A 72-yeаr-оld client is brоught tо the emergency depаrtment by fаmily after vomiting bright red blood and passing melena stools over the past several hours. The client has a history of peptic ulcer disease and chronic NSAID use for osteoarthritis. Assessment findings: BP: 78/48 mm Hg (MAP 58) HR: 132 bpm, sinus tachycardia, thready radial pulse CVP: 2 mmHg RR: 26/min, shallow SpO₂: 93% on room air Skin: pale, cool, diaphoretic Capillary refill: > 3 seconds Mental status: anxious, mildly confused Neck veins: flat The provider suspects hypovolemic shock from the acute GI bleed. Which clinical finding best supports the diagnosis of hypovolemic shock?