EPO2-PV: Evaluation of Pre-Oxygenation Conditions in Morbidly Obese Volunteer: Effect of Position and Ventilation Mode (EPO2-PV)

EPO2-PV: Evaluation of Pre-Oxygenation Conditions in Morbidly Obese Volunteer: Effect of Position and Ventilation Mode

Evaluation of Different Pre-Oxygenation Conditions in Morbid Obesity: Position and Ventilation Mode, in a Respiratory Physiology Laboratory, on Voluntary Subjects

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.

Ventilation: non-invasive positive pressure ventilation (NIPPV) Positive end-expiratory pressure: 10 cmH20 Pressure support: 5 - 20 cm H2O for tidal volume of 10 mL / kg (ideal body weight)

Change of functional residual capacity (FRC), in obese patient, as a result of different pre-oxygenation positions; 1- supine, 2-beach-chair, 3- reverse Trendelenburg, in two different ventilation modes : 1- spontaneous ventilation at tidal volume, 2- non-invasive positive pressure ventilation with inspiratory assistance.

Evaluation of changes in diaphragmatic amplitude and movement determined by fluoroscopy imaging after a 5 minutes pre-oxygenation period in the 6 combinations previously described.

Change in respiratory mechanics (compliance, resistance, tidal volume, positive end-expiratory pressure, maximal inspiratory pressure) evaluated at the end of a 5 minutes pre-oxygenation period in the 6 combinations previously described.

Evaluation of the patient's comfort at the end of each intervention on an analog visual scale after a 5 minutes pre-oxygenation period in the 6 combinations previously described.

Change in vital signs before and after the pre-oxygenation phase in the 6 combinations after a 5 minutes pre-oxygenation period in the 6 combinations previously described.

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).

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