The aim of this study is to demonstrate that in elderly and frail patients, a narrower control of intraoperative blood pressure (BP) by the use of a continuous and noninvasive BP monitoring, coupled with an adequate depth of anesthesia, will reduce the incidence of postoperative cognitive impairment and the hospital length of stay.

Postoperative cognitive impairment (delirium and cognitive dysfunction) are frequent and feared complications in the elderly; they increase the postoperative morbidity and mortality, worsen the cognitive and functional outcome with loss of independence and increase the hospitalization length and costs . However, the etiology of these postoperative cognitive impairment, although probably multifactorial, remains unclear and strongly debated.

The investigators hypothesize that excessive anesthesia depths associated with intraoperative hypotension may play a critical role in the pathogenesis of cognitive impairment following surgery.

Inclusion Criteria:

• elderly patients (over the age of 70) undergoing elective moderate risk surgery requiring a general anesthesia
• Patients who provide written informed consent
• patient fluent in french

Exclusion Criteria:

• Patients under 70 years of age
• Surgery under locoregional anesthesia or emergent surgery or minor risk surgery
• Patients requiring invasive blood pressure monitoring (for medical reason or high risk surgery)
• Patients with arrhythmia and/or atrial fibrillation
• Patients with preoperative delirium or cognitive dysfunction (moca test < 26)
• Patients not fluent in French
• Patients without the capacity to give written informed consent or refusal of consent
• Patients undergoing surgery or included in another protocol within 3 months