1. ABGs. Confirm pH > 7.44 and determine if primary disturbance is respiratory or metabolic (Pco2 or HCO3).
2. Electrolytes and calcium. Evaluate K+ and Cl- status; pattern may be suggestive of diagnosis (ie, hypochloremic, hypokalemic alkalosis seen with pyloric stenosis; hypokalemic alkalosis seen with Bartter syndrome). Low Ca2+ levels are noted in milk-alkali syndrome.
3. Spot urine electrolytes. Help to determine type of metabolic alkalosis and future management (ie, response to Cl- and fluid replacement).
4. Ammonia. Respiratory alkalosis, caused by stimulation of the respiratory center by hyperammonemia, is a frequent yet subtle clue to a urea cycle disorder.
5. Sweat test. Without adequate nutritional supplementation of Na+ and Cl-, infants with cystic fibrosis can have extracellular fluid losses resulting in loss of more Cl- than HCO3.
6. Salicylate level. Overdose from salicylate ingestion can cause mixed respiratory alkalosis with metabolic acidosis (high pH, low Pco2, and low HCO3).
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