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Hypocarbia: Electrolyte effects

Hypocarbia exists when PaCO2 is below 35 mmHg, which is typically the result of hyperventilation causing a respiratory alkalosis. Several electrolytes are affected by the increase in pH. Within 5-10 minutes there is drop in plasma [HCO3-] from titration of nonbicarbonate body buffers. Small increases in plasma chloride, lactate, and other unmeasured anions balance the decrease in [HCO3-]. Plasma sodium and potassium may undergo decreases. Severe hypophosphatemia can occur from movement of extracellular phosphorus intracellularly. Additionally, hypocalcemia may occur from increased binding of calcium to albumin, due to increased negative charge on albumin in alkaline states.

In contrast, chronic hypocarbia results in renal adaptation over 2-3 days. About two-thirds of the decline in plasma [HCO3-] is balanced by increase in plasma chloride, with the remainder one-third by unmeasured anions. Plasma lactate and sodium are unchanged. Phosphorus is also unchanged.