Question 3.2

Created on Sun, 05/17/2015 - 18:01
Last updated on Fri, 04/28/2017 - 17:41
Pass rate: 90%
Highest mark: 9.25

Other SAQs in this paper

Other SAQs on this topic

(Both this question and Question 3.1 use the same flavour text:)

A   20   year   old   female   in   ICU following   a  diffuse   axonal   head   injury develops a severe exacerbation of intracranial hypertension on day 3. She is mechanically ventilated, paralysed and sedated. Investigations during a subsequent episode of marked polyuria are summarised below.



Normal Range



(7.36 –7.44)


28 mm Hg

(36 – 44)


21 mmol/L

(23 – 26)

Standard base excess

-1.5 mmol/L

(-2 .0 to +2.0)


147 mmol/L

(135 – 145)


3.2 mmol/L

(3.2 – 4.5)


110 mmol/L

(100 –110)


3.0 mmol/L

(3.0 – 8.0)


65 mmol/L

(50 – 100)


4.0 mmol/L

(3.0 – 6.0)

Measured plasma osmolality*

333 mosmol/kg

(280 –290)

Urine osmolality

410 mosmol/L

(50– 1200)

a) What  is the most likely explanation  for the polyuria?  Give the reasoning behind your answer (this is answered as Question 3.1 in this paper)

b)  List the major determinants of prognosis in traumatic brain injury.

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College Answer

b)  List the major determinants of prognosis in traumatic brain injury.

Prognostic determinants:

•    Age > 60
•    Pupillary abnormalities
•    Presence of hypotension and hypoxia
•    Low GCS on presentation
•    CT scan abnormalities – intracranial collections, presence of traumatic subarachnoid haemorrhage
•     Co-morbidities


Part a) of this question (Question 3.1) was a more electrolyte-based question: "What  is the most likely explanation  for the polyuria?  Give the reasoning behind your answer."

The answer to the question about prognosis of traumatic brain injury can be found in the Brain Trauma Foundation's document on the Early Indicators of Prognosis in Severe Traumatic Brain Injury .

  • Age > 60 (poor outcome risk increases by 20-30%)
  • Pupillary abnormalities (70-90% mortality with bilaterally absent light reflex)
  • Presence of hypotension (doubles mortality)
  • Presence of hypoxia (doubles the likelihood of a poor neurological outcome)
  • Low GCS on presentation (65% mortality if the GCS is 3)
  • CT scan abnormalities (absence of abnormalities equates to a better prognosis)
  • Co-morbidities

This is discussed in greater detail in "Prognosis in severe brain injury" from the Required Reading section.


Chesnut, R. M., et al. "Part 2: Early indicators of prognosis in severe traumatic brain injury." Journal of Neurotrauma 17.6-7 (2000): 555-+.

Fearnside, Michael R., et al. "The Westmead Head Injury Project outcome in severe head injury. A comparative analysis of pre-hospital, clinical and CT variables." British journal of neurosurgery 7.3 (1993): 267-279.

Oddo, Mauro, et al. "Brain hypoxia is associated with short-term outcome after severe traumatic brain injury independently of intracranial hypertension and low cerebral perfusion pressure." Neurosurgery 69.5 (2011): 1037-1045.

McHugh, Gillian S., et al. "Prognostic value of secondary insults in traumatic brain injury: results from the IMPACT study." Journal of neurotrauma 24.2 (2007): 287-293.

Collaborators, MRC CRASH Trial, et al. "Predicting outcome after traumatic brain injury: practical prognostic models based on large cohort of international patients." bmj 336.7641 (2008): 425-9.

Stevens, Robert D., and Raoul Sutter. "Prognosis in severe brain injury." Critical care medicine 41.4 (2013): 1104-1123.

Steyerberg, Ewout W., et al. "Predicting outcome after traumatic brain injury: development and international validation of prognostic scores based on admission characteristics." PLoS medicine 5.8 (2008): e165.

Lingsma, Hester F., et al. "Early prognosis in traumatic brain injury: from prophecies to predictions." The Lancet Neurology 9.5 (2010): 543-554.

Utomo, Wesley K., et al. "Predictors of in-hospital mortality and 6-month functional outcomes in older adults after moderate to severe traumatic brain injury." Injury 40.9 (2009): 973-977.

Holcomb, Erin M., Scott R. Millis, and Robin A. Hanks. "Comorbid Disease in Persons With Traumatic Brain Injury: Descriptive Findings Using the Modified Cumulative Illness Rating Scale." Archives of physical medicine and rehabilitation 93.8 (2012): 1338-1342.