A client prescribed furosemide (Lasix) 40 mg IV is a nursing priority to assess which parameter BEFORE administration?

PRE-FUROSEMIDE ASSESSMENT: POTASSIUM: Most critical — loop diuretics (furosemide, torsemide, bumetanide) block Na-K-Cl co-transporter in the loop of Henle; significant potassium loss with every dose; hold and notify if K+ < 3.0-3.5 mEq/L (facility-specific threshold); BLOOD PRESSURE: Hold if hypotensive per orders — diuresis on an already volume-depleted patient worsens hypotension, tachycardia, and possibly syncope; URINE OUTPUT: Anuria (no urine) contraindicates furosemide — there is nothing to diurese; RENAL FUNCTION: BUN/creatinine — severe renal impairment changes dosing; ALLERGIES: Cross-reactivity with sulphonamide allergy (controversial — check facility policy); HEARING: Furosemide is ototoxic, especially with high IV doses or co-administration of aminoglycosides — inquire about hearing symptoms; WEIGHT: Daily weights are the best measure of fluid loss/gain in patients on diuretics; establish baseline before first dose.