The pharmacokinetic data indicate faster absorption and higher maximal plasma concentration of LA when ultrasound was used as a guidance technique for INB compared with the landmark-based technique. Thus, a reduction of the volume of LA should be considered when using an ultrasound-guided technique for INB.

Reliable blockade of the IPN can be achieved with ultrasonographic guidance. Because of the very close anatomical relationship between the IPN and the SN it appears inevitable to also get a variable degree of concomitant SN block. The duration of the IPN block was in the majority of subjects greater than 16 h, a finding that may make this block useful for postoperative analgesia in out-patient arthroscopic surgery.

The use of dexmedetomidine as an adjunct to an IINB resulted in reduced incidences of CHIPPS pain scores ≥4 and PAED scores of ≥11 during early recovery following pediatric inguinal hernia repair. In addition, the use of adjunct dexmedetomidine was associated with a prolongation of the period to first supplemental analgesia demand. The results of the present exploratory study must be viewed as preliminary and need further validation by future larger sized studies and/or meta-analysis.

Two separate patterns of secondary spread of caudal block could be observed, being horizontal intrasegmental redistribution and longitudinal cranial spread. The observed bi-directional movement of cerebrospinal fluid (coined 'the CSF rebound mechanism') does explain a major part of the difference between the initial ultrasound-assessed cranial level and the final level determined by cutaneous testing.

Background:  The aim of this prospective, age‐stratified, observational study was to determine the cranial extent of spread of a large volume (1.5 ml·kg−1, ropivacaine 0.2%), single‐shot caudal epidural injection using real‐time ultrasonography. Methods:  Fifty ASA I‐III children were included in the study, stratified in three age groups; neonates, infants (1–12 months), and toddlers (1–4 years). The caudal blocks were performed during ultrasonographic observation of the spread of local anesthetic (LA) in the epidural space. Results:  A significant inverse relationship was found between age, weight, and height, and the maximal cranial level reached by 1.5 ml·kg−1 of LA. In neonates, 93% of the blocks reached a cranial level of ≥Th12 vs 73% and 25% in infants and toddlers, respectively. Based on our data, a predictive equation of segmental spread was generated: Dose (ml/spinal segment) = 0.1539·(BW in kg)–0.0937. Conclusions:  This study found an inverse relationship between age, weight, and height and the number of segments covered by a caudal injection of 1.5 ml·kg−1 of ropivacaine 0.2% in children 0–4 years of age. However, the cranial spread of local anesthetics within the spinal canal as assessed by immediate ultrasound visualization was found to be in poor agreement with previously published predictive equations that are based on actual cutaneous dermatomal testing.