Anaesthesia and Morbid Obesity

By Dr Melinda Bradshaw

• Case Presentation – Emergency laparotomy in a morbidly obese patient.

• Discussion of anaesthetic issues in morbid obesity.

Case Presentation

Presenting Complaint:• 43yo male, estimated weight >170kg.• Presented to ED yesterday with 5 hours of epigastric

pain and one vomit.• Initial investigations unremarkable – WCC 13.2, mild

neutrophilia

• Initial diagnosis - acute gastritis?• Pain unrelieved by mylanta, xylocaine viscous, somac,

laxatives and IV morphine

• Overnight becomes febrile, tachycardic, hypotensive and hypoxic

• Morning examination – LIF mass with tenderness and guarding, ? irreducible hernia

• AXR reviewed – dilated loops of SB with air fluid levels. ?LIH.

• CT adomen/pelvis – incarcerated LIH and free gas in abdomen.

• Surgical review – emergency laparotomy

Past Medical History

• Morbid obesity• Heartburn and GORD

Anaesthetic History• Appendicectomy – awake fibreoptic intubation, grade 4

Drug History

• Occasional mylanta• NKDA• Smoker – 15-20 cigarettes/day

Examination

• Airway - MP 4, full dentition, short fat neck• T38, PR 130, BP 90/60 (↓180/105)

• RR 32, O2sats 96% on 6L O2 HM

1 hour previously 89%RA (↓ 98%RA)• JVPNE, dual heart sounds, nil murmurs• Lungs – difficult to hear

Investigations and Results

• FBE – Hb 166, WCC 7.2 (↓ 15.5)• UEC – 142/5.1/104/27/16/6.0/0.15 (initial urea 4.1, Cr

0.07)• LFT and clotting – normal.

• VBG – pH 7.41, pCO2 34, lactate – 3.8

• ECG – SR, LAD, LAHB• CXR – AP, chest clear

Management

• Organised to use theatre 2 instead of theatre 5.• Difficult intubation trolley• Awake patient transfer onto ambulance trolley with

hoover matt• Positioning – sitting up

• Premed - nebulised 5mL 4% lignocaine• Peripheral IV access – 16g and 18g• Initial monitoring – ECG and capnography• Awake NGT insertion and suction

• Awake direct laryngoscopy with cophenylcaine spray, grade 1 view

• RSI with fentanyl 50mg, propofol 200mg and suxamethonium 200mg.

• Oxygen/air and desflurane• Transferred to operating table intubated• Metaraminol and radial arterial line insertion• Bis monitor

• SpO2 trace – 99% saturated on FiO2 41%

Surgical findings

• Large incisional hernia, 40cm necrotic ileum, perforated ileum and peritoneal soiling.

• Ileal resection and side to side anastamosis.• Operation duration 1Hr 45mins.

Anaesthetic Summary

• ABG’s – pH 7.25, PO2 72, pCO2 51 (ETCO2 38), Bic 22, BE -6, Lactate 4.4

• Total atracurium 100mg, fentanyl 100mg, morphine 15mg, metaraminol 5mg

• Fluid resuscitation – CSL 4L, gelofusine 500mL• Tachycardic >100, systolic BP maintained 100-

120mmHg• Transferred to ICU post-op

Outcome

• NA infusion for 24hrs• Ventilated in ICU for 48 hrs on morphine and midazolam

infusions• Discharged from ICU after 2.5 days• Post op analgesia – morphine PCA, tramadol and

paracetamol.

• Post op wound infection with MRSA• Discharged from hospital after 3 weeks

Discussion

• Definition of obesity• Epidemiology• Aetiology• Clinical manifestations relevant to anaesthesia

• Preoperative Management• Perioperative Management• Postoperative Management

Definition of Obesity

BMI = Weight(kg)/Height2(m)

WHO Classification:• Normal 18.5 – 24.9• Overweight 25 - 29.9

• Obese Class 1 30 – 34.9• Obese Class 2 35 – 39.9• Obese Class 3 > 40 (Morbid obesity)• Useful measure of prevalence• Correlates with risk of co-morbidities

• Limitation - heavily muscled individuals are classified as overweight.

Excess abdominal or visceral fat• Women - waist circumference > 88cm• Men - waist circumference > 102cm• Higher risk of morbidity and mortality• Cardiovascular risk factor even if BMI in normal range

Epidemiology

OBESITY (BMI >30)World wide:• 7% of adultsUSA:• 27% of adults• 11% of children between 6-17 years of age are obese

(BMI >95th percentile)Australia:• Prevalence has more than doubled in past 20 years.• 34.1% of women, 26.8% of men.(Anaesthesia 2005)

Aetiology

• Genetic predisposition• Obesity inversely proportional to SES• Medical Disorders – Cushing’s disease, hypothyroidism,

corticosteroids, antidepressants, antihistamines• Alcohol

• Energy balance

Clinical Manifestations

Relevant to anaesthesia:• Respiratory• Cardiovascular – 37% of morbidly obese• Haematological

• Gastrointestinal• Immunological

Respiratory

• Obstructive sleep apnoea• Restrictive lung disease• Obesity hypoventilation syndrome• Respiratory failure

Obstructive Sleep Apnoea

Incidence• 5% in obese patients• Morbidly obese - 25% of women and 40% of men.Associations• Increased perioperative complications• Mallampati class 3 or 4, hypognathia and short

thyromental distanceSymptoms• Frequent episodes of apnoea or hypopnoea during sleep• Snoring, silence then gasping/choking• Daytime somnolence

Physiological changes• Hypoxaemia and hypercapnia• Activation of sympathetic NS → systemic hypertension

→ AMI, CVA, LV failure• Pulmonary vasocontriction → Pulmonary hypertension

→ RV hypertrophy and RV failure• Secondary polycythaemiaDiagnosis• Polysomnography in sleep laboratory

Restrictive lung disease

Respiratory compliance can be reduced by up to 30%• Mainly due to decreased lung compliance• Modest decrease in chest wall complianceIncreased work of breathing by up to 30%• Increased mechanical pressure from chest/abdomen• Decreased respiratory compliance• Increased metabolic demands of respiratory musclesRespiratory muscle inefficiencyDecreased maximum ventilatory capacitoryShallow, rapid breathing patternRelative hypoventilation when metabolic demands increase

Obesity Hypoventilation Syndrome

• Complication of long term OSA• Desensitization of respiratory centres to hypercapnia• Nocturnal central apnoeic events• Type 2 respiratory failure• Pickwickian syndrome – obesity, hypersomnolence,

hypoxia, hypercapnia, RV failure and polycythaemia• Increased airway resistance by up to 650%• FEV1 and max expiratory flow rate are decreased by

40%

Cardiovascular

• IHD• Ischaemic CVA• Arrhythmias• Obesity Induced Cardiomyopathy

• Cardiac Failure

CardiovascularIHD• Increased with central fat distribution• Insulin resistance and Type 2 DM• Hypertension in 50-60% of obese patients• Dyslipidaemia• HypercoagulabilityArrhythmias• Respiratory disease - hypoxaemia and hypercapnia,

OSA• Ischaemia/AMI• Increased circulating catecholamine levels• Myocardial hypertrophy• Fatty infiltration of conducting system

Obesity induced Cardiomyopathy• Increased CO by 0.1L/min/kg of adipose tissue• Increased blood volume by up to 20%• Increase in cardiac output is achieved by ventricular

dilatation and increased stroke volume• Eccentric LV hypertrophy• Decreased LV compliance and diastolic dysfunction• Elevated LVEDP and pulmonary oedema• When capacity to hypertrophy is exceeded, systolic

dysfunction occursCardiac failure• LVF – hypertension, ischaemic/obesity induced

cardiomyopathy• RVF – restrictive lung disease and pulmonary artery

vasoconstriction from persistent hypoxia → pulmonary hypertension

Haematological

• Hypercoagulability – increased fibrinogen, factor VII and factor VIII

• Decreased fibrinolysis – increased plasminogen activator inhibtor-1 levels

• Increased von Willebrand factor and platelet hyperactivity

• Polycythaemia secondary to OSA• Risk of DVT/PE following abdominal surgery is doubled

Gastrointestinal

• Increased incidence of GORD and hiatus hernia• Hyperacidic gastric fluid• 75% greater gastric volume• Increased intraabdominal pressure• Increased risk of aspiration pneumonia

Immunological• Higher rates of wound infection and delayed wound

healing• Poor antibody response to vaccinations

Preoperative Considerations

Preadmission clinic mandatoryHistory/examination• Associated disorders• Distribution of body fat• Dieting and drug treatment for obseity

Drastic dietingAmphetamines (mazindol)Phen-fen (phentermine and fenfluramine)

• Mobility/exercise tolerance• Airway

Preoperative Investigations• Bloods

- FBE for polycythaemia- Blood glucose for DM

• ECG- Often low voltage due to body fat- May underestimate degree of LV hypertrophy- Cor pulmonale – RV hypertrophy, RA deviation, RBBB, P pulmonale

• Echo/stress echo- May be difficult- LV hypertrophy- Systolic and diastolic dysfunction

• CXR• Pulse oximetery – upright and supine

Further investigation if supine O2 sats < 96%

• Respiratory function tests – if smoker or asthma/COPD• ABG – supine and upright• Overnight oximetry• Airway imaging – soft tissue X-rays, CT neck,

direct/indirect laryngoscopy

Optimization

• Fitness for surgery/risk assessment• OSA

- Consider nocturnal CPAP or BiPAP• Treat COPD/asthma• Diabetes - endocrinologist• Weight loss?

Most obesity related problems are potentially reversible with weight loss.Very few patients capable of losing weight.

Anaesthetic PlanRegional• Avoids risks of difficult intubation and aspiration• Safe and effective post operative analgesia• Can be technically very challengingEpidural• Improved postoperative respiratory function compared with opioid

analgesia • Few obese people have epidural space deeper than 8cm• Consider inserting epidural catheters the evening before• Volume of epidural space is decreased by fatty infiltration and

distension of epidural veins.• Local anaesthetic requirements are reduced by 20-25%• Spread of block can be less predictable with variability in block

height• Ultrasound has been used successfully to locate epidural space in

the obese

Spinal• Volume of CSF decreased on MRI in obese parturients• Little evidence in literature to suggest exaggerated spread spinal

block in the obese• Consider using epidural needle to help locate epidural space firstGA• Morbidly obese patients require endotracheal intubation and PPV• Discuss awake intubation• Consider post op ventilation in ICU• Discuss possibility of tracheostomyEpidural and GA• Thoracic and abdominal procedures• Decreased opioid and inhalational anaesthetic requirements• Earlier tracheal extubation• Improved post operative analgesia• Reduced postoperative pulmonary complications

Perioperative Considerations

• Premedication• Positioning and transfers• Monitoring• Airway Management• Ventilation• Pharmacology• Extubation• DVT prophylaxis

Premedication

• Avoid respiratory depressants – opioids, benzodiazepines

• H2 antagonist or proton pump inhibitor and metoclopramide

• DVT prophylaxis – heparin, calf compressors, stockings• Usual medications excluding:

Oral hypoglycaemics

ACEI

Positioning and transfer

• Operating tables designed for 120-140kg• Avoid unnecessary transfer• Special equipment – hoover matts, lifters, trapezes• Positioning for intubation• Pressure care• Supine position - left lateral tilt to avoid IVC compression• Lateral decubitus position can help reduce weight

loading on the chest

Monitoring

Arterial line• Noninvasive BP often unreliable. Overestimates systolic

and diastolic BP.• Cardiovascular comorbidities.• Monitor ABGCVC• Peripheral IV access difficult/impossible• Monitor CVP – especially if cardiac failure• RIJV with assistant to retract soft tissues• Consider portable USNerve Stimulator to monitor neuromuscular blockadeBis/entropy

Airway Management

Difficult mask ventilation• Fat face and cheeks• Upper airway obstruction – excessive palatal and

pharyngeal soft tissue, large tongue, OSA• Reduced pulmonary compliance• Desaturate rapidly after induction despite preoxygenation

– ↓ FRC and ↑ oxygen consumptionDifficult intubation• Incidence in morbidly obese is 13-18%.• Short fat neck and anterior larynx• Decreased mobility of temporomandibular and

atlantooccipital joints• Short distance between mandibular and sternal fat pads

Awake fibreoptic intubation• Most episodes of pulmonary aspiration occur from and

during “coughing” on the ETT• Consider emptying the stomach via NGT and suction

Rapid sequence induction• Insert a roll beneath the scapulas• 2 assistants – second assistant places a hand on the

patient’s chest and retracts the anterior chest wall soft tissues away from the chin

• Be prepared – short handled blade and McCoy laryngoscopes, gum elastic bougie, introducer, equipment for cricothyroidotomy, another experienced anaesthetist

VentilationIncreased demand• Increased oxygen consumption and CO2 production• Metabolic activity of excess fat and increased workload

on supportive tissues• Increased minute ventilationDecreased respiratory compliance and increased work of

breathingDecreased FRC, ERV and TLC• FRC decreases exponentially with increasing BMI• Due to mass loading and splinting of diaphragm• FRC in upright obese patient may be decreased to the

range of closing capacity• Anaesthesia reduces FRC by 50% in obese

Increased V/Q mismatch

Right to left shunt increases by 10-25% in obese when anaesthetised

Managing hypoxaemia:• Avoid lithotomy, prone or Trendelemburg positions• ETT and PPV with high tidal volumes

• May need high FiO2

• Shunt improved by addition of PEEP (but may worsen pulmonary hypertension)

• Avoid nitrous oxide

Pharmacology• Increased volume of distribution

Increased fat volumeIncreased blood volume and cardiac outputAbsolute dose should be increased, even though on a weight for weight basis the dose required will be less

• Elimination half-life of lipophilic drugs may be prolonged, eg. Thiopental, benzodiazepines, highly soluble inhalational anaesthetic agents

• Hepatic clearance is not decreased unless the patient has cardiac failure

• Renal clearance increases in obesity with increased RBF and GFR

• Increased incidence of halothane hepatitis

Recommendations:

• Avoid IM/SC routes as absorption erratic• Use short acting drugs with low lipid solubilities• Lipid soluble drugs – larger initial dose but less frequent

maintenance doses• Remifentanil or alfentanil• Atracurium or mivacurium and• Sevoflurane or desflurane

Postoperative ConsiderationsExtubation:• Awake and in a sitting position – 45 degrees• Oxygen +/- CPAP or BiPAP• Early chest physiotherapyEmergency/major surgery:• Consider ventilation post-op in ICU AnalgesiaAnalgesia• Less analgesic requirements than people with normal

BMI• Avoid excess sedation → hypoventilation and hypoxia• PCA morphine – base dose on IBWDVT prophylaxisMonitor and control BGL’s

ReferencesBooks:• Miller R.D. et al. Miller’s Anaesthesia. 6th Ed. Churchill-Livingstone

2005.• Morgan Jnr G.E., Mikhail M.S., Murray M.J. Clinical

Anaesthesiology. 4th Ed. Lange 2006.Journals:• Saravanakumar K., Rao S.G., Cooper G.M. Obesity and Obstetric

Anaesthesia. AnaesthesiaAnaesthesia 2006; 61: 36-48. • Von Ungern-Sternberg B.S., Regli A., Reber A., Schneider M.C.

Effect of obesity and thoracic epidural analgesia on perioperative spirometry. British Journal of Anaesthesia 2005; 94(1):121-127.

• Panni M.K. and Columb M.O. Obese parturients have lower epidural local anaesthetic requirements for analgesia in labour. British Journal of Anaesthesia 2006; 96(1):106-110

• Adams J.P. and Murphy P.G. Obesity in anaesthesia and intensive care. British Journal of Anaesthesia 2000; 85: 91-108.

Journals:• Ezri T., Gewurtz G., Sessler D.I., Medalion B., Szmuk P., Hagberg

C., Susmallian S. Prediction of difficult laryngoscopy in obese patients by ultrasound quantification of anterior neck soft tissue. Anaesthesia 2003; 58: 1101-1118.

• Coe A.J., Saleh T., Samuel T., Edwards R. The management of patients with morbid obesity in the anaesthetic assessment clinic. Anaesthesia 2004; 59: 570-573.

• Cheah M.H. and Kam P.C.A. Obesity: basic science and medical aspects relevant to anaesthetics. Anaesthesia 2005: 60: 1009-1021.

• Collighan N.T. and Bellamy M.C. Anaesthesia for the obese patient. Current Anaesthesia and Critical Care 2001; 12: 261-266.

• Ogunnaike B. O., Jones S.B., Jones D.B., Provost D., Whitten C.W. Anesthetic considerations for Bariatric Surgery. Anesthesia and Analgesia 2002; 95: 1793-1805.