British journal of anaesthesia
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Randomized Controlled Trial Clinical Trial
Effect of lignocaine and pH on propofol-induced pain.
Propofol has the disadvantage of pain on injection. A higher partition of propofol in the aqueous phase of the preparation causes a higher incidence of pain on injection while addition of 1% lignocaine to propofol reduces pain. The low concentration of this local anaesthetic and the rapid pain relief observed indicates that mechanisms other than local anaesthesia are involved, that is change in pH. ⋯ The concentration of propofol in the aqueous phase was lower when 1% Diprivan was mixed with 1% lignocaine (0.376 g litre-1) or HCl (0.392 g litre-1) compared with 1% Diprivan and saline (0.476 g litre-1) mixed in the same proportion. Thus pH changes may modify propofol-induced pain on injection by a mechanism different from the effect of the local anaesthetic on the vascular endothelium. Our findings may explain why lignocaine mixed with propofol causes less pain than injection of lignocaine followed by propofol.
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The auditory middle latency response (AMLR) and the 40-Hz auditory steady-state response (40-Hz ASSR) are evoked potentials which possibly arise from the same generators in the primary auditory cortex. Both responses are attenuated by most general anaesthetics. Ketamine, however, has been reported to have no effect on the AMLR. ⋯ The 40-Hz ASSR and EEG revealed no consistent differences between conscious and unconscious patients. No relationship could be demonstrated between the increase in amplitude of the 40-Hz ASSR or of relative theta power (the hallmark of ketamine effect) and loss of responsiveness to commands. We conclude that ketamine, unlike other anaesthetics, increases the amplitude of the 40-Hz ASSR.
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Randomized Controlled Trial Comparative Study Clinical Trial
Central nervous and cardiovascular effects of i.v. infusions of ropivacaine, bupivacaine and placebo in volunteers.
We have compared the incidence of CNS symptoms and changes in echocardiography and electrophysiology during i.v. infusions of ropivacaine, bupivacaine and placebo. Acute tolerance of i.v. infusion of 10 mg min-1 was studied in a crossover, randomized, double-blind study in 12 volunteers previously acquainted with the CNS effects of lignocaine. The maximum tolerated dose for CNS symptoms was higher after ropivacaine in nine of 12 subjects and higher after bupivacaine in three subjects. ⋯ A threshold for CNS toxicity was apparent at a mean free plasma concentration of approximately 0.6 mg litre-1 for ropivacaine and 0.3 mg litre-1 for bupivacaine. Bupivacaine increased QRS width during sinus rhythm compared with placebo (P < 0.001) and ropivacaine (P < 0.01). Bupivacaine reduced both left ventricular systolic and diastolic function compared with placebo (P < 0.05 and P < 0.01, respectively), while ropivacaine reduced only systolic function (P < 0.01).
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Clinical Trial Controlled Clinical Trial
Extradural pain relief in labour: bupivacaine sparing by extradural fentanyl is dose dependent.
The minimum local analgesic concentration (MLAC) of bupivacaine in labour is defined as the effective concentration in 50% of subjects (EC50). We have used the technique of double-blinded sequential allocation to quantify the bupivacaine sparing effect of the addition of four different doses of extradural fentanyl in 223 labouring women. There were five groups: (1) plain bupivacaine (control); (2) bupivacaine with fentanyl 1 microgram ml-1; (3) bupivacaine with fentanyl 2 micrograms ml-1; (4) bupivacaine with fentanyl 3 micrograms ml-1; and (5) bupivacaine with fentanyl 4 micrograms ml-1. ⋯ We observed a reduction in MLAC of 18%, 31% (P = 0.03%), 55% (P < 0.0001) and 72% (P < 0.0001) with fentanyl 1, 2, 3 and 4 micrograms ml-1, respectively, demonstrating a significant negative linear trend (P < 0.0001) with increasing fentanyl dose. The incidence of pruritus was increased significantly with fentanyl 4 micrograms ml-1 (P = 0.0015). Because of this, fentanyl 3 micrograms ml-1 may be the optimal dose when the aim is bupivacaine sparing extradural analgesia during labour.
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We have compared the responses of four groups of anaesthetists, with different durations of clinical experience, to nine different simulated emergencies. Five anaesthetists in each group completed each of the nine simulated emergencies. ⋯ However, all groups made serious errors in both diagnosis and treatment, and accepted treatment guidelines were not followed. We have shown that a simple, inexpensive simulator can be used to evaluate the performance of anaesthetists of different durations of clinical experience.