Background & Objectives: For determining stress response during general anesthesia to judge the adequacy of analgesia, various symptoms, such as heart rate, blood pressure, and muscle tension, are used by clinicians, though a continuous useful measurement method remains to be established. We developed a novel arterial mechanical impedance monitoring value to indicate peripheral arterial stiffness, termed K, which is derived from blood flow force and arterial radius. We evaluated the ability of K to detect changes in the intensity of nociceptive stimulation.
Materials & Methods: Following approval from our institutional ethical review board, 30 patients scheduled to undergo a laparoscopic colectomy procedure were enrolled. During the operation, electrocardiogram findings, invasive left radial arterial blood pressure, and photo-plethysmogram amplitude at the left thumb were simultaneously measured at a sampling rate of 125 Hz using a bedside monitor (BSS-9800, NIHON KOHDEN, Tokyo, Japan) and entered into a computer. K values were calculated in real time. The patients received 3 different effect site concentrations (2, 4, 6 ng/ml) of remifentanil at 3 times during the study period. The measured values of K during the 4 ng/ml administration were used as control values (Kcontrol). K values obtained during the 6 ng/ml administration (K6ng) were normalized by dividing K6ng by Kcontrol, while those obtained during the 2 ng/ml administration (K2ng) were normalized by dividing K2ng by Kcontrol. To compare the response of K for different remifentanil concentrations, we used the normalized K2ng (nK2ng) and normalized K6ng (nK6ng) values. A paired t-test was employed for statistical analysis and the level of significance was set at P<0.05.
Results: The highest K value for remifentanil effect-site concentration was observed during the 2 ng/ml administration, while the lowest was observed during the 6 ng/ml administration (K2ng: 35.9±25.6 mmHg/%, Kcontrol: 25.0±17.9 mmHg/%, K6ng: 20.0±15.7 mmHg/%). Furthermore, nK2ng showed a significantly higher response than nK6ng (1.56±0.95 vs. 0.84±0.28, P<0.0001).
Conclusion: The response of K was significantly different between the high and low concentrations of remifentanil. Our results show that a change in K reflects the change in intensity of surgical nociceptive stimulus during general anesthesia, indicating its use as an indicator of nociceptive stimulation.
Disclosure of Interest: None declared