Start the continuous infusion of 25cc of remifantanil (labeled as a test drug) by TCI mode ( the target effect site concentration is 2.0).

While slowly injecting the prescribed dose of remimazolam over 30 seconds, observe whether it responds to the investigator's oral commands and the disappearance of the eyelash reflex for 3 minutes after administering the drug. Success in inducing loss of consciousness during anesthesia is defined as the loss of both verbal command response and eyelash reflex within 3 minutes after infusion, otherwise it is considered a failure.

The dose of remimazolam is initially 0.15 mg/kg and the next experimental dose is determined according to the biased coin design up-and-down sequential method. The standard deviation of this study is 0.05 mg.

Start the continuous infusion of 25cc of normal saline (labeled as a test drug).

While slowly injecting the prescribed dose of remimazolam over 30 seconds, observe whether it responds to the investigator's oral commands and the disappearance of the eyelash reflex for 3 minutes after administering the drug. Success in inducing loss of consciousness during anesthesia is defined as the loss of both verbal command response and eyelash reflex within 3 minutes after infusion, otherwise it is considered a failure.

The dose of remimazolam is initially 0.15 mg/kg and the next experimental dose is determined according to the biased coin design up-and-down sequential method. The standard deviation of this study is 0.05 mg.

Remimazolam is injected for 30 seconds and the experimental dose will be determined according to the biased coin design up-and-down sequential method.

If loss of consciousness is successful, the dose of the next intravenous dose of the next study subject will be reduced from the previous dose with a probability of 1/19 or the same as the previous dose with a probability of 18/19.

While slowly injecting the prescribed dose of remimazolam over 30 seconds, observe whether it responds to the investigator's oral commands and the disappearance of the eyelash reflex for 3 minutes after administering the drug. Success in inducing loss of consciousness during anesthesia is defined as the loss of both verbal command response and eyelash reflex within 3 minutes after infusion, otherwise it is considered a failure.

After injection of remimazolam, the investigator concludes the successful loss of consciousness (not respond to oral commands and the disappearance of the eyelash reflex); From remimazolam injection until loss of consciousness occurs