Pre-oxygenation increases oxygen reserves in the body to reduce the likelihood of oxygen desaturation on induction of general anaesthesia. Pre-oxygenation with facemask is the commonest method method of pre-oxygenation. High-flow nasal oxygen is a newer alternative. This study randomises participants to receive pre-oxygenation by one of three methods: facemask, high-flow nasal oxygen, high-flow nasal oxygen plus mouthpiece.
The administration of supplemental oxygen prior to induction of anaesthesia is known as pre-oxygenation. Pre-oxygenation increases oxygen reserves in the body with the purpose of delaying the time until oxygen desaturation after breathing stops (apnoea) following the administration of an anaesthetic. In the last decade, clinicians have begun utilising high-flow nasal oxygen for pre-oxygenation. However, the rationale for this is based largely on its ability to achieve ongoing oxygenation after the onset of apnoea (apnoeic oxygenation). This study isolates oxygen administration with high-flow nasal oxygen to the period when the person is breathing, without ongoing oxygen administration during the apnoea period, to quantify its effects during the pre-oxygenation period only. A third group of participants breathes oxygen through a mouthpiece in addition to receiving oxygen via high-flow nasal cannulae. The effect of these pre-oxygenation methods will be measured by the time taken until oxygen saturation levels decline to the lower end of the normal range (92%), along with other parameters such as blood oxygen levels.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
TREATMENT
Masking
NONE
Enrollment
84
Induction of anaesthesia after 2mins 45 seconds of pre-oxygenation with 1-1.5mcg/kg remifentanil plus 2-3mg/kg propofol. Propofol (10mg/kg/hr) and remifentanil (0.15mcg/kg/min) infusions commenced until study conclusion. Positive pressure ventilation commenced at Sp02 92%. Failure to intubate the patient during the first minute of apnoea results in withdrawal from the study. Blood samples obtained from an arterial catheter immediately prior to commencing pre-oxygenation, after 90 and 180 seconds of pre-oxygenation, after one minute of apnoea, and every two minutes during the apnoeic period.
University Hospital Galway
Galway, Ireland
Time to oxygen desaturation
The time period from the onset of apnoea (determined by visual inspection) until an oxygen saturation of 92% is measured by pulse oximetry.
Time frame: Immediately after the intervention
Arterial partial pressure of oxygen after pre-oxygenation.
As measured by blood gas analysis
Time frame: At 3 minutes of pre-oxygenation
Arterial partial pressure of carbon dioxide change during pre-oxygenation
As measured by blood gas analysis
Time frame: At 0 and 3 minutes
Change in arterial partial pressure of carbon dioxide during apnoea
As measured by blood gas analysis
Time frame: At 0, 1, 2 minutes and each 2 minutes thereafter
Change in acid-base status during apnoea
As measured by blood gas analysis
Time frame: At 0, 1, 2 minutes and each 2 minutes thereafter
Correlation between end-tidal carbon dioxide measurement and arterial partial pressure of carbon dioxide
The EtCO2 value used for comparison is the highest value recorded during the first five respiratory cycles by manual ventilation with the adjustable pressure-limiting valve set at 20cmH20.
Time frame: Etco2 obtained at the time of resumption of ventilation. Paco2 obtained from the preceding blood gas measurement.
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