A Magnetic Resonance Imaging Study of Changes in the Angle Between the Tracheal and Laryngeal Axes in the Sniffing, Neutral and Extended Head and Neck Positions for Videolaryngoscopy
Phase: NA
Conditions: Intubation, Intratracheal
Sponsor: University Hospitals Coventry and Warwickshire NHS Trust

 
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STUDY PROTOCOL 
A magnetic resonance imaging study of the changes in the 
angle between the tracheal and laryngeal axes in the sniffing, 
neutral and head extended positions. 
 
 
1. 
INTRODUCTION 
1.1 
Background 
The traditional method of tracheal intubation requires the insertion of a 
laryngoscope with the left hand into the oral cavity to displace the tongue and 
directly visualise the glottis.  
The “sniffing the morning air” (or “sniffing”) position has been traditionally used 
for tracheal intubation using direct laryngoscopy. This comprises of flexion of the 
lower cervical spine, extension at the atlanto-occiptal joint and a horizontal level 
between the tragus of the ear and sternum (Brindley, et al. 2010). The 
theoretical purpose of this position is to improve the glottic visualisation by 
aligning the oral, pharyngeal and tracheal axes (Figure 1, B). 
 
Figure 1. Traditional head and neck position for tracheal intubation 
A. Normal head position showing 3 axes in supine position.  
B. Sniffing the morning air position with occiput raised showing alignment 
of 3 axes.  
C. Direct laryngoscopy in the sniffing position.  
 
In recent years with the advancement of technology, videolaryngoscopy  has 
become popular and many centres are now using only videolaryngoscopes for 
tracheal intubation. Visualisation occurs “indirectly” through fibreoptic or digital 
channels. Most videolaryngoscopes use two types of blades. The Macintosh type 
for normal airway and hyper-angulated blade for difficult airway. 

 
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Hyperangulated blades such as the Glidescope LoPro (Verathon Inc, Bothwell, 
WA, USA) (Figure 2 B), McGrath Series 5 X blade (Medtronic, Minneapolis, MN, 
USA) and Storz C-Mac D-blade (Karl Storz Endoscoke, Tuttlingen, Germany) are 
more curved than the traditional standard geometry (Mcintosh blades – Figure 2 
A) used with direct laryngoscopy and are thought to improve glottis visualisation 
without significant change in head position. However, visualisation of glottis is 
one of the three steps involved in videolaryngoscopy assisted tracheal 
intubation. The other two steps include aligning the tube with the glottic inlet 
and advancing the tube through the glottis into the trachea. 
 
 
 
Figure 2. Geometrical comparison of blade types, A: Macintosh (Mac) blades and 
B: hyper angulated blade 
One of the main drawbacks in videolaryngoscopy is that despite good view of 
glottis on the screen, it can be difficult to successfully advance the tracheal tube 
into the trachea. Anterior impingement of the tracheal tube at the sub-glottic 
region is a recognised problem with hyperangulated and channelled 
videolaryngoscopes (Levitan 2011). VL directs the pre-formed tracheal tube 
anteriorly but the trachea descends posteriorly into the thorax creating an acute 
angle impeding passage of the tube (Levitan, et al. 2011). This is demonstrated 
in figure 3. This can result in difficult intubation or a failed intubation. 
Manoeuvres such as tube rotation and rotation of bougie (Mendonca, et al. 
2018) can rectify this problem to some extent.  
Aziz, et al. (2016) found that laryngoscopy was more difficult with hyper-
angulated blades in the “sniffing” position compared to neutral position 
A 
A 
B 

 
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contradictory to traditional laryngoscopy teaching. Intermediary positions 
between “sniffing” and supine should be studied as these may balance the needs 
of maintaining sufficient mouth opening and not hindering angles affecting the 
axial alignment (Levitan, et al. 2011).  Both studies recommend the benefits of a 
ramped position as it does reduce the time to desaturation and reduces 
aspiration risk compared to supine neutral positions and should be considered 
when using hyperangulated blades. Mendonca, et al. (2018) studied neutral and 
sniffing position with no difference in success rate in tracheal intubation between 
two positions.  
 
Figure 3. A) Acute angle produced by the trajectory of the tube (black 
arrow) and the trachea (green tube – marked by red arrow). B) Preformed 
acute angle stylet directing the tube anteriorly leading to anterior 
impingement. 
Using magnetic resonance imaging in awake and healthy patients, Adnet, et al. 
measured the oral, pharyngeal and tracheal axes using the neutral position, 
“sniffing” position and simple head extension and found neither position resulted 
in perfect alignment of the 3 axes. However, they didn’t study the effect of 
position on angle between tracheal and laryngeal axes. The search for further 
evidence is necessary for VL as there is a paucity of research in with regard to 
best head and neck position for videolaryngoscopy.  
 
 
 

 
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1.2 
Proposed study 
This study would assess whether differing head and neck positions would 
improve alignment between upper airway anatomical axes, in particular the 
tracheal and laryngeal axes and therefore minimise the possibility of anterior 
impingement.  
1.3 
Study population 
Staff from University Hospitals Coventry & Warwickshire NHS Trust 
1.4 
Treatment / Intervention (if applicable) 
Magnetic resonance imaging (MRI) can safely be used to assess the upper 
airway anatomy and would allow measurement of the axes described to suggest 
which head and neck position would provide best anatomical alignment to 
reduce anterior impingement. 
All the MRI scans will be conducted using 3.0 Tesla (Optima 750w, GE Medical, 
Milwaukee, WI, USA) using the cervical spine section of the coil. T2-weighted 
images in the sagittal plane will be acquired using a fast recovery fast spin echo 
(FRFSE) technique with the parameters in Table 1. The scans will take around 
two and half minutes and a member of the anaesthetic investigator team will be 
present to facilitate positional changes and maintain consistency.  
Acquisition parameters (Table 1): 
Repetition time (TR ) 
2905 ms 
Echo time (TE)  
107ms 
Field of view (FOV ) 
36 cm 
Slice thickness  
3 mm 
Slice gap  
1 mm 
ETL 
19 
Frequency matrix size 
352 
Phase matrix size 
320 
Number of excitations (NEX) 
3 
Receiver band width 
41.67 kHz 
Scan time  
2 min 34 s 
 
MRI scanning will be performed in following 3 head and neck positions: 
Neutral position- Participant lying flat on the MRI table, with a vertical gaze, 
without any pillow (no flexion, no extension of the neck). 
 

 
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Sniffing position is achieved with head resting on Oxford HELP headrest (Alma 
Medical, London) of 7cm in height to achieve neck flexion by 35o and extension 
at atlantooccipital joint to achieve face plane extension of 15o (Horton WA 1989) 
Extension position: Oxford HELP Base pillow (Alma Medical, London) is placed 
under the shoulders with head resting off the end and neck in full extension 
position.  
 
2. 
RATIONALE  
2.1 
Aims and hypothesis 
To determine which patient positioning significantly improves the alpha (α) 
angle.  It is defined as the angle between the tracheal axis (TA) and laryngeal 
axis (LA). This can be seen in Figure 4 below. 
Other two angles measured would be:  
• 
Beta (β) angle between the laryngeal axes (LA) and pharyngeal axes (LA) 
• 
Delta (δ) angle between pharyngeal axes (PA) and oral axes (OA) 
 
 
 
Figure 4. MRI scan showing tracheal, laryngeal axes and pharyngeal 
axes and corresponding α angle, β angle and δ angle 
 
• 
The tracheal axis (TA) is defined as a line passing through the centre of 
intrathoracic part of trachea to the centre of cricoid cartilage.  

 
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• 
The laryngeal axes (LA) is defined as a line passing through the centre of 
cricoid cartilage to the base of the epiglottis. 
• 
The pharyngeal axis (PA) is defined as a line passing through the anterior 
portion of the atlas and C2. 
• 
The oral axis (OA) is defined as straight line drawn parallel to the hard 
palate 
 
2.2 
Justification 
Videolaryngoscopy (VL) has become a standard of care in anaesthesia and they 
are included in airway management guidelines. VLs are gradually replacing direct 
laryngoscopes. For a direct laryngoscopy and tracheal intubation, the sniffing 
position has been considered as ideal. When this position is transferred to VL, 
problems such as anterior impingement occur where the tube tip hits the 
anterior wall of trachea and fails to advance further. Aziz, et al. (2016) found 
that the "sniffing" position made intubation more difficult than the neutral 
position. It is therefore critically important to determine what head positions are 
important to use with VL. 
The use of MRI in healthy subjects has been attempted previously to determine 
the geometrical axes within the oral cavity (Adnet, et al. 2001). These 
researchers however did not specifically consider the alpha angle we have 
defined which could reduce anterior impingement with VL. Anterior impingement 
is an important consideration as it can result in failed intubation and this is 
clinically important if VL is used as a rescue device in an emergency.  
We hypothesise that the position that improves the alpha angle the most would 
be considered as the ideal position for videolaryngoscopy and tracheal 
intubation. Due to the widespread and increasing use of videolaryngoscopes, this 
study would help us to recommend an ideal head and neck position. This will 
further help to improve the first attempt success rate of tracheal intubation.  
2.3 
Assessment and management of risk 
There are no anticipated risks in undergoing MRI scan. Participants will have to 
complete the MRI safety checklist and have this reviewed by a radiographer for 
any risks before they can enter the scanner. 
 
Process if inadvertent abnormality is found:  Participants will be asked to 
consent to any abnormal finding of significance to be reported to their GP 
 
Other considerations:  
• 
Risk of claustrophobia and loud noise can occur during the scan. Ear 
defenders and an emergency button will be provided as per standard MRI 
practice.  
• 
Participants will be given the option to withdraw at any stage if they feel 
that they are not able to tolerating lying down within the MRI Scanner.  
• 
We would also advise participants who are pregnant or who have devices 
or medical conditions that can be exacerbated by these experiences to not 
partake. 

 
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3. 
OBJECTIVES AND OUTCOME MEASURES/ENDPOINTS 
3.1 
Primary objective 
• 
Measurement alpha (α) angle between the tracheal axis (TA) and 
laryngeal axes (LA) in three different positions. 
The primary objective is to identify which of the three head and neck positions 
we have identified ("sniffing", extension of neck and neutral position) improves 
the alpha angle when examined under MRI. We hypothesise the position that 
most improves the alpha angle would reduce the incidence of anterior 
impingement with videolaryngoscopy. We hypothesise the position that brings 
the alpha angle closest to 180° would reduce the incidence of anterior 
impingement and therefore considered best for tracheal intubation using VL. 
3.2 
Secondary objectives 
The other two angle measurements include  
Beta (β) angle between laryngeal (LA) and pharyngeal axes (PA). This is the 
alignment between line passing through the voice box and pharynx (on the MRI 
image line passes through the top part of second cervical vertebra) 
Delta (δ) angle between pharyngeal axes (PA) and oral axes (OA). This is the 
alignment between pharyngeal axis and the line passing parallel to the palate. 
The MRI reports will be interpreted by a Consultant Radiologist.  
3.3 
Primary endpoint/outcome 
The alpha (α) angle in degrees. 
3.4 
Secondary endpoints/outcomes 
The Beta (β) angle and Delta (δ) angle in degrees 
 
4. 
STUDY DESIGN 
Controlled trial without randomisation  
 
5. 
STUDY SETTING 
Single centre study at University Hospitals Coventry and Warwickshire NHS Trust 
 
6. 
ELIGIBILITY CRITERIA 
6.1 
Inclusion criteria 
• 
Able to provide consent 
• 
Volunteers, UHCW staff, aged > 18 years 
• 
Medically able and willing undertake MRI scanning.  

 
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• 
Should pass the MRI safety check list to enter the MRI suite. All 
participants will complete an MR safety questionnaire immediately prior to 
their MR scan 
 
6.1 
Exclusion criteria 
• 
Unable to provide consent 
• 
Not willing to have MRI scan or unable to undergo MRI scanning and 
restricted neck movements. For MRI safety reasons all participants with a 
cardiac pacemaker or other electronic implants will be excluded from the 
study. 
 
 
7. 
TRIAL PROCEDURES  
Screening 
Step 1 – Convenience sampling used to recruit participants (UHCW Staff) by the 
investigators. Inclusion and exclusion criteria will be discussed. Aim to recruit 2 
participants every week. We anticipate this phase will take 10 -12 weeks.  
 
Baseline 
Step 2- Information leaflet provided and study outcomes discussed. MRI safety 
questionnaire also reviewed by the potential participant. Any reasons that would 
preclude positioning in an MRI machine will also be recorded.  
 
Participants will be allowed to enough time to read and understand the 
participant information. The procedure for any abnormal findings will be 
discussed in consent and in the participant information sheet. 
 
Step 3 – For participants who would like to volunteer, consent form signed. Any 
queries clarified. Baseline demographic and airway assessment recorded. This 
data will be stored securely within the research locker located in the Anaesthetic 
department, UHCW. 
 
Pre-booked MRI slot in the future is allocated to the participant. 
 
Step 4 - Participants will be reminded about MRI slot 1 day prior to scan 
 
MRI Suite 
Step 4 – Participants attend MRI Suite, UHCW Radiology department at specified 
time. MRI Safety questionnaire reviewed again and completed for Radiology 
department. Any remaining questions answered by anaesthetic investigators 
and/or radiographer.  
 
Step 5 – MRI Conduct. Anticipate each scan will take 2.5 minutes (total 7.5 
minutes for 3 scans), with re-positioning in the middle by one of the Anaesthetic 
investigators. Including questions and filling out questionnaire anticipate this will 
take 30 minutes per participant in total.  
 
There is capacity to scan 2 participants per week on   per pre-booked MRI slot 
and therefore this phase will take at the minimum 10 to 12 weeks.  
 

 
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Participant involvement ends with MRI scan in the final head and neck position. 
 
Review 
Step 6 – This sequence will produce three sagittal MRI images per participant. 
These images will have their personal data removed and will be pseudo-
anonymised (tokenization) after the images have been reviewed for any 
abnormal findings and the angles will be measured by the Consultant 
Radiologist. 
 
Step 7 – Tokenized results analysed by Anaesthetic investigator team 
 
Step 8 – Further anonymised data will be analysed by the statistician and 
anticipate this will take another 6 -8 weeks. 
 
7.1 
Recruitment 
Staff members of University Hospitals Coventry and Warwickshire NHS Trust 
(UHCW) will be invited to participate as volunteers in this study. This will be 
sampled conveniently, and the inclusion and exclusion criteria will be checked.  
They will then review the MRI safety check list for eligibility to undergo MRU 
scan. Written informed consent will be obtained from the participants. 
 
7.1.1 Screening 
Participants will be provided information regarding preparation for an MRI and 
questions related to this will be answered by the lead radiographer.  
 
Standard operating procedure for patients undertaking an MRI will be followed 
and led by the radiographer present. At the scan, a member of the anaesthetic 
investigator team will be present to re-confirm (verbal) consent and facilitate the 
scan by ensure consistency between positions.  
 
The patient will undergo three MRI scans. At the end of this the participant will 
be thanked for their involvement. We will state that if they have any questions 
to contact the research team and if they would like results of the study they can 
be contacted in the future.  
 
7.1.2 Payment 
No payment will be offered for volunteers to this study 
7.2 
Consent  
A written consent will be obtained from all participants. All investigators will be 
suitably trained to obtain consent as per Good Clinical Practice.  
MRI safety questionnaire as per Radiology Information Governance also 
required. 
7.3 
Baseline data 
Baseline demographic data: 
• 
Age 
• 
Sex 

 
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• 
Ethnicity 
• 
Height 
• 
Weight 
 
Baseline airway assessment data: 
• 
Mallampati score 
• 
Jaw protrusion 
• 
Neck movement 
• 
Thyromental distance 
• 
Sternomental distance 
 
7.4 
Long term follow-up assessments 
No long-term follow-up is planned for this study. 
7.5 
End of study definition 
This will occur when the 20th patient has their final MRI study performed 
8. 
STATISTICS AND DATA ANALYSIS 
8.1 
Sample size calculation 
Previous studies on volunteers involving radiological imaging recruited 8 , 15 and 
42 patients (Adnet. et al, Abramson. et al and Greenland. et al). We aim to 
recruit 20 volunteers (UHCW staff) to participate in the study.  
8.2 
Planned recruitment rate 
We plan to recruit 10 volunteers every 4 weeks, totally 8 weeks. This will total 
20 participants. Recruitment will be undertaken by each of the three Anaesthetic 
investigators and therefore this is a realistic target due to the relatively small 
number of participants required.  
8.3 
Statistical analysis plan 
8.3.1  Primary outcome analysis 
Data will be analysed using ANOVA or appropriate test and p value less than 
0.05 was considered statistically significant  
 
8.3.2  Secondary outcome analysis 
Data will be analysed using ANOVA or appropriate test and p value of 0.05 or 
less will be considered statistically significant  
 
8.4 
Subgroup analyses 
Subgroup analysis may be possible depending on baseline demographic data.  

 
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8.5 
Participant population 
All participant data will be included in the final analysis if they have attended for 
the MRI scanning. We will endeavour to ensure this does not occur by reminding 
participants of scheduled MRI dates and ensuring any concerns are answered 
fully.  
8.6 
Procedure(s) to account for missing or spurious data  
All data collected from the initial recruitment will be included in the study. 
Investigators will be trained and be adequately skilled to record the baseline 
demographic data and the airway assessment data. Participants will be pseudo-
anonymised. Any participants who do not attend for the MRI scanning, and 
therefore will have no MRI images for the study, will not be included in the final 
analysis.  
9. 
DATA MANAGEMENT 
9.1 
Data collection tools and source document identification 
Data will be collected by the Anaesthetic investigator team. These will be 
recorded on a case report form (CRF) including the background demographic 
data. All stored data will comply with Good Clinical Practice guidelines and 
General Data Protection Regulation (GDPR). 
9.2 
Data handling and record keeping 
All participant data will be handled by the investigator team (MRI radiographer, 
Consultant Radiologist and Anaesthetic investigator team), and protected on 
UHCW trust server which is username and password protected.   
In terms of the MRI images, these will not be linked to the volunteer’s real 
hospital data. We aim to keep confidentiality by coding each participant (pseudo 
anonymisation), and each scan (i.e. participant 1, first scan = 1A, second scan = 
1B etc).  
Hard copies of informed consent will be stored in a locked cabinet within the 
Anaesthetic department at UHCW. MRI safety questionnaires will be stored as 
per standard Radiology policy for Information Governance. Personal data will be 
collected for consent and safety checklists. Access to this data will be by the 
research team  and radiographer to ensure safety check list is correctly 
completed.  
All local investigators will be trained in accordance with the UK Policy Framework 
for Health and Social Care Research. 
9.3 
Access to Data 

 
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Direct access will be granted to authorised representatives from the Sponsor, 
host institution and the regulatory authorities to permit trial-related monitoring, 
audits and inspections - in line with participant consent. 
9.4 
Archiving 
Following the resolution of queries and confirmation of study close-out by the 
Chief Investigator, all essential documentation will transferred to a third party 
archiving service, which provides suitable fire and water-resistant facilities. 
Study files will be archived for a period of 25 years. Access to the study 
documentation will be restricted to named individuals within the study team with 
express permission from the Chief Investigator. 
10. 
TRIAL OVERSIGHT 
10.1 Role and responsibilities of the Sponsor 
UHCW has agreed to act as sponsor for this trial and will undertake the 
responsibilities of sponsor as defined by the UK Policy Framework for Health and 
Social Care Research and ICH Good Clinical Practice. An authorised 
representative of the Sponsor has approved the final version of this protocol with 
respect to the trial design, conduct, data analysis and interpretation and plans 
for publication and dissemination of results. As sponsor, UHCW provides 
indemnity for this trial and, as such, will be responsible for claims for any 
negligent harm suffered by anyone as a result of participating in this trial. The 
indemnity is renewed on an annual basis and will continue for the duration of 
this trial. 
10.1.1 Principal Investigators 
The Principal Investigator responsibilities include, but are not limited to: 
• 
Ensuring that the trial is conducted as set out in the protocol and 
supporting documents 
• 
Delegating trial related responsibilities only to suitably trained and 
qualified personnel and ensuring that those with delegated responsibilities 
fully understand and agree to the duties being delegated to them; 
• 
Ensuring that CVs and evidence of appropriate training for all Site staff are 
available in the Trial Site File 
• 
Ensuring that all delegated duties are captured in the study Delegation 
Log 
• 
Ensuring all Adverse Events are documented and reported promptly to the 
Trial Manager; 
• 
Accountability for trial treatments at their site; 
• 
Ensuring the trial is conducted in accordance with ICH GCP principles;  
• 
Allowing access to source data for monitoring, audit and inspection; 
• 
Ensuring that all source data is complete and provided to the Trial 
Manager at regular intervals 

 
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11. 
MONITORING, AUDIT & INSPECTION 
The study will be monitored by the Research and Development Department at 
UHCW as representatives of the Sponsor, UHCW. This is to ensure the study is 
conducted as per protocol, adhering to Good Clinical Practice and Research 
Governance.  
12. 
ETHICAL AND REGULATORY CONSIDERATIONS 
12.1 Ethical approval and research governance 
The study will be conducted in compliance with the principles of the ICH GCP 
guidelines and in accordance with all applicable regulatory guidance, including, 
but not limited to, the UK policy framework for health and social care research. 
Ethical approval for this study will be sought from the Research Ethics 
Committee combined with Health Research Authority (HRA) approval. No study 
activities will commence until favourable ethical opinion and HRA approval has 
been obtained. Progress reports and a final report at the conclusion of the trial 
will be submitted to the approving REC within the timelines defined by the 
committee. Confirmation of capacity and capability will be obtained from the 
R&D department prior to commencement of the study at all participating sites. 
12.2 Data protection and patient confidentiality 
The study will comply with the current Data Protection regulations and regular 
checks and monitoring will be undertaken by the Trial Manger to ensure 
compliance. Participants will be assigned a unique identifier upon enrolment in to 
the study to allow pseudonymisation of patient-identifiable data. Access to 
patient identifiable data will be restricted to members of the study co-ordination 
team who require it for the performance of their role.  Electronic data will be 
stored on password protected encrypted drives and hard copies of study 
documents will be stored in locked filing cabinets in secure entry-card protected 
sites. 
12.3 Safety reporting 
Regarding incidental findings of anomalies on MRI scanning: 
During consenting we will ask volunteers to consent for the investigators to be 
allowed to write to their General Practitioner (GP) if any untoward findings are 
found incidentally on the reported MRI scans by the Consultant Radiologist. The 
process will include a copy of the MRI report with a supplementary letter written 
to the GP asking them to follow-up with the volunteer in regards to their 
incidental MRI findings. 

 
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13. 
DISSEMINATION POLICY 
The results of this study are to be presented locally at the UHCW Department of 
Anaesthesia Quality Improvement Meeting (QIPS), which is held monthly. This 
may promote education on altering head positioning when videolaryngoscopy is 
used.  
We will aim to publish the results within an anaesthetic journal for dissemination 
to a wider audience. As this the first MRI study looking at best head and neck 
position for videolaryngoscopy, we hope in the future that this study would 
provide the first step into providing formal guidance for positioning with 
videolaryngoscopy.  
We will aim to publicise the results to the wider public through a plain English, 
lay summary of findings. 
14. 
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