16. Bariatric Surgery Flashcards
A 45-year-old woman presents at your pre-operative assessment clinic.
She has been listed for bariatric surgery. Her weight is 150 kg and her
height 168 cm.
Classify obesity
The commonest way to classify obesity is using the Body Mass Index (BMI). This
is the weight in kg divided by the square of the patient’s height in metres. This
was recommended by the US National Institutes of Health in 1998 and has
been widely adopted by many medical organisations.
Classification BMI (kg/m2)
Healthy weight 18.5−24.9
Overweight 25−29.9
Obesity I 30−34.9
Obesity II 35−39.9
Obesity III 40 or more
How does waist circumference factor into the classification of obesity?
Body fat distribution provides additional risk that is not given simply by the
BMI. Two practical methods to localise body fat distribution that have a great
degree of epidemiological correlates are:
The waist circumference is a convenient and simple measurement that
correlates well with BMI and with risk factors for cardiovascular disease.
It is measured in centimetres at the midpoint between the lower border of the
rib cage and the upper border of the pelvis.
A waist circumference of >102 cm (∼40 inches) in men and >88 cm (∼35 inches) in women
is consistent with abdominal obesity and
puts patients at increased risk for metabolic complications.
The waist to hip ratio (WHR).
A WHR of >1.0 in men and >0.85 in women correlates with abdominal fat accumulation.
Waist circumference
For men, a waist circumference of less than 94 cm is low, 94–102 cm is
high and more than 102 cm is very high.
For women, a waist circumference of less than 80 cm is low, 80–88 cm is
high and more than 88 cm is very high.
What drug management is available for treating obesity?
- Orlistat
- Sibutramine
- Rimonabant
Orlistat
Orlistat should be prescribed only as part of an overall plan for managing
obesity in adults who meet one of the following criteria:
BMI of 28.0 kg/m2 or more with associated risk factors.
BMI of 30.0 kg/m2 or more.
Orlistat is the saturated derivative of lipstatin which is a potent natural
inhibitor of pancreatic lipase.
Orlistat is derived from Streptomyces
toxytricini. It reduces weight by around 9% on average and decreases
progression to diabetes in high-risk patients. Adverse gastrointestinal
effects are common and there may be a link to aggravation of existing
hypertension.
Sibutramine
Sibutramine, a monoamine-reuptake inhibitor,
inhibits the reuptake of norepinephrine, serotonin and dopamine,
causing anorexia.
It should be prescribed only as part of an overall plan for managing obesity in adults who
meet one of the following criteria:
BMI of 27.0 kg/m2 or more and other obesity-related risk factors such as
type 2 diabetes or dyslipidaemia.
BMI of 30.0 kg/m2 or more.
Side effects include: dry mouth, insomnia,
anorexia and a stimulatory effect on heart rate and blood pressure.
Rimonabant
Selective cannabinoid type1 (CB1) endocannabinoid receptor antagonist.
Blocking endogenous cannabinoid binding to neuronal CB1 receptors,
may aid appetite control and weight reduction.
Licensed for use as an adjunct to diet and exercise for the treatment of:
Obese patients (BMI ≥ 30 kg/m2)
Overweight patients (BMI > 27 kg/m2) with associated
risk factor(s) such as type 2 diabetes or dyslipidaemia.
NB: The European Medicines Agency has since recommended the
suspension of marketing of rimonabant due to its psychological side
effects.
What are the indications for bariatric surgery?
Bariatric surgery is recommended as a treatment option for adults with obesity
if all of the following criteria are fulfilled (as per NICE Guidelines):
BMI ≥ 40 kg/m2 or
Between 35 kg/m2 and 40 kg/m2 with other significant disease (for example,
type II diabetes or high blood pressure) that could be improved if they lost
weight.
All appropriate non-surgical measures have been tried but have failed to
achieve or maintain adequate, clinically beneficial weight loss for at least
6 months.
The patient has been receiving or will receive intensive management in a
specialist obesity service.
The patient is generally fit for anaesthesia and surgery.
The patient commits to the need for long-term follow-up.
First-line option (instead of lifestyle interventions or drug treatment) for
adults with a BMI of more than 50 kg/m2 for whom surgical intervention is
considered appropriate.
Surgical approaches
- Malabsorptive
Jejuno-ileal bypass
Biliopancreatic bypass - Restrictive
Vertical banded gastroplasty
Gastric banding
Roux-en-Y gastric bypass
What are the anaesthetic considerations in bariatric surgery?
Pre-operative evaluation – with particular focus on issues pertinent to the
obese patient.
These include:
1. Airway evaluation and preparation for a potentially difficult intubation.
- Cardiovascular status:
Systemic hypertension
Pulmonary hypertension
Cardiac failure
Ischaemic heart disease - Investigations:
ECG, CXR, echocardiography
(tricuspid regurgitation may indicate pulmonary hypertension). - Baseline ABG
(will guide post-operative respiratory management
in terms of assessing carbon dioxide retention and parameters for weaning). - Antibiotic prophylaxis –
laparoscopic bariatric surgery has an infection rate of 3%–11% - DVT prophylaxis – morbid obesity is an independent risk factor for sudden
post-operative death due to PE. - Prophylaxis against aspiration pneumonitis
What are the important intra-operative factors?
- Positioning
Specialised table to accommodate the patient
Protection of pressure areas –
ulnar neuropathy, brachial plexus and sciatic nerve palsies have been described.
- Respiratory changes
Decrease in vital capacity and ventilation perfusion mismatch.
Potential complications include mediastinal emphysema,
pneumothorax and gas embolism.
- Cardiovascular changes
An increase in systemic vascular resistance as a result of an increase in
intra-abdominal pressure (IAP).
Compression of the inferior vena cava by increased IAP will decrease venous
return.
Renal blood flow and GFR are decreased by an increase in IAP.
Invasive arterial monitoring may be required due to difficulties with correct
NIBP cuff sizes.
What post-operative analgesia would you recommend?
Multimodal analgesia
Local anaesthetic should be infiltrated into the port sites at the end of surgery.
Regular simple analgesics, e.g. paracetamol, codeine or dihydrocodeine, tramadol.
PCA morphine if required.
Post-operative opioids via PCA have not been found to cause morbidity in
terms of cardiorespiratory compromise in these patients and provide
adequate analgesia.
Caution is advised with regards to the use of NSAIDs because of the concern
about gastric ulcers following bariatric surgery
Key recommendations from AAGBI ‘Glossy’
All trained anaesthetists should be competent in the management of
morbidly obese patients and familiar with equipment and local protocols.
All patients should have height, weight and BMI recorded.
Every hospital – named consultant anaesthetist and a named theatre
team member to ensure appropriate equipment and processes.
Protocols including details of availability of equipment should be readily
to hand in all locations where morbidly obese patients may be treated.
Mandatory manual handling courses should include the management of the morbidly obese.
Pre-op assessment is a key component of management.
Early communication between staff is essential and scheduling of
surgery should include provision for sufficient additional time, resources and personnel.
Absolute BMI should not be used as the sole indicator of suitability for surgery.
