British journal of anaesthesia
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Comparative Study
Differential B and C fibre block by an amide- and an ester-linked local anaesthetic.
The relative sensitivity of sympathetic preganglionic and postganglionic axons, B and C fibres, respectively, to two structurally dissimilar local anaesthetics was examined. The concentration of amethocaine (ester-linked tertiary amine) or prilocaine (amide-linked secondary amine) required to reduce the B fibre compound action potential by 50% was one-third of the concentration required to depress the C fibre potential to a similar extent. Both local anaesthetic agents also showed the action potential propagation through B fibres more than through C fibres. Similar results have been reported previously for lignocaine (amide-linked tertiary amine).
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A questionnaire was sent to all centres of cardiac surgery in the United Kingdom, enquiring into their current use of hypothermia. Moderate hypothermia without cardiopulmonary bypass and the Drew technique of profound hypothermia are becoming less popular, each technique being used in only two of the 30 centres which replied. ⋯ Although some centres use moderate hypothermia out of habit, the main benefits from its use are considered to be the protection afforded to the myocardium and a greater safety margin in the event of technical difficulties. Profound hypothermia, usually induced by means of the pump oxygenator, followed by circulatory arrest is becoming increasingly popular for the correction of complex congenital anomalies in infants.
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Seven patients with intracranial disorders were studied during recovery from anaesthesia with nitrous oxide and halothane. Arterial, intracranial, and central venous pressure, and arterial carbon dioxide tension were measured and compared with the patient's clinical state. No patient had evidence of increased brain volume when the dura was closed. ⋯ In the following minutes, until the patients were awake, the intracranial pressure decreased to normal or near normal values, with minimal change in PaCO2. In these seven patients in whom there were no signs of brain swelling, the skull was closed, the patients were allowed to resume spontaneous respiration, and anaesthesia was terminated without major changes in intracranial pressure or cerebral perfusion pressure. However, hyperventilation is advocated after operation in patients with marked brain swelling.
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In 10 patients receiving prolonged respirator treatment, respiratory deadspace was measured at 12, 18 and 24 b.p.m. and with two different minute volumes. The physiological deadspace (the sum of apparatus, anatomical and alveolar deadspaces) was derived using the Bohr equation, and the anatomical and alveolar deadspaces were measured by carbon dioxide analysis. Tracheal pressure was measured concurrently. ⋯ The VD/VT ratio did not vary with frequency or minute volume. A relationship between tracheal end inspiratory pressure and anatomical deadspace was found, with a correlation coefficient of 0.80. The slope of the regression line indicated a high airway compliance of approximately 10 ml/cm H2O.