Anesthesia and analgesia
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Anesthesia and analgesia · Jul 1998
Desflurane and the nonimmobilizer 1,2-dichlorohexafluorocyclobutane suppress learning by a mechanism independent of the level of unconditioned stimulation.
We previously demonstrated that anesthetics and non-immobilizers suppress learning and memory in rats. In the training portion of the test, rats received a light plus a footshock and learned to associate the two, as evidenced by subsequent potentiation of the response (jumping) to light plus a noise (fear-potentiated startle). However, anesthetics and nonimmobilizers also decreased the response of animals receiving footshocks during training, which suggests that the reduction in fear-potentiated startle might reflect analgesia, rather than an impairment of learning and memory. Furthermore, although we previously demonstrated that the nonimmobilizer 2,3-dichlorohexafluorocyclobutane (2N) could completely abolish learning, we did not demonstrate the minimal dose required. In the present study, we eliminated analgesia as a confounding factor by training rats breathing desflurane and 2N with footshock intensities that produced responses at least equal to those produced in control animals. Both desflurane and 2N suppressed learning at 0.2 times the minimum alveolar anesthetic concentration (MAC) or the MAC predicted from lipid solubility, despite the increased footshock intensity. This partial pressure of desflurane equals that previously shown to suppress learning at lower footshock intensities. We conclude that suppression of learning and memory by desflurane and 2N does not result from decreased sensitivity to the unconditioned stimulus (the footshock) and that the potency of 2N is consistent with its lipophilicity. ⋯ General anesthesia eliminates recall of intraoperative events, including pain. Using an animal model, we refuted the hypothesis that lack of recall results from the analgesia (i.e., the reduced response to painful stimuli produced by inhaled drugs) rather than from a direct effect on learning.
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Anesthesia and analgesia · Jul 1998
Medial canthus single-injection episcleral (sub-tenon anesthesia): computed tomography imaging.
Single-injection medial canthus periocular anesthesia is a promising regional anesthesia technique for ophthalmic surgery. The purpose of this computed tomography (CT) study was to confirm that this technique is an episcleral injection and to explain why it provides a good akinesia of the globe. Four fresh nonpreserved cadavers (eight eyes) were injected with fractioned various volumes of a contrast media using a previously described technique. For each injection and each eye, CT scans were performed in three planes of the space, and the site and spread of the injection was observed. We confirm that single-injection medial canthus periocular anesthesia is, in fact, an episcleral anesthesia, which explains the good sensory block of the globe. When larger volumes are injected, the contrast media spreads to the lids and extraocular muscle sheaths. We believe that this may explain why this technique provides good sensory and motor block of the globe and eyelids. This technique is a promising alternative to both retro- and peribulbar anesthesia. ⋯ We describe medial canthus single-injection periocular anesthesia by a computed tomography injection study in eight human cadaver eyes. It was confirmed to be an episcleral injection. Akinesia of the eyeball is provided by spreading of the local anesthetic solution from the episcleral space to the rectus muscle sheaths.