Question 10

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.

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.