Stage 3 — Prioritize hypotheses. Mr. T, 64, had PCI with a drug-eluting stent yesterday for NSTEMI and receives aspirin, ticagrelor, a weight-based heparin infusion, and a morphine PCA (1 mg demand dose, 8-minute lockout, no basal infusion, patient-only activation). At 0200 he was drowsy but conversant with pain 3/10. At 0630, respirations are 10/min and shallow, SpO2 is 92% on 2 L/min, heart rate is 78 in sinus rhythm, and BP is 108/62 mm Hg, similar to overnight. Pain is 1/10. He arouses only to firm voice; pupils are 2 mm, equal, and reactive, and he moves all extremities. His wife says she pressed the PCA button while he slept; the pump shows 14 deliveries in four hours. The 0200 aPTT was 92 seconds (target 60 to 90), and there is no overt bleeding. Complete the diagram by selecting the condition the client is most likely experiencing, 2 actions the nurse should take to address that condition, and 2 parameters the nurse should monitor to assess the client's progress.

Quick answer
Condition: opioid-induced respiratory depression. Actions: stop the PCA, stay, and support his breathing, and give titrated naloxone per protocol if breathing stays poor. Monitor: sedation level on the POSS and end-tidal carbon dioxide.

Why this is correct
The PCA is safe only because a sleepy patient stops pressing the button. When his wife pressed it for him, that safeguard was bypassed and 14 doses were delivered. Sedation rises before respirations fall, so increasing sedation with slow, shallow breathing, small pupils, and a very low pain score fits opioid excess. The first actions remove the source and protect breathing; naloxone is titrated in small doses so ventilation returns without causing severe pain or withdrawal. Sedation scores and capnography detect hypoventilation earlier than pulse oximetry, especially when the client is on oxygen.

Easy analogy or mental picture
A PCA is a self-closing tap: when the person holding it falls asleep, the water stops. Proxy dosing is someone else holding the tap open while the person sleeps.

Memory hook
Sleepy + slow + small pupils after PCA = stop, stay, support, then small naloxone doses.

NCLEX decision rule
For suspected opioid-induced respiratory depression, stop the opioid and support breathing first, then reverse with titrated naloxone. Monitor sedation and ventilation (capnography), not just SpO2.

Why the other choices are wrong
Intracranial hemorrhage is a real concern with heparin and dual antiplatelets, but his pupils are equal and reactive and he moves all extremities, so a stat head CT is not the first action and aPTT tracks anticoagulation rather than this problem. Recurrent ischemia with low output is excluded by a stable BP of 108/62 and sinus rhythm at 78, so troponin follows the wrong condition. Expected sleep is tempting because pain is controlled, but a rate of 10 with shallow breaths and arousal only to firm voice is not normal sleep. Adding oxygen and waiting an hour hides hypoventilation behind a normal SpO2. A full rapid 2 mg push is outdated for postoperative opioid patients because it can trigger severe pain, hypertension, and withdrawal. Serum potassium relates to the potassium infusion, a separate hazard.