British journal of anaesthesia
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Randomized Controlled Trial Comparative Study Clinical Trial
Non-invasive measurement of cardiac output during induction of anaesthesia and tracheal intubation: thiopentone and propofol compared.
We have investigated the haemodynamic changes in response to induction of anaesthesia and tracheal intubation in patients who received either thiopentone 5 mg kg-1 or propofol 3 mg kg-1 followed by atracurium 0.5 mg kg-1 and fentanyl 1.5 micrograms kg-1. Anaesthesia was maintained with 0.6% enflurane and 50% nitrous oxide in oxygen with assisted ventilation. Cardiac output and heart rate (HR) were monitored continuously with a transthoracic impedence monitor. ⋯ Both variables increased from preinduction values 1 min after tracheal intubation (P less than 0.001). In contrast, both MAP and SVR decreased after induction in the propofol group (P less than 0.001) and did not differ from preinduction values 1 min after tracheal intubation. MAP and SVR were greater in the thiopentone group compared with the propofol group after induction and tracheal intubation (P less than 0.01).
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We have studied, in six normal subjects, the effect of nitrous oxide sedation on the ventilatory pattern and oxygen saturation using pulse oximetry (SpO2) after hyperventilation to an end-tidal carbon dioxide partial pressure (PE'CO2) of 3 kPa. This value of PE'CO2 was shown to be less than the apnoeic threshold of all these subjects when their ventilation vs PE'CO2 response curves were plotted. All subjects became apnoeic when told to relax following hyperventilation while breathing 75% nitrous oxide for 90 s. ⋯ It was concluded that subjects who are sedated with nitrous oxide behave similarly to those who are anaesthetized rather than to those who were fully conscious, in that they become apnoeic below the apnoeic threshold point. The reduction in SpO2 after hyperventilation was explained almost entirely by apnoea and may explain abnormalities of respiratory control and hypoxaemia in patients recovering from general anaesthesia or sedation accompanied by hypocapnia. This mechanism may be of importance in obstetric patients after breathing Entonox, when apnoea and hypoxaemia may reduce oxygen delivery to the fetus.
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A computer controlled infusion device for propofol was used to induce and maintain general anaesthesia in 20 children undergoing minor surgical procedures. The device was programmed with an adult pharmacokinetic model for propofol. During and after anaesthesia, blood samples were taken for measurement of propofol concentrations and it was found that the values obtained were systematically overpredicted by the delivery system algorithm. New pharmacokinetic microconstants were derived from our data which reflected more accurately the elimination and distribution of propofol in a prospective study involving another 10 children.
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Electrocardiographic (ECG) changes are reported frequently after subarachnoid haemorrhage (SAH). The aim of this study was to investigate the functional significance of ECG changes by echocardiographic assessment of cardiac function. Forty-five patients with intracranial aneurysms were studied. ⋯ These patients had only minor ECG abnormalities, but severe neurological dysfunction. Conversely, patients with other ECG abnormalities including the deep inverted T waves associated usually with SAH, had normal echocardiograms. We conclude that the ECG is not an accurate predictor of myocardial function after SAH and that myocardial dysfunction is related more closely to severity of neurological condition.