ANAESTHESIA FOR OBESE PATIENTS

DR. THOMASSPECIALIST IN ANAESTHESIA,

AL BUKARIYA GENERAL HOSPITAL,

OBESITY• Obesity is one of the most common nutritional

disorders• Adipose tissue is a normal constituent of the

human body that serves the important function of storing energy as fat for mobilization in response to metabolic demands. Obesity is an excess body fat frequently resulting in a significant impairment of health. The body cannot store proteins &carbohydrates, so excess proteins & carbohydrates are converted to fat in the body. An imbalance between energy intake & expenditure causes obesity

• obesity is defined as a bodyweight 20% or more above the ideal body weight

Body mass index (BMI)

• A measure of obesity is the Body mass index (BMI)

• A BMI of 28 for men and 27 for women correspond to 20% above Ideal body weight

• Body mass index (BMI) = weight in kgs height in meters2• Eg. A man with 150 kg and 1.8 M tall has a

BMI of 47 which is more than 100% above the ideal body weight. A similar patient with weight 80 kg has BMI of 25.

• A BMI higher than 28 is associated with increased morbidity due to stroke, IHD, DM 3-4 times higher than in the general population

Obesity – Incidence

• Saudi Arabia: Among the 15 to 70 year age group the

prevalence of obesity is 20.26%.It is alarmingly high in the infertile Saudi females.

• USA: A BMI >30. 1980….14.5%

1998….22%

300,000 deaths in the US in each year are associated with obesity .

• In the black females older than 45, there is a incidence of 60%

Pathogenesis

Aetiology: A complex multifactorial disease.

»Prevalence increases with age»Genetic factors are present »Environment also has some

influence.»Others are Cushing's syndrome,

hypothyroidism, disorders of hypothalamus, insulinoma

Pathogenesis• The current availability of caloric dense foods &

sedentary life style promote weight gain• If daily energy intake exceeds energy

expenditure by 2 % then the cumulative effect after one year is about 2 to 3 kg increase in body weight

• The dietary composition has only a minor role in the pathogenesis of obesity

• Surplus calories are converted to triglycerides and stored in the adiposities. This storage is regulated by the enzyme lipoprotein lipase. This activity of the enzyme varies in different parts of the body

• A central (abdominal) distribution is common in men and peripheral distribution of fat (hip, buttocks & thighs) common in females

• Abdominal fat deposits are metabolically more active and are thus associated with a higher incidence of metabolic complications like DM, IHD, stroke and CHF

Physiological disturbances

1. Obstructive sleep apnea: (OSA) 5% obese patients develop OSA characterized by frequent episodes of

apnea during sleep; airway obstruction manifesting as snoring & day time somnolence due to interrupted sleep during night

physiological changes of OSA include arterial hypercarbia, polycythemia, SHT, pulmonary hypertension and right ventricular failure

Physiological disturbances 2. Obesity hypoventilation syndrome:

long term consequence of OSA Nocturnal episodes of central apnea

reflects progressive desensitization of respiratory centers for hypercarbia

at its extreme obesity hypoventilation syndrome ends in Pickwickian syndrome

Pickwickian syndrome is characterized by obesity, daytime sleep, arterial hypoxemia, polycythemia, hypercarbia, respiratory acidosis, pulmonary HT& RV failure

Physiological disturbance

3. Respiratory system: restrictive ventilation defect:

due to weight added to thoracic cage & abdominal weight impeding diaphragm motion especially in supine position

results in decrease in FRC, ERV & TLC FRC decrease to the point of closing capacity &

resulting in V/Q mismatch, R – L shunting & arterial hypoxemia

anaesthesia adds to these changes such that a 50% decrease in FRC occurs( normally FRC 20% decreases)

PEEP improves FRC and oxygenation at the expense of cardiac output

decreased FRC impairs the ability of obese pts to tolerate apnea such as during laryngoscopy & intubation

Physiological disturbances• Gas exchange:

– arterial oxygenation may deteriorate markedly on induction of anesthesia & increased FIO2 needed to maintain an acceptable PaO2

– administration of ventilatory depressant drugs and supine position will aggravate the hypoxemia & can lead to CO2

retention

Physiological disturbances

• Lung compliance & resistance:– increasing obesity causes decrease in

compliance & resistance– due to accumulation of fat in & around the

chest wall, & increased pulmonary blood volume

– decrease lung compliance causes decreases in FRC & impaired gas exchange

– these changes leads to rapid shallow breathing & increased work of breathing, mostly during supine position

Physiological disturbances4. Cardiovascular system:

Mild to moderate SHT is present in 50 to 60% Each kg of fat contains 3000 M of blood vesselsCardiac output is increased by 0.1litre/ min for

each Kg weight gain, cardiomegaly & SHT reflect increased CO

Hyperinsulinemia also contribute to SHT by activating sympathetic nervous system

Pulmonary hypertension is common due to chronic arterial hypoxemia & increased pul. blood volume

Obesity is an independent risk factor for IHD – more common in those with central distribution of fat. Other factors like SHT, DM, hypercholestrolemia also contribute to IHD

Physiological disturbances

Cardiovascular system: SHT leads to concentric LVH &

progressively non-compliant LV which when combined with hypervolemia increases the risk of CHF

Fatty infiltration of myocardium is uncommon and is not responsible for CHF

Cardiac arrhythmias may be precipitated by arterial hypoxemia, hypercarbia & IHD

Ventricular dysfunction & hypertrophy increases with the duration of obesity

Physiological disturbances

5. Gastro-intestinal system:Obese patients are at increased risk of aspiration

pneumonia due to increased intra-abdominal pressure, delayed gastric emptying & high incidence of hiatal hernia

Abnormal LFT & fatty liver changes are commonVolatile anesthetic agents are defluorinated to a

greater extent, but no evidence of exaggerated anesthetic induced hepatic dysfunction

Gall bladder & biliary tract disease is increased to 3 folds in obese patients, may be due to abnormal cholesterol metabolism

Physiological disturbances

6. Diabetes mellitus:Glucose tolerance curves are often

abnormal & incidence of DM is increased to several folds in obese patients.

There is resistance of peripheral tissues to the effects of insulin in the presence of increased fat, this results in NIDDM

Physiological disturbances

7. Thrombo-embolic disease:The risk of DVT in obese patients

undergoing surgery is double that of non-obese

This is due to polycythemia, increased intra-abdominal pressure and immobilization leading to venous stasis & increased pressure in deep veins

Pharmacokinetics of drugs• The physiological changes associated with

obesity lead to alteration in drug distribution, binding & elimination of many drugs

• Hepatic clearance of drugs is not altered• Renal clearance of drugs is increased due to

increased RBF & GFR• Drug dosage calculation based on actual

body weight can result in excessive plasma concentration as the fat has a low blood flow

• The calculation of the initial dose should be based on Ideal Body Weight (lean body mass)

• Ideal body weight can be assumed as 100kg for men and 80 kg for females

• Subsequent doses are dependent on the response to the initial dose

Treatment of Obesity

• Purpose is to decrease morbidity & not to meet a cosmetic standard of thinness

• A weight loss of 5 to 20 kg will decrease systemic blood pressure and enhance the control of diabetes mellitus

Treatment of Obesity• Behavioral therapy:

– life style alterations in the form of increased physical activity

– exercise• Medical treatment:

– serotonin inhibitors – acts as appetite suppressants but also produce undesirable side-effects . Ex: Fenfluramine

– sibutaramine – appetite suprresnts- inhibits reuptake of serotonin & nor-epinephrine

– orlistat – is a lipase inhibitor not absorbed from the stomach

• Surgical treatment:– gastroplasty– most common – intestinal

obstruction & electrolytes are common after this operation

– Vertical banded gastroplasty/ gastric bypass done only for severe cases of obesity – BMI > 40

Management of Anaesthesia• Pre-operative evaluation

– History • Duration of obesity, other associated

problems• Previous operations and anaesthesia• Medical treatments.

– Investigations• CBC, Urine examination• LFT, RFT, ECG, ECHO, • ABG, X ray Chest

Anaesthesia• Assessment of Airway

– Difficulties with mask ventilation and tracheal intubation may be present, due to• Fat face, fat cheek• Short neck• Excessive palatal and pharyngeal soft

tissues• Restriction in mouth opening.• Limited cervical and mandibular mobility.• Large breasts.

• Awake tracheal intubation may be considered.

Anaesthesia• Premedication

– Obese patients are at increased risk of pulmonary aspiration, due to increased gastric acidity, gastric fluid volume and intragastric pressure.• H2 receptor antagonists• cimetidine, ranitidine, NPA• Metoclopramide• Ondansetron

– Narcotic premedication may be avoided.– Anxiolytic- midazolam/diazepam/lorazepam

Anaesthesia• Induction of Anaesthesia.

– Pulse oximeter, ECG, NIBP, Capnogram – Venous access.– Preoxygenation for 3 minutes.– In predetermined patients awake intubation– Induction with propofol, thiopentone may be

considered. Dose to be calculated on ideal body weight.

– Cricoid pressure (Sellick’s) /short duration larngoscopy/ endotracheal intubation with cuffed tube

Anaesthesia

• Maintenance– Controlled ventilation using large tidal

volume is the choice.– PEEP may improve oxygenation but the

associated decrease in CO offsets the benefits.

– Prone and head down position can further decrease chest wall compliance and the PaO2

– Desflurane,sevoflurane and Isoflurane are better choices.

Anaesthesia• extubation can be done after full

recovery from the depressant effects of the anesthetics

• head-up position during recovery is ideal

• post operative ventilation is more likely to be required in obese patients who have co-existing CO2 retention, prolonged surgery especially abdominal

Post operative complications• Arterial hypoxemia & hypoventilation

– it occurs after upper abdominal surgeries– semi-sitting position & supplemental O2

can prevent this problem– Wound infection – twice more common

than in non-obese – Deep-vein thrombosis & pul embolism

• early post-op ambulation & heparin prophylaxis can reduce these complications

– Obstructive sleep apnea– Obesity hypoventilation syndrome

Post operative analgesia• Patient controlled analgesia

– doses based on ideal body weight

• Neur-axial opioids– continuous infusion of LA & opioids

• NSAID’s• Local analgesia

– local infiltration– nerve blocks

Bibliography Anesthesia & Co-existing

diseases. Stoelting. 4th edition Harrison’s principles of Internal

medicine 15th edition Saudi journal of disability &

rehabilitation, Vol 8, No 3 Anesthesia. Miller. 5th edition

Safety features in Anaesthesia Machine

Dr. Shailendra.V.L. Specialist in Anaesthesia, Al Bukariya General Hospital Saudi Arabia.

Gas Supply

• Cylinder:– colour– high pressure releasing

safety system

• Pipeline supply:– colour– DISS

Yoke assembly

• pin index• filter• non-return valve• bourden guage

Pressure regulator

• factory, preset valves• master-slave mechanism• oxygen failure warning devices• high pressure relief valve

Flow meter• bobbin• background• lighted• knobs

– colour coded– tough coded– position

• oxygen downstream of all gases

• anti-hypoxic devices– link 28– ORMC

Vaporizer

• select-a-tec• keyed bottle filling• dial lock•

Machine back-bar

• high pressure relief valve• non-return valve•

CO2 absorber & circle system

• non-return valves• soda lime indicator• baffles in the canister• water trap• corrugated tubes• •