Anesthesiology
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Midazolam is being selected increasingly for use in patients with cardiovascular compromise. Although clinical doses of midazolam have minimal effects on cardiac function, the influence of midazolam (and other benzodiazepine sedatives) on cardiac arrhythmogenesis has yet to be elucidated fully. ⋯ This study has demonstrated that midazolam infusion results in either no effect (with clinical plasma midazolam concentrations) or flumazenil-reversible suppression (with supraclinical concentrations) of halothane-epinephrine arrhythmogenesis.
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Hyperventilation frequently is employed to reduce carbon dioxide partial pressure in patients in the operating room and intensive care unit. However the effect of hypocapnia on oxygenation is complex and may result in worsening in patients with preexisting intrapulmonary shunt. To better define the interplay between hypocapnia and oxygenation, the effects of hypocapnia and hypercapnia on the matching of ventilation (VA) and perfusion (Q) were studied in dogs with oleic acid-induced pulmonary edema, using the multiple inert gas elimination technique. ⋯ Both hypocapnia and hypercapnia were associated with an increased VA/Q inequality. However, PaO2 decreased and P[A-a]O2 increased with only hypocapnia. These results suggest that hyperventilation to reduce PaCO2 may be detrimental to arterial PO2 in some patients with lung disease.
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The transdermal therapeutic system (fentanyl), or TTS(fentanyl), continuously delivers fentanyl for up to 72 h. The transdermal therapeutic system (fentanyl)-100 delivers approximately 100 micrograms/h. The repeated dose pharmacokinetics of this drug using the recommended dosing interval have not been evaluated previously and were determined in the present study. ⋯ These results suggest that steady-state serum concentrations are approached by the second dose of TTS(fentanyl) and that the kinetics are stable with repeated dosing. The apparent half-life following system removal is relatively long, indicating ongoing absorption from a subcutaneous depot.
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Volatile anesthetics depress global left ventricular function by altering intracellular calcium (Ca2+) homeostasis at several sites within the myocyte. Although extracellular Ca2+ partially reverses the negative inotropic effects of volatile anesthetics, the actions of extracellular Ca2+ on anesthetic-induced diastolic dysfunction are unexplored. This investigation examined and compared the direct effects of extracellular Ca2+ on left ventricular systolic and diastolic function in conscious and anesthetized dogs. ⋯ Although CaCl2 produced positive inotropic effects in both the conscious and anesthetized states, CaCl2 did not alter diastolic function in conscious dogs. In contrast, CaCl2 reversed halothane- and isoflurane-induced negative lusitropic actions. The results of the present investigation suggest that improvement of left ventricular performance by CaCl2 during volatile anesthesia may be related to actions in diastole as well as systole.
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Propofol anesthesia often is associated with marked decreases in arterial blood pressure. Previous investigations in vivo have provided conflicting reasons for this clinical finding, including propofol-induced decreases in preload or afterload and/or direct myocardial depressant effects. Interpretation of the results of these studies is complicated by use of indices of myocardial contractility that may only indirectly indicate changes in inotropic state or are significantly dependent on ventricular loading conditions. ⋯ The results indicate that the significant decrease in systemic arterial blood pressure observed during continuous propofol anesthesia in dogs is a result of direct negative inotropic actions of propofol along with its direct effects upon arterial and venous vascular tone.