Comparison of intermediate vs subcutaneous cervical plexus block for carotid endarterectomy.

BACKGROUND: Carotid endarterectomy surgery can be performed under regional anaesthesia alone or under general anaesthesia. However, there are several types of regional block available and reported complication rates after superficial cervical plexus blocks are significantly lower than deep blocks. It is not known if subcutaneous and intermediate blocks are equally effective, although anatomical evidence suggests that the latter (where the injectate diffuses below the deep cervical fascia) might provide superior quality of intraoperative anaesthesia. METHODS: Forty-four patients were randomized to receive either subcutaneous or intermediate cervical plexus blocks for carotid endarterectomy. The primary endpoint was supplemental lidocaine requirement during surgery. Secondary outcome measures included: total amount of fentanyl administered during surgery, recall of pain scores during surgery, complications, and patient and surgeon satisfaction. RESULTS: There was no statistically significant difference for median (range) lidocaine supplementation between the subcutaneous and intermediate groups 65 (20-170) mg vs. 85 (30-345) mg, respectively; P=0.31. There were no statistical differences in the secondary outcome measures and no major complications during the study. CONCLUSIONS: Intermediate and subcutaneous cervical plexus blocks are equally effective for carotid endarterectomy. This study adds to the body of evidence supporting the safe use of superficial blocks for this type of surgery.

Evaluation of a cerebral oximeter as a monitor of cerebral ischemia during carotid endarterectomy.

BACKGROUND: Stroke is an important contributor to perioperative morbidity and mortality associated with carotid endarterectomy (CEA). This investigation was designed to compare the performance of the INVOS-3100 cerebral oximeter to neurologic function, as a means of detecting cerebral ischemia induced by carotid cross-clamping, in patients undergoing carotid endarterectomy with cervical plexus block. METHODS: Ninety-nine patients undergoing 100 CEAs with regional anesthesia (deep or superficial cervical plexus block) were studied. Bilateral regional cerebrovascular oxygen saturation (rSO2) was monitored using the INVOS-3100 cerebral oximeter. Patients were retrospectively assigned to one of two groups: those in whom a change in mental status or contralateral motor deficit was noted after internal carotid clamping (neurologic symptoms; n = 10) and those who did not show any neurologic change (no neurologic symptoms; n = 90). Data from 94 operations (neurologic symptoms = 10 and no neurologic symptoms = 84) were adequate for statistical analyses for group comparisons. A relative decrease in ipsilateral rSO2 after carotid occlusion (calculated as a percentage of preocclusion value) during all operations (n = 100) was also calculated to determine the critical level of rSO2 decrease associated with a change in neurologic function. RESULTS: The mean (+/- SD) decrease in rSO2 after carotid occlusion in the neurologic symptoms group (from 63.2 +/- 8.4% to 51.0 +/- 11.6%) was significantly greater (P = 0.0002) than in the no neurologic symptoms group (from 65.8 +/- 8.5% to 61.0 +/- 9.3%). Logistic regression analysis used to determine if a change in rSO2, calculated as a percentage of preclamp value, could be used to predict change in neurologic function was highly significant (likelihood ratio chi-square = 13.7; P = 0.0002). A 20% decrease in rSO2 reading from the preclamp baseline, as a predictor of neurologic compromise, resulted in a sensitivity of 80% and specificity of 82.2%. The false-positive rate using this cutoff point was 66.7%, and the false-negative rate was 2.6%, providing a positive predictive value of 33.3% and a negative predictive value of 97.4%. CONCLUSION: Monitoring rSO2 with INVOS-3100 to detect cerebral ischemia during CEA has a high negative predictive value, but the positive predictive value is low.

An assessment of contributions made by extracranial tissues during cerebral oximetry.

This study was designed to determine the extent of contribution made by extracranial tissues to estimation of regional cerebrovascular saturation (ScO2) during cerebral oximetry. Thirty four patients undergoing carotid endarterectomy under regional anesthesia were studied. Bilateral ScO2 monitoring with two INVOS 3100 A cerebral oximeters was used. Effect of occlusion of external carotid artery (ECA) for five minutes on ScO2 readings followed by occlusion of internal and common carotid arteries was studied. ScO2 readings at 1 minute intervals were stored on computer disks for off-line analysis. Numerical data were subjected to a two way repeated measures analysis of variance to study the effect of side (ipsilateral or contralateral) and phase (pre clamp, ECA clamp, ICA clamp and post clamp) of operation. A value of p<0.05 was considered significant. There was no significant change in ScO2 on the contralateral side. On the ipsilateral hemisphere ScO2 decreased from 67.4+/-8.5 to 65.6+/-8.3 with ECA occlusion and to 61.4+/-9.6 after ICA occlusion returning to 64.8+/-9.8 after all clamps were released. Decrease after ECA occlusion was not significant (p = 0.12) while that after ICA occlusion was significant when compared to pre clamp value (p<0.001). After release of all clamps ipsilateral ScO2 returned toward baseline but remained significantly lower (p<0.05) than pre clamp values. When readings from two hemispheres were compared, a significant difference (p<0.001) was noted during ICA occlusion only. We conclude that the mathematical algorithm used for calculation of ScO2 by INVOS 3100 A cerebral oximeter measures predominantly the intracranial cerebrovascular saturation.

Prospective, randomized comparison of deep or superficial cervical plexus block for carotid endarterectomy surgery.

BACKGROUND: Carotid endarterectomy may be performed under cervical plexus block with local anesthetic supplementation by the surgeon as necessary during surgery. It is unclear, however, whether deep or superficial cervical plexus block offers the best operating conditions or patient satisfaction. Therefore, the authors compared the two in patients undergoing carotid endarterectomy. METHODS: Forty patients undergoing carotid endarterectomy were randomized to receive either a superficial or a deep cervical plexus block with 20 ml bupivacaine, 0.375%. Outcomes subjected to statistical analysis included supplemental anesthetic supplementation with lidocaine, 1%, by the surgeon, dermatomes affected by the block, paresthesia during block placement, postoperative pain scores, and analgesic requirements. RESULTS: Median supplemental lidocaine requirements were 6 ml (range, 0.5 to 20 ml) in the deep block group and 6 ml (range, 0 to 20 ml) in the superficial block group (P = 0.7323). Patients in the deep block group who reported paresthesia during block placement required less lidocaine supplementation (median, 2; range, 0.5 to 20 ml) than the 9.5 ml (range, 6 to 15.5 ml) required by those who did not experience paresthesia (P = 0.0113). Compared with patients in the superficial block group, those in the deep block group were less likely to need analgesia in the first 24 h after operation (P = 0.047), and those who required analgesia received it later (6.6 +/- 4.1 vs. 3.9 +/- 1.4 h after operation; Student's t test, P = 0.02). One patient in each group expressed dissatisfaction with the technique. CONCLUSIONS: Carotid endarterectomy may be performed satisfactorily during superficial or deep cervical plexus block placement with no differences in terms of supplemental local anesthetic requirements, although this is influenced by whether paresthesia is elicited during placement of the deep block. Therefore, the clinician's decision to use one block rather than another need not be based on any assumed superiority of one block based on intraoperative conditions or patient satisfaction.

Cerebral oximetry in patients undergoing carotid endarterectomy under regional anesthesia.

BACKGROUND AND PURPOSE: Near-infrared spectroscopy is a technique that can potentially monitor changes in cerebral oxygenation. There are at present limited clinical data regarding the value of this technology in relating neurological outcome to cerebrovascular hemoglobin oxygen saturation (ScO2). This investigation reports changes in ScO2 due to carotid cross-clamping during carotid endarterectomy in awake patients. METHODS: ScO2 was monitored in 38 adult patients undergoing 41 carotid endarterectomies under regional anesthesia. Ipsilateral and contralateral hemispheres were monitored simultaneously during 36 operations, with ipsilateral monitoring alone in the remaining 5 operations. RESULTS: No significant difference was detected between ipsilateral and contralateral ScO2 during preclamp or postclamp periods. Carotid cross-clamping caused a statistically significant (P < .01) decrease in the ipsilateral ScO2, which decreased from 71.8 +/- 6.91% to 65.8 +/- 8.2%, while the contralateral ScO2 remained stable at 70.5 +/- 7.5% and 70.3 +/- 7.9%. The change in ipsilateral ScO2 ranged from +2.6% to -28.6% of the preclamp value. The difference between ipsilateral and contralateral ScO2 during cross-clamping was statistically significant (P < .001). The duration of cross-clamping was 39 +/- 11 minutes (range, 18 to 89 minutes). The decrease in ipsilateral ScO2 was highly variable from patient to patient and did not correlate with the duration of cross-clamping. CONCLUSIONS: These results suggest that carotid artery occlusion causes a statistically significant but variable decrease in ScO2 in the majority of patients. Data in this investigation provide a range of ScO2 values that was not associated with a clinically detectable neurological dysfunction.

Anaesthetic management of caesarean section for a mother with pre-eclampsia, the Klippel-Feil syndrome and congenital hydrocephalus.

A mother with the Klippel-Feil syndrome, congenital hydrocephalus and increased intracranial pressure presented for delivery by Caesarean section at 33 weeks because of pre-eclampsia. Anaesthetic management comprised awake intubation using the fibreoptic bronchoscope, followed by induction and maintenance of general anaesthesia for the delivery of a live male infant. This case report describes the problems arising under these circumstances and the relative merits of different anaesthetic techniques.

Anaesthesia for evacuation of retained products of conception. Comparison between alfentanil plus etomidate and fentanyl plus thiopentone.

Forty-four patients presenting for evacuation of retained products of conception were anaesthetized with either fentanyl and thiopentone, or alfentanil with etomidate, along with 70% nitrous oxide in oxygen. There was no difference between the two techniques in indices of immediate recovery (time to opening eyes and obeying a simple command), but the rate of return of higher mental functions (assessed by a coin counting test) was significantly better using the alfentanil-etomidate technique. There was no statistically significant difference between the techniques for apnoea or abnormal movements during anaesthesia, but alfentanil with etomidate was associated with significantly more pain on injection and a higher frequency of postoperative vomiting (40%).