Anesthesia and analgesia
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Anesthesia and analgesia · Jun 2003
The effect of hypothermia on myogenic motor-evoked potentials to electrical stimulation with a single pulse and a train of pulses under propofol/ketamine/fentanyl anesthesia in rabbits.
In the present study, we investigated the effect of hypothermia on myogenic motor-evoked potentials (MEPs) in rabbits. The influence of stimulation paradigms to induce MEPs was evaluated. Twelve rabbits anesthetized with ketamine, fentanyl, and propofol were used for the study. Myogenic MEPs in response to electrical stimulation of the motor cortex with a single pulse and a train of three and five pulses were recorded from the soleus muscle. After the control recording of MEPs at 38 degrees C of esophageal temperature, the rabbits were cooled by surface cooling. Esophageal temperature was maintained at 35 degrees C, 32 degrees C, 30 degrees C, and 28 degrees C, and MEPs were recorded at each point. MEP amplitude to single- pulse stimulation was significantly reduced with a re-duction of core temperature to 28 degrees C compared with the control value at 38 degrees C (0.8 +/- 0.4 mV versus 2.3 +/- 0.3 mV; P < 0.05), whereas MEP amplitude to train-pulse stimulation did not change significantly during the cooling. MEP latency was increased linearly with a reduction of core temperature regardless of stimulation paradigms. In conclusion, these results indicate that a reduction of core temperature to 28 degrees C did not influence MEP amplitudes as long as a train of pulses, but not a single pulse, was used for stimulation in rabbits under propofol/ketamine/fentanyl anesthesia. ⋯ Intraoperative monitoring of myogenic motor-evoked potentials (MEPs) may be required under hypothermic conditions because of its neuroprotective efficacy. However, data on the influence of hypothermia on myogenic MEPs are limited. The results indicate that multipulse stimulation may be better than single-pulse stimulation when monitoring MEPs during hypothermia.
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Anesthesia and analgesia · Jun 2003
Comparative StudyCutaneous analgesia after transdermal application of amitriptyline versus lidocaine in rats.
Amitriptyline, a tricyclic antidepressant, has potent local anesthetic properties. However, there is no report of cutaneous analgesic effects after transdermal application. We report here that transdermally applied amitriptyline is more potent than lidocaine in providing cutaneous analgesia in rats. Solutions of amitriptyline base in 50, 100, and 500 mM concentrations were applied as a patch to rats, and their effects were compared with those of lidocaine base at the same concentrations and of the vehicle alone (45% water, 45% isopropyl alcohol, and 10% glycerin). Rats in each test group developed a concentration-dependent cutaneous analgesic block in the areas to which the drugs were applied; however, amitriptyline produced a longer block than lidocaine at the same concentration. The development of amitriptyline as a longer-lasting topical analgesic may improve our ability to treat chronic pain, such as neuropathic pain and neuralgia, and to prevent pain in procedures such as venipuncture. ⋯ The tricyclic antidepressant amitriptyline, often used perorally for the management of chronic pain, is shown here to be more potent than lidocaine in providing cutaneous analgesia when applied transdermally with an occlusive dressing in rats.
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Anesthesia and analgesia · Jun 2003
Comment Letter Case ReportsAnesthesia of a patient with cured myasthenia gravis.
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Anesthesia and analgesia · Jun 2003
Antinociceptive potentiation and attenuation of tolerance by intrathecal electric stimulation in rats.
We tested whether intrathecal electric stimulation would reduce the tolerance to chronic morphine use and the severity of precipitated morphine withdrawal. Rats received intrathecal electrode catheter implantation and a continuous intrathecal infusion of morphine (2 nmol/h) or saline for 7 days. Intrathecal electric stimulations (0, 20, or 200 V) were performed once daily during the same period. Daily tail-flick and intrathecal morphine challenge tests were performed to assess the effect of intrathecal electric stimulation on antinociception and tolerance to morphine. Naloxone withdrawal (2 mg/kg) was performed to assess morphine dependence, and changes in spinal neurotransmitters were monitored by microdialysis. The antinociceptive effect of intrathecal morphine was increased by 200 V of electric stimulation. The magnitude of tolerance was decreased in the rats receiving the 2 nmol/h infusion with 200 V of intrathecal electric stimulation compared with the control group (morphine 2 nmol/h alone) (AD(50), 13.6 vs 124.7 nmol). The severity of naloxone-induced withdrawal was less in the rats receiving 200 V of stimulation. Intrathecal stimulation thus enhances analgesia and attenuates naloxone-induced withdrawal symptoms in rats receiving chronic intrathecal morphine infusion. Increases in spinal glycine release may be the underlying mechanism. This method may merit further investigation in the context of the long-term use of intrathecal opioids for controlling chronic pain. ⋯ Control of chronic pain is a major health problem. We show here that direct electrical stimulation of the spinal cord in rats enhances analgesia and attenuates naloxone-induced withdrawal symptoms. This may warrant further investigation in the context of long-term use of intrathecal opioids for controlling chronic pain.