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.

• Manual Mask Ventilation (Procedure): Patients will receive manual mask ventilation with 100% oxygen using a reservoir bag. This procedure will be performed by an experienced anesthesiologist or anesthesia resident for 2 minutes following the administration of induction agents, allowing for adequate muscle relaxation prior to endotracheal intubation.
• AutoFlow Mechanical Mask Ventilation (Procedure): Patients will receive mask ventilation delivered mechanically by the anesthesia workstation. The device will provide 100% oxygen for 2 minutes following the administration of induction agents. The ventilator settings will be standardized to an AutoFlow mode with a tidal volume (VT) of 6 mL/kg (based on ideal body weight), a respiratory rate of 12 breaths/minute, a peak pressure limit of 30 cmH₂O, and a Positive End-Expiratory Pressure (PEEP) of 5 cmH₂O

Primary outcomes

• Change in Cerebral Regional Oxygen Saturation (s-rSO2) [Baseline prior to pre-oxygenation (T1), immediately after pre-oxygenation (T2), post-induction/pre-intubation following 2 minutes of mask ventilation (T3), and immediately post-intubation (T4).]: Bilateral cerebral regional oxygen saturation will be continuously measured using a Near-Infrared Spectroscopy (NIRS) device (INVOS™ oximeter) with sensors placed on the right and left frontal regions. The changes in s-rSO2 values will be recorded to evaluate the impact of manual versus AutoFlow mask ventilation during the induction of general anesthesia.

Secondary outcomes

• Change in Peripheral (Somatic) Regional Oxygen Saturation (p-rSO2) [Baseline prior to pre-oxygenation (T1), immediately after pre-oxygenation (T2), post-induction/pre-intubation following 2 minutes of mask ventilation (T3), and immediately post-intubation (T4).]: Bilateral peripheral regional oxygen saturation will be measured using NIRS sensors placed on the volar surfaces of the right and left forearms to evaluate tissue oxygen delivery and peripheral perfusion.
• Mean Arterial Pressure (MAP) [Baseline prior to pre-oxygenation (T1), immediately after pre-oxygenation (T2), post-induction/pre-intubation following 2 minutes of mask ventilation (T3), and immediately post-intubation (T4).]: Hemodynamic stability will be evaluated by recording Mean Arterial Pressure (MAP) using standard non-invasive monitor. Measurements will be tracked to ensure parameters remain within a ±20% margin of the baseline during induction.
• Peripheral Oxygen Saturation (SpO2) [Baseline prior to pre-oxygenation (T1), immediately after pre-oxygenation (T2), post-induction/pre-intubation following 2 minutes of mask ventilation (T3), and immediately post-intubation (T4).]: Standard systemic oxygen saturation will be monitored non-invasively via pulse oximetry.
• End-Tidal Carbon Dioxide (EtCO2) [Post-induction/pre-intubation following 2 minutes of mask ventilation (T3), and immediately post-intubation (T4).]: The efficacy of the mask ventilation techniques will be evaluated by recording End-Tidal Carbon Dioxide (EtCO2).
• Heart Rate [Baseline prior to pre-oxygenation (T1), immediately after pre-oxygenation (T2), post-induction/pre-intubation following 2 minutes of mask ventilation (T3), and immediately post-intubation (T4).]: Hemodynamic stability will be evaluated by recording Heart Rate (HR) using standard non-invasive monitor.
• Peak Inspiratory Pressure (PIP) [Post-induction/pre-intubation following 2 minutes of mask ventilation (T3), and immediately post-intubation (T4).]: The efficacy of the mask ventilation techniques will be evaluated by recording Peak Inspiratory Pressure (PIP).
• Tidal Volume (VT) [Post-induction/pre-intubation following 2 minutes of mask ventilation (T3), and immediately post-intubation (T4).]: The efficacy of the mask ventilation techniques will be evaluated by recording delivered Tidal Volume (VT).

Sex: All, ages: 65 Years to any

Inclusion Criteria:

* Patients aged 65 years and older.
* Patients scheduled to undergo elective surgery requiring endotracheal intubation under general anesthesia.
* Patients with an American Society of Anesthesiologists (ASA) physical status of I, II, or III.
* Volunteer patients who are willing to participate and provide written informed consent.

Exclusion Criteria:

* Patients with severe heart failure or severe pulmonary disease.
* Patients with a presence or history of brain tumors or cerebrovascular accidents (CVA/stroke).
* Patients with impaired cooperation or cognitive dysfunction (e.g., dementia, delirium, Alzheimer's disease).
* Patients with a known history or preoperative prediction of a difficult airway.
* Patients with a known allergy to the monitoring sensor materials.

• Burkhart CS, Rossi A, Dell-Kuster S, Gamberini M, Mockli A, Siegemund M, Czosnyka M, Strebel SP, Steiner LA. Effect of age on intraoperative cerebrovascular autoregulation and near-infrared spectroscopy-derived cerebral oxygenation. Br J Anaesth. 2011 Nov;107(5):742-8. doi: 10.1093/bja/aer252. Epub 2011 Aug 10. PMID 21835838
• Ishiyama T, Kotoda M, Asano N, Ikemoto K, Shintani N, Matsuoka T, Matsukawa T. Effects of hyperventilation on cerebral oxygen saturation estimated using near-infrared spectroscopy: A randomised comparison between propofol and sevoflurane anaesthesia. Eur J Anaesthesiol. 2016 Dec;33(12):929-935. doi: 10.1097/EJA.0000000000000507. PMID 27802250
• Groene P, Rapp M, Ninke T, Conzen P, Hofmann-Kiefer K. Impact of mild hypo- and hyperventilation on cerebral oxygen supply during general anesthesia. Perioper Med (Lond). 2025 Mar 17;14(1):30. doi: 10.1186/s13741-025-00517-9. PMID 40091065

• EYÜP HORASANLI, Professor, Study director, Ankara Bilkent City Hospital Department of Anesthesiology and Reanimation