What is the priority nursing diagnosis for a client with acute heart failure exacerbation presenting with severe shortness of breath, pink frothy sputum, and crackles throughout lung fields?

This presentation describes acute pulmonary edema — fluid in the alveoli — a life-threatening complication of acute heart failure. The priority diagnosis is impaired gas exchange because oxygen cannot diffuse across fluid-filled alveoli. Other features: orthopnea (unable to lie flat), paroxysmal nocturnal dyspnea, S3 gallop, jugular venous distention, peripheral edema, decreased urine output. Immediate management (LMNOP or Lasix-Morphine-Nitrates-Oxygen-Position): (1) High-Fowler's position to ease breathing; (2) High-flow oxygen — non-rebreather mask or BiPAP/CPAP, possibly intubation if severe; (3) IV diuretics (furosemide) — rapid diuresis to reduce preload; (4) IV nitroglycerin — vasodilator, reduces preload and afterload; (5) Morphine — reduces anxiety, decreases preload through venodilation (controversial in some recent guidelines because of associations with worse outcomes); (6) Continuous monitoring of vital signs, oxygen saturation, urine output, cardiac rhythm; (7) Address the underlying cause (ischemia, hypertensive emergency, valvular disease, atrial fibrillation, medication noncompliance, dietary indiscretion). Once stabilized: optimize chronic heart failure medications (ACE inhibitor/ARB, beta-blocker, mineralocorticoid receptor antagonist, SGLT2 inhibitor).