Essential Facts on the Go: Internal Medicine (20 page)

Remember 1 mmol of unmeasured acid titrates 1 mmol of bicarbonate. If ΔGap is greater than zero, there is an underlying metabolic alkalosis; if it is less than zero, then there is an underlying non-AG metabolic acidosis
.

In patients with normal anion gap metabolic acidosis, calculate the urinary AG
.

In metabolic acidosis from bicarbonate loss in diarrhea, the urinary anion gap (UAG) is typically –20 to –50 mmol/L. A positive UAG indicates an inappropriately low urinary NH4+ level, suggesting that renal tubular acidosis is responsible
.

In metabolic alkalosis, measure urine chloride
.

A low urine chloride suggests volume depletion, most often from vomiting or recent diuretic use. A normal or high urine chloride suggests mineralocorticoid excess or alkali loads
.

V_3_a
Hyponatremia

V_3_b
Hypernatremia

Always hyperosmolar (√ serum Osm, √ urine Osm), ([Na+] > 145)

Always a water problem, sometimes a salt problem

Symptoms = lethargy/AMS, weakness, irritability, seizure, coma, death

Treatment: (enteral water administration is ideal)

Assess volume status

Calculate amount + rate of infusate infusion

Do not correct > 10 mEq/L × 24 h