Factors Determining Oxygen Wash in During Pre-oxygenation

Study Overview
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Brief Summary
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Earlier studies has shown a correlation between older age and longer time for the rise in the end-tidal O2 concentration during pre-oxygenation. In this study the investigators aim to analyse this correlation more closely and investigate if the arterial partial pressure of oxygen (PaO2) as measured before the start of pre-oxygenation, with the patient breathing air, is a better predictor than age for estimating the time necessary for achieving the goal of pre-oxygenation.

Detailed Description
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Before induction of general anaesthesia pre-oxygenation is a recommended procedure to enhance the time available for solving a problem with the airway or intubation during induction. This can be accomplished by letting the patient breath normal tidal volumes with 100% oxygen for 3 to 5 minutes during pre-oxygenation. If there is airway closure during tidal volume breathing, pre-oxygenation needs longer time to achieve a maximum effect. Airway closure increases with advanced age and a few earlier studies has also shown a correlation between older age and longer time for the rise in the end-tidal O2 concentration during pre-oxygenation. Pre-oxygenation is a strongly recommended safety procedure before starting anaesthesia but has at least one major side affect: it is the main reason for the development of atelectasis in the lungs during anaesthesia. Atelectasis impairs oxygenation during anaesthesia and probably increase the risk for postoperative pulmonary complications. Postoperative complications are more common with advanced age and it is important to understand the mechanisms and risk factors involved. In this study, the investigators hypothesise that the PaO2 as measured before the start of pre-oxygenation, with the patient breathing air, is a better predictor than age for estimating the time necessary for achieving the goal of pre-oxygenation. If this assumption is correct it might have implication for how pre-oxygenation should be adjusted with advancing age.

Official Title
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Factors Determining End-tidal O2 Concentration in During Pre-oxygenation

Conditions
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Airway Complication of Anesthesia

Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Patients scheduled for general anaesthesia in American Society of Anesthesiology (ASA) physical status classification grade I-III. Body mass index over 18.5 and less than 30 kg/m2 Peripheral oxygen saturation 92% or more on air. Exclusion Criteria: ASA IV. Patients with active smoking and former smokers with a history of smoking more than 6 pack-years. Chronic obstructive lung disease. Bloodgas with PaO2 ≤ 8 kilopascal (kPa) or PaCO2 ≥ 6.5 kPa. Continuous positive airway pressure treatment at night. Heart failure or angina pectoris. Hemoglobin value less than 100 g/L. Pregnancy. Any neuromuscular or neurologic illness reducing ventilatory capacity. Any endocrine disease influencing basic metabolic demand. Not possible to achieve a tight mask seal. Patient unable to follow instructions.

Ages Eligible for Study
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Minimum Age: 40 Years
Maximum Age: 79 Years

Sexes Eligible for Study
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All

Study Plan
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How is the study designed?
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Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Age group 40-49<br>30 patients will be stratified to this age group. | |
| Age group 50-59<br>30 patients will be stratified to this age group. | |
| Age group 60-69<br>30 patients will be stratified to this age group. | |
| Age group 70-79<br>30 patients will be stratified to this age group. | |

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| PaO2 breathing air before start of pre-oxygenation and the rise in end-tidal O2 during pre-oxygenation. | An arterial bloodgas with the patient in the supine position breathing air will be analysed with regards to PaO2 and correlated to the rise in end-tidal O2 concentration during pre-oxygenation. | 5 minutes. | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Age and the rise in end-tidal O2 during pre-oxygenation. | Age will be correlated to the rise in end-tidal O2 during pre-oxygenation. | 5 minutes. |