Shoulder surgery is commonly performed under interscalene brachial plexus block . The advantages of the sitting position include excellent intra-articular visualization, minimal traction on the brachial plexus and no need for repositioning in case of conversion to open surgery . Many factors commonly contribute to discomfort in awake patients who require sedation: proximity of the surgical field, pain or traction upon the operated shoulder. Providing safe and effective sedation in the sitting position may be challenging because of the difficulties in managing the airway in case of respiratory or cardiovascular complications. A few authors have investigated target-controlled propofol sedation as an adjunct to regional anaesthesia and have found that target concentrations providing adequate sedation ranged between 0.93 and 1.6 μg mL−1 [3-6].
Activation of the Bezold-Jarisch reflex leading to life-threatening hypotensive/bradycardic events (HBE) is another issue of shoulder arthroscopy performed under interscalene block in the sitting position. It has been reported in 17-31% of the cases [7,8]. Decreasing anxiety and cardiovascular stress by sedation might prevent such a worrisome complication [8,9], but this remains to be demonstrated.
The aim of this prospective study was thus to assess sedation with a target-controlled propofol infusion during arthroscopic shoulder surgery under interscalene brachial plexus block, to determine the optimal target concentration, and to evaluate the effect of sedation on Bezold-Jarisch reflex.
After approval by our local institutional review board and obtaining informed consent, ASA I-II patients, between 18- and 75-yr old, scheduled for shoulder surgery in the sitting position under interscalene block were prospectively studied. Exclusion criteria were: treatment with beta-adrenergic receptor blocking drugs, severe heart disease, cardiac conduction defects, psychiatric disorders, chronic respiratory failure and allergy to local anaesthetics.
Oral premedication with hydroxyzine 1 mg kg−1 was given 2 h before arrival in the operating theatre. An intravenous (i.v.) catheter was inserted into a vein of the forearm on the side opposite to surgery and 10 mL kg−1 of lactated Ringer's solution were administered before placing the patient in the sitting position. Standard anaesthetic monitors were applied (electrocardiogram, pulse oximetry and non-invasive blood pressure (BP)). The block was performed following the technique described by Winnie . A 20-G insulated 50-mm bevelled needle (Stimuplex®; Pajunk, Melsungen, Germany) connected to a nerve stimulator (Stimuplex®; Braun, Geisingen, Germany) set to deliver a 1.5 mA, 2 Hz and 0.1 ms stimulus was introduced until a contraction of the biceps muscle was obtained at a current of 0.5 mA or less. After negative blood aspiration, 30 mL of ropivacaine 0.75% (Naropeine®; Astra-Zeneca, Rueil-Malmaison, France) without epinephrine or other additives were slowly injected. Effectiveness of the block was determined by pinprick in the area innervated by the axillary nerve and by assessing deltoid muscle strength. In case of block failure, patients were excluded from the study. In case of shoulder arthroscopy, the posterior incision site was infiltrated with 5 mL 2% lidocaine by the surgeon. The arthroscopic irrigation solution contained 1:3 000 000 epinephrine in isotonic sodium chloride. In case of vasovagal syncope during venous catheter insertion or block placement, patients were given atropine i.v. but were not excluded from analysis.
The target-controlled propofol infusion (Vial Master TCI® infusion pump, Vial, France, Diprifusor® pharmacokinetic module, Diprivan® 50 mL pre-filled syringes; Astra-Zeneca, Rueil-Malmaison, France) was started immediately after positioning the patient on the operating table. The initial target concentration was 1 μg mL−1. The infusion rate was adjusted every 15 min according to the level of sedation by increasing or decreasing the target concentration by 0.2 μg mL−1 steps. The Wilson sedation scale used to assess the level of sedation ranges from a score of 1 (fully awake and oriented) to 5 (eyes closed and unrousable to mild physical stimuli) . The aim was to maintain the patient drowsy but reactive to verbal commands (score of 3). The 15-min interval between target concentration adjustments was chosen to limit the number of awakenings during the operation. Supplemental oxygen was given during the procedure through a nasal cannula. If the patients complained of pain during surgery, they were given alfentanil bolus doses (300 μg i.v. per bolus, no more than 600 μg total for the procedure). Patients were not informed of the variations of target concentrations.
The Bezold-Jarisch reflex was defined as a heart rate (HR) <50 bpm and/or a decrease in HR of >30 bpm in <5 min and systolic arterial pressure <90 mmHg. It was treated with atropine and/or ephedrine by the attending anaesthetist. HR, systolic and diastolic arterial pressures, and arterial oxygen saturation were recorded every 10 min. Intraoperative agitation, severe hypoxaemia and pain uncontrolled by propofol sedation and/or alfentanil, justified conversion to general anaesthesia.
Features of propofol sedation were recorded as follows: maximal target concentration, minimal target concentration, optimal target concentration (defined by the target concentration during more than 50% of the operation), and cumulative propofol dose. Patients' characteristics were also recorded.
Data are presented as mean ± SD. Regarding the comparison between patients with and without Bezold-Jarisch reflex, statistical analyses were performed using t-test or χ2-test as appropriate. P < 0.05 was considered significant.
One hundred and forty patients were prospectively studied (Table 1). The interscalene block was successful in all patients. Arthroscopic rotator cuff repair was the most frequent surgical procedure.
Nine patients (6.4%) experienced transient bradycardia (<50 bpm) during venous catheter insertion or block placement. This was interpreted as a vasovagal reflex and some of them received i.v. atropine (average dose 0.43 ± 0.41 mg) and/or ephedrine (8.30 ± 6.40 mg).
Twenty-six patients (18.6%) required alfentanil during the surgical procedure (total dose 344 ± 168 μg). The target concentration in these patients did not differ significantly from that in those not requiring alfentanil (1.09 ± 0.30).
No respiratory complications (hypoxaemia, apnoea, dyspnoea) were reported. Two patients experienced intraoperative agitation, but none required conversion to general anaesthesia.
Descriptive data of the target-controlled infusion are given in Table 2. The optimal target concentration was 0.85 ± 0.24 μg mL−1.
Eight patients (5.7%) experienced a Bezold-Jarisch reflex during surgery. The optimal propofol target concentration was lower in these patients (P < 0.05) (Table 3). All episodes of Bezold-Jarisch reflex were successfully treated with ephedrine (5.6 ± 4.1 mg) and/or atropine (0.50 ± 0.26 mg). None of the patients who had received atropine for preoperative vasovagal syncope during venous catheter insertion or block placement suffered an intraoperative HBE.
This study has documented that 0.85 μg mL−1 was the optimal target concentration of propofol for providing adequate and safe sedation for shoulder surgery under interscalene brachial plexus block. The low incidence of Bezold-Jarisch reflex compared to previous reports in the literature [7,8] suggests a preventive effect of sedation. This is supported by the lower target concentration in patients who experienced Bezold-Jarisch reflex during the surgical procedure.
In 40 patients undergoing surgery under local anaesthesia, Skipsey and colleagues found an optimal target concentration was 0.93 μg mL−1 . In patients undergoing muscle biopsy under femoral block the target concentration of propofol was 1.6 μg mL−1 . In another study, Casati and colleagues documented that patients were rousable to verbal command at a mean concentration of 1.3 μg mL−1 . In the current study, we defined that sedation should maintain the patients drowsy but rousable to verbal command, corresponding to a score of 3 of the Wilson sedation scale. For this we required a lower target concentration than some previous studies [5,6]. All patients were initially premedicated with 1 mg kg−1 hydroxyzine, and then also received alfentanil if requested. The co-induction effects of different sedative drugs are well established; accordingly, this co-induction could have affected the target concentration of propofol required to achieve a pre-defined degree of sedation. However, the target concentration in the patients who received alfentanil was not different from others, so that such a low dose probably did not influence the sedation level or the propofol requirements in these patients. Alfentanil was only used to provide analgesia to supplement incomplete blocks and was effective in keeping sedation requirements similar to those with more complete blocks.
Inadequate sedation leading to anxiety and agitation may be dangerous in patients in the sitting position undergoing shoulder arthroscopy. Careful monitoring and adaptation of the sedation level is therefore mandatory and is best achieved through target-controlled administration. In this series, only two patients were transiently agitated but none required general anaesthesia.
This study demonstrates the safety of target-controlled sedation with propofol during shoulder surgery in the sitting position. Under the conditions of this study, no patient experienced respiratory failure due to the combination of ipsilateral phrenic paralysis related to interscalene block , and depression of respiratory drive by propofol . Nevertheless, we and others recommend that supplemental oxygen should be administered throughout the procedure .
A target-controlled infusion of propofol has been shown to provide better sedation for monitored anaesthesia care during regional anaesthesia than intermittent bolus injections or manually controlled infusions . Compared with manually controlled infusions for general anaesthesia in ear nose and throat surgery, target-controlled infusions of propofol result in shorter recovery, better haemodynamic stability and less apnoea, with no difference regarding the consumption of propofol . Nevertheless, target-controlled administration requires specialized and expensive equipment (50 mL pre-filled syringes, infusion pumps). As mentioned in the results section, the mean dose of propofol was less than 200 mg (20 mL) so that in most cases propofol was wasted. The optimization of the cost/benefit ratio probably needs the manufacturers to provide 20 or 30 mL pre-filled syringes. Further investigations should compare cost as well as effectiveness of both techniques of administering propofol for sedation.
During shoulder surgery in the sitting position under intersalene block, the explanation of the activation of the Bezold-Jarisch reflex involves hypovolemia and sympathetic hyperactivity . The sitting position causes pooling of blood in the legs, thus reducing venous return [9,16]. Sympathetic hyperactivity is due to the stressful situation and to the administration of epinephrine via the irrigation solution or the local anaesthetic [9,17]. Beta-blockers have been proven to decrease Bezold-Jarisch reflex to an incidence of 5% when compared with glycopyrrolate and placebo . Anticholinergic drugs have no effect on Bezold-Jarisch reflex, and the patients who received preoperative atropine were not excluded from analysis. Other methods of preventing Bezold-Jarisch reflex, such as elastic leg stockings or volume loading have not been proven to be effective. Epinephrine containing anaesthetic solutions could increase sympathetic tone and activate the Bezold-Jarisch reflex . All our patients were volume loaded and received only ropivacaine without epinephrine for their block. In our study, the arthroscopic irrigation solutions contained epinephrine to prevent excessive bleeding in the surgical field and subsequently the need for hypotensive agents that may induce an HBE. Compared to the previously reported incidence of 17 to 31% [7,8], the very limited number of such events observed in this study allows us to hypothetize that sedation could reduce the likelihood of the Bezold-Jarisch reflex. Sedation might decrease sympathetic tone by decreasing anxiety. The difference in the target concentrations between patients who experienced an HBE and those who did not, is quite surprising because their level of sedation was comparable. The target concentration of propofol should likely be high enough (more than 0.8 μg mL−1) to ensure autonomic nervous system depression and thus avoid Bezold-Jarisch reflex. The other explanation for this is that the interval chosen to adjust the sedation was too large, with the result that some patients were sometimes less sedated. Further controlled studies are nevertheless needed to confirm the preventive role of sedation on the occurrence of Bezold-Jarisch reflex.
We conclude that the target-controlled infusion of propofol is a safe and effective technique for sedation when combined with ISB during shoulder surgery in the sitting position. Accurate sedation could also prevent the occurrence of Bezold-Jarisch reflex during such procedures. However, a randomized study would be needed to formulate definitive conclusions.
Special thanks to the anaesthetist nurses of the department of anaesthesiology (Clinique Générale, Annecy, France) for their excellent technical contribution to this work.
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