QUIZ 2. HEMODYNAMIC CHANGES DURING CAROTID ENDARTERECTOMY.

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Correct answer is B. The carotid sinus is the mediator of bradycardia. These baroreceptors, which receive afferents via the glossopharyngeal nerve and affect heart rate control via the vagus nerve, normally respond to blood vessel stretch stimuli to protect the brain from hypertension. The baroreceptor reflex also can be activated when the carotid sinus is surgically manipulated, causing abrupt bradycardia and hypotension. Cessation of surgical stimulus usually restores heart rate. Pretreatment with atropine or epinephrine can be effective in avoiding bradycardia and can be used when cessation of surgical manipulation does not result in restoration of an adequate heart rate. When atropine is used for treatment of bradycardia, a minimum dose of 0.5 mg is advised, as lower doses actually increase vagal activity via a centrally mediated effect. Infiltration of the carotid bifurcation with a local anesthetic is a controversial intervention to preempt bradycardia. Many studies have found this technique to be ineffective and to result in both postoperative hypotension and hypertension. The carotid body is a chemoreceptor that detects oxygen partial pressure; it has no role in the bradycardic response to surgical manipulation.