Anesthesia Depth Monitoring, Anesthetic Consumption, Inhalational Anesthesia, Minimal-flow Anesthesia, Retrograde Intrarenal Surgery (RIRS), Sevoflurane, Urolithiasis
Conditions
Keywords
minimal-flow anesthesia, low-flow anesthesia, sevoflurane, retrograde intrarenal surgery (RIRS), volatile consumption, environmental sustainability, MAC, BIS
Brief summary
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.
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.
Interventions
DRUGSevoflurane 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.
DRUGSevoflurane 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.
Sponsors
Dr. Lutfi Kirdar Kartal Training and Research Hospital
Study design
Allocation
RANDOMIZED
Intervention model
PARALLEL
Primary purpose
TREATMENT
Masking
NONE
Intervention model description
This was a prospective, two-arm, parallel-group study in which patients undergoing retrograde intrarenal surgery (RIRS) were randomly assigned to receive either minimal-flow (0.5 L/min) or low-flow (1.0 L/min) sevoflurane anesthesia. Participants were allocated to one group only and followed independently throughout the procedure. No crossover between groups occurred. The study aimed to compare anesthetic consumption, depth of anesthesia, and cardiorespiratory safety between the two anesthetic flow techniques.
Eligibility
Sex/Gender
ALL
Age
18 Years to 65 Years
Healthy volunteers
No
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
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Total Sevoflurane Consumption (mL) | End of surgery (approximately 60-90 minutes after anesthesia induction) | 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. |
Other
| Measure | Time frame | Description |
|---|---|---|
| Vaporizer Shut-off Time (minutes) | Intraoperative | Time in minutes from the start of surgery to the moment the sevoflurane vaporizer was turned off. |
| End-Tidal CO₂ (EtCO₂) Levels (mmHg) | Throughout surgery | Mean and peak end-tidal CO₂ levels measured intraoperatively at 10-minute intervals. |
| BIS Values During Maintenance (BIS Index Units) | Throughout surgery | Bispectral Index values recorded at 10-minute intervals during the maintenance phase of anesthesia to assess anesthetic depth. |
| Time to Reach 1 MAC (minutes) | Intraoperative (within first 10 minutes of anesthesia) | Time in minutes from anesthesia induction to reaching 1 Minimum Alveolar Concentration (MAC) of sevoflurane, as recorded by the anesthesia machine. |
| Respiratory Rate (breaths per minute) | Throughout surgery | Intraoperative respiratory rates monitored and recorded to assess ventilatory response under different flow settings. |
| Oxygen Saturation (SpO₂, %) | Throughout surgery | Minimum oxygen saturation values recorded intraoperatively to evaluate respiratory safety. |
| MAC Values During Maintenance (MAC Units) | Throughout surgery | MAC values recorded during anesthesia maintenance to assess depth and consistency of volatile agent effect. |
Countries
Turkey (Türkiye)
Outcome results
None listed