Sensory Changes and Pain After Abdominal Hysterectomy

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 (T0) and at 1 h (T1), 6 h (T6), and 24 h (T24) 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-T1 was negatively correlated with VAS-T1 at rest and during motion (rest: VAS-T1r = - 0.274, P = 0.008; motion: VAS-T1r = - 0.298, P = 0.004). PTV-T1 was negatively correlated with VAS-T1 during motion (r = - 0.213, P = 0.04). Lower VAS-T1 scores (< 4) at rest and during motion were associated with higher PT-T1 (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-T1. Increased rescue analgesic administration was associated with PTV elevation. However, the incidence of dizziness in patients with moderate PTV-T24 was lower than that in patients with high or low PTV-T24 (χ2 = 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.

Kétamine à faibles doses : antihyperalgésique, non analgésique

Recent data in animal experiments as in clinical trials have clearly reported that pain modulation is related to an equilibrium between antinociceptive and pronociceptive systems. Therefore, the apparent pain level could not only be a consequence of a nociceptive input increase but could also result from a pain sensitization process. Glutamate, via NMDA receptors, plays a major role in the development of such a neuronal plasticity in the central nervous system, leading to a pain hypersensitivity that could facilitate chronic pain development. By an action on NMDA receptors opioids also induce, in a dose dependent manner, an enhancement of this postoperative hypersensitivity. "Antihyperalgesic" doses of ketamine, an NMDA receptor antagonist, were able to decrease this central sensitization not only in painful animal but also in human volunteers exposed to different pain models, or in the postoperative period. Many studies have reported that ketamine effects are elicited when this drug is administered the following manner: peroperative bolus (0.1 to 0.5 mg/kg), followed by a constant infusion rate (1 to 2 microg/kg per min) during the peroperative period and for 48 to 72 hours after anaesthesia. Those ketamine doses improved postoperative pain management by reducing hyperalgesia due to both surgical trauma and high peroperative opioid doses. This antihyperalgesic action of ketamine also limited the postoperative morphine tolerance leading to a decrease in analgesic consumption and an increase in the analgesia quality.