After skin wheal placement and needle entry, the goal is continuous visualization of the needle tip as it is advanced toward the target nerve or fascial plane. In our practice, small volumes of normal saline are frequently used for hydrolocation (to confirm needle tip position) and hydrodissection (to open appropriate fascial planes). Once the ideal location is achieved, anesthetic should be injected in 3–5 mL aliquots, with pauses between injections to confirm negative aspiration and reassess the patient for early signs of local anesthetic systemic toxicity. Maintaining needle tip visualization under ultrasound guidance remains the most effective method to prevent inadvertent intravascular or intraneural injection.⁵

For higher-volume blocks — such as the serratus anterior plane block or erector spinae plane block — additional time between aliquots is warranted. Clinicians should monitor closely for changes in heart rate, blood pressure, or mental status. In our experience, slowing the injection process not only improves safety but also reduces operator stress during these procedures.

Post-Block Pain Planning: Completing the Arc

The post-block phase is often underappreciated, yet it is critical to long-term analgesic success. As the block wears off, patients may experience abrupt and severe pain—commonly referred to as rebound pain. Although the precise mechanism and evidence base remain incompletely defined, this phenomenon is well recognized and should be anticipated whenever a single-injection nerve block is performed.

Clinicians should establish a clear post-block medication strategy for all patients receiving single-shot UGNBs. We recommend a scheduled multimodal analgesia regimen (for discharged and admitted patients) for the first 24 hours following the block. In our experience, “as needed” dosing should be discouraged, because patients frequently decline analgesics while the block is effective, and request medication only after the block is starting to wear off. The resultant increased pain can be extremely distressing and very difficult to control.

Patient and staff education is essential. A multimodal regimen incorporating NSAIDs, acetaminophen, and, when appropriate, short-course opioids can significantly reduce the severity of rebound pain. After the initial 24-hour period, patients can taper medications as tolerated. Clear written instructions and discharge counseling should accompany all outpatient blocks.⁶

Although continuous peripheral nerve catheters may mitigate rebound pain, they are not commonly used in the ED setting due to logistical and follow-up limitations. As such, thoughtful post-block planning remains essential for single-shot techniques.