Cardiac pathology, hypoxia, light plane of anesthesia, use of agents like β-blockers, α2
-agonists, potent narcotics, and other anesthetic drugs may all lead to bradycardia or asystole during an ongoing surgery. The asystole may also be produced through paradoxal cardiovascular reflexes.[3
] Neurogenic bradycardia that may result in cardiac arrest is a rare, but well recognized complication during anesthesia. An acute increase in intracranial pressure and a subsequent secondary brainstem compression may be the reason. Sometimes, it may occur due to the vagal stimulation caused by any space occupying lesion in the medulla.[4
] These reactions may be elicited by the activation of trigeminocardiac reflex due to the direct stimulation of the trigeminal nerve or its branches in the dura mater or the cerebellar tentorium.[5
] The trigeminal nerve and the cardio-inhibitory vagus nerve constitute the afferent and efferent pathways of the reflex arc. Sudden asystolemay occur regardless of pressure on the brainstem during posterior fossa surgery.[6
The impulses from the glossopharyngeal nerve travelvia the tractus solitarius
of midbrain, and then to, the dorsal motor nucleus of vagus nerve. Activation of the reflex may, thereby, cause reflex bradycardia and sometimes asystole forming vago-glossopharyngeal reflex arc. The carotid sinus nerve (Hering's nerve), responsible for the conduction of impulses from the body and the carotid sinus, runs in the main trunk of the glossopharyngeal nerve and ends in the dorsal nucleus of the vagus nerve. It has been suggested that artificial synapses develop in the proximal portion of the glossopharyngeal nerve stimulating the carotid sinus via somatosensorial impulses.[7
] It may also be due to the overflow of responses from the ninth cranial nerve into the vagal motor nucleus during handling of posterior fossa tumors. With the removal of the surgical stimulus, the bradycardia usually improves and pharmacological treatment is not required. Moreover, the drugs if given may mask the signs of brainstem handling and may permanently damage the cranial nerve nuclei.
Intraoperative cardiac arrest in patients placed in position other than supine poses a challenge in terms of resuscitation. Here, Case 1 was operated in sitting position,whereas Case 2 in lateral position. Repositioning these patients is difficult, as it not only needs manpower to safely turn the patient supine,but also delays cardiopulmonary resuscitation. Otherwise, resuscitation has to be carried out in unconventional positions.[8
To conclude, the most possible explanation for asystole in the first case was due to the vago-glossopharyngeal reflex and in the second case, it was due to the direct handling of brainstem. The ability to predict the risk of asystole may better prepare clinicians to anticipate, identify, and manage an episode. It may also be suggested that in large posterior fossa tumors, specific history of symptoms related to glossopharyngeal neuralgia (paroxysmal neuralgic pain in the throat and neck precipitated by swallowing, chewing or coughing) should be taken. Transcutaneous pacing should be considered during the surgery in view of bradycardia and risk of asystole, especially in high risk patients. The importance of having the knowledge, vigilance, equipment, and skills to deal rapidly with such a case will be crucial for the patient's survival.