Blood Pressure Instability After Carotid Endarterectomy

Incidence

Blood pressure instability is commonly seen in CEA patients during and immediately following the procedure. In most cases this is manifested as episodic bouts of hypertension, but in some patients there is sudden hypotension, often associated with bradycardia. In many patients there are fluctuating episodes of hypertension alternating with hypotension. These fluctuations are difficult if not impossible to predict. In general, postoperative hypertension following CEA is transient and peaks in the first few hours after surgery. In approximately 80% of cases the hypertension resolves within 24 hours following surgery, and in 60% within the first 16 hours after CEA.

The incidence of significant hypertension among this patient population varies widely from series to series. On balance, severe hypertensive episodes have been documented in 19% to 66% of cases, with more than 40% requiring medical treatment. Significant bouts of hypotension have been reported in from 8% to 12% of patients undergoing CEA.

A number of factors can increase the risk of perioperative blood pressure instability among patients undergoing CEA ( Box 1 ). Clearly, preexisting hypertension, especially poorly controlled hypertension, is a risk factor for intraoperative and postoperative hypertension. Intraoperative factors can also predispose to perioperative hypertension. For example, clamping the carotid arteries reduces cerebral blood flow, which is typically accompanied by a compensatory increase in arterial pressure promoted by the baroreceptor reflex (see later) and increased sympathetic nervous system activity. This is usually reversed with restoration of flow, either through placement of a carotid shunt or completion of the endarterectomy and unclamping the vessels.

The degree of hemodynamic lability depends on a number of factors, including the degree of carotid stenosis, the extent of collateral flow, the duration of clamping, and the anesthetic technique employed. In regard to the anesthesia, it is reported that these intraoperative changes may be somewhat attenuated among patients undergoing CEA under deep general anesthesia compared with regional or cervical block anesthesia.

The technique of CEA can also influence the incidence of perioperative blood pressure instability. Specifically, there is evidence that postoperative hypertension is much more common after eversion endarterectomy compared with standard endarterectomy. Among 218 patients undergoing CEA either by the conventional or eversion technique, those undergoing eversion CEA experienced a significantly elevated postoperative blood pressure compared with those undergoing conventional CEA. Intravenous antihypertensive medications were required in 24% of the eversion patients versus only 6% of the conventional CEA patients. Eversion CEA requires transection of the internal carotid artery (ICA) or bulb, with transection of the carotid sinus nerve fibers located in the adventitia of the proximal ICA. Interruption of the baroreceptor reflex mechanism can be assumed to occur in this fashion, contributing to the development of hypertension. In contrast, the longitudinal endarterectomy and patch repair in conventional CEA minimizes the disruption of the carotid sinus nerve fibers.

Significant contralateral carotid atheromatous disease, previous contralateral endarterectomy, and previous contralateral radical neck surgery can also predispose to perioperative hypertension by affecting the baroreceptor mechanism.

On the other hand, identification of predictors of clinically significant hypotension following CEA remains elusive. Several investigators have reported conflicting results, with several studies failing to identify any specific patient characteristics that predispose to the development of hypotension. However, in one study of 1474 CEAs, it was noted that preoperative nitrate use and tobacco use identified patients at risk for postoperative hypotension and an increase in morbidity and mortality.