Excessive mouth opening with a dental gag triggered the reflex of the trigeminal and vagal nerves, immediately causing a rare case of asystole. The boy made a full recovery, the authors wrote.
"The trigeminovagal reflex was most likely elicited by stretching the masticatory muscles and triggering an afferent response of the mandibular branch of trigeminal nerve," wrote the group, led by Dr. Hiroshi Hoshijima, PhD, an assistant professor at the Tohoku University Graduate School of Dentistry in Sendai, Japan.
Rare but serious reflex
The trigeminal nerve is a complex cranial nerve that controls sensation in the face and motor functions, including chewing. When this nerve is stimulated, it triggers the trigeminovagal reflex, causing the sudden onset of bradycardia, hypotension, and cardiac arrest.
The trigeminovagal reflex is rare, occurring in about 2% of maxillofacial surgeries. It is defined as a decrease in heart rate and drop in arterial blood pressure of at least 20% compared to blood pressure prior to trigeminal nerve stimulation.
The use of lighter anesthesia during surgery is one risk factor for triggering the reflex. Younger patients are also at a higher risk, the authors noted.
Multiple attempts to complete surgery
In the documented case, a healthy boy was at the dentist to have maxillary supernumerary teeth extracted. After tracheal intubation, anesthesia was induced with sevoflurane (8%), nitrous oxide (4 L/min), and oxygen (2 L/min). Anesthesia was then maintained with sevoflurane (1%-1.5%), air (2 L/min), oxygen (1 L/min), and remifentanil (0.2-0.3 µg/kg/min).
The clinicians opened the boy's mouth with a dental mouth gag at the beginning of the procedure and an electrocardiogram (ECG) showed asystole for 20 seconds. They prepared to administer chest compressions and use a defibrillator when the boy's heart rate spontaneously returned to baseline within 60 seconds.
After observing the patient for a few minutes, the dental team restarted the procedure and reopened the boy's mouth with the gag. The patient's heart rate suddenly decreased from 100 beats per minute (bpm) to 70 bpm when the interincisal distance of his mouth opening surpassed approximately 40 mm. His heart rate spontaneously returned to baseline within 15 seconds. These events occurred one more time, but his heart rate returned to baseline within one minute.
Fortunately, the surgery was completed without complications. The boy experienced no breathing or neurological problems, and he was discharged two hours after he woke up from the anesthesia, according to the authors.
Clinicians should be mindful of the possibility of triggering the trigeminovagal reflex when performing dental procedures that require excessive mouth opening, they wrote.
"This maneuver should be carefully performed because of the rare possibility of severe bradycardia or cardiac arrest, particularly under general anesthesia," Hoshijima and colleagues concluded.
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