Metabolic acidosis is a low blood pH caused by too much acid or too little bicarbonate in the body. The anion gap splits the causes into high-gap ones such as ketoacidosis, lactic acidosis, kidney failure and toxins, and normal-gap ones such as diarrhea and renal tubular acidosis.
Key symptoms
- Deep, fast breathing (Kussmaul breathing)
- Nausea, vomiting and abdominal pain
- Fatigue and weakness
- Confusion or drowsiness
- Symptoms of the cause: diarrhea, thirst and frequent urination, toxin ingestion
What you find on exam
- Fast, deep breathing
- Fast heart rate and low blood pressure
- Signs of dehydration
- Fruity breath, poor perfusion or altered mental status
Tests
- Blood gas: low pH, low bicarbonate and a compensating low PaCO2
- Anion gap from sodium, chloride and bicarbonate
- Glucose, ketones, lactate, creatinine and potassium
- Serum osmolality and toxicology screen for toxic alcohols or salicylates
Treatment basics
- Treat the cause: insulin and fluids for DKA, fluids and antibiotics for sepsis
- Restore volume with IV fluids
- Replace potassium carefully
- IV sodium bicarbonate only in selected severe cases
- Dialysis for toxic alcohols, salicylates or kidney failure
Red flags
- pH below 7.1 or worsening despite treatment
- Altered mental status or tiring breathing
- Suspected toxic alcohol or salicylate ingestion
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Sources: NCCPA PANCE Content Blueprint; NBOME COMLEX-USA clinical presentations; AAMC Core Entrustable Professional Activities (Core EPAs). Written by Making Synapses. Making Synapses is not affiliated with these organizations.