Minimal Flow AnesthesiaNCT07092046
Minimal Flow Anesthesia and Infection Risk
A study testing Sevoflurane (Volatile Anesthetic), Propofol 1% and Remifentanil 2 MG in people with Minimal Flow Anesthesia and General Anaesthesia, run by Ankara City Hospital Bilkent at 1 site in Turkey (Türkiye).
Trial summary
This study is being done to find out if the heat and moisture that build up during minimal flow anesthesia can lead to the growth of germs (microorganisms) inside the anesthesia equipment. Read more about this study
- Who is it for?
- Ages 18 to 65 yearsHealthy volunteers can take part
- Conditions the study is for
- Minimal Flow Anesthesia, General Anaesthesia, Inhalation Anesthesia
- What is being tested?
- Sevoflurane (Volatile Anesthetic), Propofol 1% and Remifentanil 2 MG
- Type of treatment
- Injection or infusion, Surgery or procedure
- Could I receive a placebo?
- No, everyone receives an active treatment
- How many people
- 140 participants
- Where
- 1 siteTurkey (Türkiye)
- Study dates
- 1 Aug 2025to 15 Apr 2026
- Phase
- Interventional
- Are there results?
- Yes, posted in the registrySummary in the doctors' view
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 to 65 years
- All sexes
- Healthy volunteers accepted
- Adult, Older adult
Who may be able to join
- A total of 140 voluntary patients will be included in the study.
- Patients will be aged between 18 and 65 years.
- Both male and female patients will be enrolled.
- All patients will be classified as c physical status I or II.
- Patients will undergo elective surgical procedures.
- The study will be conducted in the operating rooms of Ankara Bilkent City Hospital, affiliated with the Ministry of Health of the Republic of Türkiye.
- -
Who cannot join
- Patients who do not consent to participate
- Patients outside the age range of 18-65 years
- Patients classified as ASA (American Society of Anesthesiologists) III, IV, or V
- Patients scheduled for emergency surgery
- Patients with uncontrolled hypertension
- Patients with significant cardiac diseases (e.g., heart failure, coronary artery disease, arrhythmia, valvular heart disease)
Show all 31Show fewer
- Patients with significant pulmonary diseases (e.g., Chronic Obstructive Pulmonary Disease, Restrictive Pulmonary Disease, Asthma)
- Patients with neuromuscular disorders
- Patients with poorly controlled diabetes mellitus
- Patients with metabolic disorders
- Patients with immunodeficiency
- Patients with significant anemia
- Patients with bleeding diathesis
- Patients with liver and/or kidney diseases
- History of cardiac surgery
- History of intracranial surgery
- History of pulmonary surgery
- History of head and neck surgery
- Anticipated difficult airway or difficult intubation
- Patients with alcohol or drug dependence
- Pregnant or lactating women
- Known allergy to anesthetic agents
- Body mass index (BMI) > 30 kg/m²
- Presence of sepsis or active infection
- Baseline body temperature < 35°C or > 38°C
- Patients who have received antibiotics in the past month
- Patients with malignancies
- Withdrawal Criteria Patients who develop hemodynamic instability during the intraoperative period
- Patients requiring interruption of minimal flow anesthesia for more than 5 minutes
- Patients whose anesthesia circuit becomes disconnected intraoperatively
- -
Trial locations and contacts
1 site in 1 country.
About this study
Official title: How Safe is Minimal Flow Anesthesia in Terms of Infection?
This study is being done to find out if the heat and moisture that build up during minimal flow anesthesia can lead to the growth of germs (microorganisms) inside the anesthesia equipment. Minimal flow anesthesia (using fresh gas flow of 0.5 liters per minute or less) is known to help protect the lungs and the environment. However, it may also cause water to collect in the equipment, which could allow germs to grow. In this study, we want to see whether this type of anesthesia is safe when it comes to the risk of germs in the equipment.
Read the detailed description
Introduction Inhalation anesthesia is commonly administered using fresh gas flows between 2-6 L/min (liters per minute ). When this flow is reduced to 1 L/min, it is referred to as low-flow anesthesia, and when set at 0.5 L/min, it is known as minimal-flow anesthesia. The high-flow technique maintains a continuous supply of fresh gas within the system. However, since the patient inhales only a small portion of this gas, the majority is expelled into the anesthetic gas scavenging system. While this approach enables rapid adjustment of gas concentrations (O₂, anesthetic agents), the gases within the circuit remain cold and dry due to the removal of heat and humidity from the patient's lungs by soda lime. Additionally, a considerable amount of anesthetic gas is wasted.
In contrast, using fresh gas flows of ≤1 L/min decreases the amount of gas delivered from the vaporizers to the breathing circuit. This results in slower changes in gas concentrations but offers important advantages. Low-flow and minimal-flow anesthesia humidify and warm the inspired gases, which protect the patient's lungs. Compared to cold, dry gases, this improves mucociliary clearance, reduces damage to the respiratory epithelium, and lowers the release of inflammatory mediators. Low-flow anesthesia is a safe and effective practice that benefits patients and also provides economic and environmental advantages.
Minimal-flow anesthesia helps reduce heat loss through the respiratory tract and prevents the drying of mucosal surfaces, both of which are more common with higher flow rates. Additionally, it significantly decreases the amount of wasted fresh gas and inhaled anesthetic released into the atmosphere. Together, these effects may result in reduced airway inflammation and infection, lower environmental emissions, and cost savings.
Modern anesthesia machines support the safe delivery of low-flow anesthesia by utilizing closed breathing circuits that minimize leaks, manage humidity, ensure accurate gas delivery, and provide advanced monitoring and ventilator technologies.
Study Objective The primary objective of this study is to determine whether the increased humidity and temperature generated during minimal-flow anesthesia contribute to microbial colonization in the anesthesia circuit.
Methods A total of 140 patients undergoing elective surgical procedures will be included in this randomized, prospective, double-blind clinical trial. Eligible participants will be between 18 and 65 years of age, of either sex, and classified as ASA (American Society of Anesthesiologists) physical status I or II based on routine preoperative evaluation.
All participants will be informed about the study, including its objectives and potential risks, and written informed consent will be obtained. Patient demographics, including age, weight, ASA classification, and presence of chronic diseases, will be recorded prior to surgery. Randomization will be performed using the sealed envelope method.
Prior to each surgery, anesthesia circuits will undergo leak testing and gas monitor calibration. Disposable anesthesia circuits, bacterial filters, and masks will be used. The CO₂ absorbent (Sorbo-lime®, Berkim, Turkey) will be replaced daily. All anesthesia procedures will be performed using a GE Avance CS2 anesthesia machine. Standard intraoperative monitoring will include ECG (electrocardiogram ), non-invasive arterial blood pressure, SpO₂ (peripheral capillary oxygen saturation), respiratory rate, and ETCO₂ (End-tidal carbon dioxide). These parameters will be recorded at five-minute intervals. Body temperature monitoring will be added for study purposes.
Upon arrival in the operating room, nasopharyngeal swab samples will be collected under sterile conditions using dry sterile swabs (Dry SWAB) by trained personnel. All patients will undergo preoxygenation with 100% oxygen via face mask for three minutes at a fresh gas flow rate of 3 L/min during spontaneous ventilation. Anesthesia induction will be achieved using intravenous Lidocaine 1 mg/kg (milligrams per kilogram), Propofol 2 mg/kg, Fentanyl 1 mcg/kg (micrograms per kilogram), and Rocuronium 0.6-1 mg/kg, followed by endotracheal intubation.
Maintenance of anesthesia will be achieved using Sevoflurane to maintain MAC 1 (minimum alveolar concentration), along with a continuous Remifentanil infusion 0.02-0.2 mcg/kg/min (micrograms per kilogram per minute). Ventilator settings will include a tidal volume of 8 mL/kg (milliliters per kilogram), a respiratory rate of 12 breaths/min (minute), and an inspiratory-to-expiratory (I:E) ratio of 1:2. Anesthesia duration, vital parameters, body temperature, fresh gas flow settings, and ventilator settings will be recorded.
In both groups, fresh gas flow (O₂ 45%, Air 55%) will begin at 3 L/min. Once the MAC reaches 1, the flow rate will be reduced to 2 L/min in the normal-flow group and 0.5 L/min in the minimal-flow group. Ten minutes before the end of surgery, the fresh gas flow will be increased to 3 L/min in both groups, anesthetic agents will be discontinued, and 100% oxygen will be administered. Neuromuscular blockade will be reversed using Sugammadex 2-4 mg/kg, and patients will be extubated.
Swab samples will also be collected from the inspiratory and expiratory limbs of the disposable anesthesia circuits before connecting to the anesthesia machine and immediately after disconnection at the end of surgery-totaling four swabs per patient. All samples (nasopharyngeal and circuit swabs) will be labeled with the patient's name, date, site, and time of collection, then transported to the microbiology laboratory in a suitable transport medium at room temperature. Samples will be delivered to the laboratory within 15 minutes.
Microbiological analysis will be performed by inoculating the samples on 5% sheep blood agar using a dilution method. Incubation will be conducted at 35-37°C for 48 hours. Microbial growth will be assessed by a microbiologist, and species identification will be performed using an automated system (MALDI-TOF MS).
- Conditions
- Minimal Flow Anesthesia, General Anaesthesia, Inhalation Anesthesia, Infection Risk, Anesthesia Circuit, Microbial Colonization
- Being tested
- Sevoflurane (Volatile Anesthetic), Propofol 1%, Remifentanil 2 MG, Rocuronium 50 mg/5 ml, Lidocaine %2 ampoule
- Keywords
- minimal flow anesthesia, Anesthesia Circuit, Infection Risk, Microbial Colonization
- Medical subject headings
- Communicable Diseases
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Sevoflurane (Volatile Anesthetic)Drug
An inhalational anesthetic agent will be used for the maintenance of anesthesia, administered at a concentration of 2-3% in a gas mixture consisting of 40% oxygen and air.
Propofol 1%Drug
An intravenous hypnotic agent will be used for anesthesia induction at a dose of 2-3 mg/kg.
Remifentanil 2 MGDrug
A short-acting opioid will be administered intravenously for maintenance of anesthesia at a dose of 0.02-0.2 micrograms per kilogram per minute (μg/kg/min).
Rocuronium 50 mg/5 mlDrug
A neuromuscular blocking agent will be administered intravenously at a dose of 0.6-1.2 mg/kg for induction, and 0.15 mg/kg for maintenance of muscle relaxation during surgery.
Lidocaine %2 ampouleDrug
This agent will be administered intravenously at a dose of 1-1.5 mg/kg prior to anesthesia induction to reduce injection pain and facilitate smooth induction.
Ephedrine Hydrochloride 0,05 mg/ml ampouleDrug
This agent will be administered intravenously at a dose of 0.1 mg/kg to treat intraoperative hypotension that does not respond to fluid replacement or adjustment of anesthetic depth.
Sugammadex 200 MG in 2 ML InjectionDrug
Sugammadex will be administered intravenously at a dose of 2 mg/kg or 4 mg/kg, depending on the degree of neuromuscular blockade.
Fentanyl (IV)Drug
Fentanyl will be administered intravenously as part of the anesthesia induction regimen, at a dose ranging from 1 to 2 micrograms per kilogram (µg/kg).
Atropine Sulphate 0.5mg/ml ampouleDrug
In cases of intraoperative bradycardia, defined as a heart rate (HR) below 45 beats per minute (bpm), 0.5 mg of the agent will be administered intravenously.
Peripheral Intravenous CannulationProcedure or surgery
All participants received peripheral intravenous cannulation using 18-20 G IV cannulas placed on the dorsum of the hand before anesthesia induction.
Mechanical VentilationProcedure or surgery
Following endotracheal intubation, mechanical ventilation will be initiated using volume-controlled settings, with a tidal volume (TV) of 6-8 mL/kg, respiratory rate (RR) of 12 breaths per minute, and fraction of inspired oxygen (FiO₂) set at 50%. Ventilator parameters will be adjusted to maintain end-tidal carbon dioxide (ETCO₂) between 30 and 36 mmHg.
Peripheral Intravenous CannulationProcedure or surgery
All participants will undergo peripheral intravenous cannulation with 18-20 gauge (G) IV (intravenous) cannulas placed on the dorsum of the hand prior to anesthesia induction.
Crystalloid solutionsDrug
Participants will receive calculated maintenance fluid therapy with crystalloids administered via intravenous infusion, both prior to and throughout the surgical procedure.
Endotracheal IntubationProcedure or surgery
Following induction of anesthesia and establishment of neuromuscular blockade, endotracheal intubation will be performed using a standard technique in all participants.
American Society of Anesthesiologists (ASA) Standard MonitorsProcedure or surgery
Routine monitoring in accordance with American Society of Anesthesiologists (ASA) guidelines, including noninvasive blood pressure, electrocardiogram (ECG, D2 lead), end-tidal carbon dioxide (ETCO₂), and peripheral oxygen saturation (SpO₂), will be performed in all patients starting from the preoperative period and continuing throughout the surgery.
Minimal-Flow AnesthesiaProcedure or surgery
In the minimal-flow anesthesia group, after induction and once a minimum alveolar concentration (MAC) of 1 is achieved, the fresh gas flow will be reduced to 0.5 L/min with a mixture of 45% oxygen (O₂) and 55% air, and maintained throughout the surgical procedure. At the end of surgery, the flow will be increased to 3 L/min to facilitate emergence. Disposable anesthesia circuits, bacterial filters, and face masks will be used for each patient, and carbon dioxide (CO₂) absorbers will be replaced daily.
Normal-Flow AnesthesiaProcedure or surgery
In the normal-flow anesthesia group, after induction and once a minimum alveolar concentration (MAC) of 1 is achieved, the fresh gas flow will be adjusted to 2 L/min and maintained during the surgical procedure. For emergence, the flow will be increased to 3 L/min. Disposable anesthesia circuits will be used, and daily maintenance protocols, including replacement of carbon dioxide (CO₂) absorbers, will be applied in the same manner as in the minimal-flow group.
Anesthesia Circuit SamplingDiagnostic test
Sterile swab samples will be collected from both the inspiratory and expiratory limbs of the anesthesia circuit-once prior to circuit connection and again immediately after disconnection at the end of the surgical procedure. All samples will be processed for microbial culture and species-level identification.
Body Temperature MonitoringProcedure or surgery
In addition to routine monitoring-including electrocardiogram (ECG), non-invasive blood pressure, peripheral oxygen saturation (SpO₂), and end-tidal carbon dioxide (ETCO₂)-body temperature will be continuously monitored in both study groups throughout the surgical procedure using appropriate thermal sensors. Temperature measurements will be recorded at 5-minute intervals and used to assess the impact of different fresh gas flow rates on intraoperative thermoregulation.
Nasopharyngeal Swab CollectionDiagnostic test
A sterile nasopharyngeal swab (Dry SWAB) will be collected from each patient upon arrival in the operating room, prior to anesthesia induction. Each sample will be labeled with the patient's identification number, date, time, and collection site, and will be transferred in appropriate transport medium to the microbiology laboratory for culture and microbiological analysis.
Microbiological Culture and IdentificationDiagnostic test
All collected swab samples-including both nasopharyngeal and anesthesia circuit specimens-will be cultured using the serial dilution method on 5% sheep blood agar within 15 minutes of arrival at the microbiology laboratory. Cultures will be incubated at 35-37°C for 48 hours. Colony growth will be evaluated by a clinical microbiologist, and microorganisms will be identified to the species level using an automated MALDI-TOF MS (Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry) system.
| Study group | Role | What they receive |
|---|---|---|
| Minimal Flow Anesthesia (0.5 L/min) | Active comparator | Participants in this group will receive minimal-flow inhalation anesthesia, administered at a fresh gas flow rate of 0.5 L/min (Liters per minute). This technique helps preserve heat and humidity within the anesthesia circuit while reducing both anesthetic gas waste and environmental impact. The study aims to evaluate whether this lower flow rate contributes to circuit condensation and microbial colonization in the breathing system. Receives: Drug: Sevoflurane (Volatile Anesthetic); Drug: Propofol 1%; Drug: Remifentanil 2 MG; Drug: Rocuronium 50 mg/5 ml; Drug: Lidocaine %2 ampoule; Drug: Ephedrine Hydrochloride 0,05 mg/ml ampoule; Drug: Sugammadex 200 MG in 2 ML Injection; Drug: Fentanyl (IV); Drug: Atropine Sulphate 0.5mg/ml ampoule; Procedure: Peripheral Intravenous Cannulation; Procedure: Mechanical Ventilation; Drug: Crystalloid solutions; Procedure: Endotracheal Intubation; Procedure: American Society of Anesthesiologists (ASA) Standard Monitors; Procedure: Minimal-Flow Anesthesia; Diagnostic Test: Anesthesia Circuit Sampling; Procedure: Body Temperature Monitoring; Diagnostic Test: Nasopharyngeal Swab Collection; Diagnostic Test: Microbiological Culture and Identification |
| Standard Flow Anesthesia (2 L/min) | Active comparator | Participants in this group will receive inhalation anesthesia with a continuous fresh gas flow rate of 2 liters per minute (L/min) throughout the surgical procedure. This represents conventional-flow anesthesia, in which higher gas turnover allows for rapid adjustments in anesthetic concentrations but may lead to increased loss of heat and humidity within the breathing circuit. Receives: Drug: Sevoflurane (Volatile Anesthetic); Drug: Propofol 1%; Drug: Remifentanil 2 MG; Drug: Rocuronium 50 mg/5 ml; Drug: Lidocaine %2 ampoule; Drug: Ephedrine Hydrochloride 0,05 mg/ml ampoule; Drug: Sugammadex 200 MG in 2 ML Injection; Drug: Fentanyl (IV); Drug: Atropine Sulphate 0.5mg/ml ampoule; Procedure: Peripheral Intravenous Cannulation; Procedure: Mechanical Ventilation; Drug: Crystalloid solutions; Procedure: Endotracheal Intubation; Procedure: American Society of Anesthesiologists (ASA) Standard Monitors; Procedure: Normal-Flow Anesthesia; Diagnostic Test: Anesthesia Circuit Sampling; Procedure: Body Temperature Monitoring; Diagnostic Test: Nasopharyngeal Swab Collection; Diagnostic Test: Microbiological Culture and Identification |
What is being measured
The primary outcome is the main question the study is designed to answer.
Microbial Contamination of the Inspiratory Limb
Presence of microbial contamination in samples collected from the inspiratory limb of the anesthesia breathing circuit. Contamination was defined as microbiological growth identified by culture and MALDI-TOF MS analysis.
Measured: At the end of anesthesia (immediately after disconnection of the breathing circuit)
Microbial Contamination in the Expiratory Limb
Presence of microbial contamination in samples collected from the expiratory limb of the anesthesia breathing circuit. Contamination was defined as microbiological growth identified by culture and MALDI-TOF MS analysis.
Measured: At the end of anesthesia (immediately after disconnection of the breathing circuit)
Contamination in the Nasal Filter
Microbial contamination was defined as the isolation of any bacterial or fungal microorganism from cultures obtained from the nasal filter of the anesthesia breathing circuit at the end of surgery. Results are reported as the number and percentage of participants with positive cultures in each study group.
Measured: Assessed at the end of surgery following exposure during the intraoperative period
Secondary outcomes (4)
Heart Rate at Defined Perioperative Time Points (Bpm)
Heart rate (HR) will be measured non-invasively using standard monitoring equipment in accordance with American Society of Anesthesiologists (ASA) guidelines. Measurements will be recorded at 15-minute intervals, beginning 10 minutes prior to anesthesia induction and continuing until 45 minutes after the termination of anesthesia. The objective is to compare heart rate trends and perioperative variability between the two study groups: minimal-flow and normal-flow anesthesia.
Measured: From 10 minutes before induction to 45 minutes after anesthesia termination
Peripheral Oxygen Saturation (SpO₂) at Defined Perioperative Time Points (%)
Peripheral oxygen saturation (SpO₂) will be continuously monitored using pulse oximetry as part of standard monitoring in accordance with American Society of Anesthesiologists (ASA) guidelines. Measurements will be recorded at 15-minute intervals, beginning 10 minutes prior to anesthesia induction and continuing until 45 minutes after the termination of anesthesia. The objective is to compare heart rate trends and perioperative variability between the two study groups: minimal-flow and normal-flow anesthesia.
Measured: From 10 minutes before induction to 45 minutes after anesthesia termination
End-Tidal Carbon Dioxide (ETCO₂) Levels at Defined Perioperative Time Points (mmHg)
End-tidal carbon dioxide (ETCO₂) will be continuously measured via the ventilator as part of standard intraoperative monitoring. Measurements will be recorded at 15-minute intervals, beginning 10 minutes prior to anesthesia induction and continuing until 45 minutes after the termination of anesthesia. The objective is to compare heart rate trends and perioperative variability between the two study groups: minimal-flow and normal-flow anesthesia.
Measured: From 10 minutes before induction to 45 minutes after anesthesia termination
Mean Arterial Pressure at Defined Perioperative Time Points (mmHg)
Mean arterial pressure (MAP) will be measured non-invasively using standard monitoring equipment in accordance with American Society of Anesthesiologists (ASA) guidelines. Measurements will be recorded at 15-minute intervals, beginning 10 minutes prior to anesthesia induction and continuing until 45 minutes after the termination of anesthesia. The objective is to compare heart rate trends and perioperative variability between the two study groups: minimal-flow and normal-flow anesthesia.
Measured: From 10 minutes before induction to 45 minutes after anesthesia termination
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted29 Jul 2025
- Study start1 Aug 2025
- Primary completion1 Aug 2025
- Study completion15 Apr 2026
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Posted resultsParticipant flow, outcome measures and adverse events reported by the sponsor.
- Other trials for Minimal Flow AnesthesiaStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase N/A
- Primary purpose
- Other
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- Triple blind
- Who is masked
- Participant, Investigator, Outcomes assessor
- Enrolment
- 140 participants (actual)
Sponsor and investigators
- Lead sponsor
- Ankara City Hospital Bilkent
- Sponsor type
- University, hospital or other
- Responsible party
- Principal investigator, Aysun ERŞEN YÜNGÜL, Ankara City Hospital Bilkent
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07092046
- Sponsor's protocol ID
- EthicsApproval: E2-25-11471
- Status last verified
- Jul 2026
- First submitted
- 20 Jul 2025
- Last updated
- 5 Oct 2026
- Results posted
- Yes, on ClinicalTrials.gov
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- No
Study at a glance
From the registry record, last updated by the sponsor on 5 Oct 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- How Safe is Minimal Flow Anesthesia in Terms of Infection?
- ClinicalTrials.gov ID
- NCT07092046
- Acronym / sponsor ID
- EthicsApproval: E2-25-11471
- Conditions
- Minimal Flow Anesthesia, General Anaesthesia, Inhalation Anesthesia, Infection Risk, Anesthesia Circuit, Microbial Colonization
- Keywords
- minimal flow anesthesia, Anesthesia Circuit, Infection Risk, Microbial Colonization
- Study type
- Interventional
- Recruitment status
- Completed
- Enrolment
- 140 participants (actual)
- Lead sponsor
- Ankara City Hospital BilkentUniversity, hospital or other
- Study start
- 1 Aug 2025 (actual)
- Primary completion
- 1 Aug 2025 (actual)
- Study completion
- 15 Apr 2026 (actual)
- First posted
- 29 Jul 2025 (actual)
- Results
- Posted 5 Oct 2026
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
This study is being done to find out if the heat and moisture that build up during minimal flow anesthesia can lead to the growth of germs (microorganisms) inside the anesthesia equipment. Minimal flow anesthesia (using fresh gas flow of 0.5 liters per minute or less) is known to help protect the lungs and the environment. However, it may also cause water to collect in the equipment, which could allow germs to grow. In this study, we want to see whether this type of anesthesia is safe when it comes to the risk of germs in the equipment.
Detailed description
Introduction Inhalation anesthesia is commonly administered using fresh gas flows between 2-6 L/min (liters per minute ). When this flow is reduced to 1 L/min, it is referred to as low-flow anesthesia, and when set at 0.5 L/min, it is known as minimal-flow anesthesia. The high-flow technique maintains a continuous supply of fresh gas within the system. However, since the patient inhales only a small portion of this gas, the majority is expelled into the anesthetic gas scavenging system. While this approach enables rapid adjustment of gas concentrations (O₂, anesthetic agents), the gases within the circuit remain cold and dry due to the removal of heat and humidity from the patient's lungs by soda lime. Additionally, a considerable amount of anesthetic gas is wasted.
In contrast, using fresh gas flows of ≤1 L/min decreases the amount of gas delivered from the vaporizers to the breathing circuit. This results in slower changes in gas concentrations but offers important advantages. Low-flow and minimal-flow anesthesia humidify and warm the inspired gases, which protect the patient's lungs. Compared to cold, dry gases, this improves mucociliary clearance, reduces damage to the respiratory epithelium, and lowers the release of inflammatory mediators. Low-flow anesthesia is a safe and effective practice that benefits patients and also provides economic and environmental advantages.
Minimal-flow anesthesia helps reduce heat loss through the respiratory tract and prevents the drying of mucosal surfaces, both of which are more common with higher flow rates. Additionally, it significantly decreases the amount of wasted fresh gas and inhaled anesthetic released into the atmosphere. Together, these effects may result in reduced airway inflammation and infection, lower environmental emissions, and cost savings.
Modern anesthesia machines support the safe delivery of low-flow anesthesia by utilizing closed breathing circuits that minimize leaks, manage humidity, ensure accurate gas delivery, and provide advanced monitoring and ventilator technologies.
Study Objective The primary objective of this study is to determine whether the increased humidity and temperature generated during minimal-flow anesthesia contribute to microbial colonization in the anesthesia circuit.
Methods A total of 140 patients undergoing elective surgical procedures will be included in this randomized, prospective, double-blind clinical trial. Eligible participants will be between 18 and 65 years of age, of either sex, and classified as ASA (American Society of Anesthesiologists) physical status I or II based on routine preoperative evaluation.
All participants will be informed about the study, including its objectives and potential risks, and written informed consent will be obtained. Patient demographics, including age, weight, ASA classification, and presence of chronic diseases, will be recorded prior to surgery. Randomization will be performed using the sealed envelope method.
Prior to each surgery, anesthesia circuits will undergo leak testing and gas monitor calibration. Disposable anesthesia circuits, bacterial filters, and masks will be used. The CO₂ absorbent (Sorbo-lime®, Berkim, Turkey) will be replaced daily. All anesthesia procedures will be performed using a GE Avance CS2 anesthesia machine. Standard intraoperative monitoring will include ECG (electrocardiogram ), non-invasive arterial blood pressure, SpO₂ (peripheral capillary oxygen saturation), respiratory rate, and ETCO₂ (End-tidal carbon dioxide). These parameters will be recorded at five-minute intervals. Body temperature monitoring will be added for study purposes.
Upon arrival in the operating room, nasopharyngeal swab samples will be collected under sterile conditions using dry sterile swabs (Dry SWAB) by trained personnel. All patients will undergo preoxygenation with 100% oxygen via face mask for three minutes at a fresh gas flow rate of 3 L/min during spontaneous ventilation. Anesthesia induction will be achieved using intravenous Lidocaine 1 mg/kg (milligrams per kilogram), Propofol 2 mg/kg, Fentanyl 1 mcg/kg (micrograms per kilogram), and Rocuronium 0.6-1 mg/kg, followed by endotracheal intubation.
Maintenance of anesthesia will be achieved using Sevoflurane to maintain MAC 1 (minimum alveolar concentration), along with a continuous Remifentanil infusion 0.02-0.2 mcg/kg/min (micrograms per kilogram per minute). Ventilator settings will include a tidal volume of 8 mL/kg (milliliters per kilogram), a respiratory rate of 12 breaths/min (minute), and an inspiratory-to-expiratory (I:E) ratio of 1:2. Anesthesia duration, vital parameters, body temperature, fresh gas flow settings, and ventilator settings will be recorded.
In both groups, fresh gas flow (O₂ 45%, Air 55%) will begin at 3 L/min. Once the MAC reaches 1, the flow rate will be reduced to 2 L/min in the normal-flow group and 0.5 L/min in the minimal-flow group. Ten minutes before the end of surgery, the fresh gas flow will be increased to 3 L/min in both groups, anesthetic agents will be discontinued, and 100% oxygen will be administered. Neuromuscular blockade will be reversed using Sugammadex 2-4 mg/kg, and patients will be extubated.
Swab samples will also be collected from the inspiratory and expiratory limbs of the disposable anesthesia circuits before connecting to the anesthesia machine and immediately after disconnection at the end of surgery-totaling four swabs per patient. All samples (nasopharyngeal and circuit swabs) will be labeled with the patient's name, date, site, and time of collection, then transported to the microbiology laboratory in a suitable transport medium at room temperature. Samples will be delivered to the laboratory within 15 minutes.
Microbiological analysis will be performed by inoculating the samples on 5% sheep blood agar using a dilution method. Incubation will be conducted at 35-37°C for 48 hours. Microbial growth will be assessed by a microbiologist, and species identification will be performed using an automated system (MALDI-TOF MS).
Study design
- Primary purpose
- Other
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- Triple blind (participant, investigator, outcomes assessor)
- Number of arms
- 2
| Arm | Type | Receives |
|---|---|---|
| Minimal Flow Anesthesia (0.5 L/min) | Active comparator | Drug: Sevoflurane (Volatile Anesthetic), Drug: Propofol 1%, Drug: Remifentanil 2 MG, Drug: Rocuronium 50 mg/5 ml, Drug: Lidocaine %2 ampoule, Drug: Ephedrine Hydrochloride 0,05 mg/ml ampoule, Drug: Sugammadex 200 MG in 2 ML Injection, Drug: Fentanyl (IV), Drug: Atropine Sulphate 0.5mg/ml ampoule, Procedure: Peripheral Intravenous Cannulation, Procedure: Mechanical Ventilation, Drug: Crystalloid solutions, Procedure: Endotracheal Intubation, Procedure: American Society of Anesthesiologists (ASA) Standard Monitors, Procedure: Minimal-Flow Anesthesia, Diagnostic Test: Anesthesia Circuit Sampling, Procedure: Body Temperature Monitoring, Diagnostic Test: Nasopharyngeal Swab Collection, Diagnostic Test: Microbiological Culture and IdentificationParticipants in this group will receive minimal-flow inhalation anesthesia, administered at a fresh gas flow rate of 0.5 L/min (Liters per minute). This technique helps preserve heat and humidity within the anesthesia circuit while reducing both anesthetic gas waste and environmental impact. The study aims to evaluate whether this lower flow rate contributes to circuit condensation and microbial colonization in the breathing system. |
| Standard Flow Anesthesia (2 L/min) | Active comparator | Drug: Sevoflurane (Volatile Anesthetic), Drug: Propofol 1%, Drug: Remifentanil 2 MG, Drug: Rocuronium 50 mg/5 ml, Drug: Lidocaine %2 ampoule, Drug: Ephedrine Hydrochloride 0,05 mg/ml ampoule, Drug: Sugammadex 200 MG in 2 ML Injection, Drug: Fentanyl (IV), Drug: Atropine Sulphate 0.5mg/ml ampoule, Procedure: Peripheral Intravenous Cannulation, Procedure: Mechanical Ventilation, Drug: Crystalloid solutions, Procedure: Endotracheal Intubation, Procedure: American Society of Anesthesiologists (ASA) Standard Monitors, Procedure: Normal-Flow Anesthesia, Diagnostic Test: Anesthesia Circuit Sampling, Procedure: Body Temperature Monitoring, Diagnostic Test: Nasopharyngeal Swab Collection, Diagnostic Test: Microbiological Culture and IdentificationParticipants in this group will receive inhalation anesthesia with a continuous fresh gas flow rate of 2 liters per minute (L/min) throughout the surgical procedure. This represents conventional-flow anesthesia, in which higher gas turnover allows for rapid adjustments in anesthetic concentrations but may lead to increased loss of heat and humidity within the breathing circuit. |
Who may qualify
- Ages
- 18 to 65 years
- Sex
- All
- Healthy volunteers
- Accepted
- Age groups
- Adult, Older adult
Key inclusion criteria (7 listed)
- A total of 140 voluntary patients will be included in the study.
- Patients will be aged between 18 and 65 years.
- Both male and female patients will be enrolled.
- All patients will be classified as c physical status I or II.
- Patients will undergo elective surgical procedures.
Key exclusion criteria (31 listed)
- Patients who do not consent to participate
- Patients outside the age range of 18-65 years
- Patients classified as ASA (American Society of Anesthesiologists) III, IV, or V
- Patients scheduled for emergency surgery
- Patients with uncontrolled hypertension
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| Sevoflurane (Volatile Anesthetic)An inhalational anesthetic agent will be used for the maintenance of anesthesia, administered at a concentration of 2-3% in a gas mixture consisting of 40% oxygen and air. | Drug | Minimal Flow Anesthesia (0.5 L/min), Standard Flow Anesthesia (2 L/min) |
| Propofol 1%An intravenous hypnotic agent will be used for anesthesia induction at a dose of 2-3 mg/kg. | Drug | Minimal Flow Anesthesia (0.5 L/min), Standard Flow Anesthesia (2 L/min) |
| Remifentanil 2 MGA short-acting opioid will be administered intravenously for maintenance of anesthesia at a dose of 0.02-0.2 micrograms per kilogram per minute (μg/kg/min). | Drug | Minimal Flow Anesthesia (0.5 L/min), Standard Flow Anesthesia (2 L/min) |
| Rocuronium 50 mg/5 mlA neuromuscular blocking agent will be administered intravenously at a dose of 0.6-1.2 mg/kg for induction, and 0.15 mg/kg for maintenance of muscle relaxation during surgery. | Drug | Minimal Flow Anesthesia (0.5 L/min), Standard Flow Anesthesia (2 L/min) |
| Lidocaine %2 ampouleThis agent will be administered intravenously at a dose of 1-1.5 mg/kg prior to anesthesia induction to reduce injection pain and facilitate smooth induction. | Drug | Minimal Flow Anesthesia (0.5 L/min), Standard Flow Anesthesia (2 L/min) |
| Ephedrine Hydrochloride 0,05 mg/ml ampouleThis agent will be administered intravenously at a dose of 0.1 mg/kg to treat intraoperative hypotension that does not respond to fluid replacement or adjustment of anesthetic depth. | Drug | Minimal Flow Anesthesia (0.5 L/min), Standard Flow Anesthesia (2 L/min) |
| Sugammadex 200 MG in 2 ML InjectionSugammadex will be administered intravenously at a dose of 2 mg/kg or 4 mg/kg, depending on the degree of neuromuscular blockade. | Drug | Minimal Flow Anesthesia (0.5 L/min), Standard Flow Anesthesia (2 L/min) |
| Fentanyl (IV)Fentanyl will be administered intravenously as part of the anesthesia induction regimen, at a dose ranging from 1 to 2 micrograms per kilogram (µg/kg). | Drug | Minimal Flow Anesthesia (0.5 L/min), Standard Flow Anesthesia (2 L/min) |
| Atropine Sulphate 0.5mg/ml ampouleIn cases of intraoperative bradycardia, defined as a heart rate (HR) below 45 beats per minute (bpm), 0.5 mg of the agent will be administered intravenously. | Drug | Minimal Flow Anesthesia (0.5 L/min), Standard Flow Anesthesia (2 L/min) |
| Peripheral Intravenous CannulationAll participants received peripheral intravenous cannulation using 18-20 G IV cannulas placed on the dorsum of the hand before anesthesia induction. | Procedure or surgery | Minimal Flow Anesthesia (0.5 L/min), Standard Flow Anesthesia (2 L/min) |
| Mechanical VentilationFollowing endotracheal intubation, mechanical ventilation will be initiated using volume-controlled settings, with a tidal volume (TV) of 6-8 mL/kg, respiratory rate (RR) of 12 breaths per minute, and fraction of inspired oxygen (FiO₂) set at 50%. Ventilator parameters will be adjusted to maintain end-tidal carbon dioxide (ETCO₂) between 30 and 36 mmHg. | Procedure or surgery | Minimal Flow Anesthesia (0.5 L/min), Standard Flow Anesthesia (2 L/min) |
| Peripheral Intravenous CannulationAll participants will undergo peripheral intravenous cannulation with 18-20 gauge (G) IV (intravenous) cannulas placed on the dorsum of the hand prior to anesthesia induction. | Procedure or surgery | Minimal Flow Anesthesia (0.5 L/min), Standard Flow Anesthesia (2 L/min) |
| Crystalloid solutionsParticipants will receive calculated maintenance fluid therapy with crystalloids administered via intravenous infusion, both prior to and throughout the surgical procedure. | Drug | Minimal Flow Anesthesia (0.5 L/min), Standard Flow Anesthesia (2 L/min) |
| Endotracheal IntubationFollowing induction of anesthesia and establishment of neuromuscular blockade, endotracheal intubation will be performed using a standard technique in all participants. | Procedure or surgery | Minimal Flow Anesthesia (0.5 L/min), Standard Flow Anesthesia (2 L/min) |
| American Society of Anesthesiologists (ASA) Standard MonitorsRoutine monitoring in accordance with American Society of Anesthesiologists (ASA) guidelines, including noninvasive blood pressure, electrocardiogram (ECG, D2 lead), end-tidal carbon dioxide (ETCO₂), and peripheral oxygen saturation (SpO₂), will be performed in all patients starting from the preoperative period and continuing throughout the surgery. | Procedure or surgery | Minimal Flow Anesthesia (0.5 L/min), Standard Flow Anesthesia (2 L/min) |
| Minimal-Flow AnesthesiaIn the minimal-flow anesthesia group, after induction and once a minimum alveolar concentration (MAC) of 1 is achieved, the fresh gas flow will be reduced to 0.5 L/min with a mixture of 45% oxygen (O₂) and 55% air, and maintained throughout the surgical procedure. At the end of surgery, the flow will be increased to 3 L/min to facilitate emergence. Disposable anesthesia circuits, bacterial filters, and face masks will be used for each patient, and carbon dioxide (CO₂) absorbers will be replaced daily. | Procedure or surgery | Minimal Flow Anesthesia (0.5 L/min) |
| Normal-Flow AnesthesiaIn the normal-flow anesthesia group, after induction and once a minimum alveolar concentration (MAC) of 1 is achieved, the fresh gas flow will be adjusted to 2 L/min and maintained during the surgical procedure. For emergence, the flow will be increased to 3 L/min. Disposable anesthesia circuits will be used, and daily maintenance protocols, including replacement of carbon dioxide (CO₂) absorbers, will be applied in the same manner as in the minimal-flow group. | Procedure or surgery | Standard Flow Anesthesia (2 L/min) |
| Anesthesia Circuit SamplingSterile swab samples will be collected from both the inspiratory and expiratory limbs of the anesthesia circuit-once prior to circuit connection and again immediately after disconnection at the end of the surgical procedure. All samples will be processed for microbial culture and species-level identification. | Diagnostic test | Minimal Flow Anesthesia (0.5 L/min), Standard Flow Anesthesia (2 L/min) |
| Body Temperature MonitoringIn addition to routine monitoring-including electrocardiogram (ECG), non-invasive blood pressure, peripheral oxygen saturation (SpO₂), and end-tidal carbon dioxide (ETCO₂)-body temperature will be continuously monitored in both study groups throughout the surgical procedure using appropriate thermal sensors. Temperature measurements will be recorded at 5-minute intervals and used to assess the impact of different fresh gas flow rates on intraoperative thermoregulation. | Procedure or surgery | Minimal Flow Anesthesia (0.5 L/min), Standard Flow Anesthesia (2 L/min) |
| Nasopharyngeal Swab CollectionA sterile nasopharyngeal swab (Dry SWAB) will be collected from each patient upon arrival in the operating room, prior to anesthesia induction. Each sample will be labeled with the patient's identification number, date, time, and collection site, and will be transferred in appropriate transport medium to the microbiology laboratory for culture and microbiological analysis. | Diagnostic test | Minimal Flow Anesthesia (0.5 L/min), Standard Flow Anesthesia (2 L/min) |
| Microbiological Culture and IdentificationAll collected swab samples-including both nasopharyngeal and anesthesia circuit specimens-will be cultured using the serial dilution method on 5% sheep blood agar within 15 minutes of arrival at the microbiology laboratory. Cultures will be incubated at 35-37°C for 48 hours. Colony growth will be evaluated by a clinical microbiologist, and microorganisms will be identified to the species level using an automated MALDI-TOF MS (Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry) system. | Diagnostic test | Minimal Flow Anesthesia (0.5 L/min), Standard Flow Anesthesia (2 L/min) |
Primary outcome
Microbial Contamination of the Inspiratory Limb
Time frame: At the end of anesthesia (immediately after disconnection of the breathing circuit)
Presence of microbial contamination in samples collected from the inspiratory limb of the anesthesia breathing circuit. Contamination was defined as microbiological growth identified by culture and MALDI-TOF MS analysis.
Microbial Contamination in the Expiratory Limb
Time frame: At the end of anesthesia (immediately after disconnection of the breathing circuit)
Presence of microbial contamination in samples collected from the expiratory limb of the anesthesia breathing circuit. Contamination was defined as microbiological growth identified by culture and MALDI-TOF MS analysis.
Contamination in the Nasal Filter
Time frame: Assessed at the end of surgery following exposure during the intraoperative period
Microbial contamination was defined as the isolation of any bacterial or fungal microorganism from cultures obtained from the nasal filter of the anesthesia breathing circuit at the end of surgery. Results are reported as the number and percentage of participants with positive cultures in each study group.
4 secondary outcomes
Heart Rate at Defined Perioperative Time Points (Bpm)
Time frame: From 10 minutes before induction to 45 minutes after anesthesia termination
Peripheral Oxygen Saturation (SpO₂) at Defined Perioperative Time Points (%)
Time frame: From 10 minutes before induction to 45 minutes after anesthesia termination
End-Tidal Carbon Dioxide (ETCO₂) Levels at Defined Perioperative Time Points (mmHg)
Time frame: From 10 minutes before induction to 45 minutes after anesthesia termination
Mean Arterial Pressure at Defined Perioperative Time Points (mmHg)
Time frame: From 10 minutes before induction to 45 minutes after anesthesia termination
Results and safety
Loading the posted results from ClinicalTrials.gov…
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 5 Oct 2026.
- Posted resultsParticipant flow, baseline, all outcome measures and adverse events.
- Individual participant dataSharing planned: No
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.
The record lists no contact. Use the official record to reach the sponsor.
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A study testing Sevoflurane (Volatile Anesthetic), Propofol 1% and Remifentanil 2 MG in people with Minimal Flow Anesthesia and General Anaesthesia, run by Ankara City Hospital Bilkent at 1 site in Turkey (Türkiye).
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 7 inclusion and 31 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: finished, as of the sponsor's last update on 5 Oct 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in Turkey (Türkiye). Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
Yes. Results are posted in the registry (first posted 5 Oct 2026). A summary is in the For doctors view, and the full results are on ClinicalTrials.gov.
How can a doctor refer a patient or contact the research team?
The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Microbial Contamination of the Inspiratory Limb (time frame: At the end of anesthesia (immediately after disconnection of the breathing circuit)). The study lists 3 primary outcomes in all. It is what the study was designed to measure, not a finding.
Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 5 Oct 2026.