Anesthesiology
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Clinical Trial Controlled Clinical Trial
Intrathecal injection of morphine for obstetric analgesia.
Intrathecal injection of morphine was used to provide obstetric analgesia in 20 primiparous women in labor. When the cervix was at least 3 cm dilated, morphine, 1 or 2 mg, was injected intrathecally. In all parturients, labor pains were completely relieved after 15-60 min and analgesia lasted as long as eight to 11 hours. ⋯ However, supraspinal effects of morphine cannot be excluded. The low lipid solubility of morphine can explain its slow onset and prolonged duration of action. Also, this will result in minimal systemic absorption of morphine, which protects the fetus and results in selective maternal analgesia.
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To determine the effects of a step change in end-expiratory pressure on functional residual capacity (FRC) and lung-thorax compliance (CLT), 10 cm H2O positive end-expiratory pressure (PEEP) was applied in eight patients who needed mechanical ventilation for acute pulmonary failure. Of the total change in FRC, 66 +/- 5.3 per cent (mean +/- SEM) was complete within the next breath, and 90 per cent change was achieved in 4.6 +/- 1.4 breaths (24 +/- 6.4 sec). There was no statistically significant difference between times to 90 per cent FRC change with application and with removal of PEEP. ⋯ These data define a time-dependent increase in lung volume that resembles pressure-volume hysteresis in normal man. Possible mechanisms include surface tension changes, recruitment of nonventilated lung, and stress relaxation of lung and chest wall. This study may explain the greater efficiency of PEEP compared with large tidal-volume ventilation in increasing PaO2 in patients with acute pulmonary failure.
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The differential sensitivities of mammalian nerve fibers to various local anesthetic agents were investigated. Lidocaine, tetracaine, etidocaine, and bupivacaine demonstrated a consistent pattern of conduction blockade in which the large fast-conducting A fibers were blocked at the lowest drug concentration, the intermediate B fibers were blocked at a higher drug concentration, and the smallest, slowest-conducting C fibers required the highest drug concentration for conduction blockade. ⋯ These findings indicate that local anesthetic agents are similar to other biological stress modalities in terms of their differential effects on nerve fibers of various sizes and conduction velocities, i.e., the large fast-conducting fibers are more susceptible to conduction blockade than are the smaller, slower-conducting fibers. Discrepancies between results of this study and previous reports in the literature are discussed.