Manual Versus Autoflow Ventilation During Anesthesia Inductıon in Geriatric Patients

Ventilation strategies applied during the induction of general anesthesia have a significant impact on cerebral and peripheral oxygenation in geriatric patients. During the induction phase, respiratory and hemodynamic changes become more pronounced due to age-related physiological alterations such as diminished cardiopulmonary reserve, increased chest wall rigidity, decreased pulmonary elasticity, and impaired cerebral autoregulation. These changes increase the vulnerability of elderly patients to hypoxemia, hypocapnia, and imbalances in oxygen delivery. In particular, even brief episodes of hypoxemia or hypocapnia during induction may adversely affect cerebral oxygenation in this population.

Manual mask ventilation may result in unintentional hyperventilation or hypoventilation, potentially leading to hypocapnia and subsequent disturbances in cerebral oxygenation. In contrast, AutoFlow ventilation provides controlled ventilation with predefined parameters and may ensure more stable oxygen delivery.

This study is designed as a prospective, single-center, randomized controlled trial to compare the effects of manual ventilation and AutoFlow ventilation applied during the induction of general anesthesia on cerebral regional oxygen saturation (s-rSO₂) and peripheral (somatic) regional oxygen saturation (p-rSO₂) in geriatric patients. The primary hypothesis is that AutoFlow ventilation provides more stable cerebral and peripheral oxygenation compared to manual ventilation during the induction period.

The study will be conducted in the General and Oncology Operating Rooms of Ankara Bilkent City Hospital. Patients aged 65 years and older, of both sexes, classified as American Society of Anesthesiologists (ASA) physical status I-III, and scheduled for elective surgery requiring endotracheal intubation under general anesthesia will be included. A total of 106 patients (53 per group) will be enrolled based on power analysis, accounting for a potential 10% data loss.

Upon arrival in the operating room following standard preoperative fasting, demographic data (age, sex, height, weight, body mass index) and clinical characteristics (comorbidities, ASA classification) will be recorded. Standard ASA monitoring, including electrocardiography, non-invasive blood pressure, and pulse oximetry, will be applied. Cerebral and peripheral oxygenation will be continuously monitored using near-infrared spectroscopy (NIRS) with sensors placed bilaterally on the frontal region and on the volar surface of the forearms. Baseline values will be recorded before preoxygenation (T1).

Preoxygenation will be performed using 100% oxygen with a flow rate of 10 L/min until end-tidal oxygen (ETO₂) reaches 85% and plateaus for at least 30 seconds. Measurements at this stage will be recorded as T2.

Anesthesia induction will be standardized using fentanyl (1 µg/kg), lidocaine (1 mg/kg), propofol (2-3 mg/kg), and rocuronium (0.6-1 mg/kg), while maintaining hemodynamic stability within ±20% of baseline values. Following induction, mask ventilation with 100% oxygen will be applied for 2 minutes.

Patients will be randomly assigned using a computer-based block randomization method into two groups: manual ventilation and AutoFlow ventilation. In the manual ventilation group, ventilation will be performed by an experienced anesthesiologist or anesthesia resident using a reservoir bag. In the AutoFlow group, ventilation will be delivered by the anesthesia machine using predefined settings: tidal volume of 6 mL/kg (ideal body weight), respiratory rate of 12 breaths per minute, peak pressure limit of 30 cmH₂O, and positive end-expiratory pressure (PEEP) of 5 cmH₂O.

At the end of the 2-minute ventilation period before laryngoscopy, measurements will be recorded as T3 (post-induction, pre-intubation), including heart rate, mean arterial pressure, s-rSO₂, p-rSO₂, end-tidal carbon dioxide (EtCO₂), and peak inspiratory pressure (PIP). After endotracheal intubation and confirmation of tube placement, mechanical ventilation will be initiated and final measurements will be recorded as T4 (post-intubation).

To ensure standardization, NIRS device settings, including alarm limits, noise-reduction filters, and averaging time (8 seconds), will be kept constant for all patients. Factors that may affect measurements, such as motion artifacts, extremity temperature, arrhythmias, or vasopressor use, will be recorded.