Effect of Arterial Carbon Dioxide Levels on Cerebral Blood Flow and Cerebral Autoregulation in Steep Trendelenburg Position During Robot-assisted Prostatectomy, and Its Effect on Postoperative Cognition - A Clinical Blinded Randomized Trial

Detailed Description: The carotid artery carries blood into the brain. Therefore, blood flow levels in the carotid artery may be used to assess brain perfusion. Brain perfusion is carefully regulated by the body, to ensure that the brain always receives enough oxygen and nutrients. During prostate surgery using laparoscopic techniques, the patient lies tilted on the operating table, with their head markedly lower than their legs. The investigators aim to study the effect on cerebral blood flow of a head-down tilted body position in combination with anesthesia and laparoscopic surgery, and particularly how cerebral blood flow is influenced by the participants' breathing pattern. The study aims to achieve insights that may be used to improve the treatment of vulnerable surgical patients, such as those with cerebrovascular disease or severe heart disease.

Anesthesia and surgery will proceed as usual, with the exception that the respiratory support the participants receive during the surgery will be adjusted as described below. The participants will receive standard monitoring of heart rate, blood pressure, and blood oxygen levels. Before surgery, the anesthesia team will per routine insert two plastic cannulas into the left arm for administering medication, and a plastic cannula into the participant's left wrist for close monitoring of the participant's blood pressure.

Study participants will undergo four additional steps:

1. Before surgery, an anesthesiologist will insert a thin plastic cannula into a superficial vein on the side of the neck. The cannula is the same type as the ones used on the arm and has a diameter of 1.1 mm. The purpose of this cannula is to measure the pressure of the blood returning from the brain to the heart. The procedure involves brief, moderate pain associated with the needle insertion. The plastic cannula will be removed before the participant wakes up from anesthesia.
2. Just before and during surgery, a trained anesthesiologist will perform ultrasound measurements on the right side of the participant's neck, temple, and the outside of the eyelid. Each measurement lasts 4-5 minutes. This will not prolong the time spent in the operating room. The measurements will cause no discomfort.
3. All patients undergoing prostate removal with robotic surgery receive respiratory support with a ventilator during anesthesia. In this study, the investigators will adjust the ventilator to control the carbon dioxide (CO2) levels towards either the lower or upper normal range for CO2. A blinded randomization will determine the group assignment. Regardless of which group a participant is assigned to, their CO2 level will be maintained within a range routinely used during anesthesia and considered completely safe.

In the project, the investigators will collect and record participant information. The investigators will store recordings of the participants' pulse, blood pressure, breathing depth and rhythm, levels of oxygen and CO2 in the participants' blood, medication doses used during surgery, and results of blood tests taken during surgery. From the participants' medical records, the investigators will retrieve and record the participants' age, gender, height, weight, whether the participants have chronic diseases, and which regular medications the participants use.