A client with a nasogastric (NG) tube is about to receive a tube feeding. Which verification is ESSENTIAL before starting?

NG TUBE PLACEMENT VERIFICATION — CRITICAL SAFETY ISSUE: Feeding through a misplaced NG tube (especially one accidentally in the lung) can cause aspiration pneumonia and death. VERIFICATION METHODS (from most to least reliable): ASPIRATION AND PH TESTING: Aspirate stomach contents; pH of 5.5 or below suggests gastric placement; if pH is above 6, tube may be in small intestine or respiratory tract; X-RAY: Gold standard for confirming initial placement; required for initial placement confirmation before first use in most facilities; MEASUREMENT MARKING: Verify that the external tube marking at the naris matches the documented insertion measurement — migration of the tube is detected this way; VISUAL INSPECTION: Aspirate color (gastric = cloudy/yellow-green; respiratory = clear/white); OUTDATED METHOD: Auscultation ('whoosh' test) — injecting air and listening for sound — is NO LONGER RECOMMENDED as a primary verification method; it has caused deaths when air sound was heard from a tube in the respiratory tract; PN SCOPE: Verify before each feeding or medication; document verification method and results.