Anaesthesia
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The pharmacokinetic and pharmacodynamic interactions between propofol and adjuvant agents have increasingly been recognised as clinically important and the improved knowledge of these interactions is being used to optimise the quality of intravenous anaesthesia. It is now known that propofol interferes with opioid metabolism, thereby increasing the plasma concentrations of the opioids, while opioids such as alfentanil increase propofol concentrations by reducing both the distribution and clearance of propofol. ⋯ From the pharmacodynamic interaction data, optimal target propofol-opioid concentrations and optimal infusion regimens have been developed that ensure adequate anaesthesia in 50% and 95% of patients with the most rapid recovery possible. These optimal target propofol concentrations and infusion regimens are affected by the opioid with which propofol is combined, as well as the duration of infusion.
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The availability of fast-acting intravenous drugs for anaesthesia has encouraged anaesthetists to gain a practical understanding of the pharmacodynamics and pharmacokinetics of these drugs to optimise their administration. 'Diprifusor' technology uses pharmacokinetic modelling to control the infusion rate of a pump, providing the anaesthetist with direct control of the blood concentration rather than indirect control by the infusion rate. The 'Diprifusor' electronics module is a dual microprocessor component that can be incorporated into an infusion pump to provide this mode of administration. This paper describes the module's infusion control system, prefilled syringe recognition system and the safety aspects addressed by the design.
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Randomized Controlled Trial Clinical Trial
Dorsal column function after epidural and spinal blockade: implications for the safety of walking following low-dose regional analgesia for labour.
Walking after regional blockade for labour using low-dose combinations of bupivacaine and fentanyl is possible due to the maintenance of lower limb motor power. In order to investigate concerns that dorsal column function, important in maintaining balance, is impaired after such techniques, clinical assessment of lower limb proprioception and vibration sense was evaluated in parturients after either low-dose epidural (n = 30) or spinal blockade (n = 30) for labour analgesia and compared with spinal anaesthesia (n = 30) for elective Caesarean section using a larger total dose of local anaesthetic. Of the patients receiving low-dose regional labour analgesia 7% (n = 4) had abnormal dorsal column function compared with 97% (n = 29) receiving spinal anaesthesia for Caesarean section (p < 0.001). ⋯ There were no significant differences between the low-dose groups with respect to sensory block, motor block or dorsal column function. Overall, 90% of patients receiving low-dose bupivacaine/fentanyl regional labour analgesia had both normal lower limb motor power and dorsal column function. Assessment of these parameters is recommended before allowing patients to walk after low-dose regional techniques for labour.
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This paper describes practical aspects relating to the safe use of target controlled infusion systems in anaesthesia. Consideration is given to the correct use of syringes and infusion lines for any target controlled infusion system. ⋯ Particular features of these systems are discussed. Finally, the practical consequences of possible misuse of infusion systems incorporating pharmacokinetic models are considered.
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Randomized Controlled Trial Clinical Trial
Influence of pre-anaesthetic medication on target propofol concentration using a 'Diprifusor' TCI system during ambulatory surgery.
The effects of pre-anaesthetic medication on target propofol concentration, induction dose, time to induction, and discomfort on infusion were studied in 45 female patients undergoing ambulatory gynaecological procedures using 'Diprifusor' target controlled infusion of propofol. The patients were randomly allocated to receive either no premedication (group 1) or premedication with diazepam alone (group 2) or in combination with alfentanil (group 3). ⋯ There were no significant between-group differences in discomfort on infusion or target concentration during maintenance. For short ambulatory procedures, the recommended initial target concentration of propofol is 4 micrograms.ml-1 in premedicated and 6 micrograms.ml-1 in unpremedicated patients.