“[This is] the best evidence to date to support bolus-based regimens for popliteal–sciatic catheters after foot and ankle surgery.”

Continuous peripheral catheters provide prolonged analgesia, reduce opioid consumption, and enhance patient satisfaction after painful surgeries. Although these clinical benefits have been firmly established, the optimal strategy for catheter dosing regimens has not. Available options include continuous infusion, patient-controlled boluses, and pump-programmed intermittent boluses. To date, there is limited evidence to endorse one technique over another to improve clinical outcomes, and contemporary regimens sometimes include all three.  Adding to the complexity, the clinical advantages of modern pump technology and the regimens that can be reliably delivered are unclear.

The randomized clinical trial by Finneran et al. in this issue of Anesthesiology elegantly addresses these important questions. The authors compared the effects of two different catheter dosing regimens on outcomes after ambulatory foot and ankle surgery. The study was powered for two primary endpoints: pain on postoperative day 1 and time until local anesthetic reservoir exhaustion. Additional outcomes included opioid consumption, sleep quality, and satisfaction with postoperative analgesia. Seventy patients received preincision popliteal–sciatic blocks, and a catheter was placed for postoperative use. Half of the patients were randomized to receive a continuous infusion of local anesthetic (6 ml/h) initiated before discharge, and the other half received automated boluses (8 ml every 2 h) initiated 5 h after discharge, using a start-delay timer. All patients had access to self- administered boluses on an as-needed basis. The automated bolus/delayed start regimen was hypothesized to produce at least noninferior analgesia and to conserve local anesthetic volume, thereby extending the duration of catheter use and analgesia. To their surprise, the authors found superior analgesia, lower median pain scores on postoperative day 1, 83% less opioid consumption, and significantly longer time to local anesthetic reservoir exhaustion (postoperative day 5) among patients randomized to the automated bolus regimen.

The results of the current study are compelling not just because they shed light on the nature of the optimal dosing regimen for home catheter use, but also because they provide a basis for future comparative research into the site- and procedure-specific applications for peripheral catheters. Previous studies comparing bolus with continuous regimens have yielded conflicting results.  Reasons for this are multifactorial and likely reflect anatomic differences at the target site, the techniques used to guide placement (ultrasound vs. nerve stimulation), the choice of local anesthetic and catheter type (stimulating vs. nonstimulating), and the outcomes assessed. The informing evidence base also suffers from substantial trial heterogeneity, small sample sizes, and lack of standardized interventions—all of which hamper our ability to conclude the superiority of any technique. This well-designed and adequately powered study is a clear methodologic advance over previous work and provides the best evidence to date to support bolus-based regimens for popliteal–sciatic catheters after foot and ankle surgery.

The results also provide a strategy to optimize and extend the duration of postoperative analgesia beyond that which can be conventionally achieved using a catheter-based system. A major limiter of the duration of catheter use (assuming proper function) is the volume of the local anesthetic reservoir, and this may be exhausted before the satisfactory resolution of surgical pain. On the other hand, catheters are commonly placed with a single-shot block, and there is dubious value of using a catheter while the initial block is still providing analgesic benefits. Use of the delay start timer and low(er) volumes per dose neatly address these drawbacks of traditional dosing regimens.

Although the study answers several important questions, it raises several more. The clinical significance of the outcomes needs to be confirmed, placed in the context of the recovery trajectory after foot and ankle surgery, and compared to other techniques in this surgical population. Notable by its absence is a comparator arm in which patients received single-shot popliteal–sciatic block (with adjuvants or long-acting local anesthetic) and comprehensive multimodal analgesia. The assumption—albeit supported by a wealth of published data1 —is that any catheter is at least non inferior to a non–catheter-based analgesic regimen. What remains to be addressed is whether a 5-day duration of regional analgesia is necessary or sufficient for optimal recovery or represents a substantial advantage over other techniques in this surgical population.

Indeed, since all patients had access to self-administered boluses of local anesthetic to “top up” their catheter as desired, it is unclear why there were any differences in pain scores between the groups in the early postoperative period (or at least up until reservoir exhaustion in the continuous infusion group). The authors’ interpretation is that patients were “saving” their local anesthetic to maximize the duration of the catheter use. An alternative explanation is that higher pain scores did not represent meaningful differences in recovery status or pain states, and patients did not need to lower their pain scores further by administering a local anesthetic bolus. Provocatively, this interpretation may be supported by the data regarding other secondary outcomes: total opioid consumption was significantly different between the groups, but impressively low in both. Likewise, patient-reported satisfaction scores were statistically higher among patients randomized to automated boluses at postoperative days 1 and 4, but the absolute scores for satisfaction were very high in both groups at all times.

Nonetheless, the prolonged duration of analgesia achieved with conservation of local anesthetic volume is impressive and suggests that pump technology that can deliver automated bolus dosing with delayed start infusions could become the new standard. The authors conclude that their results represent a paradigm shift in catheter-based care. This is likely to sound humbling to those who work in settings without catheter services and bold to those who do. Moreover, what should the clinician practicing in a setting without a catheter program take away from the study? The question is somewhat rhetorical but highlights the persistent gap between centers that have and those that do not have catheter programs. In this regard, it is as if we are living in a multiverse of peripheral catheters, where a few centers advance the care and research informing optimal use, even fewer do so via ambulatory-based programs, and most have no program at all. Other than an aspirational message, the results presented do not advance this issue or help to expand the benefits of catheters to more patients.

The research by Finneran et al.5  is a welcome addition to the body of work directed toward improving recovery and outcomes after painful surgeries. The work represents a significant step forward in understanding the anatomic, site-specific properties of catheters and the infusion systems required for targeted analgesia. What remains to be achieved—more than 70 yr after the first description of a continuous peripheral nerve catheter —is an understanding of the barriers to the broader adoption of catheter programs and their suitability for nonspecialist practices.