Trajectory of pain threshold and its association with acute pain after thoracic surgery: a prospective observational study

BACKGROUND: Postoperative analgesic management is an ongoing challenge. The pain threshold (PT) is an objective index that reflects the body’s sensitivity to pain and can be used for quantitative pain assessment. We hypothesized that the PT is correlated with postoperative pain and can thus be used to guide postoperative pain management. METHODS: This study involved 93 patients who underwent thoracoscopic surgery from December 2019 to February 2020. The PT was measured with transcutaneous electrical stimulation before surgery (T(0)) and at 1 h (T(1)), 6 h (T(6)), and 24 h (T(24)) after surgery. The visual analogue scale (VAS) score was used to evaluate the severity of postoperative pain at the same time. The PT variation (PTV) after surgery was calculated as the ratio of the postoperative PT to preoperative PT. RESULTS: The postoperative PT was higher than the preoperative PT and showed a downward trend within 24 h after surgery; the PTV also showed a downward trend within 24 h after surgery. PT-T(1) was negatively correlated with VAS-T(1) at rest and during motion (rest: VAS-T(1)r = − 0.274, P = 0.008; motion: VAS-T(1)r = − 0.298, P = 0.004). PTV-T(1) was negatively correlated with VAS-T(1) during motion (r = − 0.213, P = 0.04). Lower VAS-T(1) scores (< 4) at rest and during motion were associated with higher PT-T(1) (rest: t = 2.452, P = 0.016; motion: t = 2.138, P = 0.035). The intraoperative sufentanil dose was associated with a postoperative increase in PTV-T(1). Increased rescue analgesic administration was associated with PTV elevation. However, the incidence of dizziness in patients with moderate PTV-T(24) was lower than that in patients with high or low PTV-T(24) (χ(2) = 8.297, P = 0.015). CONCLUSIONS: The postoperative PT was higher than the preoperative PT and showed a downward trend within 24 h after surgery; PTV also showed a downward trend within 24 h after surgery. The PT and PTV were negatively correlated with the pain intensity at rest and during motion and were associated with perioperative analgesic consumption and the incidence of adverse events.