British journal of anaesthesia
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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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We have studied the effect of thiopentone, etomidate and propofol on systemic vascular resistance (SVR) during cardiopulmonary bypass with constant pump flow in 30 patients undergoing elective coronary artery bypass surgery. SVR decreased to 78% of control values after thiopentone 4 mg kg-1, to 72% of control after etomidate 0.3 mg kg-1, and to 68% of control after propofol 2 mg kg-1; it returned to control values 10 min after administration of thiopentone and propofol and 7 min after administration of etomidate. Analysis of variance showed that there were no significant differences in the changes in SVR between the groups.
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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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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.
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Randomized Controlled Trial Comparative Study Clinical Trial
Propofol sedation for outpatient upper gastrointestinal endoscopy: comparison with midazolam.
The objectives of this study were to assess midazolam and propofol as sedative agents for outpatient gastrointestinal endoscopy, with particular reference to recovery profile, amnesic effects, and haemodynamic state and oxygenation during the procedure. Forty consecutive patients were allocated randomly to two groups. Patients in group I (n = 19) received midazolam 81 (SEM 32) micrograms kg-1; those in group II (n = 21) received propofol 950 (400) micrograms kg-1. ⋯ Oxygen desaturation from baseline was similar in both groups (P less than 0.01). An increase in heart rate and decrease in mean arterial pressure were noted in both groups. Propofol provided more rapid recovery compared with midazolam, but was associated with pain on injection, a short amnesia span, and reduced patient acceptance.