Perioperative UtiLisation of SupplEmental Oxygen

Over 3 million patients receive oxygen (O2) during general anaesthesia (GA) in the UK annually, and a large number of these also have co-morbid respiratory diseases such as Asthma or COPD. The World Health Organisation (WHO) recently recommended that all surgical patients receive 80% O2 throughout GA and for 6 hours in recovery to reduce Surgical Site Infections (SSIs). However, a recent Cochrane systematic review found no evidence of benefit from this approach and some evidence that harm could be increased (including mortality).

Excess oxygen has been associated with worse outcomes in many areas of medicine (including acute respiratory illnesses), possibly due to increased Reactive Oxygen Species (ROS) production: ROS can cause oxidative stress and damage proteins, DNA, and lipids. Observational data from our group shows most surgical patients currently receive nearer 55% O2 under GA. The effect of intraoperative O2 concentration on other surgical outcomes remains unknown.

This project will determine whether giving lower concentrations of oxygen to surgical patients during anaesthesia can reduce levels of oxidative stress during surgery (particularly in the lungs); investigate how this affects other organs; and evaluate the feasibility of performing a large (multi-centre) effectiveness study to define 'safe' oxygen administration concentrations during surgery.

Patient undergoing elective major surgery will be randomised to receive 80% (WHO's recommendation); 55% (current usual care) or 30% oxygen (intervention) throughout anaesthesia. Endotracheal aspirates will be sampled along with paired central venous and arterial blood samples throughout surgery to monitor levels of oxidative stress and organ function. Patients will be followed up for 7 days after surgery.

Inclusion criteria

• Age ≥16yrs - no upper limit
• Undergoing elective surgical procedure
• Planned for placement of arterial line and central venous catheter as part of routine anaesthetic delivery
• Written informed consent

Exclusion criteria

• Withdrawal of written consent or unable to give informed written consent
• Pregnant at time of enrolment
• Neurosurgery, cardiothoracic surgery or any other operation involving 1 lung ventilation at any point during procedure
• Baseline SpO2 < 90%
• Severe COPD (3 or 4 on GOLD criteria), Interstitial lung disease or other severe respiratory inflammatory co-morbidity (including already on home oxygen)
• BMI > 35
• Assessed as having a potentially difficult airway or being difficult to ventilate (defined as concern documented at anaesthetic assessment)
• Participating in another research trial with similar interventions or outcomes.
• Sickle cell disease
• Thalassemia Major
• Under custody