None listed
Conditions
Brief summary
One of the most serious complications of general anaesthesia in pregnant women is hypoxic brain injury and fetal and/or maternal death related to difficulty oxygenating a pregnant woman. This is due to inability of the anaesthetist to intubate the trachea and ventilate a pregnant woman because of the changed anatomy and physiology of pregnant women leading to the known problem of the difficult obstetric airway. The latest obstetric airway management guidelines by the Obstetric Anaesthetists’ Association (OAA) & Difficult Airway Society (DAS) discuss the importance of pre-oxygenation in managing pregnant women undergoing general anaesthesia as it increases oxygen reserve in the lungs during apnoea. The guidelines recommend that the end-tidal oxygen fraction (FetO2) of equal to or greater than 90%, indicating effective lung denitrogentation, should be achieved prior to induction of anaesthesia. The current way anaesthetists pre-oxygenate pregnant women undergoing general anaesthesia is to use a tight fitting face mask to deliver 100% inspired oxygen. The new guideline also states an alternative method. The guidelines states that nasal oxygenation, to facilitate bulk flow of oxygen to the alveoli could be considered as part of 1. Pre-oxygenation - A pre-oxygenation method and 2. Apnoeic oxygenation - A technique to increase apnoeic time. The guideline suggests that the anaesthetist should consider attaching nasal cannulae with 5 l.min-1 oxygen flow before starting pre-oxygenation, to maintain bulk flow of oxygen (O2) during intubation attempts, or attach nasal oxygenation after pre-oxygenation during the apnoeic period. There is also mention of humidified high flow nasal oxygenation however no data exists in pregnant women as to its safety or efficacy or acceptability by pregnant women. It is possible that a new pre-oxygenation technique, using high flow humidified nasal oxygen, may have an application in pregnant women however before this new pre-oxygenation technique is considered, it should be equivalent (at least) to the current available technique in terms of safety and efficacy i.e. be able to obtain FetO2 of at least 90% after three minutes of pre-oxygenation. Currently there are no studies reporting FetO2 values in pregnant women with high-flow humidified nasal oxygen delivery systems and no studies reporting the use of nasal high flow oxygen to increase apnoea times therefore it is unclear whether humidified high flow nasal oxygenation, is safe and beneficial in pregnant women. In this prospective study we aim to recruit two groups of women. The first group of women will be those who will electively undertake high flow humidified nasal oxygenation in order to examine this technique in the setting of pre-oxygenation (Pre-oxygenation group). The second group of women will be those who are undergoing general anaesthesia for caesarean section and will have high flow humidified nasal oxygenation after induction of anaesthesia.
Interventions
In this prospective study we aim to recruit two groups of women. Each woman will be placed on a hospital bed in an optimally ramped position and with a right lateral pelvic wedge to minimise aortocaval compression. Baseline vital signs will be measured. Whilst the woman is breathing room air (FiO2 21%) 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 obser
In this prospective study we aim to recruit two groups of women. Each woman will be placed on a hospital bed in an optimally ramped position and with a right lateral pelvic wedge to minimise aortocaval compression. Baseline vital signs will be measured. Whilst the woman is breathing room air (FiO2 21%) 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. The face mask will then be removed. High flow humidified nasal cannulae (Optiflow (Trademark)) will then be inserted into the woman’s nostrils by the trained investigator (anaesthetist, anaesthetic registrar, trained medical student, or nurse). Humidification will be set at 44 mg/l and oxygen concentration will be 100%. The oxygen flow will be commenced (first 30 seconds at 30 l.min-1, then next 150 seconds at 50 l.min-1). Each woman will be instructed to take deep breaths. At the end of three minutes the woman will be asked to hold her breath in inspiration while the nasal cannulae are quickly removed and the tightly fitting face mask (connected to 6 l.min-1 air FiO2 100%) will be applied. The woman will then be asked to exhale normally and breathe normally. The second group of women will be those who are undergoing general anaesthesia for caesarean section. Each woman will be placed on a hospital bed in an optimally ramped position and with a right lateral pelvic wedge to minimise aortocaval compression. Baseline vital signs will be measured. A tightly fitting face mask (connected to at least 6 l.min-1 oxygen (at the discretion of the treating anaesthetist) FiO2 100%) will be applied by the anaesthetist or anaesthetic registrar and a good seal obtained (indicated by capnography trace). Once the woman’s FetO2 reaches 90% or at the discretion of the anaesthetist/anaesthetic registrar, general anaesthesia will be induced with cricoid pressure applied. The face mask will then be removed. High flow humidified nasal cannulae (Optiflow (trademark)) will then be inserted into the woman’s nostrils by the trained investigator (anaesthetist, anaesthetic registrar, medical student, or nurse). Humidification will be set at 44 mg/l and oxygen concentration will be 100%. The oxygen flow will be commenced at 70 l.min-1. Chin lift and jaw thrust will be performed. At the discretion of the treatment anaesthetist once muscle relaxation deemed to have taken effect tracheal intubation will be attempted and oxygenation and ventilation will occur once successful. (the Apnoeic oxygenation group). After successful intubation of the trachea has been achieved nasal humidified oxygenation will cease and the nasal cannulae will be removed.
Sponsors
The Royal Women's Hospital
Study design
Allocation
Non-randomised trial
Intervention model
Other
Primary purpose
Prevention
Masking
Open (masking not used)
Eligibility
Sex/Gender
All
Age
18 Years to 40 Years
Healthy volunteers
Yes
Inclusion criteria
Pre-oxygenation group - Pregnant women at term ( greater than or equal to 36 weeks gestation) Apnoeic oxygenation group - Any pregnant woman undergoing general anaesthesia caesarean section
Exclusion criteria
Significant nasal pathology
Outcome results
None listed