Background & Objectives: In 2004, our study group introduced a method to indicate arterial mechanical properties by use of a mechanical impedance model, which we termed arterial stiffness K, which is derived from blood pressure and photo-plethysmogram amplitude. Later, we showed that arterial stiffness K can be used as a sensitive stress response monitor during general anesthesia. However, it is unclear whether differences in K actually indicate changes in the intensity of a noxious stimulus. Thus, we compared K between two groups exposed to 2 and 6 ng/ml remifentanil concentration at the stimulation of laryngoscopy.
Materials & Methods: Following approval from our institutional ethical review board, 30 patients were enrolled and randomly divided into two remifentanil concentration groups (2 and 6 ng/ml). In all, anesthesia was induced by propofol, after which desflurane and the predefined concentration of remifentanil were used. Prior to induction of anesthesia, a photo-plethysmogram probe was attached to the thumb of the measured upper limb and a catheter was placed into the radial artery on the same side. Waveforms were monitored using a bedside monitor (BSS-9800, NIHON KOHDEN, Tokyo, Japan), then values for K were calculated using the online personal computer. The concentration of desflurane was constantly maintained during the measurement period. After a steady concentration of remifenitanil was achieved for at least 3 minutes, the laryngoscopy was performed, with the values for K before and after the procedure recorded and analyzed. Statistical analysis was performed using Welch’s t-test, with 5% set as the level of significance.
Results: The values for K before the laryngoscopy were not significantly different between the groups (2 ng/ml group 15.4±7.2 mmHg/%, 6 ng/ml group 14.8±8.9 mmHg/%; P=0.85). In contrast, K after the procedure was approximately 2 times greater in the 2 ng/ml group (44.0±26.6 mmHg/% vs. 24.9±21.1 mmHg/%, P=0.04). The ratio of K before and after the laryngoscopy in the 2 ng/ml group was also significantly greater (3.0±1.6 vs. 1.5±0.5, P=0.001).
Conclusion: The value for arterial stiffness K reacts in response to stimulus intensity and can be used an indicator of nociceptive stimulus.
Disclosure of Interest: None declared