Evaluation of Sevoflurane Consumption During Initial Phase of Minimal-Flow Anesthesia in Retrograde Intrarenal Surgery

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

• Adults aged 18 to 65 years

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

• ASA Physical Status III or higher

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