Anesthesia and analgesia
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Anesthesia and analgesia · Dec 1998
Blockade of the sciatic nerve in the popliteal fossa: a system for standardization in children.
The sciatic nerve can be blocked at different levels, providing excellent surgical and postoperative anesthesia and analgesia. We report a series of 50 blocks performed via the popliteal fossa in children. Localization of either the tibial or peroneal nerve was facilitated by a nerve stimulator. The local anesthetic solution was injected at the point where nerve stimulation was achieved with 0.4 mA at an impulse width of 1.0 ms. The depth of insertion of the stimulation cannula correlated with the age, weight, and height of the patients. The best predictor for depth of insertion was the patient's weight. The minimal depth of insertion was 13 mm. No failure of blockade was seen in this case series. Blockade of the sciatic nerve can easily be performed in the popliteal fossa even in small children. ⋯ Blockade of the sciatic nerve can easily be performed in the popliteal fossa even in small children. The depth of insertion of the stimulation cannula can best be estimated according to the weight of the patient. The minimal depth required was 13 mm.
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Anesthesia and analgesia · Dec 1998
The role of the N-methyl-D-aspartic acid receptor in the relaxant effect of ketamine on tracheal smooth muscle.
Ketamine and magnesium (Mg2+), well known bronchodilators, have been used to treat patients with status asthmaticus. Both can block the N-methyl-D-aspartic acid (NMDA) receptor. NMDA receptors exist in the airway, and their activation seems to be linked to the release actions of sensory neuropeptides resulting in increased airway tone. We sought to determine whether ketamine relaxes the guinea pig trachea contracted by histamine by blocking the NMDA receptor. Female guinea pigs (250-400 g) were killed with an overdose of pentobarbital. The trachea was removed and cut spirally into strips 3 mm wide and 15 mm long. The strips were mounted in a 10-mL organ bath filled with Tyrode's solution bubbled through with 95% O2/5% CO2 at 37 degrees C. Strip contractions were measured isometrically with a force displacement transducer. We then studied the effect of NMDA receptor antagonists on histamine-induced tracheal contraction. In this protocol, we examined the effect of ketamine, Mg2+, zinc (Zn2+), or MK-801 (a noncompetitive NMDA receptor blocker) on strips contracted by 10(-5) M histamine. After full contraction was attained, ketamine (0.5-1.5 mM), MgSO4 (2-8 mM), ZnCl2(0.2-0.8 mM), or MK-801 (1.5-6 x 10(-5) M) was added, and the strip tension was measured again. We also studied the effect of NMDA on the relaxation by ketamine. After full contraction by 10(-5) M histamine, 0.5-1.5 mM KET was added alone or in combination with 0.1 mM NMDA, and the strip tension was measured again. Finally, we measured the effect of MK-801 on the relaxant effect of ketamine. After full contraction by 10(-5) M histamine, 0.5-2 mM ketamine was added alone or in combination with 0.75 or 1.5 x 10(-5) M MK-801, and the strip tension was measured again. All NMDA receptor antagonists tested reversed the tracheal contraction induced by histamine in a dose-dependent manner. However, neither the agonist NMDA nor the noncompetitive receptor blocker MK-801 affected tracheal relaxation induced by ketamine. We conclude that ketamine relaxes the tracheal smooth muscle contracted by histamine through a mechanism independent of NMDA receptors. The decreased bronchomotor tone induced by ketamine is probably due to interference with a Ca2+-requiring step necessary to maintain the contraction caused by histamine. ⋯ Stimulation of the N-methyl-D-aspartic acid (NMDA) receptor in the airway results in airway constriction. The bronchodilator ketamine blocks the NMDA receptor. However, ketamine relaxes the guinea pig trachea contracted by histamine through a mechanism independent of the NMDA receptor.