British journal of anaesthesia
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Randomized Controlled Trial Comparative Study Clinical Trial
Skin vasomotor reflex induced by laryngoscopy: comparison of the McCoy and Macintosh blades.
We studied 22 female patients (ASA I or II) to investigate if laryngoscopy and intubation induced the skin vasomotor reflex (SVmR), and to compare the effects of the McCoy and Macintosh blades on the SVmR. Anaesthesia was induced with fentanyl, midazolam, vecuronium and nitrous oxide. In 11 patients, the vocal cords were seen for 3 s with the McCoy blade. ⋯ In the other 11 patients, the first and second laryngoscopies, respectively, were performed with the Macintosh and McCoy blades. Laryngoscopy alone and intubation with laryngoscopy significantly reduced skin blood flow in the ring finger of all patients (P < 0.01), indicating that both procedures provoked the SVmR. The magnitude of the SVmR and haemodynamic changes did not differ significantly between the two groups.
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We have examined the spectral components of heart rate variability (HRV) during induction of anaesthesia with thiopentone, tracheal intubation and subsequent inhalation of isoflurane-nitrous oxide. Commonly used spectral analysis methods such as fast Fourier transformation or autoregressive modelling require stationary data and are not suitable for the rapidly changing HRV data in this period. An advanced spectral analysis method, time-frequency analysis, which can treat non-stationary data, was used in this study. ⋯ Mid-frequency power (MF, 0.08-0.15 Hz), high-frequency power (HF, 0.15-0.5 Hz) and MF/HF ratio at baseline, after induction (before intubation), immediately after intubation and during maintenance periods were calculated and compared. MF and HF powers decreased after induction and were reduced further in the maintenance period but MF/HF ratio remained unchanged after induction. Immediately after intubation MF and HF powers did not differ significantly from the immediate pre-intubation values, but MF/HF ratio did.