EPO2-A: Evaluation of Pre-Oxygenation in Morbid Obesity: Effect of Position and Positive Pressure Ventilation
Condition: Obesity, Morbid
MeSH terms: Obesity; Obesity, Morbid
Study type: Interventional

Summary: 
      The risk of complication associated with airway in obese patient is important. The result of
      pre-oxygenation gives the clinician a prolonged non-hypoxic apnea time. The relation between
      FRC and non-hypoxic apnea time has been correlated. However, the best condition to accomplish
      the pre-oxygenation in morbidly obese patient has yet to be described in the medical
      literature. A study previously done in our hospital (EPO2-PV) compared the effect of
      different positions and ventilation modes on the FRC in the laboratory. A significant
      difference has been established on the FRC between the inverse Trendelenburg position with
      positive pressure ventilation and the head up ("beach-chair") position without positive
      pressure. The current study, EPO2-A is designed to compared the two positions and ventilation
      modes during the induction of general anesthesia on morbidly obese and correlate the
      difference in FRC to difference in apnea time.
    

Detailed description: 
      Obesity prevalence in the population is increasing. Thus a growing number of obese patient
      need surgical interventions. These patients have a four time higher risk of suffering of
      serious complication in relation with their airway management compare with non-obese
      patients. This is explained by an increased incidence of difficulty with the ventilation and
      intubation of the obese. The time available for the clinician to manage the airway is define
      by the non hypoxic apnea time. This laps of time is dependent of the oxygen stocks of the
      patient, which are dependent of the functional residual capacity (FRC) and his oxygen
      consumption. For a non-obese patient, a normal pre-oxygenation of three minutes at 100% of
      oxygen allows a non hypoxic apnea time (oxygen saturation > 90%) of 8,9 minutes. However, for
      the morbidly obese, this time is cut to less than three minutes.

      The major goal of the pre-oxygenation is to increase the alveolar partial pressure of oxygen
      available in the end-expiratory pulmonary volume. This can be done by replacing the nitrogen
      in the alveolus by oxygen and by increasing the pulmonary stocks, the FRC. It has been
      demonstrated that the FRC after the induction of anesthesia is cut by half for the obese.
      This reduction is explained by a diminished thoracic compliance and an increase of the
      dependent lung regions' atelectasis because of a more cephalic position of the diaphragm.

      Various pre-oxygenation methods have been described to prolong the non hypoxic apnea time in
      the obese population. Some proposed pre-oxygenation strategies with the patient in the head
      up position (beach chair). It is a position derived from the ramped position described as the
      best to visualized the obese patients' glottis. Others proposed pre-oxygenation strategies
      with positive pressure ventilation, but only the supine position has been studied
      concomitantly.

      Individually, these techniques of pre-oxygenation are superior to the combination of supine
      position and no positive pressure. Indeed, studies demonstrated that the beach chair position
      (derived from the ramped position) or the positive pressure pre-oxygenation in supine
      position diminished the time needed to obtain a satisfactory pre-oxygenation (End-expiratory
      oxygen fraction >0,9) and a longer non hypoxic apnea time. Sill, these strategies have never
      been combined in the same protocol.

      The beach chair position without positive pressure ventilation has become the standard of
      care because it is the position that allows the best glottis view. Though, it has been shown
      by Boyce and coll. that the reverse Trendelenburg position, and not the beach chair,
      increased the non hypoxic apnea time, the recuperation time and the minimal saturation
      obtained compared to the supine position. We think that there is an advantage to use the
      reverse Trendelenburg position to optimize the non hypoxic apnea time. Indeed, our hypothesis
      is that there will be less pressure on the diaphragm in comparison with the beach char
      position.

      A studied realized by our group (EPO2-PV) evaluated the effect of three positions (Reverse
      Trendelenburg, beach chair and supine) and two ventilation strategies (spontaneous
      ventilation with or without positive pressure) on morbidly obese FRC in laboratory. The
      results showed a statistically significant difference on the FRC after a pre-oxygenation with
      positive pressure compared with the pre-oxygenation without positive pressure, and this
      regardless of the position. Moreover, for both ventilation strategies, results demonstrated a
      statistically significant superiority between the FRC obtained after pre-oxygenation in
      reverse Trendelenburg compared with the beach chair and the supine position. No improvement
      has been shown with the beach chair position.

      Thereby, the current study will try to correlate the FRC results obtained in laboratory in
      actual non hypoxic apnea time in the operating room. This research design tries to compare,
      in patient receiving general anesthesia for bariatric surgeries, the effect of the
      pre-oxygenation with positive pressure and the reverse Trendelenburg position, on the non
      hypoxic apnea time in comparison with the actual standard of care, beach chair position
      without positive pressure ventilation.
    

Intervention name(s): Beach chair (BC) and ZEEP; Reverse Trendelenburg and NIPPV
Intervention type(s): Procedure; Procedure
Intervention description(s): Table Position: Beach chair, Inclination of the upper part of the table at 25 degrees, breaking at the patient's hips ZEEP: 3 minutes pre-oxygenation with tidal volumes, FiO2 100%, mouth piece used as a ventilatory interface; Table Position: Reverse Trendelenburg, Inclination of the whole table at 25 degrees from an horizontal plane, head up.
NIPPV: 3 minutes of pre-oxygenation with 8 cm H2O positive pressure and 10 cm H2O PEEP. Trigger set at 1,5 L/min, mouth piece is used as a ventilatory interface
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Single (Participant)
Primary purpose: Prevention
Keywords: Morbid Obesity; Bariatric Surgery; Pre-Oxygenation; Anesthesia Induction; Positive pressure ventilation; Non hypoxic apnea time; Positive-Pressure Respiration; Anesthesia, General