European Journal of Cardiovascular Medicine

Modern day Surgeries need General Anaesthesia, which provides patient safety, stability while undergoing the surgery, and fast recovery period after the surgery concludes. The conventional General Anaesthesia method uses a large amount of fresh gas flow rate to safely give the patient the oxygen/volatile anaesthetic agent, to decrease the chance the patient will breathe their own exhaled gas back into their lungs and give the anaesthetist rapid control of the depth of anaesthesia during the surgical procedure, but this method of administering anaesthesia produces an increased amount of anaesthetic used, makes the operating room more unclean, and causes the patient to lose a larger amount of heat and humidity from the lungs [1,2]. The Low flow Anaesthesia method is a cost-effective method of General Anaesthesia, along with it being more environmentally friendly, by using low flow rates after the desired depth of anaesthesia has been reached. Advances in anaesthetic workstation, gas monitoring systems, and delivery of volatile anaesthetics, have improved on both the safety and the ease of using Low Flow techniques for everyday Clinical Practice, [3] as the Low Flow Anaesthesia technique will have exhaled gases going back into the airway, this has made it possible to continue supplying the patient with humidity/temperature. This has allowed us to eliminate wasted anaesthetic gases that would normally occur in a High Flow technique and minimize the environment from exposure to volatile anaesthetic gases [4].

While these benefits exist, there are still many questions about how the effects of low-flow anaesthesia can impact an individual’s intraoperative hemodynamic stability and postoperative recovery. For example, using less fresh gas could theoretically impact the amount of oxygen delivered to a patient as well as the amount of carbon dioxide a patient can remove, both of which will determine the patient’s depth of anaesthesia and could contribute to fluctuations in a patient’s hemodynamic (e.g., changes of heart rate or blood pressure) or delays in a patient’s emergence from anaesthesia [5]. The importance of maintaining stable hemodynamic status during surgery is most significant in elective surgical patients, in whom perioperative variations in heart rate and blood pressure have been associated with many poor perioperative outcomes. The recovery from anaesthesia is also an important factor in determining the quality of a patient’s experience during the procedure (including the surgical time in the operating room), how efficiently the operating room functions, and how much postoperative care is utilized [6]. Although available studies suggest that patients can undergo low-flow anaesthesia safely when appropriately selected; variability in design and structures, anaesthetic protocols, and how outcomes were defined leads to conflicting results across studies. Further, only a limited amount of data are available from a hospitals performing high-volume surgical procedures as to the recovery characteristics in relation to hemodynamic parameters [7,8].

Therefore, it is of interest to evaluate and compare the effects of low-flow versus conventional anaesthesia on intraoperative hemodynamic stability and postoperative recovery profiles in patients undergoing elective surgeries under general anaesthesia.

Study Design and Setting This prospective comparative study was conducted in the Department of Anaesthesiology at GMC Rajouri & AH hospital over a 12-month period (January 2024 – December 2024). The study was initiated after obtaining approval from the Institutional Ethics Committee, and written informed consent was obtained from all participants. Study Population Adult patients scheduled for elective surgical procedures under general anaesthesia were assessed for eligibility. Inclusion criteria Age between 18 and 60 years American Society of Anaesthesiologists (ASA) physical status I or II Elective surgeries of expected duration ≥60 minutes Procedures requiring general anaesthesia with endotracheal intubation Exclusion criteria ASA physical status III or higher Anticipated difficult airway Known cardiovascular, respiratory, hepatic, or renal disease Body mass index >30 kg/m² Pregnancy Emergency surgeries Surgeries requiring deliberate hypotension or associated with major fluid shifts Sample Size Calculation The sample size was calculated based on the primary outcome variable, mean arterial pressure (MAP), to detect a clinically meaningful difference between the low-flow and conventional anaesthesia groups. The formula used for comparison of two independent means was: n=(2σ^2 (Z_(1-α/2)+Z_(1-β) )^2)/d^2 Where: n= required sample size per group σ= pooled standard deviation Z_(1-α/2)= standard normal deviate for a two-sided alpha error of 5% (1.96) Z_(1-β)= standard normal deviate for 80% power (0.84) d= minimum clinically significant difference between group means Based on previously published anaesthesia studies, the pooled standard deviation (σ) of MAP was assumed to be 10 mmHg, and the minimum clinically significant difference (d) was considered to be 5 mmHg. n=(2×(10)^2×(1.96+0.84)^2)/(5)^2 ┤ n=(2×100×(2.8)^2)/25 n=(200×7.84)/25=62.72 Thus, the calculated sample size was approximately 63 patients per group. Considering feasibility, study duration, and possible dropouts, 60 patients were included in each group, giving a total sample size of 120 patients. Group Allocation Eligible patients were randomly allocated into two groups using a simple randomization technique: Group L (Low-flow anaesthesia): Fresh gas flow ≤1 L/min after an initial equilibration period Group C (Conventional anaesthesia): Fresh gas flow 3–4 L/min maintained throughout surgery Anaesthetic Technique All patients received a standardized premedication according to the institutional protocol. In the operating room, standard monitoring (electrocardiography, non-invasive blood pressure, pulse oximetry, capnography, and anaesthetic gas concentration monitoring) was established. General anaesthesia was induced using intravenous drugs at standardized doses, and an appropriate neuromuscular blocker facilitated endotracheal intubation. General anaesthesia was maintained with a volatile anaesthetic agent mixed with oxygen and N2O. In the L Group, the fresh gas flow rate was reduced to less than or equal to 1 L /min after induction, while the C Group continued with conventional fresh gas flow rates throughout the entire procedure. Mechanical ventilation was adjusted to maintain normocapnia in both groups. Patients in both groups received standardized intraoperative fluid administration, analgesia, and neuromuscular blockade. Data Collection Hemodynamic parameters such as heart rate, systolic blood pressure, diastolic blood pressure and mean arterial pressure were measured at base line (pre-induction), following induction, following intubation, at 5 minutes, 15 minutes, 30 minutes and 60 minutes following induction, every 30 minutes until extubation. Postoperative recovery parameters included the time from when the patient opened their eyes to a verbal command, the time it took from the end of surgery until they were extubated, and the Modified Aldrete Score at 0, 5, 10 and 15 minutes after leaving the recovery room. Intraoperative and postoperative complications were recorded and treated as per the established facility protocols of the institution. Statistical Analysis Microsoft Excel was used to perform the data analysis, where the statistical software produced by Microsoft was utilized to enter and analyze the data. Continuous variables are reported as a mean ± standard deviation, while categorical variables are reported as corresponding frequencies and percentages. An independent Student's t-Test for Continuous Variables, Chi-square for Categorical Variables were used in the analysis for comparing groups with regards to the data collected. A p value < 0.05 indicates statistical significance.

During the study, 120 subjects were analyzed. Sixty of these subjects were administered with low-flow anaesthesia (Group L), and the other sixty subjects received conventional anaesthesia (Group C). Both groups were similar at the baseline concerning demographics and clinical characteristics. The researchers examined the intraoperative hemodynamic data throughout the following three prescribed times to determine whether both methods of providing anaesthesia produced the same degree of cardiovascular stability. In addition to this information regarding intraoperative hemodynamic, the researchers assessed the emergence time and Modified Aldrete score (a post-anaesthesia recovery metric) to quantify the postoperative recovery of both groups. The primary focus for this study was to determine if there were any differences between groups in regard to the hemodynamic trends, recovery characteristics, and safety issues around both anaesthetic techniques.

Baseline Characteristics

Table 1. Baseline demographic and clinical characteristics of study participants

This table compares baseline variables between the two groups to ensure homogeneity and minimize confounding factors.

Table 2. Surgical and anaesthesia-related characteristics

This table demonstrates comparability of operative exposure and anaesthetic duration between the two groups.

Intraoperative Hemodynamic Parameters

Table 3. Comparison of heart rate at predefined intraoperative time points

This table evaluates heart rate trends to assess cardiovascular stability during different phases of anaesthesia.

Table 4. Comparison of systolic blood pressure (mmHg)

This table compares systolic blood pressure responses across intraoperative time points.

Table 5. Comparison of mean arterial pressure (mmHg)

Mean arterial pressure trends reflect overall hemodynamic stability during anaesthesia.

Table 6. Incidence of intraoperative hemodynamic events

This table compares clinically significant hemodynamic disturbances and need for intervention.

Recovery Profile

Table 7. Comparison of emergence characteristics

This table evaluates early recovery by measuring emergence and extubation times.

Table 8. Modified Aldrete score comparison

This table assesses immediate postoperative recovery using a standardized scoring system.

Postoperative Safety

Table 9. Immediate postoperative adverse events

This table summarizes postoperative complications observed in the recovery room.

Table 10. Overall perioperative safety profile

This table presents the cumulative safety outcomes across both groups.

Table 1, shows that both study groups did not differ significantly from one another based upon demographic variables such as age, sex distribution, BMI, and ASA physical status. These results indicate that the randomization process was adequately performed with no baseline demographic bias affecting the hemodynamic or recovery results. In addition, Table 2, indicates that the type and duration of surgery (and also, anaesthetic exposure) were similar between the groups; this indicates that any differences noted between groups relating to intraoperative stability or recovery must be due to the different anaesthetic techniques used and not because of the procedural aspects of the study. Table 3, shows that heart rate changes during induction, intubation, maintenance, and extubation were similar in both the low-flow and conventional anaesthesia groups. This suggests that low-flow techniques did not contribute to increased sympathetic stimulation or cardiovascular stress during the critical phases of anaesthesia. Referring to Table 4, it is readily apparent that systolic blood pressure changes recorded at various key points in time during the intraoperative period were similar for both study groups. This indicates that low-flow anaesthesia provides similar levels of control over anaesthetic depth and stress response compared to conventional anaesthetic techniques. As indicated in Table 5, the trends of mean arterial pressures were similar throughout the study in both groups. This indicates that adequate perfusion pressures and hemodynamic stability equivalent to those of standard anaesthesia techniques were maintained using low-flow anaesthesia. In Table 6, we see that there were very few clinically important hemodynamic complications and that the incidence was fairly comparable between treatment groups. This further supports the cardiovascular safety of using low-flow anaesthesia in elective surgical patients. Table 7, shows that patients treated with low-flow anaesthesia had quicker emergence and extubation times than those treated with traditional techniques; suggesting a more efficient ability to rapidly remove anaesthesia during the transition to waking up; this correlated with earlier return to the patient’s protective breathing reflexes. In Table 8, the patients receiving low-flow anaesthesia were assigned higher Modified Aldrete scores when assessed shortly after completion of the surgical procedure, suggesting a better quality of immediate recovery from surgery and possibly an earlier release from the post-anaesthesia care unit. Finally, as shown in Table 9, the results showed no significant difference in the occurrences of postoperative adverse events between the low-flow and traditional anaesthesia groups. Thus, it can be stated that low-flow anaesthesia will not increase the risk of experiencing early postoperative complications, including hypoxia, delayed awakening, and postoperative nausea/vomiting, compared to traditional methodology. Additionally, as demonstrated in Table 10, the overall safety profile for both types of anaesthesia was similar with no increases in the total number of adverse events and/or post-recovery delays with use of the low-flow technique.

This study was designed to compare patients undergoing elective surgery under conventional versus low-flow anaesthesia. Based on results from this study, low-flow anaesthesia maintained intraoperative hemodynamic stability comparable to traditional anaesthesia, and produced a modest but clinically significant difference in early recovery time frames between the two groups. There were no increased perioperative complications in patients receiving low-flow anaesthesia when compared with traditional anaesthesia [9,10]. An important factor in determining the overall safety of patients during the perioperative period is the hemodynamic stability of patients receiving general anaesthesia. This is particularly true during periods of heightened sympathetic stimulation, including induction, laryngoscopy/intubation, and emergence [11]. In our study, heart rates and blood pressures of both groups were very similar throughout the intraoperative period. In both groups, heart rate and blood pressure rapidly increased after tracheal intubation, which is consistent with what has been documented regarding the pressor effect of airway procedures [12]. Importantly, the magnitude and duration of these events were no greater for patients receiving low-flow anaesthesia, indicating that patients receiving lower fresh gas flows were not at greater risk for loss of cardiovascular control when modern anaesthesia workstations and appropriate hemodynamic monitoring have been implemented [13].

Throughout the intraoperative phase, mean arterial pressure, a critical variable representing organ perfusion levels, remained within clinically permissible boundaries in both study arms. The absence of substantial differences in MAP between treatment arms supports the ability of low flow anaesthesia to provide a stable level of anaesthesia without resulting in hypotension or excessive hemodynamic fluctuations. The implications of these results are particularly important in the case of elective surgery since maintaining stable perfusion pressure helps decrease the incidence of perioperative complications[14]. The incidence of intraoperative hemodynamic events (i.e., hypotension, hypertension, bradycardia, and tachycardia) was also low and comparable between the treatment arms, and there was no significant difference in the need for pharmacological intervention (i.e., usage of either vasopressor or anticholinergic agents) [15]. Thus, these findings provide further support for a cardiovascular safety profile of low flow anaesthesia, and agree with earlier research that has largely put to rest concerns regarding inadequate delivery of anaesthetics or CO2 rebreathing during low flow anaesthesia techniques due to modern anaesthesia machines that include integrated gas monitoring and safety alerts[16].

Low-flow anaesthesia was associated with a shorter time to opening the eyes and time to extubation, indicating an improved recovery profile. The earlier time of awakening may be due to the smaller amounts of volatile anaesthetics accumulating in the breathing circuit and in body tissues; thus during the washout phase of anaesthesia, volatile agents can be eliminated more quickly. Clinically, the earlier return of consciousness and airway reflexes results in smoother emergence, increased patient comfort, and improved operating room productivity [17]. This data is further validated by having higher Modified Aldrete scores in the immediate post-operative period for the low-flow group as compared to the conventional group. Both groups had similar Modified Aldrete scores at the 15 minute time period after arriving at the post-anaesthesia care unit, but because of the earlier scores from the low-flow group, it would appear that this group was able to achieve their recovery milestones earlier than their higher-volume counterparts in the post-anaesthesia care unit. Rapid turnover and efficient use of recovery room resources will be critical considerations in high-volume setups [18].

Postoperative outcomes were similar between both groups and there were no differences in rates of hypoxia, delayed emergence from anaesthesia and postoperative nausea/vomiting between these two groups. In addition, the fact that an increased rate of respiratory issues did not occur in the group receiving low-flow anaesthesia is significant because concerns related to hypoxia and hypercapnia have historically restricted the use of low-flow anaesthesia techniques. As a result, the results of this research study indicate that in the properly selected patient with appropriate monitoring, the use of low-flow anaesthesia techniques does not increase the risk for early postoperative complications [19].

In addition to clinical outcomes, low-flow anaesthesia has some other benefits that were not measured in this study but should nonetheless be considered when determining what form of anaesthesia will be used during surgical procedures. By reducing the amount of fresh gas flow used during a procedure using a low-flow anaesthesia technique, there will be a direct reduction in the consumption of halogenated anaesthetic agents and there will also be a reduction in the amount of halogenated anaesthetic agents released into the operating room. Furthermore, the use of lower amounts of fresh gas flow will conserve heat and moisture in the patients' lungs, which adds to the already known benefits of cost-effectiveness and reduced environmental impact associated with using lower volumes of fresh gas flow because they are less expensive than traditional methods [20].

There are limitations to the present study that should be taken into account. The sample population consisted only of ASA I and II patients undergoing elective surgery, therefore, the results cannot necessarily be extrapolated to patients in the higher risk category and/or patients undergoing emergency procedures. Additionally, the study did not evaluate long-term outcomes or perform any type of cost analysis. Future research evaluating higher risk patients in multiple surgical specialties and conducting an economic analysis will provide additional information regarding the use of low-flow anaesthesia in a variety of clinical settings.

In conclusion, low-flow anaesthesia has been shown to be safe and effective as an alternative to conventional anaesthesia for elective surgery. The use of low-flow anaesthesia produces equi-hemodynamic stability intraoperatively and exhibits enhanced early recovery while not increasing peri-operative complications. Therefore, the results of this study provide justification for further implementation of low-flow anaesthesia into the practice of modern, efficient, patient-centered anaesthesiology.

Compared to standard anaesthesia techniques; low-flow anaesthesia generates comparable hemodynamic stability (during the entire surgery) a lower rate of adverse perioperative events. Patients recovering from surgeries under low-flow anaesthesia have been shown to recover sooner than those recovering under standard methods; due to this; low-flow anaesthetic techniques should be incorporated as part of best practice for patient recovery as well as cardiovascular safety within the operating room.

1.             Bangaari A, Bangia R, Puri GD. Prevalence of low flow anesthesia and its cost comparison with other anesthesia techniques in an Indian tertiary care center. Acta Anaesthesiol Taiwan. 2005 Sep;43(3):141-5. PMID: 16235462.

2.             Tempia A, Olivei MC, Calza E, Lambert H, Scotti L, Orlando E, Livigni S, Guglielmotti E. The anesthetic conserving device compared with conventional circle system used under different flow conditions for inhaled anesthesia. Anesth Analg. 2003 Apr;96(4):1056-1061. doi: 10.1213/01.ANE.0000050558.89090.95. PMID: 12651660.

3.             Khanna P, Haritha D, Das A, Sarkar S, Roy A. Utility of high-flow nasal oxygen in comparison to conventional oxygen therapy during upper gastrointestinal endoscopic procedures under sedation: A systematic review and meta-analyses. Indian J Gastroenterol. 2023 Feb;42(1):53-63. doi: 10.1007/s12664-022-01308-6. Epub 2023 Feb 13. PMID: 36780095; PMCID: PMC9924186.

4.             Arslan M, Gişi G, Öksüz G, Öksüz H, Bilal B, Boran ÖF, Çalışır F. Are high fresh gas flow rates necessary during the wash-in period in low-flow anesthesia? Kaohsiung J Med Sci. 2020 Oct;36(10):834-840. doi: 10.1002/kjm2.12251. Epub 2020 Jun 15. PMID: 32543056; PMCID: PMC11896391.

5.             Bingül ES, Savran Karadeniz M, Şentürk E, Vuran Yaz İ, Atasever AG, Orhan Sungur M. Feasibility and Safety Properties of Metabolic-Flow Anesthesia Driven by Automated Gas Control® in Pediatric Patients: A Prospective Observational Study. Medicina (Kaunas). 2025 Apr 24;61(5):786. doi: 10.3390/medicina61050786. PMID: 40428744; PMCID: PMC12113539.

6.             Moosavi Tekye SM, Alipour M. Comparison of the effects and complications of unilateral spinal anesthesia versus standard spinal anesthesia in lower-limb orthopedic surgery. Braz J Anesthesiol. 2014 May-Jun;64(3):173-6. doi: 10.1016/j.bjane.2013.06.014. Epub 2013 Oct 25. PMID: 24907876.

7.             Fulton R, Millar JE, Merza M, Johnston H, Corley A, Faulke D, Rapchuk I, Tarpey J, Lockie P, Lockie S, Fraser JF. High flow nasal oxygen after bariatric surgery (OXYBAR), prophylactic post-operative high flow nasal oxygen versus conventional oxygen therapy in obese patients undergoing bariatric surgery: study protocol for a randomised controlled pilot trial. Trials. 2018 Jul 27;19(1):402. doi: 10.1186/s13063-018-2777-2. PMID: 30053897; PMCID: PMC6062994.

8.             Mostad D, Klepstad P, Follestad T, Pleym H. Desflurane consumption with automated vapour control systems in two different anaesthesia machines. A randomized controlled study. Acta Anaesthesiol Scand. 2021 Aug;65(7):895-901. doi: 10.1111/aas.13825. Epub 2021 May 4. PMID: 33788249.

9.             Roerick O, Seitz T, Mauser-Weber P, Palmaers T, Weyand M, Cesnjevar R. Low-flow perfusion via the innominate artery during aortic arch operations provides only limited somatic circulatory support. Eur J Cardiothorac Surg. 2006 Apr;29(4):517-24. doi: 10.1016/j.ejcts.2005.12.048. Epub 2006 Feb 28. PMID: 16504530.

10.          Kondoh K, Atiba A, Nagase K, Ogawa S, Miwa T, Katsumata T, Ueno H, Uzuka Y. Performance of a new carbon dioxide absorbent, Yabashi lime® as compared to conventional carbon dioxide absorbent during sevoflurane anesthesia in dogs. J Vet Med Sci. 2015 Aug;77(8):961-5. doi: 10.1292/jvms.14-0279. Epub 2015 May 4. PMID: 25843038; PMCID: PMC4565819.

11.          Biro P. Untersuchung der Frischgasentkopplung und des Beatmungsvolumens. Das Dräger Sulla 808V Anästhesiegerät [The effect of fresh-gas decoupling on respiratory volume. Draegar Sulla 808V anesthesia ventilator]. Anaesthesist. 1997 Nov;46(11):949-52. German. doi: 10.1007/s001010050491. PMID: 9490582.

12.          Morioka T. [A suction bottle for post-anesthesia evaluation of the distribution of consumed carbon dioxide absorber granules in the canister]. Masui. 2004 Nov;53(11):1311-4. Japanese. PMID: 15587189.

13.          Yahagi M, Hiruta R, Miyauchi C, Tanaka S, Taguchi A, Yaguchi Y. Comparison of Conventional Anesthesia Nurse Education and an Artificial Intelligence Chatbot (ChatGPT) Intervention on Preoperative Anxiety: A Randomized Controlled Trial. J Perianesth Nurs. 2024 Oct;39(5):767-771. doi: 10.1016/j.jopan.2023.12.005. Epub 2024 Mar 21. PMID: 38520470.

14.          Caruso TJ, Lawrence K, Tsui BCH. Regional anesthesia for cardiac surgery. Curr Opin Anaesthesiol. 2019 Oct;32(5):674-682. doi: 10.1097/ACO.0000000000000769. PMID: 31356362.

15.          Barakat H, Al Nawwar R, Abou Nader J, Aouad M, Yazbeck Karam V, Gholmieh L. Opioid-free versus opioid-based anesthesia in major spine surgery: a prospective, randomized, controlled clinical trial. Minerva Anestesiol. 2024 Jun;90(6):482-490. doi: 10.23736/S0375-9393.24.17962-X. PMID: 38869262.

16.          Tochie JN, Bengono Bengono RS, Metogo JM, Ndikontar R, Ngouatna S, Ntock FN, Minkande JZ. The efficacy and safety of an adapted opioid-free anesthesia regimen versus conventional general anesthesia in gynecological surgery for low-resource settings: a randomized pilot study. BMC Anesthesiol. 2022 Oct 24;22(1):325. doi: 10.1186/s12871-022-01856-6. PMID: 36280804; PMCID: PMC9589676.

17.          Levene JL, Weinstein EJ, Cohen MS, Andreae DA, Chao JY, Johnson M, Hall CB, Andreae MH. Local anesthetics and regional anesthesia versus conventional analgesia for preventing persistent postoperative pain in adults and children: A Cochrane systematic review and meta-analysis update. J Clin Anesth. 2019 Aug;55:116-127. doi: 10.1016/j.jclinane.2018.12.043. Epub 2019 Jan 11. PMID: 30640059; PMCID: PMC6461051.

18.          Yang Y, Wang C, Cao G, Li H, Yang L, Xi J, Sun C, Lu H, Liu Y, Guo J, Yue C. Risk of Postoperative Nausea and Vomiting After Total Hip or Knee Arthroplasty Under Spinal Anesthesia: Randomized Trial Comparing Conventional Antiemetics with or without the EmeTerm Bracelet. J Bone Joint Surg Am. 2025 May 21;107(10):1063-1072. doi: 10.2106/JBJS.24.00773. Epub 2025 Mar 28. PMID: 40153477.

19.          Wu Y, Chen J, Ma W, Guo L, Feng H. Virtual reality in preoperative preparation of children undergoing general anesthesia: a randomized controlled study. Anaesthesiologie. 2022 Dec;71(Suppl 2):204-211. English. doi: 10.1007/s00101-022-01177-w. Epub 2022 Aug 1. PMID: 35925196.

20.          Evangelista TMP, Pua JHC, Evangelista-Huber MTP. Wide-Awake Local Anesthesia No Tourniquet (WALANT) versus Local or Intravenous Regional Anesthesia with Tourniquet in Atraumatic Hand Cases in Orthopedics: A Systematic Review and Meta-Analysis. J Hand Surg Asian Pac Vol. 2019 Dec;24(4):469-476. doi: 10.1142/S2424835519500619. PMID: 31690188.