General anesthesia is an essential component of modern surgical practice, providing hypnosis, analgesia, amnesia, and optimal operating conditions while maintaining physiological stability throughout the perioperative period. Inhalational anesthetic agents such as sevoflurane and desflurane are commonly used for maintenance of general anesthesia because of their predictable pharmacokinetic characteristics, rapid adjustment of anesthetic depth, and relatively rapid emergence. The efficiency and physiological effects of inhalational anesthesia, however, are influenced not only by the choice of volatile agent but also by the fresh gas flow (FGF) delivered through the anesthesia breathing system. Traditionally, relatively high or conventional fresh gas flows have been used to facilitate rapid control of inspired anesthetic concentrations and reduce concerns regarding rebreathing. Improvements in anesthesia workstations, gas monitoring, carbon dioxide absorption systems, and volatile anesthetic delivery have made the routine use of substantially lower fresh gas flows increasingly feasible and safe [1]. Low-flow anesthesia generally refers to an anesthetic technique in which fresh gas flow is reduced sufficiently to permit substantial rebreathing of exhaled gases after carbon dioxide absorption. Although definitions vary among studies, flow rates around 1 L/min or less are frequently used during the maintenance phase, whereas conventional or high-flow techniques commonly use substantially higher flow rates [1,2]. Reducing fresh gas flow increases utilization of exhaled anesthetic gases that would otherwise be discarded through the scavenging system. Consequently, low-flow anesthesia decreases consumption of volatile anesthetic agents and medical gases, thereby reducing anesthetic expenditure and environmental release of greenhouse gases [2]. In addition, greater rebreathing allows better preservation of the temperature and humidity of inspired gases, which may reduce respiratory heat and moisture loss during prolonged anesthesia [1,3]. Despite these advantages, maintenance of patient safety remains the primary consideration when low-flow anesthesia is used. Inadequate fresh gas flow could theoretically increase the risk of hypoxic gas mixtures, carbon dioxide accumulation, delayed alteration of anesthetic concentrations, or accumulation of potentially undesirable compounds if appropriate monitoring and equipment are not available. Modern anesthesia machines equipped with continuous inspired oxygen, end-tidal carbon dioxide, volatile anesthetic concentration, airway pressure, and respiratory volume monitoring have substantially improved the safety of reduced-flow techniques [1]. Clinical studies have also demonstrated that low-flow anesthesia can provide cardiovascular and respiratory conditions comparable with conventional-flow techniques when carefully administered. Bilgi et al. reported that low-flow inhalational anesthesia was associated with better preservation of mucociliary activity and pulmonary function than high-flow anesthesia in patients receiving desflurane and nitrous oxide [3]. Doger et al., in a randomized study involving patients undergoing laparoscopic abdominal surgery, found no significant differences between low-flow and high-flow sevoflurane anesthesia in heart rate, mean arterial pressure, oxygen saturation, or end-tidal carbon dioxide values [4]. Hemodynamic stability is particularly important during general anesthesia because substantial changes in heart rate or arterial blood pressure can compromise tissue perfusion and increase perioperative risk. Concerns that reduced fresh gas flow might adversely affect anesthetic depth or cardiovascular stability have therefore been an important focus of clinical research. Park et al. compared minimal-flow with conventional high-flow desflurane anesthesia during prolonged laparoscopic procedures and found no clinically significant differences in hemodynamic or respiratory variables between the groups [5]. Similarly, Öterkuş et al. evaluated low-flow and high-flow anesthesia in obese patients undergoing laparoscopic sleeve gastrectomy and observed comparable heart rate, arterial blood pressure, peripheral oxygen saturation, end-tidal carbon dioxide, arterial blood gas parameters, and recovery characteristics [6]. These findings suggest that appropriately monitored low-flow anesthesia can maintain physiological stability even in patients undergoing procedures associated with considerable respiratory and cardiovascular alterations. The potential influence of fresh gas flow on postoperative recovery is another clinically relevant consideration. Rapid emergence, early restoration of protective airway reflexes, timely extubation, and achievement of adequate post-anesthesia recovery scores contribute to efficient operating-room turnover and may reduce the duration of post-anesthesia care. Recovery from inhalational anesthesia depends on several variables, including the solubility of the volatile anesthetic, duration of administration, anesthetic concentration, ventilation, patient characteristics, and concomitant medications. Because low-flow systems contain a larger reservoir of anesthetic gas, concerns have been raised regarding slower elimination of volatile agents toward the end of anesthesia. Nevertheless, clinical evidence has generally demonstrated satisfactory recovery profiles when low-flow techniques are appropriately managed. Prasad et al. found postoperative respiratory function after low-flow anesthesia to be comparable with that following high-flow anesthesia [7], while minimal-flow anesthesia with modern volatile agents has also been associated with acceptable postoperative recovery and stable physiological parameters [8]. Furthermore, optimization of the anesthetic regimen can influence recovery even when low fresh gas flows are used. Sert et al. demonstrated that low-flow sevoflurane anesthesia combined with remifentanil was associated with reduced sevoflurane consumption and faster early recovery compared with low-flow sevoflurane without remifentanil, while hemodynamic parameters remained comparable [9]. These findings indicate that low-flow anesthesia itself does not necessarily compromise emergence and that recovery may depend more strongly on anesthetic selection, concentration, adjunct medications, duration of surgery, and appropriate washout at the conclusion of anesthesia. Beyond individual patient outcomes, reducing unnecessary fresh gas flow has become increasingly relevant to environmentally responsible anesthesia practice. Volatile anesthetics released into the atmosphere contribute to the environmental footprint of surgical care, and reducing fresh gas flow is recognized as an effective means of decreasing anesthetic consumption and waste-gas emissions [10]. Nevertheless, environmental and economic benefits should not supersede clinical safety, and comparative assessment of intraoperative hemodynamics and postoperative recovery remains necessary before broader implementation across different surgical populations. Although previous investigations support the feasibility and safety of low-flow anesthesia, differences in patient populations, surgical procedures, anesthetic agents, flow-rate definitions, and recovery assessment methods have resulted in variability among published findings. Direct comparisons focused simultaneously on intraoperative hemodynamic stability and recovery characteristics remain clinically relevant. Therefore, the present study was undertaken to comparatively evaluate low-flow and conventional-flow anesthesia with respect to intraoperative hemodynamic stability and postoperative recovery, with the objective of determining whether reduced fresh gas flow can provide an effective and clinically safe alternative to conventional-flow anesthesia without adversely affecting perioperative patient outcomes.

Study Design and Setting This prospective, randomized, comparative study was conducted in the Department of Anaesthesiology, Government Medical College (GMC), Datia, Madhya Pradesh, India, over a period of three months March 2025 to May 2025. The study was designed to compare low-flow anesthesia with conventional-flow anesthesia with respect to intraoperative hemodynamic stability and postoperative recovery characteristics in adult patients undergoing elective surgical procedures under general anesthesia. Study Population A total of 60 patients scheduled for elective surgical procedures under general anesthesia were included in the study. Patients fulfilling the eligibility criteria were allocated in a 1:1 ratio into two groups of 30 patients each. Group LF: Low-flow anesthesia group (n = 30) Patients received maintenance anesthesia with a fresh gas flow of 1 L/min after completion of the initial wash-in period. Group CF: Conventional-flow anesthesia group (n = 30) Patients received maintenance anesthesia with a fresh gas flow of 3 L/min. Except for the fresh gas flow rate, the anesthetic technique, monitoring, ventilation strategy, anesthetic agent, analgesia, and recovery protocol were standardized between the two groups. Inclusion Criteria Patients aged 18–60 years, of either sex, belonging to American Society of Anesthesiologists physical status I or II, scheduled for elective surgery under general anesthesia with endotracheal intubation and an anticipated duration of anesthesia of at least 60 minutes were considered eligible for inclusion. Only patients who provided written informed consent were enrolled. Exclusion Criteria Patients were excluded if they had ASA physical status III or higher, significant cardiovascular or respiratory disease, severe hepatic or renal dysfunction, anticipated difficult airway, known hypersensitivity to any of the study medications, pregnancy or lactation, emergency surgery, requirement for postoperative mechanical ventilation, significant preoperative hemodynamic instability, or any condition considered by the attending anesthesiologist to interfere with the study protocol or assessment of recovery. Sample Size and Group Allocation The final sample comprised 60 patients, with 30 patients in each study group. Eligible participants were randomized in a 1:1 ratio using a computer-generated random allocation sequence. Group assignments were placed in sequentially numbered, opaque, sealed envelopes, which were opened immediately before induction of anesthesia by an anesthesiologist responsible for administering the study intervention. The investigator responsible for postoperative recovery assessment was kept unaware of group allocation wherever feasible. Preanesthetic Assessment All patients underwent a detailed preanesthetic evaluation before surgery. Demographic characteristics including age, sex, body weight, height, body mass index, ASA physical status, relevant medical history, current medications, and details of the planned surgical procedure were recorded. Routine laboratory investigations and other investigations were performed according to institutional practice and the clinical condition of the patient. Patients were instructed to comply with standard preoperative fasting recommendations. Appropriate premedication was administered according to the institutional anesthesia protocol. Intraoperative Monitoring After arrival in the operating room, standard monitoring was instituted and included continuous electrocardiography, non-invasive blood pressure measurement, pulse oximetry, capnography, inspired and expired oxygen concentrations, end-tidal carbon dioxide (EtCO₂), inspired and end-tidal volatile anesthetic concentration, airway pressure, tidal volume, respiratory rate, and minimum alveolar concentration where available. Baseline heart rate, systolic blood pressure, diastolic blood pressure, mean arterial pressure, and peripheral oxygen saturation were recorded before induction of anesthesia. Standardized Anesthetic Technique An intravenous line was secured and an appropriate crystalloid infusion was initiated. Patients were preoxygenated with 100% oxygen for approximately 3 minutes. General anesthesia was induced using intravenous propofol approximately 2 mg/kg and fentanyl 2 µg/kg. Neuromuscular blockade was achieved with rocuronium 0.6 mg/kg or an equipotent non-depolarizing neuromuscular blocking agent according to institutional availability. Following adequate neuromuscular blockade, direct laryngoscopy and endotracheal intubation were performed using an appropriately sized cuffed endotracheal tube. Correct tube placement was confirmed by bilateral chest expansion, auscultation, and continuous capnography. Anesthesia was maintained with sevoflurane in an oxygen-air mixture using a circle breathing system. The end-tidal concentration of sevoflurane was adjusted to maintain an appropriate age-adjusted anesthetic depth, approximately 0.8–1.2 minimum alveolar concentration, together with clinically acceptable hemodynamic parameters. Mechanical ventilation was standardized using a tidal volume of approximately 6–8 mL/kg predicted body weight, with respiratory rate adjusted to maintain EtCO₂ between 35 and 45 mmHg. Positive end-expiratory pressure of approximately 5 cm H₂O was applied unless clinically contraindicated. Fresh Gas Flow Protocol Immediately after induction and tracheal intubation, an initially higher fresh gas flow was used in both groups for approximately 10 minutes to achieve adequate denitrogenation and establishment of the desired anesthetic concentration. Thereafter, fresh gas flow was adjusted according to group allocation. In Group LF, total fresh gas flow was reduced to 1 L/min during the maintenance phase. In Group CF, total fresh gas flow was maintained at 3 L/min during the maintenance phase. The oxygen concentration was adjusted as necessary to maintain adequate inspired oxygen concentration and peripheral oxygen saturation. Continuous monitoring of FiO₂, EtCO₂, inspired and expired sevoflurane concentration, airway pressures, and oxygen saturation was performed throughout anesthesia. Low-flow sevoflurane protocols using approximately 1 L/min after an initial higher-flow period have been evaluated in previous clinical studies. Assessment of Hemodynamic Parameters The principal intraoperative variables recorded were: heart rate, systolic blood pressure, diastolic blood pressure, mean arterial pressure, peripheral oxygen saturation, and end-tidal carbon dioxide. Measurements were documented at the following predefined time points: before induction as baseline, immediately after induction, immediately after tracheal intubation, and at 5, 10, 15, 30, 45, 60, 90 minutes, and thereafter at 30-minute intervals when applicable, as well as at the completion of surgery. Hemodynamic stability was evaluated according to changes in heart rate and mean arterial pressure relative to baseline values. The frequency of clinically relevant hypotension, hypertension, bradycardia, and tachycardia and any intervention required for their management were also recorded. Hypotension was operationally defined as a reduction in mean arterial pressure of more than 20% from the preoperative baseline or an absolute MAP below 65 mmHg. Bradycardia was defined as a heart rate below 50 beats/min. These events were treated according to standard institutional protocols and all rescue interventions were documented. Study Outcomes The primary outcome was the difference in intraoperative hemodynamic stability between low-flow and conventional-flow anesthesia, assessed primarily through serial heart rate and mean arterial pressure measurements and the incidence of clinically significant hemodynamic disturbances. The secondary outcomes included time to eye opening, time to response to verbal commands, time to extubation, Modified Aldrete Score, time required to achieve an Aldrete Score ≥9, intraoperative SpO₂ and EtCO₂ trends, and the occurrence of anesthesia-related adverse events. Safety Assessment All patients were continuously observed for hypoxemia, hypercapnia, hypotension, hypertension, bradycardia, tachycardia, bronchospasm, excessive airway pressure, delayed emergence, postoperative nausea and vomiting, or any other anesthesia-related adverse event. If patient safety required deviation from the assigned fresh gas flow, appropriate corrective measures were immediately undertaken and the event was recorded. Statistical Analysis Data were entered into Microsoft Excel and subsequently analyzed using IBM SPSS Statistics, version 26. Continuous variables were assessed for distributional normality using the Shapiro-Wilk test and graphical inspection. Normally distributed continuous variables were expressed as mean ± standard deviation and compared between groups using the independent-samples Student's t test. Non-normally distributed variables were presented as median with interquartile range and compared using the Mann-Whitney U test.

A total of 60 patients undergoing elective surgery under general anesthesia were included in the study and randomized equally into the low-flow anesthesia group (Group LF, n = 30) and conventional-flow anesthesia group (Group CF, n = 30). All enrolled patients completed the study protocol and were included in the final analysis. No patient required withdrawal because of severe intraoperative complications or failure of the assigned fresh gas flow technique. The two groups were comparable with respect to age, sex distribution, body mass index, ASA physical status, duration of surgery, and duration of anesthesia. None of the baseline differences reached statistical significance, indicating satisfactory comparability between the groups before evaluation of the study outcomes. Table 1. Baseline demographic and perioperative characteristics of the study groups Variable Group LF (n = 30) Group CF (n = 30) P value Age, years 39.7 ± 10.8 40.3 ± 11.2 0.833 Male sex, n (%) 17 (56.7) 16 (53.3) 0.795 Female sex, n (%) 13 (43.3) 14 (46.7) BMI, kg/m² 23.9 ± 2.7 24.1 ± 2.8 0.779 ASA physical status I, n (%) 19 (63.3) 18 (60.0) 0.791 ASA physical status II, n (%) 11 (36.7) 12 (40.0) Duration of surgery, min 96.3 ± 20.7 94.8 ± 22.1 0.787 Duration of anesthesia, min 112.5 ± 22.4 110.2 ± 23.6 0.700 Heart rate showed the expected peri-induction variation in both groups. A modest reduction was observed after induction, followed by a transient increase after endotracheal intubation. Thereafter, heart rate gradually returned toward baseline and remained stable throughout the maintenance period. No statistically significant differences in heart rate were observed between Group LF and Group CF at any individual measurement point. Repeated-measures analysis demonstrated a significant effect of time (P < 0.001), reflecting the physiological response to induction and intubation, but no significant overall group effect (P = 0.821) or group-by-time interaction (P = 0.967). Table 2. Comparison of intraoperative heart rate between low-flow and conventional-flow anesthesia Time point Group LF, beats/min Group CF, beats/min P value Baseline 78.4 ± 9.2 77.9 ± 8.8 0.831 After induction 74.6 ± 8.6 75.1 ± 8.4 0.820 After intubation 87.2 ± 10.1 86.6 ± 9.7 0.815 5 min 80.8 ± 8.9 81.3 ± 9.0 0.829 15 min 77.6 ± 8.3 78.1 ± 8.5 0.819 30 min 75.8 ± 8.1 76.4 ± 8.2 0.777 45 min 75.2 ± 7.9 75.7 ± 8.0 0.809 60 min 74.9 ± 7.8 75.4 ± 8.1 0.808 90 min 75.0 ± 7.7 75.8 ± 8.0 0.695 End of surgery 76.1 ± 8.0 76.8 ± 8.1 0.738 Values are mean ± standard deviation. Repeated-measures analysis: time effect, P < 0.001; group effect, P = 0.821; group × time interaction, P = 0.967. Mean arterial pressure decreased moderately after induction in both groups, increased transiently following tracheal intubation, and subsequently remained within clinically acceptable limits. No significant differences were detected between the two groups at any recorded interval. The change in MAP over time was statistically significant (P < 0.001); however, there was no significant overall effect attributable to fresh gas flow group (P = 0.742) and no significant group-by-time interaction (P = 0.948). Table 3. Comparison of intraoperative mean arterial pressure between the two study groups Time point Group LF, mmHg Group CF, mmHg P value Baseline 91.8 ± 8.4 92.1 ± 8.1 0.888 After induction 82.6 ± 7.8 83.0 ± 7.9 0.845 After intubation 96.4 ± 9.1 97.1 ± 9.0 0.765 5 min 89.2 ± 8.0 89.8 ± 8.2 0.775 15 min 86.8 ± 7.5 87.2 ± 7.7 0.839 30 min 85.9 ± 7.3 86.4 ± 7.5 0.794 45 min 85.3 ± 7.2 85.8 ± 7.4 0.792 60 min 84.9 ± 7.1 85.6 ± 7.5 0.712 90 min 84.7 ± 7.0 85.4 ± 7.2 0.704 End of surgery 87.2 ± 7.4 87.9 ± 7.6 0.719 Values are mean ± standard deviation. Repeated-measures analysis: time effect, P < 0.001; group effect, P = 0.742; group × time interaction, P = 0.948. Peripheral oxygen saturation remained consistently above 98% in both groups throughout anesthesia. No episode of clinically significant intraoperative hypoxemia was observed. End-tidal carbon dioxide showed a mild progressive increase following initiation of controlled ventilation but remained within the predefined target range of 35–45 mmHg. There was no significant difference in EtCO₂ between the groups at any recorded interval. Table 4. Comparison of intraoperative oxygenation and end-tidal carbon dioxide Parameter/time Group LF Group CF P value SpO₂ (%) Baseline 99.1 ± 0.8 99.0 ± 0.9 0.651 15 min 99.0 ± 0.7 99.0 ± 0.8 1.000 30 min 98.9 ± 0.8 98.9 ± 0.8 1.000 60 min 98.8 ± 0.8 98.9 ± 0.7 0.608 90 min 98.8 ± 0.9 98.8 ± 0.8 1.000 End of surgery 99.0 ± 0.8 99.0 ± 0.7 1.000 EtCO₂ (mmHg) 5 min 36.2 ± 2.3 36.0 ± 2.2 0.731 15 min 36.8 ± 2.4 36.6 ± 2.3 0.743 30 min 37.2 ± 2.5 37.0 ± 2.4 0.753 60 min 37.6 ± 2.6 37.4 ± 2.5 0.762 90 min 37.8 ± 2.5 37.6 ± 2.6 0.762 End of surgery 37.1 ± 2.4 37.0 ± 2.4 0.872 SpO₂: peripheral oxygen saturation; EtCO₂: end-tidal carbon dioxide. Values are mean ± standard deviation. No significant group-by-time interaction was identified for either SpO₂ or EtCO₂. Recovery characteristics were satisfactory in both groups. Patients receiving low-flow anesthesia showed numerically shorter times to eye opening, response to verbal commands, tracheal extubation, and achievement of a Modified Aldrete Score ≥9; however, none of these differences reached statistical significance. The mean time to eye opening was 8.6 ± 2.0 minutes in Group LF compared with 9.1 ± 2.2 minutes in Group CF (P = 0.361). Similarly, mean extubation time was 10.7 ± 2.2 minutes versus 11.3 ± 2.3 minutes, respectively (P = 0.306). Table 5. Comparison of postoperative recovery characteristics Recovery parameter Group LF (n = 30) Group CF (n = 30) P value Time to spontaneous eye opening, min 8.6 ± 2.0 9.1 ± 2.2 0.361 Time to response to verbal command, min 9.4 ± 2.1 9.9 ± 2.2 0.371 Time to extubation, min 10.7 ± 2.2 11.3 ± 2.3 0.306 Time to Modified Aldrete Score ≥9, min 14.8 ± 2.8 15.6 ± 3.0 0.290 PACU duration, min 39.3 ± 6.0 41.1 ± 6.4 0.265 Aldrete score on PACU arrival 7.3 ± 0.9 7.2 ± 0.8 0.650 Aldrete score at 5 min 8.1 ± 0.8 8.0 ± 0.8 0.630 Aldrete score at 10 min 8.8 ± 0.7 8.6 ± 0.8 0.305 Aldrete score at 15 min 9.4 ± 0.6 9.2 ± 0.7 0.239 Aldrete score at 30 min 9.9 ± 0.3 9.8 ± 0.4 0.278 At 10 minutes after arrival in the PACU, an Aldrete score ≥9 was achieved by 18 patients (60.0%) in Group LF and 15 patients (50.0%) in Group CF. By 15 minutes, the corresponding proportions increased to 27 patients (90.0%) and 25 patients (83.3%), respectively. All patients in both groups achieved an Aldrete score ≥9 by 30 minutes. The incidence of intraoperative hemodynamic disturbances was low in both groups. Hypotension occurred in 3 patients (10.0%) in Group LF and 4 patients (13.3%) in Group CF. Bradycardia was observed in 2 patients (6.7%) and 1 patient (3.3%), respectively. None of these differences was statistically significant. No patient developed significant hypoxemia, clinically important hypercapnia, bronchospasm, or delayed emergence. Postoperative nausea and vomiting occurred in 3 patients (10.0%) in Group LF compared with 4 patients (13.3%) in Group CF. Table 6. Comparison of intraoperative hemodynamic events and postoperative adverse outcomes Event Group LF n (%) Group CF n (%) P value Hypotension 3 (10.0) 4 (13.3) 1.000 Hypertension 2 (6.7) 3 (10.0) 1.000 Bradycardia 2 (6.7) 1 (3.3) 1.000 Tachycardia 3 (10.0) 4 (13.3) 1.000 Vasopressor requirement 2 (6.7) 3 (10.0) 1.000 Clinically significant hypoxemia 0 (0.0) 0 (0.0) — Significant hypercapnia 0 (0.0) 0 (0.0) — Bronchospasm 0 (0.0) 0 (0.0) — Postoperative nausea/vomiting 3 (10.0) 4 (13.3) 1.000 Delayed emergence 0 (0.0) 0 (0.0) — The principal finding of the study was that low-flow anesthesia maintained intraoperative hemodynamic stability comparable to conventional-flow anesthesia. Heart rate, mean arterial pressure, peripheral oxygen saturation, and end-tidal carbon dioxide remained within clinically acceptable ranges throughout anesthesia, without significant differences between groups. Low-flow anesthesia was also associated with a postoperative recovery profile comparable to conventional-flow anesthesia. Although eye-opening time, response to verbal commands, extubation time, achievement of an Aldrete score ≥9, and PACU duration were numerically shorter in the low-flow group, the differences did not reach statistical significance. Importantly, reducing the maintenance fresh gas flow to 1 L/min was not associated with an increased incidence of intraoperative hemodynamic disturbances, hypoxemia, hypercapnia, delayed emergence, or other clinically important adverse events. Figure 1 illustrates serial changes in mean intraoperative heart rate among patients receiving low-flow and conventional-flow anesthesia. In both groups, heart rate decreased after induction, increased transiently following endotracheal intubation, and subsequently declined toward baseline during maintenance of anesthesia. The trends remained closely comparable throughout the intraoperative period, with no significant overall difference between the groups or group-by-time interaction (P = 0.967). These findings indicate that low-flow anesthesia maintained heart rate stability comparable to conventional-flow anesthesia. Figure 2 compares postoperative recovery times between patients receiving low-flow and conventional-flow anesthesia. Patients in the low-flow group showed slightly shorter mean times to spontaneous eye opening, response to verbal commands, tracheal extubation, and achievement of a Modified Aldrete Score ≥9. However, the differences between the two groups were not statistically significant. These findings indicate that low-flow anesthesia provided a recovery profile comparable to conventional-flow anesthesia and did not delay early postoperative recovery. Figure 3 demonstrates the progressive improvement in Modified Aldrete Scores during postoperative recovery in the PACU. Both groups showed a steady rise in recovery scores from arrival through 30 minutes. The low-flow group had slightly higher mean Aldrete Scores at each assessment point, reaching 9.4 at 15 minutes and 9.9 at 30 minutes, compared with 9.2 and 9.8, respectively, in the conventional-flow group. Overall, the recovery pattern was comparable between groups, indicating that low-flow anesthesia did not delay early postoperative recovery.

The present prospective comparative study evaluated the effects of low-flow anesthesia and conventional-flow anesthesia on intraoperative hemodynamic stability and postoperative recovery in 60 patients undergoing elective surgery under general anesthesia. The principal finding was that reducing the fresh gas flow to 1 L/min during the maintenance phase did not adversely affect intraoperative cardiovascular or respiratory stability. Heart rate, mean arterial pressure, peripheral oxygen saturation, and end-tidal carbon dioxide remained within clinically acceptable limits in both groups. In addition, postoperative recovery characteristics, including time to eye opening, response to verbal commands, tracheal extubation, Modified Aldrete Score, and duration of stay in the post-anesthesia care unit, were comparable between the two groups. These findings support the clinical feasibility of low-flow anesthesia when administered using a modern circle breathing system with appropriate monitoring. The demographic and perioperative characteristics of the two study groups were comparable. There were no statistically significant differences in age, sex, body mass index, ASA physical status, duration of surgery, or duration of anesthesia. This baseline comparability is important because patient age, physical status, body composition, duration of anesthesia, and surgical duration can independently affect cardiovascular responses and recovery from general anesthesia. Therefore, the differences observed during the intraoperative and postoperative periods were unlikely to have resulted from major baseline imbalance between the groups. One of the primary concerns regarding low-flow anesthesia is whether reduction in fresh gas flow may cause variations in delivered volatile anesthetic concentration and consequently compromise cardiovascular stability. In the present study, heart rate showed an expected reduction following induction and a transient increase after tracheal intubation in both groups. Thereafter, heart rate remained relatively stable throughout the maintenance period. There was no significant overall difference between the low-flow and conventional-flow groups and no significant group-by-time interaction. Chatrath et al. similarly reported satisfactory hemodynamic stability during low-flow sevoflurane anesthesia and demonstrated that low-flow techniques could provide adequate anesthetic conditions when volatile anesthetic concentrations were carefully monitored [11]. The present findings are also supported by Negargar et al., who compared low-flow sevoflurane and low-flow isoflurane anesthesia and evaluated heart rate and arterial blood pressure at different intraoperative intervals. Although some differences were observed at individual time points, the cardiovascular parameters remained within acceptable clinical limits [12]. This is consistent with the present study, in which minor changes in heart rate occurred during different phases of anesthesia but did not translate into clinically significant instability. Mean arterial pressure followed a similar pattern in both study groups. MAP decreased following induction, increased transiently after tracheal intubation, and subsequently stabilized during maintenance. The significant effect of time most likely reflected the expected physiological responses to induction, airway manipulation, and surgical stimulation. However, there was no significant overall group effect or group-by-time interaction. Thus, reducing fresh gas flow to 1 L/min did not increase the risk of clinically relevant arterial pressure instability compared with conventional-flow anesthesia. Elmacioglu et al. investigated the effect of different fresh gas flow rates during volatile anesthesia and observed that low fresh gas flow could be used without clinically significant deterioration in hemodynamic variables [13]. Their study additionally demonstrated reduced volatile anesthetic consumption at lower fresh gas flow rates [13]. Although desflurane was evaluated in their investigation, the findings support the broader principle that reduction in fresh gas flow itself does not necessarily compromise cardiovascular stability when anesthetic depth, oxygen concentration, and ventilation are adequately monitored. Respiratory safety is another important concern during low-flow anesthesia because increased rebreathing could theoretically lead to accumulation of carbon dioxide or inadequate inspired oxygen concentration. In the present study, peripheral oxygen saturation remained approximately 99% throughout anesthesia in both groups, and no patient developed clinically significant hypoxemia. End-tidal carbon dioxide also remained within the predefined target range of 35–45 mmHg, with no significant difference between the two groups. These results suggest that low-flow anesthesia at 1 L/min can maintain satisfactory oxygenation and ventilation when used with controlled mechanical ventilation, an efficient carbon dioxide absorber, continuous monitoring of inspired oxygen, capnography, and modern anesthesia equipment. Simsek et al. evaluated different flow strategies during sevoflurane anesthesia and subsequently maintained anesthesia using very low fresh gas flow. They demonstrated that reduced-flow anesthesia could be administered efficiently while substantially decreasing sevoflurane consumption [14]. Similarly, Joshiraj et al. evaluated an over-pressure wash-in technique using a fresh gas flow of 0.5 L/min and reported that the technique was feasible and safe while reducing oxygen, air, and sevoflurane consumption [15]. Postoperative recovery was another important outcome evaluated in the present study. The mean time to spontaneous eye opening was 8.6 ± 2.0 minutes in the low-flow group compared with 9.1 ± 2.2 minutes in the conventional-flow group. Time to response to verbal commands and tracheal extubation was also numerically shorter in patients receiving low-flow anesthesia. However, none of these differences reached statistical significance. These findings demonstrate that low-flow sevoflurane anesthesia did not delay emergence from anesthesia. This observation is clinically important because one theoretical concern regarding reduced fresh gas flow is that greater retention of anesthetic gas within the breathing circuit might prolong elimination of the volatile agent at the end of surgery. In the present study, fresh gas flow was increased after discontinuation of sevoflurane, facilitating washout of the volatile anesthetic from the breathing system and lungs. Chatrath et al. reported satisfactory recovery following low-flow sevoflurane anesthesia, with sevoflurane producing faster recovery compared with low-flow isoflurane anesthesia [11]. The relatively low blood-gas solubility of sevoflurane contributes to its rapid elimination after discontinuation and may explain why the low-flow technique did not adversely influence recovery in the present investigation. The Modified Aldrete Score was used to provide a more comprehensive assessment of postoperative recovery. In the present study, the mean Aldrete Score increased progressively in both groups following admission to the PACU. At 10 minutes, 60.0% of patients in the low-flow group and 50.0% in the conventional-flow group had achieved an Aldrete Score of at least 9. By 15 minutes, the corresponding proportions were 90.0% and 83.3%, respectively. All patients in both groups achieved an Aldrete Score ≥9 within 30 minutes. Although the low-flow group demonstrated numerically more rapid achievement of satisfactory recovery criteria, the difference was not statistically significant. Therefore, the results should be interpreted as demonstrating comparable recovery, rather than superiority of low-flow anesthesia. Lebanidze and Peshkov evaluated recovery following low-flow anesthesia in elderly patients and reported favorable postoperative recovery characteristics compared with higher-flow anesthesia [16]. Differences between their observations and the absence of a statistically significant recovery advantage in the present study may be related to variation in patient age, surgical procedures, duration of anesthesia, volatile anesthetic concentrations, and definitions of postoperative recovery. Nevertheless, both studies support the conclusion that appropriately administered low-flow anesthesia does not prolong postoperative recovery. The frequency of intraoperative hemodynamic disturbances and postoperative complications was low in both groups in the present study. Hypotension occurred in 10.0% of patients in the low-flow group and 13.3% of patients in the conventional-flow group. Bradycardia occurred in 6.7% and 3.3% of patients, respectively. No statistically significant differences were observed in hypotension, hypertension, bradycardia, tachycardia, or vasopressor requirement. Postoperative nausea and vomiting occurred in 10.0% of patients receiving low-flow anesthesia and 13.3% receiving conventional-flow anesthesia. Importantly, there were no episodes of clinically significant hypoxemia, significant hypercapnia, bronchospasm, or delayed emergence in either group. These findings further indicate that reduction in fresh gas flow to 1 L/min did not result in an increased incidence of clinically significant perioperative adverse events. Safety concerns regarding prolonged exposure to low-flow sevoflurane have historically included the possibility of degradation products and potential renal effects. Kharasch et al. evaluated prolonged low-flow sevoflurane and isoflurane anesthesia and found no clinically significant postoperative deterioration in renal or hepatic function attributable to low-flow sevoflurane administration [19]. Although renal and hepatic biochemical parameters were not specifically assessed in the present study, these previous findings provide supportive evidence regarding the safety of appropriately monitored low-flow sevoflurane anesthesia [19]. Another important advantage of low-flow anesthesia is the potential reduction in volatile anesthetic consumption. Although anesthetic consumption was not directly quantified in the present investigation and therefore cannot be considered an outcome of this study, substantial evidence indicates that volatile anesthetic utilization decreases as fresh gas flow is reduced. Ekbom et al. demonstrated that the amount of sevoflurane vaporized during anesthesia was strongly influenced by fresh gas flow and that increasing the flow resulted in greater anesthetic consumption [17]. Ryu et al. similarly demonstrated that implementation of a low fresh gas flow strategy substantially reduced sevoflurane consumption and increased the number of anesthesia hours obtainable from each bottle of sevoflurane [18]. These findings highlight an important potential economic advantage of low-flow anesthesia. The reduction in anesthetic consumption associated with lower fresh gas flows also has broader environmental implications because volatile anesthetic agents released through scavenging systems ultimately enter the atmosphere. Although environmental emissions were not directly measured in the present study, reducing unnecessary volatile anesthetic consumption represents an additional potential advantage of low-flow anesthesia. However, such economic and environmental considerations should only be pursued when patient safety and adequate anesthetic depth can be ensured. Several strengths of the present study deserve consideration. Both groups were managed using a standardized general anesthetic protocol, with fresh gas flow being the principal difference between the groups. Serial measurements of heart rate and mean arterial pressure allowed evaluation of the entire intraoperative hemodynamic pattern rather than isolated measurements. Respiratory variables, including SpO₂ and EtCO₂, were also evaluated at multiple time points. Furthermore, postoperative recovery was assessed using both objective recovery times and the Modified Aldrete Score. Nevertheless, the study has certain limitations. First, the sample size was relatively small, with only 30 patients in each group, which may have limited the ability to identify small differences or uncommon adverse events. Second, this was a single-center study and therefore the findings may not be generalizable to all patient populations and healthcare settings. Third, the study primarily included ASA physical status I and II patients; therefore, the safety of low-flow anesthesia in patients with significant cardiovascular, respiratory, renal, or hepatic comorbidities requires further evaluation. Another limitation was that volatile anesthetic consumption was not directly quantified. Inclusion of anesthetic consumption would have allowed assessment of the economic efficiency of the low-flow technique. Similarly, carbon dioxide absorbent consumption and environmental impact were not studied. Postoperative assessment was predominantly limited to early recovery, and longer-term pulmonary, renal, hepatic, or neurocognitive outcomes were not evaluated. Larger multicenter randomized studies are therefore warranted to confirm these findings in different surgical populations and higher-risk patients. Future studies should incorporate objective measurement of volatile anesthetic consumption, carbon dioxide absorbent use, cost-effectiveness, and environmental impact. Comparison of different low-flow and minimal-flow thresholds may also help determine the optimal fresh gas flow that provides the greatest economic and environmental advantages without compromising clinical safety. Overall, the present study demonstrates that low-flow sevoflurane anesthesia at a maintenance fresh gas flow of 1 L/min provides intraoperative hemodynamic and respiratory stability comparable to conventional-flow anesthesia. Heart rate, mean arterial pressure, oxygen saturation, and end-tidal carbon dioxide remained within clinically acceptable ranges in both groups. Low-flow anesthesia did not significantly prolong eye opening, response to verbal commands, tracheal extubation, achievement of a Modified Aldrete Score ≥9, or PACU stay. Furthermore, no increase in clinically significant perioperative adverse events was observed. These findings support low-flow anesthesia as a feasible and clinically safe alternative to conventional-flow anesthesia in appropriately selected patients when modern anesthesia equipment and continuous monitoring are available.

Low-flow anesthesia using a fresh gas flow of 1 L/min provided intraoperative hemodynamic and respiratory stability comparable to conventional-flow anesthesia in patients undergoing elective surgery under general anesthesia. Heart rate, mean arterial pressure, oxygen saturation, and end-tidal carbon dioxide remained within clinically acceptable limits in both groups, with no significant differences in overall trends. Postoperative recovery was also comparable between the two techniques. Patients receiving low-flow anesthesia showed slightly shorter times to eye opening, response to verbal commands, extubation, and achievement of a Modified Aldrete Score ≥9; however, these differences were not statistically significant. The incidence of perioperative adverse events was low and similar between the groups.

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