Randomization, blinding and allocation concealment
Visceral pain, hyperalgesia, pain
66 patients requiring general anesthesia were randomized into the control group (group C) or esketamine group (group E) using a computer-generated random sequence placed in sequentially numbered opaque envelopes, which were opened before surgery. The drugs were prepared in 20-ml syringes labeled as the “study drug” and then placed into opaque envelopes before the study by an independent anesthesiologist. Another experienced anesthesiologist implemented anesthesia, and a specialized anesthesia nurse, blinded to the group allocation, performed the postoperative data collection. Patients, clinicians, and nurses were blinded to group assignment and study drugs for the duration of the trial. Incisional pain is defined as a pain restricted to incision site on abdominal wall. Visceral pain is defined as a deep, dull and hard-to-locate pain, while opioid-induced hyperalgesia (OIH) is defined as an increased sensitivity to normally painful stimuli in LC. Patients were educated to distinguish these three types of pain from our definitions.