Compared with control, ISB reduced pain with motion at 2, 4, and 6 hours after shoulder surgery by 4.76 cm (−7.65 to −1.88; P < 0.0001), 2.98 cm (−5.95 to −0.01; P = 0.01), and 2.20 cm (−4.34 to −0.06; P = 0.008), respectively (Table 3). No further pain with motion benefits attributable to ISB were observed beyond 6 hours (Table 3). Figure 7 plots the changes in the pain with motion (VAS scores, weighed mean difference) between the 2 groups over time.
The time to first postoperative analgesic request after shoulder surgery was prolonged in patients who received an ISB compared with those who did not. The prolongation, expressed as lower CI limit (point estimate), was at least 7.77-fold (point estimate 8.04-fold) (Fig. 8).
ISB reduced postoperative opioid (IV morphine equivalent) consumption for the 0 to 12 hours interval by 12.1 mg (−21.75 to −2.45; P = 0.001), or a 48.3% relative reduction, compared with control (Fig. 9A and Table 3). However, the ISB and control groups had similar postoperative opioid consumption during the 12 to 24 hours interval (Fig. 9B) as well as during the 0 to 24 hours interval as a whole (Table 3).
No significant differences in postoperative opioid consumption between the ISB and control group were observed between 24 and 48 hours postoperatively (Table 3). Furthermore, the opioid consumption during the 24 to 36 hours and 36 to 48 hours intervals was not statistically different between the 2 groups.
The incidence of PONV during the first 24 hours after shoulder surgery was reduced in the ISB group by an OR (99% CI) of 0.41 (0.18–0.92; P = 0.004), or a 59% decrease in the odds, compared with control (Table 3 and Fig. 10). Inconsistency of reporting precluded quantitative and qualitative evaluation of the effect of ISB on postoperative pruritus and sedation.
Patient satisfaction with pain relief measured on a VAS scale was higher for the ISB group by 0.55 (0.15–0.95; P = 0.0004), or a 6.0% relative increase, compared with control (Table 3 and Fig. 11).
We performed a qualitative assessment on 2 outcomes: block-related complications and postoperative functional outcomes. None of the trials reviewed herein reported any block-related complications. Heterogeneous functional recovery assessment protocols in the 2 trials63,74 that examined this outcome prevented any conclusions beyond absence of the effect of ISB on this particular outcome.
This quantitative systematic review underscores the early clinical benefits of ISB in the setting of shoulder surgery; single-shot ISB offers effective pain control up to 8 hours, an opioid-sparing effect up to 12 hours, reduction in PONV up to 24 hours, and expedited PACU and hospital discharge. However, our results suggest that the duration of analgesia associated with ISB in the setting of shoulder surgery is limited to 6 and 8 hours with motion and at rest, respectively, which is not as prolonged as traditionally described.12–15 Importantly, patients receiving an ISB can experience more pain between 16 and 24 hours postoperatively than those without ISB, and their analgesic outcomes are not different from their control counterparts at any time beyond that point. Such findings should be presented to patients in risk-benefit and informed consent discussions regarding the duration of ISB analgesia.
The role of ISB for shoulder surgery has recently been brought to the fore. Clinical studies,25 retrospective data,92 and cadaveric data93,94 suggest that the nerve roots of the interscalene brachial plexus may be particularly susceptible to nerve injury from ISB; indeed, ISB is associated with higher risks of transient26,95 and long-term27 neurologic complications compared with other peripheral nerve blocks. Although ISB has traditionally been associated with transient diaphragmatic paresis and the risk of pneumothorax, more recent data28,29 implicate ISB in delayed-onset phrenic nerve damage96 and permanent unilateral diaphragmatic paralysis.29,97,98 Taken together, it is not surprising that some experts have questioned the opportunity cost of ISB in favor of alternative local anesthetic–based analgesic strategies for shoulder surgery.1,28,99–102 Evidence suggests that supraclavicular brachial plexus,103 suprascapular nerve,16,99,100 and axillary nerve blocks,16,100 as well as subacromial bursa104 and intraarticular105 local anesthetic instillation, may offer analgesic benefits for patients undergoing shoulder surgery. However, none of these techniques has been shown to be superior or as effective as ISB.
Our review has several limitations. First, the source data were drawn from diverse settings in which anesthetic and analgesic management varied, leading to considerable heterogeneity affecting primary and secondary outcome results. We also did not stratify our results according to the specific type of shoulder surgery. The duration and severity of postoperative pain may vary depending on the type of shoulder surgery (i.e., rotator cuff repair, Bankart repair, superior labrum anterior posterior repair, shoulder open reduction and internal fixation, and shoulder arthroplasty). Most of the RCTs reviewed herein involved a small number of subjects, with a maximal group size of 40 patients. Such small trials tend to increase the possibility of reporting results by random chance and increase the risk of estimation of treatment by publication bias. Third, although our secondary outcome analysis of the repeated comparisons of pain severity scores and opioid consumption used a conservative 99% CI as well as a P = 0.01 threshold of statistical significance, this analysis may still be subject to multiple testing bias. Fourth, individual patient data were not available for analysis, which precludes the use of a composite outcome inclusive of both opioid consumption and pain scores.106 Fifth, analgesic techniques other than ISB, such as subacromial or intraarticular104,105 local anesthetic infiltration as well as suprascapular and axillary nerve blocks,99,100 have been shown to provide pain relief after shoulder surgery, whether in conjunction or as alternatives to ISB. The effect of these techniques on the duration of ISB analgesia is beyond the scope of our review. Additionally, we excluded local anesthetic adjuvants and continuous ISB analgesic options capable of prolonging pain relief associated with ISB. Finally, none of the trials reviewed herein reported the presence and/or severity of preoperative pain, which prevented any correlation between this predictor of postoperative pain107 and the duration of ISB analgesia.
In contrast, our results also have several points of strength. Our literature search was exhaustive, included all relevant databases, and the inclusion criteria we used limited the evidence reviewed to RCTs. All foreign-language articles meeting the inclusion criteria were translated and included. Finally, despite the heterogeneity characterizing the primary outcome results, these results remained robust despite our attempts to explore heterogeneity according to its identified potential sources. These factors underscore the validity of our results.
In conclusion, ISB can provide effective analgesia up to 6 hours with motion and 8 hours at rest after shoulder surgery, with no demonstrable benefits thereafter. Patients who receive an ISB can suffer rebound pain at 24 hours but experience similar pain severity later compared with those who do not receive an ISB. ISB can also provide an opioid-sparing effect and reduce opioid-related side effects in the first 12 and 24 hours postoperatively, respectively. These findings are useful to inform preoperative risk-benefit discussions regarding ISB for shoulder surgery.
The authors thank Marina Englesakis, Research Librarian, University Health Network, Toronto, Ontario, Canada.
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