Obesity and its anesthetic implications

1. Obesity and its anesthetic implications Presenter: Ekta Gupta Moderator: Dr J S Dali www.anaesthesia.co.inanaesthesia.co.in@gmail.com

2. Introduction • Normal body composition (avg. young adult ♂) • 18% BW is protein • 7% BW is mineral • 18-25% BW is fat • 60% BW is water OBESITY – abnormally high % of BW as fat / excess adipose tissue mass

3. BMI = Body weight (kg) / Height(m)2

4. Others • BW ≥ 20-25% above “Ideal body weight” • IBW - weight a/w lowest mortality rate for a given height and gender • Skin fold thickness – calipers • Triceps > 20mm • Scapula inferior angle • Densitometry – underwater weighing • CT/MRI • Electrical impedance

5. Distribution of fat • Central / Peripheral distribution • Intraabdominal & abdominal s/c fat closely a/w CVS disease vs. s/c fat in buttocks and lower extremities • Abnormal body circumference indices

6. Associated with • Hypertension, dyslipidemia, CAD, Stroke, PVD, thromboembolic disease, obesity cardiomyopathy • Restrictive lung disease, OSA, OHS, cor pulmonale • Type 2 DM, Cushing’s, hypothyroidism, infertility • Cholelithiasis, GERD, Cirrhosis • Renal calculi • Osteoarthritis • Breast, prostate, colorectal, GB, kidney and uterine cancer • Emotional and altered body image disorders

7. Respiratory system

8. Pathophysiology • Increased metabolic demand • Increased work of breathing • Decreased respiratory system compliance • Fixed thoracic cage • Elevated diaphragm • Parenchymal changes • Increased respiratory resistance • Decreased lung volumes

9. MV increased at rest Work of breathing increased at rest.

10. Lung volumes decreased • ERV, FRC • VC, TLC • MVV, MBC

11. OBESITY OBESITY

12. Relationship of FRC and CC

13. Obesity Hypoventilation Syndrome • ? Extreme obesity ? Severe OSA • Central apneic events • Chronic alveolar hypoventilation • Chronic daytime hypoxemia • RVF • = Pickwickian syndrome

14. Preoperative evaluation • Spirometry, CXR No predictive value or utility in patient optimization in the absence of uncharacterized symptoms and signs of pulmonary disease • Daytime hypoxemia • Room air pulse oximetry • If < 96% - further evaluation ? OHS • ABGA, ECG, CXR, TEE • Discussion with patient – weight loss, CPAP therapy

15. Cardiovascular system

16. Pathophysiology • Increased absolute blood volume↔ increased body tissue • CO increased (0.01L/min/kg adipose tissue, SV increased) • LVEDP increased - diastolic dysfunction • + HT - obesity cardiomyopathy (systolic dysfunction) • LVF

18. Accelerates atherosclerosis - IHD • Limited mobility – appear asymptomatic even in presence of significant cardiac impairment • Poor tolerance for stress induced by hypotension, hypertension, tachycardia, fluid overload • Intraop ventricular failure • Intraop dysrhythmias • Venous stasis, pulmonary embolism (PE)

19. Preoperative evaluation • HT • Arrange NIBP cuff (L = 80% arm Ө, W = 40% arm Ө ) • Recent ECG • LVH • Arrhythmias • Cor pulmonale • IHD • Screen for CHF • Echo if doubt

20. DVT prophylaxis(if high baseline risk of periop PE) • s/c heparin 5000 IU before surgery and continued later • s/c enoxaparin 40mg BD • IVC filter

21. Airway

22. Age > 55yrs BMI > 26kg/m2 Edentulous H/O snoring Beard Airway obstruction Soft tissue ↑ Large tongue Sniffing position A-O and C spine mobility limited – upper thoracic & low cervical fat pads Short thick neck +DM – stiff joint syndrome Difficult seal Thick submental fat pad Difficult mask ventilation

23. Difficult laryngoscopy & intubation • BMI • MMP score ≥ III • Neck circumference • > 44cm – 5% • > 60cm – 35%

24. Preoperative evaluation • Routine • Special • Neck circumference • Previous anesthetic exposure • Discuss and familiarize for awake intubation • OSA

25. Pharmacokinetics • VD increased • Increased total body fat, lean body mass • Increased blood volume, CO • Altered protein binding • Hyperlipidemia • Increased α-1 acid glycoprotein • Prolonged elimination t½ despite unchanged or increased clearance

26. Dosing for IV drugs • Weakly or moderately lipophilic drugs - LBW LBW = IBW + 20% (TBW – IBW) • NDMR • Alfentanil, Remifentanil • Highly lipophilic drugs - TBW • Thiopental, Propofol • BZDs • Fentanyl (derived pharmacokinetic body weight) • Sufentanil

27. GIT and obesity • Increased volume & acidity of gastric contents • Gastric emptying ↑ / ↓ • Increased incidence of GERD • Barrier pressure b/w stomach & LES • Increased risk for pulmonary aspiration

28. Aspiration prophylaxis • Ranitidine and metoclopramide iv 30 min before surgery – cost effective • Fasting guidelines same as non obese population

29. Liver • Histology – fatty infiltration • Biochemical – ALT increased • No correlation with capacity to metabolize drugs

30. Renal and endocrine • Kidney • Glomerular hyperfiltration • Impaired natriuresis • Hyperinsulinemia • Type II DM – insulin resistance • Cancers • Increased ILGF – 1 • Stimulates cell proliferation • Decreases apoptosis

31. Metabolic syndrome (syndrome X) • ≥ 3 of the following: • Abdominal obesity (waist circumference) • Dyslipidemia • TG ≥ 150mg/dl • HDL < 40mg/dl(♂), 50mg/dl(♀) • Hypertension (>130/85 mm Hg) • Fasting glucose > 110mg/dl

32. Others • Evaluate IV accessibility • Peripheral vasculature • ? CVP ?? USG • Feasibility of RA – technically difficult • Evaluate landmarks • Arrange equipment and expertise • ? nerve stimulator, ? longer needles, ? USG, ?? fluoroscopy

33. Intra-operative management

34. Early challenges • Operating table • Join two regular tables • Extra width • Max. weight limit increased • NIBP/Arterial line • IV access

35. Positioning • Strapping to OT table/ malleable bean bag • Padding pressure areas to prevent pressure necrosis • Avoid neural injuries • High risk of post-op • Ulnar neuropathy • Brachial plexus traction injuries

36. Airway management • Facilitated laryngoscopy and intubation • ILMA • 100% successful ventilation • 96% successful intubation • Elective awake fiber-optic intubation safest

37. Induction of anesthesia • Increase apneic oxygenation reserve • Ramped position • Head above horizontal plane of chest • Horizontal plane between sternal notch and EAM • ?? RSI --------- ?? cricoid

39. Preoxygenation • TVB, 3 minutes, 5-10L/min O2 • 4 deep (VC) breaths, 30 sec, 5-10L/min O2 • 8 deep breaths, 60 sec, > 10L/min O2 • 10cm H2O CPAP X 5 min f/b 10cm H2O PEEP • Head up reverse trendelenburg position

41. Ramped position • Stacking– towel or folded blankets under shoulders and head so that head above horizontal plane of chest

42. HELP • Head elevated laryngoscopy position • Troop head elevation pillow + standard intubation pillow

43. CRICOID PRESSURE SUCCINYLCHOLINE

44. ? RSI • Ability to mask ventilate not tested before giving muscle relaxant - ? CICV • SAP decreased despite pre-oxygenation • FRC reduced • Atelectasis promoted • Cricoid pressure - potential for airway deformation • Airway obstruction • Poor CL grade

45. Ventilation • Tidal volume < 13ml/kg • Increased PIAP, EEAP, lung compliance • No improvement in PaO2 • PEEP – only consistently useful ventilatory parameter

46. Anesthetic agents • Rapid emergence and return of protective airway reflexes • BIS titrated anesthesia • Prefer shorter acting drugs • Predictable neuromuscular blockade • Prefer drugs with organ independent metabolism • Use neuromuscular monitoring

47. Neuromuscular blockade • Cis-atra↔ Vec and roc ↔ Pancuronium • Succinylcholine • Plasma cholinesterase activity increased –TBW dosing

48. Inhalational anesthetics • Desflurane ↔ Sevoflurane ↔ Isoflurane • Desflurane better than propofol • Controlled “titration off” of the anesthetics near the end of surgical procedure

49. Regional anesthesia • SAB • Unpredictable height • Greater respiratory embarrassment • Epidural block • LA dose requirement 25% less • Epidural space volume reduced • Fatty infiltration • Vascular engorgement • Easiest in lumbar region

50. Emergence • Extubate in semi recumbent position • Supplemental oxygen • Postoperative CPAP or BiPAP • Adequate analgesia • Elastic binder for abdominal support • Deep breathing exercises with incentive spirometer