Anaesthesia
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Infusion pumps incorporating 'Diprifusor' for the administration of propofol by target controlled infusion are now commercially available and are becoming more widely used. This paper considers possible future applications of target controlled infusion and summarises results obtained using prototype systems as a component of other control techniques and with other drugs. These include studies with patient-controlled systems for the administration of analgesia or sedation and a closed loop control system for the administration of propofol. Among currently available analgesic drugs, alfentanil and remifentanil are considered to be the most suitable for administration by target controlled infusion, but commercial systems for these agents are not yet available.
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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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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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The pharmacokinetic profile of propofol is an advantage in neurosurgery, where the rapid return of cognitive function is essential for an early postoperative assessment of neurological status. Administration of propofol by 'Diprifusor' target controlled infusion allows induction of anaesthesia in neurosurgical patients without significant reduction of mean arterial pressure or occurrence of apnoeic episodes. This short paper describes our experience of 'Diprifusor' target controlled infusion for neuroanaesthesia in a series of 20 patients undergoing craniotomy for excision of epileptic foci. The results have been compared with ten similar operations where propofol infusion was controlled manually.
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Review Case Reports
Recurrent respiratory depression after total intravenous anaesthesia with propofol and alfentanil.
Since first commented upon by Lamarche in 1984, several cases of recurrent respiratory arrest after alfentanil infusions have been reported. In all these cases the alfentanil infusions have been used to supplement conventional anaesthetic techniques with nitrous oxide and/or inhalational agents and in most cases rather high total alfentanil doses have been administered. We have seen two cases of severe recurrent respiratory depression in healthy patients after relatively minor procedures performed under total intravenous anaesthesia with propofol-alfentanil infusions, air-oxygen ventilation and muscle relaxation, where the alfentanil doses administered were quite small. These cases are presented in detail and compared within a tabulated presentation with the earlier published cases of alfentanil-related recurrent respiratory depression.