None listed
Conditions
Brief summary
This is a randomised controlled trial (highest quality evidence) aimed at comparing a newer technique in oxygen delivery (high flow nasal oxygen) to current industry standard technique (face mask oxygen). The study design simulates conditions immediately before the start of a general anaesthetic to test a crucial safety step called preoxygenation. The specific population we are studying are obese, pregnant people who are in late pregnancy (more than 36 weeks). This group is at a high risk of oxygen problems after the start of a general anaesthetic which makes preoxygenation additionally important. Our hypothesis is that high flow nasal oxygen is not worse than face mask oxygen for preoxygenation in this patient group. The results will inform anaesthetic practice for this high risk patient group.
Interventions
The intervention will be preoxygenation with high flow humidified nasal oxygen for a total duration of 3 minutes according to the protocol as follows. The approximate total duration of the testing will take 30 minutes.
High flow humidified nasal oxygen protocol
With 10 l.min-1 of room air (FiO2 21%) running in the anaesthetic circuit, a tightly fitting face mask will be applied by a trained investigator (anaesthetist, anaesthetic registrar, medical student, or nurse) and a good seal and ideal
The intervention will be preoxygenation with high flow humidified nasal oxygen for a total duration of 3 minutes according to the protocol as follows. The approximate total duration of the testing will take 30 minutes. High flow humidified nasal oxygen protocol With 10 l.min-1 of room air (FiO2 21%) running in the anaesthetic circuit, a tightly fitting face mask will be applied by a trained investigator (anaesthetist, anaesthetic registrar, medical student, or nurse) and a good seal and ideal fitting will be determined by observing the capnography trace as the woman breathes. (This step may be omitted if the participant undergoes the face mask oxygen protocol first as per randomization). The face mask will then be removed. The oxygen concentration in the anaesthetic circuit will be increased to 100% (FiO2 100%) with flows remaining at 10 l.min-1 until the oxygen concentration rises to 100% as determined by real time oxygen analysis on the anaesthetic machine. After this has been achieved, high flow humidified nasal cannulae (Optiflow Switch™ by Fisher & Paykel Healthcare - TGA approved) will be placed into the woman’s nostrils by the trained investigator (anaesthetist, anaesthetic registrar, medical student, or nurse). The oxygen flow will be commenced (first 30 seconds at 30 l.min-1, then next 150 seconds at 70 l.min-1). Each woman will be instructed to breathe normally with her mouth closed as much as possible. The percentage of time mouth closure is achieved will be recorded to the closest percentage of 0%, 25%, 50%, 75% or 100%. If the maximum (70 l.min-1) flow rate is not tolerated, it will be reduced to 60 l.min-1 and then to 50 l.min-1 before aborting the protocol. At the end of three minutes the participant will be asked to hold their breath in inspiration while the tightly fitting face mask (connected to 10 l.min-1 FiO2 100%) will be applied over the nasal cannulae occluding the compressible arm. The woman will then be asked to exhale normally and breathe normally and the first four etO2 concentration values measured by the end tidal gas analyzer on the anaesthetic machine will be recorded. Other variables including end-tidal carbon dioxide concentration, peak oxygen saturation values and tidal volumes will be recorded.
Sponsors
Dr Patrick CF Tan
Study design
Allocation
Randomised controlled trial
Intervention model
Crossover
Primary purpose
Prevention
Masking
Open (masking not used)
Eligibility
Sex/Gender
All
Age
18 Years to 50 Years
Healthy volunteers
No
Inclusion criteria
Pregnant people with uncomplicated pregnancies greater than or equal to 36 weeks’ gestation, BMI greater than or equal to 30 kg.m-2
Exclusion criteria
Significant nasal pathology, severe systemic disease excluding obesity (as defined by an American Society of Anesthesiologists (ASA) physical status score of 4), preeclampsia of any degree, overwhelming sepsis, in labour or multiple pregnancy
Outcome results
None listed