PACU Emergencies: MH, LAST, Aspiration, and Deterioration

Malignant Hyperthermia Pattern

Malignant hyperthermia (MH) is a hypermetabolic crisis in genetically susceptible patients exposed to triggering agents: volatile anesthetics (sevoflurane, isoflurane, desflurane) or the depolarizing paralytic succinylcholine. Hyperthermia is often a late sign, so do not wait for a high temperature.

The earliest and most sensitive clue is an unexplained, rapidly rising end-tidal carbon dioxide (ETCO2) despite adequate ventilation, accompanied by tachycardia, masseter or generalized rigidity, mixed acidosis, hyperkalemia, dysrhythmias, cola-colored (myoglobinuric) urine, and eventually a temperature rise that can exceed 1 C every few minutes.

The first response is crisis activation. Call for help, notify anesthesia and the surgeon, and obtain the MH cart. Per the Malignant Hyperthermia Association of the United States (MHAUS), the antidote is dantrolene 2.5 mg/kg IV, repeated every few minutes until the crisis reverses, commonly totaling up to about 10 mg/kg. Deliver high-flow 100% oxygen with hyperventilation, begin active cooling (cold IV saline, surface cooling) targeting roughly 38 C and stopping near that point to avoid overshoot hypothermia, and support treatment of hyperkalemia, acidosis, dysrhythmias, and renal protection.

The MHAUS hotline (1-800-644-9737 in the US) provides real-time expert guidance.

LAST Pattern

Local anesthetic systemic toxicity (LAST) can follow peripheral nerve blocks, neuraxial dosing, wound infiltration, or continuous local anesthetic infusions, especially with bupivacaine. Early neurologic findings include circumoral (around-the-mouth) numbness, metallic taste, tinnitus, dizziness, agitation, confusion, tremor, or seizure. Cardiovascular toxicity follows with hypotension, conduction delay, ventricular dysrhythmias, or arrest.

First actions: stop the local anesthetic, call for anesthesia help, secure the airway and oxygenation, and treat seizures (benzodiazepines preferred; avoid large propofol doses in unstable patients). The specific antidote is 20% lipid emulsion per the American Society of Regional Anesthesia (ASRA) protocol: for a patient under 70 kg, a bolus of 1.5 mL/kg lean body weight followed by an infusion of 0.25 mL/kg/min; for a patient over 70 kg, a 100 mL bolus followed by a 200-250 mL infusion over 15-20 minutes. Do not delay, because neurologic symptoms can progress to cardiovascular collapse within minutes.

Aspiration and Airway Contamination

Aspiration risk rises with depressed airway reflexes, vomiting, ileus, pregnancy, obesity, emergency or full-stomach surgery, opioids, and delayed gastric emptying. If aspiration is suspected, position the patient laterally to protect the airway when safe, suction the mouth and pharynx, apply oxygen, assess lung sounds and SpO2, and prepare for bronchoscopy, intubation, chest imaging, or higher-level monitoring. Persistent wheeze, crackles, fever, hypoxemia, or respiratory distress requires escalation; chemical pneumonitis can evolve over hours.

Deterioration Without a Label

Not every emergency announces itself. A patient may first show restlessness, new confusion, increasing oxygen need, tachycardia, a narrowing pulse pressure, decreasing urine output, or a rhythm change. Treat deterioration as real until proven otherwise. Reassess airway, breathing, and circulation; verify monitors and lines; inspect wounds and drains; review recent medications; and call for help early rather than waiting for confirmatory data.

Protocol Thinking

For rare crises, the correct answer is rarely solitary heroics. Use the emergency cart or cognitive-aid checklist, assign clear roles, request additional staff, and follow facility protocol for medications, labs, cooling, lipid therapy, documentation, and transfer to a higher level of care. The nurse's value is early recognition plus organized escalation while basic oxygenation, ventilation, and perfusion support continue uninterrupted.

Communication Under Pressure

Use a short structured report: procedure, anesthetic and block exposure, current ABC status, vital-sign trend, rhythm, temperature, neurologic status, output or bleeding, suspected complication, and interventions already started. The exam favors answers that mobilize the team while the nurse continues immediate bedside stabilization.

Distinguishing the Hyperthermic Emergencies

Several conditions raise temperature, and the exam tests your ability to separate them by their triggers and associated findings. Malignant hyperthermia follows volatile agents or succinylcholine and pairs hyperthermia with rigidity, rising ETCO2, and hyperkalemia. Neuroleptic malignant syndrome follows dopamine antagonists (including some antiemetics) and develops over days with lead-pipe rigidity and altered mental status. Serotonin syndrome follows serotonergic drugs and shows hyperreflexia, clonus, and agitation over hours. A simple infection or warming-blanket overshoot produces fever without rigidity or a rising ETCO2.

Why Early Beats Perfect

The defining feature of every PACU crisis is that waiting for confirmatory labs or peak vital-sign abnormality costs survival. Dantrolene given early in MH and lipid emulsion given early in LAST both work far better before circulatory collapse than after. The exam consistently rewards the answer that acts on the pattern, mobilizes help, and prepares the antidote rather than the answer that gathers more data, repeats vitals, or waits for the physician to arrive before starting oxygen and protocol activation.

The Nurse's Role in a Coded Response

During a declared emergency, perianesthesia nurses are often the team members who recognized the problem and who know the cart contents, the drug concentrations, and the patient's anesthetic history. Useful tasks include assigning a recorder, calculating weight-based doses (dantrolene 2.5 mg/kg, lipid emulsion 1.5 mL/kg under 70 kg), drawing labs (arterial blood gas, potassium, lactate, coagulation studies), and preparing transfer to intensive care. Organized, role-based teamwork built on early recognition is the competency these emergency items are designed to measure.