1) What is your diagnosis?

                        A- Definitely MH

                        B- Probably MH

                        C- Light anesthesia

                        D- Not MH

2) What action should be taken first?

A-  Administer dantrolene 2.5 mg/kg IV

B-   Actively cool the patient

C-   Discontinue inhalation agent

D-   Abort the surgery

3) The most sensitive and useful monitor for the early diagnosis of a hypermetabolic event is:

A- EKG

B- Temperature monitor

C- ETCO2

D- Pulse oximeter

E- Blood pressure monitor

4) Caffeine halothane contracture testing is indicated in all the following except?

A- Clinical history suspicions for malignant hyperthermia

B- A first-degree relative of a patient with documented MH

C- Unexplained muscular rigidity with MH suspicion

D- Sudden cardiac arrest on induction of anesthesia

5) One of the following arterial blood gas (FiO2 of 50%) makes MH unlikely (PH/PCO2/PaO2/Bicarb/BE):

A- 7.10/ 41/ 90/ 14/ -9

B- 7.10/ 56/ 109/ 16/ -8

C- 7.15/ 72/ 188/ 21/ -1

D- 7.01/ 72/ 105/ 13/ -10

Answers:

1)      This infant underwent 2 previous general anesthetics without complications. However, that does not rule out MH. The signs and symptoms are of MH so far, but each on of them can be explained separately also. Increased in HR could be a sign of light anesthesia and increased surgical manipulations. Increased of ETCO2 could be a sign of hypoventilation as surgeon is working in the abdomen of a small infant and mechanical push against the diaphragm is not uncommon. Using warm forced-air can explain the rapid temperature increases especially in an infant. However, MH can not be ruled out yet.

Answer B

2)      At any time MH is suspected, discontinuing the inhalation agent should be the first approach. Total intravenous anesthesia (TIVA) is very easy to administer nowadays and is proven to be safe in case of MH. If the episode is truly MH, discontinuing the inhalation agent could be a life saver. If the episode is not MH, TIVA is just another anesthetic that may help in the differential diagnosis.

Answer C

3)      MH is a hypermetabolic event and like most other hypermetabolic events it results in increased CO2 production and O2 extraction.

Answer C

4)      Currently, the in vitro contracture test (IVCT) is the gold standard for diagnosing MH. However, the IVCT is very expensive, requires a surgical procedure that can only be performed on-site in one of approximately 10 specialized testing centers in the US, and has 97% sensitivity and 78% specificity. Consequently, IVCT is only indicated in patients who have had clinical episodes and (possibly) their immediate family members. Sudden cardiac arrest on induction of general anesthesia is most likely an indication for arrhythmias and not MH.

Answer D

5)      In a true MH episode, arterial blood gas most likely reflects a metabolic acidosis state. Although variations exist, an arterial blood gas that shows respiratory acidosis without any metabolic effects makes the diagnosis of MH unlikely.

Answer C

Narrative

Inhalation agent was discontinued and 100% oxygen was administered. TIVA was initiated using propofol infusion at 200 mcg/kg/min. Forced-air temperature was decreased to 32°. Another dose of fentanyl administered (2 mcg/kg) and respiratory rate increased to 40 per minute. Despite all these measures, HR remained at 180 b/min, BP stable, and ETCO2 around 58 mmHg. However, temperature stabilized at 38 and decreased slowly thereafter. A 10 ml/kg bolus of normal saline was administered.

When intraabdominal surgical manipulation stopped (90 minutes later), HR decreased to 140s b/min and ETCO2 to 37 mmHg. TIVA was discontinued and the trachea was extubated. Vital signs were stable thereafter.

Mohanad Shukry, MD

Children's Hospital of Oklahoma

Oklahoma City, OK