Comparison of plasma compartment versus two methods for effect compartment--controlled target-controlled infusion for propofol.

BACKGROUND: Target-controlled infusion (TCI) systems can control the concentration in the plasma or at the site of drug effect. A TCI system that targets the effect site should be able to accurately predict the time course of drug effect. The authors tested this by comparing the performance of three control algorithms: plasmacontrol TCI versus two algorithms for effect-site control TCI. METHODS: One-hundred twenty healthy women patients received propofol via TCI for 12-min at a target concentration of 5.4 microg/ml. In all three groups, the plasma concentrations were computed using pharmacokinetics previously reported. In group I, the TCI device controlled the plasma concentration. In groups II and III, the TCI device controlled the effect-site concentration. In group II, the effect site was computed using a half-life for plasma effect-site equilibration (t1/2k(eo)) of 3.5 min. In group III, plasma effect-site equilibration rate constant (k(eo)) was computed to yield a time to peak effect of 1.6 min after bolus injection, yielding a t1/2keo of 34 s. the time course of propofol was measured using the bispectral index. Blood pressure, ventilation, and time of loss of consciousness were measured. RESULTS: The time course of propofol drug effect, as measured by the bispectral index, was best predicted in group III. Targeting the effect-site concentration shortened the time to loss of consciousness compared with the targeting plasma concentration without causing hypotension. The incidence of apnea was less in group III than in group II. CONCLUSION: Effect compartment-controlled TCI can be safely applied in clinical practice. A biophase model combining the Marsh kinetics and a time to peak effect of 1.6 min accurately predicted the time course of propofol drug effect.

The performance of 10 different methods for the estimation of sperm concentration.

OBJECTIVE: To evaluate the performance of different methods of sperm counting using latex beads and sperm suspension. DESIGN: A quality-control study. SETTING: University-based andrology laboratory. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Counting latex beads six times in two standard suspensions using 10 methods and counting spermatozoa with 4 methods. RESULT(S): When air-displacement pipettes were used, the disposable chambers Standard Count (Leja, Amsterdam, Holland), Cellvision (Anthos-ec, Heerhugowaard, The Netherlands), and Cell Vu (Fertility Technologies, Inc. Natick, MA) showed small variation and correct estimation of bead concentration. All the reusable chambers gave relatively large variability, with tendency to underestimate (improved Neubauer; Hawksley, Lancing, United Kingdom) or to overestimate the bead concentration. The use of plunger-displacement pipettes resulted in an overestimation of bead concentration in medium but not in seminal plasma. Counting the sperm suspension using plunger-displacement pipettes indicated that the Bürker hemocytometer overestimated concentration relative to that obtained by Cellvision and Makler Counting Chambers (Sefi Medical Instruments, Haifa, Israel) and that the improved Neubauer presented the lowest variability (7.1%). CONCLUSION(S): The improved Neubauer hemocytometer is the standard for sperm counting, though disposable chambers give reliable results as well. If beads are used to evaluate the accuracy of counting chambers, it is recommended to dilute them with seminal plasma.