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Thoracic electrical bioimpedance measurement of cardiac output and cardiovascular responses to the induction of anaesthesia and to laryngoscopy and intubation

Noninvasive methods of determining cardiac output (by thoracic electrical bioimpedance) and arterial pressure (by intermittent oscillometry) were used to record minute‐by‐minute changes in heart rate, mean arterial pressure, stroke volume, cardiac output and systemic vascular resistance following induction of general anaesthesia and laryngoscopy and intubation in 60 healthy female patients who were either unpremedicated, or premedicated with temazepam or papaveretum‐hyoscine. Anaesthesia was induced with a sleep dose (3–5 mg.kg−1) of thiopentone and maintained with 70% nitrous oxide in oxygen with 0.5–1% enflurane. Tracheal intubation was facilitated by administration of vecuronium 0.1 mg.kg−1. Mean arterial pressure and cardiac output decreased maximally 5 min after induction in all premedication groups by mean estimates of 21–25% and 14–22% respectively. Heart rate increased initially one minute after induction, but decreased to less than the baseline value 5 min after induction. Systemic vascular resistance was unchanged. The stimulus of laryngoscopy and tracheal intubation was accompanied by a significant pressor response and tachycardia one minute after intubation (with mean increases in mean arterial pressure and heart rate of 29–34% and 22–33% respectively). The increase in mean arterial pressure was secondary to an increase in systemic vascular resistance (36–57%), and was accompanied by a decrease in stroke volume (– 25 to –31%). These changes were significant in all three groups. Cardiac output decreased only in unpremedicated patients. There were wide variations in the different haemodynamic indices. The 5th and 95th centiles for the decreases in mean arterial pressure and cardiac output during induction were –17 to –26, –21 to –33, and –21 to –35mmHg, and –0.7 to –2.0, –0.7 to –2.3, and –0.2 to –1.31.min−1 respectively in unpremedicated patients and those premedicated with papaveretum‐hyoscine, or temazepam. Corresponding values for increases in mean arterial pressure and systemic vascular resistance, and decreases in stroke volume following laryngoscopy and intubation, were 16 to 33, 16 to 31.5, and 15 to 31 mmHg; 5.0 to 8.6, 3.5 to 10.2, and 4.3 to 7.8 mmffg.min.−1; and –19 to –31, –11 to –32.5, and –9 to –21 ml respectively.