A Comparative Evaluation of Sevoflurane Consumption and Anesthetic Depth During the Initial Phase of Minimal-Flow Versus Low-Flow Anesthesia in Patients Undergoing Retrograde Intrarenal Surgery (RIRS)
A Comparative Evaluation of Sevoflurane Consumption and Anesthetic Depth During the Initial Phase of Minimal-Flow Versus Low-Flow Anesthesia in Patients Undergoing Retrograde Intrarenal Surgery (RIRS)
This study aimed to compare the effects of minimal-flow (0.5 L/min) and low-flow (1.0 L/min) sevoflurane anesthesia on agent consumption, anesthetic depth, and cardiorespiratory safety during retrograde intrarenal surgery (RIRS). A total of 62 adult patients undergoing elective RIRS were enrolled in this single-center interventional trial. Patients were divided into two groups based on the fresh gas flow rate used during the maintenance phase of anesthesia. The primary outcome was total sevoflurane consumption at the end of anesthesia. Secondary outcomes included time to reach 1 minimum alveolar concentration (MAC), vaporizer shut-off time, BIS values, MAC levels, and respiratory parameters. The study found that minimal-flow anesthesia was as effective and safe as low-flow anesthesia, with lower agent consumption and no adverse effects on hemodynamic or respiratory parameters. These findings support the use of minimal-flow anesthesia for improved cost-efficiency and environmental sustainability.
This prospective, single-center, interventional study was designed to evaluate and compare the effects of minimal-flow and low-flow anesthesia on sevoflurane consumption, anesthetic depth, and respiratory parameters during retrograde intrarenal surgery (RIRS). After obtaining ethics committee approval (Decision No: 2024/16/925, Date: 17.09.2024), a total of 62 adult patients undergoing elective RIRS under general anesthesia were enrolled and divided into two groups based on the fresh gas flow rate used during the maintenance phase of anesthesia.
In Group 1 (Minimal-flow group), the fresh gas flow was reduced to 0.5 L/min after the initial 10 minutes of anesthesia. In Group 2 (Low-flow group), a 1.0 L/min flow rate was maintained. Both groups received the same induction and maintenance protocols with sevoflurane, and depth of anesthesia was monitored via BIS (Bispectral Index). Key variables measured included the total amount of sevoflurane consumed (mL), the time to reach 1 MAC, the vaporizer shut-off time, intraoperative BIS and MAC values, EtCO₂, and respiratory rate. Safety outcomes such as hemodynamic stability and desaturation were also recorded.
The primary outcome was total sevoflurane consumption. Secondary outcomes included anesthetic depth consistency (BIS/MAC), respiratory parameters, and time-based metrics. Statistical analysis revealed that minimal-flow anesthesia significantly reduced sevoflurane usage without compromising patient safety or anesthetic depth.
The results support the clinical use of minimal-flow anesthesia as a safe, cost-effective, and environmentally favorable alternative to low-flow techniques in selected urological procedures.
Inclusion Criteria:
ASA (American Society of Anesthesiologists) Physical Status I or II
Scheduled to undergo elective retrograde intrarenal surgery (RIRS) under general anesthesia
Provided written informed consent
Able to cooperate with preoperative evaluation procedures
Exclusion Criteria:
History of respiratory disease (e.g., asthma, COPD, restrictive lung disease)
Known hepatic or renal dysfunction
Neurological or psychiatric disorders that may affect BIS monitoring or anesthetic response
Known allergy or hypersensitivity to sevoflurane or other volatile anesthetics
Pregnancy or breastfeeding
Obesity (BMI > 30 kg/m²)
Anticipated difficult airway or history of intubation complications
Participation in another clinical trial within the past 30 days