CICM SAQ 2011.1 Q22

Questions

22. A 45 year old man was admitted to the intensive care unit after sustaining 40% BSA burns in a house fire. He was transported initially to a local hospital where initial resuscitation was commenced including mechanical ventilation for suspected inhalational injury. On arrival in your ICU an arterial blood gas was taken which is shown below:

  • a) List four potential contributing causes of the metabolic derangement
  • b) How would you classify the acid base derangement and explain your reasoning?
  • c) The serum albumin is 18g/L. Outline how would this affect the anion gap.
  • d) Whilst on your ward round the RMO asks your opinion on the Stewart approach to acid base physiology. List the 3 independent variables that comprise this approach

Answers

Answer and interpretation

a) List four potential contributing causes of the metabolic derangement

  • Shock/Underesuscitation/hypovolaemia (elevated Hb and Lactate)
  • Normal (0.9%) Saline fluid resuscitation
  • Carbon monoxide poisoning
  • Cyanide toxicity from smoke inhalation (elevated anion gap acidosis)
  • Other missed injuries e.g. abdominal trauma, bleeding etc leading to hypoperfusion/shock
  • Potential concurrent ingestions e.g. methanol, ethylene glycol

b) How would you classify the acid base derangement and explain your reasoning?

  • Mixed metabolic acidosis (Note: CO2 is also high for pH but less relevant because patient on IPPV)
  • Delta ratio indicates a greater fall in [HCO3-] than expected given increase in AG. This can be explained by a mixed metabolic acidosis, i.e. a combined high anion gap and normal anion gap acidosis.

c) The serum albumin is 18g/L. Outline how would this affect the anion gap.

  • The plasma proteins are the major source of unmeasured anions. Hypo albuminemia may mask an increased concentration of gap anions by lowering the value of the anion gap. Adjustment of the anion gap can be made by the application of correction factors (see Figge et al, CCM 1998).

d) Whilst on your ward round the RMO asks your opinion on the Stewart approach to acid base physiology. List the 3 independent variables that comprise this approach

  • Strong ion difference
  • Partial CO2 tension
  • Total concentration of weak acid (ATOT)

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Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also the Innovation Lead for the Australian Centre for Health Innovation at Alfred Health and Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of two amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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