Retrospective Analysis of Adverse Events of Continuous Interscalene Block Administered Using the Catheter-Over-Needle Method.

Purpose Continuous interscalene block is widely used for pain management in shoulder surgery. However, continuous interscalene block using the catheter-through-needle method reportedly causes adverse events, such as pericatheter leakage of the local anesthetic, phrenic nerve paralysis, and hoarseness. Because we expected the catheter-over-needle method to reduce those adverse events, we analyzed cases in which continuous interscalene block was administered using the catheter-over-needle method to determine when and what adverse events occurred. Methods We retrospectively reviewed anesthesia and medical records of adult patients who inserted the catheter with a continuous interscalene block administered with the catheter-over-needle method at our hospital from July 2015 to July 2017. Results During the surveillance period, 122 adult patients inserted the catheter with a continuous interscalene block administered using the catheter-over-needle method. We found no case of pericatheter local anesthetic leakage. Other adverse events—dyspnea, hoarseness, insufficient anesthetic effect, dizziness, cough reflex during drinking, or ptosis—were observed in 42 cases (34.4%). Most of the adverse events occurred on postoperative day 2. The median time between surgery and onset of the adverse event was 28.5 hours. Conclusions The catheter-over-needle method may prevent the pericatheter leakage of the local anesthetic. However, the number of other adverse events that occurred with continuous interscalene block was remarkable. During continuous interscalene block, patients must be observed carefully for adverse events, especially on postoperative day 2.


Background
Shoulder surgery is known to have the potential to cause severe pain not only postoperative but also during rehabilitation. Continuous interscalene block incorporating basal infusion of local anesthetic and patient-controlled boluses is one of the most effective and frequently used analgesic techniques after both major and minor shoulder surgery [1][2][3][4]. Many authors have supported the efficacy and safety of continuous interscalene block with ambulatory patients [5][6][7][8][9]. These reports focused on adverse events of continuous interscalene block provided by the catheter-through-needle 3 method [10,11]. In the catheter-through-needle method, the outer diameter of the catheter is smaller than the initial needle-punctured hole. Therefore, there is a potential for pericatheter leakage of the local anesthetic and perineural catheter dislocation.
In the catheter-over-needle method, in contrast, the catheter fits tightly in the puncture hole, which reportedly reduces the incidence of pericatheter local anesthetic leakage and perineural catheter dislocation [12,13]. However, the incidence of the adverse events resulting from continuous interscalene block using this method has not been fully explored; the only adverse events mentioned have been pericatheter leakage of the local anesthetic and perineural dislocation of the catheter. The purpose of this study was to determine which adverse events occurred with continuous interscalene block by this method and when they occurred.

Methods
After obtaining institutional board approval (registration number 29-3), we reviewed the anesthesia records and medical records of all adult patients who inserted the catheter with a continuous interscalane block administered by anesthesiologists via the catheter-over-needle method at Ehime Prefectural Imabari Hospital from July 2015 to July 2017. We excluded the patients in whom the catheter was inserted by orthopedists. We collected data about patient characteristics, the incidence of pericatheter leakage of the local anesthetic, insufficient anesthetic effect (postoperative pain numerical rating scale score 3 or higher), and symptoms suggestive of a neurological complication (e.g. dyspnea, hoarseness, dizziness, cough reflex during drinking and ptosis) from the time of insertion of the catheter to its removal. The study was registered with the UMIN Clinical Trials Registry (UMIN000037673).

Catheter insertion procedure
In all patients, the catheter was inserted just before induction of general anesthesia in the operating room, without preoperative sedation or premedication. Each patient was placed in the supine position, the arm on the side to be operated on was at the patient's side, and the head was

Perioperative management
In all patients, a standard anesthetic technique was used, wherein the non-invasive arterial blood pressure, electrocardiogram, and oxygen saturation were routinely monitored in the operating room. General anesthesia was induced with propofol (1.5-2 mg/kg), remifentanil (0.15-0.3 μg/kg/min), and rocuronium bromide (0.8 mg/kg) and maintained with sevoflurane (1.5%-2%) and remifentanil (0.15-0.3 μg/kg/min). The airway was secured with an LMA ProSeal TM laryngeal mask (Teleflex, Westmeath, Ireland). After a patient's emergence from anesthesia, the catheter was connected to an elastomeric pump (Coopdech ® Balloonjector ® : Daiken Medical Co., Ltd Osaka, Japan), and the patient received an infusion of 0.2% ropivacaine at 4 or 6 ml/h and was given access to a patient-controlled system to receive a bolus of 5mL with lock out time 30 min. Drugs used for postoperative analgesia were 50mg of flurbiprofen axetil, 1000mg of acetaminophen intravenously, or delivered via local anesthetic bolus, depending on patients' and nurses' preference. If adverse events occurred, the local anesthetic flow was stopped or decreased until the event subsided, and then the flow of local anesthetic was restarted. patients, in which the patient did not wish to continue infusion or the catheter was removed accidentally, infusion was stopped before postoperative day 4. Table 1 shows the characteristics of the study population. Almost all symptoms were mild and well tolerated. More than two adverse events were observed in 7 cases. Most of the adverse events occurred on postoperative day 2. From the start of the continuous infusion until the onset of the adverse event, the median time was 28.5 hours. Table 3 shows the differences between patients with different rates of local anesthetic flow. There were no differences between these groups in the incidence of dyspnea (P = 0.867), hoarseness (P = 0.757), dizziness (P = 0.624), cough reflex during drinking (P = 0.106), and ptosis (P = 0.189).

Discussion
In this study, continuous interscalene block administered with the catheter-over-needle method prevented pericatheter leakage of the local anesthetic. The incidences of the adverse events during this period of anesthesia were seems to lower than those reported for the catheter-through-needle method [10]. However, even with the catheter-over-needle method, the number of adverse events during continuous interscalene block was remarkable.
Catheter-over-needle method reduce pericatheter leakage of the local anesthetic [13]. In addition, we used the medical glue on the catheter insertion site that reportedly prevents such leakage during continuous perineural infusion [14]. These two steps completely prevented pericatheter leakage of the local anesthetic in our cases.
Adverse symptoms suggestive of neurological complications (dyspnea, hoarseness, cough reflex during drinking, and ptosis) were observed in 19 cases. The catheter-over-needle method with inplane ultrasound guidance enabled to place the catheter tip in the interscalene space in the brachial 8 plexus under direct visualization and tight fixation [15]. Such placement helped prevent perineural catheter tip dislocation and may have reduced the incidence of unintended nerve block caused by inappropriate catheter tip position. Thus, the incidence of adverse events involving continuous interscalene block may be expected lower with the catheter-over-needle method than with the catheter-through-needle method. However, even when the catheter tip was in the correct position, local anesthetics may spread to the anterior of the anterior scalene muscle, which results in phrenic nerve block and dyspnea [16]. Similarly, when local anesthetics spread to anterior of the anterior scalene muscle through the prevertebral layer of deep cervical fascia, the recurrent laryngeal nerve is blocked, which causes hoarseness or cough reflex during drinking, or both [17]. Moreover, when local anesthetics spread to the cervical sympathetic ganglion, ptosis is observed as a part of Horner's syndrome [18]. Sympathetic block or systemic local anesthetic toxicity causes dizziness. We could not find significant differences in the incidence of the adverse events with regard to local anesthetic flow rate. Anatomical differences between patients (e.g. variations in nerve position or differences in connective tissue looseness around the interscalene space) may account for the extent of neurological complications.
All these symptoms were mild in this study and were administered by a decrease or temporary cessation of local anesthetic flow. Most of the adverse events occurred on postoperative day 2, and the median time from the start of continuous infusion to the onset of the adverse event was 28.5 hours. Thus, patients must be observed carefully after surgery, especially on postoperative day 2. We were able to treat these adverse events by decreasing or stopping local anesthetic flow.
The possible reasons for insufficient effect of anesthesia in 13 cases even after the effective interscalene block are as follows: The interscalene block cannot cover the intercostal brachial nerve that innervates areas of the axilla, the lateral aspect of the chest, and the medial aspect of the arm.
To cover the incision of the intercostal brachial nerve area, serratus plane block or local infiltration of anesthetic into the incision may be used [19]. Intraoperative and postoperative routine protocols for systemic and structured oral analgesia are also rescuing the insufficient effect case.
This study had some limitations. It was retrospective, and the sample size was small. Another prospective study is needed to compare the incidence of adverse events with the catheter-overneedle method and those with the catheter-through-needle method. However, our findings indicated the possibility that adverse events were less frequent than those reported with the catheter-throughneedle method.
In conclusion, even in this small study, the incidences of the adverse events with the continuous interscalene block with the catheter-over-needle method were remarkable. Therefore, patients must be observed carefully during the continuous interscalene block, especially on postoperative day 2, and patient education about adverse events is crucial.