Comparison of the analgesic efficacy of superficial and deep serratus anterior plane blocks in patients undergoing breast cancer surgery: a prospective randomized single blind study

Abstract

Background

This study aimed to investigate the efficacy of superficial and deep serratus anterior plane blocks (SAPB) for simple mastectomy and modified radical mastectomy (MRM). The primary outcome was cumulative morphine consumption at 24 h. Secondary aims included pain scores, rescue analgesic and antiemetic requirement, nausea and vomiting incidence, and patient satisfaction.

Methods

Patients were randomized to the superficial or deep SAPB group. Superficial or deep SAPB was applied with 30 ml of 0.25% bupivacaine above or below the serratus anterior muscle, respectively. Postoperative pain control was provided by patient-controlled analgesia (PCA) with morphine. Pain was assessed in the post-anesthesia care unit (PACU), whereas both pain and morphine consumption were evaluated at 2, 6, 12, and 24 h postoperatively. Rescue analgesic and anti-emetic requirement, rescue analgesic dose, PCA bolus request count, nausea and vomiting severity, and satisfaction scores were also evaluated.

Results

Cumulative morphine consumption at 24th hour was similar between groups (p = 0.248, effect size = -0.17). Numeric rating scale (NRS) pain scores were slightly lower in the Deep SAPB group at PACU at 6, 12, and 24 h (p < 0.001, p = 0.020, 0.034, and 0.020, respectively; effect sizes = -0.46, -0.33, -0.31, and − 0.33, respectively). Anti-emetic use was lower (p = 0.017, effect size = 0.370), whereas patient satisfaction was higher in the deep SAPB group (p = 0.024, effect size = 0.280). There was no significant difference in PCA bolus request count, rescue analgesic requirement, and dose.

Conclusions

Although cumulative morphine consumption was similar, deep SAPB yielded slightly lower NRS scores, reduced the need for antiemetics, and modestly higher patient satisfaction, warranting further studies to determine the clinical advantage.

Trial registration

The study was prospectively registered in ClinicalTrials.gov on 29 May 2024 and can be retrieved via https://clinicaltrials.gov/study/NCT06438211 (NCT06438211).

Introduction

Breast cancer remains the primary cause of morbidity and mortality among women worldwide [1]. Surgical excision is the gold standard, despite advances in therapies such as hormone therapy and chemoradiotherapy [2–4]. Breast cancer surgery varies from lumpectomy, where just the tumor is removed, to MRM, which involves removing the entire breast along with the axillary lymph nodes. Moderate to severe acute postoperative pain occurs in up to 50–60% of cases due to the complex innervation of the breast [5, 6]. Surgery involving dissection of the pectoral muscles and axillary lymph nodes can further contribute to severe acute pain [7].

Opioids have been the mainstay of postoperative pain management; however, their use is limited by side effects such as nausea, vomiting, urinary retention, pruritus, sedation, and respiratory depression [8]. Therefore, multimodal management of acute pain after breast cancer is of utmost importance to reduce opioid dosage [9]. Various regional techniques have been utilized, such as paravertebral block (PVB), intercostal block, and fascial plane blocks [10].

PVBs have been considered the gold standard; however, they require expertise, involve multiple needle entries, and carry risks of serious complications such as pneumothorax and vascular injury [11]. Fascial plane blocks have become more popular due to their ease of application, improved safety profile, and comparable analgesic effects to PVBs [12]. SAPB was first described in four volunteers as the injection of local anesthetic above or below the serratus anterior muscle. Both approaches consistently produced cutaneous sensory loss on the ipsilateral hemithorax [13]. Since then, SAPB has been used for cardiothoracic, breast, and rib fracture analgesia [14–16].

However, the literature comparing the analgesic effects of superficial versus deep serratus anterior plane blocks (SAPB) is scarce, especially in the setting of breast cancer surgery. Both approaches are recognized as effective parts of a multimodal pain management strategy for breast procedures; nonetheless, differences in anatomy and technique between the superficial and deep injection planes can affect how the local anesthetic spreads and how reliably the block is achieved. Human cadaveric studies showed that dye injection with 20 ml volume of superficial or deep serratus anterior plane resulted in comparable dye spread [17]. However, another cadaveric study, which compared two volumes (20 vs. 40 ml) at the deep plane of the serratus anterior, showed that the higher volume led to greater craniocaudal spread and staining of the pectoral muscles [18]. Also, both SAPB techniques mostly exert analgesic effects by blocking the lateral cutaneous branches of the intercostal nerves; deep SAPB may offer intercostal nerve spread, though it is limited [19, 20]. These anatomical factors have sparked interest in whether the depth of SAPB placement impacts postoperative pain control in breast cancer surgeries involving the medial side of the breast, such as simple mastectomy and MRM.

Therefore, we hypothesized that deep SAPB would be more effective than superficial SAPB in patients undergoing simple mastectomy or MRM. We aimed to compare postoperative cumulative 24 h morphine consumption, pain scores, rescue analgesic and antiemetic requirement, postoperative nausea-vomiting (PONV), and patient satisfaction.

Methods

This single-centre, prospective, randomized, and single (patient) blinded study was approved by the Erciyes University Clinical Research Ethical Board (No. 2024/58) and registered in the Clinicaltrials.gov on May 29, 2024 (No. NCT06438211; https://www.clinicaltrials.gov). Written informed consent was obtained from all patients before enrollment. All the procedures were conducted at Erciyes University Hospital in accordance with the principles of the 2013 Declaration of Helsinki and Consolidated Standards of Reporting Trials (CONSORT) guidelines.

Between June 01, 2024, and May 31, 2025, ASA physical status I – III female patients aged 18–75 who were diagnosed with unilateral breast malignancy and scheduled for simple mastectomy or MRM with axillary lymph node dissection are enrolled. We preferred to enrol single surgeon’s (M.G.) patients due to the fact that the surgeon is a risk factor acute pain severity [21]. Patients were excluded if they had any of the following conditions: allergy to amid local anesthetics, previous opioid prescription, opioid addiction or dependence, precense of neuropathic pain and medications such as gabapentinoids, tricyclic antidepressants, serotonin-norepinephrine reuptake inhibitors, alcohol addiction or dependence, cognitive impairment, psychiatric illness, previous breast surgery or procedures which can impede the injectate spread on block site, diabetes mellitus.

Age, weight, height, and body mass index (BMI) were recorded during the preoperative evaluation visit.

The patients were randomised into two groups using a computer-generated list of random numbers (https://www.randomizer.org). Based on this list, sealed opaque envelopes were prepared for each patient by the investigator (A.T.). On the morning of surgery, the investigator (A.U.) opened the envelopes and assigned the patients to the superficial (Superficial SAPB group) or deep block group (Deep SAPB group).

Superficial SAPB procedure

All procedures were performed after induction of anaesthesia and endotracheal intubation and before incision. When the patient was supine, the ipsilateral arm was abducted 90 degrees. After sterile preparation, the linear ultrasound probe was placed longitudinally over the anterior chest on the midclavicular line to count ribs. When the fourth and fifth ribs were detected, the probe was moved posteriorly to the midaxillary line and rotated sagittally. An 80 mm echogenic block needle was introduced medial to lateral in an in-plane technique between the latissimus dorsi muscle and the serratus anterior muscle. After verification of spread with serum physiologic, 30 ml of 0.25% bupivacaine was injected with intermittent aspiration.

Deep SAPB procedure

All procedures were performed after induction of anaesthesia and endotracheal intubation and before incision. When the patient was supine, the ipsilateral arm was abducted 90 degrees. After sterile preparation, the linear ultrasound probe was placed longitudinally over the anterior chest on the midclavicular line to count ribs. When the fourth and fifth ribs were detected, the probe was moved posteriorly to the midaxillary line and rotated sagittally. An 80 mm echogenic block needle was introduced medial to lateral in an in-plane technique between the serratus anterior muscle and the external intercostal muscle. After verification of spread with serum physiologic, 30 ml of 0.25% bupivacaine was injected with intermittent aspiration.

Anesthesia management

Upon entering the operating room, patients were monitored with electrocardiography, pulse oximetry, and non-invasive blood pressure measurements following ASA guidelines. Maintenance fluid therapy was initiated with balanced crystalloids at 5 – 10 ml/kg. Preoxygenation was performed with a face mask delivering 6 L/min of oxygen for two minutes prior to anesthesia induction. Induction of anesthesia was achieved with 1 – 2 mg/kg propofol (primed with 2 ml 2% lidocaine to prevent injection pain), 1 – 2 mcg/kg fentanyl and 0.4 − 0.6 mg/kg rocuronium bromide administered intravenously.

For anesthesia maintenance, sevoflurane was administered at 1 minimum alveolar concentration with a 50% oxygen–50% air mixture, and remifentanil at 0.1 – 0.2 mcg/kg/min. Additional muscle relaxation, when needed, was provided with 0.1 mg/kg rocuronium bromide as an intravenous bolus. 200 mg sugammadex was administered intravenously to antagonise muscle relaxation at the end of anesthesia, and patients were extubated upon meeting extubation criteria.

In the PACU, standard monitoring was continued, and patients were re-instructed on the use of the PCA device. Patients were transferred to the general surgery ward once their Modified Aldrete score, assessed after 60–90 min PACU stay, reached 9 or above.

Postoperative analgesia and PONV management

Thirty minutes before the end of surgery, patients received 0.05 mg/kg intravenous morphine and 1 g intravenous paracetamol. Paracetamol was continued in the ward at 8-hour intervals. For PONV prophylaxis, 1 mg intravenous granisetron was administered 30 min before the end of the anesthesia.

Postoperative pain management was standardized for all patients to minimize confounding analgesic effects. All patients were informed about the usage of the PCA device at the preoperative visit. In the post-anaesthesia care unit, a PCA device was connected for each patient, and instructions for its use were reiterated. The device was programmed to deliver 1 mg morphine bolus doses on demand, a 15-minute lockout interval, a 4-hour limit of 12 mg morphine, and no basal infusion. If the patient experienced moderate to severe pain (NRS ≥ 4), 50 mg dexketoprofen was administered intravenously for rescue analgesia. The maximum daily dose of dexketoprofen was 150 mg. Rescue antiemetic therapy consisted of intravenous granisetron 1 mg and was administered to all patients who developed postoperative nausea lasting more than 10 min or any vomiting episode within the first 24 h after surgery.

Outcomes

Primary outcome

The primary outcome was cumulative morphine consumption within 24 h postoperatively. Morphine consumption from the PCA device was recorded at postoperative 2, 6, 12, and 24 h.

Secondary outcomes

Secondary outcomes included postoperative pain scores, rescue analgesic requirement and dose, PCA bolus request count, postoperative nausea and vomiting (PONV) incidence as reflected by protocol-driven anti-emetic use, PONV severity, and patient satisfaction. Postoperative pain scores at rest were assessed verbally using the NRS in the PACU (at 1 h) and at 2, 6, 12, and 24 h postoperatively in the surgical ward. NRS is an 11-point scale ranging from 0 (no pain) to 10 (worst pain). Rescue analgesic data from the patient’s file were recorded at postoperative hours 2, 6, 12, and 24. Rescue analgesic requirement was reported as the number and percentage of patients who required rescue analgesia. The rescue analgesic dose was reported as the total dose per patient during the first 24 postoperative hours. The PCA bolus attempt count from the PCA device was recorded at postoperative hours 2, 6, 12, and 24. PONV was analyzed primarily as a patient-level binary outcome (presence or absence within 24 h). In addition, symptom severity was descriptively classified based on the predominant clinical presentation (no symptoms, nausea only, or nausea with vomiting), with each patient assigned to a single category. Transient nausea that lasts less than 10 min and resolves spontaneously without intervention was not regarded as clinically significant PONV and was not documented as an event. Patient satisfaction was scored on 5-point scale as “1: Very Dissatisfied”, “2: Dissatisfied”, “3: Neutral”, “4: Satisfied”, “5: Very Satisfied”, and evaluated at postoperative 24 h at ward.

Patients were monitored for adverse events related to the SAPB procedure and postoperative pain management during both intraoperative and postoperative periods. These events included signs of local anesthetic systemic toxicity, pneumothorax, hematoma, sedation, and respiratory depression.

Sample size calculation and statistical analysis

The sample size was calculated using G*Power (version 3.1.9.6; Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany). In a previous study on MRM patients, superficial SAPB showed that cumulative morphine consumption via PCA within 24 h was 9.7 ± 2.1 mg [22]. Although there is no established minimal clinically important difference value for opioid consumption for breast cancer surgery, 10 mg intravenous morphine equivalent has been used pragmatically for regional analgesia studies for breast surgery [23]. We considered that using absolute minimal clinically important difference values may have a weakness due to the anticipation of lower opioid consumption when comparing two blocks instead of block vs. no intervention [24]. Therefore, a pragmatic assumption of a relative 20% reduction in cumulative morphine consumption during the postoperative 24 h between the two study groups was adopted. 26 patients per group would provide 90% power to reject the null hypothesis of equal mean cumulative morphine consumption in a two-sample, two-sided test at a 0.05 significance level. Considering the dropout rate of 20% to account for potential protocol deviations, incomplete postoperative data collection, early discharge, or inability to use patient-controlled analgesia during the follow-up period reliably, 64 patients were decided to enroll [25].

Of the 64 randomized patients, one patient was excluded from the final analysis due to accidental disconnection of the patient-controlled analgesia device, which precluded reliable opioid consumption assessment. No additional dropouts, missing data, or protocol deviations occurred. Analyses were therefore conducted on a per-protocol basis.

Data were analyzed and visualized using R Studio (version 2024.12.1; Posit Software, PBC, Boston, USA). Data normality was evaluated using the Shapiro-Wilk test. Continuous data following a normal distribution are presented as mean ± standard deviation, and non-normally distributed continuous data are presented as median (Q1, Q3). Categorical data are presented as numbers or percentages. Intergroup differences in normally distributed continuous data were assessed using independent samples t-test, while non-normally distributed data were analyzed using the Wilcoxon-Mann-Whitney test. Categorical variables were analyzed using the Pearson Chi-squared, Fisher’s Exact, or Fisher-Freeman-Halton (Monte Carlo) test. Effect sizes were presented as Cohen’s d, Cliff’s delta, Cramer’s V for independent samples t-test, Wilcoxon-Mann-Whitney test, and categorical tests. Differences were considered statistically significant at P < 0.05.

Results

A total of 84 patients were assessed for eligibility, of whom 20 were excluded after the inclusion and exclusion criteria. Sixty-four patients were randomly allocated into two groups in equal numbers. One patient was excluded from the final analysis due to accidental PCA disconnection (Fig. 1). There were no differences between the two groups in terms of age, weight, height, body mass index, and procedure duration (Table 1).

Fig. 1.

Consort flow diagram. SAPB: Serratus anterior plane block

Table 1.

Demographic and baseline characteristics

	Deep SAPB group (n = 32)			Superficial SAPB group (n = 31)			P value
Age, years	54.2	±	11.4	53.6	±	10.6	0.810 †
Weight, kg	70.8	±	6.8	72.4	±	7.8	0.405 †
Height, cm	158.3	±	5.7	157.5	±	3.3	0.481 †
BMI, kg/m2	28.4	±	3.3	29.3	±	3.6	0.314 †
Surgical procedure (1/2) *, n (%)	10 / 22 (31.3/ 68.7)			14 / 17 (45.2 / 54.8)			0.256 ‡
Procedure time, min	155.6	±	27.68	151	±	17.8	0.516 †

Values presented as mean ± standard deviation, and patient number (n) and percentage (%)

^*: 1: Simple mastectomy + sentinel lymph node biopsy, 2: MRM

†: Independent samples t-test

‡: Pearson chi-squared test

Cumulative morphine consumption was similar between groups at all time points (Table 2; Fig. 2).

Table 2.

Comparison of opioid consumption and postoperative pain scores

	Deep SAPB group (n = 32)	Superficial SAPB group (n = 31)	Median Difference [95% CI]	P value*	Effect size [95% CI]
	M (Q1 – Q3)	M (Q1 – Q3)
Morphine, mg
2 h	3.0 (2.0–3.0)	3.0 (2.0–3.0)	0.0 [-1.0–1.0]	0.900	-0.02 [-0.28–0.25]
6 h	5.0 (3.8–7.3)	5.0 (4.0–7.0)	0.0 [-1.0–1.0]	0.739	-0.05 [-0.34–0.24]
12 h	7.5 (6.0–13.0)	11.0 (7.0–13.5)	-3.5 [-6.0–4.0]	0.265	-0.16 [-0.45–0.13]
24 h	12.0 (9.0–17.0)	14.0 (9.0–20.0)	-2.0 [-6.5–3.0]	0.248	-0.17 [-0.46–0.14]
NRS
PACU	2.0 (2.0–2.0)	3.0 (2.0–3.5)	-1.0 [-1.0–0.0]	< 0.001	-0.46 [-0.67 – -0.24]
2 h	3.0 (2.0–4.0)	3.0 (2.0–5.0)	-1.0 [-2.0–1.0]	0.208	-0.18 [-0.45–0.09]
6 h	2.0 (1.8–3.0)	3.0 (2.0–5.0)	-1.0 [-2.0–1.0]	0.020	-0.33 [-0.58 – -0.09]
12 h	3.0 (2.0–4.0)	4.0 (3.0–5.0)	-1.0 [-2.0–0.5]	0.034	-0.31 [-0.57 – -0.04]
24 h	3.0 (2.0–4.0)	4.0 (3.0–5.5)	-1.0 [-2.5–0.0]	0.020	-0.33 [-0.60 – -0.08]

M Median, Q1 First quartile, Q3 Third quartile, CI Confidence interval

*: Wilcoxon-Mann-Whitney test

Fig. 2.

Comparison of postoperative opioid consumption

NRS scores were slightly lower in the deep SAPB group, except for 2 h (Table 2; Fig. 3).

Fig. 3.

Comparison of pain scores. NRS: Numeric rating scale-11, PACU: Post-anesthesia care unit

The rescue analgesia requirement, the rescue analgesic dose, and the PCA bolus attempt count were similar between groups. Clinically significant PONV (antiemetic requirement) was significantly lower in the deep SAPB group; however, the present study was not powered to detect this difference (p = 0.017, 1-β = 57.2%). Patient satisfaction scores were slightly higher in the deep SAPB group compared to the superficial SAPB group (p = 0.024) (Table 3). No block-related serious adverse events were observed during the study period.

Table 3.

Comparison of secondary outcomes

	Deep SAPB group (n = 32)	Superficial SAPB group (n = 31)	P value	Effect size
Rescue analgesic requirement, n (%)	9.0 (28.1)	11.0 (35.5)	0.530*	0.045
Rescue analgesic Dose, dexketoprofen, mg	0.0 (0.0–50.0)	0.0 (0.0–75.0)	0.252†	-0.14
PCA bolus attempt count	47.8 ± 21.4	58.1 ± 23.7	0.074‡	0.459
PONV symptom profile (patient-level), n (%)
No nausea/vomiting	21.0 (65.6)	11.0 (35.5)	0.059§	0.302
Only nausea	8.0 (25.0)	14.0 (45.2)
Nausea and vomiting	3.0 (9.4)	6.0 (19.4)
PONV incidence (Anti-emetic requirement), n (%)	11.0 (34.4)	20.0 (64.5)	0.017 *	0.370
Patient satisfaction score	4.0 (4.0–5.0)	4.0 (4.0–4.0)	0.024†	0.280

Values presented as mean ± standard deviation, median (interquartile range), and patient number (n) and percentage (%)

PCA Patient controlled analgesia

PONV Post-operative nausea and vomiting

^*: Pearson chi-squared test

†: Wilcoxon-Mann-Whitney test

‡: Independent samples t-test

§: Fisher – Freeman – Halton test (Monte Carlo)

Discussion

The present study showed that cumulative morphine consumption within 24 h was similar between deep and superficial SAPB. Except at 2 h, pain scores were slightly lower in the deep SAPB group; however, these findings should be interpreted as exploratory because of the increased risk of type I error from multiple unadjusted comparisons and because some 95% confidence intervals for the median differences included zero.

Deep SAPB blocks the lateral cutaneous branches of the intercostal nerves before piercing the serratus anterior muscle. In contrast, superficial SAPB primarily blocks lateral branches after being divided into anterior and posterior ramii. Therefore, it can be assumed that the block targeting lateral branches before ramification may provide more effective analgesia. Additionally, intercostal spread is more possible with the deep SAPB block, but this effect is inconsistent [19]. Moreover, blockade of nerves that run within a plane is not the only mechanism of fascial plane blocks. Diffusion of local anesthetics into surrounding muscles, fascia, and other tissues can block nociceptive signals arising from these structures and contribute to analgesia. This mechanism may be significant for rib fracture analgesia, since tissue distribution due to trauma can facilitate spread to muscles and deeper planes, such as the intercostal space [26]. Furthermore, systemic absorption of local anesthetics can produce some degree of analgesia [27]. Structural properties of a fascia, such as viscosity, density, cellular composition, and fascial gliding, can play important roles in injectate spread [28, 29]. Cadaveric studies have demonstrated potential leakage of the injectate from the superficial plane to the subcutaneous fat, although the risk is considered low [17, 30]. Moreover, local anesthetics may spread more widely than superficial injection in deep SAPB due to the less distensibility of the fascia, and mechanical forces caused by respiratory movements [31]. All the above-mentioned factors can contribute to opioid-independent analgesia mechanisms. While there were no significant changes in opioid consumption in our study, the patient satisfaction level was slightly higher in the deep SAPB. Deep SABP may provide more pronounced myofascial relaxation, since pectoral fascia and muscle manipulation, and arm position for axillary dissection during surgery can be pain generators [32]. These factors may contribute to modestly higher patient satisfaction levels.

Previous studies comparing preoperative deep and superficial SAPB that included MRM patients found that there was no significant difference between groups in terms of opioid consumption [33, 34]. Similarly, a retrospective propensity-matched study found deep SAPB to be non-inferior, yet not superior, to superficial SAPB regarding opioid consumption and pain scores [35]. However, this cohort consists of a broad spectrum of breast cancer surgery, and no information was available about the quadrant of partial mastectomies. Furthermore, some patients were on chronic opioid therapy. Edwards et al. [36], found post-block 24 h opioid consumption was lower with deep SAPB. However, post-operative opioid consumption did not differ. In this study, axillary lymph node dissection was performed in only a minority of cases, whereas most patients received tissue expanders after unilateral or bilateral mastectomy. A tissue expander adds strain to the pectoral muscles, which can increase the severity of pain. Deep SAPB may offer a potential advantage over superficial SAPB in attenuating this pain source, given that the injectate has been shown to spread to the pectoral muscles. Accordingly, this may contribute to the comparable postoperative opioid consumption between groups.

The type of surgery has been known to be a factor for postoperative acute pain severity after breast cancer surgery [21]. Both simple mastectomy and MRM procedures involve the complete removal of breast tissue; however, the MRM includes axillary lymph node dissection [37]. The axillary area has complex innervation from the high thoracic spinal nerves and the brachial plexus [5]. Therefore, extensive tissue manipulation in this area may introduce additional pain generators. Single-level injection at T4-5 is unlikely to cover the axilla [17]. Thus, either deep or superficial SAPB may not inhibit pain transmission arising from the axilla. This may explain comparable cumulative opioid consumption between groups.

The optimal timing of block placement remains controversial. While preoperative administration aligns with the principles of preemptive analgesia, procedural anxiety may be a concern for certain patients. However, studies suggested that analgesic efficacy is the same regardless of timing. Therefore, we performed the blocks after anesthesia induction, before incision. We aimed to ensure patient comfort and to respect patient privacy, although this practice has been known to prevent sensory evaluation and dermatomal mapping. However, the incision was placed after 30 min of induction, and the time between induction and incision is likely sufficient to take the block action [38]. As with other fascial plane blocks, variability in local anesthetic distribution can occur between individuals. When injections are performed in planes near the surgical area, manipulation and suction during lymph node removal may affect the spread of the anesthetic in some patients. This variability indicates differences in how the block disperses rather than a lack of effectiveness and may partly explain why opioid use was similar across groups.

In this study, cumulative morphine use was similar across groups. Although the median difference was approximately 2 mg—meeting the predefined 20% reduction threshold—the confidence intervals were wide, precluding definitive conclusions. Thus, relying solely on opioid consumption may not fully reflect the postoperative patient experience. Prior research comparing deep and superficial SAPB has shown comparable PONV rates, with inconsistent results on patient satisfaction. In our findings, fewer patients experienced clinically significant PONV, and satisfaction scores were slightly higher in the deep SAPB group. PONV was assessed at the patient level, emphasizing clinically significant PONV instead of counting episodes.

While multimodal PONV prevention is recommended in guidelines, routine dexamethasone was not administered in this cohort due to surgical preference and concerns about perioperative glycemic control and wound healing in breast cancer surgery [39]. Differences in surgical procedures, PONV management protocols, and outcome definitions across studies may partly account for differences in reported PONV and satisfaction outcomes. Therefore, our results regarding PONV and patient satisfaction should be viewed as hypothesis-generating rather than conclusive, and further research is necessary to examine patient-centered outcomes alongside opioid use.

Our study has some limitations. Heterogeneity of surgical procedures may have influenced the observed efficacy of SAPB and potentially attenuated differences between groups, particularly with respect to opioid consumption as the primary outcome, as discussed above. Block success rates and sensory coverage could not be confirmed. They may have varied among patients because dermatomal sensory mapping was not performed, as blocks were administered after anesthesia induction to ensure patient comfort. Additionally, SAPB was performed as a single injection at one level, which might not be enough to guarantee consistent axillary coverage, especially in patients undergoing MRM. Also, there is a risk of injectate suctioning at the superficial plane, as previously discussed. Consequently, neither pinprick nor cold sensation was assessed before or after surgery. A lack of a control group with only PCA may be added as another limitation.

In conclusion, both deep and superficial SAPB can be used for analgesia after simple mastectomy and MRM since both techniques did not differ in terms of opioid consumption. However, deep SAPB was associated with slightly lower pain scores and higher satisfaction, suggesting a possible clinical advantage that warrants further study. Future research should incorporate detailed dermatomal mapping, compare pre- and post-induction block timing, and evaluate multi-injection strategies to optimize axillary analgesia and clarify the role of SAPB in breast cancer surgery analgesia standards.

Abbreviations

ASA

American Society of Anesthesiologists

BMI

Body mass index

MRM

MRM

NRS

Numeric rating scale

PACU

Postanesthesia care unit

PCA

Patient-controlled analgesia

PONV

Postoperative nausea and vomiting

PVB

Paravertebral block

SAPB

Serratus anterior plane block

Authors’ contributions

AÜ and ES contributed to the realization of this study. AT, ES, and MG collected data and drafted the manuscript. ES performed the statistical analysis. AÜ and GT revised the manuscript. All authors approved the final manuscript.

Funding

No funding to declare.

Data availability

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

The study protocol was approved by the local ethics committee (Erciyes University Clinical Research Ethical Board (No. 2024/58)) and registered in Clinicaltrials.gov on May 29, 2024 (No. NCT06438211; https://www.clinicaltrials.gov). The procedures were carried out in full compliance with the principles of the Declaration of Helsinki. All participants provided written informed consent for their inclusion in the study.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.