British journal of anaesthesia
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We have investigated the relationship between the auditory evoked response (AER) and simple tests of conscious awareness at four end-expiratory concentrations (0.0, 0.1, 0.2 and 0.4 MAC) of isoflurane in oxygen in each of eight anaesthetist volunteers, in random order, at least 1 week apart. The early cortical AER was recorded from electrodes at the vertex and inion. Amplitudes of the waves Pa, Nb and Pc and latencies of the waves Na, Pa, Nb, Pb and Nc were measured. ⋯ Amplitudes were greatest and the latencies shortest when there was full response to command. (Nb latency increased from 47.5 to 54.5 ms between partial and no response.) The close correlation between the effects of concentration and level of response, and between concentration and the AER implied that it was difficult to demonstrate those changes in the AER which specifically relate to changes in response. At 0.2 MAC, however, which was the concentration at which all subjects showed some deficit, the response to a shock word was distinguished clearly by Nb latency. In eight of 24 possible comparisons (eight AER variables and three types of psychological test) the AER fitted the response more closely than concentration.
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The thrombelastograph (TEG) and bleeding time were performed before and 6 h after a single oral dose of aspirin 600 mg in a group of eight healthy volunteers and 12 pregnant patients. Measured TEG variables (r, k, r+k times and maximum amplitude) were unaltered after aspirin although there was a significant prolongation of the bleeding time in both groups. Although the TEG appeared not to detect aspirin-induced changes in platelet function, the TEG measures all phases of coagulation and the unaltered TEG after aspirin suggested a functioning coagulation system.
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Randomized Controlled Trial Clinical Trial
Learning during general anaesthesia: implicit recall after methohexitone or propofol infusion.
Forty-four patients undergoing coronary artery surgery were allocated randomly to receive an infusion of propofol or methohexitone as a hypnotic supplement to a fentanyl-based anaesthetic technique. A taped message was played to the patients, consisting of 10 words associated with prompt sentences and a suggestion for a specific postoperative behavioural response. Twenty patients (10 propofol and 10 methohexitone) (perioperative group) were exposed to the taped message during surgery and in the immediate postoperative period and the other 24 patients (postoperative group) were exposed to the tape only in the postoperative period, after return to the intensive care unit (ICU). ⋯ The patients who were played the tape whilst receiving identical infusion regimens for sedation in the ICU did not demonstrate implicit recall of the word associations in either the propofol or the methohexitone groups. There was no evidence of a response to the specific behavioural suggestion during the postoperative interview. The results confirm that auditory perception can occur during clinically adequate anaesthesia, and that suppression of auditory awareness or learning is a function of both the pharmacological degree of sedation and the degree of surgical stimulation.
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Randomized Controlled Trial Clinical Trial
The laryngeal mask airway for intraocular surgery: effects on intraocular pressure and stress responses.
Tracheal intubation, performed routinely during general anaesthesia in patients undergoing intraocular surgery, may have adverse effects on cardiovascular function and intraocular pressure. This study assessed the suitability of the laryngeal mask airway (LMA) as a substitute for tracheal intubation. ⋯ Mean (SEM) rate-pressure product was significantly smaller in the LMA group compared with the TT group after both insertion (8276 (730) vs 13307 (1348), P < 0.01) and removal (10152 (595) vs 14137 (1044), P < 0.01) of the airway device. The change in intraocular pressure was significantly less in the LMA group at all time points after airway instrumentation than that in the TT group, with the greatest difference after extubation (-2.3 (2.4) mm Hg vs 14.5 (3.4) mm Hg, P < 0.01).