What is a PECS block (pectoral nerve block)?

What is a PECS Block?

A PECS (pectoral nerves) block is an ultrasound-guided interfascial plane block that involves injecting local anesthetic between chest wall muscle layers to provide analgesia for breast surgery by blocking the pectoral nerves, intercostal nerves (III-VI), intercostobrachial nerve, long thoracic nerve, and thoracodorsal nerve. 1

Two Types of PECS Blocks

PECS-1 Block

• Involves injection of local anesthetic between the pectoralis major and pectoralis minor muscles to block the lateral and medial pectoral nerves 1
• Originally designed for breast expanders and subpectoral prosthesis placement where pectoral muscle distension causes significant pain 2

PECS-2 Block (Modified PECS Block)

• Includes the PECS-1 injection PLUS a second, deeper injection between the pectoralis minor and serratus anterior muscles 1
• Provides more extensive coverage by blocking the intercostobrachial nerve, intercostal nerves III-IV-V-VI, long thoracic nerve, and thoracodorsal nerve in addition to the pectoral nerves 3
• This is the preferred version for most breast surgeries including mastectomy, wide excisions, and axillary procedures 2

Clinical Indications and Efficacy

When to Use PECS Blocks

• PECS blocks are recommended (Grade A) for major breast surgery when axillary node dissection is NOT performed OR when paravertebral block is contraindicated 1
• For breast-conserving surgery, PECS blocks moderately reduce postoperative opioid use, prolong time to analgesic rescue, and decrease pain scores compared to systemic analgesics alone (Strength of Recommendation A) 4
• For mastectomy, PECS blocks provide opioid-sparing effects similar to paravertebral blocks and are recommended when paravertebral block cannot be performed (Strength of Recommendation A) 4

Comparative Effectiveness

• PECS-2 blocks significantly reduce intraoperative opioid requirements and postoperative pain scores compared to no block or placebo 1
• In the first 2 hours postoperatively, PECS-2 provides lower pain scores than paravertebral block, but after 18 hours paravertebral block becomes superior 1
• Meta-analyses demonstrate comparable overall pain relief and opioid consumption between PECS and paravertebral blocks 1
• PECS blocks reduce 24-hour postoperative opioid consumption in 93.3% of studies 5

Critical Technical Considerations

Anatomical Limitations

• Neither PECS nor paravertebral blocks reliably provide sufficient analgesia to the axilla (T1 nerve distribution) 1
• Supplemental local anesthetic wound infiltration is recommended for axillary coverage 1, 3
• Injecting deep to serratus anterior (subserratus plane) produces significantly less axillary spread than conventional PECS-2 6
• For axillary dissection, the conventional PECS-2 injection between pectoralis minor and serratus anterior is superior to subserratus placement 6

Procedural Requirements

• Ultrasound guidance is recommended for performing PECS blocks 3
• Calculate safe local anesthetic doses based on patient weight to prevent systemic toxicity 7

Integration into Multimodal Analgesia

Mandatory Concurrent Medications

• PECS blocks MUST be integrated into a multimodal regimen including scheduled paracetamol and NSAIDs/COX-2 inhibitors 1, 3
• Administer these medications "round-the-clock" rather than as-needed for optimal effect 7
• Add pre-operative gabapentin (Grade A) and intra-operative dexamethasone (Grade B) 1, 7
• Reserve opioids for rescue analgesia only 1, 3

Common Pitfall to Avoid

• Nearly 90% of studies evaluating PECS blocks failed to administer basic analgesics (paracetamol, NSAIDs) optimally, undermining their conclusions 7
• The combination of paracetamol plus NSAID/COX-2 inhibitor provides superior analgesia compared to either drug alone 7

Optimization Strategies

• Combining PECS-2 with transversus thoracic muscle plane block provides lower pain scores and less rescue analgesia than PECS alone 1, 3
• PECS blocks combined with continuous local anesthetic wound infusion provide better 24-hour analgesia than either technique alone 3

When PECS Blocks Are Inferior

• Erector spinae plane (ESP) block demonstrates superior pain control and lower opioid consumption compared to PECS blocks after the first postoperative hour in breast surgery 1, 8
• However, PECS blocks remain the recommended interfascial plane block alternative to paravertebral block per current guidelines 1