Anaesthetic consideration in morbidly obese in

non-bariatric surgeryModerated by :Prof Shahla Haleem

Presented by : Dr Nida FatimaDepartment of anesthesiology and critical care

JNMCH AMU Aligarh

Introduction• Prevalence: increasing worldwide• Incidence:

Worldwide : 20 to 30% of adultsIndia : 10-15% of adults

• Precursor of morbidity & premature mortality• BMI >35 kg/m2 at aged 50 years have double

the risk of premature death.• challenge for the anaesthesiologist.

Aetiology

Definition• IDEAL BODY WEIGHT (IBW)

For men: IBW (kg) = height (cm) – 100 For women: IBW (kg) = height (cm) – 105

• OVER WEIGHT: an excess of total body weight • OBESITY : Body weight > 20 % of IBW • MORBID OBESITY(MO): Body weight > twice IBW or IBW + 50kg

OBESITY AND ASSOCIATED RISKS ACC TO BMI

OTHER FACTORS & ASSOCIATED RISKS • Central, Android (Upper body obesity) • Peripheral, Gynecoid (lower body obesity) • Obese with ↑ abdominal circumference (> 102 cm.in men and >88 cm in women) • With high waist – hip ratio (>1.0 in men, >0.85

in women) have greater risk

MEDICAL & SURGICAL CONDITIONS WITH OBESITY

Cardiovascular• Hypertension • Cardiomyopathy • Ischaemic Heart

Disease • Peripheral vascular

Disease • Cerebrovascular

Disease

• Cor pulmonale• Pulmonary

Embolism • Deep Vein

Thrombosis • Varicose veins • Hyperlipidemia

Respiratory• Restrictive lung disease • Obstructive Sleep Apnoea

(OSA)

Gastrointestinal• Hiatus hernia • Inguinal hernia

Genitourinary• Menstrual abnormalities• Renal calculi

• Obesity Hypoventilation syndrome

(Pickwickian Syndrome)

• Gall stones• Gastro esophageal Reflux

Malignancy• Breast• Prostate• Endometrial

Endocrine• Diabetes mellitus• Hypothyroidism

Musculoskeletal• Osteoarthritis

• Colorectal• Cervical

• Infertility• Cushing’s disease

• Back pain

PATHOPHYSIOLOGY• Resting blood flow to fat is 2 to 3 ml/100gm/min.• With increasing obesity the percentage of perfusion

to fat decreases i,e not in direct proportion• 1 kg increase in fat above IBW needs 20 to 30 ml

increase in C.O.• For every 13.5 kg of fat added, app. 25 miles of neo-

vascularisation is added to the body.

CARDIOVASCULAR SYSTEM

Cardiovascular 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

Cardiovascular disorders

• S. Hypertension • P. Hypertension h/o exertional dyspnea, fatigue,

syncope]• IHD.• VH [inc. in PVR & PAP, SV, BV, CO] &

Cardiomyopathy.• CHF [Rapid weight gain indicates worsening CHF]

Cardiovascular Complications• Sudden cardiac death.• Cerebrovascular disease.• Deep vein thrombosis.• Pulmonary embolism

RESPIRATORY SYSTEM

• The overall respiratory problem is one of restrictive lung disease.

• Chest wall and lung compliance ↓ d/t accumulation of fat on the thorax and abdomen.

• Decreased pulmonary compliance leads to ↓ ↓ ↓ FRC (primarily a result of ↓ ERV, ↓ VC, & ↓ TLC).

• Under anesthesia, FRC of the obese patient decreases about 50% as compared to 20% reduction for the non-obese patient.

Increased fatDecreased respiratory muscle function

Decreased chest wall complianceIncreased elastic resistance

Increased pulmonary blood flow

Decreased lung compliance

Decreased total respiratory compliance in supine position

↓FRC, ↓VC, ↓TLC

Shallow & rapid breathingIncreased work of breathing

Limited maximum ventilatory capacity

RESTRICTIVE LUNG DISEASE

FRC below CCSmall airway closure

V/Q mismatch & left to right shuntArterial hypoxemia

• Reduction in ERV:I. Encroachment of

abdominal contents on the diaphragm.

II. Chest wall fat decrease respiratory system compliance.

III. Impairment of respiratory muscle

IV. Mechanical disadvantage

V. Fatty infiltration of the respiratory muscles in extreme obesity.

Oxygenation:

• decrease with BMI due to the reduction in FRC

• increase of shunt fraction.

• Oxygen consumption is increased with mild exercise in the morbid obese.

Obstructive Sleep Apnea:• Prevalence:Up to 5% obese .• Apnea= No airflow >10 s,

despite continuous respiratory effort against a closed glottis.

• Hypopnea/hypoventilation= TV <50% for >10 s.

• Desaturation= SpO2 reduction by >4%.

Obstructive Sleep Apnea/Hypopnea Syndrome

Severity of sleep apnea:apnea/hypopnea index (AHI)=total number of apneas and hypopneas total sleep time• Mild disease: AHI of 5 to 15 events /hour

• Moderate disease: AHI of 15 to 30 events/ hour

• Severe disease: AHI of ≥ 30 events /hour

Systemic Pathophysiology of OSA

Sleep Nocturnal Social Isolation

Snoring, breathlessness

Obstructed breathing O2, CO2 Arousal

Myocardial Ischemia Pulmonary Hypertension Systemic Hypertension

Arrhythmias R V H L V H

Diagnosis of OHA• Polysomnography,• Sleep study :

1. electroencephalogram,

2. electrocardiogram,

3. electrooculogram,

4. capnogram,

5. nasal or oral airflow,

6. Oesophageal pressure,

7. Arterial blood pressure,

8. Pharyngeal & extremity

9. Pulse oximetry,

10. Room noise

EMG

TREATMENT OF OSADuration of CPAP

EFFECT

2 weeks Corrects abnormal ventilatory drive

3 weeks Increases LVEF in CHF

4 weeks Reduces B.P, HR, 35% increase in E.F

4-6 weeks Reduced tongue volume & increased pharyngeal space

8 weeks Reduction in CVS risk

3-6 months Reduction in PAH

Effects 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

GASTROINTESTINAL SYSTEM

• Prolonged Gastric Emptying time, Decreased Gastric pH,

• Increased chances of Hiatal Hernia.

• Increased risk of Aspiration Pneumonitis.

• Inguinal hernia.

HEPATOBILIARY SYSTEM

1. Nonalcoholic Fatty Liver disease 2. Nonalcoholic Steatohepatitis.3. Cholelithiasis,4. Biliary tract disease, 5. Hepatitis,6. Intra and Extra hepatic Cholestasis.

ENDOCRINE SYSTEM

• Type II DM is common in Obese patients.

• Secondary obesity may be associated with:- Hypothyroidism Cushing’s disease Hypogonadism Hypothalamic Disorders

Obesity and Diabetes• adipose tissue proinflammatory mediators• (TNF-α, IL-6)

• signalling off of insulin down regulation of PPAR-γ

insulin resistance

Type II diabetes

METABOLIC SYNDROME

Waist circumference >102cm in men >88cm in women

Metabolic Syndrome

Triglycerides >150mg/dl

HDL cholesterol<40mg/dl in men <50 mg/dl in women

Blood pressure>=130/85 mm of hg

Fasting Glucose>=110mg/dl

Features Associated with Metabolic Syndrome

• Abdominal obesity • Atherogenic dyslipidemia (TGs, ↓ HDL-C, Apo B, small

LDL particles) • Insulin resistance with or without glucose intolerance • Proinflammatory state (hs CRP) • Prothrombotic state (PAI-1, ↓ FIB) • Others (endothelial dysfunction, micro albuminuria,

polycystic ovary syndrome, hypoandrogenism, non alcoholic fatty liver disease, hyperuricemia)

PHARMACOLOGY

• Drug dosing should take into consideration the volume of distribution (VD) for administration of the loading dose, and on the clearance for the maintenance dose.

• Dosing should be calculated based on LBW/TBW.

• IBW (kg) = height (cm) – xwhere x is 100 for adult males

105 for adult females.

• Lean body weight (LBW) is the total body weight (TBW) minus the adipose tissue

• In morbidly obese patients, increasing the IBW by 20 to 30% gives an estimate of LBW.

• The VD in obese patients is affected by

• reduced total body water, • increased total body fat, • increased lean body mass, • Altered tissue protein

binding,

• increased blood volume & cardiac output,

• increased blood concentrations of free fatty acids, cholesterol, and organomegaly.

• Plasma protein binding– Adsorption of lipophilic

drugs to lipoproteins (increases free fraction of drug)

– Plasma albumin unchanged

– Increased alpha 1 glycoprotein

• Drug clearance• Increased RBF• Increased GFR• Increased tubular

secretion• Decreased Hepatic

blood flow in CCF

• Increased Vd prolongs drug elimination half-life even when clearance is unchanged or increased.

• Drugs that undergo phase I metabolism (oxidation, reduction, hydrolysis) are generally unaffected by changes induced by obesity, while phase II reactions (glucuronidation, sulfation) are enhanced

• Renal clearance of drugs is increased .

• Highly lipophilic substances such as barbiturates and benzodiazepines show significant increases in VD for obese individuals

• Exceptions to this rule include the highly lipophilic drugs Digoxin, Procainamide, And Remifentanil

• IBW- Propofol, Vec, Rocuronium, Remifentanyl

• TBW- Thio, Midaz, Sch, Atra, Cis-atra, Fentanyl, Sufentanil

• Maintainence- Propofol- TBW Sufentanil- IBW

Pre-anesthetic Assessment• Detailed history to rule out or find co morbid conditions, 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 sleepDaytime sleepiness.Fatigue?

Special drug history needs to be taken

• Fenfluramine [heart & lung effect-stop 2 wks],

• Sibutramine [arrhythmias & hypertension],

• Orlistat [ needs supplementation of vitamins A,D,E,K].

• Respiratory system:-• smoking history, • exercise tolerance,• history of hypoventilation

and somnolence,

• Pulmonary function tests with spirometry • Polysomnography• Sleep study

• Work of breathing ↑• Max Voluntary Venti ↓

AIRWAY CHALLENGESI. Airway obstruction with light to moderate sedation II. Difficult to mask ventilate III. Higher incidence of difficult intubation and failed

intubation in MO. IV. Presence of hypopharyngeal adipose tissue ,

interferes with the line of sight (LOS) at direct laryngoscopy.

V. Presence of pre-tracheal adipose tissue, worsens the laryngoscopic view.

PHYSICAL EXAMINATION

• Respiratory. • Cardiovascular.• Endocrine.• Gastrointestinal.• Renal and Genitourinary.• Musculoskeletal.

Airway EvaluationSPECIFIC ASSESSMENTS

1. Body mass index [BMI]: incidence of difficult intubation ranges between

13-24% in obese patients.

2. Neck circumference: obese patients with neck circumference > 50 cm had a greater

chance of problematic intubations than those < 50 cm. 3. Length of neck

short neck [actual length not defined] is associated with a 5-fold increase in difficult airway.

4. Anterior neck soft tissue: a) superior predictor of difficult intubation in obese patients than obesity per se or a thick neck.

• B) obtained by ultrasound quantification of soft tissue at the level of the 1. vocal cords

2. thyroid isthmus and 3. supra-sternal notch.

Averaged value >28 mm predicts difficult laryngoscopy

AIRWAY EXAMINATION

• Atlanto-occipital joint extension, • Mallampati classification,• 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.

InvestigationsRoutine Tests

1. Hematological work-up2. ECG3. Chest X-ray4. Blood Glucose5. Lipid Profile6. Liver Function Tests7. S. Creatinine

Special Investigations• Sleep Studies• Cardiac Stress Test• Echocardiography• Radionucleotide ventriculography• PFT, Spirometry• ABG• Thyroid Function Tests

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 (0.4 mg), an anticholinergic used to dry the upper airway,

1. Continue antihypertensive medication [ACE Inhibitors?].

2. Start prophylactic Antibiotic for wound infection3. Heparin prophylaxis against DVT4. H2 receptor antagonist [proton pump inhibitor].5. Anti-aspiration prophylaxis

Metoclopramide to increase gastric emptying, and non particulate antacids

Highly lipophilic drugs have increased volume of distribution (VD)

• doses acc. to patient's total body weight (TBW).

• Examples are thiopental, propofol, BZD, fentanyl, dexmedetomidine, succinylcholine, atracurium

Weakly lipophilic or lipophobic drugs have unchanged VD.

• Doses acc. to patient's lean body weight (LBW), LBW = IBW + 20% to 40% IBW.

• Examples of this group are ketamine, vecuronium, rocuronium , remifentyl ( lipophilic)

Pre-emptive analgesia:

with medications that do not cause respiratoryDepression.

• NMDA (N-methyl-D-aspartate) antagonists• alpha-2-receptor agonists• NSAIDs (non-steroidal anti-inflammatory drugs)• GABA – like compounds

Monitoring

• Pulse oximetry, • Electrocardiogram,• Noninvasive blood pressure, • End-tidal carbon dioxide, • Temperature, • Hourly urine output • Peripheral nerve stimulator • Bispectral index(BIS )

• Invasive arterial monitoring is used in severe cardiopulmonary disease or poor fit of the non-invasive blood pressure cuff

• Central venous access is typically used when there are difficulties obtaining peripheral access

• pulmonary artery catheter in pulmonary hypertension, cor pulmonale, or LVF

Patient Positioning

• Awake pt. can self-position on OR table.• HELP [Stacked or Ramped] position from

scapula to the head to be arranged.• Padding of all pressure point.• Maintain & pre-oxygenate in head-up

position. • pneumatic leggings or compression

stockings to be applied.

• RAMPING ADVANTAGES: Improves laryngoscopic viewThe gradient for passive regurgitation is reducedThe safe apnea period is increased.

• 25-30 degrees Reverse Trendelenburg position with manual PEEP/NIPPV improves oxygenation

• For HELP placement, the preformed Troop Elevation Pillow may be used in place of folded towels or blankets .

Effect of various positions:• 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

Positioning for Laparoscopic Surgery:• The head-down tilt of 10–20 degrees : increase in central blood volume and a decrease in vital

capacity and diaphragmatic excursion.

• reverse Trendelenburg (rT) position : improved pulmonary dynamics but reduced venous return.

These changes associated with positioning may be influenced by the extent of the tilt, the patient’s age,

PREOXYGENATION

• Obese patients initially be placed in a ramped position and then in the reverse trendelenburg position before preoxygenation.

• Patients are then preoxygenated for 3 to 5 minutes with 100% oxygen under positive pressure 8 to 10 cm H2o

• After induction, maintain 10 to 12 cm H2O PEEP , but care must be taken to treat any hypotension that may occur.

INDUCTION

• In current anesthetic practice propofol is the IV induction agent of choice for obese patients

• Sevoflurane may be considered because of a more consistent and rapid recovery profile. Halothane may be used

• Maintainence with desflurane or sevoflurane

• Nitrous oxide not recommended for maintenance use as it causes intestinal inflation and is emetogenic.

• N2O use is contraindicated with pre existing severe pulmonary hypertension.

• Remifentanil is the intraoperative narcotic of choice because of its rapid onset, consistent profile, and rapid offset

• Dose of succinylcholine is increased [1.2-1.5 mg/kg]. Non-depolarizing relaxants show variability in response hence titrate dose with PNS.

Factors responsible for difficult laryngoscopy & intubation in obese patient?

• Fat face & cheeks.• Large breasts in females.• Limited range of motion of head, neck, & jaw.• Small mouth & a large tongue.• Excessive palatal & pharyngeal tissue.• Short thick [large circumference] neck.• High Mallampati scores [III or IV].• O2 desaturation is more rapid.

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.

• During difficult intubation, nerve blocks may “unprotect” the airway.

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

If the intubating conditions are suboptimal, a noninvasive alternative airway management device is utilized.

LMA fastrach, LMA CTrach

• Bullard Laryngoscope , Polio blade or McCoy laryngoscope ± gum elastic bougie]

• Failed intubation or CVCI management includes Proseal LMA, combitube.

• PLMA

• Combitube

• LMA Classic

• Emergency cricothyrotomy.

Maintenance of anesthesia

• 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), and

• avoid using long acting agents (e.g. morphine, valium, pancuronium)

• Ventilation: Use large tidal volumes 15-20ml/kg ideal body wt. Titrate PEEP to maintain oxygen saturation.

INTRAOPERATIVE OXYGENATION• No effect on increasing TV (Pressure controlled ventilation

with low tidal volumes 6-8ml/kg TBW )• VC and recruitment maneuvers

– Increases oxygenation– Decrease atelectasis– Shortens PACU stay– Less respiratory complications.

• recruitment maneuver consists of --providing escalating levels of PEEP in 5 cm increments upto a maximum airway pressure of 40-42cm H2O, continue for 10 breaths and reduce PEEP back to basal levels.

FLUID MANAGEMENT: • Although the total circulating blood volume is

increased, it is less than normal on a weight basis, since fat contains little water.

• Adequate preoperative hydration and higher intraoperative fluid administration (20-40 ml/kg) reduce postoperative complications

• Blood loss is usually greater.

• Excess adipose tissue may mask peripheral perfusion, making fluid balance difficult to assess.

• Early infusion of colloids and blood products may be necessary because they are less able to compensate for small volumes lost, – but rapid infusion of excessive amounts should be

avoided because pre-existing CCF is common

Pre-requisites for extubation

• Intact neurologic status, fully awake and alert, with head lift greater than 5 s

• Hemodynamic stability

• Normothermia.

• Train-of-four (TOF) reversal by PNS (T4/T1 >0.9). Full reversal of NM blocking agents.

• Respiratory rate (10 - 30/min) • SPO2 >95% onFIO2 0.4• Acceptable ABG (FIO2 of 0.4: pH, 7.35 to 7.45; PaO2, >80 mm

Hg; PaCO2, < 50 mm Hg).• Generating Tidal volume (TV) >5 mL/kg ideal body weight

EXTUBATION

• if no C/I , Reverse Trendelenburg or semi-sitting position,

• Use OPA/ NPA. 2-person mask ventilation on standby.

• If initial difficult airway– extubate over an airway exchange catheter.

• If the pt was on CPAP preoperatively, then arrange for CPAP post-extubation.

Post op complications

• Post-anesthetic hypoxemia• Respiratory depression• Early ventilatory failure with need for reintubation• Positional ventilatory collapse• Hemodynamic instability, • PONV• Venous thromboembolism

Postoperative pain

• Epidural opioids + local anesthetics

• PCA is also a desirable option.

• Parenteral NSAID’s can reduce the dose of narcotics.

• IM injections tend to become SC and demonstrate unpredictable blood levels & effects. IV analgesics are preferred.

• Risk of hypoxemia shall persist for 4-7 days. Supplemental O2 is mandatory in the sitting or semi-recumbent position as & when required. Monitor SpO2.

• Aggressive pulmonary care with incentive spirometry, cough, deep breathing & early ambulation.

• Increased incidence of wound infection• Continue LMWH & leg compression stockings.

Measures to avoid pulmonary complications:

1. Keep pt. in semi-recumbent position (30- 45 degrees).

2. Use humidified gases; Start chest physical therapy (P.T.)early.

3. Nocturnal use of nasal continuous positive airway pressure (CPAP) at 10-15cmH2O, if there is presence of

Obstructive Sleep Apnea.

REGIONAL ANAESTHESIA• Under-utilized (PCA is >90%) in this patient

population• technical difficulties, • increased incidence of epidural failure and catheter

dislodgment, • decreased epidural space form intra-abdominal

pressure causing unpredictable spread of local anaesthetics, variable block level

• For epidural catheter insertion ,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.

Considerations in Obstetrics:

• chronic htn, pregnancy induced htn (preeclampsia) and diabetes (2 to 8fold increase in incidence).

• difficulty in labour, or abnormal labour, induced labour, CS.• fetal macrosomia, with attendant risks and difficulty in delivery.• greater blood loss during c/s, longer surgery postoperative

complications• Increased risk of anaesthesia related maternal

morbidity/mortality during c/s, when compared with non-obese pts.

• Increased risk of fetal morbidity/mortality , fetal distress.

• Cephalad retraction of panniculus in morbidly obese during c/s may lead to hypotension & foetal compromise, as well as maternal difficulty in breathing (secondary to extra weight on the chest).

• Loss of intercostal muscle function during spinal anesthesia may create greater breathing problems in the obese parturient, when compared with the nonobese pt.

• Supine and trendelenburg positions may further decrease FRC, increasing the likelihood of hypoxemia.

• Use of PEEP to increase oxygenation may decrease cardiac output, and possibly compromise uterine blood flow.

• The anesthesiologist’s main concern -to avoid an emergency situation requiring urgent endotracheal intubation.

Epidural anesthesia offers several advantages:

• easily titratable local anesthetic dose and level of anaesthesia,

• ability to extend the block for surgical delivery and prolonged surgery,

• slower and more easily controllable hemodynamic changes,

• decreased potential for excess motor blockade • postoperative analgesia

SUMMARY• Detailed history • Examination• Investigation• Aspiration prophylaxis• Minimal sedation• Positioning • Preoxygenation• Prepare for difficult airway• Follow extubation criteria• Arrange fop CPAP and mechanical ventilation• Adequate pain relief. Pulmonary care and DVT prophylaxis

DIAGNOSIS OF COMORBIDITY & OPTIMIZATION

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