Efficiency of Preoxygenation in Obese Patients: Pressure Assisted Versus Traditional Method
Condition: Obesity
MeSH terms: Obesity
Study type: Interventional

Summary: 
      The purpose of this clinical trial is to evaluate whether pre-oxygenation of obese patients
      with BiPAP 4cm H2O, renders any benefit to the quality of pre-oxygenation measured by the
      expired oxygen fraction (FeO2) and whether it is as well tolerated as the traditional method
      of spontaneous breathing for 3 minutes.
    

Detailed description: 
      Traditional pre-oxygenation in obese patients has been proven to allow a time of apnea far
      reduced when compared with patients closer to their ideal body weight. This effect is
      attributable to several factors :

        -  Reduced FRC

        -  Increased closing capacity

        -  Diminished tidal volume due to increased resistance of the airway, diminished compliance
           of the thoracic cage and diminished strength and endurance of respiratory muscles.

        -  Increase in atelectasis formation upon induction of general anaesthesia.

        -  Increased O2 consumption due to the increased workload of respiratory muscles and to the
           general increase in metabolism.

        -  Increase in true shunt. Studies have demonstrated a reduction in atelectasis formation
           by application of CPAP during pre-oxygenation and PEEP during anaesthesia. Also, 25º
           inclination of the patient in the supine position, on the operating table, has
           demonstrated prolongation of time of apnea in a significant amount. Outside the
           operating room, PEEP of 5 cmH2O has been demonstrated useful in prolonging time of apnea
           when used during pre-oxygenation in hypoxic patients requiring tracheal intubation in
           the intensive care.

      Yet, few studies have evaluated BiPAP in the operating room setting as to the effect on FeO2
      and to the tolerance by the patients.

      Thus, it is our intent to evaluate the efficiency of application of an inspiratory assistance
      pressure of 4cmH2O and PEEP 4cmH2O during a 3 minutes pre-oxygenation trial as to the level
      of FeO2 attained, the rate of attainment of FeO2 > 90% and the tolerance by the patient of
      the procedure, when compared with a 3 minute trial of the traditional method.

      For this purpose, consenting, non pre-medicated obese patients scheduled for surgery in the
      operating ward of our institution will be brought earlier to the operating room, the day of
      their surgery. In an idle operating room, they will go through two trials of 100% O2
      pre-oxygenation lasting 3 minutes each, at an interval of 20 minutes during which the
      patients will rest in a semi-sitting position, breathing spontaneously at ambient air. The
      order of the two trials will be randomly assigned between standard pre-oxygenation vs BiPAP
      pre-oxygenation. Both patients and anesthesia assistants providing the pre-oxygenation will
      be blinded as to the ongoing trial. Data from the anesthesia machine will be recorded
      visually to be analysed subsequently by a blinded third party. During each trial, the comfort
      of the patient on a local 4 point scale will be graded every minute.

      At the end of the study period, patients will be returned to the waiting area of the
      operating ward before the scheduled time of their surgery. The protocol is intended to not
      interfere with the planned anesthesia technique or the surgery in any way.
    

Intervention name(s): Standard preoxygenation; BiPAP assisted preoxygenation
Intervention type(s): Procedure; Procedure
Intervention description(s): Spontaneous breathing of 100% oxygen in a facemask for 3 minutes.; Spontaneous breathing of 100% oxygen in a facemask with application of an inspiratory pressure of 4cm H2O and a positive end-expiratory pressure of 4cm H2O, for 3 minutes.
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Triple (Participant, Care Provider, Outcomes Assessor)
Primary purpose: Prevention
Keywords: preoxygenation; method; efficiency; obesity; BiPAP; FeO2