Anesthesiology
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After upper abdominal surgery, patients have been observed to have alterations in respiratory movements of the rib cage and abdomen and respiratory shifts in pleural and abdominal pressure that suggest dysfunction of the diaphragm. The validity of making such deductions about diaphragm function from these observations is open to discussion. ⋯ Indirect measurements of respiratory muscle action based on pressure and chest wall motion are easier than are assessments based on implanted electromyogram electrodes and sonomicrometers that measure electric activity and muscle length, respectively, directly. Interpretation requires numerous assumptions and detailed analysis of phase relations among the variables. In patients after thoracic surgery, however, these measurements strongly point to a shift in the distribution of motor output toward muscles other than the diaphragm.
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Aqueous suspensions of the local anesthetic n-butyl-p-aminobenzoate (BAB), epidurally applied in terminal cancer patients, resulted in a sensory blockade, lasting up to several months. To investigate the mechanism of action on the cellular level, the effect of 100 microM BAB on Na+ action potentials and on Na+ currents in dorsal root ganglion neurons from neonatal rats was studied. ⋯ BAB dramatically increased the firing threshold, and in part of the sensory neurons, it blocked the action potential. The inactivation of the fast Na+ channels, but not of the slow Na+ channels, was increased by BAB. Thus, the block of fast Na+ channels by BAB may contribute to epidural analgesia. At exposure times of 10 min, the effect of BAB was not reversible. This probably originates from its high lipid-solubility, which may be an important factor in determining the duration of the block in vivo.
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Minimum alveolar concentration (MAC) is decreased in pregnancy, but it is not known how quickly after delivery MAC returns to normal. We measured the MAC of isoflurane in a group of women undergoing elective tubal ligation after delivery. ⋯ The MAC of isoflurane was reduced in women 24-36 h postpartum and gradually increased to normal values by 72 h postpartum.