Anesthesiology
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Comparative Study
Inconsistent esophageal Doppler cardiac output during acute blood loss.
Application of the Doppler principle can provide relatively noninvasive and continuous measurement of cardiac output. However, it is based on certain assumptions that may introduce error. Esophageal Doppler cardiac output was compared with Fick cardiac output during acute blood loss (35-45% estimated blood volume) in eight anesthetized pigs. ⋯ A sign test for mean differences indicated that Doppler derived cardiac output was higher than Fick cardiac output, and the chance of this occurring if the true difference was zero was less than 1 in 1,000. A test for homogeneity of correlations was also rejected. Inaccuracies in individual assumptions in the computation of esophageal Doppler cardiac output, especially unaccounted changes in aortic diameter, are responsible for the inconsistent and unpredictable values of Doppler cardiac output obtained in this experimental model of hemorrhage.
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Comparative Study
The cerebral pressure-flow relationship during 1.0 MAC isoflurane anesthesia in the rabbit: the effect of different vasopressors.
The influence of different vasopressors on the cerebral pressure-flow relationship during 1.0 MAC isoflurane anesthesia has been studied. Mean arterial pressure (MAP) was increased by one of three vasopressors [angiotensin II (AT), norepinephrine (NE), or phenylephrine (PE)] in three groups of New Zealand white rabbits (n = 11, 10, and 9, respectively). Regional cerebral blood flow (CBF) was measured at five intervals by the injection of radioactive microspheres at a stable 2.05% (1.0 MAC) end-tidal isoflurane concentration (baseline) and following elevation of mean arterial pressure (MAP) by 20%, 40%, 60%, and 80% above baseline MAP with either AT, NE, or PE. ⋯ For all regions examined, the slope of the pressure-flow curve was significantly less steep when MAP was elevated with AT versus NE or PE (P less than 0.05 Tukey's studentized range test). There was no difference in slope between the NE and PE groups for any region. These results indicate that either NE and PE result in indirect cerebral vasodilation or that AT has intrinsic cerebral vasoconstrictive effects during 1.0 MAC isoflurane anesthesia in the rabbit.(ABSTRACT TRUNCATED AT 250 WORDS)
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Blood pressure is usually well maintained during epidural or spinal anesthesia even in the presence of extensive sympathetic blockade. The authors investigated whether hormonal systems support arterial pressure and how the circulation copes with a hypoxic challenge when activation of the sympathetic nervous system is selectively impaired by neural blockade. Accordingly, the effects of high epidural anesthesia alone and combined with hypoxia were evaluated in seven awake trained dogs. ⋯ During hypoxemia vasopressin concentrations increased 35-fold to 64 pg/ml +/- 38 (P less than 0.0001) compared to base line only during epidural anesthesia, but not after epidural saline (2 pg/ml +/- 2), while other hormones showed no significant differences. The authors conclude that high epidural anesthesia in awake unsedated dogs: 1) almost completely abolishes the normal cardiovascular response to hypoxemia while promoting vasopressin secretion; 2) preserves the ventilatory response to hypoxemia; and 3) is associated with increased vasopressin concentrations, most likely to compensate for decreased cardiac filling and/or arterial blood pressure when sympathoadrenal responses are impaired. Thus, the changes in cardiovascular vital signs in response to severe hypoxemia are markedly blunted when spinal sympathetic outflow is selectively eliminated by epidural anesthesia.
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A new percutaneous approach to central venous catheterization was recently described which seemed to offer advantages over others commonly used. To evaluate the technique, it was successfully used in 102 consecutive patients for monitoring, drug infusion, pulmonary arterial catheterization, and parenteral nutrition. There was a low incidence of complications, the most frequent being arterial puncture. The results confirm that this is an effective and relatively safe technique that deserves consideration in patients who require central venous catheterization.
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Biography Historical Article
Early intravenous anesthesia: an eyewitness account.
Descriptions of the earliest iv injections of various substances by individuals who actually witnessed the experiments in 1656 are presented. Of particular interest is an apparently overlooked account of an experiment in which opium was administered intravenously to a dog many years before 1674 as related by the physician and anatomist Thomas Willis. ⋯ There he was a very close professional associate of Christopher Wren who originated the practice of iv injection. These eyewitness accounts are worthy of note because the articles usually cited to establish Wren as the first individual to administer a drug intravenously were not written by anyone who actually observed the experiments.