The Effects of Low Flow and Normal Flow Desflurane Anesthesia

This prospective, randomized-controlled, observational study was approved by the ethics committee of Van Yuzuncu Yıl University (Date: 16.04.2021, Decision no: 05-27). The study was performed according to the World Medical Association's Declaration of Helsinki. All enrolled patients provided written informed consent.

In this prospective study; the patients were randomly divided into 2 groups according to the fresh gas flow applied. 'Group D' (n=30) was given to the low flow anesthesia group; the group in which normal flow anesthesia was administered was named 'Group N' (n=30).

Before anesthesia, automatic calibration of the anesthesia device (Primus, Drager) and leak tests were performed. In addition, the leak test was repeated manually for each patient. Alarm limits of the anesthesia device; The lower limit of inspired oxygen concentration (FiO2) was set to 30%, upper limit of inspired CO2 to 3%, and upper limit of end-tidal carbon dioxide (etCO2) to 45 mmHg.

The disconnection alarm was set to be 5 cmH2O lower than the peak pressure, the occlusion alarm was set to 30 cmH2O, the lower expiratory gas volume lower limit was set to be 500 mL below the desired minute volume (MV).

Soda lime (Sorbo-lime, Berkim, Turkey) was used as carbon dioxide absorbent. Soda lime was checked frequently for color and changed at appropriate times. Disposable anesthesia circuit and bacterial filter were used for each case.

Electrocardiography (ECG), peak heart rate (CTA), peripheral oxygen saturation (SpO2), non-invasive blood pressure and bispectral index (BIS) monitorisation (A-2000 Aspect medical systems, USA) were performed on all patien.

As a standard, vascular access was established with a 20-gauge (G) intraket from the dorsal of the hand or antecubital fossa in each patient and, a balanced electrolyte solution was infused of 8-10 ml/kg/hr.

All patients were preoxygenated with 100% O₂ for three minutes. For anesthesia induction, 0.03 mg/kg midazolam, 1-1.5 mcg/kg fentanyl, 2 mg/kg propofol and 0.6 mg/kg rocuronium were administered iv. Intubation was performed after adequate muscle relaxation was achieved. During mechanical ventilation; Tidal volume, PEEP, respiratory rate, etCO₂, and inspiration:expiration ratio were adjusted to be 7-10 ml/kg, 5 cmH2O, 12-14/min, 30-40 mmHg, 1:2 respectively.

Both groups were given a mixture of 50% O2 + 50% air + 6-7% desflurane in a 4 L/min fresh gas flow (FGF) until the minimum alveolar concentration (MAC) value was 1.

When the MAC value of desflurane was 1, FGF was reduced to 0.5 L/min (60% O2+40% dry air+8% desflurane) in Group D. In Group N, anesthesia was maintained by reducing FGF to 2 liters per minute (40% O2+60% air+6% desflurane). It was aimed to keep the MAC value between 0.9-1.1 and BIS values between 40-60 by titration of desflurane in all patients. Hemodynamic data, SpO2 and BIS values of the patients were recorded. It was recorded before induction, after induction, when switching to low/normal flow anesthesia, and during extubation.

Venous blood samples were obtained before induction, after surgery, and at the postoperative 24th hour to evaluate liver and kidney functions.

The SPSS 27.0 program was used to evaluate the data obtained in this study. In the descriptive statistics of the data, mean, standard deviation, median minimum, maximum, frequency and ratio values were used. The distribution of variables was measured with the Kolmogorov-Smirnov test. The mann-whitney u test was used in the analysis of quantitative independent data. Wilcoxon test was used in the analysis of dependent quantitative data. Chi-square test was used in the analysis of qualitative independent data, and the fischer test was used when the chi-square test conditions were not met. Statistical significance value was accepted as p<0.05 in all tests.

Inclusion criteria

• Patients with an American Society of Anesthesiologists (ASA) status of class I-III,
• Aged between 65 and 100 years,
• Scheduled to undergo general anesthesia and, the surgeries that will take longer than 1 hour.

Exclusion criteria

• ASA class ≥ III patients
• Thorasic surgery
• Neurosurgery
• Cardiorespiratory disease,
• Uncontrolled diabetes mellitus,
• Coagulation disorders,
• Preoperative liver and renal dysfunction,
• History of malignant hyperthermia,
• Using nephrotoxic or hepatotoxic drugs,
• Major bleeding (>1000 cc) is predicted in the operation,
• Chronic alcoholism,
• Patients with drug use or withdrawal symptoms