Evaluation of Cerebral Perfusion in Supine and Steep Trendelenburg Positions During Robotic Prostatectomy

The use of robotic endoscopic radical prostatectomy has the potential to improve surgical outcomes and reduce complications compared to open radical prostatectomy. Robotic endoscopic abdominal surgery involves carbon dioxide (CO₂) insufflation to create pneumoperitoneum and requires the Trendelenburg position to provide adequate surgical visualization.

An increase in intra-abdominal pressure due to pneumoperitoneum leads to various physiological changes. The combination of steep Trendelenburg positioning and pneumoperitoneum during robotic prostatectomy is known to cause intracranial hypertension. The elevation of intra-abdominal pressure and Trendelenburg positioning increases intracranial pressure (ICP) and alters cerebral blood flow (CBF). These changes in cerebral hemodynamics may have detrimental effects on cerebral oxygenation.

Several invasive and non-invasive techniques are available for monitoring ICP and cerebral perfusion pressure (CPP). Among non-invasive methods, Transcranial Doppler ultrasonography (TCD) and Near-Infrared Spectroscopy (NIRS) are reliable and safe monitoring tools.

TCD measures blood flow velocities in the major arteries of the Circle of Willis. Based on TCD-derived data, several formulas have been proposed to estimate ICP, such as the Pulsatility Index (PI) and Resistance Index (RI).

PI is calculated using the formula:

PI = (Peak systolic velocity - End diastolic velocity) / Mean velocity. A normal PI typically ranges between 0.5 and 1.2. Under normal systemic hemodynamic conditions, an elevated PI (particularly \>2) suggests reduced cerebral perfusion pressure (CPP).

RI is calculated as:

RI = (Peak systolic velocity - End diastolic velocity) / Peak systolic velocity.

An RI greater than 0.75-0.8 is considered abnormal. RI is conceptually similar to PI (both increase in cases of low CPP), although PI is more widely used in clinical practice.

Normal ICP values vary with age and body position, but are generally 5-15 mmHg in healthy supine adults, 3-7 mmHg in children, and 1.5-6 mmHg in infants.

In cases of elevated ICP or circulatory hypotension, cerebral perfusion pressure (CPP) decreases. CPP is calculated as the difference between mean arterial pressure (MAP) and ICP. MAP is obtained by adding one-third of the pulse pressure (the difference between systolic and diastolic pressure) to the diastolic pressure.

NIRS technology was recently developed to enable continuous and non-invasive monitoring of regional cerebral tissue oxygen saturation for various clinical indications. The differing absorption spectra of oxygenated and deoxygenated hemoglobin at different light wavelengths allow for assessment of the balance between cerebral oxygen supply and demand.

In this study, the correlation between cerebral oxygen saturation measured by NIRS and estimated ICP calculated from TCD-derived middle cerebral artery (MCA) flow velocity and pulsatility index was evaluated. In addition, arterial blood gas parameters (PCO₂, PO₂, hemoglobin), end-tidal CO₂ (EtCO₂), and mean arterial pressure (MAP) were included in the analysis.

Preoperative and postoperative Mini-Mental State Examination (MMSE) tests were administered to assess potential cognitive changes and to compare our non-invasive monitoring results with clinical outcomes.

• Mean Arterial Pressure (MAP) at Predefined Perioperative Time Points [Time frame: 1.Upon arrival in the operating room 2.10 minutes after endotracheal intubation 3.30 minutes after placement in the Trendelenburg position 4.10 minutes before returning to supine 5.Postoperative 1 hour]
• End-Tidal CO₂ (EtCO₂) at Predefined Perioperative Time Points [Time frame: 1.Upon arrival in the operating room 2.10 minutes after endotracheal intubation 3.30 minutes after placement in the Trendelenburg position 4.10 minutes before returning to supine 5.Postoperative 1 hour]