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Dr. Ajith Kumar J MD
Dept. of Emergency Medicne
Travancore Medicity, Kollam
India
editor
In metabolic acidosis the anion gap may be either high or normal. That is it may either wide anion gap acidosis or a normal anion gap acidosis.
Normal value : 12 ± 4 mEq/L.
Anion Gap
Where, MA: Measured anion , MC: Measured cations, UC : Unmeasured cations, UA: Unmeasured anions
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Wide Anion Gap Acidosis
CATEGORY | ETIOLOGY |
Renal Failure | Uremia |
Lactic Acidosis | Sepsis, Shock , Liver disease, Isoniazid, Iron , Carbon monoxide, Methhemoglobin, Metformin , Cyanide |
Ketoacidosis | Diabetic ketoacidosis, Alcholic ketoacidosis, Starvation ketoacidosis |
Poisoning | Methanol , ethylene glycol, Salicylates, CO, Cyanide |
High Anion Or Negative Anion Gap
Sometimes There wont be any metabolic acidosis but anion gap will be abnormal . If anion gap is present without Acid Base disturbance then it can be
ANION GAP | CAUSE | EXAMPLES |
High | Decreased unmeasured cations | Hypomagnesemia, Hypokalemia , Hypocalcemia |
Low or Negative | Increased unmeasured cation | High lithium, unmeasured positively charged proteins ( ie myeloma, polyclonal gammopathies) |
Decreased unmeasured anion | Hypoalbumin , Hypogammaglobulin | |
Measured confounder | Bromide , high triglycerides. |
Non Anion Gap Acidosis/Normal Anion Gap Acidosis
WITH TENDENCY TO HYPERKALEMIA | WITH TENDENCY TO HYPOKALEMIA |
Subsidising diabetic ketoacidosis | Renal tubular acidosis , Type I |
Early Uremic acidosis | Renal tubular acidosis , Type II |
Early obstructive uropathy | Acetazolamide |
Renal tubular acidosis IV | Acute diarrhea with losses of HCO3- & K+ |
Hypoaldosteronism | Uretrosigmoidostomy with increased resorption of [H+] & [Cl-] and losses of HCO3- & K+. |
Infusion or ingestion of HCl | Obstruction of artificial ileal bladder |
Potassium sparing diuretics | Dilutional acidosis |
Nonanion gap acidosis occurs in the setting of bicarbonate loss, but without the presence of additional pathological anion. In a non anion gap acidosis [Cl-] is increased to maintain electroneutrality and the calculated anion gap remains normal.
Check the urine anion gap (UNa + UK – UCl)
It is used in a case of normal anion gap acidosis to known whether the loss via GI source or renal loss.
If urine anion gap is positive, it is a renal cause (e.g. RTA; really only validated for types I, IV)
If urine anion gap is negative, the cause is extra-renal (Appropriate renal response is to increase ammonium excretion as NH4Cl, which causes the UAG to become negative, usually ranging from -20 to -50 mEq/L.
Gap – Gap acidosis / Mixed acid base disorder(Third Acid Base Disorder)
The third acid base disorder is diagnosed by comparing the excess AG to HCO3 deficit.
Gap- gap ratio = (Measured AG – 12) / (24 – Measured HCO3)
Gap- gap ratio = (∆AG)/ (∆HCO3-)
Ratio <1 is suggestive of concomitant normal anion gap acidosis
Ratio >1 is suggestive of concomitant metabolic alkalosis.
OR
Add the delta gap to the patient’s bicarbonate if it is < 22, there is a concomitant non-gap metabolic acidosis; if it is > 26, there is a concomitant metabolic alkalosis.
Influence Of Albumin In Anion Gap
OR
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Updated on : 21/7/2015
Reference
Tintinalli
The ICU ; Paul marino
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emmedonline
Dr. Ajith Kumar J MD
Dept. of Emergency Medicne
Travancore Medicity, Kollam
India
editor