Low Flow Anesthesia
Conditions
Keywords
general anesthesia, green anesthesia, low flow anesthesia
Brief summary
This study aims to evaluate whether adjusting the fresh gas flow rate to low-flow immediately after intubation, without performing a wash-in, is a reliable approach with respect to depth of anesthesia and oxygenation.
Detailed description
Low-flow anesthesia is defined as the delivery of fresh gas flow at a rate of 0.5-1 L/min on the anesthesia machine . Due to its advantages such as reducing costs, decreasing environmental pollution related to anesthetic gases, preserving mucociliary activity, softening secretions, and reducing heat loss, it has attracted considerable attention from anesthesiologists in recent years. However, the main concerns involve maintaining adequate ventilation, ensuring sufficient tissue oxygen delivery, and achieving adequate depth of anesthesia. Therefore, additional monitoring is required for the safe application of low-flow techniques. Exhaled gas volume, airway pressure, fraction of inspired oxygen (FiO₂), volatile anesthetic agent concentration, carbon dioxide concentration, and peripheral oxygen saturation (SpO₂) should be closely monitored. Arterial blood gas sampling is the gold standard for monitoring oxygenation. The Patient State Index (PSI) is a processed EEG index derived from frontal EEG signals that numerically expresses the level of anesthesia/sedation on a scale from 0 to 100. PSI is generated based on spectral and coherence analyses of data obtained from four-channel EEG monitors such as Masimo SedLine®, using advanced artifact filtering, and was developed for objective monitoring of the level of consciousness during general anesthesia. PSI values between 25 and 50 generally indicate an adequate depth of anesthesia, whereas higher values suggest a reduction in anesthetic depth. In low-flow anesthesia, after induction the patient is connected to mechanical ventilation, and the volatile agent is adjusted to 1 MAC with 50% O₂. Subsequently, wash-in is achieved by administering fresh gas flow at 4-6 L/min for approximately 10 minutes, after which the flow is reduced. However, some studies have reported that initiating anesthesia maintenance directly with low fresh gas flow, without performing wash-in, may also be a feasible approach. To date, no study has evaluated the reliability of initiating low fresh gas flow during mechanical ventilation without performing wash-in, using arterial blood gas analysis and PSI monitoring. This study aimed to compare the reliability of techniques involving reduction of fresh gas flow using the traditional wash-in method versus without wash-in, in terms of hypoxia and depth of anesthesia, using serial arterial blood gas measurements and PSI monitoring.
Interventions
DEVICEInitiation of low-flow anesthesia without wash-in following intubation
After endotracheal intubation, fresh gas flow is set to 0.75 L/min with 60% O₂. The sevoflurane vaporizer is initially set to 8%, and the sevoflurane concentration is subsequently titrated according to the target MAC value. Anesthesia depth and oxygenation are monitored using PSI monitoring and serial arterial blood gas measurements.
Sponsors
Erzincan Binali Yildirim Universitesi
Study design
Allocation
RANDOMIZED
Intervention model
CROSSOVER
Primary purpose
OTHER
Masking
NONE
Eligibility
Sex/Gender
ALL
Age
18 Years to 65 Years
Healthy volunteers
Yes
Inclusion criteria
* ASA physical status I-II * Cases lasting longer than 30 minutes * Non-laparoscopic surgical procedures
Exclusion criteria
* Patients with life-threatening renal, cardiac, or hepatic disease * Patients with chronic pulmonary diseases such as asthma or COPD * Patients with intraoperative hemodynamic instability * Patients with a body mass index (BMI) lower than 20 or higher than 30
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Comparison of arterial oxygen partial pressure (PaO₂) values between groups | Measured at 10, 20, 30, and 45 minutes after induction of anesthesia and before the end of surgery. | Comparison of arterial oxygen partial pressure (PaO₂) and Patient State Index (PSI) values between groups. |
| Comparison of Patient State Index (PSI) values between groups. | Continuously monitored intraoperatively and recorded at 10, 20, 30, and 45 minutes after induction of anesthesia. | PSI is an EEG-based index ranging from 0 to 100. Lower values indicate deeper anesthesia; the target range is 25-50 during general anesthesia. |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| Mean alveolar concentration (MAC) values | Continuously monitored intraoperatively and recorded at 10, 20, 30, and 45 minutes after induction of anesthesia. | Comparison of MAC values between groups during anesthesia maintenance. |
| Total sevoflurane consumption | From induction of anesthesia until the end of surgery (average duration approximately X minutes). | Comparison of total sevoflurane consumption between groups. |
| Time to reach target MAC level | Time (minutes) from completion of endotracheal intubation to achievement of MAC 1.0, as measured on the anesthesia monitor | Time required to achieve target MAC level after intubation |
Countries
Turkey (Türkiye)
Outcome results
None listed