Rocuronium administration in children during isoflurane anesthesia: neuromuscular effects

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.

META-ANALYSIS OF THE DIFFERENCES IN THE TIME TO ONSET OF ACTION BETWEEN ROCURONIUM AND VECURONIUM

1. The aim of the present study was to conduct a meta-analysis of the magnitude of differences in the onset of action (T(max)) between rocuronium and vecuronium. 2. A search was made in PubMed, EMBASE Drugs and Pharmacology, Cochrane Controlled Trials Register and Cochrane Database on Systematic Reviews. Studies comparing the T(max) at the adductor policies between rocuronium and vecuronium administered as an intravenous bolus were included in the study. Twenty-nine effect sizes obtained from 21 studies were included. 3. The result of the meta-analysis of differences was -57.9 s (95% confidence interval -71.4 to -44.3 s), favouring rocuronium over vecuronium. The smallest difference in T(max) between these neuromuscular-blocking agents was observed in children (-19.1 s). The difference in T(max) between rocuronium and vecuronium in female patients was -38.7 s. The difference in T(max) between rocuronium and vecuronium measured by electromyography was approximately 50% shorter than that determined by acceleromyography or mechanomyography. In a subanalysis between rocuronium 600 mg/kg versus vecuronium 100 mg/kg, the difference in T(max) between them was very similar to that obtained in the general meta-analysis. 4. According to subanalyses of patient age and sex, drug dose and neuromuscular monitoring systems, the T(max) of rocuronium was approximately 20-70 s faster than that of vecuronium.

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.

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.

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

BACKGROUND: Infants usually respond differently to a neuromuscular relaxant compared to children or adults. Isoflurane is commonly used as an anesthetic gas in infants. In an RCT design, we investigated whether a dose of mivacurium 250 &mgr;g/kg results in faster onset of action than 200 &mgr;g/kg in infants under isoflurane anesthesia. Spontaneous recovery times and cardiovascular response were also evaluated. METHODS: Twenty-four low surgical risk children, aged 6-24 months, undergoing an elective surgery and requiring tracheal intubation were selected. After anesthetic induction, patients randomly received an iv bolus dose of mivacurium 200 or 250 &mgr;g/kg. After maximal relaxation, the patient was intubated. Isoflurane was administered to maintain anesthetic level during the surgical procedure. Neuromuscular function was monitored by accelerometry (TOF-Guard) at the adductor pollicies. The first twitch (T) of the TOF and the T4/T1 were measured. The time-course of heart rate and systolic and diastolic blood pressure were analysed by transforming them into their respective areas under the curve. RESULTS: Mivacurium 250 &mgr;g/kg produced a maximal T block faster than 200 &mgr;g/kg, i.e. 2.4 +/- 1.1 vs. 3.5 +/- 1.4 min (p < 0.05). Spontaneous recovery times were similar in both groups. Heart rate was similar between doses while systolic and diastolic blood pressures were lower with the higher dose (p < 0.05). Flushing was observed in two cases, one in each group. CONCLUSIONS: The maximal effect of mivacurium 250 &mgr;g/kg, in infants under isoflurane anesthesia, was present one minute faster than 200 &mgr;g/kg. However, it produced a significant cardiovascular response.