British journal of anaesthesia
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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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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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Randomized Controlled Trial Comparative Study Clinical Trial
Antagonism of intense atracurium-induced neuromuscular block in children.
Antagonism of intense neuromuscular block induced by atracurium 0.5 mg kg-1 was attempted in four groups of six children using one of two doses of neostigmine (0.05 mg kg-1 and 0.1 mg kg-1) or of edrophonium (0.5 mg kg-1 and 1.0 mg kg-1) when the first twitch of the post-tetanic count (PTC1) was 10% of control. For comparison with normal practice, a fifth group received neostigmine 0.05 mg kg-1 when the first twitch of the train-of-four was 10% of control. ⋯ Doubling the doses of the anticholinesterases did not reduce the recovery time and had the effect of increasing variability. We conclude that there is no clinical advantage in attempting to antagonize intense neuromuscular block in children using normal or increased doses of neostigmine or edrophonium.
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Comparative Study
Comparison of invasive and non-invasive measurements of continuous arterial pressure using the Finapres.
A comparison was made of arterial pressures measured invasively from a radial arterial cannula and non-invasively from the middle finger using the 2300 Finapres (Ohmeda) during induction and maintenance of anaesthesia. Digital outputs of both pressures were captured directly onto computer hard disk; data recorded during flushing of the arterial line were excluded from analysis. We studied 53 patients undergoing cardiac, major vascular and neurosurgical procedures; 17705 comparisons of systolic, diastolic and mean pressure were analysed. ⋯ However, patient data sets showed marked variability in average pressure differences (invasive minus Finapres) when examined individually or grouped by operation type. Unexplained variations in pressure difference with time and absolute pressure were observed also. Whilst providing useful beat-to-beat information on arterial pressure trends, the Finapres cannot be recommended as a universal substitute for invasive arterial pressure monitoring.
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We have examined the safety of induced hypotension produced by extradural anaesthesia in patients with medically controlled hypertension. The haemodynamic response to induced hypotension was assessed in 38 non-hypertensive and 31 controlled hypertensive patients. All received extradural anaesthesia to T4 or above which decreased mean arterial pressure to 52 mm Hg and 55 mm Hg in normotensive and hypertensive patients, respectively. ⋯ None developed acute renal failure or stroke. There were three deaths; one of a patient who had hypertension. This suggests that induced hypotension with extradural anaesthesia is a safe technique for patients with medically controlled hypertension undergoing total hip arthroplasty.