Inclusion Criteria:  Patients...  at least 18 years of age scheduled for elective major surgery under general anesthesia that requires continuous invasive arterial blood pressure monitoring using a radial arterial catheter for clinical indications not related to the study  Exclusion Criteria:  Clinical indication to insert the arterial catheter before anesthetic induction ("awake arterial catheter"; this is usually the case in patients with severe cardiovascular diseases, such as heart failure or left ventricular assist device) emergency surgery American Society of Anesthesiologists physical status classification V or VI need for femoral artery catheterization heart rhythms other than sinus rhythm.