OBESITY & ANAESTHESIA 

Speaker: Dr. RAJESH CHOUDHURI Moderator: Dr. A. Chakrabarty, Asst. Proff

DEPARTMENT OF ANAESTHESIOLOGY AGMC & GBP HOSPITAL, AGARTALA

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The heaviest person in medical history was Jon Brower

Minnoch (USA 1941–

83)635 kg

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Obesity: Definition•A condition in which excess body fat may put a person at health risk. (laymen)•A chronic metabolic disorder that is primarily induced and sustained by an over consumption or underutilization of caloric substrate (Medical)•The American Heart Association (AHA) defines obesity as body weight 30 percent greater than the ideal body weight (Precise)

EPIDEMIOLOGY• 23 % are obese of world population.• 5% are morbidly obese.• Mortality is 2.96 times higher in obese.• Obesity is a global health problem &

prevalence varies with socio economic status.

• In affluent countries like U.S the poor have the highest prevalence.

• In developing countries it is the affluent that are at the highest risk.

• Recently there is increase in incidence of childhood & adolescent obesity & importantly these children remain obese as adults.

Equations• Ideal body weight in Kg (IBW)• (Broca’s Index)

– Height in centimeters - 100 for men– Height in centimeters - 105 for women – -----------------------------------------------------

• Body mass index (BMI)– weight in Kg / Height (m) 2

WHO CLASSIFICATION OF OBESITY

BMI STATUS< 18.5 underweight

18.5–24.9 normal weight25.0–29.9 overweight30.0–34.9 class I obesity(Obese)35.0–39.9 class II obesity (Morbidly obese)

≥ 40.0 class III obesity(Super morbidly obese)

DISEASES LINKED TO OBESITY

DISEASES LINKED TO OBESITY• Hypertension is about 6 times more frequent in obese subjects than in lean men and women • A 10-kg higher body weight is associated with a 3.0-mm Hg higher systolic and a 2.3-mm Hg higher diastolic blood pressure. These increases translate into an estimated 12% increased risk for CHD and 24% increased risk for stroke .• Diabetes Mellitus Type 2 prevalence is 2.9 times higher in the obese than in non-obese for those 20-75 years of age.• Morbidity due to Cardio-vascular diseases has been reported to be almost 90 % in those with severe obesity.• Psychological Complications of Obesity: Emotional distress,

Discrimination, Social stigmatization, Anxiety, fear, hostility and insecurity .

Respiratory Pathophysiology in Obesity• Obesity increases the work of breathing.• Excess metabolically active adipose tissue plus workload on

supportive respiratory muscle : CO2 production(Hypercarbia) O2 consumption(Hypoxia)• There is restrictive lung disease because :Decreased chest wall

compliance :Diaphragm pushed cephalad :Decreased lung volume :Supine and trendelenberg position FRC, ERV & TLC and FEV1.

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

Respiratory Pathophysiology in ObesityOBSTRSUCTIVE SLEEP APNEA SYNDROME:• Frequent episodes of apnea or hypopnea during sleep. Total

cessation of airflow for = 10 sec. 5 or more episode per hr. or 30 per night are counted as clinically significant.

Symptoms: Daytime sleepiness or fatigue , dry mouth or sore throat upon awakening , headaches in the morning , trouble concentrating, forgetfulness, depression, or irritability , night sweats, restlessness during sleep , sexual dysfunction , snoring , sudden awakenings with a sensation of gasping or choking , difficulty getting up in the mornings.• Perioperative complications of OSAS: Hypertention ,

hypoxia ,myocardial infarction , arrhythmias , pulmonary edema ,stroke,difficult intubation—induction , upper airway obstruction—recovery.• Diagnosis :confirmed with a polysomnographic study.

Respiratory Pathophysiology in ObesityObesity 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.

Asthma: asthmatic symptoms ( wheezing, dyspnoea, reduced exercise capacity) are reported by around 25% in obese population.( 5% in general population ) brochodilator reversibility may not be found.

Respiratory system changes & OSA :Implications for anaesthesia

• As oxygen reserve is reduced, they desaturate rapidly when apneic therefore should be well pre oxygenated before intubation.• Higher inflation pressure needed because of decreased chest wall

compliance• Application of PEEP to improve oxygenation• Patient should be trained with CPAP or BIPAP machine preoperatively• PFT should be done to anticipate need for post operative ventilation• Avoid sedative premedication• Since these patients are hypoxemic and hypercapnic ABG should be

done preoperatively.• All respiratory and sleep-related comorbidities should be identified,

investigated,and treated.

CARDIOVASCULAR MANIFETATIONS• O2 demand and delivery: O2 demand increases in proportion to the increase in

fat free mass( FFM); FFM increases with TBW , but with a decreasing curve gradient.

• Blood volume: TBW ratio- decreases from around 70 ml/ Kg to 40 ml/ Kg at a BMI of 70 Kg/ sqm.

• Cardiac output: increases with BMI. ( linear in relation to body surface area and fat free mass gain) . Fat perfusion decreases as BMI increases. Stroke volume increases , but HR usually unchanged.

• LVH and dilatation: Due to arterial Htn. and increases cardiac workload. Reduced ventricular wall compliance and diastolic dysfunction.

• Electrophysiology: AF is the commonest arrhythmia, prevalence increases with BMI. LAD ( physical displacement of the heart and rotation). Conduction anomalies-PR and QRS prolongation, fascicle block / BBB( beningn). QTc prolongation.

• Pulmonary Htn. and cor pulmonalae: associated with sleep disordered breathing.

Cardiovascular manifetations• Increased incidence of arterial disease: associated with

both primary obesity and its comorbid diseases( hyperlipidaemia, DM etc).

50% increased risk for CAD in overweight than normal . > 2.5 times increased incidence of CAD in severely obesed.

• Inc risk of DVT• Inc. intra-abdominal pressure• Polycythemia• Inc. pressure in deep veins• Immobilization-venous stasis

GI changes & its implications• Increased abdominal pressure Increased gastro

esophageal reflux Hiatal hernia may be associated.• After 8 hours of fast 85%-90% morbidly obese patients have

gastric volume greater than 25 ml and gastric ph less than 2.5 .Hence Metaclopromide,Rantidine should be given.• Increased risk of aspiration• Diabetics are at risk for gastroparesis.• Need a rapid sequence intubation technique after adequate

pre-oxygenation.• Fatty infiltration of liver , abnormal liver function.

Volatile anaesthetics defluorinated to greater extent-halothane hepatitis. Abnormal cholesterol metabolism.

Metabolic Syndrome Criteria Defining Value

Abdominal obesity Waist circumference >102 cm in men and >88 cm in women

Triglycerides ≥150 mg/dL

High-density lipoprotein cholesterol

<40 mg/dL in men and <50 mg/dL in women

Blood pressure ≥130/85 mm Hg

Fasting glucose ≥110 mg/dL

*Three of five criteria must be met.

Pharmacological concernsFactors affecting the pharmacokinetic and

pharmacodynamic properties of Drugs in obesity

KINETIC PROPERTY EFFECT OF INCREASING OBESITY

Blood volume and cardiac output Increased

Adipose and lean body mass Increased

Hepatic blood flow and glucuronidation rate

Increased

GFR and renal excretion Increased

Cytochrome P450 isoenzymes Variable

Renal tubular reabsorbtion decreased

Pharmacological concernsOBESITY & DRUGS DOSES

LIPID SOLUBLE WATER SOLUBLE

Inc. vol of distribution Limited vol of distribution

Larger loading doses to produce same plasma concentration but maintenance doses less frequent-slow clearance

Doses not influenced by fat stores

Doses based on actual body wt.

Doses based on ideal body wt. – to avoid overdosing

Pharmacological concerns• Commonly used anesthetic drugs can be dosed according to

total-body weight (TBW) or IBW based on lipid solubility. • Lean body mass ---for dosing hydrophilic medications. As

expected, the volume of distribution is changed in obese patients with regard to lipophilic drugs. Consequently, dosing of commonly used anesthetic drugs such as propofol, vecuronium, rocuronium, and remifentanil is based on IBW. In contrast, thiopental, midazolam, succinylcholine, atracurium, cisatracurium, fentanyl, and sufentanil should be dosed on the basis of TBW.

Maintenance doses of propofol should be based on TBW. Conversely, based on real body weight, smaller amounts of propofol are needed to anesthetize the patient.• Halogenated anaesthetics: Morbidly obese pt. Metabolize

halothane and enflurane more resulting in high serum and urine level or fluoride.

Anaesthetic considerations: preoperative• HISTORY: Duration of obesity & associated problems.

Previous operation & anaesthesia. Medication

• INVESTIGATIONS: Blood ,Urine ,LFTs,RFTs,ECG,X-Ray chest,Echocardiography,ABGs.

• RISK FOR ASPIRATION PNEUMONIA: Premedication: Anticholinergic agent, H2-antagonist,Metoclopramide,Sodium citrate(oral antacid 30 ml of 0.3M). LMWH subcutaneous(DVT prophylaxis)

• AVOID RESPIRATORY DEPRESSANT• IM- Injections…Unreliable.• Treatment and optimization of co morbid conditions such as

hypertension, CAD, diabetes, venous thromboembolism, and/or obstructive sleep apnea.• IV & IA access: Technical difficulties

Airway assessment in obese• Difficulty in mask ventilation• 15% of obese patients are a difficult intubation• Temporomandibular joint-limited mobility• Atlanto-ooccipital—limited mobility• Narrow upper airway• Distance b/w mandible & sternal fat pads-limited• Large breasts• Excessive palatal & Pharyngeal soft tissue.• Short and thick neck(if circumference >14cm then difficult intubation)• Difficult intubation--Consider FOB

Obesity & Regional Anesthesia• Regional anesthesia• Technically more difficult:Obscured landmarks

Difficult positioning Extensive layers of adipose tissue

– Long spinal needle required– Require 20 – 25% less Local Anesthetic Drugs

for Spinal or Epidural anesthesia because of• (Epidural fat and distended epidural veins)

• Combined Epidural / General (GA) preferred to decrease GA requirement

• Epidural anesthesia postoperative respiratory complications

Anesthetic Considerations: Intraoperative• Induction of Anaesthesia

• Pulse oximeter, ECG, NIBP, Capnogram • Venous access.• Preoxygenation for 3 minutes in slight head up position.• 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.• HOB elevated (back-up Fowler or reverse Trendelenburg) 30°• Use of CPAP during induction• Confirmation of intubation: by ETC02.

Position for intubation• Supine sniffing position with 30° back-up position provides optimal conditions for successful intubation.• Aligning the external auditory meatus with the sternum horizontally has been shown to improve the laryngoscopic view

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Best Position for Intubation External auditory meatus and sternal notch at same level

Maintainace of anaesthesia• Ventilatory Management: Prevent/reverse atelectasis:

Restrict the use of Fio2 to < 0.8 during Maintain lung recruitment: Use PEEP (10-12 cm/H2O) Avoid lung overdistension: Use tidal volume of 6-10 mL/kg of ideal body weight Keep peak-inspiratory pressure < 30 cm/H2o Consider mild permissive hypercapnia if necessary

• Desflurane,sevoflurane and Isoflurane are better choices.

• Fluid management: Reduction in total body water to 40% of TBW. Relative dehydration may be present.

Poor tolerance to fluid load.• Avoid rapid rehydration, to Lessen cardiopulmonary

compromise. Administer Hetastarch at recommended volumes per kilogram of IBW -20 mL/kg

Anesthetic Considerations• 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 .• POSTOPERATIVE COMPLICATIONS:

respiratory failure: Major complication.

Inc risk-Pre-ops hypoxia/Thoracic & upper abdominal Surgery deep venous thorombosis

pulmonary embolismwound infection

• proper analgesia: with PCA, Epidural analgesia, NSAIDs, local infiltration of LAs.