The Effect Of Low-Flow And Hıgh-Flow Anesthesıa On Intracranıal Pressure

Laparoscopic surgical procedures commonly involve the establishment of pneumoperitoneum (PP) and the application of the Trendelenburg position (TP) to optimize surgical exposure. These interventions are known to increase intra-abdominal pressure and may influence venous return, intrathoracic pressure, and cerebral hemodynamics. The combined use of pneumoperitoneum and Trendelenburg positioning is considered to have the potential to increase intracranial pressure (ICP). Therefore, the intraoperative assessment of intracranial dynamics is of clinical importance.

Optic nerve sheath diameter (ONSD) measurement is a noninvasive, reproducible, and bedside-applicable method used to assess changes in intracranial pressure. ONSD is considered to correlate with ICP alterations. Cerebral oxygenation can be evaluated using near-infrared spectroscopy (NIRS), a noninvasive technique that enables continuous monitoring of cerebral tissue oxygenation.

Low-flow anesthesia is based on the reduction of fresh gas flow rates and offers several advantages, including decreased anesthetic gas consumption, preservation of heat and humidity in the respiratory tract, and reduced environmental impact. However, data regarding the effects of low-flow anesthesia on cerebral physiology and intracranial dynamics remain limited. In surgical settings where pneumoperitoneum and Trendelenburg positioning are applied, evaluating the impact of different fresh gas flow rates on intracranial pressure and cerebral oxygenation is particularly important.

This prospective, randomized study was conducted in patients scheduled for elective laparoscopic hysterectomy at Bursa City Hospital. Patients aged between 18 and 75 years with an American Society of Anesthesiologists (ASA) physical status of I-II were included. Patients meeting predefined exclusion criteria were not enrolled in the study. Written informed consent was obtained from all participants prior to inclusion.

Patients were randomized into two groups using the closed-envelope method to receive either low-flow or high-flow anesthesia. Standard monitoring, including electrocardiography, noninvasive blood pressure, peripheral oxygen saturation, and NIRS monitoring, was applied to all patients. General anesthesia induction and maintenance were performed according to standardized protocols. Mechanical ventilation was provided in volume-controlled mode, and ventilator parameters were maintained within standard ranges.

Pneumoperitoneum was established using carbon dioxide (CO₂) insufflation at a predefined pressure range and was maintained throughout the surgical procedure. Following the establishment of pneumoperitoneum, patients were placed in the Trendelenburg position at a predefined angle, which was maintained during the operation.

Optic nerve sheath diameter measurements were performed using ultrasonography with minimal pressure applied to the globe. Measurements were obtained at predefined time points. Cerebral oxygenation was continuously monitored using NIRS throughout the intraoperative period. In addition, hemodynamic and respiratory parameters, including heart rate, arterial blood pressure, end-tidal carbon dioxide (EtCO₂), and ventilatory variables, were recorded.

Within the scope of this study, the effects of low-flow and high-flow anesthesia on intracranial dynamics and cerebral oxygenation were planned to be comparatively evaluated, and the study was conducted in accordance with the predefined protocol.

Inclusion criteria

• Female patients aged 18-75 years
• Scheduled for elective laparoscopic hysterectomy
• American Society of Anesthesiologists (ASA) physical status I-II
• Ability to provide written informed consent

Exclusion criteria

• Septicemia
• Risk of malignant hyperthermia
• Uncontrolled diabetes mellitus
• Chronic alcohol use
• Prolonged fasting
• Body mass index (BMI) > 40 kg/m²
• Intracranial space-occupying lesions (e.g., tumors, metastases, abscesses, hematomas, aneurysms)
• History of head trauma or cerebrovascular stroke within the preceding six months
• Known heart failure
• Diagnosis of glaucoma
• Prior carotid surgery or carotid artery stenosis
• ASA physical status ≥ III
• Requirement for massive blood transfusion
• Conversion from volume-controlled to pressure-controlled mechanical ventilation during surgery
• Intraoperative conversion to open surgery
• Patient refusal to participate