Obesity

 

GUIDELINES | SOBA UK

 

Disease:

Classification

BMI:

·     Class 1: >30

·     Class 2: >35

·     Class 3: >40

Others:

·     Neck circ: >43cm male, >41cm female – important for breathing

·     Waist circ: >102cm male, >83cm female – important for metabolic

·     Body fat %

Weight types

·     Total = measured

·     Ideal = (height – 100) if male, (height – 105) if female

·     Lean = fancy equations, limit 100kg if male, 70kg if female

·     Adjusted = ideal + 40% of excess

Main problems

1.      Obesity itself

o  Difficult airway

o  Difficult IV access

o  Difficult drug dosing

o  Difficult monitoring

o  Difficult positioning

o  Difficult surgery

2.      Sleep-disordered breathing

o  Beware if undiagnosed/untreated

o  Main risks: post-op airway disaster, pulmonary hypertension

3.      Metabolic syndrome:

o  Inflammatory / endocrine / immune / coagulation

o  Features: obesity, dyslipidaemia, hypertension, hyperglycaemia

o  Main risks: AMI, VTE, SSI

 

Complications:

Cardiovascular

Obesity:

·     High cardiac output (risk of awareness, drug accumulation)

·     Conduction disease – AF, SCD

·     Cardiomyopathy

Inflammation:

·     Hypertension

·     Concentric LVH

·     Ischaemic heart disease

·     Stroke

Sleep-disordered breathing:

·     Pulmonary hypertension

·     Cor pulmonale

Respiratory

·     Sleep-disordered breathing

·     Oxygenation: ↓FRC -> small airway closure -> shunt

->Rapid desaturation

·     Ventilation: ↓compliance

->Poor tolerance of supine and Trendelenburg position

Other relevant

·     T2DM

·     GORD

·     NAFLD

 

Drug dosing:

Total

·     Sux (↑PChE)

·     LMWH

Adjusted

·     Sugammadex

·     Neostigmine

·     Antibiotics

·     Propofol infusion

Lean

·     Everything else

 

Preparation issues:

Monitoring

·     Forearm NIBP:

o  Overestimates - accurate ±10mmHg if SBP <140

o  Monitor trend

·     A-line: low threshold for use

·     BIS: for drug accumulation vs awareness

·     NMT: for immobility with minimal opioid + safe extubation

Access

·     Ultrasound guidance by default

·     PIVC: long

·     A-line: long, low threshold for use

·     CVC: low threshold for use (consider post-op blood tests)

Positioning

·     Many hands

·     Big table

·     Hovermat

·     Oxford ramp

·     Armboards/straps/pads

*Beware nerve injury in the obese*

 

Induction issues:

Airway difficulty

Problems:

·     ↓Cavity

·     ↓Positioning

·     ↓Time

Main things:

·     Consider: awake intubation

·     Planning: A, B, C, D

·     Assistance: nurse + anaesthetist/trainee

Aspiration

Problems:

·     ↑Intra-abdominal pressure (mechanical pressure)

·     ↓Emptying (? T2DM -> gastroparesis)

·     ↑Volume (large meals)

·     Sphincter incompetence (GORD, hiatus hernia)

·     Insufflation (difficult bag-mask ventilation)

Mitigation:

·     Secure: always intubate

·     ↓Food: light meal, 6h fast, prokinetic

·     ↓Air: two hands + guedel + low pressure

·     ↓Acid: H2A, PPI, sodibic

·     ↓Time: mRSI

Awareness

Problem:

·     ↑Cardiac output -> ↑distribution

·     ↑Difficulty -> ↑delay

Mitigation:

·     Propofol TCI vs turn on vapouriser early

·     Fast relaxant (1.2mg/kg roc)

·     Fast opioid (20mcg/kg IBW alf)

 

Induction plan:

Goals

·     No CICO

·     No aspiration

·     No awareness

Position

·     Oxford ramp + head cushion

·     Aim: semi-recumbent, tragus level with sternal angle, sniffing

·     Benefits: axis alignment, patency, ↑FRC, ↑compliance

·     Alternatives: jack knife table, pillows & blankets

Oxygenation

·     Before: face mask etO2 >90%, SpO2 >92% 3 mins

·     During: HFNP

Drugs

·     Alfentanil 20mcg/kg LBW

·     Propofol 2mg/kg LBW + re-dose 1mg/kg if delay

·     Rocuronium 1.2mg/kg LBW

·     Metaraminol 5mcg/kg/h LBW

·     Sugammadex 16mg/kg ABW available

Procedures

1.    Bag-mask ventilation: two hands + guedel

2.    Intubation: VL + hyperangulated + ETT + stylet

3.    LMA backup: iGel 4 and 5

4.    FONA backup: big midline incision + bougie + 6.0 ETT

 

Emergence/post-op issues:

Extubation

·      Transfer onto bed

·      Same position as induction

·      Recruitment

·      Pre-oxygenation

·      Pull tube after inspiration

·      Straight onto CPAP 10cmH2O

*Beware extubation disaster – common in closed claims*

Observation

Risk factors for disaster:

·      Patient: OSA severe/untreated, abnormal airway, comorbidities

·      Anaesthetic: GA, post-op opioid +++

·      Surgery: affects airway

·      Post-op care: CPAP forbidden, supine position

Options:

·      Low risk: regular ward bed

·      Medium risk: regular ward bed + continuous oximetry

·      High risk: HDU

Analgesia

Prefer:

·      Regional

·      Paracetamol

·      COX2i

·      Clonidine

·      Atypical opioid

·      Ketamine

·      Lignocaine

Avoid:

·      Pure opioid

·      Long-acting opioid

·      Benzo

Thromboprophylaxis

·     Early mobilization

·     Calf compressors – correct size

·     Anticoag – correct dose (e.g. 100-150kg -> enoxaparin 40mg bd)

 

 

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