Anesthesiology
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Spinal cholinergic receptors have been shown to have a potent antinociceptive action, an effect that can be mimicked by spinal cholinesterase inhibitors. We (1) characterized the cholinergic receptor system through which intrathecally applied cholinesterase inhibitors produce their antinociceptive effect and (2) examined their interaction with spinal mu opioid and alpha 2-adrenergic receptors. ⋯ These data indicate that analgesia after spinal cholinesterase inhibition is mediated through muscarinic, but not nicotinic cholinergic, opioid, or alpha 2-adrenergic receptor systems, and that these spinal effects of cholinesterase inhibition interact synergistically with the antinociceptive effects of intrathecal mu and alpha 2 agonists.
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Continuation of intrathecal anesthesia into the postoperative period has been limited by important safety concerns. Principal among these has been the assumption that extended intrathecal therapy leads to spinal (epidural and intrathecal) space infections. To address the role of extended intrathecal catheter therapy as a cause of infections, we cultured all intrathecal catheters used to provide postoperative analgesia. ⋯ Application of semiquantitative culture methods assisted in explaining the results seen in group 2 as secondary to contamination of the catheter that occurred on removal. Higher numbers of bacteria (group 3) may define a population at increased risk for infectious complications. The results of this study do not absolutely resolve the issue of infectious risk associated with postoperative intrathecal catheter use, nor do they define a safe period beyond which the risk of continued catheter use would be unacceptable. However, it appears that limited periods of use (96 h or less) is not associated with either frequent local or spinal infections. Semiquantitative culture methods may help identify individuals (with catheter cultures yielding more than ten colonies) at increased risk for infectious complications and in need of closer observation.
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Local anesthetics are known to inhibit the voltage-gated sodium current (INa) of the nerve membrane, but it has not been fully studied whether anesthetic concentrations of local anesthetics depress the voltage-gated calcium current (ICa) of mammalian neurons. The effects of local anesthetics on ICa evoked in cultured rat dorsal root ganglion cells were studied. ⋯ These results suggest that both HVA-ICa and LVA-ICa are depressed by tetracaine used at the concentrations required for spinal anesthesia and that the L-type Ca2+ channel among Ca2+ channel subtypes is the most susceptible to tetracaine. A good correlation between local anesthetic potencies to inhibit HVA-ICa and their anesthetic potencies implies that the inhibition of calcium influx through voltage-gated channels may contribute to spinal anesthetic mechanisms.
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It is known that peripheral nerve injury induces time-dependent changes in dorsal horn function. The current study investigated the time dependency of the effects of intrathecal morphine and MK-801, an N-methyl-D-aspartate antagonist, on the thermal hyperesthesia evoked by unilateral constriction injury to the sciatic nerve in the rat. ⋯ These data indicate that (1) an N-methyl-D-aspartate receptor-mediated spinal facilitation may be the common mechanism maintaining the thermal hyperesthesia evoked by the constriction injury, and (2) the effects of intrathecal morphine on this thermal hyperesthesia are time-dependent.
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Letter Case Reports
Severe air embolism caused by a pulmonary artery introducer sheath.