British journal of anaesthesia
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Clinical Trial Controlled Clinical Trial
Ketamine infusions: pharmacokinetics and clinical effects.
The clinical effects and pharmacokinetics of ketamine, administered as an i.v. infusion, were studied in 31 patients. Anaesthesia was induced with ketamine 2 mg kg-1 i.v. and maintained using an i.v. infusion of ketamine, supplemented by nitrous oxide. The plasma concentrations of ketamine, nor-ketamine and dehydro-nor-ketamine were analysed using gas-liquid chromatography. ⋯ Maximum concentration of nor-ketamine was 4.7 +/- 2.4 mumol litre-1 and of dehydro-nor-ketamine 3.2 +/- 1.9 mumol litre-1. There were transient increases (15-30% of pre anaesthetic values) in arterial pressure, heart rate and cardiac output during operation. No post-operative respiratory depression was seen.
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Comparative Study
Maternal blood-gas tensions (PAO2-PaO2), physiological shunt and Vd/Vt during general anaesthesia for Caesarean section.
Measurements of maternal blood-gas tensions, (PAO2-PaO2), calculated pulmonary venous admixture (physiological shunt) and deadspace/tidal volume ratio (VD/VT) were made in 14 patients undergoing Caesarean section. Measurements were carried out after induction of general anaesthesia, and before delivery, with the patient tilted to the left. With a mean inspired oxygen concentration of 67.5% mean PaO2 was 44.3 kPa, mean (PAO2-PaO2) 18.4 kPa, mean Vd/Vt 32% and mean physiological shunt 9.5%. The findings are compared with published values for non-anesthetized pregnant patients.
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The haemodynamic changes following the administration of morphine 0.15 and 0.30 mg kg-1 i.v. were studied in 11 patients, free from known cardiac disease. All patients were acutely ill and their lungs were being ventilated mechanically. ⋯ In contrast, several changes were observed in patients receiving 0.30 mg kg-1: an immediate and prolonged decrease in the cardiac index was noted along with transient decreases in heart rate, stroke volume index, arterial pressure and left stroke work index. These results suggest that the haemodynamic cost of morphine 10 mg is negligible but could be significant when 20 mg has been administered and must be weighed against its beneficial effects in the critically ill patient.
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The use of a halothane meter in routine paediatric anaesthesia with controlled ventilation is described. The results demonstrate the accuracy achieved in the control of the alveolar halothane concentration. Measurement of the alveolar halothane concentration revealed responses to surgical stimulation otherwise obscured by neuromuscular blockade, and this may indicate insufficient depth of anaesthesia.