A 180cm, 200kg man presents to ICU following emergency cholecystectomy.  How does his obesity affect his physiology and how may it influence his ICU management?

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College Answer

a)         Obesity affects the physiology of several systems:

Cardiovascular- there is increased left and right ventricular stroke work with a tendency to left ventricular hypertrophy.

Hypertension is significantly correlated with obesity

Respiratory- total respiratory compliance is reduced by decreased chest wall compliance with fat accumulation subcutaneously and intraabdominally. There is a reduction in FRC caused by

reduced ERC. If FRC is less than closing capacity, hypoxia may ensue.

b)         Obesity influences his ICU management via:

1)   interference with normal physiology (as above)

2)   coexisting  medical  problems  (hypertension,  ischaemic  heart  disease,  diabetes,  sleep apnoea, pulmonary hypertension)

3)   technical difficulties with

-intravenous access

-intubation

-     monitoring devices (eg NIBP cuffs)

-     bed size (nerve compression)

4) difficulty mobilising

-     DVT

-     Pressure areas

Discussion

Paul Marik has published an excellent review of this in 1998.

Since the late 1990s, obesity has remained obesity, and so I think this article is still very relevant.

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.

References

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.