Utility of Ultrasonography for Confirmation of Successful Caudal Epidural Injection

Caudal epidural injection is the most commonly performed regional anesthetic procedure in infants and children and is used to provide perioperative analgesia for many lower abdominal, lower extremity, and urological procedures. Utilizing sterile technique, a needle is advanced through the sacral hiatus and local anesthetic is injected into the epidural space. Local anesthetic spreads cranially and results in significant sensory (+/- motor) blockade, depending on local anesthetic concentration and volume1. Recent studies have used ultrasound to assess cranial spread during caudal blockade, specifically evaluating how speed of injection and different volumes can affect cranial spread2,4. Other studies have investigated redistribution and secondary spread after initial injection of local anesthetic by utilizing ultrasound assessment of the epidural space3.

Although no current standard exists for confirming successful caudal epidural injection, several findings may indicate a proper needle position and can predict successful block5. Some of these findings include: tactile appreciation of the "pop" through the sacrococcygeal ligament, negative blood or cerebrospinal fluid aspiration, negative test dose, appropriate resistance during injection, no subcutaneous swelling during injection, no motor or hemodynamic response to skin incision, and no need for administration of supplemental analgesics. Although several studies have shown that real-time ultrasound guidance can be used during needle insertion for caudal block, this does not guarantee adequate cranial spread and may be technically challenging for a trainee performing the block. Furthermore, many of the tactile findings that indicate successful entry into the appropriate space can only be appreciated by the trainee, not the supervising anesthesiologist, which complicates supervision of this technique. At present, difficulty in reliably predicting block failure may lead to overuse of narcotics to prevent pain in patients with potentially failed blocks or could lead to inadequate analgesia in patients too young to reliably communicate their pain level.

The purpose of our study is to evaluate whether utilizing ultrasound assessment during caudal epidural injection can reliably identify unrecognized and unsuccessful nerve blocks during the procedure, guide proper technique, and alter pain management outcome measurements for patients.

The proposed study will not change the current practice with regard to patient selection for caudal epidural injection and will not change the performance of the procedure itself. This study may impact the practice of general pediatric anesthesiologists by providing evidence that ultrasound is a useful tool for determining successful caudal epidural injection, may help identify unrecognized failed blocks earlier and will evaluate which level(s) of anesthesia training would most benefit from this assessment tool.

Patients will be randomized using pre-made folders containing an assignment to either the control group or study group. In the study group, ultrasound will be utilized in the caudal block to confirm placement. In the control group, the caudal block will be done without ultrasound to assist with caudal epidural injection. In the operating room, once the anesthesia team is prepared to begin the caudal epidural injection, the patient will be placed in the lateral decubitus or prone position, with knees and hips flexed. The attending for the caudal block will mark the site on the patient per the site marking policy at Lurie Children's; this is not necessarily the attending of record for the remainder of the case. Once the sacrum is prepped, the anesthesia provider will proceed with the caudal epidural injection in the usual fashion. The injected solution will be 1 mL/kg of 0.2% ropivacaine with 1:200k epinephrine, rounded up to the next mL, which is consistent with the current standard practice at Lurie Children's. After injection of test dose (10% of the total block volume), a one-minute pause will begin to assess for a response. During this pause, prior to injection of the remaining dose of local anesthetic, a 13-6 MHz, linear ultrasound probe with a sterile covering and ultrasound gel will be placed over the patient's lumbar spine, cranial to the point of entry for the caudal block. The caudal block needle insertion site and sterile field will be observed and undisturbed. The ultrasound probe will be positioned paramedian along the non-dependent side of the spine, obtaining a long axis view of the epidural and intrathecal space. The cephalad end of probe will be placed at the level of the iliac crest. Once the ultrasound probe is positioned properly and the one-minute pause has finished, the remaining dose of local anesthetic will be administered by the anesthesia provider as an ultrasound clip of epidural spread is visualized.