Ultrasound assessment of cranial spread during caudal blockade in children: effect of the speed of injection of local anaesthetics.

BACKGROUND: Despite caudal blockade being the most widely used regional anaesthetic procedure for infants and children undergoing subumbilical surgery, the question whether the injection velocity of the local anaesthetic itself affects its spread in the epidural space has not yet been investigated. Thus, the aim of the present study was to measure the cranial spread of caudally administered local anaesthetics in infants and children by means of real-time ultrasonography, with a special focus on comparing the effect of using two different speeds of injection. METHODS: Fifty ASA I-II infants and children, aged up to 6 yr, weighing up to 25 kg, undergoing subumbilical surgery, were enrolled in this prospective, randomized, observer-blinded study. Caudal blockade was performed under ultrasound observation using ropivacaine 1 ml kg(-1) 0.2% or 0.35% and an injection given at either 0.25 ml s(-1) or 0.5 ml s(-1), respectively. RESULTS: Ultrasound observation of the local anaesthetic flow and the extent of cranial spread was possible in all patients. All caudal blocks were considered successful, and all surgical procedures could be completed without any indications of insufficient analgesia. No statistically significant difference could be observed between the two injection speeds regarding the cranial spread of the local anaesthetic in the epidural space. CONCLUSIONS: The main finding of the present study is that the speed of injection of the local anaesthetic does not affect its cranial spread during caudal blockade in infants and children. Therefore, the prediction of the cranial spread of the local anaesthetic, depending on the injection speed, is not possible.

Pharmacokinetics of the local anesthetic ropivacaine after transversus abdominis plane block in healthy volunteers.

PURPOSE: The transversus abdominis plane (TAP) block is a regional anesthetic technique used for pain control following abdominal surgical procedures. While a minimum of systemic side effects is usually expected after local anesthesia, it is unknown to which extent systemic absorption and redistribution to the abdominal wall contributes to the effects of anesthetics. The aim of this study was to determine concentration-time profiles of ropivacaine after the injection of 150 mg of ropivacaine into the lateral abdominal wall in various compartments. METHODS: The microdialysis technique was used to measure ropivacaine in plasma as well as at abdominal wall sites cranial from the injection site (below the 12th rip) and caudal from the injection site (cranial from the iliac crest) and in the skeletal muscle tissue of the contra lateral thigh of eight healthy volunteers. RESULTS: The mean exposure to ropivacaine measured as the area under the concentration-time curve was significantly higher at the two abdominal sites (240.9 ± 409.1  and 86.18 ± 133.50 µg h/mL, respectively) than in plasma (5.1 ± 1.0 µg h/mL) or in peripheral tissue (1.1 ± 1.2 µg h/mL). While the high mean concentrations of ropivacaine measured at the abdominal wall sites support the topical concept of the TAP block, the observed variability was striking. CONCLUSIONS: While the systemic pharmacokinetics was comparable between subjects, the local distribution of ropivacaine was highly variable after TAP block.

Caudal anaesthesia under sedation: a prospective analysis of 512 infants and children.

BACKGROUND: Caudal anaesthesia is a common procedure for infants and children undergoing subumbilical surgery, mostly performed in conjunction with general anaesthesia. Even if complications are rare, the risk of postoperative apnoea is significant, especially in infants born preterm or operated upon before 46 weeks of post-conceptual age. Caudal block in sedated, spontaneously breathing patients might be a safe alternative. METHODS: We investigated 512 infants and children. Premedication consisted of midazolam, sedation was induced with i.v. nalbuphine 0.1 mg kg(-1) and propofol 1 mg kg(-1), and maintained with propofol 5 mg kg(-1) h(-1) in children, if necessary. Caudal block was performed with ropivacaine 1 ml kg(-1) (0.2% or 0.35%). RESULTS: Data were obtained from 228 infants and 284 children. Median (IQR) age was 1.3 (0.2, 3.4) yr; median body weight was 10.0 (4.8, 15.3) kg. Two hundred and thirty-three (45.51%) were born preterm and 47 (9.18%) were operated upon before 46 weeks of post-conceptual age. Caudal block was successful in 98.05% and adverse events occurred in 7.03% patients. The incidence of adverse events was not higher in born preterm or operated upon before 46 weeks of post-conceptual age than in term born infants (P=0.35 and 0.35, respectively), or in infants vs children (P=0.61). There was no correlation between the incidence of adverse events and continuous sedation (P=0.07), coexisting diseases (P=0.11), or ASA classification (P=0.33). CONCLUSIONS: Caudal anaesthesia under sedation is associated with high success rates and a low incidence of adverse events, but requires careful and anticipatory perioperative management.

Minimal local anaesthetic volumes for sciatic nerve block: evaluation of ED 99 in volunteers.

BACKGROUND: This randomized, double-blinded volunteer study was designed to evaluate the ED(99) volume of local anaesthetic for sciatic nerve blocks using a step-up/step-down methodology. METHODS: A maximum of 20 volunteers were included to receive an ultrasound-guided sciatic nerve block with mepivacaine 1.5% and a starting volume of 0.2 ml mm(-2) cross-sectional nerve area. In cases of a complete sensory block, the volume was reduced by 0.02 ml mm(-2) cross-sectional nerve area until the first block failed. Thereafter, the volume of local anaesthetic was increased by 0.02 ml mm(-2) cross-sectional nerve area. After three cycles of successful/failed blocks, the ED(99) volume of local anaesthetic could be calculated by a probability function. The influence of the volumes of local anaesthetics on sensory onset times and duration of sensory block was evaluated by linear regression. RESULTS: The ED(99) volume of local anaesthetic for sciatic nerve block was calculated with 0.10 ml mm(-2) cross-sectional nerve area. The correlation between the volume of local anaesthetic and the sensory onset time was weak (r=0.14), whereas the correlation between the volume of local anaesthetic and the duration of sensory block was moderate (r=0.65). CONCLUSIONS: This is the first study where an ED(99) volume of local anaesthetic for sciatic nerve block has been evaluated. The resulting local anaesthetic volume of 0.10 ml mm(-2) cross-sectional nerve area seems to have no impact on sensory onset time, whereas the duration of sensory block is shorter.