Prediction of levobupivacaine concentrations in neonates and infants following neuraxial rescue blocks

Second infant spinal anesthetic: Incidence, dose modification, and adverse events after initial failure

INTRODUCTION

Infant spinal anesthesia is an important technique in premature and ex-premature infants undergoing lower abdominal surgery. Previous studies of infant spinal anesthesia report high failure rates, but fail to adequately identify contributing factors. The aim of this study is to retrospectively review spinal anesthetics from a quaternary anesthetic centre to determine overall spinal failure rate, incidence of second spinal attempts and adverse events associated with a second spinal anesthetic.

METHODS

A retrospective review of infant spinal anesthetics performed between May 2016 and June 2023.

RESULTS

Five hundred and fifty-one infants (mean postmenstrual age 42.9 weeks and weight 3873 g) were included. The overall success rate on first attempt was 86.5% with a further 5.1% requiring a successful second spinal anesthetic after initial failure. Spinal anesthetic failure requiring conversion to general anesthesia occurred in 9.4% of cases The causes of failed spinal anesthetic were inability to access the subdural space (dry tap 4.2%), inadequate motor blockade (2.9%), and repeated bloody taps (2.2%). Spinal anesthetic failure was significantly increased in cases where the anesthetist was routinely performing less than 5 spinal anesthetics per year [OR 2.21 (95% CI 1.28, 3.83, p = .004)] but only weakly associated with years of pediatric anesthetic experience. Failure rates were 21.4% with styletted spinal needles and 9.2% for non styletted [OR 2.68 (95% CI 1.23-5.86, p = .012)]. The incidence of perioperative apnoea was 6.7% with the highest rate in infants in which failed spinal anesthesia required conversion to general anesthesia (25%). There were 28 cases where initial spinal anesthetic failed to produce adequate anesthesia and a repeat spinal anesthetic was performed. Repeat spinal anesthesia was successful in 92.8% of cases with awake caudal anesthesia successful in 7.2% of cases. In three cases high spinal blockade occurred, one after a single spinal and two after a repeat spinal. Both repeat spinal high block cases required intubation and brief resuscitation.

CONCLUSION

Infant spinal anesthesia is associated with high success rates if experienced anesthetists are present or performing the block. Repeat spinal anesthesia may be associated with an increased incidence of high spinal block. Greater awareness of the slow onset of high block should promote techniques aimed at minimizing cephalad spread of local anesthetic including slight head up positioning during surgery.

Pharmacokinetic Pharmacodynamic Modelling Contributions to Improve Paediatric Anaesthesia Practice

The use of pharmacokinetic-pharmacodynamic models has improved anaesthesia practice in children through a better understanding of dose-concentration-response relationships, developmental pharmacokinetic changes, quantification of drug interactions and insights into how covariates (e.g., age, size, organ dysfunction, pharmacogenomics) impact drug prescription. Simulation using information from these models has enabled the prediction and learning of beneficial and adverse effects and decision-making around clinical scenarios. Covariate information, including the use of allometric size scaling, age and consideration of fat mass, has reduced population parameter variability. The target concentration approach has rationalised dose calculation. Paediatric pharmacokinetic-pharmacodynamic insights have led to better drug delivery systems for total intravenous anaesthesia and an expectation about drug offset when delivery is stopped. Understanding concentration-dependent adverse effects have tempered dose regimens. Quantification of drug interactions has improved the understanding of the effects of drug combinations. Repurposed drugs (e.g., antiviral drugs used for COVID-19) within the community can have important effects on drugs used in paediatric anaesthesia, and the use of simulation educates about these drug vagaries.