Comparison of the Effects of High, Low and Minimal Flow Anesthesia Managements on ORI and Partial Oxygen Pressure

The aim of our study is to show that continuous oxygen reserve index monitoring is a non-invasive monitoring method that can be used as a supporting parameter to PaO2 in blood gas in hypoxia and hyperoxia monitoring when different fresh gas flow is used in general anesthesia.

Ninety patients included in the study were classified into three groups. After the high flow period, FGF and inspired oxygen fraction (FiO2) was set to be 4 L/m and 40% in group H (high flow), 1 L/m and 50% in group L (low flow) and 0.5 L/m and 68% in group M (minimal flow), respectively.

Patients were transferred into the operating room, monitored and premedication with 0.03 mg/kg of midazolam was administered. Subsequently, the right radial artery was cannulated under local anesthesia and basal blood samples were taken. After preoxygenation (100% O2, 6 L/min, 3 min.), anesthesia induction was performed with intravenous administration of 40-60 mg lidocaine, 2 mg/kg propofol, 0.6 mg/kg rocuronium and 1.5 mcg/kg fentanyl. Patients were ventilated in volume-controlled mode (Dräger Perseus® A500 Anaesthesia Workstation, Dräger, Germany) that allows continuous monitorization of airway pressure, exhaled gas volume, FiO2, volatile anesthetic substance concentration, and CO2 concentration within the scope of the Common European Standard EN 740. Medical air was used as the carrier gas. End-tidal carbon dioxide (EtCO2) was continuously monitored after intubation, and tidal volume and ventilation rates were adjusted to maintain EtCO2 at 30-40 mmHg. In maintenance, general anesthesia was provided in all three groups by inhalation of remifentanil 0.05-0.2 mcg/kg/min and FGF 4 L/min 50% oxygen-medical air mixture with 6-8% desflurane. After intubation, 6% desflurane was administered with a fresh gas flow of 4 L/min for 10 minutes in all three groups, and the MAC value was adjusted to 1.

Thereafter, oxygen 1 L/min, and medical air 3 L/min (FGF 4 L/min, FiO2 40%) were administered to patients in group H for high-flow anesthesia; oxygen 0.37 L/min, medical air 0.63 L/min (FGF 1 L/min, FiO2 50%) to patients in group L for low-flow anesthesia; oxygen 0.3 L/min and medical air 0.2 L/min (FGF 0.5 L/min, FiO2 68%) to patients in group M under minimal flow anesthesia. After reaching adequate MAC values after 10 minutes of intubation, FiO2 was reduced to 40% in Group H, keeping the FGF unchanged; in Group L fresh gas flow was reduced to 1 L/min, in Group M fresh gas flow was reduced to 0.5 L/min, and the scale setting of desflurane was adjusted in order to achieve MAC 1 for the remainder of the surgery.

A disposable sensor (RD Rainbow Lite Set ORI Probe, Masimo Corp. Irvine CA), shielded from light, was placed on the left index finger to record the data displayed with Masimo Radical 7 pulse CO-Oximeter (Masimo Corp. Irvine CA).

At the end of the surgical procedure in all patients, the vaporizer was turned off and high FGF (4 L/min, FiO2 100%) was applied to ensure rapid removal of the anesthetic gases from the lungs, and manual ventilation was started. Sugammadex (2-4 mg/kg iv.) was administered to reverse the residual muscle relaxation at the end of the operation in patients who did not experience complications during the operation, and after spontaneous breathing was achieved, the patients were extubated in the operating room.

Eligibility Criteria:
Inclusion Criteria:

* ASA II and III patients,
* Aged between 18-75 years,
* who were scheduled to undergo elective open abdominal surgery lasting \<60 minutes under general anesthesia

Exclusion Criteria:

* refusal of consent to study inclusion by the patient or his/her guardian,
* inability to use the sensor due to finger deformation or hypoperfusion,
* having a history of malignant hyperthermia,
* presence of clinically significant anemia, morbid obesity, alcohol or drug addiction, having a severe cardiac, renal or hepatic impairment,
* having a history of cerebrovascular disease,
* being a pregnant or presently lactating and having local anesthetic or opioid sensitivity