Anesthesiology
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The effects of halothane and isoflurane on regional cerebral blood flow (CBF) were studied in 18 New Zealand White rabbits anesthetized with nitrous oxide (N2O) and morphine sulfate (MS) at three different levels of PaCO2. CBF was measured using the hydrogen clearance technique. Monitored variables were intracranial pressure (ICP), central venous pressure, heart rate, mean arterial pressure, electroencephalogram, arterial blood gases, end-tidal (ET) volatile anesthetic, and ET CO2. ⋯ During normocapnia, CBF was unchanged with the addition of 1 MAC isoflurane in all regions and during hypercapnia, CBF increased significantly only in the dorsal hippocampus following addition of 1 MAC isoflurane to the MS/N2O background anesthetic. Volatile anesthetic administration was associated with significant, although small, increases in ICP at all PaCO2 levels. We conclude that 1 MAC concentrations of halothane and isoflurane have opposite effects on CBF when added to a N2O/MS anesthetic during hypocapnia and that the effects of isoflurane on regional CBF are dependent on PaCO2 in rabbits under the anesthetic conditions of this experiment.
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Comparative Study
Transcutaneous O2 and CO2 monitoring of neurosurgical patients: detection of air embolism.
Transcutaneous oxygen tension (PtcO2) and transcutaneous carbon dioxide tension (PtcCO2) were monitored in 60 patients undergoing neurosurgical procedures. Twenty-six patients were in the sitting position and underwent routine monitoring for air embolism. Seventeen episodes of air embolism were diagnosed by precordial Doppler ultrasound or transesophageal echocardiography, and the PtcO2 decreased early during the course of each episode. ⋯ Correcting the PtcCO2 by the patient's baseline PtcCO2/PaCO2 ratio, PtcCO2 monitoring correctly reflected hypocarbia, normocarbia, and hypercarbia in 92% of the cases. PtcO2 monitoring was useful in detecting venous air embolism and may respond sooner than PETCO2. PtcCO2 monitoring was not useful as an early detector of air embolism.
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Intravenous cannulation by an epidural catheter may complicate epidural anesthesia. Local anesthetic solutions containing epinephrine produce tachycardia and hypertension when given intravenously and may identify intravenous placement. The authors studied the maternal and fetal effects of intravenous epinephrine-containing solutions in ten chronically instrumented gravid ewes. ⋯ All epinephrine-containing solutions decreased uterine blood flow (UBF) (P less than 0.001), and, for doses of 10 to 20 micrograms, this decrease lasted more than 3 min. Fetal heart rate and mean arterial blood pressure did not change following any test solution, nor did maternal or fetal arterial blood gas values. The authors conclude that small intravenous boluses of epinephrine decreased UBF in these animals.