The morbidly obese trauma patient

Morbid obesity complicates trauma by interfering with airway assessment and management, by making ventilation more difficult, by obscuring positive clinical findings, by frustrating imaging, and by interfering with surgical access. Morbidly obese patients have injuries which are usually less severe than the injuries of a lighter person from a similar vehicle accident, but their limb injuries are usually worse, and they are more likely to have thoracic injuries.

Question 6 from the first paper of 2014 asked specific details about the management of the morbidly obese trauma patient. There have not been any previous questions of this sort. The pass rate was 51%. The next time this appeared was Question 20 from the first paper of 2021. 

A discussion of the various general problems with managing a morbidly obese patient in the ICU will not take place here. Trauma will be the focus.

Change in the pattern of injuries associated with morbid obesity

• Injury scores are lower in obese patients (Arbabi et al, 2003)
• Pattern of blunt trauma is different (Boulanger et al, 1992)
  • Injuries that are more likely:
    • pulmonary contusion
    • rib fractures
    • pelvic injuries
    • kneedislocations (Fuchs et al, 2014)
    • extremity fractures
    • proximal upper extremities seem to get it worst (Evans et al, 2011)
  • Injuries that are less likely:
    • head injuries
    • liver injuries
• "Obese people injured in vehicular crashes had a similar injury pattern with no difference in seating position, direction of impact, seat belt use, and ejection."

Influence of morbid obesity on the primary and secondary survey

1. - Difficult airway; difficult bag-mask ventilation more likely than actual difficult intubation.
   - Short handle may be required for direct laryngoscopy; most people would just resort to the videolaryngoscope.
   - When intubating, the FRC is small and the patient will become hypoxic rapidly, which means fewer attempts will be possible.
   - Increased risk of obstruction, even when awake
   - When obtunded, a virtual certainty of obstruction
    
2. - Poor chest wall compliance
   - Increased risk of atelectasis
   - Obesity hypoventilation syndrome
   - Difficult access for chest drains
   - Difficult windows for trauma TTE
   - Difficult auscultation and percussion, eg. for pneumothorax
   - Increased aspiration risk
    
3. - Difficulty measuring accurate blood pressure (need for appropriate size cuff)
   - Realistic possibility that no cuff will be appropriate and arterial access may be required
   - Difficult IV access- CVC as well as PIVC; the college answer recommends to go straight for the intraosseous needle
   - Intraosseous access is hardly fool-proof and can also be frustrated by obesity, considering especially the likelihood of there being bilateral knee prostheses
   - Possibility of pulmonary hypertension, cor pulmonale or CCF makes haemodynamic management more complex
    
4. - Likely, CO₂ retention and narcosis (influences doses of induction drugs)
   - Medullary sensitivity to CO₂ will be even more reduced by opiates
   - Some sort of syndromic condition may complicate neurological assessment (eg. Prader Willi syndrome)
    
5. - Log rolling will require additional assistants, or some sort of unusual equipment.

Influence of morbid obesity of FAST assessment

• Morbid obesity is one of the limitations of FAST
• Difficult insonation of the appropriate spaces; image quality is likely to be poor
• Pericardial fat can be misinterpreted as clotted blood
• Perinephric fat may be misinterpreted as intraperitoneal free fluid
• The advantage is, if you can't fit into the CT scanner this is all you've got.

Influence of morbid obesity on imaging

• MRI may be impossible
• Angiography may be impossible (table weight tolerance may be exceeded)
• CT may also be impossible
  • If CT is possible, the degradation of the image by artifact may render more difficult the interpretation of fine detail, eg. aortic intimal tears or abdominal visceral injuries
• X-rays (actually, any imaging requiring ionising radiation) will require an increased dose per image. Given the prolonged ICU stay, the total dose may be considerable.

Influence of morbid obesity on ICU management of severe trauma

• Rhabdomyolysis is more likely, due to longer extraction times and therefore longer crush injury, greater pressure etc
• Intra-abdominal pressure will appear to be high (Lambert et al, 2005) - on average 12 cmH₂O, as oppose to 0 in skinny controls. This is a direct pressure effect of visceral obesity and is not a "true" abdominal compartment syndrome.
• Nutritional requirements will be unusual:  hypocaloric high-protein feeding is recommended, where you supply 60-70% of energy requirements, and oversupply protein (2.0-2.5g/kg of ideal body weight)
• Pharmacokinetics of drugs will be altered: more on this elsewhere. Specifically, this influences the effectiveness of thromboprophylaxis in trauma
• Obesity increases the risk of multi organ system failure (OR = 1.8), possibly owing to the chronic inflammatory state of obesity ( Ciesla et al, 2006)
• Special lifting and bed equipment will be required

Influence of morbid obesity on recovery from trauma

• Twice as likely to get a bloodstream, respiratory or urinary tract infection while in hospital (Bochicchio et al, 2006)
• Length of ICU stay is increased (almost doubled in some studies)
• For every unit increase in BMI, the functional recovery rate was reduced by 4% as measured by Functional Independence Measurement (FIM) scores (Dhungel et al, 2015). Delay in recovery from trauma is directly influenced by the severity of obesity.

Influence of morbid obesity on outcomes from trauma

• Controlling for other variables, morbidly obese trauma patients were 7.1 times more likely to die in hospital accoding to Bochicchio et al (2006)- the most common reason for death being sepsis. Weirdly, Jose Diaz et al found something comepletely different in 2009. In the latter audit morbid obesity was not an independent risk factor of trauma mortality, but hyperglycaemia somehow was. Then, hilariously, Evans et al (2011) found that underweight trauma patients had the increased mortality, and the obese population did really well. In short, nobody knows what the hell is going on.