High Fresh Gas Flow After Intubation

Atelectasis is common during and after general anesthesia. Atelectasis develops early if preoxygenation with 100% oxygen is used and continuously used during induction until endotracheal intubation. The investigators hypothesize that a rapid anti-preoxygenation maneuver immediately after confirming a successful intubation, reduces the area of atelectasis as investigated by computed tomography compared to a standard procedure.

Handling of the airway during induction and intubation is performed in a conventional manner. Initial ventilatory settings are also done in a conventional manner.

Handling of the airway during induction and intubation is performed in a conventional manner. Immediately after confirming a successful intubation the effect of preoxygenation is eliminated with an anti-preoxygenation maneuver.

Handling of the airway during induction and intubation is performed in a conventional manner. Initial ventilatory settings are also done in a conventional manner. As soon as correct position of the endotracheal tube is confirmed, controlled ventilation is started with a tidal volume of 7 mL/kg ideal body weight, PEEP 6 or 8 cm H2O (8 if BMI >25) and a respiratory frequency of 10. The fresh gas flow is set to 1 Liter per minute with an oxygen mixture of 40%, aiming for an inspired FiO2 of 30-35%. Unless the patient´s SpO2 falls below 90%, the FiO2 remains unchanged throughout the procedure.

Handling of the airway during induction and intubation is performed in a conventional manner. Immediately after confirming a successful intubation, the effect of preoxygenation is eliminated with a fresh gas flow of 10 L/min of air, delivered with volume controlled ventilation consisting of tidal volumes of approximately 15 ml/kg ideal body weight, a positive expiratory pressure of 10 cm H20 and a respiratory frequency of 10. As soon as the end tidal O2 reaches 25%, the ventilator settings are adjusted to normal values (same as in the control group), i.e. tidal volume 7 mL/kg ideal body weight, PEEP 6 or 8 cm H2O (8 if BMI >25). The mixture of oxygen in the fresh gas is increased to 40% and the fresh gas flow is set to 1 Liter per minute, aiming for an inspired FiO2 of 30-35%. Unless the patient´s SpO2 falls below 90%, the FiO2 remains unchanged throughout the procedure.

The area of atelectasis in the lungs is assessed by computed tomography (CT) 10 mm above the dome of the right diaphragm and expressed in cm2 and as % of the total lung area in the particular scan.

Inclusion Criteria: Healthy patients, American Society of Anesthesiology (ASA) I-II Patients scheduled for orthopaedic day case surgery in general anaesthesia Exclusion Criteria: ASA class III or higher Body Mass Index (BMI) 30 or higher Arterial oxygen saturation (SpO2) <94% breathing air Chronic Obstructive Pulmonary Disease (COPD) Ischemic heart disease Haemoglobin <100g/L Known or anticipated difficult airway and/or intubation Active smokers and ex-smokers with a history of more than 6 pack years Need for interscalene or supraclavicular regional anaesthesia with risk of phrenic nerve paralysis