Medical Dogma - busting myths

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Medical Dogma - busting myths

  1. 1. Tan Hon Liang Singapore General Hospital Anaesthesiology and Critical Care
  2. 2. No conflicts of interest to disclose
  3. 3. Disclaimer My opinion. Feel free to disagree.
  4. 4. The Inevitable Question
  5. 5. My Objectives Dissect Dogma. Discuss Philosophy. Revise Stats. EntertainYou.
  6. 6. Illustration of Dogma
  7. 7. Illustration of Dogma
  8. 8. Illustration of Dogma
  9. 9. Illustration of Dogma
  10. 10. Illustration of Dogma
  11. 11. Illustration of Dogma "The experiments of Harry Harlow and his associates at the Primate Laboratory of the University ofWisconsin are described in the textbook Principles of General Psychology (1980 JohnWiley and Sons)”
  12. 12. Brilliant illustration of Dogma!
  13. 13. Except… Not described in Harlow’s literature. Not described in the said textbook.
  14. 14. The Reality 1996
  15. 15. The Reality It was made up?!
  16. 16. The experiment on Dogma is itself a !
  17. 17. The Reality  Monkeys trained to avoid manipulating an object .  Untrained animal placed in cage with a trained animal and the object.  1 trained animal pulled untrained animal away from object.  2 trained animals exhibited "threat facial expressions while in a fear posture" when untrained animal approached the object.
  18. 18. See how dogma can be perpetuated?
  19. 19. Dogma is Learnt Behaviour
  20. 20. Dogma is Learnt Behaviour Deer-ma!
  21. 21. Overcoming dogma is difficult. Humans also like maintaining old boundaries
  22. 22. Dogma in Medicine  List of Dogma  Use of CVP to guide fluid resuscitation  Use of NGT aspirates to determine feed tolerance in ICU  Use of rapid sequence induction/cricoid pressure, esp in children  Use of resonium in hyperkalemia acute management  Use of fluid boluses to treat oliguria  Use of IVC ultrasound to determine fluid status  Pulmonary edema management  Blah Blah Blah….  Long list if only you looked.
  23. 23. But things are about to change…
  24. 24. Scientometrics  The science of measuring and analyzing science.  Facts are not eternal.  In fact, Fact has a half-life.
  25. 25. So what is the half life of facts in Medicine?
  26. 26. Half Life of Surgical Facts  260 abstracts  1935 to 1994  Estimated half-life of facts in surgical literature was 45 years.
  27. 27. Half Life of Medical Facts  Original articles and meta-analyses from 2 journals (Lancet and Gastroenterology).  1945 to 1999  Cirrhosis or hepatitis in adults.  By 2000, 60% of 474 conclusions were still considered true, 19% obsolete, and 21% false.
  28. 28. Half Life of Medical Facts  Half-life of medical fact (in cirrhosis and hepatitis) was 45 years.
  29. 29. Half Life of Medical Facts  NEJM. 10 years (2001-2010). 2044 original articles: 1344 concerned a medical practice:  981 (73.0%) examined a new medical practice  363 (27.0%) tested an established practice.  146 (40.2%) reversed practice.  138 (38.0%) reaffirmed it.  79 (21.7%) inconclusive.  Half Life of Medical Facts may well be shortening.
  30. 30. Overcoming dogma is difficult. But someone has to start somewhere.
  31. 31. So we begin… 1 of 5
  32. 32. Glasgow Coma Scale
  33. 33. GCS is a reliable predictor of outcomes. True or False
  34. 34. GCS is applicable in all ICU patients. True or False
  35. 35. GCS 8 and below = no gag = aspiration risk = must intubate True or False
  36. 36. AtThe Beginning  15 point scale.  E4V5M6  Original 14 point scale  revised in 1976 with the addition of a sixth point in the motor response  Designed forTraumatic Head Injury  six hours after head trauma
  37. 37. Glasgow Coma Scale  American College of Surgeons Committee onTrauma  European Society of Intensive Care Medicine  Eastern Association for the Surgery ofTrauma  GCS <9 recommended threshold for intubation
  38. 38. Glasgow Coma Scale Problems  1 year, retrospective review. Blunt trauma patients with presumed head injury with GCS less than or equal to 13  120 patients.  A significant number of patients with a GCS of less than or equal to 9 required emergent intubation.  A significant minority of patients with a GCS score of 10-13 required emergent intubation (20%) or had intracranial pathology on head CT scan (23%).
  39. 39. Glasgow Coma Scale Problems  Problem with the Score  120 mathematical combinations!  18 possible permutations exist for GCS 9  17 for scores 8 and 10  14 for scores 7 and 11  10 for scores 6 and 12  Therefore, not all GCS 9 are equal.
  40. 40. Stats What type of scale is GCS? Nominal Ordinal Continuous
  41. 41. Ordinal The difference between unit values is not consistent and compares only better with worse
  42. 42. Glasgow Coma Scale Problems  Problem with the Score  E  Spontaneous (4) : indicative of activity of brainstem arousal mechanisms but not necessarily of attentiveness  Vegetative States: Eyes may spontaneously open. “Lights on, but nobody at home”.  Noxious stimulus: grimace and eye closure.Then how?  Eye injury.  Drugs: muscle relaxants, sedation.
  43. 43. Glasgow Coma Scale Problems  Problem with the Score  V  Facial injury.  Focal neurological injury:  Broca’s aphasia  Wernicke’s aphasia  Conductive aphasia  Language.  Intubation, tracheostomy.  Drugs: muscle relaxants, sedation.
  44. 44. Glasgow Coma Scale Problems  Problem with the Score  M  Motor skew  No correlation to severity:  M3: internal capsule or cerebral hemispheres injury  M2: midbrain to upper pontine damage
  45. 45. Glasgow Coma Scale Problems  > 90% publications use 14-item GCS.  Timing of the initial GCS assessment inconstant.  GCS components seldom utilized: loss of information.  Confounders often not reported and, if they are, not in a standardized manner.  “current inconsistent and inappropriate use of GCS diminishes its reliability in both a clinical and a scientific context.”
  46. 46. Glasgow Coma Scale Problems  French. 60 subjects.  Observer bias.  Errors up to 2 points.
  47. 47. Glasgow Coma Scale Problems  Prospective observational study. 208 adult patients. Emergency Department. Hong Kong.  Cotton bud and soft tracheal suction catheter to stimulate the posterior pharyngeal wall (gag reflex) GCS Gag Present Gag Absent ≤8 36.4% (12/33 ) 63.6% (21/33) 9-14 62.9% (39/62) 37.1% (23/62) 15 77.9% (88/113) 22.1% (25/113)
  48. 48. Glasgow Coma Scale Problems  Designed forTraumatic Head Injury  six hours after the occurrence of head trauma  Cannot be used for other pathological states.  73 patients.Drug or alcohol intoxication. GCS 3 to 14.  No patient with a GCS <9 aspirated or required intubation.  1 patient required intubation; this patient had a GCS of 12 on admission to the ward.
  49. 49. GCS is a reliable predictor of outcomes. False Not precise. Many limitations.
  50. 50. GCS is applicable in all ICU patients. False Designed for trauma. May not be applicable to poisoning, medical diseases.
  51. 51. GCS <9 = no gag = aspiration risk = must intubate False Not all need intubation.
  52. 52. Summary  Many limitations.  GCS for head injury. Be careful about extrapolating to other conditions.  Not reliable prognostic factor.  Not all GCS < 9 require intubation.
  53. 53. 2 of 5
  54. 54. CentralVenous Pressure What are the indications for measuring CVP?
  55. 55. Indications for CVC  Hemodynamic monitoring including central venous pressure (CVP), central venous oxygen saturation (SCvO2) or for insertion of a pulmonary arterial catheter.  For infusion of irritants (eg. vasopressors,TPN, chemotherapy)  Transvenous cardiac pacing  Plasmapheresis, apheresis, hemodialysis or CRRT  Poor peripheral venous access
  56. 56. CVP can be used to monitor hemodynamics True or False
  57. 57. CVP predicts volume status True or False
  58. 58. CVP predicts fluid responsiveness True or False
  59. 59. Change in CVP reflects change in Cardiac Output True or False
  60. 60. CVP  25 patients.Thoracotomy. 8 on CPB.  Blood volume estimates with tagged albumin.  Complex measurement technique.
  61. 61. CVP  Review/case series of 14 different cases, including a neonate.  Descriptive: benefit using CVP for additional information.
  62. 62. CVP Myth Buster  Simultaneous measurement of CVP and PCW in patients with AMI, during volume expansion or diuresis.  CVP:  no consistent relation to PCW.  Did not predict changes in PCW during fluid therapy.  3 patients with pulmonary edema had normal CVP.  “CVP in AMI at best of limited value, and at worst seriously misleading”.
  63. 63. CVP Myth Buster  500 ml of 5 % albumin. 1 hour. 22 patients with CVP greater than 15 cm. H2O.  CVP decreased in 14 (64 percent).  CVP increased slightly but not significantly in 8 (36 percent).  “High initial CVP is not a reliable index of either hypervolemia or cardiac failure in critically ill patients”.
  64. 64. Many many other studies concur.
  65. 65. Stats What is Correlation Coefficient?
  66. 66. Correlation Coefficient
  67. 67. Correlation Coefficient
  68. 68. Guess the correlation of CVP to hemodynamic status?
  69. 69. CVP Myth Buster  24 studies. Pooled correlation coefficient between  CVP and measured blood volume  0.16 (95% CI, 0.03 to 0.28)  Baseline CVP and change in stroke index/cardiac index  0.18 (95% CI, 0.08 to 0.28).  Delta CVP and change in stroke index/cardiac index  0.11 (95% CI, 0.015 to 0.21).  Baseline CVP was 8.7+/-2.32 mm Hg in the responders compared to 9.7+/-2.2 mm Hg in nonresponders.
  70. 70. Stats What is a Receiver Operating Characteristic Curve (ROC)?
  71. 71. Receiver Operating Characteristic Curve (ROC)  True positive rate (Sensitivity) plotted against false positive rate (100-Specificity) for different cut-off points.
  72. 72. Receiver Operating Characteristic Curve (ROC)  Test with perfect discrimination: ROC curve passes through the upper left corner (100% sensitivity, 100% specificity).  Therefore the closer the ROC curve is to the upper left corner  The higher the AUC of ROC curve = higher overall accuracy of test.
  73. 73. CVP Myth Buster  The pooled area under the ROC curve was 0.56 (95% CI, 0.51 to 0.61).
  74. 74. Tale of 7 Mares  7 Horses. Standing position in “standing dock”  Bled for 1 hours at 16 mL/kg/h.  Central venous pressure (CVP), central venous blood gas, blood lactate concentration, and heart rate measured.  Only study to show reliable correlation.
  75. 75. Half Life of Medical Fact 49 years 46 years Not too far off!
  76. 76. CVP Myth Buster  43 studies  AUC 0.56 (95% CI, 0.54-0.58) with no heterogenicity between studies.  0.56 (95% CI, 0.52-0.60) for studies done in ICU.  0.56 (95% CI, 0.54-0.58) for studies in OT.
  77. 77. CVP can be used to monitor hemodynamics False No, it cannot and should not.
  78. 78. CVP predicts volume status False
  79. 79. CVP predicts fluid responsiveness False Passive Leg Rising works better
  80. 80. Change in CVP reflects change in Cardiac Output False
  81. 81. Summary  CVC: 1. For infusion of irritants (eg. vasopressors,TPN, chemotherapy) 2. Transvenous cardiac pacing 3. Plasmapheresis, apheresis, hemodialysis or CRRT 4. Poor peripheral venous access 5. Liver surgery
  82. 82. 3 of 5
  83. 83. Treatment of Hyperkalemia
  84. 84. Treatment of hyperkalemia  Calcium  Insulin – Dextrose  Sodium bicarbonate  Beta agonist  Resonium  Hemodialysis
  85. 85. Resonium is a resin which binds only potassium and aids excretion. True or False
  86. 86. Resonium should be used to treat acute hyperkalemia True or False
  87. 87. Resonium is safe and effective. True or False
  88. 88. Resonium  Approved by FDA in 1958.  4 years before drug manufacturers were required to prove the effectiveness and safety.  Quoted studies of efficacy:
  89. 89. Resonium Myth Buster  8 patients: 5 given resonium, 3 given sorbitol (laxative)  0 K+ diet: High sugar syrup only.  K+ checked on Day 5.  Resonium 6.6 -> 5.2  Sorbitol 6.3 -> 4.6
  90. 90. Resonium Myth Buster  Uncontrolled study. 32 patients. Acute and chronic renal failure.  23 of 30 cases: K+ fell by at least 0.4 mmol/L in the first 24 hours.  Low K+ diet.  20% Dextrose IV. Insulin. NaHCO3.  No statistical analysis.
  91. 91. Won’t get published in NEJM now!
  92. 92. But does Resonium work? “I swear I have seen it work acutely”
  93. 93. Resonium – Does it work?  1 mmol K+ binds 1 g of resin.  In vivo, sodium only partially released: efficiency is 33%.  Bind any cation: Calcium, hydrogen, Magnesium  10 mmol of K+ bound and excreted per 30-g dose.  What doses have you seen prescribed in your hospital?  How much K+ would that clear?
  94. 94. Resonium – why it seems to work?  Given with laxatives/sorbitol – poop works.  Sodium exchanged: possibly absorbed: plasma expansion = dilution!  Other things you did worked.  Low K+ diet  Insulin-Detrose  Dialysis  Spurious in the first place?
  95. 95. Resonium Myth Buster  Increase insoluble K+ output but decrease soluble K+ output: no significant effect on total K+ output.  Did not decrease serum K+ at 4, 8 and 12 hr.  Single-dose resin-cathartic therapy produces no or only trivial reductions in K+.
  96. 96. Resonium Myth Buster  FDA warning:  Severe constipation.  Colonic necrosis.  Wisdom of using Resonium challenged.
  97. 97. Resonium is a resin which binds potassium and aids excretion. False
  98. 98. Resonium should be used to treat acute hyperkalemia False
  99. 99. Resonium is safe and effective. False
  100. 100. Resonium works and should be given to treat acute hyperkalemia. No, it does not. No, it has no role.
  101. 101. Summary  No role in acute hyperkalemia.  Can be harmful.  Avoid in constipated patient, uremia, critically ill or post abdominal surgery.
  102. 102. 4 of 5
  103. 103. UterineTilt in Obstetric Patients Is it your OT routine?
  104. 104. The gravid uterus causes IVC and aortic compression. True or False
  105. 105. IVC compression and the fetus is harmed. True or False
  106. 106. Left lateral tilt is a solution. True or False
  107. 107. So how much do you tilt? 5, 10, 15, 30, 90?
  108. 108. 2 Questions Maternal vs fetal
  109. 109. Fetal Effects
  110. 110. Left LateralTilt averts fetal harm?  20 term parturients  Neither the left or the right pelvic-tilt position associated with a significant change in leg blood flow or maternal heart rate compared to the supine position.  Fetal heart rate and umbilical Doppler resistance did not change in any position.
  111. 111. Left LateralTilt averts fetal harm?  25 term parturients.  Supine and in both right and left 5 degrees and 10 degrees lateral tilt positions.  No significant difference among fetal variables in the various maternal position.
  112. 112. Left LateralTilt averts fetal harm?  25 term parturients.  4 positions (random order): supine with a 15-degree left tilt, sitting, and left lateral and right lateral positions.  No significant differences in fetal heart rate, pulsatility index, or resistivity index among positions.
  113. 113. Maternal Effects
  114. 114. Maternal Harm?  157 term parturients. Suprasternal doppler. NIBP of upper and lower limbs  11 patients CO decreased >20%, without changes in SBP, when tilted to <15°: attributable to IVC compression.  Only 1 patient in the supine had aortic compression with the SBP in the upper limb 25 mm Hg higher than the lower limb
  115. 115. Maternal Harm?  573 pregnant subjects undergoing antepartum Non-Stress Test.  Only 2% had presyncopal symptoms when supine  (did not affect the NST, either in terms of reactivity or any pathological findings)
  116. 116. The Angle Matters Often too little.
  117. 117. Angle Matters  157 term parturients. Random position : 0°, 7.5°, 15°, and full left lateral tilt.  CO 5% higher when patients were tilted at ≥15° compared with <15°.
  118. 118. Angle Matters  16 anaesthetists. Almost all less than 15 degree tilit  Visually guess was grossly inaccurate in 42 of 43 patients.  Average tilt given was only 8.09 degrees
  119. 119. How you position might matter.
  120. 120. How to get the tilt matters  51 term parturients  Random left lateral, supine-to-tilt and left lateral-to-tilt positions using a Crawford wedge.  Femoral vein area, femoral vein velocity, femoral artery area, pulsatility index, resistance index and right arm MAP and HR.  Moving from the full left lateral to the lateral tilt position may prevent aortocaval more than when from a supine to left lateral tilt position.
  121. 121. The gravid uterus causes IVC and aortic compression. True But not all symptomatic.
  122. 122. IVC compression and the fetus is harmed. Maybe. Current evidence suggest not.
  123. 123. Left lateral tilt is a solution. True But correct angle needed. Full left lateral is better if you need it.
  124. 124. Summary  ~1-4% of term parturient affected.  Majority not symptomatic.  Fetal compromise might be over-emphasized.  Visual estimated (agar agar) token tilt is pointless.  Tilt often overestimated visually.  Want to do it, then do it properly: full lateral (then possibly tilt back).
  125. 125. 5 of 5 hallelujah
  126. 126. Treating Oliguria/AKI in ICU Preventing dialysis dependence/progression of renal failure
  127. 127. Treating Oliguria/AKI in ICU  Diuretic  Fluid bolus  Increase blood pressure  Dialysis  (Do nothing)
  128. 128. Theoretical Basis  Diuretic  Paralyze energy dependent ion exchangers: Reduce oxygen consumption in kidneys.  Fluid bolus  Improve preload  Increase blood pressure  Improve renal perfusion  Dialysis  Partial replacement of kidney function.  (Do nothing)
  129. 129. Loop diuretics/frusemide can treat/prevent AKI. True or False
  130. 130. Loop Diuretic/Frusemide  54 critically ill surgical patients.  Frusemide increased urine output, COsm, and CNa.  Produced no change in GFR, RPF, RBF, and RBF distribution.
  131. 131. Loop Diuretic/Frusemide  In-hospital mortality RR 1.11 (95% CI 0.92 to 1.33)  Renal replacement therapy RR 0.99 (95% CI 0.80 to 1.22),  Possibly increased risk of temporary deafness and tinnitus with high doses RR 3.97 (95% CI 1.00 to 15.78).
  132. 132. Frusemide  Loop diuretics increased incidence of AKI (NNH = 8 (95% CI: 5 to 15).
  133. 133. Loop diuretics/frusemide can treat/prevent AKI. False Urine for the sake of urine is not useful acutely.
  134. 134. Loop diuretics/frusemide may still have a role. But not acutely. In volume management in latter stages.
  135. 135. AKI/Oliguria can be treated with fluid boluses. True or False
  136. 136. Fluid Bolus  Theory:  Increase preload. Prevent ischemia.  Prevent renal hypoperfusion.  Reality:  Post-mortem kidney biopsy  Capillary leukocytic infiltration and apoptosis predominate.  Not ischemic necrosis
  137. 137. Fluid Bolus  Reality:  No consistent renal histopathological changes in human or experimental septic AKI.  Majority of studies reported normal histology or only mild, nonspecific changes.  ATN was relatively uncommon.
  138. 138. Fluid Bolus  Reality  Renal vasculature cannulated: hyperdynamic instead of ischemic.
  139. 139. Not much point giving fluid bolus thinking it will improve renal perfusion! Except in acute hypovolemia/hemorrhagic shock
  140. 140. Excessive fluid is not harmless
  141. 141. Excessive Fluid  Less fluid, better oxygenation.  Although no difference in mortality.  Less fluid, but no increase risk in dialysis rates.  Infer: fluid does not affect dialysis rate.
  142. 142. Excessive Fluid  10 ICU. Italy.  601 patients: 132 had AKI. Mortality 50% in this group.  Non-survivors had higher mean fluid balance (1.31 ± 1.24 versus 0.17 ± 0.72 L/day; P <0.001) compared to survivors.
  143. 143. Beyond initial resuscitation, fluid bolus maybe pointless and potentially harmful.
  144. 144. AKI/Oliguria can be treated with fluid boluses. False And it might even be harmful. Avoid “therapeutic drowning”
  145. 145. Summary  In the treatment of oliguria/AKI in ICU:  Diuretic: no acute role.  Fluid bolus: no role unless acute hypovolemia/hemorrhage.  Increase blood pressure: yes, if baseline BP is high.  Dialysis: trend to mortality benefit if started early.  Doing nothing is not unreasonable.
  146. 146. Conclusion
  147. 147. Half of what we do is wrong We just don’t know which half.
  148. 148. Trust no one (and everything you were ever told) Including what I just told you.
  149. 149. ThankYou tan.hon.liang@sgh.com.sg
  150. 150. In case you are not convinced  The abstract that says it all.

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