DAS Small Research Grants

Background
The traditional way of inserting an endotracheal tube (plastic tube to help patients breathe during general anaesthetic) is to use an instrument called a laryngoscope. This is a metal device comprising of a light source and a blade. This is placed into patient's mouth and allows visualisation of vocal cords and voice box (larynx) so the endotracheal tube can be inserted into the upper trachea. This method is known as direct laryngoscopy. The view which is obtained during direct laryngoscopy can be described according to the Cormack-Lehane (CL) classification based on structures seen. This provides clear information from one anaesthetist to another on the ease (or difficulty) of intubating the trachea under direct vision.

Videolaryngoscopes (VL) use video camera technology to view the airway structures and facilitate tracheal intubation. In contrast to a traditional laryngoscope, VL utilises indirect laryngoscopy via the camera. The use of VLs have increased rapidly and there are now many different devices available. Currently, CL classification is used to describe the view obtained during indirect laryngoscopy. Different VL devices all have a slightly different approach to facilitate intubation. The use of CL classification could potentially provide false reassurance as it only provides the information of the view obtained at direct laryngoscopy and not the ease of intubation. We developed a new VL scoring system which we believe will give sufficient information for reproducible results across operators and devices.

Aims
We developed a grid system which describes the view obtained during intubation. Our scoring system involves nine-panel square grid over a VL video-screen with each square representing a specific quadrant. The study will allow us to evaluate the ease of use of the grid system and how reproducible it is when communicating with other anaesthetists when compared to CL classification.

Methodology
This will be a manikin based, proof of concept study. We aim to recruit both trainee anaesthetists and consultant anaesthetists with varying degrees of experience in the use of VLs. We will compare how the grid system scores against the CL classification in terms of accuracy, reliability and ease of use.

Expected outcomes
We hypothesise that our new scoring system will be reproducible, easy to use and allow clear communication regarding the view obtained at intubation.

Implications
The results of this manikin study will determine whether there is value in evaluating this scoring system in patients, and if so, will lead to clinical studies and potentially a new description of VL intubation.

Background
Patients with head and neck cancer may receive radiotherapy treatment, and can present for surgery as part of their treatment, or later once their cancer is treated.

This will necessitate administering a general anaesthetic during which we insert a "breathing tube" to protect the patient's airway by keeping it open. Despite assessing every individual patient, we sometimes encounter unanticipated difficulty inserting the breathing tube once the patient is asleep.

The Difficult Airway Society (DAS) has published guidelines on managing this scenario. If "Plan A" (inserting a breathing tube) fails, they recommend inserting a laryngeal mask airway (LMA) as a "Plan B" rescue measure. This alternative airway device sits above the vocal cords, as opposed to a breathing tube that passes between the vocal cords to sit below them. If LMA insertion is successful this can then be used to provide oxygen to the patient.

DAS recommend using a newer "second generation LMA" in their guidelines. This is based on previous research, demonstrating that a successful insertion should be achievable within the maximum two attempts that DAS recommend. The research carried out on this has so far been confined to manikin studies and patients with normal airway anatomy.

Aims
Our clinical experience is that this particular device can sometimes be challenging to insert in patients with previous radiotherapy. We aim to study the success rate of using a second generation LMA (an i-Gel) in patients presenting for planned surgery who have had previous head and neck radiotherapy. This will then allow us to assess how well these devices perform as a rescue measure in this subset of patients, if following the current guidelines published by DAS for management of an unanticipated difficult airway.

Methodology
We will recruit and consent patients who have had previous head and neck radiotherapy, presenting for planned surgery where they are scheduled to have a general anaesthetic and breathing tube inserted.

Once they are anaesthetised we will insert an i-Gel LMA, and assess whether or not this has been successful by assessing if we have an open airway via the device. If the first attempt is unsuccessful we can repeat this as per the DAS guidelines up to a maximum of two attempts. Following this intervention, the anaesthetist will then insert a breathing tube as planned and the patient will proceed to surgery.

Expected outcomes
The potential outcomes of this study will be either that we find the i-Gel performs as a successful rescue device in patients with previous head and neck radiotherapy (defined as a successful insertion within two attempts as per the DAS guidelines), or that it does not.

Implications
If we find the i-Gel performs well in this subgroup of patients this will provide further weight to the DAS recommendations. If we find that it does not perform well, this may have implications for modifying the current guidelines to include separate guidance for this group of patients, which may lead to further work being carried out in this area.

Background
Prior to administering a general anaesthetic, it is important to fill a patient's lungs with oxygen, which gives them a reservoir of oxygen for their body to use after they stop breathing. This increases the time available for a breathing tube to be sited, after which the anaesthetist will take over their breathing for them. The practice is called pre-oxygenation and is especially important in pregnant women due to their increased oxygen requirement compared to normal adults resulting in a more rapid drop in blood oxygen levels after general anaesthesia along with changes to their body during the pregnancy that can make siting of a breathing tube more difficult and therefore take longer to do.

Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE) is a novel method of pre-oxygenation that delivers fast-flowing oxygen continuously through the nose. It has the added benefit of supplying oxygen to the lungs even after breathing has stopped and can significantly prolong the time before blood oxygen levels fall after breathing is stopped in normal adults. Despite this added benefit, it is ineffective at restoring blood oxygen levels after they have already fallen so adequate pre-oxygenation before anaesthesia is essential.

General anaesthesia in pregnant women is usually performed in emergency situations where preparation time for the anaesthetists is limited. Pregnant women are likely to benefit from THRIVE pre-oxygenation for the reasons listed above, but the amount of THRIVE required to achieve adequate pre-oxygenation has yet to be defined. The Difficult Airway Society guidelines recommend aiming for an oxygen level of 90% in the lungs with pre-oxygenation.

Aims
We wish to determine the number of maximal breaths required with THRIVE to fully pre-oxygenate the lungs of pregnant women at term and investigate the effect of doing it with their mouth open or closed.

Methodology
We will recruit and consent women immediately before they are due to have an elective Caesarean section. They will be randomised to start with mouth open or closed and be assigned a number of maximal breaths to perform. They will be fully monitored whilst THRIVE is delivered and after the set number of breaths are complete, the THRIVE will be removed as they breathe into an anaesthetic breathing circuit via a tight-fitting mask. Standard gas monitoring attached to the breathing circuit will determine the oxygen level achieved in their lungs. This will be repeated twice for each participant, once with mouth open and once with mouth closed.

To determine the number of breaths required we will use an up-down sequential allocation methodology, increasing or decreasing the number between each participant depending on how they perform. The end result will equate to the number of breaths required for 90% of pregnant women to achieve a 90% oxygen level in their lungs.

Expected outcomes
Over the course of the study, we will narrow down to the smallest number of breaths required to achieve pre-oxygenation.

Implications
Anaesthetists may use this information to rapidly and safely pre-oxygenate pregnant women before general anaesthesia using THRIVE.

Background
When a patient is unconscious either through administration of general anaesthesia, a medical condition or as a result of alcohol or illicit drug use it is necessary to secure and protect their airway. This is usually achieved by the use of a plastic tube (Endotracheal tube) inserted via the mouth through the vocal cords and in to the upper trachea. The endotracheal tube has a small balloon on it which is inflated to further protect the airway.

These tubes are inserted with the aid of a laryngoscope. The laryngoscope is a metal device with a light source and a handle with a hinged "blade." This is inserted in to the mouth of the unconscious patient and used to lift the oral structures such that a view of the vocal cords can be achieved and the tube passed between the cords. This is direct laryngoscopy.

In some patients direct laryngoscopy may not be possible and in these cases indirect laryngoscopy can be performed. This often uses a video camera system with the camera head in a modified version of the laryngoscope mentioned above. Previously the blades used in these systems were designed to be cleaned in between patient uses however there has been a move to single use plastic blades for infection control purposes.

There have been case reports of these plastic blades breaking in use and where as there is an international standard for direct laryngoscopes there is no such standard for the indirect laryngoscopes.

Aims
We hope to evaluate a number of the single use plastic blades produced by the major manufacturers of video laryngoscope systems and develop standards for the assessments of products.

Methodology
This will be a lab bench based study looking at the strength, rigidity and illumination provided by various video laryngoscope single use blades in comparison to the existing standards for direct laryngoscope blades.

Expected outcomes
The single use video laryngoscope blades should perform to the same standard as the direct laryngoscope blades.

Implications
The performance of the various blades under test may have implications for recommendations for use by expert bodies e.g. DAS and for agreement of national standards similar to that which exist for direct laryngoscope blades.