Randomization and blinding
According to a computer-generated (Microsoft Excel) random number table, participants were randomly assigned at 1:1 ratio to the two groups. The patients were unaware of the group allocation as this assignment was concealed in an opaque and sequentially numbered envelope. An investigator not involved in the trial opened the envelope to the attending anesthetists responsible for preparing the magnesium sulfate or normal saline. All data were acquired by the second investigator blinded to the group assignment. The statisticians and staff were also blinded to the treatment assignments in the ward and PACU.