Anesthesiology
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To study the cardiovascular effects of low blood ionized calcium ion concentrations [Ca2+] induced by citrate infusion followed by high [Ca2+], induced by CaCl2 infusion awake and during enflurane (2.5% ET), halothane (1.2% ET), and isoflurane (1.6% ET) anesthesia, dogs were chronically instrumented to measure heart rate, aortic, left atrial, and left ventricular (LV) blood pressures, and cardiac output. In conscious dogs low [Ca2+] (decreased 0.35 mM); increased heart rate (HR) and mean aortic pressure (MAP) and decreased stroke volume (SV) and LV dP/dtmax. Low [Ca2+] increased HR during all three anesthetics and decreased LV dP/dtmax except during isoflurane anesthesia. ⋯ Cardiac output increased during halothane and isoflurane anesthesia but was unchanged during enflurane. It would appear that the hemodynamic sensitivity for the effects of changing [Ca2+] was enflurane greater than halothane greater than isoflurane greater than awake. The results suggest that the effects of changes in [Ca2+] induced by citrate and CaCl2 infusion are modified by the three volatile anesthetics.
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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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The effects of flumazenil, a benzodiazepine antagonist, on the rate of cerebrospinal fluid (CSF) formation (Vf), resistance to reabsorption of CSF (Ra) and the electroencephalogram (EEG) was determined in 12 dogs anesthetized with halothane (0.4%, end-expired) and nitrous oxide (66%, inspired) in oxygen. In six dogs the responses to flumazenil were measured during administration of midazolam (1.6 mg/kg followed by 1.25 mg.kg-1.h-1, intravenously) given along with inhalational anesthesia, whereas in the other six dogs the responses to flumazenil were measured during inhalational anesthesia without midazolam. Vf and Ra were determined using ventriculocisternal perfusion, and EEG activity was evaluated using aperiodic analysis. ⋯ At elevated CSF pressure the changes were less consistent. It is concluded that smaller doses of flumazenil (which cause no EEG changes with the present method of analysis) and larger doses of flumazenil (which reverse midazolam-induced increase of theta and alpha activity) produce no change of Vf and no consistent change of Ra. Although flumazenil given in the presence of midazolam may increase Ra, thereby increasing CSF pressure and impairing contraction of CSF volume, this effect is not likely to be clinically important.
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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.