British journal of anaesthesia
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Randomized Controlled Trial Clinical Trial
Factors affecting assessment of cerebral autoregulation using the transient hyperaemic response test.
The transient hyperaemic response in the middle cerebral artery blood flow velocity on the release of brief compression of the ipsilateral common carotid artery has been validated as an indicator of cerebral autoregulation. We evaluated, in three stages, the effect of experimental factors such as duration of compression of the common carotid artery and magnitude of the decrease in blood flow velocity during common carotid artery compression on the transient hyperaemic response. In stage 1, 13 healthy volunteers underwent six transient hyperaemic response tests each; two tests each for either 3, 6 or 10 s duration of compression of the common carotid artery. ⋯ We conclude that experimental factors such as duration of common carotid artery compression and magnitude of the decrease in blood flow velocity during common carotid artery compression can significantly influence the transient hyperaemic response. These factors should be controlled if the transient hyperaemic response test is used for a comparison between repeated measurements. A compression time of 10 s and a compression ratio of 40% or more, allow maximum expression of the hyperaemic response in healthy volunteers.
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The pharmacokinetic models proposed for atracurium or cisatracurium are based on the assumption that spontaneous degradation via Hofmann elimination proceeds in vivo at the same rate as measured in vitro at pH 7.4 and 37 degrees C. As different degradation rates have been reported for all 10 stereoisomers of atracurium measured together, for each of its three isomeric groups, and for the single isomer cisatracurium, we studied if the rate is dependent on factors other than pH and temperature. In vitro degradation of atracurium and cisatracurium was studied at 37 degrees C and pH 7.4 in nine incubating solutions containing one of three buffer systems (phosphate, HEPES or Tris) and additives (sodium chloride, potassium sulphate or glucose). ⋯ At the same total buffer concentration (50 mmol litre-1), degradation was fastest in the phosphate, intermediate in the HEPES and slowest in the Tris buffer. Degradation rates of cisatracurium in sodium phosphate 50 mmol litre-1 and Sörensen (Na-K phosphate) buffer 66.7 mmol litre-1 were similar to those of atracurium. We conclude that, at constant pH and temperature, the degradation rate of atracurium was dependent on the total concentration of the base in the incubating solution.
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Clinical Trial
Patient-maintained remifentanil target-controlled infusion for the transition to early postoperative analgesia.
We studied 30 male patients in the early postoperative period to assess the efficacy, safety and feasibility of a patient-demand, target-controlled infusion (TCI) of remifentanil. All patients received the same TCI-based propofol-remifentanil anaesthetic for elective orthopaedic surgery. At the end of surgery, infusion of remifentanil was reduced progressively until patients were breathing spontaneously. ⋯ Nausea occurred in 26.6% of patients and 10% vomited. The majority of patients were only slightly sedated. These results imply an effective tool without respiratory side effects in the early postoperative period after anaesthesia using remifentanil as the analgesic component.
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We report changes in arterial blood-gas tensions for up to 5 min of apnoeic oxygenation in 26 anaesthetized paediatric patients (21 children, five infants). Changes in oxygen and carbon dioxide tension were greatest in the first minute of apnoeic oxygenation. In subsequent minutes, rates of change in gas tension were approximately constant. ⋯ The small number of infants studied showed rapid decreases in oxygen tension which if sustained would be expected to limit the safe duration of apnoeic oxygenation, unlike adults where apnoeic oxygenation is limited by hypercapnia. Extrapolation of our results suggests that when preoxygenation has been successful, apnoeic oxygenation could continue safely in children for at least 10 min. Infants may become hypoxic after only 2 min.
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Based on volume-flow relationships, CNS agents that are highly lipid soluble (log octanol-water partition coefficient > 2) are expected to have equilibration half-times (T1/2 kE0) that are proportional to brain solubility. Propofol, the most lipophilic anaesthetic in clinical use, has T1/2 kE0 values of 1.7 and 2.9 min in rats and humans, respectively, compared with an expected value of at least 8 min. ⋯ Brain:plasma and brain:blood partition coefficients were 8.2 (SD 1.6) and 3.0 (0.5), respectively. T1/2 kE0 predictions based on brain: blood partitioning in rats are more in agreement with the observed equilibration half-time, suggesting that drug bound to the formed elements of blood participates in the uptake and transfer of propofol to its effect site.