Obesity & AnaesthesiaDr Ikhwan Wan Mohd Rubi MD (UKM)MO Anaesthesiology, HSNZ
1/6 Malaysians are either overweight/obese- Malaysia Ministry of Health
• “Malaysia is leading in the prevalence of obesity among Southeast Asian countries. Almost one in two Malaysians are either overweight or obese, placing them at a high risk for diabetes,”says Datin Paduka Santha Kumari, chairman of the Selangor branch of the Malaysian Diabetes Association.
Classical description of obesity
Intraperiotenal fat
(liver,omentum)
Peripehral fat(arms,legs,buttoc
k)
Waist hip ratio: >0.94 in men >0.8 in women
Health risk associated with obesity (Evidence Level B)
Comorbid• BMI alone is a poor predictor of comorbidity, surgical and
anesthetic difficulty• Fat distribution (waist/collar circumference) > predictive of
CVS/Respiratory comorbid• Android fat distribution
• Makes intra-abdominal surgery > difficult• Greater difficulty in airway management/ventilation• Greater risk of metabolic and CVS complication
• Risk of comorbid increases the duration of obesity (fat years)
• Presence and severity of comorbid may be masked by sedentary lifestyle
• TRUE significance obesity related illness may only emerge during perioperative phase.
RESPIRATORY SYSTEM• OSA• Obesity Hypoventilation Syndrome• Airway Assessment• Obesity and gas exchange• Lung volume• O2 consumption and CO2 production• Gas exchange• Lung Compliance and resistance• Respiratory efficiency and work of breathing• Implication for anesthesia
CVS SYSTEM• Cardiovascular derangemnt• HPT• IHD• Blood Volume• Cardiac arrhythmia• Cardiac function
Obstructive Sleep Apnea• Up to 5% of obese
patients have clinically significant obstructive sleep apnea
• Apnea is defined as 10 seconds or more of total cessation of airflow despite continuous respiratory effort against a closed glottis
ObesityEffects on Blood Volume
• Total blood volume is increased in the obese, but on a volume-to-weight basis, it is less than in nonobese individuals(50ml/kg compared to 70ml/kg)
• Most of this extra blood volume is distributed to the fat organ
ObesityCardiovascular Effects
• Cardiac output increases as much as 20 – 30 ml/kg of excess body fat secondary to ventricular dilatation and increasing stroke volume
• The increased left ventricular wall stress leads to:
• Hypertrophy• Reduced compliance• Impaired left ventricular filling • Obesity cardiomyopathy
ObesityEffects on Gastrointestinal System
• Gastric volume and acidity are increased• Most fasted morbidly obese patients presenting for
elective surgery have gastric volumes in excess of 25 ml and gastric fluid pH less than 2.5 ( the generally accepted volume and Ph indicative of high risk for pneumonitis should regurgitation and aspiration occur).
• Gastric emptying may actually be faster in the obese, but because of their larger gastric volume (up to 75% larger), the residual volume is larger.
ObesityObesity and Diabetes
• Impaired glucose tolerance in the morbidly obese is reflected by a high prevalence of type II diabetes mellitus as a result of resistance of peripheral fatty tissues to insulin
• Greater than 10% of obese patients have an abnormal glucose tolerance test, which predisposes them to wound infection and an increased risk of myocardial infarction during periods of myocardial ischemia
ObesityEffects on the Airway
• Anatomic changes that contribute to potential for difficult airway management
• Limitation of movement of the atlantoaxial joint and cervical spine by upper thoracic and low cervical fat pads
• Excessive tissue folds in the mouth and pharynx• Short thick neck• Suprasternal, presternal and posterior cervical fat• Very thick submental fat pad
• Obstructive sleep apnea• Predisposes to airway difficulties during anesthesia• OSA patients have excess tissue deposited in their lateral
pharyngeal walls which may not be recognized during routine airway examination
Preoperative Assessment(AAGBI/SOBA)• Obese patient may present for
ELECTIVE/EMERGENCY surgery/ Obstetric Analgesic/Anesthesia
• Similar between ELECTIVE/EMERGENCY• Multidiscipline- where deem necessary• Respiratory physician, Cardiologist, Endocrinologist,
Dietitian
• Specific attention to comorbid• Cardiovascular/Respiratory/Metabolic• Obese patient may have limited mobility, may appear
relatively asymptomatic despite significant cardiorespiratory dysfunction
Preop. Assessment (Respiratory)
• Previous anesthetic experiences• Attention should focus on the cardiorespiratory system
and airway• Assess for Obstructive Sleep Apnea and Obesity
Hypoventilation Syndrome• STOP – BANG (5 or more)• Snoring (loudly)• Tired (often tired/sleepy at day time)• Observed (has anyone observed you stop breathing during
sleep)• Pressure (has you been treated for/ has high blood pressure)• BMI>35kg/m2• Age>50 years old• Neck Circumference >40cm• Gender-Male
Preoperative Assessment (Respiratory)
Preoperative Assessment (Cardiovascular)• Check for HPT• Assess for IHD (angina/Exertional dyspnea)• Assess symptoms and sign of cardiac failure• Effort tolerance (walk to the length of the ward)• Ability to lie flat/supine• Position of sleeping• Orthopnea/ Paroxysmal Nocturnal Dyspnea
Airway Assessment• Head and Neck flexion/Extension/lateral rotation (cervical limit)• Jaw mobility/Mouth opening• Oropharynx (excessive palatal and pharnygeal soft tissue) and
dentition • Patency of nostril• Previous anaesthetic experiences• Mallampati score• Neck Circumference (>17.5in/40cm)
• The single biggest predictor of problematic intubation in morbidly obese patients
• 40 cm neck circumference = 5% probability of a problematic intubation• 60 cm neck circumference = 35% probability of a problematic
intubation
• Fat face & cheeks, large breast, short neck, large tongue, high anterior larynx
Airway assessment• Role of imaging if time permit - soft tissue xray/CT
scans with consultation with Otolaryngologist for direct/indirect laryngoscopy
• Consider and discuss re: Awake fibre optic intubation with patient
Anticipate difficult ventilation/intubation
Investigation• Tailored to individual (comorbid/type/urgency of
surgery)• FBC, Electrolytes, Renal, Liver function, Blood
Glucose (Basic)• Arterial Blood Gas (maybe useful) in suspected
respiratory comorbid (OSA, OHS, pulmonary disease)-provide guide to weaning and expecting postoperative respiratory support
• Preoperative ECG (to exclude significant rhythm disturbances, cor pulmonale, guide for further extensive study
• Echocardiography• Transthoracic may be difficult (poor window)• May estimate systolic and diastolic function, chamber
dimension
• CXR - assess CTR, evidence of cardiac failure• Pulmonary function test – may reveal restrictive
pattern but not done on all patients• Exercise ECG testing (stress test)- impracticle
Pharmacokinetics of anaesthetic agenst• Calculation of appropriate dose may be difficult• Should based Actual Body Weight or Ideal Body
Weight?• Most PF of anaesthetic agents influenced by mass
of adipose tissue, producing prolonged and less predictable effect
• Volume of central compartment is largely unchanged
• BUT dosages of lipophilic drugs need to be adjusted due to changes in Vd
• Less fat soluble drugs show little or no change in Vd• lean body mass/ IBW + 20%
• Exception: Scolene based on ABW, sames as
ObesityEffects on Drug Distribution
• Volume of Distribution in Obese patients is affected by:
• Reduced total body water• Increased total body fat• Increased lean body mass• Altered protein binding• Increased blood volume• Increased cardiac output
ObesityEffects on Drug Elimination
• Hepatic clearance is not usually effected• Renal clearance of drugs is increased in obesity
because of increased renal blood flow and glomerular filtration rate
ObesityHow does it effect drug dosing?
• Highly Lipophilic• Barbiturates and benzodiazepines have an increased volume
of distribution
• Less Lipophilic• Little or no change in volume of distribution with obesity
• Increased blood volume in the obese patient decreases the plasma concentrations of rapidly injected intravenous drugs.
• Fat has poor blood flow and doses calculated on actual body weight could lead to excessive plasma concentrations.
* Review Barash et al table 47-5*
ObesityInduction of General Anesthesia
• Adequate preoxygenation • Rapid desaturation because of increased oxygen
consumption and decreased FRC• Positive pressure ventilation during preoxygenation
decreases atelectasis formation and improves oxygenation
• Patient position• The head-up (reverse tredelenburg) position provides
the longest safe apnea period during induction of anesthesia
ObesityPatient positioning
• Supine• Causes ventilatory impairment and inferior vena cava
and aortic compression
• Trendelenburg• Further worsens FRC and should be avoided
• Reverse tredelenburg• Increased compliance results in lower airway pressures
• Prone • Detrimental effects on lung compliance, ventilation and
arterial oxygenation• Increased intra-abdominal pressure worsens IVC and
aortic compression and further decreases FRC
Obesity Ventilating the obese patient
• Tidal volumes greater than 13 ml/kg offer no added advantage
• Increasing tidal volume beyond 13 ml/kg increases PIP without improving arterial oxygen tension
• Positive end-expiratory pressure (PEEP) is the only ventilatory parameter that has consistently been shown to improve respiratory function in obese patients
• PEEP may reduce venous return and cardiac output
The Future is BIG!
Recommended
