British journal of anaesthesia
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Comparative Study
Measurement of cardiac output by transoesophageal Doppler echocardiography in anaesthetized horses: comparison with thermodilution.
In order to determine if transoesophageal Doppler echocardiography could be used to estimate cardiac output in anaesthetized horses, we have compared the technique with estimations of cardiac output by thermodilution in eight healthy adult thoroughbreds. Measurements of aortic blood flow velocity were made by high pulse repetition frequency (HPRF) and continuous wave (CW) Doppler echocardiography from a 3.5-MHz transoesophageal probe. Cardiac output was increased during the study by administration of dobutamine, providing a range of cardiac output measurements by thermodilution from 15.0 to 64.4 liter min-1. ⋯ There were significant differences in bias between both Doppler techniques and thermodilution for individual horses. As a result, for any individual horse, limits of agreement between the techniques were closer (HPRF = +/- 6.4 litre min-1, CW = +/- 7.6 litre min-1). We conclude that transoesophageal echocardiography provided an alternative, effective and non-invasive method for measurement of cardiac output in anaesthetized horses.
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Although subjects often report difficulty with swallowing shortly after receiving neuromuscular blocking agents, difficulty with swallowing during recovery from neuromuscular blocking agents appears to be infrequent. We have used electromyography to compare onset and recovery at the diaphragm and geniohyoid airway muscles after an intubating dose of mivacurium (0.2 mg kg-1) to determine if the geniohyoid muscles were particularly sensitive to neuromuscular blocking agents. Twelve adults undergoing elective surgery were anaesthetized with propofol and fentanyl and the trachea intubated without neuromuscular blocking agents. ⋯ Recordings were also made of the mechanical response of the adductor pollicis to supramaximal ulnar nerve stimulation. There was no difference in the rate of onset of block for geniohyoid muscles and the diaphragm, but recovery to 25% and 90% of the control response was shorter at the diaphragm (median 14.5 (95% confidence limits 12.9-15.3) min and 23.8 (21.7-26) min) than at the geniohyoid muscle (19.4 (15.6-20.1) min and 29.2 (26.3-31.4) min), respectively (P < 0.05). When the train-of-four ratio of the mechanical response of the thumb reached 70%, the diaphragm and geniohyoid muscles had recovered completely in all patients.
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We have studied the effects of volatile anaesthetics on lower oesophageal sphincter (LOS) tone in three groups of eight pigs allocated randomly to receive end-tidal concentrations of 0.5, 1.0 and 1.5 MAC of desflurane, isoflurane or halothane for 15 min. LOS and oesophageal barrier pressures (BrP = LOSP - gastric pressure) were measured using a manometric method. The decrease in BrP paralleled the decrease in LOS pressure and was significant at 0.5 MAC for isoflurane and at 1.0 MAC for halothane. ⋯ At 1.0 MAC the effect of isoflurane on BrP was significantly different from desflurane (P < 0.001) and halothane (P < 0.02) whereas the effect of desflurane on BrP was not significantly different from halothane. At 1.5 MAC the effect of isoflurane on BrP was significantly different from desflurane (P < 0.01) and halothane (P < 0.05) whereas the effect of desflurane on BrP was not significantly different from halothane. We conclude that desflurane maintained BrP and this may be clinically important in patients at high risk of regurgitation.
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Editorial Historical Article
Ether anaesthesia comes to London. December 1846.
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Randomized Controlled Trial Comparative Study Clinical Trial
Dose-response relationships for neostigmine antagonism of rocuronium-induced neuromuscular block in children and adults.
Dose-response relationships for the antagonism of intermediate-acting neuromuscular blocking agents have not been evaluated previously in children. We have examined the dose-response relationships for neostigmine antagonism of 90% rocuronium-induced neuromuscular block in children and adults, during nitrous oxide-1 MAC of isoflurane anaesthesia. We studied 40 children, aged 2-10 yr, and 50 adults, aged 18-60 yr; all received a single bolus dose of rocuronium 0.6 mg kg-1 and accelerometry was used to monitor neuromuscular transmission. ⋯ The effective doses of neostigmine required to achieve a TOF ratio of 80% (ED80) after 10 min in children and adults were, respectively, 7.10 (5.2-9.8) micrograms kg-1 and 56.56 (45.5-71.9) micrograms kg-1 (P < 0.001). There was no advantage in administering doses of neostigmine greater than 20 micrograms kg-1 to antagonize 90% rocuronium-induced neuromuscular block in children. In contrast, it appeared prudent to use neostigmine 50 micrograms kg-1 or more for adequate antagonism of a similar degree of block in adults.