Anesthesiology
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Impulse block by LA occurs through the inhibition of voltage-gated Na+ channels. Both protonated and neutral LAs can inhibit Na+ channels though interference with the conformational changes that underly the activation process (the sequence of events that occurs as channels progress from the closed resting state to the open conducting state). The occlusion of open channels contributes little to the overall inhibition. ⋯ If one accounts for the membrane-concentrating effects of LA hydrophobicity that are expressed as membrane: buffer partition coefficients equal to 10(2)-10(4), then the apparent LA affinities are low. The equilibrium dissociation constants calculated on the basis of free drug in the membrane are 1-10 mM, with a correspondingly weak binding to the inhibitory LA site. The stereospecificity of LA action is also relatively nonselective, suggesting a loose fit between ligand and binding site.(ABSTRACT TRUNCATED AT 400 WORDS)
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Randomized Controlled Trial Clinical Trial
Labor analgesia with epidural bupivacaine plus fentanyl: enhancement with epinephrine and inhibition with 2-chloroprocaine.
Epidural injection of drug combinations may decrease toxicity by decreasing the dose of each component, but may also result in detrimental drug interactions. In this study interactions among bupivaciane, fentanyl, epinephrine, 2-chloroprocaine, and lidocaine for epidural analgesia during labor were examined. In part 1 of the study, healthy parturients received in a random manner either 10 ml of 0.25% bupivacaine with 5 micrograms/ml fentanyl (n = 50), or 10 ml of this combination with 3.33 micrograms/ml freshly added epinephrine (n = 50). ⋯ The lidocaine test dose group had a greater duration of analgesia than the 2-chloroprocaine test dose group (median duration of 164 vs. 91 min, P less than 0.05). The authors conclude that the addition of epinephrine 3.33 micrograms/ml significantly increases the duration of analgesia obtained from 0.25% bupivacaine with 5 micrograms/ml fentanyl. However, prior injection of 2-chloroprocaine, but not lidocaine, significantly decreases the duration of analgesia achieved with this BFE mixture.
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Anesthetic management and outcome were examined in patients with negative in vitro contracture tests for malignant hyperthermia (MH). Contracture testing was performed in a standardized fashion using 3% halothane alone and incremental doses of caffeine alone. Medical records were examined for 54 anesthetic exposures in 42 MH(-) patients who had received anesthesia since their MH testing. ⋯ Two of these patients also receive prophylactic iv dantrolene. These results suggest that "triggering" anesthetic agents may be safely administered to patients who test MH(-) by in vitro contracture testing. However, until the anesthetic experience of larger numbers of MH(-) patients is known, these results should be interpreted cautiously.
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The present study evaluated responses to train-of-four (TOF) stimulation at a range of stimulating currents. Traditionally TOF has been applied with a supramaximal stimulus but this may be quite uncomfortable for the awake patient. In the first part of this study, 12 healthy volunteers quantified (by 10-cm visual analog scale) the discomfort associated with TOF stimulation at 20, 30, and 50 mA. ⋯ Although single twitch heights increased significantly as amperage was increased, there was no statistical difference in the T4/T1 ratios at the three different currents. The mean +/- SD T4/T1 ratios at 20, 30, and 50 mA were 0.795 +/- 0.247, 0.798 +/- 0.237, and 0.802 +/- 0.233, respectively (P = ns). It is concluded that TOF monitoring using a submaximal stimulus is more comfortable for the awake patient who is suspected of residual weakness, and that T4/T1 testing can be reliably accomplished intraoperatively as well as postoperatively using submaximal stimuli.
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A questionnaire inquiring about existing and desirable work and rest patterns appeared in a newsletter mailed to about 22,000 anesthesiologists and anesthesiology residents and 24,000 nurse anesthetists (CRNA). Almost 3,000 anonymous replies were received and analyzed. Respondents reported mean work weeks of 47.5 h (CRNA) to 69.8 h (residents), longest continuous period of administering anesthesia without a break of 6.6 h (CRNA) to 7.7 h (residents), and longest period of administering anesthesia with or without breaks of 14.1 h (CRNA) to 20 h (resident). ⋯ The majority of respondents recalled having made errors in the administration of anesthesia that they attributed to fatigue. These results may not be representative of work patterns or attitudes among American anesthesia providers because of the small sample size and the resultant potential for bias. Yet, the subject deserves attention and further study because fatigue can affect professional performance, ability to learn, and family life.