Osmolar Gaps: How does EtOH contribute to osmolar gaps? Can osmolar gaps be used to rule out toxic alcohols? - PowerPoint PPT Presentation

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Osmolar Gaps: How does EtOH contribute to osmolar gaps? Can osmolar gaps be used to rule out toxic alcohols?

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Ethanol and the Osmolar Gap Several studies have noted the increase in osmolar gap with rising EtOH in a NON 1:1 relationship Many different EtOH conversion factors ... – PowerPoint PPT presentation

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Title: Osmolar Gaps: How does EtOH contribute to osmolar gaps? Can osmolar gaps be used to rule out toxic alcohols?


1
Osmolar GapsHow does EtOH contribute to osmolar
gaps?Can osmolar gaps be used to rule out toxic
alcohols?
  • Rob Hall PGY4
  • Lab Rounds
  • Jan 15, 2004

2
Why review?
  • Osmolar gaps arent perfect thus why use?
  • Routine measurement of toxic alcohols is
    impractical
  • Labor intensive
  • Long turn around time
  • Only measured in tertiary care centers
  • Osmolar gaps thus likely have some role and we
    need to know the major limitations

3
Osmolar Gap Osmolality - Osmolarity
  • Osmolality
  • Solute/kg of solvent
  • Lab measures
  • Osmolarity
  • Solute/liter of solution
  • You calculate!

4
Ddx of Osmolar Gap
P Proteins
A Alcohols (EtOH, methanol, ethylene glycol, isopropanol, propylene glycol, diethylene glycol, triethylene glycol)
S Sugars (mannitol, glycerol, sorbital)
C Contrast dyes
A Acidosis (ketoacidosis, lactic acidosis)
L Lipids
A Acetone
5
Osmolar Gaps
  • Which formula is best?

6
Osmolarity Formulas
  • Other formulas.

7
Osmolarity Formulas
  • Calgary
  • 1.86Na BUN glucose 9
  • Why 1.86 93 is in Na, Cl- (ionized form) and
    the remainder is in the NaCl (nonionized form)
  • Why 9 factor intercept for multiple regression
    line
  • Thought to be the best formula Dorwat. Clin
    Chemistry 1975.
  • NB EtOH is not automatically added!
  • Edmonton
  • 2Na BUN glucose
  • Serum is only 93 water 1.86/0.93 2

8
Case 1
  • Intoxicated male
  • Na 140, BUN 5, Gluc 5, EtOH 75
  • Osmolality 385
  • Osmolarity 2(140)5575 365
  • Osm gap 20
  • How does EtOH effect osmolar gaps?

9
Ethanol and the Osmolar Gap
  • Several studies have noted the increase in
    osmolar gap with rising EtOH in a NON 11
    relationship
  • Many different EtOH conversion factors have been
    developed
  • Geller 1986 1.20
  • Galvan 1992 1.14
  • Synder 192 1.20
  • Hoffman 1993 1.09
  • Pappas 1985 1.12
  • Britten 1972 1.74
  • Glasser 1973 1.1

10
Ethanol and the Osmolar Gap
  • Purssell. Ann Emerg Med 2001 38 653-659.
  • Derived a formula to account for the relationship
    between ethanol and osmolar gap
  • Prospectively validated
  • Best formula EtOH (mmol/L) X 1.25

11
Explanation for EtOH X 1.25
  • Ethanol has a non-ideal osmotic behavior
  • Ethanol has a non-ideal osmotic behavior because
    molecules form physiochemical bonds with other
    molecules resulting in an effect on osmolarity
    that is non-uniform

12
Data from our own Lab!
This data supports the 1.25 EtOH conversion
13
Case 1
  • Osmolality 385
  • Osmolarity 2(140)5575 365
  • Osm gap 20
  • How does EtOH effect osmolar gaps?
  • EtOH X 1.25 94
  • Osmolality 385
  • Osmolarity 384
  • Osm gap 1

14
Case 2
  • 35 yo male
  • Took a swig of a mug that had antifreeze
  • Na 140, BUN 5, Gluc 5, EtOH 25
  • Osmolality 321
  • NO anion gap (HCO3 24)
  • Osmolarity 2Na BUN Gluc EtOH X 1.25 321

15
Case 2
  • Osmolar gap 321 - 321 0
  • What is a normal osmolar gap?

16
What is a Normal Osmolar Gap?
  • Hard to define!
  • Depends on..
  • Lab method of osmolality determination
  • Osmolarity formula used
  • Lab error of Na, BUN, Gluc, EtoH
  • EtOH conversion factors used
  • There are few studies documenting what normal
    osmolar gaps are in the population

17
What is a Normal Osmolar Gap?
  • Traditional Normal Osmolar Gap is lt 10
  • Case 2 osmolar gap 0
  • Can osmolar gaps be used to rule out toxic
    alcohol ingestions?
  • Is there a cutoff where toxic alcohols should
    be routinely measured?

18
Normal Osmolar GapHoffman. J Toxicol Clin
Toxicol. 19932Na BUN Gluc EtOH
-14
10
4
-2
-8
19
When should toxic alcohols be measured? AMA
guidelines
  • Calgary (1.86Na BUN Gluc EtOH 9)
  • Osmolar gap gt 10 measure methanol and ethylene
    glycol
  • Edmonton (2Na BUN Gluc EtOH)
  • Osmolar gap gt 2 measure ethylene glycol
  • Osmolar gap gt 5 measure methanol

20
Can these cut offs r/o a significant toxic
alcohol ingestion?
  • Baseline -14
  • Osm gap 0
  • Methanol level of 14!!!

-14
0
21
Additional problems
  • What is the normal distribution for the formula
    that we use in Calgary for osmolarity?
  • What is the true effect of EtOH?
  • What is a significant toxic alcohol level?
  • Nobody really knows!
  • Evidence for when to dialyze based on case series
    and case reports.
  • Are you willing to miss a methanol level of 5,
    10, or 15 mmol/L?

22
So what is the utility of the osmolar gap?
23
Conclusions 1
  • EtOH has contributes more to osmolarity than
    expected EtOH X 1.25 is likely the best
    conversion factor
  • Which formula to use for osmolarity?
  • It doesnt really matter, just be aware of
    suggested cut offs for toxic alcohol measurement
    and the inherent limitations of such cut offs

24
Conclusions 2
  • Osmolar gaps are NOT 100 reliable to exclude
    treatable toxic alcohol ingestions
  • Low suspicion ------ check osmolar gap
  • High suspicion ------ low threshold to check
    toxic alcohol levels regardless of osmolar gap
  • Remember osmolar gaps are irrelevant when the
    patient has an AGMA from toxic metabolites

25
REMINDER how often to measure levels
  • Dialysis of Methanol
  • Methanol vs time to level lt 6 mmol/L
  • 160 12hrs
  • 100 10hrs
  • 55 8hrs
  • 30 6hrs
  • 15 4hrs
  • 7 3hrs
  • Ethanol therapy alone for Methanol
  • ADH is blocked by EtOH excretion by
    pulmonary/renal
  • T1/2 increases A LOT
  • T ½ 30-70hrs
  • Dont measure levels q 4hrs!
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