Minimal Flow Anesthesia and Infection Risk

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.

An intravenous hypnotic agent will be used for anesthesia induction at a dose of 2-3 mg/kg.

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).

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.

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.

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 will be administered intravenously at a dose of 2 mg/kg or 4 mg/kg, depending on the degree of neuromuscular blockade.

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).

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.

All participants received peripheral intravenous cannulation using 18-20 G IV cannulas placed on the dorsum of the hand before anesthesia induction.

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.

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.

Participants will receive calculated maintenance fluid therapy with crystalloids administered via intravenous infusion, both prior to and throughout the surgical procedure.

Following induction of anesthesia and establishment of neuromuscular blockade, endotracheal intubation will be performed using a standard technique in all participants.

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.

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.

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.

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.

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.

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.

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.