A comparison of injection of local anesthetic through a catheter versus a needle for interscalene catheter placement has shown improved pain scores and reduced opioid requirements, suggesting that needle injection may be associated with secondary block failure.
According to the study, patients receiving local anesthesia via a catheter rather than a needle had better pain scores at 24 hours and lower opioid requirements in the PACU as well as at 24 hours.
“These results indicate that injection of local anesthetic via the catheter may provide better analgesia than injection through the needle prior to the insertion of a catheter,” said Daniel Moy, MD, from the Department of Anesthesiology and Perioperative and Pain Medicine at Stanford University School of Medicine, in California. “It’s possible that injection of local anesthetic through the needle may mask improper final placement of the catheter, which would obviously lead to poorer postoperative analgesia.”
Although the interscalene continuous peripheral nerve block is an effective regional anesthesia technique for prolonged analgesia after upper extremity surgery, as Dr. Moy noted, secondary block failure, defined as failure of the block catheter to provide postoperative analgesia, is a frequent known complication (J Hand Surg Am 2014;39:324-329).
“We hypothesized that injection of local anesthetic through the needle prior to the insertion of a catheter can lead to undiagnosed improper catheter placement, potentially resulting in a higher catheter failure rate compared to injection through the catheter only,” Dr. Moy said.
To test this hypothesis, Dr. Moy and his colleagues performed a retrospective chart review of all patients receiving an interscalene catheter for postoperative analgesia at a single institution from July 2015 to June 2016. Patients admitted for less than 24 hours and patients on greater than 30 milligram morphine equivalents (MME) per day were excluded from the study.
Investigators determined the injection technique by a procedure note in the electronic medical record. A secondary survey of the attending physicians was then performed to confirm injection technique and practices. Patients for whom injection technique could not be confirmed also were excluded from the study, the authors noted.
The study’s primary outcome was visual analog scale (VAS) pain scores at 7 a.m. post-op day 1. Secondary outcomes included opioid requirements in the PACU and 24 hours after discharge from the PACU.
A Unique Study
As Dr. Moy reported at the 2017 annual meeting of the American Society of Regional Anesthesia and Pain Medicine (abstract 3347), 306 patients received interscalene catheters for in-patient surgery during the study period, and 205 met the inclusion criteria.
“There was a bit of a size difference in our populations,” Dr. Moy acknowledged. “Twenty-four patients received injection of local anesthetic through the needle, and 181 received injections through the catheter.”
Despite the discrepancy in population size, however, primary and secondary outcomes met significance. Patients receiving injection via catheter had lower postoperative VAS pain scores compared with patients receiving the injection through the needle technique (2.3 vs. 3.4; P=0.0418). In addition, patients in the catheter group had lower opioid requirements in the PACU (17 vs. 31 MME; P=0.0445). Opioid requirements 24 hours after discharge from the PACU also were significantly lower in the catheter group compared with patients receiving injection through the needle (64 vs. 130 MME; P=0.0003).
Dr. Moy emphasized that head-to-head assessments of these techniques in the literature are limited. Only one prior study has compared these two injection modalities, he noted, but only to assess the effect on primary failure and not on secondary failure (Reg Anesth Pain Med 2007;32:296-302).
The study may be the first of its kind, but it still has limitations, Dr. Moy said, including its retrospective design. According to Dr. Moy, it’s possible that observed differences are linked to other factors, such as technical variations, within each supervising attending’s practice.
“At our institution, attendings have certain preferences with their injection technique,” Dr. Moy said. “Although all of our blocks were placed by trainees, either residents or fellows, there may be a difference in attending supervision, which would obviously be a confounding factor.”
Katharine Fleischmann, MD, an anesthesiologist at Massachusetts General Hospital, in Boston, asked Dr. Moy whether catheters are placed with hydrodissection at his institution.
“Saline is consistently used to hydrodissect at our institution, but to varying degrees,” Dr. Moy replied. “Syringes are usually loaded with 10 cc to 20 cc of saline, but all of this is rarely used.”
Lane Crawford, MD, an anesthesiologist at Massachusetts General Hospital, asked whether incidents of primary failure of a catheter were recognized with this analysis.
“Unfortunately, these data were not quite granular enough on our charting to capture that information, but that is something we would really like to know,” Dr. Moy said.