Pain sensitivity: a feasible way to predict the intensity of stress reaction caused by endotracheal intubation and skin incision?

Abstract

Recent studies have shown that pain sensitivity has a significant relationship with clinical pain and may also predict the intensity of pain and analgesic consumption after surgery. However, the correlation between pre-operative pain sensitivity and stress response during anesthesia has not been investigated. Therefore, we aimed to explore the relationship between pre-operative pain sensitivity and stress responses during intubation and skin incision in this study. Fifty women (ASA I-II) aged 20-55 years, undergoing elective abdominal surgery requiring at least a 10-cm-long skin incision were studied. Pain sensitivity, including pain threshold and pain tolerance was measured before surgery. In this study, experimental pain was induced by potassium ion conducted via continuous current. When patients reported feeling pain or acted to stop pain, the intensity of the current was recorded to register pain threshold and pain tolerance. The State-Trait Anxiety Inventory (STAI) was used to examine the pre-operative mental status. General anesthesia was induced with intravenous fentanyl and a target-controlled infusion of propofol. Blood samples for norepinephrine (NE) detection were collected at 10 min after entering the operating theater, immediately before intubation, 2 min after intubation, immediately before skin incision and 2 min after incision. Mean arterial blood pressure (MAP) and heart rate (HR) were recorded at the same time. Pearson's correlation test (SPSS 13.0) was then used to analyze the relationship between pain sensitivity and the changes in MAP, HR and NE level. A total of fifty women were enrolled in the study. Their pre-operative pain threshold and pain tolerance were 0.90 ± 0.40 mA and 2.53 ± 0.77 mA,respectively. Changes in MAP, HR and NE before and after intubation or skin incision were significantly related with pre-operative pain tolerance (P < 0.05); however, pain threshold was not correlated with changes in MAP, HR and NE (P > 0.05). The STAI score did not correlate with the stress response either (P > 0.05). Pain tolerance had a significant relationship with stress response during intubation and skin incision. We may initially use pain tolerance to direct opioid usage in the future.