Metabolic acidosis resident survival guide
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Ogheneochuko Ajari, MB.BS, MS [2]
Overview
Overview
Metabolic acidosis is a state in which the blood pH is low (less than 7.35) due to a decreased blood concentration of bicarbonate.
Causes
Causes
Life Threatening Causes
Common Causes
Normal Anion Gap Metabolic Acidosis
The mnemonic for the most common causes of a normal-anion gap metabolic acidosis is “DURHAM.”
- D– Diarrhea, dilutional (rapid infusion of IV fluids that are free of bicarbonate)
- U– Ureteral diversion
- R– Renal tubular acidosis, renal failure (early)
- H– Hyperalimentation
- A– Addison’s disease, acetazolamide, ammonium chloride
- M– Miscellaneous: congenital chloride diarrhea, amphotericin B, toluene, cholestyramine, posthypocapnea
High Anion Gap Metabolic Acidosis
The mnemonic “MUDPILES” is used to remember the common causes of a high anion gap.
- M – Methanol/ Metformin
- U – Uremia
- D – Diabetic ketoacidosis
- P – Paraldehyde/ Propylene glycol
- I – Infection/ Ischemia/ Isoniazid
- L – Lactic acidosis
- E – Ethylene glycol/ Ethanol
- S – Salicylates/ Starvation
Management
Management
Step 1
| pH<7.35 And [HCO3–]<24 meq/L | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Metabolic acidosis | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Calculate the anion gap (AG) Na+ – Cl– – HCO3– | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Low AG AG<8 | Normal AG 8<AG<16 | High AG AG>16 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Check albumin Correct the AG if albumin is low For every decrease of 1 g/dl of albumin, AG is decreased by 2.5 meg/L | Check Ca2+, Mg2+, K+, immunoglobulins High levels of these unmeasured cations decrease the AG | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Check urine AG Na+ + K+ – Cl– | Check ΔAG/ΔHCO3– | R/O low Ca2+, Mg2+, K+ | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Negative urine AG GI causes RTA type II | Positive urine AG Renal failure RTA type I RTA type IV | ΔAG/ΔHCO3–<1 High AG metabolic acidosis combined with normal AG metabolic acidosis | 1<ΔAG/ΔHCO3–<2 Pure high AG metabolic acidosis | ΔAG/ΔHCO3–>2 High AG metabolic acidosis combined with metabolic alkalosis | |||||||||||||||||||||||||||||||||||||||||||||||||||||
Step 2
Shown below is the algorithm summarizing the management of metabolic acidosis
| History, symptoms and physical examination Blood pH < 7.35 | |||||||||||||||||||||||||||||||||||||||||
| Physical examination Eyes Extremities Neurologic (cranial nerves) | Labs/EKG Anion gap, Arterial blood gas analysis Electrolytes (Na, K, Cl, HCO3) CBC Serum lactate, ketone Urinalysis Toxicological screening (salicylate, methanol, ethylene glycol) EKG for arrhythmias | History Arrhythmias Kussmaul breathing Headache, altered mental status | |||||||||||||||||||||||||||||||||||||||
| Place patient on EKG monitor for arrhythmias, hyperkalemia | Replace electrolytes if there are losses | If DKA, IV Insulin, normal saline Potassium and phosphate may be necessary | Send consult to nephrologist for dialysis for renal failure, poisoning | Toxicological consult | |||||||||||||||||||||||||||||||||||||
| IV bicarbonate if there is cardiac arrhythmias 50-100mmol while monitoring arterial blood gas readings | Detoxification agents/toxin antidotes Fomepizole Activated charcoal Emesis Folic acid for methanol overdose Thiamine and pyridoxine for ethylene glycol overdose | ||||||||||||||||||||||||||||||||||||||||
Do’s
Do’s
- Treatment of the underlying cause should be the primary therapeutic goal.
- Bicarbonate should be given only when there is a severe case of acidosis with an arterial pH of less than or equal to 7.2
- Patient should be placed on SaO2 and blood pressure/heart rate monitor
- Consider intubation and ventilation for airway if the SaO2 level is deteriorating or there is a loss of consciousness
- Consider doing catherization to monitor the urine output and obtaining urine for urinalysis
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