Obesity and Critical Illness

Reviewed and revised 31 December 2015


  • Obesity is the chronic abnormal or excessive accumulation of fat in adipose tissue to the extent that health may be impaired
  • degrees of obesity are defined by body mass index (BMI)


  • morbidly obese patients do not have increased ICU mortality, and although they have longer hospital stays they have better in-hospital mortality rates
  • a modestly increased BMI actually confers a survival advantage to the individual
  • this is probably because the benefit of excess adipose tissue (which acts as a reservoir for energy, hormones, and anti-inflammatory mediators) exceeds the negative physiologic consequences of obesity
  • This probably does not hold true once BMI is > 40 kg/m2 (class III obesity)


BMI = weight (kg) divided by (height (m))2

BMI Prime = actual BMI / normal BMI

CategoryBMI range – kg/m2BMI Prime
Very severely underweightless than 15less than 0.60
Severely underweightfrom 15.0 to 16.0from 0.60 to 0.64
Underweightfrom 16.0 to 18.5from 0.64 to 0.74
Normal (healthy weight)from 18.5 to 25from 0.74 to 1.0
Overweightfrom 25 to 30from 1.0 to 1.2
Obese Class I (Moderately obese)from 30 to 35from 1.2 to 1.4
Obese Class II (Severely obese)from 35 to 40from 1.4 to 1.5
Obese Class III (Very severely obese)over 40over 1.5


  • Males = 50kg + 0.9kg for each cm > 150cm in height
  • Females = 45 kg + 0.9kg for each cm > 150cm in height


  • Males = height – 100
  • Females = height – 110



  • recent weight loss or gain
  • impact of size on ADLs
  • co-morbid conditions
    -> OSA, HT, IHD, DM, hyperlipadaemia, cardiomyopathy, CVA, PVD, OA, gall stones, asthma, GORD, cor pulmonale, RHF, hypothryoidism


  • BMI
  • increased risk of difficult intubation and ventilation – risk factors:
    • 1. neck circumference >40cm
    • 2. large tongue
    • 3. palatal, pharyngeal and upper thoracic fat pads
    • 4. decreased atlanto-axial motion -> through airway assessment and previous anaesthetic history review
  • CVS: BP, RVH and pulmonary hypertension
  • RESP: quiet
  • ABDO: scars, subcutaneous gastric band reservoir



  • SpO2 on RA
  • ABG: looking for hypoxaemia and chronic CO2 retention
  • ECG: LVH, right heart strain, RAD, arrhythmias


  • UEC (renal impairment)
  • FBC (polycythemia)
  • LFTs (NASH, biliary disease)


  • ECHO: pulmonary hypertension or ventricular dysfunction important
  • CXR: cardiomegaly or stigmata of LVF

Special tests

  • Spiromertry: obstructive lung disease
  • Sleep study: if OSA suspected


Acute management problems

  • negative attitudes to obesity
  • transport and positioning
  • difficult procedures: IV access, intercostal catheter insertion, difficult intubation, neuraxial blocks, surgery
  • monitoring problems
  • difficult airway maintenance
  • impaired ventilation
  • disordered gas exchange
  • altered pharmacokinetics
  • haemodynamic instability
  • aspiration risk


  • ensure adequate starving times and use of antacids, prokinetics
  • assess for AFOI
  • discussion about risks of anaesthesia and surgery -> increased risk with maintaining ventilation, securing airway, cardiovascular risks; heart failure, MI, post-operative analgesia (epidural, rectus sheath catheters, PCA) need for HDU monitoring post operatively, extubation to BIPAP/CPAP, risks of pressure sores.
  • bring home NIV into hospital

Intraoperative issues

  • physical and environmental issues; insure we have an appropriate sized table, and adequate numbers of nursing, anaesthetic and surgical staff and expertise
  • difficult IV access
  • big NIBP cuff or IABP may be required
  • preoxygenation sitting up (shown to increase time from apoea to desaturation) – rapid desaturation once apnoeic because of decreased FRC and increased O2 requirement
  • use apneic oxygenation
  • secure airway using AFOI via mouth (topicalise airway using lignocaine 10% spray, co-phenylcaine spray, 3mL of lignocaine 4% to via cricothyroid puncture)
  • if performing laryngoscopy – have an assistant displace breast tissue downwards
  • IV induction agent (increased dose because of greater Vd) and relaxant (same Vd for NDNMBD)
  • BIS monitoring
  • maintenance using remifentanil (start at 0.1mcg/kg/min) and desflurane
  • ventilate using controlled ventilation and PEEP (these patients won’t tolerate SV)
  • protect pressure areas
  • position to avoid aorto-caval compression (left tilt)
  • of using epidural use 75% of normal dose c/o engorged epidural veins and fat decreasing volume of epidural space.

ICU care

  • risk of CVS complications -> invasive monitoring
  • extubate sitting (be prepared to reintubate)
  • thromboprophylaxis important (2 x risk of VTE)
  • mobilize early
  • humidified O2, chest physio -> decreased atelectasis
  • HDU or ICU care
  • use of BIPAP or CPAP
  • good analgesia

Ventilation Strategy

  • suction secretions
  • sit up
  • high PEEP (weight/10 as a guide)
  • volume or pressure mode
  • prolonged inspiratory time -> 1:1 to 1:2 (if not gas trapping)
  • plateau pressure < 35cmH2O
  • may require high FiO2
  • may require paralysis (permissive hypercapnoea)
  • chest physio
  • aim for SpO2 > 90%
  • review CXR


References and Links


Journal articles

  • 2013 AHA/ACC/TOS guideline for the management of overweight and obesity in adults. A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and The Obesity Society. Obesity 2013; [Free Full Text]
  • Bajwa SJ, Sehgal V, Bajwa SK. Clinical and critical care concerns in severely ill obese patient. Indian J Endocrinol Metab. 2012 Sep;16(5):740-8. PMC3475897.
  • Brown CV, Velmahos GC. The consequences of obesity on trauma, emergency surgery, and surgical critical care. World J Emerg Surg. 2006 Sep 6;1:27. PMC1586188.
  • Falagas ME, Kompoti M. Obesity and infection. Lancet Infect Dis. 2006 Jul;6(7):438-46. PMID: 16790384.
  • Hogue CW Jr, Stearns JD, Colantuoni E, Robinson KA, Stierer T, Mitter N, Pronovost PJ, Needham DM. The impact of obesity on outcomes after critical illness: a meta-analysis. Intensive Care Med. 2009 Jul;35(7):1152-70. PMID: 19189078.
  • Karmali S, Johnson Stoklossa C, Sharma A, Stadnyk J, Christiansen S, Cottreau D, Birch DW. Bariatric surgery: a primer. Can Fam Physician. 2010 Sep;56(9):873-9. PMC2939109.
  • Malhotra A, Hillman D. Obesity and the lung: 3. Obesity, respiration and intensive care. Thorax. 2008 Oct;63(10):925-31. PMC2711075.
  • Modica MJ, Kanal KM, Gunn ML. The obese emergency patient: imaging challenges and solutions. Radiographics. 2011 May-Jun;31(3):811-23. PMID: 21571658. [Free Fulltext]
  • Mokhlesi B, Kryger MH, Grunstein RR. Assessment and management of patients with obesity hypoventilation syndrome. Proc Am Thorac Soc. 2008 Feb 15;5(2):218-25. PMC2645254.
  • Nightingale CE et al. Peri-operative management of the obese surgical patient 2015. Anaesthesia 2015. PMID 25950621
  • Pickkers P, de Keizer N, Dusseljee J, Weerheijm D, van der Hoeven JG, Peek N. Body mass index is associated with hospital mortality in critically ill patients: an observational cohort study. Crit Care Med. 2013 Aug;41(8):1878-83. PMID: 23685638.

FOAM and web resources

CCC 700 6

Critical Care


Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of three amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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