Look at that caudal go!
Eshel A. Nir, MD, Myron Yaster MD and Lynne G. Maxwell MD
Ahh, the caudal block, the Swiss army knife of pediatric regional anesthesia! Safe, effective, easy to perform. In today’s PAAD, Kim et al.1.wondered if “ultrasound could be used to increase the accuracy of the block by visual confirmation of the drug-spreading.” First introduced into modern pediatric practice by the late Mexican pediatric anesthesiologist, Dr. Estela Melman,2 and later popularized by Drs. Raafat Hannallah, Linda Jo Rice, Lynn Broadman3 and others, the caudal block became the most common pediatric regional anesthetic block.4 Over the past 10-15 years, it lost its “sexiness” with the advent of more specific ultrasound guided peripheral and truncal nerve blocks. Are you using caudals in your practice or are they fading into oblivion? And if you are, how are you performing the block? With surface landmarks or ultrasound? Indeed, it’s been my observation that the caudal is increasingly becoming an ultrasound guided block or being replaced by specific nerve blocks.5
Before getting to today’s PAAD, I’d like to point out that it came as a suggestion from one of our readers, Dr. Eshel Nir, whom I met last February while I was volunteering at the Rambam Hospital in Haifa. Going forward, I’m hoping you, the readers, will become a more common source of articles for the PAAD. Exploring your suggestions will greatly expand the number of journals and articles we can review in the PAAD. Sooooo, if you find an article that you think may be of interest to the pediatric anesthesia community, please contact me and/or send me a first draft of your thoughts. There is no guarantee that I’ll use your suggested articles, but I will if I and our editorial council think it is PAAD worthy! Myron Yaster MD
Original article
Kim HJ, Kim H, Lee S, Koh WU, Park SS, Ro Y. Reconsidering injection volume for caudal epidural block in young pediatric patients: a dynamic flow tracking experimental study. Reg Anesth Pain Med. 2024 May 7;49(5):355-360. doi: 10.1136/rapm-2023-104409. PMID: 37429622.
When performing a caudal what’s the volume of drug you need to inject to obtain maximal spread and success? The classic formula that most people use has withstood the test of time: 0.5 mL/kg for coverage of sacral dermatomes (S1-S5), 1 mL/kg for the inguinal canal and lower abdomen below the umbilicus (T10 and below) and 1.25 mL/kg for thoracic dermatomes (T6 and below), i.e. coverage below the nipple line.
In today’s PAAD, Kim et al. “aimed to estimate the cephalad spread of injection volume by caudal route using dynamic ultrasound imaging in 40 young (6-24 months) pediatric patients undergoing foot surgery.”1 The authors commented that previous caudal ultrasound studies6-8 mostly dealt with procedural time, needle visualization and procedural success, yet they quote Brenner et al9 and Sinha et al10 who used ultrasound to assess cranial spread of caudally administered local anesthetic in 2011 and 2017 respectively, correlating volume injected (0.5, 1.0, 1.25 ml/kg) with extent of spread. Their study populations were also older (Brenner 1mos – 6 years [penile, anal, inguinal surgery], Sinha 1-6 years [surgery not specified]).
What did they find? “After inducing general anesthesia (with thiopental, yes thiopental!!!), an angiocatheter was inserted into the sacral canal under ultrasound guidance.” Prior to performing the caudal, ultrasound was used to identify and mark the T12-L1 intralaminar space in preparation to identify the extent of cranial spread. “Thereafter, the probe was placed in the paramedian sagittal oblique position, and prepared 0.15% ropivacaine was injected, 1 mL at a time” over 3 seconds incrementally, waiting 5 seconds after each injection, “up to a total of 1 mL/kg”. The ultrasound probe was moved cranially following the bulk flow of local anesthetics. “Our primary outcome was the required volume of local anesthetics to reach each level of interlaminar space.”1
“The dynamic flow tracking was available in 39 patients, and the required volume of the injectate to reach L5–S1, L4–L5, L3–L4, L2–L3, L1–L2, T12–L1, and T11–T12 was 0.125, 0.223, 0.381, 0.591, 0.797, 0.960, and 1.050 mL/kg, respectively. The required volume to reach the immediate upper spinal level was inconsistent across various spinal levels.”1 One of their conclusions was that the volume needed for foot surgery (L4-5) (0.223 ml/kg) may be less than what is routinely used. However, this conclusion ignores the common use of a tourniquet for these procedures and the fact that using larger volumes will result in a block of longer duration.
In my (MY) practice I routinely used 1 mL/kg in all patients because of simplicity. Kim et al. found that this dose routinely spread to the T12-L1 level. Can the use of ultrasound to show the spread of local anesthetic improve success? Unfortunately, we don’t know because the visualization of sonographic local anesthetic spread was not correlated to either SENSORY or MOTOR blockade because the patients were anesthetized with a vapor anesthetic. Further, Kim et al. point out that they “estimated the cranial spread of local anesthetics immediately after the injection.” A previous article found that there is a secondary spread 15 minutes after injection.11 Thus, the actual block range may be more than the ultrasound findings suggest. In addition, the slow, incremental and intermittent rate of injection (1ml/3 seconds with 5 seconds between aliquots) may affect the extent of spread. The Brenner and Sinha studies, injected continuously at a rate of 0.5 ml/second (50% faster), utilizing an infusion pump. These rates probably differ from the uncontrolled rates used clinically. Perhaps, the most important use of ultrasound is to demonstrate that the local anesthetic is being injected into the epidural space which will hopefully ensure a successful block.
The authors conclude that “based on our study results, local anesthetics of 0.223 mL/kg , 0.591 mL/kg, and 0.797 mL/ kg could provide sufficient analgesia for localized foot, knee, and hip surgeries, respectively. However, because the required volume of the local anesthetics cannot be calculated linearly, the real-time dynamic flow tracking technique is recommended for caudal epidural block in young pediatric patients.
We’ll conclude as we started. Are you using caudals in your practice or is fading into oblivion? And if you are, how are you performing the block with surface landmarks or ultrasound? How are you dosing your caudals? Send your thoughts and comments to Myron who will post in a Friday reader response.
References
1. Kim HJ, Kim H, Lee S, Koh WU, Park SS, Ro Y. Reconsidering injection volume for caudal epidural block in young pediatric patients: a dynamic flow tracking experimental study. Regional anesthesia and pain medicine 2024;49(5):355-360. (In eng). DOI: 10.1136/rapm-2023-104409.
2. Ahmed Z, Mai C, Skinner KG, Yaster M. At the birth of pediatric anesthesia in Mexico: An interview with Dr. Estela Melman, a pioneering woman in medicine. Paediatric anaesthesia 2018;28(12):1066-1070. (In eng). DOI: 10.1111/pan.13518.
3. Hannallah RS, Broadman LM, Belman AB, Abramowitz MD, Epstein BS. Comparison of caudal and ilioinguinal/iliohypogastric nerve blocks for control of post-orchiopexy pain in pediatric ambulatory surgery. Anesthesiology 1987;66(6):832-834.
4. Polaner DM, Taenzer AH, Walker BJ, et al. Pediatric Regional Anesthesia Network (PRAN): a multi-institutional study of the use and incidence of complications of pediatric regional anesthesia. Anesthesia and analgesia 2012;115(6):1353-64. (In eng). DOI: 10.1213/ANE.0b013e31825d9f4b.
5. Adler AC, Belon CA, Guffey DM, Minard CG, Patel NV, Chandrakantan A. Real-Time Ultrasound Improves Accuracy of Caudal Block in Children. Anesthesia and analgesia 2020;130(4):1002-1007. (In eng). DOI: 10.1213/ane.0000000000004067.
6. Jain D, Hussain SY, Ayub A. Comparative evaluation of landmark technique and ultrasound-guided caudal epidural injection in pediatric population: A systematic review and meta-analysis. Paediatric anaesthesia 2022;32(1):35-42. (In eng). DOI: 10.1111/pan.14332.
7. Boretsky KR, Camelo C, Waisel DB, et al. Confirmation of success rate of landmark-based caudal blockade in children using ultrasound: A prospective analysis. Paediatric anaesthesia 2020;30(6):671-675. (In eng). DOI: 10.1111/pan.13865.
8. Ponde V, Shah D, Nagdev T, Balasubramanian H, Boretsky K. Ultrasound determination of the dural sac to sacrococcygeal membrane distance in premature neonates. Regional anesthesia and pain medicine 2022;47(5):327-329. (In eng). DOI: 10.1136/rapm-2021-103344.
9. Brenner L, Marhofer P, Kettner SC, et al. Ultrasound assessment of cranial spread during caudal blockade in children: the effect of different volumes of local anaesthetics. British journal of anaesthesia 2011;107(2):229-35. (In eng). DOI: 10.1093/bja/aer128.
10. Sinha C, Kumar A, Sharma S, et al. Ultrasound assessment of cranial spread during caudal blockade in children: Effect of different volumes of local anesthetic. Saudi journal of anaesthesia 2017;11(4):449-453. (In eng). DOI: 10.4103/sja.SJA_284_17.