Osmolal or Osmolar Gap: Difference between revisions

Revision as of 00:38, 4 May 2011

Definitions

Osmolarity = the total number of particles in solution per liter

Osmolality = the number of particles per kilogram of solvent

Background

Serum osmolality should be measured by the freezing-point depression method rather than by the vapor pressure method, since the latter technique will underestimate the concentrations of volatile alcohols (methanol, ethylene glycol, and isopropanol).

Calculations

Calculated Osm

Calculated Osm = 2 x Na + (glu/18) + (BUN/2.8) + (ethanol/4.6) + (methanol/2.6) + (ethylene glycol/5) + (acetone/5.5) + (isopropanol/5.9)

Normal = 275-295

Osmolal Gap

Osmolal Gap = measured osm - calculated osm

(Normal = (-)14-10 mOsm/L)

DDX

Increased)

Alcohols
1. methanol
2. ethylene glycol
3. isopropanol
Sugar
1. glycerol
2. manitol
Ketones
1. acetone

Authors:

@@ Line 17: / Line 17: @@
 (Normal = (-)14-10 mOsm/L)
-===Estimating Toxic Alcohol Concentration===
-Toxic alcohol (mg/dL) = Osmolal gap x Conversion Factor
-^Parent compounds are responsible for the osmolar gap while their metabolites are responsible for anion gap changes
 ==DDX==