To evaluate the influence of vasoactive medication on the spinal vasculature, we have chosen patients scheduled for arterial dilation of the lower limb as our study population. In these patients the spinal cord perfusion is not compromised. However, most patients will suffer from hypotension during surgery, due to the non-invasive type of surgery and the vasodilating effects of the anesthetics. Therefore, bolus administration of vasoactive medication (ephedrine, phenylephrine) is routinely required in order to increase the blood pressure.

The aim of the study is to observe the influence of a bolus administration of ephedrine and phenylephrine on the spinal vasculature, measured by NIRS.

During the preoperative visit, baseline MAP (mean arterial blood pressure) will be defined.

All patients receive standard anesthesia care during the surgical procedure. Before induction of anesthesia, 6 additional sensors (stickers) are applied to the back of the patient (at three levels: 2 at the upper thoracic level, 2 at the lower thoracic level and 2 at the lumbar region). 2 sensors are routinely applied to the forehead to measure the cerebral oxygenation and a BIS sensor is applied to measure the depth of anesthesia. Through an intravenous line anesthetics will be administered. Vasopressor agents will be administered through a second intravenous line. After induction of anesthesia, an endotracheal tube is placed. According to the estimated duration of surgery a bladder catheter is placed.

If - after induction of anesthesia- MAP has decreased more than 20%, a vasopressor agent will be administered in order to increase the blood pressure to normal (preoperative) values. According to the MAP, several bolus administrations and incremental bolus dosages might be needed to reach the target blood pressure range (MAP decrease less than 20%). According to the group to which the patient has been randomized, a bolus of ephedrine and/or phenylephrine will be administered.

The study will be completed when MAP decreases more than 20% from baseline for the 4th time.

A total amount of Ephedrine and Phenylephrine resp. of 140 mg and 1500 μg will not be exceeded.

If the administration of the vasopressor study medication does not achieve the desired result, the patient will receive an appropriate treatment.

The endovascular surgical procedure can start without delay and the duration of surgery will not be prolonged because of the measurements and blood pressure management.

Inclusion Criteria:

• Patients > 18y
• scheduled for dilation of arterial blood vessels of the lower limb

Exclusion Criteria:

• Age < 18y
• BMI > 30
• severe valvular disease
• previous aortic surgery
• paraplegia/ paraparesis
• renal replacement therapy