Normally, higher levels of preoperational stress or anxiety affect behavior and recovery after the operation. Moreover, patients undergoing mastectomy are usually young women, and this demographic is known to experience higher levels of stress and anxiety than any other. Anesthetizing patients involves more than just anesthesia in operation; it also includes all of the preoperative treatments for optimizing a patient's condition and promoting quick postoperative recovery. Pharmacological premedication for anxiolysis or amnesia before anesthesia has been a common means of sedation that many studies have investigated. However, such studies have focused on alleviating patients' anxiety and on how far patients can obey induction for sedation; there has been no research on post-operational prognoses, the ultimate purpose of reducing anxiety.

The well-known effect of pharmacological premedication is to reduce the capacity of the anesthetic. However, it is not confirmed whether this effect leads to better recovery after anesthesia, as this question has not been researched. Furthermore, recently some have argued strongly that premedication actually prolongs recovery and that it does not need to be applied to every patient. Recently, therefore, the use of pharmacological premedication has been left to the discretion of institutes or doctors in many cases.

Among types of premedication, midazolam belongs to the class of short-acting benzodiazepines and is frequently used, as it induces meaningful anterograde amnesia and causes fewer aftereffects such as respiratory problems. In addition, its effects have already been demonstrated. However, research on the improvement of functional health after anesthesia-i.e., patients' quick return to normal life-is still poor and needs to be advanced.

When measuring the degree of recovery, recent studies tend to focus on measuring how quickly patients are able to return to normal life rather than the recovery of specific symptoms. To this end, the most widely used method is the Quality of Recovery 40 (QoR-40) survey. It has a total of 40 items, which are classified into five categories: emotional state, physical comfort, psychological support, physical independence, and pain. Questions are answered using a 5-point scale, with 1 being worst and 5 being best. It takes 6.3 minutes on average to complete, and its test-retest reliability, internal consistency, and split-half coefficient have led it to be recognized as the most effective survey method. Moreover, it has been used in many studies investigating how the type of operation, method of anesthesia, additional medication, and gender affect anesthesia and the operation. Its validity for such research has been verified.

Therefore, investigators can investigate the degree of postoperational functional recovery through the QoR-40 by comparing cases in which an operation is performed with or without midazolam.

Inclusion Criteria:

• Women aged between 20 and 65 years who are scheduled to undergo mastectomy because of breast cancer, who are classified as 1-2 according to the American Society of Anesthesiologists (ASA) physical status classification, and who use Korean as their mother tongue will be chosen as participants after obtaining informed consent from them; some may be excluded from participation according to certain criteria.

Exclusion Criteria:

• Patients who recently have been taking medicine that can affect the CNS, such as sedatives and sleeping pills
• people who drink more than one bottle of alcohol every day
• patients with prior experience of anesthesia or operation
• people with a BMI of 30 or higher
• pregnant women
• patients who are known to be allergic to propofol
• patients whose breasts are going to be dissected and then immediately re-constructed using their own body tissue.