Anaesthesia
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Comparative Study Clinical Trial Controlled Clinical Trial
Evaluation of the HemoCue for measuring intra-operative haemoglobin concentrations: a comparison with the Coulter Max-M.
We compared haemoglobin concentration values obtained using a portable haemoglobinometer, the HemoCue, in the operating theatre with the results obtained by the Coulter Max-M in the laboratory. Haemoglobin concentrations were measured on 52 arterial blood samples obtained from 13 patients during aortic surgery, in theatre with the HemoCue and again by the Coulter Max-M. Twenty routine samples from the laboratory were also analysed by both methods. ⋯ The coefficients of repeatability of the 20 samples analysed in duplicate on each device were 0.26 g.dl-1 and 0.33 g.dl-1, respectively. The coefficients of variance were 0.74% (HemoCue) and 0.93% (Coulter). With adequate training and monitoring, the HemoCue provides comparable haemoglobin results for near-patient testing in theatre.
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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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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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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.