An interventional study of Sevoflurane Anesthesia with Minimal-flow and Sevoflurane Anesthesia with Low-flow in Retrograde Intrarenal Surgery (RIRS), Urolithiasis and Minimal-flow Anesthesia, sponsored by Dr. Lutfi Kirdar Kartal Training and Research Hospital. Completed at 1 site in Turkey (Türkiye). Open to participants aged 18 Years to 65 Years. Per ClinicalTrials.gov, last updated 2025-11-25.
Sponsored by Dr. Lutfi Kirdar Kartal Training and Research Hospital · Not applicable, Interventional, and Treatment
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.
278 studies on the registry are indexed under Urolithiasis; 70 are open to participants now.
This study's enrollment of 62 is below the median of 100 across 197 interventional studies indexed under Urolithiasis.
Browse Urolithiasis studies →Dr. Lutfi Kirdar Kartal Training and Research Hospital is the lead sponsor of 76 studies on the registry; 9 are open to participants now.
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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
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
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. 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.
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.
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.
Time frame: End of surgery (approximately 60-90 minutes after anesthesia induction)
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.
Time frame: 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.
Time frame: Intraoperative
End-Tidal CO₂ (EtCO₂) Levels (mmHg)
Mean and peak end-tidal CO₂ levels measured intraoperatively at 10-minute intervals.
Time frame: 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.
Time frame: Throughout surgery
MAC Values During Maintenance (MAC Units)
MAC values recorded during anesthesia maintenance to assess depth and consistency of volatile agent effect.
Time frame: Throughout surgery
Respiratory Rate (breaths per minute)
Intraoperative respiratory rates monitored and recorded to assess ventilatory response under different flow settings.
Time frame: Throughout surgery
Oxygen Saturation (SpO₂, %)
Minimum oxygen saturation values recorded intraoperatively to evaluate respiratory safety.
Time frame: Throughout surgery
Plan to share: No — 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
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Dr. Lutfi Kirdar Kartal Training and Research Hospital