Propofol context-sensitive decrement times in children

A new view on old problems in paediatric anaesthesia: premedication, postoperative agitation and dosing

PURPOSE OF REVIEW

The aim of this review is to discuss recent developments in paediatric anaesthesia, which have evolved in an undulating fashion.

RECENT FINDINGS

The role and efficacy of pharmacological premedication is reevaluated. The anxiolytic and sedative properties of midazolam and α 2 -agonists have now been defined more precisely. Both classes of drugs have their unique profile, and there is no reason to condemn one or the other. Midazolam is an excellent anxiolytic, whereas dexmedetomidine is superior in the postoperative period and for sedation during diagnostic imaging.A total intravenous technique with propofol is often considered to be the standard for the prevention of emergence agitation; but alternatives do exist, such as a co-medication with dexmedetomidine or opioids. In clinical reality, a multimodal approach may often be advisable.The theoretical basis for propofol dosing has recently been adapted. In contrast to previous beliefs, the context-sensitive half-life of propofol seems to be quite short beyond the first year of life.

SUMMARY

Midazolam and dexmedetomidine are not interchangeable; each compound has its pros and cons. As an anxiolytic drug, midazolam indisputably deserves its place, whereas dexmedetomidine is a better sedative and particularly beneficial in the postoperative period. New data will allow more precise age-adapted dosing of propofol.

Interactions of the protease inhibitor, ritonavir, with common anesthesia drugs

The protease inhibitor, ritonavir, is a strong inhibitor of CYP 3A. The drug is used for management of the human immunovirus and is currently part of an oral antiviral drug combination (nirmatrelvir-ritonavir) for the early treatment of SARS-2 COVID-19-positive patients aged 12 years and over who have recognized comorbidities. The CYP 3A enzyme system is responsible for clearance of numerous drugs used in anesthesia (e.g., alfentanil, fentanyl, methadone, rocuronium, bupivacaine, midazolam, ketamine). Ritonavir will have an impact on drug clearances that are dependent on ritonavir concentration, anesthesia drug intrinsic hepatic clearance, metabolic pathways, concentration-response relationship, and route of administration. Drugs with a steep concentration-response relationship (ketamine, midazolam, rocuronium) are mostly affected because small changes in concentration have major changes in effect response. An increase in midazolam concentration is observed after oral administration because CYP 3A in the gastrointestinal wall is inhibited, causing a large increase in relative bioavailability. Fentanyl infusion may be associated with a modest increase in plasma concentration and effect, but the large between subject variability of pharmacokinetic and pharmacodynamic concentration changes suggests it will have little impact on an individual patient, especially when used with adverse effect monitoring. It has been proposed that drugs that have no or only a small metabolic pathway involving the CYP 3A enzyme be used during anesthesia, for example, propofol, atracurium, remifentanil, and the volatile agents. That anesthesia approach denies children of drugs with considerable value. It is better that the inhibitory changes in clearance of these drugs are understood so that rational drug choices can be made to tailor drug use to the individual patient. Altered drug dose, anticipation of duration of effect, timing of administration, use of reversal agents and perioperative monitoring would better behoove children undergoing anesthesia.

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.