Utility of the Pectoral Nerve Block (PECS II) for Analgesia Following Transaxillary First Rib Section

Abstract

Background:

The transaxillary approach to resection of the first rib is one of several operative techniques for treating thoracic outlet syndrome. Unfortunately, moderate to severe postoperative pain is anticipated for patients undergoing this particular operation. While opioids can be used for analgesia, they have well-described side effects that has led investigators to search for clinically relevant alternative analgesic modalities. We hypothesized that a regional analgesic procedure, commonly called a pectoral nerve (PECS II) block, which anesthetizes the second through sixth intercostal nerves as well as the long thoracic nerve and the medial and lateral pectoral nerves, would improve postoperative analgesia for patients undergoing a transaxillary first rib resection.

Methods:

We performed a retrospective study by reviewing the charts of all patients that had undergone a transaxillary first rib resection for thoracic outlet syndrome during the defined study period. Patients that received a PECS II block were compared to those that did not. The primary outcome was a comparison of numeric rating scale pain scores during the first 24 hours following the operation. Secondary outcomes included cumulative opioid consumption during the same time period.

Results:

Pain scores during the first 24 hours following the operation were not statistically different between groups (Block Group: 3.9 [2.1–5.3] [median (IQR 25–75%)] versus Non-block Group: 3.6 [2.4–4.1]; P = 0.40. In addition, opioid use through the first 24 hours after the operation was not significantly different (43.5 [22.0–81.0] [median morphine equivalents in mg’s] versus 42.0 [12.5–75.0]; P = 0.53).

Conclusions:

An ultrasound-guided PECS II nerve block did not reduce postoperative pain scores or opioid consumption for patients undergoing a transaxillary first rib resection. However, a prospective, randomized, study with improved power would be beneficial to further explore the potential utility of a PECS II block for patients presenting for this surgical procedure.

INTRODUCTION

Thoracic outlet syndrome (TOS) involves compression of the upper extremity neurovascular bundle as it travels distally between the first fib, the thoracic vertebra, and the manubrium of the sternum.¹ Impingement of the brachial plexus, subclavian artery, and/or subclavian vein may occur as these structures travel distally through this space from the neck to the axilla, leading to a variety of symptoms depending on the anatomic structure(s) being compressed (pain, upper extremity numbness, venous or arterial thrombosis, claudication, or ischemia). Surgical intervention, when indicated, typically involves resection of the first rib and sometimes the anterior scalene muscle.¹ While a variety of surgical approaches, including supraclavicular, infraclavicular, and thoracoscopic-assisted techniques have been described, a transaxillary (TA) approach is also commonly employed.

Regardless of the approach, invasive operations performed on the thoracic wall, such as resection of the first rib, can be associated with moderate to high levels of postoperative pain given respiratory dynamics and the essential constant movement of the thorax. In today’s healthcare environment, regional anesthesia techniques represent an attractive option for providing postoperative pain control, reducing opioids, and hastening hospital discharge. While intercostal, paravertebral, and epidural procedures have all been utilized to varying degrees for thoracic wall procedures and could be an option for patients undergoing first rib resection, each has their own potential advantages and disadvantages.² Intercostal nerve blocks, while moderately easy to perform require multiple injections as each nerve must be anesthetized independently. Although paravertebral blocks (PVB) can be performed with either a single level, large volume injection or multiple levels, smaller volume injections, each injection carries a risk of pneumothorax and the reported duration of analgesia is relatively short.³ Catheter placement into either the thoracic epidural space or the paravertebral space certainly could extend the duration of analgesia, but both are not appropriate for patients who are expected to have a short length-of-stay and are considered to be relatively contraindicated for patients who are actively anticoagulated.⁴

At our institution, surgical repair of TOS is typically performed via the TA approach. This involves an incision in the axillary region, just below the hair line and between the borders of the latissimus dorsi and pectoralis major muscles, dissection into the axilla, and resection of a portion of the first rib and anterior scalene muscle.¹ Patients usually remain hospitalized for only a single night and are frequently on anticoagulant medications preoperatively given the vascular compression often associated with the condition. This makes single injection blocks, which can be performed away from the neuraxis, an attractive approach to postoperative pain control. One newer potential option is the pectoral nerve (PECS II) block, which is an interfascial plane block first described in 2012 as a modification of the original pectoral nerve (PECS I) block.^{5, 6} This block is purported to anesthetize the second (intercostobrachial nerve) through sixth intercostal nerves as well as the long thoracic nerve and the medial and lateral pectoral nerves.⁷ While this block is frequently utilized for breast operations, its utility for proximal arteriovenous fistula creation involving the axillary region and for arthroscopic shoulder operations involving a subpectoral approach for biceps tenodesis has also been described.^{8, 9}

Based on these prior studies, which demonstrated the efficacy of utilizing a PECS II block for operations in/near the axilla and chest wall, as well as the presumed anatomic coverage of the block, we hypothesized that patients undergoing TA first rib resection who received a PECS II block would have improved pain control in the immediate 24-hour period following their operation when compared to patients who did not receive a block.

MATERIALS AND METHODS

Institutional review board (IRB) approval for the study (IRB00061243) was obtained prior to data collection. The design was a retrospective comparative study in which data were collected exclusively from the institutional electronic medical record (EMR) database. A query was performed to identify patients, as well as their surgeon, who underwent TA first rib resection between December 1, 2017 and August 30, 2019. The start date of the study was chosen because it correlated with the arrival of an experienced surgeon who began performing these particular procedures at our institution. All patients undergoing TA first rib resection during this time period were included in the study. There were no exclusion criteria.

Of note, regional analgesia was not routinely performed for these procedures at the beginning of the study period, but then PECS II blockade became the standard approach for these patients, thus providing appropriate comparison groups for this study. The PECS II block involves two separate ultrasound-guided injections, routinely performed through a single needed insertion located caudal to and at the junction of the medial and lateral thirds of the clavicle. The first injection, typically 20 cc’s, is performed between the pectoralis minor muscle and the serratus anterior muscle. The needle is then withdrawn, and the second injection, typically 10 cc’s, is performed between the pectoralis major and pectoralis minor muscles.

Demographic data, including gender, age, body mass index (BMI), operative side, operative indication, and preoperative opioid/nonopioid prescription use were recorded for each patient. The primary outcome of the study, which was defined a priori, was a comparison of numerical rating scale (NRS) pain scores (scale 0–10, with 0 being no pain and 10 being the worse pain imaginable) between patients who received a PECS II block (Block Group) and those who did not (Non-block Group). The time period for the primary outcome encompassed the first 24-hours following the operation, with the start time of the interval defined as the end of intraoperative anesthesia care (anesthesia stop-time) as listed in the EMR. A difference of 2-points on the NRS was defined as statistically (and clinically) relevant for the purposes of the study.¹⁰ All pain scores recorded in the EMR within 24 hours of the anesthesia stop-time were included in the analysis. A mean pain score was created for each individual patient and the subsequent group means were then utilized to compare the 2 groups.

Secondary outcomes included cumulative opioid consumption during the same 24-hour time period, with all opioids converted to morphine milligram equivalents (MME) to allow for comparison.¹¹ In addition, the preoperative, intraoperative, and postoperative administration of adjuvant medications that may have impacted analgesia were also collected, including acetaminophen, non-steroidal anti-inflammatories, gabapentinoids, diazepam, ketamine, and dexamethasone. All intraoperative opioids were also recorded (whether by bolus or continuous infusion) and converted to fentanyl equivalents to allow for comparison.¹² Block timing, medications, and doses/volumes were also collected from the EMR.

Statistical analyses were performed using the Wilcoxon Two-sample Test to test for differences between the two groups for continuous measures, with Fisher’s Exact Test used to test for differences between groups for categorical outcomes. P-values < 0.05 were assumed to be statistically significant. SAS (version 9.4, Cary, NC, USA) was used for all analyses.

RESULTS

The EMR query identified 31 total patients who underwent TA first rib resection during the defined study period. All operations were performed by a single surgeon. Twenty-one patients were found to have received a PECS II block (Block Group), while 10 patients did not (Non-block Group). Demographic data for the patients are shown in Table I.

Table I.

Demographic information

	Block group (n = 21)	Non-block group (n = 10)
Gender, n (%)
Male	5 (24)	4 (40)
Female	16 (76)	6 (60)
Operative side, n (%)
Right	13 (62)	8 (80)
Left	8 (38)	2 (20)
Operative indication, n (%)
Neurogenic	10 (48)	3 (30)
Venous	9 (43)	5 (50)
Arterial	0 (0)	1 (10)
Neurogenic & Venous	1 (5)	0 (0)
Neurogenic & Arterial	1 (5)	1 (10)
Preoperative NRS Pain Scoresa
Median (IQR)	0 (0–0.5)	0 (0–4)
Age, Mean years (SD)	30.7 (10.7)	24.9 (11.0)
BMI, Mean kg/m2 (SD)	24.7 (5.6)	23.9 (3.8)

SD, standard deviation; BMI, body mass index; NRS, Numeric Rating Scale; IQR, Interquartile range.

^aPreoperative pain scores were not documented on three patients (two in the block group and in the non-block group) and these were not included in the analyses.

In regard to the primary outcome of NRS pain scores during the first 24-hours following the operations, no statistical difference was found between the two groups (Block Group: 3.9 [2.1–5.3] [median (IQR 25–75%)] versus Non-block Group: 3.6 [2.4–4.1]; P = 0.40. In addition, no statisticaldifference was found for the secondary outcome of cumulative MMEs through the first 24 hours after the operations (43.5 [22.0–81.0] vs. 42.0 [12.5–75.0]; P = 0.53).Group comparisons for the administration of preoperative, intraoperative, and postoperative analgesic medications are shown in Figure 1. In summary, no significant differences were found regardless of the medication class or timing.

Fig. 1.

Adjuvant analgesic medication administration. No significant differences between groups. APAP, acetaminophen; NSAID, nonsteroidal anti-inflammatory drugs; GBP, gabapentinoids; Dex, dexamethasone.

Cumulative intraoperative fentanyl equivalents did not differ between groups, (median micrograms [IQR], 432.8 [377.6–600.7] vs. 462.7 [307.2–661.4]; P = 0.97. Notably, all but three patients received an intraoperative sufentanil infusion. Of the remaining 3 patients who did not, 2 were treated with a remifentanil infusion, while one received only boluses of fentanyl.

All regional blocks were noted to be performed at the end of the operation. All blocks were performed with 0.25% bupivacaine with epinephrine and alpha-2 agonist (clonidine or dexmedetomidine) additives. All but one block was performed with a total of 30 mL (20 mL for the injection within the plane between the pectoralis minor and serratus muscles and 10 mL for the injection within the plane between the pectoralis major and pectoralis minor muscles as originally described by Blanco).⁶ In one block, the dose for the first injection was reduced to 15 mL.

Only 2 patients, both in the Block-group, were noted to be prescribed opioid medications preoperatively: one for hydromorphone orally and the other for tramadol orally. Two total patients had prescriptions for nonopioid analgesic medications: one for pregabalin (in the Non-block Group) and one for celecoxib (in the Block-group).

DISCUSSION

The results of this study suggest that PECS II blockade for patients undergoing TA first rib resection for TOS may not provide significant clinical benefits in terms of reducing NRS pain scores or opioid consumption in the first 24 hours following the operation; as we found no statistical differences between the Block-Group and Non-block Group.

Anatomically, there may be a reason to explain the results of this study. The PECS II nerve block should result in coverage of the axillary region and the incisional site, given that it has been shown to reliably anesthetize the intercostobrachial nerve (anterior branch of the second thoracic intercostal nerve) as well as the lateral cutaneous branches of the third through sixth thoracic intercostal nerves.⁷ However, because the injection site for the PECS II block occurs at the anterolateral portion of the rib near the anterior axillary line, it likely will not anesthetize the collateral branch of the intercostal nerve, which separates from the intercostal nerve proper posteriorly at the angle of the rib.¹³ Because this branch is responsible for innervation to the intercostal muscles, the parietal pleura, and the periosteum of the rib, it could explain why patients in the Block-Group still had moderate pain and required opioids to the same extent as those in the Non-block Group.¹⁴ Given that a portion of the first rib is entirely resected, the lack of coverage to the periosteum could be of particular clinical importance as periosteal pain can be severe.¹⁵ Essentially, periosteal pain may be a greater contributor to postoperative pain in this patient population than incisional pain.

To the authors’ knowledge, only one other study to-date has examined the utility of PECS II blockade for patients undergoing TA first rib resections.¹⁶ In that retrospective study, the authors compared maximal NRS pain scores between groups. In contrast, our study took into account all pain scores recorded during the time-period, which has the advantage of reducing the possibility that the maximal pain score recorded was a significant outlier. Regardless, their results also showed no difference in postoperative NRS pain scores between these 2 groups postoperatively in either the post-anesthesia care unit (PACU) or on the floor. Of note, the authors concluded that NRS pain scores were lower in the PACU based on the results of a Kruskal-Wallis test (P = 0.031). However, there actually were no significant P-values in the post-hoc pairwise tests after adjusting for multiple comparisons.

Given the potential importance of anesthetizing the intercostal nerves posteriorly enough to block the collateral branch, perhaps regional techniques commonly utilized for analgesia following thoracotomy operations, such as a PVB, would be a more appropriate alternative to PECS II blockade for patients undergoing TA first rib resections. To-date, the only 2 studies to investigate this possibility have compared PVB to no block in retrospective fashion and have not shown convincing results. While one study reported improved PACU discharge pain scores, the other found no statistical difference in postoperative pain scores at any timepoint.^{17, 18} In addition, neither study demonstrated a significant reduction in postoperative opioid consumption.^{17, 18}

For breast operations, PECS II blockade has been shown to have significant benefits compared to systemic analgesia alone and to provide equivalent analgesia when compared to PVB.¹⁹ This is likely because the breast is largely innervated by the anterior and lateral branches of the intercostal nerves.²⁰ Determining whether either of these conclusions is also true for TA first rib resections will likely require future randomized, placebo controlled, and well-blinded trials comparing PECS II to placebo as well as to more proximal blocks of the intercostal nerve (intercostal, PVB, erector spinae) for this patient population. While standardizing the use of multimodal analgesic medications would be valuable, comparisons to incisional infiltration by the surgical team at the conclusion of the operation with traditional local anesthetics and/or liposomal bupivacaine is also warranted.

This study has some limitations that warrant discussion. First, like all retrospective studies there is a potential for confounding and biases; such as sampling and collection biases. The lack of randomization could also have led to significant differences between groups. However, the demographics of our two groups appear similar. We also saw no significant differences in adjuvant medication usage at any point or intraoperative opioid administration (fentanyl equivalents). While the use of opioid infusions was not entirely consistent, only three patients did not receive a sufentanil infusion, all in the Block-Group. However, if these three patients are removed from the analysis, NRS pain score differences remain insignificant (3.7 [1.8–5.3] vs. 3.6 [2.4–4.1]; P = 0.5); as does MME usage (50.3 [21.0–92.0] vs. 42.0 [15.0–75.0]; P = 0.56). In addition, these 3 patients did not differ significantly when compared to the remainder of their cohort (NRS pain scores [P = 0.58], postoperative MMEs [P = 0.65], and intraoperative fentanyl equivalents [P = 0.39].

Secondly, the sample size for the study was admittedly small. Therefore, there is the potential for a type II error, whereby no difference between the two groups (Block versus Non-block) was concluded, but in reality, a difference does actually exist. This potential could likely only be reduced with a larger and preferably prospective trial.

Lastly, the rate of block success was not available as this is not routinely assessed and documented for surgical patients receiving analgesic blocks. Therefore, it is conceivable that there were unrecognized block failures that may have impacted the outcomes of the study. In addition, it is possible that the performance of the PECS II block at the end of the operation could have resulted in variable/altered spread compared to what is typically expected/described for this block as tissue planes may have been altered during the operation. Of note, the analgesic injection is routinely performed at the conclusion of this surgical procedure as preoperative placement might theoretically interfere with nerve monitoring, which is consistently used during the procedure.

Despite our findings, we have continued to routinely perform a PECS II block for patients presenting for a TA first rib resection based on the surgical team member’s perception that it reduces postoperative discomfort and anxiety and hastens discharge. Perhaps we failed to choose the most important outcome measures or needed a larger sample size. For this reason, we are currently planning a prospective, randomized, sham-controlled trial to further investigate the utility of a PECS II block for this patient population.

CONCLUSION

In this retrospective cohort study, postoperative NRS pain scores through the first 24 hours following the operations were not significantly affected by the administration of a PECS II block for patients undergoing a TA first rib resection when compared to control (no block). In addition, postoperative opioid consumption during the same time period was not significantly impacted. Future prospective, randomized studies are indicated, but the anatomy of the intercostal nerves and the presumed coverage of PECS II blockage may explain these findings and the lack of efficacy for patients undergoing this operation.