medical dogma - busting myths

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

"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 fact (in cirrhosis and hepatitis) was 45 years.


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%).


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


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.


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.


Problem with the Score M

Motor skew No correlation to severity:

M3: internal capsule or cerebral hemispheres injury

M2: midbrain to upper pontine damage


> 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.”


French. 60 subjects.

Observer bias. Errors up to 2 points.


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)


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

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


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?


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+.


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.


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.


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

https://www.google.com.sg/search?client=safari&rls=en&q=hallelujah&spell=1&sa=X&ei=L_Z9U7D4OceRuASk34LYDg&ved=0CCcQBSgA

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).


can treat/prevent AKI.False

Urine for the sake of urine is not useful acutely.


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.

medical dogma - busting myths

Health & Medicine

inappropriate use of

half life of facts

gcs components

item gcs

life of medical facts

life of surgical facts

point scale

resonium work