Throat Disorders Clinical Trial
Official title:
Airvo/Optiflow High Flow Nasal Oxygenation During Microlaryngeal Surgery - Assessing Effectiveness of Oxygenation and Carbon Dioxide Clearance
Optiflow high flow nasal cannula (HFNC) oxygenation is a technique to provide oxygen to patients when they are paralysed under general anaesthesia. Their lungs are not moving, but the high flow allows oxygen to travel into their lungs. This is called 'apnoeic ventilation'. The investigators will be using this for patients undergoing surgery for their throat.
Hypothesis:
Optiflow high flow nasal cannula (HFNC) oxygenation is a suitable technique for oxygenation
and ventilation (apnoeic ventilation) for patients undergoing microlaryngeal surgery.
Aims:
1. Measure continuous pulse oximetry (oxygenation) and intermittent subglottic catheter
sampling of end tidal carbon dioxide levels (ventilation) in the distal trachea during
HFNC oxygenation
2. Measure intra-tracheal airway pressure during HFNC oxygenation
Methodology:
As a pilot study, the investigators will recruit up to 20 patients within a 12 month period
scheduled for elective microlaryngeal surgery and high frequency jet ventilation. Standard
monitoring and standard conduct of anaesthesia will be carried out: induction of general
anaesthesia, insertion of a narrow catheter into the trachea and insertion of laryngeal mask
airway. In addition, the study device (HFNC) will be placed into the entrance of the
patient's nostrils. After removal of the laryngeal mask, HFNC oxygenation will commence. A
surgical suspension laryngoscope will be inserted for microlaryngeal surgery (standard
technique). The investigators will measure the adequacy of gas exchange, during of HFNC
oxygenation and complications (cardiovascular, airway and respiratory). Data will be stored
on a secure REDCap (Research Electronic Data Capture) system.
Importance:
HFNC oxygenation is a novel technique that depends on apnoeic oxygenation. Even though the
patient is paralysed and not breathing, oxygenation and carbon dioxide clearance still
occurs. This is due to the difference between the alveolar rates of oxygen removal and
carbon dioxide excretion which generates a negative pressure gradient. Oxygenation of the
patient is therefore due to the high inspiratory fraction of oxygen, apnoeic ventilation and
the small continuous positive airway pressure caused by the high flow of gas. This pressure
increases lung volume and recruits collapsed alveoli. Carbon dioxide clearance is due to gas
mixing and flushing of the airway dead space. The additional humidification of the high flow
oxygen prevents mucociliary damage of the airway.
HFNC has been shown beneficial in pre-oxygenation, oxygenation after extubation, and in the
treatment of respiratory failure and heart failure. New uses in difficult airway management
are now emerging. However, the main case series of HFNC use in difficult airways did not
measure intra-operative airway pressures end tidal oxygen and carbon dioxide; these gases
were only measured at the end of surgery and when a definitive airway was inserted. As far
as the investigators are aware, there are no data on intra-operative, intra-tracheal airway
pressures or oxygen or carbon dioxide during HFNC oxygenation. Our study aim is to fill this
knowledge gap.
Potential benefits and risks:
The use of HFNC removes obstacles form the surgical field and this may make surgery easier
and quicker to perform. Risks include: failed gas exchange, but this is minimized by
abandoning HFNC oxygenation and instituting tracheal catheter jet ventilation via the in
situ jet catheter (standard practice).
;