Cardiovascular and metabolic response to acute normovolemic anemia. Effects of anesthesia.
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BACKGROUND: The maintenance of adequate tissue oxygenation during acute anemia depends on an increase in both cardiac output and tissue oxygen extraction. This study tested the hypothesis that anesthesia blunts the cardiac output response associated with acute normovolemic hemodilution. METHODS: Forty patients undergoing major abdominal surgery were prospectively randomized to undergo acute normovolemic hemodilution (ANH) either awake (awake group, n = 20) or with fentanyl-nitrous oxide-isoflurane anesthesia (anesthetized group, n = 20). Radial and pulmonary artery catheters were placed in all patients. After hemodynamic measurements were taken, patients in the two groups underwent hemodilution to decrease their hemoglobin concentration from 13 to 8 g/dl. A total of 1,875 +/- 222 ml (mean +/- SD) of blood was collected and simultaneously replaced by the same volume of medium molecular weight hydroxyethylstarch in both groups. RESULTS: In the awake group, ANH resulted in a significant increase in cardiac index (from 3.1 +/- 0.5 to 4.8 +/- 1.0 l. min-1. m-2) related to both an increase in heart rate and stroke index. Oxygen delivery remained unchanged, but oxygen consumption increased significantly, resulting in an increase in oxygen extraction ratio. In the anesthetized group, ANH resulted in a significantly smaller increase in cardiac index (from 2.3 +/- 0.5 to 3.1 +/- 0.7 l. min-1. m-2) related solely to an increase in stroke index. Oxygen delivery decreased but oxygen consumption was maintained as oxygen extraction increased. CONCLUSIONS: Anesthesia significantly reduces the cardiac output response associated with ANH. This could be related to the effects of the anesthetic drugs on the autonomic and the cardiovascular systems. (+info)
The effect of altered cerebral blood flow on the cerebral kinetics of thiopental and propofol in sheep.
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BACKGROUND: Thiopental and propofol are highly lipid-soluble, and their entry into the brain often is assumed to be limited by cerebral blood flow rather than by a diffusion barrier. However, there is little direct experimental evidence for this assumption. METHODS: The cerebral kinetics of thiopental and propofol were examined over a range of cerebral blood flows using five and six chronically instrumented sheep, respectively. Using anesthesia (2.0% halothane), three steady state levels of cerebral blood flow (low, medium, and high) were achieved in random order by altering arterial carbon dioxide tension. For each flow state, 250 mg thiopental or 100 mg propofol was infused intravenously over 2 min. To quantify cerebral kinetics, arterial and sagittal sinus blood was sampled rapidly for 20 min from the start of the infusion, and 1.5 h was allowed between consecutive infusions. Various models of cerebral kinetics were examined for their ability to account for the data. RESULTS: The mean baseline cerebral blood flows for the "high" flow state were over threefold greater than those for the low. For the high-flow state the normalized arteriovenous concentration difference across the brain was smaller than for the low-flow state, for both drugs. The data were better described by a model with partial membrane limitation than those with only flow limitation or dispersion. CONCLUSIONS: The cerebral kinetics of thiopental and propofol after bolus injection were dependent on cerebral blood flow, despite partial diffusion limitation. Higher flows produce higher peak cerebral concentrations. (+info)
Propofol or thiopentone as induction agents in romifidine-sedated and halothane-N2O-anesthetized dogs: a preliminary study.
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The objective of this paper was to evaluate the use of romifidine as a premedicant in dogs before general anesthesia induced with propofol or thiopentone and maintained with halothane-N2O. Fifteen healthy dogs were anesthetized twice. Each dog received, as preanesthetic protocol, atropine (10 microg/kg, IM) and romifidine (40 microg/kg, IM); induction was delivered with propofol or thiopentone and anesthesia was maintained with halothane and N2O for 1 h. Some cardiovascular and respiratory variables and recovery times were recorded. Induction doses of propofol or thiopentone and the percentage of halothane necessary for maintaining anesthesia were also registered. Thiopentone as an induction agent is more respiratory depressive but is less hypotensive than propofol. Thiopentone reduces further the percentage of halothane necessary for maintaining the anesthesia. However, the quality of recovery is poorer, as the time to extubation is longer and the dogs occasionally had a violent recovery. The combination of romifidine, atropine, propofol, halothane, and N2O appears to be an effective combination for inducing and maintaining general anesthesia in healthy dogs. (+info)
Repetitive synchronized cyclical oscillations of multisystem parameters subsequent to high-dose thiopental therapy for status epilepticus secondary to herpes encephalitis.
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We report a case of status epilepticus secondary to herpes encephalitis, treated with thiopental infusion and mechanical ventilation. The computerized storage and analysis of physiological data led to the detection of repetitive synchronized cyclical oscillations of arterial pressure, heart rate, EEG parameters, peripheral temperature and core temperature. Arterial pressure oscillations have been described in patients who are severely systemically unwell; cardiovascular and brain electrical activity may also oscillate in the presence of raised intracranial pressure. In contrast, this patient had no features of severe systemic illness or of raised intracranial pressure. Our hypothesis is that high-dose thiopental may have been a cause of our findings by producing autonomic dysfunction. (+info)
Comparison of influence of thiopentone, propofol and midazolam on blood serum concentration of noradrenaline and cortisol in patients undergoing non-toxic struma operation.
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The stress hormones plasma concentration after intravenous anesthetics (thiopentone, propofol, midazolam) administration in patients who underwent non-toxic struma operation was estimated. The goal of the study was to answer what stage of the general anesthesia and the surgery is the most dangerous for the cardiovascular system in term of stress hormones concentration and which of induction anesthetics used significantly alleviates undesirable reactions to surgical trauma and general anesthesia. 45 women aged 43 +/- 11, who underwent non-toxic struma operation and 16 women who underwent biliary gall-stones operation served as the 'study group and controls', respectively. Both groups were divided into 3 subgroups (in each a different anesthetic was used). Blood samples were taken at moments of increased stress during general anesthesia and operation. Intubation performed by laryngoscopy was found as the most stressful moment at which stress hormones are released intensively and can initiate cardiovascular disorders. According to our investigations, the suppression of the stress hormones (noradrenaline and cortisol) release was observed when propofol and midazolam were used for anesthesia induction for non-toxic struma surgery in contrast to thiopentone administration. (+info)
Plasma protein binding of thiopental in patients with impaired renal or hepatic function.
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Binding of thiopental to proteins in plasma from healthy, cirrhotic, and uremic subjects was studied using equilibrium dialysis. In plasma from healthy volunteers 28.0 plus or minus 0.9 per cent of thiopental was unbound. In plasma from patients with hepatic disease 53.0 plus or minus 2.1 per cent was unbound, while in patients with renal disease 55.7 plus or minus 1.5 per cent remained unbound. The decreased binding in uremia could not be explained completely by competitive displacement by nitrogenous end products or by hypoalbuminemia, although hypoalbuminemia may account for the decreased binding in cirrhotic patients. (+info)
Effects of anesthetics on ponto-geniculo-occipital waves from the oculomotor nucleus of the cat.
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Effects of anesthetics and doxapram on pontogeniculo-occipital (PGO) waves from the oculomotor nucleus were studied in acute experiments in cats paralyzed by gallamine triethiodide. The anesthetic agents studied in the present experiment (thiopental, ketamine, Innovar, nitrous oxide, and halothane) decreased, while doxapram increased, the total number of PGO waves. As the doses of anesthetics increased, PGO waves were abolished, but they returned to control levels or below control levels when the concentrations of anesthetics were decreased. The results indicate that the anesthetics studied inhibit the activity of the central mechanism associated with the oculomotor system. PGO waves may prove a useful index of the level of anesthesia. (+info)
Decamethonium and serum potassium in man.
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Decamethonium and succinylcholine were used to study the effects of depolarizing muscle relaxants on serum potassium in 60 patinets, free of neuromuscular disease, during major orthopedic surgery. Significant increases in serum K+ were found after administration of decamethonium or succinylcholine in the usual clinical doses. The abnormal elevations of serum K+ found in patients with burns, massive trauma, or muscle denervation are thus accentuations of the process that occurs in normal man following use of these depolarizing drugs. The administration of any depolarizing agent to these abnormal patient groups would, therefore, appear contraindicated. (+info)