Anesthesia and analgesia
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Anesthesia and analgesia · Dec 1998
End-tidal sevoflurane concentration for tracheal extubation and skin incision in children.
We sought to determine minimum alveolar anesthetic concentrations for skin incision (MAC) and for tracheal extubation (MAC(Ex)) for sevoflurane and its associated awakening time and respiratory complications during emergence from sevoflurane anesthesia in children. We studied 40 (20 in each group) unpremedicated pediatric patients ranging in age from 2 to 8 yr. For MAC(Ex) determination, anesthetic induction, tracheal intubation, and maintenance of anesthesia were performed with sevoflurane and N2O in oxygen. However, N2O administration was discontinued at the end of surgery. The ratio of the predetermined end-tidal to inspiratory concentration was maintained at 0.95-1.00 for at least 15 min. The trachea was gently extubated, and smooth tracheal extubation was defined by the absence of gross purposeful muscular movements. In addition, the respiratory complications and awakening time were investigated during emergence from anesthesia for each patient. For MAC determination, anesthesia induction and tracheal intubation were performed with 5% sevoflurane in oxygen. After the predetermined end-tidal sevoflurane concentration had been established and maintained for at least 15 min, skin incision was attempted. Patients' responses to skin incision were described as "no movement" or "movements." The MAC or MAC(Ex) for sevoflurane was 2.22% +/- 0.13% (mean+/-SD) or 1.70%+/-0.12%, and the 95% effective dose (ED95) for smooth extubation was 1.87% (95% confidence limits 1.75%-2.62%), respectively, in children. During emergence from anesthesia, none of patients held their breath or experienced laryngospasm in the current study. One patient in a subgroup at 1.5% coughed before tracheal extubation. All 10 patients with smooth tracheal extubation had hemoglobin oxygen saturation levels of > or =98% in this study. Awakening time was 9.7+/-3.7 min in the subgroup that received 1.75% sevoflurane. In conclusion, the MAC(Ex) and ED95 values of sevoflurane were 1.64% and 1.87%, respectively, in children. The MAC(Ex) to MAC ratio for sevoflurane was 0.8 in children within the same age range and mean age. ⋯ Because tracheal extubation of anesthetized patients may be advantageous in certain clinical situations, we performed this study. The ratio minimum alveolar anesthetic concentrations for skin incision and for tracheal extubation for sevoflurane was 0.8 in children within the same age range and mean age. No patient in the current study had laryngospasm.
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Anesthesia and analgesia · Dec 1998
In vitro investigation of cerebrospinal fluid leakage after dural puncture with various spinal needles.
Postspinal headache is one of the most common complications of spinal anesthesia and has repeatedly led to controversy concerning needle size and configuration. In an in vitro investigation, we measured cerebrospinal fluid (CSF) leakage with Sprotte, Whitacre, Quincke, and Atraucan needles under physiological conditions in human dura. The puncture characteristics were examined under an electron microscope. The pencil-point needles show 2-3 times less leakage of CSF compared with the cutting Quincke needles of corresponding size. Between the Sprotte and the Whitacre needles, there were no significant differences. The least loss of CSF occurred with the 26-gauge Atraucan needle. Under the electron microscope, a sharply delineated, persistent perforation channel was shown with the Quincke needles, which may explain the high CSF loss. With pencil-point needles, which push the tissue apart bluntly, a large opening on the inside is found, with some tearing of the dura. However, in contrast to the cutting needles, a persistent perforation channel is not manifested. The 26-gauge Atraucan needle, which both cuts and pushes apart conically, shows a relatively discrete opening on the inside, with slight tears in the dura and arachnoidea but without a visible perforation channel. The results of our study show that larger needles (26-gauge Atraucan) that are easier to handle can lead to good and, in some cases even better, puncture results if they have characteristics of both the cutting and the pencil-point needles. ⋯ We compared several brands of pencil-point and standard cutting spinal needles of varying sizes. All pencil-point needles had less cerebrospinal fluid leakage, the least loss occurring with 26-gauge Atraucan needles. Electron microscopic examination of the dura after puncture showed characteristic findings with each needle type. We conclude that the combined cutting and pencil-point characteristics seen in the Atraucan needle may have clinical advantages.
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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.