Stage 3 — Prioritize hypotheses. The 37-year-old client admitted 2 days ago for acute psychosis received several IM haloperidol doses over 48 hours, then a higher scheduled dose. Yesterday a neck spasm resolved after IM diphenhydramine. The client takes no antidepressant and has had no surgery or anesthesia. At 0400 the client is mute and opens the eyes only to a loud voice; the limbs resist passive movement evenly through the range; there is no clonus; pupils are 4 mm and brisk; the skin is diaphoretic. Temperature 40.2 C, HR 132/min, RR 30/min, BP 176/102 mm Hg at 0200 and 88/50 mm Hg now. Creatine kinase 6,800 U/L, potassium 5.6 mEq/L, creatinine 1.7 mg/dL, urine dark. 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
Neuroleptic malignant syndrome. Take action: hold all haloperidol and begin active external cooling. Monitor: core body temperature and serum creatine kinase.

Why this is correct
NMS follows dopamine blockade, especially rapid dose escalation and IM dosing. The tetrad is present: hyperthermia, lead-pipe rigidity, altered mental status, and autonomic instability, with rhabdomyolysis shown by CK, potassium, creatinine, and dark urine. The fever is produced by rigid muscle and central dysregulation, so external cooling is required. Temperature and CK trends show whether the hypermetabolic process and muscle injury are settling.

Easy analogy or mental picture
Blocking dopamine is like cutting the brake cable to the body's thermostat and muscles: temperature climbs and muscles lock. Remove the scissors (stop haloperidol), cool the engine from outside, and read the heat gauge and the muscle-damage meter.

Memory hook
Neuroleptic + Rigid + Hot + Confused = NMS: STOP and COOL; watch TEMP and CK.

NCLEX decision rule
When a toxidrome follows a drug, pick the one whose trigger and exam pattern both match, stop the trigger, and monitor the vital sign and lab that define its severity.

Why the other choices are wrong
Serotonin syndrome needs a serotonergic drug and produces clonus and hyperreflexia, which are absent, so cyproheptadine and ankle clonus track the wrong problem. Malignant hyperthermia follows volatile anesthetics or succinylcholine, which the client has not received, and end-tidal CO2 is its monitoring marker. Anticholinergic toxicity causes dry skin and dilated pupils; this client is diaphoretic with 4-mm pupils. Benztropine treats acute dystonia but does not reverse NMS rigidity. Antipyretics such as acetaminophen do little for NMS hyperthermia, so they cannot be the main cooling step.