Peroperative Use of Positive End-expiratory Pressure Prevents Formation of Atelectasis as Studied by Computerised Tomography at End of Surgery

Study Overview
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Brief Summary
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Atelectasis is common during and after general anaesthesia and a number of interventions have been suggested in order to prevent their formation. The use of Positive End Expiratory Pressure (PEEP) during general anaesthesia has in recent years been questioned. The investigators hypothesize that the use of PEEP as a single intervention improves oxygenation and prevents atelectasis as investigated by computed tomography compared to a control group with zero PEEP.

Official Title
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Peroperative Use of Positive End-expiratory Pressure Prevents Formation of Atelectasis as Studied by Computerised Tomography at End of Surgery

Conditions
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Atelectasis

Intervention / Treatment
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* Procedure: Positive end-expiratory pressure
* Procedure: Control group, zero PEEP


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Healthy subjects, American Society of Anesthesiology (ASA) I-II. Patients scheduled for non-abdominal day case surgery under general anaesthesia. Exclusion Criteria: ASA class III or higher. Body Mass Index (BMI) 30 or higher. Arterial oxygen saturation (SpO2) <96% breathing air. Chronic Obstructive Pulmonary Disease (COPD). Ischaemic heart disease. Known or anticipated difficult airway. Active smokers and ex-smokers with a history of more than 6 pack years. Need for interscalene or supraclavicular plexus block for postoperative pain relief (risk of phrenic nerve paralysis).

Ages Eligible for Study
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Minimum Age: 40 Years
Maximum Age: 75 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Prevention
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Double


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Active Comparator: PEEP group<br>Induction and maintenance of anaesthesia in a conventional manner. Peroperative ventilatory settings using positive end-expiratory pressure. | Procedure: Positive end-expiratory pressure<br>* Induction of anaesthesia is performed in a conventional manner using a target controlled infusion of propofol and remifentanil. Intubation of the trachea is facilitated by rocuronium. As soon as correct position of the endotracheal tube is confirmed, controlled ventilation is started with a tidal volume of 7 mL/kg body weight and a respiratory frequency of 10. The fresh gas flow is set to 1 litre/min with an oxygen mixture of 40%, aiming for an inspired oxygen fraction (FiO2) of 30-35%. Positive end-expiratory pressure is set to 6 or 8 cm H20 (8 if BMI>25) in the intervention group. Unless the patient´s SpO2 falls below 90%, the FiO2 remains unchanged throughout the procedure.<br>|
| Active Comparator: Control group zero PEEP<br>Induction and maintenance of anaesthesia in a conventional manner. Peroperative ventilatory settings using zero end-expiratory pressure. | Procedure: Control group, zero PEEP<br>* Induction of anaesthesia is performed in a conventional manner using a target controlled infusion of propofol and remifentanil. Intubation of the trachea is facilitated by rocuronium. As soon as correct position of the endotracheal tube is confirmed, controlled ventilation is started with a tidal volume of 7 mL/kg body weight and a respiratory frequency of 10. The fresh gas flow is set to 1 litre/min with an oxygen mixture of 40%, aiming for an inspired oxygen fraction (FiO2) of 30-35%. Zero PEEP is used. Unless the patient´s SpO2 falls below 90%, the FiO2 remains unchanged throughout the procedure.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Area of atelectasis expressed as centimeter^2 | The area of atelectasis in the lungs is assessed by computed tomography (CT) 5-10 mm above the dome of the right diaphragm and expressed in centimeter^2 and as a percentage of the total lung area in the particular scan. | Within 1-2 hours, just before emergence from anesthesia.The outcome measure (atelectasis) will be investigated at just one point i.e. end of surgery but before emergence from anaesthesia. | 
| Measurement of aeras with different aeration in the particular CT scan. | The areas of different aeration are assessed by computed tomography (CT) 5-10 mm above the dome of the right diaphragm and expressed in centimeter^2 and as a percentage of the total lung area in the particular scan. | Within 1-2 hours, just before emergence from anesthesia.The outcome measure (atelectasis) will be investigated at just one point i.e. end of surgery but before emergence from anaesthesia. | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Oxygenation, oxygen tension in arterial blood expressed in kilo Pascal (kPa) | Arterial blood gas samples will be drawn and analyzed at the same time as the computed tomography scan will be undertaken. | Within 1-2 hours, just before emergence from anesthesia. At end of surgery but before emergence from anaesthesia, at the same time as the lungs are investigated by computed tomography. | 
| Oxygenation, oxygen tension in arterial blood expressed in kilo Pascal (kPa) | Arterial blood gas samples will be drawn and analyzed 15 minutes after emergence from anesthesia and extubation. | Within 2 hours perioperatively, 15 minutes after extubation. | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Atelectasis, Positive End-Expiratory Pressure, Oxygenation, Anaesthesia, Computed tomography