Anesthesia and analgesia
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Anesthesia and analgesia · Dec 1998
Characteristics of tolerance to somatic and visceral antinociception after continuous epidural infusion of morphine in rats.
A continuous epidural infusion of morphine may cause a complicated tolerance to develop, depending on the spinal and supraspinal sites. We designed this study to clarify the characteristics of the tolerance to somatic and visceral antinociception after epidural morphine infusion. Rats received epidural infusion of morphine at the rates of 50 or 100 microg kg(-1) h(-1), or isotonic sodium chloride solution for 7 days. The tail-flick (TF) test and colorectal distension (CD) test were used to measure the somatic and visceral antinociceptive effects, respectively. Nociceptive tests were performed on Days 1, 2, 3, 4, and 7. After 7 days, time-response curves after epidural morphine (10 microg) or intraperitoneal morphine (3 mg) challenge tests were conducted to assess the magnitude of tolerance. Epidurally infused morphine significantly increased percent maximal possible effects (%MPEs) (P < 0.05) in both the TF and CD tests, depending on the concentration of morphine. In the epidural morphine challenge test, increases in %MPEs were significantly attenuated (P < 0.05) in the morphine-infused group compared with the isotonic sodium chloride solution-infused group. The increases in %MPEs in the intraperitoneal challenge test were also attenuated in the morphine-infused group. We conclude that morphine tolerance to both somatic and visceral antinociception develops rapidly during epidural infusion and is based on the development of tolerance at the systemic, as well as the epidural, level. ⋯ A continuous epidural infusion of morphine rapidly induces tolerance to visceral and somatic antinociception in rats. This development is based on the development of tolerance at the systemic, as well as the epidural, level.
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Anesthesia and analgesia · Dec 1998
Nitrous oxide and carbon dioxide have no effect on the blood-gas solubilities of sevoflurane and isoflurane.
Nitrous oxide (N2O) has been shown to decrease the solubility (lambdaB:G) of volatile anesthetics in human blood and, consequently, affect their rate of uptake. If this is true, then carbon dioxide (CO2) may also have an effect, which is important because methods that measure the tension of volatile anesthetics in blood washout CO2 in the process. Blood samples were obtained from fasted, healthy volunteers and patients undergoing major surgery. Each sample was divided into two aliquots: one was equilibrated at 37 degrees C in a closed glass tonometer with a mixture of isoflurane 1% and sevoflurane 2% in a test gas mixture of either 50:50 N2O/O2 or 5:95 CO2/O2; the other aliquot was equilibrated with isoflurane and sevoflurane in O2 alone as a control. Using a two-stage headspace technique using gas chromatography, we measured the lambdaB:G of isoflurane and sevoflurane in the presence and absence of the test gas in each subject. There was no significant difference between the lambdaB:G of sevoflurane and isoflurane obtained from the N2O group and their controls or between the CO2 group and their controls. We conclude that neither N2O nor CO2 has an effect on the lambdaB:G of sevoflurane or isoflurane in the concentrations tested. ⋯ The blood solubilities of sevoflurane and isoflurane were measured with and without nitrous oxide and carbon dioxide. No differences were found. Nitrous oxide does not affect the kinetics of other anesthetics by altering their solubility. Carbon dioxide tensions need not be controlled when measuring anesthetic tensions in blood.
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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
Intrathecal metabotropic glutamate receptor antagonists do not decrease mechanical hyperalgesia in a rat model of postoperative pain.
Spinal metabotropic glutamate receptors (mGluR) have been implicated in hyperalgesia after injury. The purpose of this study was to examine the effects of intrathecal (IT) mGluR antagonists on mechanical hyperalgesia in a rat model of human postoperative pain. The hindpaw withdrawal threshold to punctate stimulation using von Frey filaments and the response frequency to a nonpunctate stimulus applied directly to the wound were also measured. The effects of 1T (+)-alpha-methyl-carboxyphenylglycine ([+]-MCPG), (S)-carboxyphenylglycine ([S]-4-CPG), (RS)-alphacyclopropyl-4-phosphonophenylglycine ([RS]-CPPG) and L-2-amino-3-phosphonopropionic acid (L-AP3) on incision-induced mechanical hyperalgesia were examined. The withdrawal thresholds to punctate stimuli were not different from vehicle treatment after the IT administration of (+)-MCPG (100, 500 nmol), (S)4CPG (30, 100 nmol), (RS)-CPPG (100, 500 nmol), or L-AP3 (1, 30, 100 nmol). None of the IT mGluR antagonists decreased the response frequency to the nonpunctate stimulus. The largest dose of (+)-MCPG produced sufficient receptor antagonism because spontaneous nociceptive behaviors caused by the IT administration of a mGluR agonist were reduced. ⋯ Spinal metabotropic glutamate receptors antagonists, antinociceptive in some models of persistent pain, are not necessary for the maintenance of mechanical hyperalgesia in this rat model, which suggests that blockade of spinal metabotropic glutamate receptors may not be useful for the treatment of pain after surgery.
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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.