Non Invasive Pressure Support Ventilation (NIPPV) Versus Recruitment Maneuver (RM) and Preoxygenation

• Oxygenation (PaO2) measured 5min after the onset of mechanical ventilation [ Time Frame: 5 min after the oneset of mechanical ventilation ] [ Designated as safety issue: Yes ]
  

• - FRC after tracheal intubation and after 5 min of mechanical ventilation [ Time Frame: after 5 min of mechanichal ventilation ] [ Designated as safety issue: Yes ]
  

Procedure: NIPPV and IRM
• non invasive positive pressure support ventilation (NIPPV group)
• alveolar recruitment maneuver (IRM group)

Atelectasis formation during general anesthesia, leading to reduced end-expiratory lung volume, is an important cause of intrapulmonary shunt leading to impaired gas-exchange and hypoxemia. During general anesthesia and the immediate postoperative period, morbidly obese patients, who develop a larger amount of atelectasis than non-obese patient, are more likely to present impairment of gas exchange and respiratory mechanics. Noninvasive positive-pressure support ventilation (NIPPV) and positive end-expiratory pressure (PEEP) are effective to provide oxygenation during intubation of hypoxemic patients. Recent data suggest that NIPPV enhances preoxygenation in morbidly obese patients. Moreover, the application of PEEP during induction of anesthesia prevents atelectasis formation and increases nonhypoxic apnea duration in obese patients despite the use of high-inspired oxygen fraction. However, the use of both NIPPV is widely used in the operating room, because of technical and materials constraints.

Several trials have demonstrated that alveolar recruitment maneuvers (RM) are effective to remove atelectasis and improve lungs mechanics and gas-exchange.

The purpose of this randomized and controlled study is to compare the effects of two ventilatory strategies during anesthesia induction of morbidly obese patients on both gas-exchange and functional residual capacity (FRC) modifications: 1- Control group: preoxygenation using 100% O2 via a face-mask and PEEP 10 cmH2O after intubation; 2- NIPPV group: preoxygenation using NIPPV and PEEP 10 cmH2O after intubation; 3- RM group: preoxygenation using 100% O2 via a face-mask and early RM plus PEEP 10 cmH2O after intubation.