Articles: anesthetics.
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Acta Anaesthesiol Scand · Jan 1978
Longitudinal spread of intraneurally injected local anesthetics. An experimental study of the initial neural distribution following intraneural injections.
Unexpected spinal anesthesia, occurring after peripheral nerve blocks close to the spine, may be caused by a centripetal spread of the local anesthetic along the injected nerve to the spinal cord. In order to analyze the pathway of such a spread, a radioactive local anesthetic mixed with a fluorescent dye was injected into difrerent compartments of the rabbit sciatic nerve, and the early distribution of these tracers was studied by scintillation counting and fluorescence microscopy. Epineurial (extrafascicular) injections were of low injection pressure (25-60 mmHg) (3.3-7.9 kPa) and limited spread, while endoneurial (intrafascicular) injections reached higher pressures (300-750 mmHg) (39.9-99.7 kPa) and caused a rapid spread over long distances within the fascicle. ⋯ However, 20% of endoneurial injections reached the spinal cord, where the injectate primarily spread in the thin subpial space. Our experimental findings suggest that intraneural injections of local anesthetics are responsible for the reported cases of unexpected spinal anesthesia due to inadvertent intrafascicular spread. Although intrafascicular injections are rarely made, we recommend that intraneural injections of local anesthetics or other solutions close to the spine should be avoided, as they may cause unexpected spinal anesthesia or lesion of the cord.
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Acta Anaesthesiol Scand · Jan 1978
The clinical character of local anesthetics: a function of frequency-dependent conduction block.
It is clinically recognized fact that some local anesthetics have a proclivity for inhibition of motor nerves, while others preferentially affect sensory and sympathetic fibers. On the basis that sensory fibers have a frequency threshold for transmission of nociceptive stimuli and that somatic motor fibers have no such frequency threshold, we hypothesized that this variation may be due to differences in the effect of local anesthetics on axonal refractory period. Frog sciatic nerves were partially blocked with lidocaine, bupivacaine, tetracaine and etidocaine, and then stimulated in trains of 17 pulses, at frequencies between 3 and 100 Hz. ⋯ At a comparable level of partial block (50% at 100 Hz), tetracaine and etidocaine showed only a 10% difference between 3 and 100 Hz, while with bupivacaine and lidocaine there was a 30% drop between these two frequencies. This excellent correlation between the laboratory and clinical phenomenon supports our hypothesis. Local anesthetics which have a minimal effect on the refractory period yield enhanced motor block; whereas local anesthetics with a large effect on the refractory period are relatively more potent blockers of sensory and sympathetic transmission.
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Topically applied anaesthetics are potentially dangerous, as frequent and continuous application may lead to anaesthetic-induced keratitis. Three patients with serious corneal lesions are described.
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Malignant hyperthermia is now recognized as a distinct entity in anesthetic practice and can be considered as a pharmacogenetic disease of obscure etiology occuring in man and pigs with a dominant inheritance. A close association with myopathy has been noted. Commonly used muscle relaxants or anesthetic drugs can act as triggering agents in genetically susceptible patients, who develop a real hypermetabolic state, characterized by a rapid rise in body temperature, muscular rigidity, tachycardia and tachypnoea, cyanosis and severe respiratory and metabolic acidosis, the lethality being about 60%. ⋯ A regime of treatment is suggested, based on current concepts of the pathogenesis. It consists in establishing effective and rapid cooling, reversal of tissue hypoxia and correction of respiratory and metabolic acidosis and hyperkalemia. Specific therapy with dantrolene sodium may prove to be an answer to this serious problem.