Spectral analysis of arterial pressure variability during induction of propofol anesthesia

We studied the effect of continuous infusion of propofol on spectral components in systemic arterial pressure (SAP) signals in 35 consenting patients undergoing abdominal surgery. Anesthesia was induced with intravenous bolus administration of propofol (2.0 mg/kg), followed by infusion at either 5 mg · kg^-1 · h^-1 (Group 1, n =18) or 10 mg · kg^{- 1} · h^-1 (Group 2, n = 17). Tracheal intubation was facilitated by administration of vecuronium (0.1 mg/kg). The SAP signal was subjected to off-line spectral analysis to obtain changes in power of the very low frequency (VLF; 0.00-0.08 Hz), low frequency (LF; 0.08-0.15 Hz), high frequency (0.15-0.25 Hz), and very high frequency (VHF; 0.80-1.60 Hz) components. Venous blood for the measurement of plasma concentration of propofol was collected at 5 min before bolus injection of propofol; at 5, 10, and 15 min after infusion of propofol; and immediately after endotracheal intubation. Infusion of propofol significantly decreased the total power of SAP spectrum in both groups, especially the VLF, LF, and VHF components at all intervals except postintubation. Immediately after tracheal intubation, patients in Group 1 showed a significant increase in mean arterial pressure when compared with those in Group 2 (118 ± 5 mm Hg vs 102 ± 5 mm Hg, P < 0.05). Similar change was also seen in the VLF component (7.4 ± 0.7 mm Hg² vs 4.4 ± 0.5 mm Hg², P < 0.05). After tracheal intubation, patients in Group 1 showed 15.7-, 3.3-, and 4.4-fold increase in the VLF, LF, and VHF components, respectively. There were 14.4-, 2.8-, and 2.8-fold increases in the respective components of the SAP signal in Group 2. At all intervals, the spectral components of SAP, however, did not correlate well with the plasma concentration of propofol in either group. These results suggest that spectral analysis of SAP signals may provide an alternative for assessing autonomic activities, such as the sympathetic response, to tracheal intubation during propofol anesthesia.