HEMODYNAMIC INSTABILITY AND MYOCARDIAL-ISCHEMIA DURING CAROTID ENDARTERECTOMY - A COMPARISON OF PROPOFOL AND ISOFLURANE

The purpose of this study was to compare two anaesthetic protocols for haemodynamic instability (heart rate (HR) or mean arterial pressure ( MAP) <80 or >120% of ward baseline values) measured al one-minute inte rvals during carotid endarterectomy (CEA). One group received propofol /alfentanil (Group Prop; n = 14) and the other isoflurane/alfentanil ( Group Iso; n = 13). Periods of haemodynamic instability were correlate d to episodes of myocardial ischaemia as assessed by Holler monitoring (begun the evening before surgery and ceasing the morning of the firs t postoperative day). In Group Prop, anaesthesia war induced with alfe ntanil 30 mu g . kg(-1) iv, propofol up to 1.5 mg . kg(-1) and vecuron ium 0.15 mg . kg(-1), and maintained with infusions of propofol at 3-1 2 mg . kg(-1). hr(-1) and alfentanil at 30 mu g . kg(-1). hr(-1). In G roup Iso, anaesthesia was induced with alfentanil and vecuronium as ab ove, thiopentone up to 4 mg . kg(-1) and maintained with isoflurane an d alfentanil infusion. Phenylephrine was infused to support MAP at 110 +/- 10% of ward values during cross-clamp of the internal carotid art ery (ICA) in both groups. Emergence hypertension and/or tachycardia wa s treated with labetalol, diazoxide or propranolol. Myocardial ischaem ia was defined as ST-segment depression of greater than or equal to 1 mm (60 msec past the J-point) persisting for greater than or equal to one minute. For the entire anaesthetic course (induction to postemerge nce), there was no difference between groups for either duration or ma gnitude outside the <80 or >120% range for HR or MAP. However, when th e period of emergence from anaesthesia (reversal of neuromuscular bloc kade to postextubation) was assessed, more patients were hypertensive (P = 0.004) and required vasodilator therapy in Group Iso (10/13 vs 5/ 14; P = 0.038 Fisher's Exact Test). The mean dose of labetalol was gre ater in Group Iso (P = 0.035). No patient demonstrated myocardial isch aemia during ICA cross-clamp. On emergence, 6/13 patients in Group Iso demonstrated myocardial ischaemia compared with 1/14 in Group Prop (P = 0.029). Therefore, supporting the blood pressure with phenylephrine , during the period of ICA cross-clamping, appears to be safe as we di d not observe any myocardial ischaemia at this time. During emergence from anaesthesia, haemodynamic instability was associated with myocard ial ischaemia. Under these specific experimental conditions, with emer gence, hypertension and myocardial ischaemia were more prevalent with more frequent pharmacological interventions in patients receiving isof lurane.