway

  • Obesity is associated with a higher risk of developing airway problems under anaesthesia, with NAP4 revealing:
    • 2x rate of adverse events (esp. with SAD)
    • Higher failure of rescue techniques

  • Routine airway assessment should be performed, with particular emphasis on identifying:
    • Mallampati III (predicts difficult facemask ventilation and intubation)
    • Neck circumference >42 cm (one of the best predictors of difficult intubation)
    • BMI >50 kg/m2 (independent predictor of both difficult intubation and facemask ventilation)
    • The presence of a beard
    • Symptoms of gastro-oesophageal reflux disease

  • Induction should take place in theatre to mitigate unnecessary transfer risk and allow greater space and access to assistance
  • Should be ramped or sat upright; maintains FRC, reduces dyspnoea and facilitates BVM/laryngoscopy

  • Need appropriate equipment to facilitate intubation, including video laryngoscopy and adjuncts
    • Routine fibreoptic intubation is not recommended
    • An airway plan should be vocalised and DAS guidelines followed
    • FONA may be more difficult with a higher risk of complications
      • May be appropriate in high risk cases to identify the depth of the cricothyroid membrane, vascular tissue, and mark relevant landmarks to improve the chance of success

  • Obesity is associated with an increased incidence of known risk factors for aspiration
    • However, obesity alone does not increase risk of reflux and pulmonary aspiration
    • In the absence of other risk factors, routine performance of RSI is not required

  • There is a higher risk of hypercapnoea and hypoxia, as increased body tissue mass and work of breathing leads to greater oxygen consumption and CO2 production
  • FRC is reduced to closing capacity and causes atelectasis and hypoxia, due to:
    • Excess adipose tissue reduces chest wall compliance
    • Lying supine
    • General anaesthesia
    • Pneumoperitoneum

Maintenance

  • NAP5 revealed an increased incidence of awareness in obese patients shortly after induction of anaesthesia, attributable to the rapid redistribution of IV agents
  • In order to reduce occurrence, should ensure:
    • Adequate dosing of IV agent
    • Prompt delivery of maintenance anaesthetic agent
    • Further bolus(es) of anaesthetic agent before airway manipulation or protracted airway manoeuvres
    • Consider using processed EEG-based depth of anaesthesia monitoring to reduce risk of awareness

  • TIVA with propofol offers a number of potential advantages over volatile anaesthesia for the obese patient:
    • Rapid offset of action
    • ‘Clear-headed’ emergence
    • Reduced incidence of laryngospasm
    • Reliable clearance of hypnotic agents
    • Reduced PONV
    • Maintained anaesthesia during protracted airway manipulation
  • Need to be mindful of the idiosyncrasies of the chosen pharmacokinetic model as obese patients were often excluded from the initial development

  • Using volatile agents with a rapid offset of action (low blood:gas partition coefficient) e.g. desflurane/sevoflurane should:
    • Limit adipose absorption
    • Reduce risk of re-sedation at emergence

Ventilation

  • Obesity is an independent risk factor for developing postoperative pulmonary complications
  • Current recommendations for ventilation include:
    • Lung protective volumes (6 - 8ml/kg)
    • Plateau pressure <30cmH2O
    • PEEP titrated to respiratory and cardiovascular state, typically 8 - 10cmH2O
  • Use of recruitment manoeuvres where there is suspicious of atelectasis/collapse
  • Minimising the effect of positioning on ventilation is important although often supine or reverse Trendelenburg which is less of an issue

Reversal and emergence

  • The hazards of airway/respiratory problems during emergency are greater in the obese population
  • To mitigate this, ensure:
    • Ventilate with 100% FiO2 until PEO2 >0.9
    • Patient is sat upright
    • Full reversal of NMBA with appropriate doses of sugammadex or neostigmine
    • Only extubate once fully awake

Analgesia

  • Multi-modal opioid-sparing analgesia is ideal to reduce risk of PONV and negative opioid-associated effects in this cohort
  • This includes:
    • Regular simple analgesia such as paracetamol ± NSAIDs if not contraindicted
    • Local anaesthetic wound infiltration ± infusion catheters e.g. rectus sheath/li>
    • Adjuncts such as magnesium, ketamine, clonidine
    • Opioids e.g. morphine IV or as a PCA post-operatively
  • IV lidocaine 1.5mkg/kg did not provide additional analgesic benefit over-and-above a morphine PCA (BJA, 2023)

Other elements of intra-operative care

  • For malabsorptive procedures it is common to check the integrity of staple lines/anastamosis
    • OG tube is advanced through the surgical anastomosis to prevent backwall suturing of anastomosis
    • Surgical and anaesthetic communication & coordination is important to guide the OGT through the anastomosis
    • Methylene blue 60mL is injected via the OGT at the end of the case to pressurize the proximal pouch and look for leaks

  • Ensure meticulous pressure care; prolonged pressure can cause ischaemia and rhabdomyolysis (classically gluteal ischaemia)
  • Appropriate intra-operative VTE prophylaxis e.g. intermittent pneumatic compression devices
  • Temperature control
  • Glucose management if patient is diabetic

PONV

  • Patients are typically high risk of PONV, by virtue of being mostly female, <50yrs old, undergoing laparoscopic surgery and often needing opioids
  • Multi-modal anti-emesis and reducing opioid use is effective e.g. two intra-operative agents with resuce medication in recovery

Anastomotic leaks

  • A rare (0.8 - 1.5%) complication although serious, increasing both morbidity (to 61%) and mortality (to 15%)
  • Higher risk in those:
    • With a BMI >50kg/m2
    • With metabolic syndrome
    • Undergoing revision surgery

  • Presents 24 - 72hrs post-operatively, typically with a persistent tachycardia ± abdominal pain, fever or outright sepsis

Venous thromboembolism

  • High risk VTE so mechanical compression devices + actual BW dosing of LMWH is required

Bleeding

  • Relatively common (up to 4%), causing melaena, haematemesis and reduced post-operative haemoglobin concentration
  • Supportive management is usually all that's required, and hypovolaemia is rare
  • Typical sites are either the staple line (sleeve gastrectomy) or anastomosis sites (gastric bypass)

Other risks

  • Higher risk of pulmonary complications from being obese

  • Nutritional deficiency is common, and dietetic-involved protocol-driven meal plans are recommended