II. Physiology
- See Acid-Base Homeostasis
-
Anion Gap
- Anion Gap is maintained by near balance of key cations (sNa+) and key anions (sCl-, sHCO3-)
- In Non-Anion Gap Metabolic Acidosis, only measured cations and anions are affected
- In Diarrhea, bicarbonate is lost and compensated by chloride increase
- In Anion Gap Metabolic Acidosis, unmeasured anions are increased
- Increased Lactic Acid or Ketoacids, for example, result in a significant Anion Gap
III. Types
- Elevated Anion Gap Metabolic Acidosis
- Hyperchloremic Metabolic Acidosis (normal Anion Gap)
- See Hyperchloremia
IV. Causes: Common
- Most common causes of Anion Gap Metabolic Acidosis in seriously ill patients
- Most common causes of Non-Anion Gap Metabolic Acidosis
- Gastrointestinal or renal losses of bicarbonate
- Volume Resuscitation with Normal Saline
V. Causes: Metabolic Acidosis and Elevated Anion Gap (Mnemonic: "MUD PILERS")
- Methanol, Metformin
- Uremia
- Diabetic Ketoacidosis (DKA), Alcoholic Ketoacidosis or Starvation Ketosis
- Paraldehyde, Phenformin (neither used in U.S. now)
- Propofol Infusion Syndrome has been proposed as a replacement in mnemonic
- Iron, Isopropyl Alcohol, and Isoniazid (due to Seizures)
- Lactic Acidosis
- Ethylene Glycol, Ethyl Alcohol
- Rhabdomyolysis
- Salicylates (do not miss Chronic Salicylate Poisoning)
- Other Causes
- Hyperalbuminemia
- Administered anions
VI. Causes: Metabolic Acidosis and Normal Anion Gap (Hyperchloremia)
-
Hypokalemia with Metabolic Acidosis
- Diarrhea
- Ureteral diversion
- Uretero-sigmoidostomy
- Ileal Bladder
- Ileal ureter
- Renal Tubular Acidosis (proximal or distal)
- Mineralocorticoid Deficiency
- Angiotensin Deficiency: Liver Failure
- ACE Inhibitor
- Renin Deficiency
- Aging
- Extracellular fluid volume expansion
- Lead
- Beta Blockers
- Prostaglandin Inhibitor
- Methyldopa
- Carbonic anhydrase inhibitor
- Acetazolamide
- Mefenamic acid
- Post-hypocapnia
- Excessive Normal Saline infused (liters)
-
Hyperkalemia (or normal Potassium) Metabolic Acidosis
- Renal Failure (Early)
- Renal Disease
- SLE Interstitial Nephritis
- Amyloidosis
- Hydronephrosis
- Sickle Cell Nephropathy
- Acidifying agents
- Ammonium Chloride
- Calcium Chloride
- Arginine
- Sulfur toxicity
- Mnemonic: USED CARP (incomplete)
- Ureteral diversion
- Small Bowel Fistula
- Extra Chloride (ammonium chloride, Calcium Chloride)
- Diarrhea
- Carbonic anhydrase inhibitors (Acetazolamide, Mefenamic acid)
- Adrenal Insufficiency
- Renal Tubular Acidosis
- Pancreatic Fistula
- (2016) CALS Manual, 14th ed, 1: 44
VII. Causes: Metabolic Acidosis and Elevated Osmolal Gap
- Toxic Alcohol ingestion
- Eythylene glycol
- Methanol
- Serum Ketones are increased (Ketosis)
VIII. Labs: General
-
Arterial Blood Gas
- Arterial pH decreased
- Serum bicarbonate decreased
-
PaCO2 decreased
- PaCO2 drops 1.2 mmHg per 1 meq/L bicarbonate fall
- Calculated PaCO2 = 1.5 x HCO3 + 8 (+/- 2)
- Useful in High Anion Gap Metabolic Acidosis
- Measured PaCO2 discrepancy: respiratory disorder
- Serum Chemistry panel
- Anion Gap
- Increased in high Anion Gap Metabolic Acidosis
- See labs below to further differentiate cause of Metabolic Acidosis with Anion Gap
- Excess Anion Gap <23 mEq/L
- Suggests Non-Anion Gap Metabolic Acidosis
- Serum Potassium
- Investigate normal Anion Gap Metabolic Acidosis
- See above
- Serum Chloride
- Elevated in normal Anion Gap Metabolic Acidosis
- Serum bicarbonate
- Decreased in increased Anion Gap Metabolic Acidosis
- Bicarbonate decrease matches Anion Gap increase
- Anion Gap
- Urinalysis with Urine pH
-
Urine Anion Gap (obtain urine Electrolytes)
- Decreased Urine Anion Gap <-10
- Extrarenal Non-Anion Gap Metabolic Acidosis
- Increased Urine Anion Gap >+10
- Renal Non-Anion Gap Metabolic Acidosis
- Decreased Urine Anion Gap <-10
IX. Labs: Consider in Metabolic Acidosis with Increased Anion Gap
- Basic chemistry panel as above (Serum Glucose, Blood Urea Nitrogen)
- Serum Lactate
- Serum Ketones (or Beta hydroxybutyrate)
- Salicylate Level
- Blood Alcohol level
- Ethylene Glycol level
-
Osmolal Gap
- Elevated in toxic Alcohol ingestion (Alcohol, Ethylene Glycol, Methanol, isopropanol)
- Note that Isopropanol (Isopropyl Alcohol) does not increase Anion Gap, but does increase Osmolal Gap
- Creatinine Phosphokinase (CPK)
- Iron level
- Serum Albumin
X. References
- Arieff (1993) J Crit Illn 8(2): 224-46 [PubMed]
- Narins (1982) Am J Med 72:496 [PubMed]
- Narins (1980) Medicine 59:161-95 [PubMed]
- Ghosh (2000) Fed Pract p. 23-33
- Rutecki (Dec 1997) Consultant, p. 3067-74
- Rutecki (Jan 1998) Consultant, p. 131-42
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Definition (NCI_NCI-GLOSS) | A condition in which the blood is too acidic. It may be caused by severe illness or sepsis (bacteria in the bloodstream). |
Definition (NCI) | Increased acidity in the blood secondary to acid base imbalance. Causes include diabetes, kidney failure and shock. |
Concepts | Pathologic Function (T046) |
MSH | D000138 |
ICD10 | E87.2 |
SnomedCT | 59455009 |
English | ACIDOSIS METABOLIC, metabolic acidosis, metabolic acidosis (diagnosis), Acidosis metabolic, Metabolic acidosis NOS, Metabolic Acidoses, Acidosis, Metabolic, Acidoses, Metabolic, Metabolic Acidosis, acidosis metabolic, metabolic acidosis disorder, Acidosis, Metabolic acidosis (disorder), acidosis; metabolic, metabolic; acidosis, Metabolic acidosis, NOS, Metabolic acidosis |
Italian | Acidosi metabolica, Acidosi metabolica NAS |
Dutch | metabole acidose NAO, acidose; metabool, metabool; acidose, metabole acidose |
French | Acidose métabolique SAI, ACIDOSE METABOLIQUE, Acidose métabolique |
German | metabolische Azidose NNB, AZIDOSE METABOLISCH, metabolische Azidose |
Portuguese | Acidose metabólica NE, ACIDOSE METABOLICA, Acidose metabólica |
Spanish | Acidosis metabólica NEOM, ACIDOSIS METABOLICA, acidosis metabólica (trastorno), acidosis metabólica, Acidosis metabólica |
Japanese | 代謝性アシドーシス, 代謝性アシドーシスNOS, タイシャセイアシドーシスNOS, タイシャセイアシドーシス |
Czech | Metabolická acidóza, Metabolická acidóza NOS, metabolická acidóza |
Hungarian | Metabolicus acidosis, Metabolikus acidosis, Metabolikus acidosis k.m.n. |
Norwegian | Metabolsk acidose |
Ontology: Metabolic acidosis, normal anion gap (NAG) (C0268033)
Concepts | Disease or Syndrome (T047) |
SnomedCT | 111377009 |
Spanish | acidosis metabólica, hiato aniónico normal, acidosis metabólica, brecha aniónica normal (trastorno), acidosis metabólica, brecha aniónica normal, acidosis metabólica, hiato aniónico normal (trastorno), acidosis metabólica, anión gap normal, acidosis metabólica, desequilibrio aniónico normal |
English | Metabolic acidosis, normal anion gap (disorder), Metabolic acidosis, normal anion gap, Metabolic acidosis, normal anion gap (NAG) (disorder), Metabolic acidosis, normal anion gap (NAG), Metabolic acidosis, normal anion gap (NAG), NOS |
Ontology: Metabolic acidosis, increased anion gap (IAG) (C0268036)
Concepts | Disease or Syndrome (T047) |
SnomedCT | 25998009 |
Spanish | acidosis metabólica, hiato aniónico aumentado (trastorno), acidosis metabólica, hiato aniónico aumentado, acidosis metabólica con anión gap aumentado, acidosis metabólica, brecha aniónica aumentada, acidosis metabólica, brecha aniónica aumentada (trastorno), acidosis metabólica, desequilibrio aniónico aumentado |
English | Metabolic acidosis, increased anion gap, Metabolic acidosis, increased anion gap (disorder), Metabolic acidosis, increased anion gap (IAG) (disorder), Metabolic acidosis, increased anion gap (IAG), Metabolic acidosis, increased anion gap (IAG), NOS |