Nuffield Department of Anaesthetics, Level 1, Oxford Radcliffe NHS Hospital, Headington, Oxford OX3 9DU, UK*Corresponding author
Accepted for publication: May 23, 2001
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Abstract |
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Br J Anaesth 2001; 87: 6414
Keywords: surgery, carotid endarterectomy; anaesthetic techniques, regional, cervical plexus block; arterial blood pressure, control
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Introduction |
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Regional anaesthesia is associated with less use of ICA shunts8 than general anaesthesia, in which many surgeons routinely use a shunt on all patients. This may be of value, as shunting has inherent disadvantages.9 Signs of impending cerebral ischaemia in an awake patient are more sensitive and specific than the indirect indicators used during general anaesthesia, such as transcranial Doppler ultrasound, EEG processing and evoked potential monitoring.10 11 Thus, a shunt is only used if neurological deficit develops after ICA cross-clamping. Some surgeons prefer an awake patient because of the reassurance of being able to converse with the patient with the ICA cross-clamped.
The awake technique allows the anaesthetic management to be changed to treat ongoing problems by feedback from the awake patient. The following three case reports illustrate such dynamic management.
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Case 1 |
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Our usual practice during awake CEA is for the anaesthetist to administer heparin 50 unit kg1, then the surgeons cross-clamp the ICA for 2 min while the anaesthetist observes the patient closely for signs of cerebral ischaemia, such as altered level of consciousness, confusion, dysphasia or altered contralateral grip strength. If there is no neurological change, then arteriotomy and endarterectomy proceed directly. If there is evidence of cerebral ischaemia, the clamp is released while a PruittIsihara shunt is prepared and inserted electively.
In this case, within 30 s of trial cross-clamping, the patient developed subtle neurological changes. He was a few seconds slower in responding to questions and did not know which day of the week it was. We have seen previously that this may be the first or only sign of impending cerebral ischaemia. At this time, the TCI pump displayed a plasma propofol concentration of 0.1 µg ml1; blood pressure was 140/75 (mean 97 mm Hg) and pulse 55 beats min1. Because his mean blood pressure was marginally (7%) lower than baseline, we decided to increase this to see whether this could reverse the neurological effects. Two doses of ephedrine 3 mg were given, together with 0.9% NaCl 250 ml. Blood pressure rose to 190/90 and heart rate to 70 beats min1. The patients neurological condition improved and the delay in response was reduced, and he was able to work out which day of the week it was (Thursday). After the patient had been reassured and after discussion with the surgeons, endarterectomy proceeded uneventfully without the use of a shunt. A Goretex patch angioplasty was performed before the clamps were released with a total cross-clamp time of 52 min. During this time, ephedrine and phenylephrine were given as required to maintain blood pressure at or above 165 systolic. A total of ephedrine 12 mg and phenylephrine 0.5 mg was administered during the cross-clamp period.
After cross-clamp release, the remainder of the operation proceeded uneventfully. The patient was kept in recovery for 2 h for close neurological and haemodynamic assessment, after which he was sent to the ward. He was discharged home on the second post-operative day.
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Case 2 |
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In this case, the 2 min trial cross-clamp was uneventful, but 25 min after arteriotomy the patient became dysphasic and confused. Arterial blood pressure at this time was 155/75 (mean 108 mm Hg) and pulse 72 beats min1. Metaraminol 0.25 mg was given, which increased the pressure to 195/95. The patients symptoms resolved completely and endarterectomy proceeded uneventfully without shunt insertion being needed. Because the internal carotid artery was of sufficient calibre, the patch angioplasty was not done and so the cross-clamp time was only 29 min. A total of five boluses of metaraminol 0.25 mg were given to maintain blood pressure until the end of the operation. After release of the cross-clamp, the patient complained of discomfort in her left chest and arm similar to her angina, although there was no change in the ST segment in leads II and V5. This pain resolved rapidly with sublingual nitroglycerin spray and reassurance. The patient was kept in recovery for 2 h for close observation as before. A 12-lead electrocardiogram was unchanged from before surgery. Her recovery was uneventful and she was discharged home on the third post-operative day.
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Case 3 |
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Discussion |
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The choice of vasopressor depends on pre-existing disease and previous medication. Ephedrine could be used if the patient is already bradycardic, for example with ß-blockers; phenylephrine or metaraminol could be used otherwise.
Of the potential benefits of awake carotid artery surgery, reducing the requirement for ICA shunt insertion is the best proven. Under general anaesthesia, shunt rates vary considerably from 0 to 100%,17 but the mean rate is greater than the 1015% reported for awake carotid surgery.18 19 Manipulation of blood pressure can reduce the requirement for shunting still further, which may be beneficial because of the risks of shunt insertion.9 These include prolongation of the cross-clamp time; cerebral ischaemia during shunt insertion and removal; risk of embolic stroke by dislodgement of plaque material during shunt insertion; and sudden profound blood loss and hypotension as a result of accidental dislodgement of the shunt. Finally, patch angioplasty is technically more difficult for the surgeon when suturing around a shunt.
In our second case, the patient developed angina as well as neurological impairment during the operation and the patients conscious state alerted us to her myocardial ischaemia. Treatment was given and the problem reversed before changes in the ECG or the patients haemodynamic status became apparent.
We consider that, with an awake patient, the anaesthetist has more options and more information to make perioperative decisions about a patients management when they develop cerebral or myocardial ischaemia after carotid cross-clamping. In high-risk patients, such as those undergoing carotid surgery, this could contribute to differences in morbidity and mortality between regional and general anaesthesia.
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References |
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