Obesity

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Physiologic and Pharmacologic Consequences of Obesity and its Anesthetic Implications : 

Physiologic and Pharmacologic Consequences of Obesity and its Anesthetic Implications Andrew R. Biegner CDR, NC, USN Naval Medical Center, San Diego Chief Anesthetist

Things I’ve Learned From My Children: 

Things I’ve Learned From My Children Garbage bags do not make good parachutes. When you hear the toilet flush and the words “Uh-oh,” it’s already too late. Super glue is forever. VCR’s do not eject PB&J sandwiches even though TV commercials show they do. A king size waterbed holds enough water to fill a 2000 sq. foot house 4 inches deep.

Objectives: 

Objectives Describe the causes of obesity and its social implications. Discuss the cardiovascular and respiratory changes that occur in morbidly obese patients. Describe what changes in gastrointestinal and hepatic function can be expected in obese patients. Review how obese patients metabolize anesthetic drugs differently from non-obese patients.

Obesity: Definition: 

Obesity: Definition A condition in which excess body fat may put a person at health risk. A metabolic disorder that is primarily induced and sustained by an over consumption or underutilization of caloric substrate

Equations: 

Equations Ideal body weight in Kg (IBW) Height in centimeters - 100 for men Height in centimeters - 105 for women Body mass index (BMI) weight in Kg / height (m) 2

Definitions: 

Definitions Obese 20% > IBW BMI > 28 – 35 Morbidly Obese 2 x IBW BMI > 35

Incidence of Obesity in North America: 

Incidence of Obesity in North America 33% are obese 5% are morbidly obese Mortality is 3.9 times that in non-obese

Causes of Obesity: 

Causes of Obesity Complex and multifactorial Genetic predisposition Socialization Age Sex Race Economic status Psychological Cultural Emotional Environmental factors Cessation of smoking

Diseases Linked to Obesity: 

Diseases Linked to Obesity Diabetes Coronary Heart Disease High Blood Pressure Stroke Arthritis Gastroesophageal reflux Cancer High cholesterol Endocrine disease

Diseases Linked to Obesity: 

Diseases Linked to Obesity Hypertrophic Cardiomyopathy Infertility Depression Obstructive sleep apnea Gallstones Fatty liver Stress incontinence Venous ulcers Sudden death

Physical Complications of Obesity: 

Physical Complications of Obesity Heart disease Type II diabetes mellitus Hypertension Stroke Cancer (endometrial, breast, prostrate, colon) Gallbladder disease Sleep apnea Osteoarthritis Reduced fertility

Psychological Complications of Obesity: 

Psychological Complications of Obesity Emotional distress Discrimination Social stigmatization

Obesity Related Diseases Treated Surgically: 

Obesity Related Diseases Treated Surgically Cholelithiasis Thromboembolism Urolithiasis Osteoarthritis Varicose veins Esophagitis Hiatus hernia Abdominal wall hernia

Obesity Related Diseases Treated Surgically: 

Obesity Related Diseases Treated Surgically Cancer Endometrial Breast Prostate Colorectal Renal Fibroadenoma of the breast Uterine fibroma Ovarian cysts Cesarean section Stress urinary incontinence

Cardiovascular Pathophysiology: 

Cardiovascular Pathophysiology Excess body mass  metabolic demand   CO  workload LVH  pulmonary blood flow and HPV Pulmonary HTN  cor pulmonale  right heart failure

Cardiovascular Pathophysiology: 

Cardiovascular Pathophysiology Stroke volume index and stroke work index are the same as non-obese SV and SW must  Proportion to body weight  SV and SW LVH dilatation

Cardiovascular Pathophysiology: 

Cardiovascular Pathophysiology  risk of arrhythmias Hypertrophy Hypoxemia Fatty infiltration of cardiac conduction system Diuretics  catecholamines Sleep apnea

Cardiovascular Pathophysiology: 

Cardiovascular Pathophysiology For every 13.5 kg of fat gained: 25 miles of neovascularization occurs Increased CO of 0.1 L/min for each kg of fat.

Cardiac Evaluation: Assess For: 

Cardiac Evaluation: Assess For Prior MI HTN Angina PVD

Cardiac Evaluation: EKG: 

Cardiac Evaluation: EKG Determination of resting rate Rhythm Ventricular hypertrophy or strain

Cardiac Evaluation: EKG: 

Cardiac Evaluation: EKG Investigate ischemic changes or evidence of coronary artery disease Low voltage EKG Excess overlying tissue Underestimate LVH

Cardiac Evaluation: EKG: 

Cardiac Evaluation: EKG Axis deviation and atrial tachyarrhythmias Sudden cardiac death is more prevalent with LVH Ventricular ectopy

Cardiac Evaluation: 

Cardiac Evaluation Indications of LV dysfunction Limitations in exercise tolerance History of orthopnea Paroxysmal nocturnal dyspnea

Cardiac Evaluation: 

Cardiac Evaluation Testing of exercise tolerance is likely to be impossible if CAD is suspected. Echocardiography Dipyridamole-thallium TEE Consult cardiologist Control of BP Treatment of heart failure Coronary angioplasty

Vascular Access: 

Vascular Access Challenging at best Excessive fat obscures blood vessels Central line placement Vessels impeded by distortions of the underlying anatomy by adipose.

Volume Replacement: 

Volume Replacement Adult total body water percentage is 60% to 65%. Severely obese total body water is 40%. Estimated blood volume in obese patient is 45 to 55 mL/kg actual body weight 70 mL/kg for the non-obese

Volume Replacement: 

Volume Replacement Avoid rapid rehydration Lessen cardiopulmonary compromise. Administer Hetastarch at recommended volumes per kilogram of IBW 20 mL/kg Albumin 5% and 25% used as indicated Support circulatory volume and oncotic pressure. Replace blood loss with crystalloid 3:1 ratio

Respiratory Pathophysiology: 

Respiratory Pathophysiology Excess metabolically active adipose +  workload on supportive muscle  CO2 production Hypercarbia  O2 consumption Hypoxia

Respiratory Pathophysiology: 

Respiratory Pathophysiology Restrictive lung disease Decreased chest wall compliance Diaphragm forced cephalad Decreased lung volumes Accentuated by supine and Trendelenberg positions FRC may fall below closing capacity Alveolar collapse Ventilation / perfusion mismatch

Changes in Pulmonary Volumes and Function Tests : 

Changes in Pulmonary Volumes and Function Tests Tidal volume Normal or decreased Inspiratory reserve volume Decreased Expiratory reserve volume Greatly decreased

Changes in Pulmonary Volumes and Function Tests: 

Changes in Pulmonary Volumes and Function Tests FRC Greatly decreased Direct inverse relationship between BMI and FRC FEV1 Normal or slightly decreased

Respiratory Pathophysiology: 

Respiratory Pathophysiology Relatively hypoxemic Occasionally hypercapnic Obesity-hypoventilation (Pickwickian syndrome) Obesity usually extreme Hypercapnia Cyanotic / hypoxemia Polycythemia Pulmonary HTN Biventicular failure Somnolence Obstructive sleep apnea syndrome (OSAS)

OSAS: 

OSAS Definition 10 seconds or more of total cessation of airflow despite respiratory efforts Clinically relevant 5 episodes per hour 30 episodes per night

OSAS: 

OSAS Snoring Dry mouth and short arousal during sleep Partners report apnea pauses during sleep

OSAS: 

OSAS More vulnerable to airway obstruction Opioids Sedatives More vulnerable in supine or Trendelenberg position

OSAS and Difficult Intubation: 

OSAS and Difficult Intubation 15% of obese patients are a difficult intubation Short thick neck Obesity and short thick neck Related to OSAS and to each other Fat in lateral pharyngeal walls are difficult to exam awake

Detecting OSAS : 

Detecting OSAS Nocturnal polysomnography

GI Pathophysiology: 

GI Pathophysiology  incidence Gastroesophageal reflux Hiatal hernia  abdominal pressure Severe risk of aspiration

GI Pathophysiology: 

GI Pathophysiology After 8 hour fast 85 – 90% of morbidly obese patients have Gastric volumes > 25 ml Gastric pH < 2.5

Pharmacological Considerations: 

Pharmacological Considerations  volume distribution  elimination half life  GFR  clearance of untransformed drugs  fat stores May  requirements for and clearance of fat soluble anesthetics

Pharmacological Considerations: 

Pharmacological Considerations More extensive metabolism of volatile anesthetics Obesity  biotransformation rate Methoxyflurane Enflurane Halothane  serum fluoride ions Associated with renal toxicity

Pharmacological Considerations: 

Pharmacological Considerations Sevoflurane increases serum inorganic fluorides levels. Metabolized 100% faster in obese patients Renal physiology can be negatively affected by elevated fluorides. Sevoflurane is inappropriate in patients with questionable kidney function.

Pharmacological Considerations: 

Pharmacological Considerations Desflurane is the most resistant to hepatic degradation < 0.02% with Desflurane 0.2% with Sevoflurane Desflurane preferred inhalational agent Low solubility profile Rapid washout Absence of hepatic and renal toxicity Support of blood pressure

Pharmacological Considerations: 

Pharmacological Considerations  volume of distribution Delayed clearance of lipid-soluble drugs Suggests larger loading doses Less frequent maintenance doses Dose based on actual body weight Opioids Benzodiazepines

Pharmacological Considerations: 

Pharmacological Considerations Water-soluble drugs Limited volume of distribution Uninfluenced by fat Base dose on IBW Neuromuscular blocking agents Intravenous anesthetics

Anesthetic Considerations: Preoperative: 

Anesthetic Considerations: Preoperative  risk for aspiration pneumonitis Consider H2 antagonist Metoclopramide Avoid unnecessary respiratory depressants Assess Cardiopulmonary reserve EKG ABG PFT’s

Anesthetic Considerations: Preoperative: 

Anesthetic Considerations: Preoperative BP with appropriate size cuff Plan / examine for venous / arterial access Possible regional anesthesia

Anesthetic Considerations: Preoperative Airway Assessment: 

Anesthetic Considerations: Preoperative Airway Assessment Limited TM joint mobility Limited atlanto-occipital mobility Narrow upper airway Small space between mandible and sternal fat pads

Anesthetic Considerations: Induction: 

Anesthetic Considerations: Induction Prepare for difficult intubation Prepare for difficult mask ventilation Induction may cause airway collapse Leading to upper airway obstruction

Induction Airway Equipment: 

Induction Airway Equipment Light wand Gum elastic bougie Oral airway LMA’s ETT with stylet

Anesthetic Considerations: Induction: 

Anesthetic Considerations: Induction Consider awake intubation Avoids airway collapse Minimal to no sedation Consider tracheotomy kit and surgeon standing by

Anesthetic Considerations: Intraoperative: 

Anesthetic Considerations: Intraoperative Awake fiberoptic intubation if difficult airway suspected Breath sounds distant ETCO2 more important Relatively high FIO2 may be needed in: Lithotomy Trendelenberg Prone

Anesthetic Considerations: Intraoperative: 

Anesthetic Considerations: Intraoperative Positioning 2 OR tables side by side If > 350 lbs Prone position is poorly tolerated Lateral decubitus is keeps abdominal weight off chest

Anesthetic Considerations: Intraoperative: 

Anesthetic Considerations: Intraoperative Morbidly obese patient should never lie flat Semi-Fowler’s position Upper body elevated 30 – 40 Semi-recumbent position Best position during post-operative period

Reverse Trendelenburg Position: 

Reverse Trendelenburg Position RTP is best intraoperative position Can ameliorate deleterious effects of supine position RTP  pulmonary compliance  FRC Returned P(A-a)O2 to baseline RTP may be a better solution than Large TV and PEEP Perilli et al. Obes Surg. 2003 Aug;13(4):605-9

Anesthetic Considerations: Intraoperative: 

Anesthetic Considerations: Intraoperative Pulmonary compliance and FRC  Worsened by GETA and high intraabdominal pressure Opening the abdomen or lifting the panniculus  FRC Improves oxygenation

Anesthetic Considerations: Intraoperative: 

Anesthetic Considerations: Intraoperative Regional anesthesia Technically more difficult Require 20 – 25% less LA for SAB or epidural anesthesia Epidural fat and distended epidural veins Epidural anesthesia may  postoperative respiratory complications

Goals for Maintenance of Anesthesia: 

Goals for Maintenance of Anesthesia Strict maintenance of airway Adequate skeletal muscle relaxation Optimum oxygenation Avoid residual effects of muscle relaxants Appropriate intraoperative and postoperative tidal volume Effective postoperative analgesia.

Anesthetic Considerations: Postoperative: 

Anesthetic Considerations: Postoperative Respiratory failure risk increased by Preoperative hypoxia Thoracic or upper abdominal surgery Vertical incision Delayed extubation until Complete reversal of muscle relaxation Patient fully awake Follows commands

Anesthetic Considerations: Postoperative: 

Anesthetic Considerations: Postoperative Supplemental O2 after extubation Transport from OR to PACU 45 degree head up position Unload diaphragm Improves oxygenation Improves ventilation

Anesthetic Considerations: Postoperative: 

Anesthetic Considerations: Postoperative Increased mortality 6.6% vs. 2.7% in non-obese Increased risk Wound infection DVT PE

Anesthetic Considerations: Postoperative: 

Anesthetic Considerations: Postoperative PCA Can provide good pain relief Dose based on IBW Epidural route is preferred Administration of smaller dose than IV route