medical dogma - busting myths
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23 May 2014 AST Talk medical, dogma, mythsTRANSCRIPT
Medical DogmaBusting Myths
AST Talk
23 May 2014
Tan Hon LiangSingapore General HospitalAnaesthesiology and Critical Care
No conflicts of interest to disclose
DisclaimerMy opinion. Feel free to disagree.
The Inevitable Question
My ObjectivesDissect Dogma.
Discuss Philosophy. Revise Stats. Entertain You.
Illustration of Dogma
Illustration of Dogma
Illustration of Dogma
Illustration of Dogma
Illustration of Dogma
Illustration of Dogma
"The experiments of Harry Harlow and his associates at the Primate Laboratory of the University of Wisconsin are described in the textbook Principles of General Psychology (1980 John Wiley and Sons)”
Brilliant illustration of Dogma!
Except…Not described in Harlow’s literature. Not described in the said textbook.
The Reality
1996
The Reality
It was made up?!
The experiment on Dogma is itself a
!
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.
See how dogma can be perpetuated?
Dogma is Learnt Behaviour
Dogma is Learnt Behaviour
Deer-ma!
Overcoming dogma is difficult.
Humans also like maintaining old boundaries
Dogma in MedicineList 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.
But things are about to change…
ScientometricsThe science of measuring and analyzing
science.
Facts are not eternal.
In fact, Fact has a half-life.
So what is the half life of facts in
Medicine?
Half Life of Surgical Facts
260 abstracts
1935 to 1994
Estimated half-life of facts in surgical literature was 45 years.
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.
Half Life of Medical Facts
Half-life of medical fact (in cirrhosis and hepatitis) was 45 years.
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.
Overcoming dogma is difficult.
But someone has to start somewhere.
So we begin…1 of 5
Glasgow Coma Scale
GCS is a reliable predictor of outcomes.
True or False
GCS is applicable in all ICU patients.
True or False
GCS 8 and below = no gag
= aspiration risk = must intubate
True or False
At The Beginning
15 point scale. E4V5M6
Original 14 point scale revised in 1976 with the addition of a
sixth point in the motor response
Designed for Traumatic Head Injury six hours after head trauma
Glasgow Coma ScaleAmerican College of Surgeons Committee on
Trauma
European Society of Intensive Care Medicine
Eastern Association for the Surgery of Trauma
GCS <9 recommended threshold for intubation
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%).
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 1110 for scores 6 and 12
Therefore, not all GCS 9 are equal.
StatsWhat type of scale is GCS?
Nominal Ordinal
Continuous
OrdinalThe difference between unit values is not consistent and
compares only better with worse
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.
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.
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
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.”
Glasgow Coma Scale Problems
French. 60 subjects.
Observer bias. Errors up to 2 points.
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)
Glasgow Coma Scale Problems
Designed for Traumatic 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.
GCS is a reliable predictor of outcomes.
False
Not precise. Many limitations.
GCS is applicable in all ICU patients.
False
Designed for trauma. May not be applicable to poisoning, medical diseases.
GCS <9= no gag
= aspiration risk = must intubate
False
Not all need intubation.
SummaryMany limitations.
GCS for head injury. Be careful about extrapolating to other conditions.
Not reliable prognostic factor.
Not all GCS < 9 require intubation.
2 of 5
Central Venous Pressure
What are the indications for measuring CVP?
Indications for CVCHemodynamic 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
CVP can be used to monitor
hemodynamics True or False
CVP predicts volume status
True or False
CVP predicts fluid responsiveness
True or False
Change in CVP reflects change in
Cardiac OutputTrue or False
CVP
25 patients. Thoracotomy. 8 on CPB.
Blood volume estimates with tagged albumin.
Complex measurement technique.
CVP
Review/case series of 14 different cases, including a neonate.
Descriptive: benefit using CVP for additional information.
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”.
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”.
Many many other studies concur.
StatsWhat is Correlation Coefficient?
Correlation Coefficient
Correlation Coefficient
Guess the correlation of CVP to
hemodynamic status?
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.
StatsWhat is a Receiver Operating Characteristic Curve (ROC)?
Receiver Operating Characteristic Curve (ROC)
True positive rate (Sensitivity) plotted against false positive rate (100-Specificity) for different cut-off points.
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.
CVP Myth Buster
The pooled area under the ROC curve was 0.56 (95% CI, 0.51 to 0.61).
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.
Half Life of Medical Fact
49 years
46 years
Not too far off!
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.
CVP can be used to monitor
hemodynamics False
No, it cannot and should not.
CVP predicts volume status
False
CVP predicts fluid responsiveness
False
Passive Leg Rising works better
Change in CVP reflects change in
Cardiac OutputFalse
SummaryCVC:
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
NOT hemodynamic monitoring
3 of 5
Treatment of Hyperkalemia
Treatment of hyperkalemia
Calcium
Insulin – Dextrose
Sodium bicarbonate
Beta agonist
Resonium
Hemodialysis
Resonium is a resin which binds only
potassium and aids excretion.
True or False
Resonium should be used to treat acute
hyperkalemiaTrue or False
Resonium is safe and effective.
True or False
ResoniumApproved by FDA in 1958.
4 years before drug manufacturers were required to prove the effectiveness and safety.
Quoted studies of efficacy:
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
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.
Won’t get published in NEJM now!
But does Resonium work?
“I swear I have seen it work acutely”
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?
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?
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+.
Resonium Myth Buster
FDA warning: Severe constipation. Colonic necrosis.
Wisdom of using Resonium challenged.
Resonium is a resin which binds
potassium and aids excretion.
False
Resonium should be used to treat acute
hyperkalemiaFalse
Resonium is safe and effective.
False
Resonium works and should be given to
treat acute hyperkalemia.
No, it does not. No, it has no role.
Summary No role in acute hyperkalemia.
Can be harmful.
Avoid in constipated patient, uremia, critically ill or post abdominal surgery.
4 of 5
Uterine Tilt in Obstetric Patients
Is it your OT routine?
The gravid uterus causes IVC and aortic
compression.True or False
IVC compression and the fetus is harmed.
True or False
Left lateral tilt is a solution.
True or False
So how much do you tilt?
5, 10, 15, 30, 90?
2 QuestionsMaternal vs fetal
Fetal Effects
Left Lateral Tilt 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.
Left Lateral Tilt 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.
Left Lateral Tilt 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.
Maternal Effects
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
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)
The Angle MattersOften too little.
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°.
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
How you position might matter.
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.
The gravid uterus causes IVC and aortic
compression.True
But not all symptomatic.
IVC compression and the fetus is harmed.
Maybe.
Current evidence suggest not.
Left lateral tilt is a solution.
True
But correct angle needed. Full left lateral is better if you need it.
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).
5 of 5hallelujah
Treating Oliguria/AKI in ICU
Preventing dialysis dependence/progression of renal failure
Treating Oliguria/AKI in ICU
Diuretic
Fluid bolus
Increase blood pressure
Dialysis
(Do nothing)
Theoretical BasisDiuretic
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)
Loop diuretics/frusemide
can treat/prevent AKI.True or False
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.
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).
Frusemide
Loop diuretics increased incidence of AKI (NNH = 8 (95% CI: 5 to 15).
Loop diuretics/frusemide
can treat/prevent AKI.False
Urine for the sake of urine is not useful acutely.
Loop diuretics/frusemide
may still have a role. But not acutely.
In volume management in latter stages.
AKI/Oliguria can be treated with fluid
boluses. True or False
Fluid BolusTheory:
Increase preload. Prevent ischemia. Prevent renal hypoperfusion.
Reality:
Post-mortem kidney biopsy Capillary leukocytic infiltration and apoptosis
predominate. Not ischemic necrosis
Fluid BolusReality:
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.
Fluid BolusReality
Renal vasculature cannulated: hyperdynamic instead of ischemic.
Not much point giving fluid bolus
thinking it will improve renal
perfusion!Except in acute hypovolemia/hemorrhagic shock
Excessive fluid is not harmless
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.
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.
Beyond initial resuscitation, fluid
bolus maybe pointless and
potentially harmful.
AKI/Oliguria can be treated with fluid
boluses. False
And it might even be harmful.Avoid “therapeutic drowning”
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.
Conclusion
Half of what we do is wrong
We just don’t know which half.
Trust no one (and everything you were ever told)
Including what I just told you.
Thank [email protected]
In case you are not convinced
The abstract that says it all.