STUDY OBJECTIVE: To compare vecuronium requirements using repetitive injections and a model-based, closed-loop, feedback-controlled infusion during isoflurane anesthesia. DESIGN: Randomized open study. SETTING: Departments of Anesthesiology and Ear, Nose, and Throat Surgery at a university hospital. PATIENTS: Twenty-two patients of ASA physical status I or II undergoing elective otolaryngological surgery requiring general anesthesia. INTERVENTIONS: Vecuronium was used for muscle relaxation. The desired level of neuromuscular transmission was set to 10% of control. All patients received vecuronium 0.08 mg/kg for intubation. Thereafter, vecuronium was injected repetitively in 11 patients (Group 1) whenever spontaneous recovery had reached the 10% level. In the other group of 11 patients (Group 2), relaxation was maintained by an adaptive closed-loop feedback system, which was based on a pharmacokinetic-dynamic model. MEASUREMENTS AND MAIN RESULTS: Neuromuscular transmission was quantified by the evoked electromyogram of the hypothenar muscles. In Group 1, the first repetition of 0.02 mg/kg had to be administered after 27.0 +/- 5.5 minutes, followed by repetitions of the same dose every 16.3 +/- 3.0 minutes. The induced neuromuscular block ranged from 83% to 100%. The mean vecuronium demand was 0.123 +/- 0.018 mg/kg/h. In Group 2, stable relaxation of 90% +/- 2% was achieved within 19.2 +/- 7.5 minutes after a period of damped oscillations. The mean offset from the target value of 90% blockade was 0.65% +/- 0.32%. The average vecuronium requirement was 0.056 +/- 0.021 mg/kg/h during steady state. The difference between the groups in muscle relaxant demand was statistically significant. CONCLUSIONS: The model-based adaptive feedback system proved to be useful in maintaining a stable degree of paralysis, adjusting relaxant input to individual demand, and minimizing drug requirement, as compared with repetitive injections.

Adolescent↗

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Pharmacokinetic evaluation of a new maintenance solution for severely injured patients.

Nine severely injured patients (SIP) and 9 healthy controls received 20 min iv infusions of Aminoplasmal-LS-10 (2.15 ml/kg body wt containing 0.215 g amino acids). Employing the values of the plasma amino acid (AA) concentrations 3, 7, 15, 30, 45, 70, and 150 min after the end of the infusion, we calculated the elimination half-life (t 1/2), the elimination constant (k2), the total clearance (Cltot), and the transfer of the individual AA. The AA showed t 1/2 between 6 (Glu) and 23 (Thr) min. Comparing the metabolic kinetics of healthy controls and SIP, there were no statistical differences in t 1/2 or in k2. In the SIP, nearly all plasma AA showed increased transfer and Cltot, significantly for Thr (p < 0.05), Pro, Gly, Ala, Arg (p < 0.02), Glu (p < 0.01), and Met (p < 0.005). In contrast, the Cltot for Phe and Tyr were decreased. Except for Phe, Tyr, Met (enhanced values) and Arg (no change), the fasting values of AA concentrations in the SIP were diminished compared to those in the healthy controls. Based on the measured transfer, we have developed a new maintenance solution adapted to SIP. Compared with Aminoplasmal, it is necessary to apply AA concentrations which are increased in Lys, His, Phe, Tyr, Val, Ala, and Ser, and reduced in Arg, Pro, Leu, Ile, and Gly.

Amino Acids↗