British journal of anaesthesia
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We have defined the infusion dose requirements of propofol to suppress consciousness and response to a variety of graded non-noxious and noxious stimuli in 52 unpremedicated patients aged 16-40 yr and 32 patients aged 41-65 yr. They were allocated to receive one of five loading dose-infusion schemes designed to establish stable conditions covering the range from wakefulness, through sedation, to loss of consciousness and anaesthesia. ⋯ In both groups the dose-response curves for suppression of proprioception, finger counting and perception of light touch in conscious patients were shifted to the left of the curves for loss of consciousness and eyelash reflex. Dose-response curves for noxious stimuli were shifted to the right of those for loss of consciousness.
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Although mixed venous oxygen saturation (SVO2) is related to the reciprocal of cardiac output (CO) if both arterial oxygen content and oxygen consumption remain constant, simultaneous alterations in the three variables may occur immediately after discontinuation of cardiopulmonary bypass (CPB). To examine if continuous monitoring of SVO2 using a fibreoptic pulmonary artery catheter would be useful for detecting alterations in CO immediately after discontinuation of CPB, we have examined the relationships between changes in SVO2, cardiac index (CI), oxygen consumption and haemoglobin concentration in 15 cardiac surgical patients. ⋯ However, changes in SVO2 did not correlate with either oxygen consumption or haemoglobin concentration. The current results suggest that continuous monitoring of SVO2 with the fibreoptic pulmonary artery catheter may be useful for detecting changes in CO after discontinuation of CPB in patients with compromised cardiac function.
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Interaction of the steroidal neuromuscular blocking drugs pancuronium, pipecuronium, rocuronium and vecuronium with cardiac muscarinic receptors in rat hearts was investigated in vitro by a tritiated N-methyl hyoscine binding assay. We showed an interaction with cardiac muscarinic receptors with a rank order of potency pancuronium > vecuronium > pipecuronium > rocuronium and demonstrated complex binding characteristics for pancuronium, vecuronium and rocuronium, with "Hill coefficient" of less than unity. We conclude that the haemodynamic differences seen during the use of these neuromuscular blocking drugs may be a result of their interactions with cardiac M2 muscarinic receptors.
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Randomized Controlled Trial Clinical Trial
Lung management during cardiopulmonary bypass: is continuous positive airways pressure beneficial?
It is not clear if the use of continuous positive airway pressure (CPAP) during cardiopulmonary bypass (CPB) improves lung function after cardiac surgery. We have measured alveolar-arterial oxygen partial pressure difference (PAO2-PaO2) in 61 patients undergoing elective coronary artery bypass surgery. ⋯ The time to extubation (P = 0.42) and early extubation (P = 0.87) were not affected by the use of CPAP. The results of this study do not support the use of CPAP during CPB as a mechanism of improving lung function after cardiac surgery.
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Comparative Study
Tracheal intubation in a mannikin: comparison of the Belscope with the Macintosh laryngoscope.
Tracheal intubation carries a risk of accidental oesophageal intubation; this is increased with inexperienced trainees, and in patients with a difficult airway. The recent introduction of an angulated laryngoscope, the Belscope, may permit a better view of the vocal cords and increase the accuracy of orotracheal intubation. To determine how easy it is to learn to use the Belscope compared with the traditional Macintosh laryngoscope, a group of medical students attempted to intubate a mannikin which had been modified to simulate a difficult intubation. Time to intubation was fast with both laryngoscopes, although faster with the Macintosh, but the Belscope produced an unexpected greater incidence of failed intubation.