Articles: anesthetics.
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Acta Anaesthesiol Scand · Apr 1983
Randomized Controlled Trial Clinical TrialPerivascular axillary block II: influence of injected volume of local anaesthetic on neural blockade.
Perivascular axillary blockade was performed on 150 patients with the aid of a catheter technique. Blockade failure due to injection outside the neurovascular sheath was found in 5.7% of the subject material. The patients were randomly allocated to three groups. ⋯ Sensory and motor blockade was tested 30 min after each injection. The following results were obtained: 1) Apart from the axillary, musculocutaneous and radial nerves, a high frequency of analgesia was found in all cutaneous areas (over 85%). 2) In the axillary area, improvements were found with increasing volume. 3) Analgesia in the musculocutaneous area occurred in 52% of the patients in group 1 (20 ml) and improved to 75% in group 2 (40 ml). However, no difference was found between group 2 and group 3 (80 ml). 4) Volume had no influence on analgesia in the radial area. 5) Motor blockade was intensified with decreasing volume, i.e. with an increase of concentration of local anaesthetic solution.
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This article reviews the actions of general anaesthetics on synapses in the mammalian central nervous system. It is shown that during general anaesthesia, anaesthetics act primarily on the chemical transmission process itself and do not affect the conduction of impulses in nerve axons or change the electrical excitability of neurones. ⋯ In addition to these effects on the neurosecretory process, anaesthetics directly affect the sensitivity of the postsynaptic receptors to transmitter substances, although the effects vary between anaesthetics and receptors. It is concluded that general anaesthesia results from a summation of a number of effects which together tend to depress the excitability of the CNS as a whole.
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Research on the benzodiazepines has shown that they have certain advantages over the opiates as premedicants. Diazepam, which produces good tranquilization, is well absorbed when given orally though absorption is influenced by other drugs given at the same time. Oral lorazepam leads to more prolonged sedation and amnesia but the final elimination is more rapid. ⋯ Ketamine is gradually finding its rightful place in anaesthesia but its use is becoming limited to anaesthesia in difficult circumstances. The future concomitant use of other drugs and separation of isomers of ketamine may again broaden its applications. The new water-soluble steroid minaxolone has its own disadvantages, and the water-soluble benzodiazepine midazolam is as unpredictable for induction of anaesthesia as diazepam.