Saturday, November 5, 2016

Why not just do an interscalene nerve block anesthetic?

Liposomal bupivacaine versus interscalene nerve block for pain control after shoulder arthroplasty: a prospective randomized trial.

These authors studied 57 patients undergoing primary shoulder arthroplasty randomized to receive either intraoperative local infiltration of local liposomal bupivacaine (LB) 20 mL bupivacaine/20 mL saline) or preoperative interscalene nerve block (INB).

 Outcomes showed a significant increase in pain in the LB group between 0 and 8 hours postoperatively (mean [standard deviation] 5.3 [2.2] vs. 2.5 [3.0]; P = .001). 

A significant increase in intravenous morphine equivalents was found in the INB group at 13 to 16 hours (mean [standard deviation] 1.2 [0.9] vs. 0.6 [0.7]; P = .01). No significant differences were found in any variable after postoperative day 0 between the 2 groups.

They concluded that an increase in early postoperative pain on the day of surgery was found with LB, whereas the INB group required more narcotics at the end of the day.

In their discussion, the authors review the safety and complication rates of INB. Weber and Jain evaluated the efficacy of INB in a review of 218 patients. They found that 13% of INBs in their study failed, and 5% of their patients had an abnormal neurologic response the day after surgery. Misamore et al demonstrated that 16% of patients undergoing INB experience immediate postoperative block side effects, with 4.4% of patients experiencing persistent neurologic complications. This study displayed similar results, with 3% of patients experiencing a persistent neurologic complication. A study by Fredrickson and Price suggested that an increase in postoperative motor blockade can be experienced with INB and is associated with a reduction in patient  satisfaction.These findings along with the desire for earlymobilization of the operative extremity suggest the utility of an alternative method for pain control in shoulder arthroplasty.

Evaluating the pharmacokinetics of INB, Busch et al found that the time of pain onset after single-injection ropivacaine INB was 10 hours. Weber and Jain similarly evaluated the efficacy of lidocaine and bupivacaine INB and found  that the mean duration of action of the block was 9 hours. This study demonstrated that INB had similar results, with  pain levels quickly rising after 8 hours postoperatively. Goon et al used a single injection of ropivacaine (25 mL 0.375%)  INB in shoulder arthroplasty patients and found the block’s  effects to last on average 18 hours. This study found similar findings with a peak in pain level seen 21 to 24 hours postoperatively  in the INB group. Whereas INB was more effective  at controlling pain in the first 8 hours postoperatively, there  was a trend toward acute rebound pain at the end of POD 0 as the block’s effects declined. 

Comment: Our reasons for avoiding interscaline blocks for shoulder arthroplasty include (1) desire for documentation of neurological status immediately after surgery, (2) wanting to avoid having a flail unprotected arm as we start immediate postoperative motion exercises, (3) eliminating the risk of block-related neurologic or pulmonary complications, (4) avoiding phrenic nerve paresis with the attendant respiratory compromise, (5) eliminating the inconvenience of a failed block, (6) reducing the cost associated with two different anesthetics (block + general), (7) avoiding the problem of acute rebound pain in the middle of the first postoperative night, and (8) the reluctance of some patients to have a needle placed in their neck.

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