CICM SAQ 2010.1 Q19

Questions

19.1.  To evaluate a new biomarker as an early index of infected pancreatic necrosis, you perform the measurement in a consecutive series of 200 critically ill patients with pancreatitis. You find that 100 of these patients had subsequently proven necrosis. Of these, 60 had a positive biomarker result. Of the remaining 100 patients without necrosis, 35 had a positive biomarker result.

Using the above data, show how you would calculate

  • a) Sensitivity
  • b) Specificity
  • c) Positive predictive value
  • d) Negative predictive value

19.2.  A randomized controlled clinical trial was performed to evaluate the effect of a new hormone called Rejuvenon on mortality in septic shock. 3400 patients with septic shock were studied (1700 placebo and 1700 in the Rejuvenon arms). The mortality rates in the placebo and the treatment arms were 30% and 25% respectively. Calculate: 

  • (a)  The absolute risk reduction
  • (b)  The relative risk reduction
  • (c)  The number needed to treat

Answers

Answer and interpretation

19.1. Calculate sensitivity, specificity, positive predictive value and negative predictive value.

  • Sensitivity = (TP/{TP+FN}) = 60/100
  • Specificity = (TN/{TN+FP}) = 65/100
  • Positive predictive value = (TP/{TP+FP}) = 60/95
  • Negative predictive value= (TN({TN+FN}) = 65/105

19.1. Calculate ARR, RRR, and NNT.

  • ARR = 5%
  • RRR = 5/30*100 = 16.6%
  • NNT =1/0.05 = 20
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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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