Chronic Pain in Mastectomy Patients; The Difference Between Pectoral Nerve Block (PECS I-II) and Erector Spinal Plane (ESP) Block
Conditions: Breast Cancer Surgery, Postoperative Pain, Acute, Postoperative Pain, Chronic, Post-mastectomy Pain Syndrome, Regional Anesthesia, Pectoral Nerve (PECS) Block, Erector Spine Plane Block, Neuropathic Pain, Mastectomy, Quality of Life (QOL)
Sponsor: Hacettepe University

 
 
Chronic Pain in Patients Undergoing 
Mastectomy: The Difference Between 
Pectoral Nerve Block (PECS I-II) and Erector 
Spinae Plane (ESP) Block 
 
APRIL 2024 
 
 
 
 
 
 
 
 
 

STUDY PROTOCOL 
 
1. Project Title: 
Chronic Pain in Patients Undergoing Mastectomy: The Difference Between Pectoral Nerve 
Block (PECS I-II) and Erector Spinae Plane (ESP) Block 
 
2. Rationale of the Project: 
Breast cancer is the most commonly diagnosed cancer among women and remains a leading 
cause of cancer-related mortality. Globally, it ranks second only to lung cancer in incidence, 
with both accounting for approximately 11.6% of all diagnosed cancer cases (1). In the 
United States, the lifetime risk for a woman to develop breast cancer is estimated at 13%, 
indicating that one in eight women will be affected during their lifetime (2). 
Over the past two decades, significant advances in breast cancer research have markedly 
improved our understanding of the disease, enabling the development of more effective and 
less toxic treatments. Enhanced public awareness and improved screening methods have 
facilitated early detection at stages amenable to surgical resection and curative therapy. 
Consequently, survival rates—especially among younger women—have substantially 
improved (3). 
Surgical treatment of breast cancer includes both conservative and non-conservative 
approaches. Conservative surgeries account for approximately 40% of all procedures, with 
quadrantectomy being the most commonly performed among them (4). However, surgical 
treatment may lead to various complications, including chronic postoperative pain (5). 
Post-mastectomy pain syndrome (PMPS) is typically defined as chronic pain in the breast or 
chest wall persisting for at least three months following cancer treatment. It arises after 
surgical interventions for breast cancer and is believed to result from primary nerve injury 
or dysfunction of the nervous system (6,7). Clinically, it presents with features of 
neuropathic pain such as burning, tingling, stabbing, or shooting sensations, and 
hyperesthesia (8). Although no standardized diagnostic criteria exist, the estimated 
incidence ranges from 40% to 50% (7,9), with about half of affected women reporting 
moderate to severe pain (10). 
Younger age (<40 years) has been identified as a major risk factor, though age does not 
appear to correlate with the intensity of reported pain (10). Severe acute postoperative pain 
is also considered a predictive factor for the development of chronic pain. Furthermore, 
radiotherapy to the breast and/or axillary region has been associated with an increased risk 
of chronic pain when compared to patients who did not receive radiation therapy (11). 
Among surgical contributors to PMPS, extensive axillary lymph node dissection is 
significant due to the increased risk of intercostobrachial nerve injury, which may lead to 
neuropathic pain (12,13). 
Strategies aimed at reducing the risk of PMPS emphasize optimizing perioperative pain 
management. Techniques such as paravertebral, erector spinae plane (ESP), and pectoral 

nerve blocks are routinely applied in appropriate surgical cases to reduce postoperative 
pain and minimize the risk of chronic pain development in many centers, including ours 
(14). Both ESP and PECS I-II blocks have demonstrated efficacy and are associated with low 
complication rates (14,15,16). 
In our study, we aim to observe the incidence of chronic pain following mastectomy in 
patients who have received either a pectoral nerve block (PECS I-II) or an erector spinae 
plane (ESP) block as part of their pain management strategy. These blocks will be 
administered by the attending anesthesiologist after general anesthesia induction and prior 
to the initiation of surgery. The choice and timing of the block will be determined 
independently by the anesthesiologist and not influenced by the study team. The primary 
outcome of this study is to compare the incidence of chronic postoperative pain between 
the two groups. The secondary outcome is to assess the impact of these blocks on acute 
postoperative pain levels and opioid requirements. 
 
3. Materials and Methods of the Study 
3.1 Study Setting 
Department of Anesthesiology and Reanimation, Hacettepe University. 
3.2 Study Timeline 
April 15, 2024 – August 15, 2024. 
3.3 Study Population, Sample Size, and Study Groups 
Following approval by the Hacettepe University Ethical Committee, patients aged 18 to 65 
years, classified as ASA physical status I–II, and scheduled to undergo elective modified 
radical mastectomy or simple mastectomy with sentinel/axillary lymph node dissection 
under general anesthesia at Hacettepe University Hospitals between April 15 and May 15, 
2024, will be included. Patients must have already been scheduled to receive either an ESP 
or PECS I-II block for postoperative pain management independently of the study. A total of 
40 patients will be enrolled, with 20 in each group at least. Patients with coagulation 
disorders, allergies to local anesthetics, obesity (BMI > 35 kg/m²), infection at the injection 
site, pre-existing neurological deficits, or unwillingness to participate, as well as those with 
failed blocks, will be excluded. The decision to perform blocks is made by the responsible 
anesthesiologist and will not be influenced by the study team. 
3.4 Study Type 
Prospective Cohort Study 
3.5. Research Method and Data Collection Tools: 
Upon admission to the operating room, non-invasive arterial blood pressure, 
electrocardiogram, and peripheral oxygen saturation monitoring will be conducted before 

the induction of general anesthesia. This is the routine monitoring protocol applied prior to 
anesthesia. All patients will receive standard general anesthesia and standard ventilation 
modes. The research team will not intervene in the anesthesia procedure. 
According to the standard anesthesia practice in these cases, anesthesia induction is 
performed with propofol (1.5–2.5 mg/kg), rocuronium (0.4–0.6 mg/kg), and fentanyl (1–2 
mcg/kg), with a 50% oxygen-air mixture. Standard ventilator settings are applied. 
Anesthesia maintenance consists of 2% sevoflurane with 50% oxygen-air mixture. These 
practices are routine in our operating theater and are not specifically designed for this 
study. In the event of any non-routine requirement, decisions will be made by the 
responsible anesthesiologist, without any intervention from the research team. The study 
will commence after anesthesia induction and block application. 
Following the induction of general anesthesia, the responsible anesthesiologist will 
independently administer either the PECS I-II or ESP block prior to surgical incision. The 
choice of block will not be influenced by the study and will be determined solely by the 
anesthesiologist, regardless of group distribution. The research team will not interfere in 
the selection or method of block administration. 
PECS I-II Block Protocol: 
With the patient in the supine position and the upper limb abducted 90°, the ultrasound 
(USG) probe is placed under the lateral third of the clavicle. After identifying the axillary 
artery and vein, the probe is aligned with the second rib. It is then moved inferolaterally to 
visualize the third rib and the pectoralis major, pectoralis minor, and serratus anterior 
muscles. A 10 cm block needle is advanced between the pectoralis major and minor muscles 
under ultrasound guidance. After confirming the site with 2–3 mL isotonic saline 
(hydrodissection), 10 mL of 0.25% bupivacaine is administered (PECS I). The probe is then 
moved toward the axilla, and when the serratus anterior muscle over the fourth and fifth 
ribs is visualized, another 20 mL of 0.25% bupivacaine is injected between the pectoralis 
minor and serratus anterior muscles (PECS II). 
ESP Block Protocol: 
The patient is placed in lateral decubitus position with the surgical side up. The ultrasound 
probe is placed longitudinally at the level of the T4–5 spinous processes and then moved 
laterally toward the surgical side. The transverse process and overlying trapezius, 
rhomboid, and erector spinae muscles are visualized. Under aseptic conditions, the block 
needle is inserted at a 30–40° cranio-caudal angle, passing through the trapezius, rhomboid, 
and erector spinae muscles. After confirming placement with 2–3 mL isotonic saline, 20–30 
mL of 0.25% bupivacaine is injected between the erector spinae muscle and transverse 
process. 
Both PECS I-II and ESP blocks will be performed under ultrasound guidance, and the needle 
position will be verified through anatomical visualization and hydrodissection. Blocks will 

be considered successful if applied by the responsible anesthesiologist under these 
conditions. 
At the end of surgery, maintenance agents will be discontinued, and intravenous 
sugammadex will be administered to reverse muscle relaxation, dosed according to patient 
weight. About 30 minutes prior to the end of surgery, 1000 mg intravenous paracetamol 
will be routinely administered for analgesia. Extubation will occur after the patient regains 
spontaneous breathing and emerges from anesthesia. This is standard procedure and will 
not be modified for the study. No interference will occur with decisions regarding 
anesthesia drugs, ventilation methods, or intubation technique. 
Postoperative Pain Control: 
In addition to routine 3×1000 mg IV paracetamol, rescue analgesia with IV tramadol (0.5 
mg/kg) will be administered as needed. These practices are part of our standard 
multimodal analgesia protocol and not specific to the study. After discharge, patients will be 
transitioned to oral paracetamol, with a recommendation of 3×500 mg daily for one month 
if necessary 
Postoperative follow-up interviews will be conducted by a study assistant. Time of initial 
pain, and whether rescue analgesia was needed within the first 24 hours, will be recorded. 
Pain levels will be assessed at 20 minutes, 6 hours, and 1 day postoperatively using the 
Numerical Rating Scale (NRS). If NRS >0, the DN4 (Douleur Neuropathique 4) questionnaire 
will be administered. At the 3-month follow-up, patients will be contacted via phone and 
evaluated with the DN2 and SF-12 questionnaires. No blood samples or invasive procedures 
will be performed for research purposes. 
The NRS is a simple and widely used 0–10 scale to assess pain severity, from "0 = no pain" 
to "10 = worst imaginable pain." It is considered valid and reliable. The DN4 questionnaire, 
administered by clinicians, includes 10 items to evaluate neuropathic pain, with a 
sensitivity of 83% and specificity of 90%. A score ≥4 indicates neuropathic pain. The SF-12 
Quality of Life questionnaire, validated in Turkish, consists of 12 items and is used to assess 
overall health status and quality of life. 
3.6. Data Collection 
Following ethics committee approval, eligible patients aged 18–65 years scheduled for 
elective modified radical mastectomy between April 15 and May 15, 2024, at Hacettepe 
University Hospital, who had already been assigned ESP or PECS I-II blocks for 
postoperative pain control independent of the study, will be enrolled. The study is 
observational, and no interventions will be made regarding clinical treatment decisions. 
Patient demographic data (ASA score, age, sex, weight, height, BMI, comorbidities) and 
intraoperative details will be recorded 

Postoperative data within the first 24 hours will be collected via face-to-face interviews and 
entered into the follow-up and DN4 forms. At 3 months, DN2 and SF-12 questionnaires will 
be administered via telephone interviews 
3.7. Data Analysis 
Normality of numeric data will be assessed using the Shapiro-Wilk test. Data following a 
normal distribution will be compared between two independent groups using the Student’s 
t-test. Non-normally distributed data will be analyzed using the Mann-Whitney U test. For 
three-group comparisons, one-way ANOVA will be used if parametric assumptions are met; 
otherwise, the Kruskal-Wallis H test will be applied. Descriptive statistics will include mean 
± standard deviation for normally distributed data, or median (minimum–maximum) for 
non-normal data. Categorical variables will be summarized as counts (percentages), and 
group comparisons will be performed using chi-square or Fisher’s exact test as appropriate. 
A p-value <0.05 will be considered statistically significant in all analyses. 
 
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