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ENHANCED CIRCULATORY CONTROL FOLLOWING CAROTID ENDARTERECTOMY

Department of Anesthesiology, Queen's University, Kingston, ON, K7L 2V7

INTRODUCTION

Patients with underlying cardiovascular disease frequently experience circulatory instability in the perioperative period, which may lead to arrhythmias and myocardial ischemia.(1) This instability may be related to a prolonged postoperative impairment of autonomic reflex mechanisms, which normally act to maintain hemodynamic equilibrium, following major surgery.(2) Surgery of the carotid artery is unique in that it may have direct effects on baroreflex function, either by surgical manipulation of the baroreceptor nerves, or due to the restoration of carotid perfusion. The purpose of this observational study was to characterize changes in the control of heart rate and blood pressure in the early recovery period from carotid endarterectomy (CEA).

METHODS

Following institutional ethics approval, 21 patients scheduled for CEA gave consent to participate. Standard monitoring and general anesthetic protocols were used. Continuous signals of blood pressure and electrocardiogram were recorded a) prior to surgery (PRE), b) 1 hour post extubation (1H), and c) 3 hours post extubation (3H). Data were analyzed using the techniques of power spectral analysis of blood pressure (BPV) and heart rate variability (HRV), and spontaneous baroreflex sensitivity, to quantify the relative parasympathetic and sympathetic influence on circulatory control.

RESULTS

Systolic blood pressure was unchanged postoperatively (132±20 PRE vs 126±36 mmHg 3H, NS), while blood pressure variability was markedly reduced at 1H (P=0.016) and 3H (P<0.001). Heart rate was decreased at 3H from PRE (71±12 vs 65±14 bpm, P=0.005), while total power of HRV was increased from PRE at 1HR and 3HR. The parasympathetic indicators of spontaneous baroreflex sensitivity and high frequency HRV were increased at 3H, but not at 1H.

DISCUSSION

Contrary to previous studies in patients undergoing non-carotid surgery,(2) CEA appears to be unique in leading to an increase in parasympathetic modulation of heart rate in the early postoperative period. This was accompanied by a decrease in lability of blood pressure. This enhanced vagal control may be protective against cardiovascular complications, although determination of the duration of this effect requires further study.

REFERENCES

1 Anesthesiology 76:342–53

2 Anesthesiology 90:681–92

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