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?
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
- monitoring devices (eg NIBP cuffs)
- bed size (nerve compression)
4) difficulty mobilising
- Pressure areas
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)
- Difficult intubation
- Difficult tracheostomy
- Difficult tracheostomy care
- 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
- 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
- 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.
- 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
- Vascular access is difficult
- Cleaning CVC sites may be problematic
- NIBP cuffs do not fit.
- 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.