Question 8

Outline how the pathophysiological changes associated with morbid obesity may impact on the management of critically ill obese patients.

[Click here to toggle visibility of the answers]

College answer

Anatomical problems:

  • Weight
    • Too heavy for certain investigations e.g. CT
    • Difficulty in establishing non-invasive monitoring such as ECG and NIBP o Too large for many ICU beds leading to discomfort o Difficult to mobilise and move around between beds-chair
    • Difficult to deliver cares due to inability to access areas required, and requiring multiple staff to do so 
  • Excess adipose tissue o Difficult venous and arterial access: establishing, securing, and suitable equipment

Increased risk of complications of vascular access o Difficult epidural access o Difficult to clinically examine o Invasive procedures e.g. chest drains more difficult.

  • Metabolic and endocrine o Altered body composition leading to different catabolism in the critically ill, and different nutritional requirements
    • Altered response to endogenous hormones in the critically ill 
    • Altered inflammatory response “Chronic inflammatory state” making interpretation of biomarkers of infection difficult
    • Increased incidence of crystal arthropathy which is often difficult to diagnose because of size
    • Insulin resistance, hyperglycaemia


  • Prone to atelectasis due to abdominal mass
  • More difficult to ventilate due to higher airway pressures with obesity acting like a restrictive lung deficit
  • Increased incidence of central and peripheral sleep apnea increasing the difficulty of ventilator weaning and extubation


  • Hypertension making BP responses more variable to sedation and catacholamines, and increasing risk of CVA’s
  • Coronary artery disease leading to potential episodes of myocardial ischaemia and arrhythmias
  • Peripheral vascular disease leading to skins changes and ulceration, with greater propensity for pressure sores and difficulties with skin integrity
  • VTE


  • Difficult bag-mask ventilation due to excess facial tissue
  • Difficult laryngoscopy 


  • Greater incidence of arthritis and bony pain
  • Increased incidence of soft tissue infections


  • Pharmaceutics o Actual weight different from ideal body weight making drug dose calculation more


  • Pharmacokinetics o Altered absorption of drugs through the sc / topical route due to altered blood flow o Altered distribution of drugs due to altered plasma proteins and fat solubility / distribution

o Altered metabolism of drugs due to impaired hepatic function o Altered excretion of drugs due to impaired renal function

  • Pharmacodynamics o Larger doses of medications often needed increasing potential for exaggerated sideeffects and toxicity 

Emotional and environment

  • Increase incidence of depression and mood disorders affecting interaction in the

critically ill

  • Prejudice and stigma of staff towards the difficulty of looking after morbidly obese patients


This question closely resembles Question 10 from the first paper of 2001. The answer to that question is reproduced here to simplify revision.

The physiological effects of obesity (as relevant to critical illness)

Airway problems

  • Difficult intubation
  • Difficult tracheostomy
  • Difficult tracheostomy care

Respiratory effects

  • Expiratory reserve volume is decreased
  • FEV1 to FVC ratio is increased.
  • VC, TLC and FRC are decreased.
  • Work of breathing is increased
  • CO2 production is increased, thus ventilatory needs are greater
  • Increased risk of aspiration pneumonia
  • Increased risk of DVT and PE

Cardiovascular effects

  • Cardiac output is increased
  • Total blood volume is increased
  • LV contractility is impaired
  • LV size and wall thickness are increased
  • Hypertension is common
  • LV diastolic pressure is increased, and fluid loading is poorly tolerated

Pharmacokinetic effects

  • Volume of distribution is increased for many lipophilic drugs
  • Hepatic clearance may be reduced
  • Renal clearance may be impaired, but this may not be predicted by standard creatinine clearance formulae.

Nutritional effects

  • Increased requirement for dietary protein, given the tendency to mobilise protein instead of fat during a stress repsonse: currently, recommendation is for 1.5-2g/kg of IBW per day

Access problems

  • Vascular access is difficult
  • Cleaning CVC sites may be problematic

Monitoring issues

  • NIBP cuffs do not fit.

Radiology problems

  • Chest Xrays may be of poor quality
  • These patients cannot fit into CT or MRI scanners.


Akinnusi, Morohunfolu E., Lilibeth A. Pineda, and Ali A. El Solh. "Effect of obesity on intensive care morbidity and mortality: A meta-analysis*." Critical care medicine 36.1 (2008): 151-158.

Marik, Paul, and Joseph Varon. "The obese patient in the ICU." CHEST Journal113.2 (1998): 492-498.

Ling, Pei-Ra. "Obesity Paradoxes—Further Research Is Needed!*." Critical care medicine 41.1 (2013): 368-369.