الفهرس 
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Abstract
General anesthesia by intubation, muscle relaxation and mechanical ventilation cause a massive impairment of respiratory functions, resulting in atelectasis and ventilation /perfusion mismatch.
Atelectasis occurs within minutes of intubation and persists in 80% of cases during the first day after extubation.
The mechanism is thought to be the result of high inspired oxygen fractions leading to oxygen resorption and alveolar collapse, this effect being reinforced in obesity via compression atelectasis. These changes result in a restrictive postoperative spirometric pattern and poor tissue oxygenation.
This study was carried on 30 patients divided into two groups, group (A) receiving 40% oxygen and group (B) receiving 90% oxygen during general anesthesia for laparoscopic cholecystectomy.
Patients with history or current symptoms of acute or chronic pulmonary or cardiac disease were excluded. Also, patients who turned on open cholecystectomy because of surgical cause were excluded.
Preoperative evaluation was done regarding history, clinical examination, investigations and adequate fasting period.
All patients received 100% oxygen at the time of induction then they were divided into two groups as illustrated above after endotracheal intubation.
At the end of surgery and after extubation all patients were spontaneously breathing with facemask providing 100% oxygen as required.
Arterial blood gas measurement was obtained after insufflation and two hours postoperatively.
Spirometry was performed preoperatively and on the first postoperative day including forced vital capacity and forced expiratory volume in the first second.
Postero-anterior and lateral chest X- ray were obtained preoperatively and on the first postoperative day.
CT scans of the chest were obtained on the first postoperative day.
Our results showed that there was no significant difference in hemodynamic parameters between patients in each group and between the two groups. Pulmonary functions were significantly reduced postoperatively compared to the preoperative values in the two groups and there was no significant difference in the postoperative values between the two groups. The incidence of atelectasis was relatively higher in the 90% oxygen group as detected by chest X-ray and CT-scan in the first postoperative day but it is of no statistical significance.
Generous perioperative oxygen delivery is common, on the grounds of offering an adequate oxygen reserve in the event of airway difficulties, also possibly improving wound healing, and reducing perioperative tachycardia and the incidence of postoperative nausea and vomiting. It is still unclear whether these effects are a function of supplemental postoperative oxygen administration or an intraoperative high oxygen supply. The negative effects of oxygen cannot be denied. atelectasis is a problem and may predispose to pulmonary complications, especially in the obese. The positive effect of an adaptive low-oxygen strategy on postoperative lung function and saturation is clear; whether this has any clinical relevance is not clear.
Our data suggest that administration of high percent oxygen during laparoscopic cholecystectomy is not associated with significant increase in atelectasis formation compared with low oxygen supplies.