BCC4: Delaney on Stats and Trials "Stuff"
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BCC4: Delaney on Stats and Trials "Stuff"

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Delaney shares insights into the mysterious world of statistics and trials. This 12 minute podcast is particularly useful for Registrars preparing for their exams and was recorded at BCC4. For similar ...

Delaney shares insights into the mysterious world of statistics and trials. This 12 minute podcast is particularly useful for Registrars preparing for their exams and was recorded at BCC4. For similar podcasts and audio; head to www.intensivecarenetwork.com and to rego for BCC5 in Cairns, check out www.bedsidecriticalcare.com

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BCC4: Delaney on Stats and Trials "Stuff" BCC4: Delaney on Stats and Trials "Stuff" Presentation Transcript

  • STATS AND TRIALS STUFF Anthony Delaney MBBS MSc FACEM FCICM Staff Specialist Malcolm Fisher Department of Intensive Care Medicine
  • Disclaimer  I ain’t a statistician  More of an enthusiastic amateur
  • So…..  Difference between mortality and survival?  How to interpret a “negative” trial result?
  • Mortality or survival?  Mortality:  Number of deaths/number at risk at the end of a period of time  28 day mortality  Rate  Survival:  Time to event analysis  How long it takes for the event to happen  If you have survived for x time, what are your chances of dying in x+1 time  Hazard
  •  Population:  >18 yo  Source of infection  Temperature >38.3oC or <35.6oC  Heart rate > 90bpm  SBP <90 mmHg for 1 hour if adequate fluids and some pressors  Urine output <0.5 ml/kg/hr for > 1 hr or PaO2/FiO2 <280  Lactate >2 mmol/L  Ventilated  Excluded:  pregnant, contra/indication to steroids, advanced cancer, AMI, PE, AIDS,
  •  Intervention:  Hydrocortisone mg q6h ivi  Fludrocortisone 50mg po daily  For 7 days  Comparison:  Placebo  For 7 days
  •  Outcome:  The primary endpoint was the 28-day survival distribution from randomisation in non- responders to the short corticotropin test
  •  Point one  Post-randomisation sub groups are dubious
  •  Is the subgroup variable a characteristic measured at baseline or after randomisation?  “The credibility of subgroup hypotheses based on post-randomisation characteristics is severely compromised, and can be rejected simply on this criterion”
  •  Subdivision of patients in ISIS-2 with respect to birth signs  Gemini and Libra shows an adverse effect on mortality
  •  Results:  300 participants  In non-responders  Placebo 73/115 (63%)  Steroids 60/114 (53%)  Hazard ratio 0.67 95% CI 0.47-0.95; P=0.02  Conclusion:  Treatment with hydrocortisone and fludrocortisone significantly reduced the risk of death in patients with septic shock and adrenal insufficiency
  • Date of download: 9/11/2013 Copyright © 2012 American Medical Association. All rights reserved. From: Effect of Treatment With Low Doses of Hydrocortisone and Fludrocortisone on Mortality in Patients With Septic Shock JAMA. 2002;288(7):862-871. doi:10.1001/jama.288.7.862 Results are according to the response to the short corticotropintest. In nonresponders, the median time to death was 12 days in the placeboand 24 days in the corticosteroid groups; in responders, 14 days in the placeboand 16.5 days in the corticosteroid groups; and in all patients, 13 days inthe placebo and 19.5 in the corticosteroid groups. Figure Legend:
  •  In nonresponders, the median time to death was 12 days in the placebo and 24 days in the corticosteroid groups;  in responders, 14 days in the placebo and 16.5 days in the corticosteroid groups;  and in all patients, 13 days in the placebo and 19.5 in the corticosteroid groups.
  • Mortality or Survival Time (days) 28 Survival 1.0 0.5
  •  i
  •  How big a difference in mortality do you think putting a tracheostomy in at Day 4 compared to Day 10 would make on 30 day mortality?  50% RRR (15% ARR)  25% RRR (7.5% ARR)  10% RRR (3% ARR)  5% RRR (1.5% ARR)
  • “Negative trials”  n
  •  Population:  Mechanically ventilated adults  Had been ventilated for 4 days and thought to require at least 7 more days of ventilation  Excluded:  Those requiring a tracheostomy, contraindication to tracheostomy, respiratory failure due to chronic neurological disease
  •  Intervention:  Trachesotomy by Day 4  Comparison:  Tracheostomy after Day 10 if still required  Outcome:  All cause mortality 30 days from randomisation
  •  Sample Size Calculation:  Baseline mortality of 30%  Absolute risk reduction 6.3% (21% RRR)  Power 80%  Alpha 5%  4% loss to follow up  N=1692
  •  Due to study fatigue and exhaustion of funding  N=899
  •  “Tracheostomy within 4 days of critical care admission was not associated with an improvement in 30 day mortality”
  •  We are 95% certain that early tracheostomy might be between  5.4% worse to 6.7% better in absolute risk  About 20% better or worse in terms of relative risk
  •  6.3% of patients had a complication of tracheostomy  53% of patients who were randomised to delayed trache didn’t need one  2 year mortality was 52.3%  Only 5 lost to follow up
  •  Conclusions:  Unable to rule out a clinically important difference between early and late trache  It probably doesn’t make a big difference to mortality  Unknown about patient perspective  Useful information about the patient cohort  Not really a “negative trial”
  • QUESTIONS??