Clinical picture and why it points to malignant hyperthermia
The patient received two classic MH triggers—
sevoflurane (a potent volatile anesthetic) and
succinylcholine (a depolarizing muscle relaxant)—and then developed a progressive, treatment-resistant rise in
end-tidal carbon dioxide (ETCO2) with tachycardia and new hyperkalemia. In malignant hyperthermia, uncontrolled release of calcium from the sarcoplasmic reticulum of skeletal muscle drives sustained muscle hypermetabolism. That produces large amounts of CO2 and heat, consumes oxygen, and leads to acidosis, muscle rigidity, and rhabdomyolysis . The rising ETCO2 is therefore not simply a ventilation problem; it reflects massively increased CO2 production.
The key discriminator here is that ETCO2 continued to climb from 50 mmHg to 62 mmHg even after ventilation was doubled. With CO2 absorbed from a pneumoperitoneum, increased minute ventilation would be expected to lower or at least stabilize ETCO2. Instead, the CO2 kept rising, which signals ongoing endogenous CO2 production—the hallmark of an MH hypermetabolic crisis.
Watch out! Core temperature was only
37.2 °C at 40 minutes. Fever is a late sign of MH because the enormous heat production may initially be masked by redistribution and anesthetic-induced vasodilation. A near-normal temperature does not exclude MH .
Why the other options are less likely
| Option | Why it does not fit this case |
|---|
| 1. Inadequate depth of anesthesia | Light anesthesia can cause tachycardia and hypertension, but it does not cause progressive hypercapnia that worsens despite doubling ventilation, nor does it produce hyperkalemia. |
| 3. Anaphylaxis to succinylcholine | Anaphylaxis typically presents with hypotension, rash, bronchospasm/wheeze, and angioedema. This patient had stable blood pressure, no rash, and no wheeze, making anaphylaxis unlikely. |
| 4. CO2 absorbed from insufflation | Absorbed CO2 raises ETCO2 early, but it responds to increased ventilation. The continued rise despite doubling ventilation, plus the new hyperkalemia and tachycardia, argues against absorption as the sole cause. |
Pathophysiology of the key findings
MH is a pharmacogenetic disorder of skeletal muscle calcium regulation. Trigger agents cause abnormal, sustained release of calcium from the sarcoplasmic reticulum, which produces persistent muscle contraction and a hypermetabolic state . The clinical consequences include increased CO2 production, increased oxygen consumption, tachycardia, tachypnea, acidosis, muscle rigidity, and rhabdomyolysis . The
hyperkalemia (
5.9 mEq/L; normal
3.5–5.0 mEq/L) results from potassium leaking out of damaged, hypermetabolic muscle cells and from rhabdomyolysis. This is a critical finding because hyperkalemia can precipitate life-threatening arrhythmias.
The combination of sevoflurane and succinylcholine exposure, progressively rising ETCO2 unresponsive to increased ventilation, tachycardia, and new hyperkalemia is the classic early pattern of an MH crisis. The absence of fever, rash, wheeze, and subcutaneous crepitus helps exclude anaphylaxis and insufflation-related CO2 absorption as the primary problem.
Clinical timing and delayed onset
MH can present during induction or later in the anesthetic course. Although many reactions occur shortly after exposure, delayed onset after sevoflurane and succinylcholine has been reported . In this case, the progressive worsening from 10 to 40 minutes—despite an initial doubling of ventilation—fits a developing hypermetabolic crisis rather than a transient response to intubation or insufflation. The circulating nurse must recognize that
early MH may present with unexplained rising ETCO2 and tachycardia before fever or rigidity appears, and that prompt recognition triggers immediate discontinuation of the triggering agent, hyperventilation with 100% oxygen, and administration of dantrolene .
Key point! In the operating room, an unexplained, persistent rise in ETCO2 after exposure to volatile anesthetics or succinylcholine should be treated as malignant hyperthermia until proven otherwise, even when temperature is normal and no rigidity is yet evident.