Severe bradycardia during scalp nerve block in patient undergoing awake craniotomy.

Sir,

Scalp nerve block is a commonly performed procedure for awake craniotomy. Though relatively safe, this procedure can sometimes produce severe hemodynamic disturbances. Here, we have highlighted such a complication and its possible explanation.

A 32-year-old patient was admitted to our hospital with complaints of left-sided headache and generalized seizures since five months. Magnetic resonance imaging revealed a left frontal mass. As the lesion was near eloquent areas (speech and motor) of the brain, the patient was scheduled for awake craniotomy (left frontal) under monitored anesthesia care (MAC). All of the laboratory investigations were within normal range. Routine monitors were attached. Intravenous fentanyl 50 mcg and propofol 30 mg were administered. On the left side, three nerves (supraorbital, supratrochlear, and zygomaticotemporal) were each blocked with 3 mL of local anesthetic mixture (5 mL of 0.25% bupivacaine with adrenaline 1: 200,000 and 5 mL of 2% lidocaine) solution. During local anesthetic infiltration over the left supratrochlear nerve, sudden bradycardia (heart rate <35 bpm) was noticed for 15 seconds followed by hypotension (blood pressure <80/46 mmHg). The surgeon was asked to stop the procedure immediately, and the hemodynamic changes reverted to normal. The patient was fully conscious during this episode; the rest of the procedure went uneventful.

Hemodynamic disturbances have been reported during local anesthetic infiltrations and usually linked to their toxic side effects or hypersensitivity reactions.[1] In addition, the usual response is hypertension followed by reflex bradycardia. The other possible mechanism maybe vasovagal which can be provoked during any sharp noxious stimuli or emotional stress.[2] However, there were no episodes of loss of consciousness and dizziness during these hemodynamic changes. Seizure episodes can also mimic these types of cardiovascular perturbations; however, there were no associated abnormal body movements.[3] Moreover, this episode occurred only during infiltration of the supratrochlear nerve and was abolished after removal of the stimulus. The probable mechanism related to this event maybe linked to the trigeminal cardiac reflex (TCR) which can be provoked by the stimulation of any sensory branch of the fifth cranial nerve and usually manifests as a sudden decrease in heart rate coupled with hypotension. This reflex can be produced by mechanical, electrical, and even chemical stimuli.[4] The rapid infiltration of local anesthetic solution might have caused local mechanical compression or stretch on the supratrochlear nerve, thus provoking this reflex. Opioid-induced sudden transient bradycardia is also unlikely, though opioids are one of the risk factors associated with TCR.[5] Thus, it is likely that the use of fentanyl just before the scalp nerve block might have been an additive to this event. The sensitivity of different branches of the trigeminal nerve for inciting TCR could be an area of further research.

In conclusion, TCR can be a manifestation of scalp nerve block (trigeminal nerve territory) and may produce catastrophic consequences if not vigilantly monitored. The slow and incremental administration of local anesthetics may reduce the chances of such an event.