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

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

Life Threatening Causes

• Diabetic ketoacidosis
• Ethylene glycol poisoning
• Lactic acidosis
• Methanol ingestion

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

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

• 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

Dont's

• Do not administer vasoconstrictors in the presence of lactic acidosis