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

Study Overview

• Status: Completed
• Conditions: Sevoflurane; Urolithiasis; Inhalational Anesthesia; Anesthesia Depth Monitoring; Retrograde Intrarenal Surgery (RIRS); Minimal-flow Anesthesia; Anesthetic Consumption
• Intervention / Treatment: Drug: Sevoflurane Anesthesia with Minimal-flow; Drug: Sevoflurane Anesthesia with Low-flow

Detailed Description

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.

• Study Type: Interventional
• Enrollment (Actual): 62
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Turkey (Türkiye)
  • Istanbul, Turkey (Türkiye), 34865
    • Kartal Dr. Lütfi Kırdar City Hospital, University of Health Sciences

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

Description

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

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Minimal-flow Sevoflurane Group; Participants in this group received general anesthesia using sevoflurane with a fresh gas flow rate reduced to 0.5 L/min after the initial 10 minutes of induction. Anesthesia depth was monitored using BIS, and agent consumption and respiratory parameters were recorded throughout the retrograde intrarenal surgery (RIRS) procedure.	Drug: Sevoflurane Anesthesia with Minimal-flow; Patients received general anesthesia with sevoflurane. After induction, the fresh gas flow rate was reduced to 0.5 L/min during the maintenance phase of anesthesia for retrograde intrarenal surgery (RIRS). Agent consumption and anesthetic depth (via BIS and MAC) were monitored.
Active Comparator: Low-flow Sevoflurane Group; Participants in this group received general anesthesia using sevoflurane with a consistent 1.0 L/min fresh gas flow during the maintenance phase. BIS monitoring, agent consumption, and respiratory parameters were recorded throughout the retrograde intrarenal surgery (RIRS).	Drug: Sevoflurane Anesthesia with Low-flow; Patients received general anesthesia with sevoflurane. A fresh gas flow rate of 1.0 L/min was maintained during the maintenance phase of anesthesia for retrograde intrarenal surgery (RIRS). BIS, MAC, and respiratory parameters were recorded.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Total Sevoflurane Consumption (mL)	Total volume of sevoflurane (in milliliters) used during the maintenance phase of general anesthesia, calculated automatically by the anesthesia machine and recorded at the end of surgery.	End of surgery (approximately 60-90 minutes after anesthesia induction)

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Time to Reach 1 MAC (minutes)	Time in minutes from anesthesia induction to reaching 1 Minimum Alveolar Concentration (MAC) of sevoflurane, as recorded by the anesthesia machine.	Intraoperative (within first 10 minutes of anesthesia)
Vaporizer Shut-off Time (minutes)	Time in minutes from the start of surgery to the moment the sevoflurane vaporizer was turned off.	Intraoperative
End-Tidal CO₂ (EtCO₂) Levels (mmHg)	Mean and peak end-tidal CO₂ levels measured intraoperatively at 10-minute intervals.	Throughout surgery
BIS Values During Maintenance (BIS Index Units)	Bispectral Index values recorded at 10-minute intervals during the maintenance phase of anesthesia to assess anesthetic depth.	Throughout surgery
MAC Values During Maintenance (MAC Units)	MAC values recorded during anesthesia maintenance to assess depth and consistency of volatile agent effect.	Throughout surgery
Respiratory Rate (breaths per minute)	Intraoperative respiratory rates monitored and recorded to assess ventilatory response under different flow settings.	Throughout surgery
Oxygen Saturation (SpO₂, %)	Minimum oxygen saturation values recorded intraoperatively to evaluate respiratory safety.	Throughout surgery

Collaborators and Investigators

• Sponsor: Dr. Lutfi Kirdar Kartal Training and Research Hospital
• Investigators: Principal Investigator: UMIT YILDIZ, M.D., Department of Anesthesiology and Reanimation, Kartal Dr. Lütfi Kırdar City Hospital, University of Health Sciences, Istanbul, Turkey

Study record dates

Study Major Dates

• Study Start (Actual): October 1, 2024
• Primary Completion (Actual): June 1, 2025
• Study Completion (Actual): September 1, 2025

Study Registration Dates

• First Submitted: November 18, 2025
• First Submitted That Met QC Criteria: November 18, 2025
• First Posted (Actual): November 25, 2025

Study Record Updates

• Last Update Posted (Actual): November 25, 2025
• Last Update Submitted That Met QC Criteria: November 18, 2025
• Last Verified: November 1, 2025

More Information

Terms related to this study

• Keywords: minimal-flow anesthesia, low-flow anesthesia, sevoflurane, retrograde intrarenal surgery (RIRS), volatile consumption, environmental sustainability, MAC, BIS
• Additional Relevant MeSH Terms: Urogenital Diseases; Male Urogenital Diseases; Urologic Diseases; Female Urogenital Diseases; Female Urogenital Diseases and Pregnancy Complications; Infections; Gram-Positive Bacterial Infections; Bacterial Infections; Bacterial Infections and Mycoses; Actinomycetales Infections; Mycobacterium Infections; Mycobacterium Infections, Nontuberculous; Mycobacterium avium-intracellulare Infection; Urolithiasis
• Other Study ID Numbers: KLKSH-ANES-SEVOMIN-RIRS-001; 2024/16/925 (Other Identifier: T.C. Sağlık Bilimleri Üniversitesi Kartal Dr. Lütfi Kırdar Eğitim ve Araştırma Hastanesi)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

IPD Plan Description

Our study is:

Single-center

Non-commercial

Conducted as part of a medical specialty thesis

There is no stated plan to share anonymized individual-level data beyond what is reported in our thesis or publication

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No