Oxygen Reserve Index Predicting Hypoxemia
Condition: Oxygen Deficiency; Apnea
MeSH terms: Hypoxia
Study type: Observational

Summary: 
      After obtaining the approval of the hospital ethics committee, this prospective,
      observational study included written informed consent from 51 participants with 19<BMI<25
      m/kg2 and 51 participants with BMI>40 m/kg2 undergoing an elective surgical requiring
      endotracheal intubation. In addition to standard monitors, an oxygen reserve index (ORI)
      sensor was placed and baseline values were recorded. The participants were preoxygenated
      until end expiratory oxygen concentration (EtO2) is reached 90%. After anesthesia induction
      and endotracheal intubation, the breathing circuit was not connected endotracheal tube until
      the peripheral oxygen saturation (SpO2) decreased until 95%.ORİ and SpO2 values were
      continuously recorded. Time of tolerable apnea, ORI warning, SpO2 warning and added warning
      were also recorded.
    

Detailed description: 
      This single-center prospective, observational study was approved by Institutional Ethics
      Committee (Decision No:2022/514/222/9, Date:30/03/2022) and was performed in accordance with
      the Declaration of Helsinki. Written, informed consent was obtained from 51 participants with
      BMI>40 kg/m2(morbidly obesity) and 51 participants with19<BMI<25 kg/m2(normal BMI), 18-75
      aged, American Society of Anesthesiologists (ASA) physical status I-III scheduled for an
      elective surgical procedure requiring general anesthesia with endotracheal intubation.
      Participants with significant history of cardiopulmonary disease, 25<BMI<40 kg m2, ASA>4
      and<18 years of age, difficult intubation, pregnancy, hemoglobinopathies and preoperative
      hemoglobin of less than 10.0 mg/dL were defined as exclusion criteria.

      Standard monitors were routinely established for each participants, including heart rate
      (HR), noninvasive blood pressure measurements. In addition, an ORi and SpO2 were measured
      simultaneously at 1-s interval with a pulse oximetry sensor (Rainbow sensor, R2-25) applied
      to the finger and connected to a Masimo Root with Radical-7 pulse oximeter (Masimo Corp.)
      Data for analysis was downloaded from the Root monitor.

      Following the placement of monitors, baseline values were recorded. Participants were then
      preoxygenated with spontaneous ventilation and 100% inspirative oxygen concentrate (FiO2) at
      a flow rate of 8 liter/minute via a tight-fitting face mask until EtO2 is reached to 90%.
      Anesthesia was induced with intravenous midazolam, fentanyl, propofol and rocuronium in 100%
      FiO2.The trachea was intubated after 3-4 minutes under direct visualization using a
      videolaryngoscope to confirm placement.The endotracheal tube was not connected to the
      breathing circuit, and the participants remained apneic. The World Health Organization
      defines intraoperative SpO2 ≥ 95% as normal in its training materials, and treatment steps
      are mentioned for SpO2 ≤ 94% [12]. However, since we included morbidly obese participants
      with limited functional residual capacities in our study and wanted to stay with in the safe
      range, we allowed SpO2 to decrease up to 95%. At the same time, the alarm point for SpO2 is
      applied as 95% in our clinic's protocol for morbidly obese patients.

      ORi and SpO2 values were recorded continuously. Subsequently, the anesthesia circuit was
      connected and patients were ventilated with 100% Fraction of Inspired Oxygen ( FiO2), tidal
      volume targeted 7 ml/kg and 5 cmH2O of positive end-expiratory pressure until ORi
      plateaued.Thereafter, anesthesia continued per routine.

      ORi and SpO2 data were compared at five specific time points: 1) baseline; 2) at the end of
      pre-oxygenation when the EtO2 reaches to 90%; 3) at the beginning of intubation; 4) when SpO2
      reaches 95%; and 6) during ventilation with 100% FiO2 when the ORi reaches a plateau.

      Investigators also recorded the tolerable apnea time defined as the time from the beginning
      of apnea until SpO2 reached 95% and ventilation was reinstated. The ORi warning time was
      defined as the time between the onset of the ORi and the SpO2 reaching 95%. Investigators
      defined the SpO2 warning time as the time for SpO2 to decrease from 97% to 95%.The added
      warning time provided by ORi was defined as the difference between ORi warning time and SpO2
      warning time The time at which the ORi alarm. Alarm activation was based on the fractional
      rate of change in ORi rather than on a specific oxygen reserve value.
    

Intervention name(s): monitoring
Intervention type(s): Device
Intervention description(s): ORI warning time, SpO2 warning time, added time were recorded.
Observational model: Case-Control
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        102 patients, ASA 1-3, 18-75 years
      
Keywords: Oxygen reserve index,; Tolerable apnea time,; Oxygen reserve index warning time,; Preoxygenation,; Percutaneous oxygen saturation warning time