Anaesthesia
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Randomized Controlled Trial
Changes in the photoplethysmogram with tracheal intubation and remifentanil concentration.
Autonomic sympathetic activation, for instance following noxious stimuli, decreases the size and flattens the shape of the photoplethysmographic peripheral pulse waveform. We report a simple measure of the waveform shape, the ratio of mean-to-peak wave amplitude, for measuring nociception level during general anaesthesia. Fifty participants, anaesthetised with propofol and remifentanil, were randomly allocated to one of three different remifentanil effect-site concentrations (1, 3 and 5 ng.ml(-1) ). ⋯ The mean (SD) ratios following intubation at remifentanil effect-site concentrations of 1 ng.ml(-1) , 3 ng.ml(-1) and 5 ng.ml(-1) , were 0.49 (0.03), 0.48 (0.03) and 0.45 (0.04), respectively. Remifentanil therefore suppressed changes in the mean-to-peak ratio caused by tracheal intubation (p = 0.006). The ratio of the mean-to-peak plethysmographic amplitude may represent a simple measure of the balance of autonomic sympathetic and parasympathetic activity under general anaesthesia, and its performance following intubation was significantly different from peak amplitude (p = 0.046).
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Blood pressure measurement is an essential physiological measurement for all critically ill patients. Previous work has shown that non-invasive blood pressure is not an accurate reflection of invasive blood pressure measurement. In a transport environment, the effects of motion and vibration may make non-invasive blood pressure less accurate. ⋯ Thus, our data show that non-invasive blood pressure is not a precise reflection of invasive intra-arterial blood pressure. Mean blood pressure measured non-invasively may be a better marker of invasive blood pressure than systolic blood pressure. Our data show no evidence of non-invasive blood pressures being less accurate in an aeromedical transport environment.