Viva 1

You are called into the resuscitation room in your Emergency Department to assess a trauma patient who has been involved in a high-speed car crash. She appears morbidly obese with an estimated weight of 170kg.

How does the pattern of traumatic injury differ in obese patients?

• 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
  • knee dislocations (Fuchs et al, 2014)
  • extremity fractures
  • proximal upper extremities seem to get it worst (Evans et al, 2011)
• Injuries that are less likely:
  • liver injuries
  • head 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."

The patient's GCS is 7. Her How does morbid obesity influence the airway assessment and management in your primary survey and management?

• 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

The patient is intubated with some difficulty. After intubation, ventilation with the Oxylog 3000 is also difficult, with high peak pressures. What are the differentials for this?

• ETT is in the right main bronchus
• Aspiration (blood, vomit, teeth)
• Pneumothorax 
• Haemothorax
• Pulmonary contusions
• Chest wall is massive and is compressing the lungs
• Increased intraabdominal pressure
• Negative pressure pulmonary oedema after prolonged airway obstruction
• Unrelated matter (eg. asthma excaerbation)

How does morbid obesity influence assessment of the chest in the primary survey?

• 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
   

How is the circulatory assessment different in the morbodily obese patient??

• 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

The emergency physician prepares to perform a FAST scan. How does morbid obesity influence the interpretation of FAST?

• 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

How does morbid obesity influence imaging in trauma?

• 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.

The FAST is negative and the patient is taken for a pan-scan CT. Please interpret this slice:

Among the findings of the abdominal CT, a gravid uterus is seen containing one foetus of approximately 24 weeks gestational age. 

(that image is stolen from Radiopedia.org)

The radiologist is contacting his medical indemnity insurer. What, realistically, is the risk to the foetus? How will you counsel the parents?

• Unless you're imaging the uterus directly, the foetus is exposed only to scatter radiation, and the dose is negligible. In scans which stop more than 30cm from the foetus, the scatter radiation dose is very low (0.001 mGy) and the risk to the foetus is minimal. However, in this case you scanned right through the foetus.
• The mammalian foetus is highly radiosensitive (Streffer et al, 2003)
• Most of our data on this comes from studies of the 1945 atomic bomb survivors from Hiroshima and Nagasaki, a group that included approximately 2800 pregnant women (McCollough et al, 2007). 
• Of these women, 500 received a foetal dose of more than 10 mGy (0.01Gy).
  • In contrast, the normal "background" exposure of a foetus is 0.5 to 1mGy over the total 9 months (Sadro et al, 2013)
• Their problems included intrauterine growth restriction, small head size,  reduced intelligence, organ malformation, and childhood cancer.
• With 10mGy, he risk of childhood cancer is increased by 40% (from 0.14% to 0.2%).
• With 150mGy, a prophylactic abortion needs to be raised as an option if the foetus is under 15 weeks.
• A multi-slice trauma series CT might approach a foetal dose of around 32mGy (Felmlee et al, 1990). That's using old scanners, mind you, taking multiple slices directly through the foetus.
• However, risk vs. benefit of a trauma scan strongly favours the scan, as maternal survival is very strongly linked to foetal survival.

(this is Table 3 from Sadre et al, 2013)

What unique abdominal injuries might you look for in this pregnant trauma patient?

Specific patterns of injury in the pregnant patient

• More common:
  • liver injury
  • spleen injury
  • retroperitoneal hemorrhage
  • uterine injury
• Less common
  • bowel injury

Abdominal trauma

• Blunt injury may cause fetal injury (1%) and premature labour
• Lap belts cause more uterine injury than shoulder belts if the lap belt is incorrectly placed across the uterus rather than the thighs.
• Penetrating trauma to the uterus is usually fatal to the foetus, and benign to the mother because the uterus protects the other organs
• The uterus is intrapelvic until week 12, then it rises into the abdomen.
  • by week 20, its reached the umbilicus
  • at week 34, it reaches the costal margins
• The bowel gets pushed into the upper abdomen – thus, more protected

Uterine and foetal trauma

• Placenta receives 20% of maternal blood flow in late pregnancy
• The placenta is not elastic – shear forces can cause abruptio placentae
• The placental vessels are exquisitely sensitive to vasoconstrictors. The catecholamine excess of haemorrhagic shock tends to rob the foetal circulation.-
  • 80% of pregnant women who survive hemorrhagic shock will lose the baby.
• Occasionally, the uterus will rupture with trauma.
  • It then becomes impossible to palpate the fundus.
  • One can occasionally palpate exposed fetal bodyparts through the abdominal wall.

What are the features of a post-traumatic placental abruption?

• Vaginal bleeding occurs in 70% of cases. A vaginal examination is mandatory.
• Uterine tenderness may be present
• Frequent uterine contractions are complained about
• "Uterine tetany" may occur
• Uterine irritability (contracts when touched)

What are the unique features of a secondary survey in the trauma patient?

• If you do a DPL, make the incision ABOVE the umbilicus.
  • of course, who does DPLs these days?...
• Look for amniotic fluid in the vagina – test it, the pH will be 7 to 7.5
• Look for the characteristic DIC of amniotic fluid embolism
• Give Rh immunoglobulin to Rh–negative mothers within 48-72 hrs

Disclaimer: the viva stem above may be an original CICM stem, acquired from their publicly available past papers. Or, perhaps it is a slightly altered version of the original CICM stem. Or, it is a completely original viva stem, concocted by the monstrously amoral author of Deranged Physiology for nothing more than his own personal amusement. In either case, because the college do not make the main viva text or marking criteria available, almost everything here has been confabulated. It might sound like a plausible viva and it could be used for the purpose of practice, but all should be aware that it does not represent the "true" canonical CICM viva station.