Question 6

With respect to the multi-trauma patient with morbid obesity:

a) Outline how the pattern of traumatic injury differs in the morbidly obese from patients with normal body habitus.

b) List the additional factors, occurring as a consequence of the patient's obesity, that need to be considered during the initial assessment.

c) List the pros and cons of focussed assessment with sonography in trauma (FAST) in the assessment of the obese multi-trauma patient.

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College Answer

 Lower injury severity scores overall.
 More severe extremity injuries.
 More thoracic injury.
 Less brain injury – controversial.
 Longer extraction time may make for higher risk for crush injury.

 Increased risk of partial airway obstruction when lying flat.
 Possibility of difficult intubation and difficult bag mask ventilation (cervical collar, neutral position, pre-existing signs of airway obstruction, possible sleep apnoea syndrome).

 Increased difficulty inserting chest drains.
 Possible obesity hypoventilation syndrome.
 Increased risk of atelectasis.

 Need for appropriately sized BP cuff.
 IV access more difficult so consider early inter-osseous access.

 Caution with analgesia.
 Clinical signs, e.g. pneumothorax, difficult to detect by palpation and auscultation.
 Log rolling requires additional assistants.

 Bedside investigation avoids transfer to CT scanner.
 Technically challenging with difficulty achieving adequate beam penetration and image quality.
 FAST is less sensitive than in non-obese.
 False positive pericardial collections are more common in the obese.


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.


Bochicchio, Grant V., et al. "Impact of obesity in the critically ill trauma patient: a prospective study." Journal of the American College of Surgeons 203.4 (2006): 533-538.

Diaz Jr, Jose J., et al. "Morbid obesity is not a risk factor for mortality in critically ill trauma patients." Journal of Trauma and Acute Care Surgery 66.1 (2009): 226-231.

Lambert, David M., Simon Marceau, and R. Armour Forse. "Intra-abdominal pressure in the morbidly obese." Obesity surgery 15.9 (2005): 1225-1232.

Boulanger, Bernard R., et al. "Body habitus as a predictor of injury pattern after blunt trauma." Journal of Trauma and Acute Care Surgery 33.2 (1992): 228-232.

Dhungel, Vinayak, et al. "Obesity delays functional recovery in trauma patients." journal of surgical research 193.1 (2015): 415-420.

Ciesla, David J., et al. "Obesity increases risk of organ failure after severe trauma." Journal of the American College of Surgeons 203.4 (2006): 539-545.

Arbabi, Saman, et al. "The cushion effect." Journal of Trauma and Acute Care Surgery 54.6 (2003): 1090-1093.

Evans, David C., et al. "Obesity in trauma patients: correlations of body mass index with outcomes, injury patterns, and complications." The American surgeon 77.8 (2011): 1003-1008.

Fuchs, I., et al. "Vascular Injury in Obese Patients after Ultra-Low-Velocity Trauma." J Anesth Clin Res 5.488 (2014): 2.