Effect of mivacurium 200 and 250 &mgr;g/kg in infants during isoflurane anesthesia: a randomized controlled trial [ISRCTN07742712]

Spontaneous recovery from neuromuscular block after a single dose of a muscle relaxant in pediatric patients: A systematic review using a network meta-analytic and meta-regression approach

BACKGROUND

Age-related differences in the pharmacokinetics and pharmacodynamics of neuromuscular blocking agents (NMBAs) and the short duration of many surgical procedures put pediatric patients at risk of postoperative residual curarization (PORC). To date, the duration of neuromuscular blocking agent effect in children has not been analyzed in a quantitative review. The current meta-analysis aimed to compare spontaneous recovery following administration of various types and doses of neuromuscular blocking agents and to quantify the effect of prognostic variables associated with the recovery time in pediatric patients.

METHOD

We searched for randomized controlled trials (RCTs) and controlled clinical trials (CCTs) that compared the time to 25% T1 (t25), from 25% to 75% T1 (RI25-75), and to ≥90% train-of-four (tTOF90) neuromuscular recovery between common neuromuscular blocking agent treatments administered as a single bolus to healthy pediatric participants. We compared spontaneous t25, RI25-75, and tTOF90 between (1) neuromuscular blocking agent treatments and (2) age groups receiving a given neuromuscular blocking agent intervention and anesthesia technique. Bayesian random-effects network and pairwise meta-analyses along with meta-regression were used to evaluate the results.

RESULTS

We used data from 71 randomized controlled trials/controlled clinical trials including 4319 participants. Network meta-analysis allowed for the juxtaposition and ranking of spontaneous t25, RI25-75, and tTOF90 following common neuromuscular blocking agent interventions. For all neuromuscular blocking agents a log-linear relationship between dose and duration of action was found. With the neuromuscular blocking agent treatments studied, the average tTOF90 (mean[CrI95]) in children (>2-11 y) was 41.96 [14.35, 69.50] and 17.06 [5.99, 28.30] min shorter than in neonates (<28 d) and infants (28 d-12 M), respectively. We found a negative log-linear correlation between age and duration of neuromuscular blocking agent effect. The difference in the tTOF90 (mean[CrI95]) between children and other age groups increased by 21.66 [8.82, 34.53] min with the use of aminosteroid neuromuscular blocking agents and by 24.73 [7.92, 41.43] min with the addition of sevoflurane/isoflurane for anesthesia maintenance.

CONCLUSIONS

The times to neuromuscular recovery are highly variable. These can decrease significantly with age and are prolonged when volatile anesthetics are administered. This variability, combined with the short duration of many pediatric surgical procedures, makes quantitative neuromuscular monitoring mandatory even after a single dose of neuromuscular blocking agent.

Mathematical analysis of a pharmacodynamic model without plasma concentrations to extend its applicability

Using a mathematical approach, we analyzed the behavior of the PD model originally described by Bragg et al. The effect was dose-dependent modified until a maximum value (E(max)) was reached. Further increments in dose prolonged the E(max), but the recovery phase did not increase beyond a calculable asymptope. In the absence of plasma concentrations, it was impossible to distinguish the rate of plasma equilibration with the effect compartment (k(e0)) from the rate of drug elimination (k(e1)). Variations on the sigmoidicity affected both the onset and offset of drug effect. Sigmoidicity and the slowest rate constant had identical effects on the spontaneous reversion of the effect, as judged by the recovery index. The IR(50), the index of potency, merely shifted the dose-response relationship to the left or right. Changes in IR(50) were compensated for by making the same proportional changes in dose.

Preferences of Mexican anesthesiologists for vecuronium, rocuronium, or other neuromuscular blocking agents: a survey

BACKGROUND: Several neuromuscular blocking (NMB) agents are available for clinical use in anesthesia. The present study was performed in order to identify preferences and behaviors of anesthesiologists for using vecuronium, rocuronium or other NMB agents in their clinical practice. MATERIAL AND METHODS: The cross-sectional survey was applied at the Updated Course of the Colegio Mexicano de Anestesiología performed last year. Of 989, 282 (28.5%) surveys were returned. RESULTS: Most anesthesiologists were working at both public and private hospitals, performed anesthetic procedures for hospitalized and ambulatory patients, and anesthetized children as well as adults. Respondents did not consider mechanomyography as the gold standard method for neuromuscular monitoring. The T25 was not recognized as a pharmacodynamic parameter that represents the clinical duration of the neuromuscular block. Most answered that vecuronium induces less histamine release than rocuronium, had never used any neuromuscular monitor, did not know the cost of vecuronium and rocuronium, and preferred rocuronium in multiple-sampling vials and vecuronium in either a vial for single or multiple sampling. Rocuronium was preferred for emergency surgery in patients with full stomach only. Almost all of anesthesiologists that conserve the unused drug did it without refrigeration and more than 30% conserve the unused drug in one syringe for further use. CONCLUSION: Vecuronium was preferred for most clinical situations, and the decision for this choice was not based on costs. Storage of unused drugs without refrigeration in a single syringe for purpose of future use in several patients represented a dangerous common practice.

Population pharmacodynamic modeling without plasma concentrations of rocuronium in children

Using the pharmacodynamic model without plasma concentrations described by Bragg et al, an individual approach resulted in highly variable parameters for rocuronium. Using a population approach of the model, the time course of the effect of an IV bolus dose of 400, 600, and 800 microg/kg of rocuronium was studied. Response was measured by accelerometry (TOF-Guard) in 45 low-risk surgical children, ages 2 to 14 years, who were receiving general anesthesia with isoflurane. Using a Bayesian approach and the software P-PHARM, response (the first twitch of the TOF) was modeled. The apparent rate constant of elimination, the rate constant for equilibrium between plasma and the effect compartment, the sigmoidicity factor of the relationship between drug concentration in the effect compartment and the effect, and the infusion rate that produces 50% of the effect at steady state were obtained. Population and individual post hoc parameters were similar among groups and variability was reduced.