Does Pulmonary Compliance Optimization Through PEEP Manipulations Reduces the Incidence of Postoperative Hypoxaemia in Bariatric Surgery?

Does Pulmonary Compliance Optimization Through PEEP Manipulations Reduces the Incidence of Postoperative Hypoxaemia in Bariatric Surgery?

Does Pulmonary Compliance Optimization Through PEEP Manipulations Reduces the Incidence of Postoperative Hypoxaemia in Bariatric Surgery?

General anesthesia, even in patients in good health, impairs gas exchanges and ventilatory mechanics. These effects result primarily from atelectasis formation. They occur in 85-90% of healthy patients in the minutes following the induction when a positive end expiratory pressure (PEEP) is not used. The functional residual capacity (FRC) of obese patients during general anesthesia is even smaller than the one of healthy patients. There is a direct relationship between the body mass index and the decrease of the functional residual capacity. Obese patients have therefore more atelectasis. The increased abdominal pressure during the pneumoperitoneum will increase the decrease of the CRF, and thus aggravate the formation of these atelectasis. Atelectasis affect the peroperative gas exchanges and are likely to be involved in the worsening of postoperative hypoxemia episodes. In addition, atelectasis alter the clearance of secretions and the lymph flow, which predispose to lung infections.Taking all these factors into account, it is logical to think that the atelectasis presence can lead to an increase of the postsurgical morbidity (respiratory distress, infections). That is why actively fighting against the formation of these atelectasis is important. There is a lack of scientific evidence to say that the strategies against atelectasis as PEEP have a significant impact on the patient's postoperative status. The expected clinical benefits balance (reduction of respiratory distress episodes, infections and mortality) versus the risks linked to the maneuvers done to reduce the development of atelectasis (barotraumas, cardiac complications) remains to be determined. The primary goal of this study is to evaluate the impact of two different alveolar recruitment strategies on the incidence of postoperative hypoxemia in obese patients after bariatric surgery. The secondary objectives of this study are to compare the number of recruitment maneuvers, the Pa02 / FI02 ratio (ratio of arterial oxygen partial pressure to fractional inspired oxygen), the dynamic compliance, the anatomic dead space and intraoperative PaCO2-EtCO2 gradient (arterial and end tidal gradient) between two alveolar recruitment strategies applied in obese patients during laparoscopic bariatric surgery (gastric bypass or sleeve gastrectomy). The tertiary objectives of this study are to report the number of respiratory complications and postoperative wound infections at the 30th postoperative day.

General anesthesia, even in patients in good health, impairs gas exchanges and ventilatory mechanics. These effects result primarily from atelectasis formation. They occur in 85-90% of healthy patients in the minutes following the induction when a positive end expiratory pressure (PEEP) is not used. These atelectasis are formed on one hand by the reduction of the functional residual capacity (FRC) following a compression mechanism (loss of the inspiratory muscle tone, which is accompanied by a chest wall configuration change and a diaphragm cephalic movement) and on the other hand by a denitrogenation absorption process (ventilation at high Fi02 (oxygen inspired fraction) causing complete absorption of O2 with lack of support for the alveolus, which then collapses). The FRC of obese patients during general anesthesia is even smaller than the one of healthy patients. There is a direct relationship between the body mass index and the decrease of the functional residual capacity. Obese patients have therefore more atelectasis. The increased abdominal pressure during the pneumoperitoneum will increase the decrease of the CRF, and thus aggravate the formation of these atelectasis. Atelectasis affect the peroperative gas exchanges and are likely to be involved in the worsening of postoperative hypoxemia episodes. In addition, atelectasis alter the clearance of secretions and the lymph flow, which predispose to lung infections.Taking all these factors into account, it is logical to think that the atelectasis presence can lead to an increase of the postsurgical morbidity (respiratory distress, infections). That is why actively fighting against the formation of these atelectasis is important. Several strategies have been studied in order to improve respiratory mechanics and reduce impaired gas exchange during laparoscopic surgery in obese patients. The position called "chair", mechanical ventilation with PEEP, recruitment maneuvers followed by the PEEP, and spontaneous ventilation with CPAP before extubation, are all strategies that have proven effective to decrease development these atelectasis. Currently, the scientific community agrees on the fact that PEEP improves intraoperative respiratory function (improved compliance, oxygenation) especially in conjunction with recruitment maneuvers. But there is a lack of scientific evidence to say that the strategies against atelectasis as PEEP have a significant impact on the patient's postoperative status. The expected clinical benefits balance (reduction of respiratory distress episodes, infections and mortality) versus the risks linked to the maneuvers done to reduce the development of atelectasis (barotraumas, cardiac complications) remains to be determined. The primary goal of this study is to evaluate the impact of two different alveolar recruitment strategies on the incidence of postoperative hypoxemia in obese patients after bariatric surgery. The secondary objectives of this study are to compare the number of recruitment maneuvers, the Pa02 / FI02 ratio, the dynamic compliance, the anatomic dead space and intraoperative PaCO2-EtCO2 gradient between two alveolar recruitment strategies applied in obese patients during laparoscopic bariatric surgery (gastric bypass or sleeve gastrectomy). The tertiary objectives of this study are to report the number of respiratory complications and postoperative wound infections at the 30th postoperative day.

In this group, a PEEP of 10 cmH20 is applied for the duration of the intervention and a recruitment maneuver is applied each time the SpO2 (oxygen pulsated saturation) drops below 95%.

In this group, 10 cmH20 PEEP is applied immediately. Then the "optimal PEEP" is sought at three key moments. It is determined by the best value of lung compliance found in the patient. It is sought by increasing or decreasing the value of the PEEP by increments or decrements of 2 cmH20. If after 6 respiratory cycles, the value of the compliance is increased, the investigator continues to increase the value of the PEEP. On the other hand, if the value of compliance is reduced, the investigator reduces the value of PEEP. The value of the PEEP selected shall in no event exceed the set pressure range (maximum pressure plate of 30 cmH20 and maximum inspiratory peak pressure 40cmH20). A recruitment maneuver is applied each time the SpO2 drops below 95%, as in the PEEP 10cmH2O group.

This will be monitored by a portable saturometer (OxyTrue A, Bluepoint, Germany). This saturometer will allow the investigators to count the number of hypoxemia episodes (Sp02<90%) and their duration in obese patients, in the postoperative period.

This will be monitored by a portable saturometer (OxyTrue A, Bluepoint, Germany). This saturometer will allow the investigators to count the number of hypoxemia episodes (Sp02<95%) and their duration in obese patients, in the postoperative period.

From the beginning of the surgery till moment 1 (after induction/intubation, patient laying flat, without pneumoperitoneum)

From moment 1 till moment 2 (after peritoneal insufflation and anti-trendenlenbourg (anti-trent) implementation)

The gradient between the partial pressure of carbon dioxide in the arterial blood (PaCO2) and the CO2 end-tidal partial pressure (EtCO2) is used to evaluate the effectiveness of alveolar recruitment.

The gradient between the partial pressure of carbon dioxide in the arterial blood (PaCO2) and the CO2 end-tidal partial pressure (EtCO2) is used to evaluate the effectiveness of alveolar recruitment.

The gradient between the partial pressure of carbon dioxide in the arterial blood (PaCO2) and the CO2 end-tidal partial pressure (EtCO2) is used to evaluate the effectiveness of alveolar recruitment.

The gradient between the partial pressure of carbon dioxide in the arterial blood (PaCO2) and the CO2 end-tidal partial pressure (EtCO2) is used to evaluate the effectiveness of alveolar recruitment.

The gradient between the partial pressure of carbon dioxide in the arterial blood (PaCO2) and the CO2 end-tidal partial pressure (EtCO2) is used to evaluate the effectiveness of alveolar recruitment.

All patients are seen at the surgical consultation on day 30 after surgery. The anamnesis performed during that consultation enables the investigators to identify patients with wound infections (defined as a need for local or oral antibiotics, additional hospitalisation or abnormal cicatrisation).

The hemodynamic and respiratory parameters of the patient are measured by means of a Datex-Ohmeda Acertys machine (Aisys type).

The hemodynamic and respiratory parameters of the patient are measured by means of a Datex-Ohmeda Acertys machine (Aisys type).

The hemodynamic and respiratory parameters of the patient are measured by means of a Datex-Ohmeda Acertys machine (Aisys type).

The hemodynamic and respiratory parameters of the patient are measured by means of a Datex-Ohmeda Acertys machine (Aisys type).

The hemodynamic and respiratory parameters of the patient are measured by means of a Datex-Ohmeda Acertys machine (Aisys type).

The hemodynamic and respiratory parameters of the patient are measured by means of a Datex-Ohmeda Acertys machine (Aisys type).

The hemodynamic and respiratory parameters of the patient are measured by means of a Datex-Ohmeda Acertys machine (Aisys type).

The hemodynamic and respiratory parameters of the patient are measured by means of a Datex-Ohmeda Acertys machine (Aisys type).

The hemodynamic and respiratory parameters of the patient are measured by means of a Datex-Ohmeda Acertys machine (Aisys type).

The hemodynamic and respiratory parameters of the patient are measured by means of a Datex-Ohmeda Acertys machine (Aisys type).

The hemodynamic and respiratory parameters of the patient are measured by means of a Datex-Ohmeda Acertys machine (Aisys type).

The hemodynamic and respiratory parameters of the patient are measured by means of a Datex-Ohmeda Acertys machine (Aisys type).

The hemodynamic and respiratory parameters of the patient are measured by means of a Datex-Ohmeda Acertys machine (Aisys type).

The hemodynamic and respiratory parameters of the patient are measured by means of a Datex-Ohmeda Acertys machine (Aisys type).

The hemodynamic and respiratory parameters of the patient are measured by means of a Datex-Ohmeda Acertys machine (Aisys type).

Inclusion Criteria: ASA score (American Society of Anesthesiologists ) of II or III BMI > 35 kg/m² Elective laparoscopic bariatric surgery: gastric bypass or sleeve Exclusion Criteria: Restrictive (CPT <65%) or obstructive (VEMS/CV < 69%) chronic lung disease Increase of the intracranial pressure History of smoking with chronic obstructive disease (VEMS/CV) Active tabagism Ongoing pregnancy History of heart failure (NYHA III or IV) or coronary artery disease Urgent surgery Allergy to a drug used within the study Lack of written informed consent

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