Anaesthetic consideration in obese patients

Management and anaesthetic consideration in obese patients during different surgery

1. Anaesthetic consideration in obese patients Moderator- Dr. Deepika Doneria Presentor - Dr. Kuldeep Sahay

2. Definition Obesity is defined as an abnormally high amount of adipose tissue compared with lean muscle mass (20% or more over ideal body weight). Ideal body weight : For men: IBW (kg)= height(cm)- 100 for women :IBW (kg)= height (cm)-105 Overweight : An excess of total body weight Obesity: Body weight>20% of IBW Morbid obesity: Body weight >twice IBW or IBW +50

3. AETIOLOGY OBESITY Social class Birth Weight & rapid early weight gain Puberty, Pregnancy and Menopause Psychology & Behaviour Genetics & Ethnic origin Disease & Disability Environment Physical Activity Diet

4. OBESITY AND BMI Classification BMI (kg/m 2 ) Underweight <18.5 Normal weight 18.5-24.9 Overweight 25.0-29.9 Obese Class 1 30-34.9 Class 2 35.0-39.9 Class 3 ( Severe, morbid) >40

5. Complications of obesity

6. Diseases Assocciated with Obesity Cardiovascular disorders In patients with clinically severe obesity, cardiac function is best at rest and exercise is poorly tolerated. Physical activity may cause exertional dyspnea and/or angina pectoris. Any increase in cardiac output is achieved by an increase in heart rate without an increase in stroke volume or ejection fraction. Systemic hypertension Coronary artery disease Heart failure

7. Systemic hypertension Obesity-induced hypertension is related to insulin effects on the sympathetic nervous system and extracellular fluid volume. Hyperinsulinemia appears to increase circulating levels of norepinephrine ; norepinephrine has direct pressor activity and increases renal tubular reabsorption of sodium and calcium, which results in hypervolemia . Cardiac output increases by an estimated 100 mL /min for each kilogram of adipose tissue weight gain. .

8. At the cellular level, insulin activates adipocytes to release angiotensinogen , which activates the renin-angiotensin-aldosterone pathway; this in turn leads to sodium retention and development of hypertension. An increase in circulating cytokines is seen in obesity, and this may cause damage to and fibrosis of the arterial wall, thereby increasing arterial stiffness. If hypertension is not well controlled, a mixed eccentric and concentric left ventricular hypertrophy can develop that eventually leads to heart failure and pulmonary hypertension .

9. In general, a decrease of 1% in body weight can decrease systolic blood pressure by 1 mm Hg and diastolic blood pressure by 2 mm Hg.

10. Respiratory System Obesity are related to decrease Lung volume, gas exchange, lung compliance and work of breathing d/t accumulation of fat in upper airway, thorax and abdomen. The overall respiratory problem is one of restrictive lung disease Decreased pulmonary compliance leads to    FRC (primarily a result of  ERV,  VC &  TLC) Under anesthesia, FRC of obese patient decreases about 50% as compared to 20% reduction for non-obese patients

11. Restrictive Lung Disease DECREASED TOTAL RESPIRATORY COMPLIANCE IN SUPINE POSITION FRC, VC, TLC INCREASED RESPIRATORY MUSCLE FUNCTION DECREASED CHEST WALL COMPLIANCE, INCREASED ELASTIC RESISTANCE SHALLOW & RAPID BREATHING INCREASED WORK OF BREATHING. FRC BELOW CV, Small airway closure V/Q mismatch , arterial hypoxemia DECREASED LUNG COMPLIANCE

12. Obstructive sleep apnea Obstructive sleep apnea (OSA) is defined as cessation of breathing for longer than 10 seconds during sleep. Hypopnea is a reduction in the size or number of breaths and some degree of arterial desaturation . Apnea occurs when the pharyngeal airways collapse. The pharyngeal muscle tone is decreased during sleep this reduced tone leads to a significant narrowing of the upper airway, resulting in turbulent airflow and snoring.

13. Physiologic changes that include arterial hypoxemia, arterial hypercarbia,polycythemia , systemic hypertension, pulmonary hypertension, and right ventricular failure and morning headaches. OSA is diagnosed using polysomnography where episodes of apnea during sleep can be observed and STOP BANG score. The severity of OSA is measured by the average number of incidents per hour. More than five incidents per hour is considered sleep apnea syndrome .

14. Treatment of OSA is aimed at applying enough positive airway pressure through a nasal mask to sustain patency of the upper airway during sleep. Nocturnal oxygen therapy is another possibility for individuals who experience significant oxygen desaturation . Obesity hypoventilation syndrome (OHS ) is the long-term consequence of OSA. It is characterized by nocturnal episodes of central apnea (apnea without respiratory efforts) reflecting progressive desensitization of the respiratory center to nocturnal hypercarbia . At its extreme, OHS culminates in pickwickian syndrome

15. GASTROINTESTINAL SYSTEM Hepatobiliary Disease: Increased threefold in obese people which reflects abnormal cholesterol metabolism. Abnormal liver function test results and fatty infiltration of the liver are frequent findings. Therefore, caution should be used when selecting medications known to cause liver dysfunction. Nonalcoholic Fatty Liver Disease/Nonalcoholic Steatohepatitis : Obesity causes an excess of intrahepatic triglycerides, impaired insulin activity, and release of inflammatory cytokines. These factors can lead to destruction of hepatocytes and disruption of hepatic physiology and architecture.

16. Cholelithiasis Biliary tract disease Hepatitis Intra and Extra hepatic cholestasis Prolonged Gastric emptying time, decreased gastric pH, Increased chances of Hiatal hernia Increased risk of aspiration pneumonitis .

17. PHARMACOLOGY T he physiologic changes associated with obesity may lead to alterations in the distribution, binding, and elimination of many drugs . Drug dosing should take into consideration the volume of distribution (V D ) for administration of the loading dose, and the clearance for the maintenance dose .

18. The VD in obese patients is affected by reduced total bodywater , increased total bodyfat, increased lean body mass, Altered tissue protein binding, • increased blood volume & cardiac output, •

19. Dosing should be calculated based on LBW/TBW.

20. PRE ANAESTHETIC ASSESSMENT Pr eanaesthetic assessment include d etailed history to rule out or find co morbid conditions , physical examination, Drug history, laboratory test and history of previous surgeries, their anesthetic challenges (i.e., ease or difficulty in securing the airway, intravenous access), need for ICU admission, surgical outcomes What history will diagnose OSA in an obese patient? Snoring or apnea during sleep& apparent arousal. Extremity movement, frequent turning in sleep Daytime sleepiness. Fatigue?

21. CVS evaluation Elicite history of symptoms and sign of right and left heart failure and history of hypertension Hepatic function test include serum albumin, bilirubin , SGOT,SGPT,ALP and lipid profile.

22. Respiratory evaluation Smoking history Exercise tolerance, History of hypoventilation and increased somnolence Pulmonary function tests with spirometry ABG Chest X ray Polysomnography Sleep study

23. AIRWAY CHALLENGES Airway obstruction with light to moderate sedation Difficult to mask ventilate Higher incidence of difficult intubation and failed intubation Presence of hypopharyngeal adipose tissue , interferes with the line of sight ( LOS)at direct laryngoscopy. Presence of pre-tracheal adipose tissue , worsens the laryngoscopic view.

24. Airway Evaluation Specific assessment 1. Body mass index (BMI): Incidence of difficult intubation ranges between 13-24% in obese patients. 2. Neck circumference Obese patients with neck circumference > 40 cm had a greater chance of problematic intubations (5%) and >60cm probability is 35%. 3.Length of neck Short neck (actual length not defined) is associated with a 5 fold increase in difficult airway. 4 . Neck circumference to thyromental distance( NC/TM) ratio is >5.0 is cutoff point for predicting difficult intubation.

25. 5 . Anterior neck soft tissue : Superior predictor of difficult intubation in obese patients than obesity per se or a thick neck . Obtained by ultrasound quantification of soft tissue at the level of the vocal cords , thyroid isthmus and supra-sternal notch. Averaged value >28mm predicts difficult laryngoscopy

26. AIRWAY EXAMINATION Mallampati classification Atlanto -occipital joint extension, Temporomandibular joint (TMJ)assessment with inter-incisor distance,mentohyoid distance,and Dentition, large protuberant teeth, Limited neck mobility Retrognathia Neck circumference, Hypertrophic tonsils and adenoids.

27. Investigations Routine Tests: 1. Hematological work up 2. ECG 3. Chest X-ray 4. Blood Glucose 5. Lipid Profile 6. Liver Function Tests 7. Serum Creatinine

28. Special investigations Sleep studies Cardiac Stress Test Echocardiography PFT, Spirometry ABG Thyroid Function Tests

29. PREMEDICATION No sedatives or narcotics should be given to a morbidly obese patient as premedication. Can be given in operating room along with supplementary oxygen to prevent hypoxia from respiratory depression. Glycopyrollate an anticholinergic used to dry the upper airway,

30. Continue antihypertensive medication. Heparin prophylaxis against DVT H2receptor antagonist [proton pump inhibitor]. Anti-aspiration prophylaxis Metoclopramide to increase gastric emptying, and non particulate antacids

31. MONITORING Pulse Oximetry Electrocardiogram Noninvasive blood pressure, End-tidal carbondioxide , Temperature, Hourly urine output

32. POSITIONING Awake patients can self position on OR table . HELP[Stacked or Ramped]position from scapula to the head to be arranged. Paddingof all pressure point. Maintain & pre-oxygenate in head-up position. pneumatic leggings or compression stockings to be applied

33. PREOXYGENATION Obese patients initially placed in a ramped position and then in the reverse trendelenburg position before preoxygenation. Patients are then preoxygenated for 3 to 5minutes with 100% Oxygen under positive pressure 8 to 10 cmH2o After induction, maintain 08 to 10cmH2O PEEP , but care must be taken to treat anyhypotension that may occur.

34. INTUBATION STRATEGY Awake FOI shall be an ideal technique but is not easy to achieve. Obscured landmark may hinder nerve block. Sedation & analgesic used during preparation may result in hypercapnia, hypoxia & airway obstruction.

35. RSI RSI could be contemplated using short acting inducing agents as propofol with succinylcholine, with the patient positioned on a ramp.

36. MAINTENANCE OF ANAESTHESIA Combined epidural/general (GA) may be beneficial to decrease GA requirements. Consider a"balanced"GA >decreases required dose of each agent, so less will be around postop. Consider using short acting agents (e.g. alfentanyl , propofol, versed, atracurium) Avoid using long acting agents (e.g. morphine, pancuronium ) Ventilation: Use large tidal volumes15-20ml/kg ideal body weight Titrate PEEP to maintain oxygen saturation .

37. PRE-REQUISITES FOR EXTUBATION Intact neurologic status, fully awake and alert, with head lift greater than 5s Hemodynamic stability Normothermia. Train-of-four (TOF)reversal by PNS(T4/T1 >0.9). Full reversal of NM blocking agents

38. Respiratory rate (10 -30/min) SPO 2 >95% on FIO2 0.4 Acceptable ABG(FIO2of 0.4: pH- 7.35 to 7.45; PaO2,>80mm Hg;PaCO2,<50 mm Hg). Generating Tidal volume (TV)>5mL/kg ideal body weight

39. POST OP COMPLICATIONS Post- anesthetic hypoxemia Respiratory depression Early ventilatory failure with need for reintubation Positional ventilatory collapse Hemodynamic instability, PONV Venous thromboembolism

40. REGIONAL ANAESTHESIA T echnical difficulties Increased incidence of epidural failure and catheter dislodgment, Decreased epidural space causing unpredictable spread of local anaesthetics, variable block level

41. For epidural catheter patients should be positioned in a sitting position, and ultrasonography guidance is recommended. For peripheral surgical procedures, peripheral nerve blocks used, provided that adequate landmarks exist.

42. Thank You