This is the first study comparing the blood pressure and heart rate changes in patients undergoing shoulder arthroscopy in the beach-chair position under general anaesthesia alone or under a combination of general anaesthesia and interscalene block. The results of this investigation showed that adding an interscalene brachial plexus block to a general anaesthetic did not increase the incidence of hypotensive or bradycardic episodes requiring therapeutic intervention.
The interscalene plexus was located by electrical stimulation. We did not use ultrasound, a very useful technique for this purpose, because we did not have the necessary equipment. However, despite its limitations, nerve stimulation is still a valid and accepted method for performing regional anaesthesia of peripheral nerves [14]. The technique is effective in experienced hands, and the block was successful in all of our patients.
There was a high incidence of low blood pressure requiring treatment with vasopressors in both groups, but the rates of 64% in the general anaesthesia group and 76% in the combination group are well within the published ranges. While the definitions of hypotension are not identical in the publications [2, 7, 11], they are similar enough to allow a comparison. Trentman et al. using criteria much more stringent than ours, reported a rate of hypotension from 54% to up to 75% in patients with chronic antihypertensive medication [7]. Kwak et al. [11], who used criteria similar to ours, reported an incidence of hypotension of 64%, while Yadeau et al. [2] observed hypotension with systolic blood pressure below 90 mmHg in virtually every patient of their study.
The maximum decrease in systolic blood pressure from baseline was significantly greater in the patients with interscalene block, but from a higher baseline, and the minimum values did not require therapy more often than in the group with only a general anaesthetic. We take this as evidence that the observed hypotension was related to setting the patient in the semi-upright position soon after the induction dose of propofol [6], since most treatment events were triggered by a decrease of systolic blood pressure after induction of anaesthesia. In a similar, smaller study on younger patients, in which all patients had an ISB while one group had an additional general anaesthetic, Ozzeybek et al. found that the combination of the two techniques caused a significantly greater decrease in arterial blood pressure than the ISB alone [9].
The heart rate was lower at all measuring points in the patients with an interscalene block. A similar percentage of patients in both groups had chronic medication with beta-adrenergic receptor blockers, and we suggest that the lower heart rate was due to the effects of the interscalene block, since it is known to induce a Bezold-Jarisch reflex with bradycardia [8]. Unfortunately we did not document the heart rate before establishing the block but only immediately prior to induction of general anaesthesia, a point in time at which the block had already taken effect. In a minority of patients, treatment was required for bradycardia complicated by hypotension, which we would consider to be a Bezold-Jarisch reflex event. This occurred in eight patients of the general anaesthesia group but in only five patients with the additional interscalene block, which argues against an increased risk of sudden hypotension and bradycardia with the combination.
While we did not expect the dose of propofol required to maintain BIS within the prescribed range to differ between the groups, but we had proposed that the administered doses of the opioid analgesic would be lower in the patients with the regional block. However, the latter was not the case, and we offer two possible explanations for this observation. The actually required maintenance doses of remifentanil or sufentanil may have been lower in the GA-ISB group, but the operations were relatively short, and the standardised high induction doses might have masked the difference. An alternative explanation is that the lack of a quantitative measure of analgesia may have led to unnecessarily high intraoperative opioid doses, since clinical signs of inadequate analgesia are not very reliable, and there are no clinical signs of more than adequate analgesia. Supplemental doses may have been administered more according to experience than to actual need, and one is more likely to increase than to reduce a standard infusion rate of remifentanil.
The time required for performing the ISB was similar to times described in the literature [15, 16]. The duration of the operation was significantly shorter in the group with the ISB, which in is accordance with published reports [15, 17, 18]. The reason for this is thought to be a reduced amount of bleeding due to the lower blood pressures in the patients with the regional block.
“Anaesthesia control time”, the cumulative time needed for induction and emergence in the operating theatre, was significantly shorter by about 13 minutes in the group with the regional block, since all preparations and the block itself were performed in a separate room parallel to the on-going operation; only the induction was performed in the operating theatre. This allowed a significantly more rapid turnover and better theatre utilisation with the interscalene block. These results are similar to those published by D'Alessio et al. [15] and Gonano et al. [19]. On the other hand, “total anaesthesia time”, the time during which an anaesthetist is occupied with the patient, was significantly longer in the group with the ISB, since a second anaesthetist was required to perform the block parallel to the on-going operation. Gonano et al. [19] compared the economical aspects of general anaesthesia versus interscalene block and found that the overall anaesthesia costs were lower with the regional technique. Although their study only compared general anaesthesia with ISB alone, the data for personnel and operating theatre costs per minute given in their publication showed that the combined general and regional technique would still cost less than using general anaesthesia alone due to the more effective theatre utilisation despite the additional cost for the second anaesthetist.
Patient satisfaction was high in both anaesthesia groups, but the groups differed in pain severity. The patients in the GA-ISB group had significantly less pain on the evening after surgery. On post surgery day one the scores also differed with a p-value of 0.06, which indicates that the lower pain severity registered in the ISB group was probably not due to chance. Such a difference that persists past the duration of action of mepivacaine could be evidence of a pre-emptive effect of the regional anaesthesia [4]. Ozzeybek et al. [9] studied the course of postoperative pain severity in patients undergoing shoulder surgery under general anaesthesia with ISB. However, since the authors failed to give the actual pain scores, it is not possible to compare their results with those in our corresponding GA-ISB group. The comparison would have been difficult in any case, since their patients had an interscalene catheter and were managed with patient-controlled interscalene analgesia for the first 48 hours.
The interpretation of our data is limited to some extent by the fact that blood pressure and heart rate values were not recorded until after the interscalene block had taken effect, and also by the fact that the anaesthetists were allowed to use either remifentanil or sufentanil or a combination of the two. A further limitation was that it was impossible to totally blind the nursing staff to the group allocation; those patients with ISB were unable to move their arms as opposed to those without ISB. This may have influenced patient treatment and dispensing of analgesics in the postanaesthetic care unit, but this unavoidable “unblinding” would not have compromised either the primary cardiovascular outcome data or the pain scores, since the former were extracted from the anaesthesia chart and monitor, and the latter were obtained by telephone interview.