epo2-pv: evaluation of pre-oxygenation conditions in morbidly obese volunteer: effect of position and ventilation mode

Conditions: Morbid Obesity; Bariatric Surgery Candidate

Summary: the risk of complications associated with airway management in obese patients is significant. the results of pre-oxygenation allow a prolonged non-hypoxic apnea time for the clinician. the increase in frc and non-hypoxic apnea time is correlated. the best condition to accomplish the pre-oxygenation in morbidly obese patient is still undetermined in medical literature. this study is designed to evaluate the effect of different positions combined with different ventilation modes during the pre-oxygenation phase of anesthesia's induction. epo2: pv will evaluate the effect of different combinations of positions and ventilation modes on pulmonary volumes (mainly functional residual capacity) in a morbidly obese volunteer.

complications related to airway management are the major contributing factor to morbidity in anesthesiology. this risk of complications markedly increases when faced with a difficult airway in an obese patient. pre-oxygenation creates a safety margin by increasing the patient's oxygen stores, through a higher functional residual capacity (frc). when pre-oxygenated, the clinician may proceed to intubation after a variable period of apnea, while maintaining oxygen saturation over 92%. in non-obese individuals, pre-oxygenation allows a non-hypoxic apnea time of eight minutes. in the obese population, however, this non-hypoxic apnea time decreases to two to three minutes. different methods of pre-oxygenation have been proposed in order to increase apnea time before significant oxygen desaturation. amongst these methods, the following are of particular interest: pre-oxygenation to vital capacity, pre-oxygenation with spontaneous ventilation and positive pressure, and pre-oxygenation with elevated head positioning ("beach-chair"). these methods have been extensively studied in individuals of normal height and weight. the main objective of pre-oxygenation is to raise oxygen levels available at the alveolar level in order to increase the non-hypoxic apnea time, before a significant desaturation occurs. this raised alveolar oxygen concentration can be done by maintaining a higher inspired oxygen fraction and by promoting a larger frc which is the oxygen reserve build through the pre-oxygenation phase. in morbid obese patients, these parameters are affected by a lower expiratory flow, lower expiratory flow and closing of small radius airways. the final result probably come from a more cephalad position of the diaphragm induced by a larger intra-abdominal volume. actually, different studies demonstrate the advantage of a beach-chair position and non-invasive positive pressure ventilation for pre-oxygenation of obese patients. these advantages are shown by a shorter time of pre-oxygenation to obtain an end-tidal o2 \> 90 % and a longer non-hypoxic apnea time (sat o2 \>90%). up to date, there is no published data on the frc as a result of different combinations of position and ventilation mode. this study will evaluate frc by helium dilution technique. we propose a crossover randomised trial on volunteers waiting for a bariatric surgery. we want to compare, in pre-oxygenation situation, without induction of general anesthesia, the effect of three positions and two ventilation modes on the frc measure.

Eligibility criteria:
inclusion criteria: * bmi 40 - 80 kg / m2 * waist circumference: men: more than 130 cm * waist circumference: women: more than 115 cm exclusion criteria: * facial hair * cranio-facial abnormality * claustrophobia * asthma * copd (defined by fev1 \< 80 %) * severe cardiovascular disease (defined by nyha ≥3) * pregnancy * tobacco use * ni-cppv intolerance documented by a respiratory specialist (pneumologist).

Keywords: morbid obesity bariatric surgery candidate pre-oxygenation functional residual capacity