Tulip GT vs Guedel+Facemask RCT in Anaesthetised Patients
Tulip GT vs Guedel+Facemask RCT in Anaesthetised Patients
Dr P N Robinson
Northwick Park Hospital
Middlesex HA1 3UJ
The Tulip GT® airway versus the Guedel airway and facemask: a randomised, controlled, cross-over clinical study comparing airway ventilation with Basic Life Support (BLS) trained airway providers in anaesthetised patients.
A. Shaikh1, P.N. Robinson2, and M. Hasan3
1 General Practitioner; Central Surgery, Gorleston and Accident and Emergency, James Paget University Hospital, Gorleston; Honorary Research Fellow, Department of Anaesthesia, Northwick Park Hospital, Middlesex, UK.
2 Consultant Anaesthetist, Department of Anaesthesia, Northwick Park Hospital, Middlesex, UK.
3 Consultant Anaesthetist, University College Hospital, London, UK.
A randomised, controlled, cross-over, human study using Basic Life Support (BLS) airway providers with annually trained Guedel airway with facemask skills compared ventilation using either the Tulip GT® airway or a Guedel airway with facemask in 60 patients after the induction of anaesthesia.
End-tidal carbon dioxide, tidal volume and peak inspiratory pressures were significantly better (p < 0.0001) for all parameters with the Tulip GT airway. The Tulip GT airway was found to be easier to insert and demonstrated a steep learning curve for the BLS trained airway providers. This study follows on sequentially from an identical study conducted in manikins. These results are similar to the manikin study and this suggests a close correlation between human and manikin studies for this airway device. No other studies comparing an identical protocol in both manikins and Humans could be found on searches. The Tulip GT airway device should be considered as an adjunct to airway management both within and outside hospitals when ventilation is being undertaken by BLS trained airway providers.
The Tulip® airways are an evolving range of single sized (Tulip Advance®) and multisized (Tulip GT® (Guedel Type)) disposable oropharyngeal airways which are hands free and directly connectable to a breathing circuit. Manikin and initial clinical studies have indicated that they may have a place in the initial airway management of the unconscious patient either within or outside hospitals. They are easy to insert, may have a steep learning curve, and therefore be useful for BLS trained airway providers in airway management [1 – 4].
The Tulip GT airway is designed to replace the Guedel airway and facemask but be hands free, directly connectable and be easier to use because it requires no mask. It presents as a right angled, 14mm x 10mm I.D. (internal diameter) oval cross-sectioned bite-proof breathing tube in which the distal end is surrounded by a single beveled, high volume, low pressure, anatomically shaped polyhedral cuff (Figure 1). After insertion, cuff inflation provides a circumferential oropharyngeal seal and secures the airway in the oropharynx posterior to the tongue. A range of tubes are made which correspond in size to the equivalent size and colour coding of the Guedel airway. The green, orange and red devices correspond
to the sizes of the small (size 2), medium (size 3) and large (size 4) Guedel airways and are identically colour coded.
This clinical study is aimed at investigating whether BLS trained users provide better ventilation in unconscious patients with the Tulip GT airway or with Guedel airway and facemask as initial investigations of the identical protocol in manikins showed statistical significance . We felt that Human study of the same protocol would reveal data about new anaesthetic device evaluation and followed our disciplined new device introduction process which commenced in 2007, pre-empting recommendations by the ADEPT publication  in 2011. The process involved bench top testing by MEDEC (Medical School of Wales, Cardiff) in 2007, MHRA (Medicines and Healthcare Regulation Authority) authorization in 2007, manikin testing with studies [2, 3; 2007-2013] and Human studies [1, 4; 2010-on going]. No other disciplined or described medical device introduction methods existed when the Tulip development program commenced in 2007.
Regional ethics committee approval and North West London Hospitals NHS Trust Research and Development (R and D) sponsorship for the study to be carried out within an NHS institution was sought and granted. All patients and inexperienced users provided written informed consent for the study.
Statistical advice was sought and the study was powered to 90% for statistical significance. The Prescott test for binary data, the Period effect and calculation for the number of discordant responses were analysed and a sample size of 60 subjects was calculated and used reproducing the protocol used in the initial manikin study . All study observations were performed by one consultant anaesthetist (NR). In this study an inexperienced airway provider was defined as anyone who had attended a Basic Life Support (BLS) skills course within the past year and felt able to manage facemask and bag ventilation using a Guedel airway as per NHS annual training requirements.
This was a ‘first contact’ Tulip GT® airway studying as the BLS trained airway providers had not previously used a Tulip GT and most had never seen one before. It was considered unethical to allow the first use on a patient without training so all users were shown how to use a Tulip GT in a in a TRUCORP™ manikin once as in our previous studies [2,3] and then allowed to practice Tulip GT insertion in the same manikin. Immediately post single event training the BLS trained airway providers were asked to use both the Guedel and Facemask, and the Tulip GT in a randomised order in an anaesthetised patient.
The patient inclusion criteria were as follows: age 18 to 70 years, ASA physical status 1 or 2, scheduled surgery (not involving the head or neck) under general anaesthesia without neuromuscular blockade. Patients were excluded if they were considered at risk of bronchospasm, regurgitation or aspiration.
General anaesthesia was standardised for all patients. A three minute pre-oxygenation was performed and anaesthesia induced with 1-2 mcg.kg-1 fentanyl and 2-4 mg.kg-1 propofol. An inhalational combination of 50% nitrous oxide in oxygen was delivered and supplemented with the appropriate anaesthetic dose of 2-4.5% sevoflurane. After induction of anaesthesia the patient underwent facemask ventilation by the consultant anaesthetist until there was sufficient depth of anaesthesia for jaw relaxation to allow for the insertion of a supraglottic airway. The consultant anaesthetist then ventilated the patients lungs 3 times to record comparative baseline results, investigate the requirement of an airway for ventilation with a facemask and to assure safety. Data was collected as to whether a Guedel airway was required for ventilation or not, as well as tidal volume, inspiratory pressures and expired CO2 data from the first three manually ventilated breaths for performance comparison with the BLS airway provider performance later. No muscle relaxants were used for this study.
The BLS airway providers then either inserted and ventilated the patients lungs with an appropriate sized Guedel airway and facemask or inserted a similar sized inflated Tulip GT airway and hand ventilated the patient in a randomised order.
Smaller adults and females used a green size 2 Guedel oropharyngeal airway, medium adults and most male patients an orange size 3, and larger males used a red size 4 respectively. The BLS trained airway providers were then asked to ventilate the anaesthetised patient using a Guedel and Facemask but it was the users choice as to whether they used a one or two handed technique as better BLS airway providers can often effectively ventilate single handed. The users were reassured before starting that should they be unable to ventilate the patients lungs effectively assistance would be provided allowing a 2 handed Facemask technique to be used as per Basic Life Support guidelines. The technique applied was recorded along with the presence of a facemask leak or not.
The order of the cross-over airway insertion was randomised using a random number chart. After the initial insertion and ventilation a sequence using the other technique to ventilate the patient was followed. The sequence was thus, either initial insertion of the Guedel airway and facemask ventilation and then insertion of the Tulip GT and ventilation or vice versa. The APL valve was set to 10 cmH2O for ventilation in all patients and the gas flow through the circle system using carbon dioxide absorption was set at 6 l/min. The Tulip GT airway was inflated after insertion with 50 – 60 ml to secure the airway according to patient or Tulip GT size and to stop any airway leak. Each Tulip GT was inflated with air using a 60 ml syringe to a volume as printed on each individual Tulip GT, with green size 2 having a recommended cuff inflation volume of 50 ml, orange size 3 60 ml and red size 4 also 60 ml.
The Tulip airways (GT® and Advance®) should be inflated to a recommended optimum of 50 cmH2O intra-cuff pressure (range 40 – 80 cmH2O), or up to a maximum recommended volume of 60 ml (adult range 40 – 60 ml) according to patient size, Tulip GT® airway labeling and instructions for use. These cuff inflation volumes are known to deliver cuff pressures of approximately 50 cmH2O (36.8 mmHg)  which is potentially below mucosal percussion pressure (54.4 cmH2O, 40 mmHg approx.) The minimum Tulip GT intra-cuff pressure to prevent ventilation leaks is approximately 30 – 40 cmH2O (33 cmH2O, 24.3 mmHg average) . For ventilation it is recommended that airway ventilation pressures be less than 20 cmH2O.
Further volumes of air were added to the cuff until there was no leak around the cuff, if this was required. The intra-cuff volumes and pressures of the Tulip GT airway were measured. The ventilation parameters of tidal volume, ventilation pressure and end-tidal carbon dioxide were recorded for the first 3 breaths for both sets of airways used by the BLS trained airway providers. For safety reasons the BLS trained airway providers were given a maximum of 60 seconds to achieve ventilation of the patients lungs and the anaesthetist was given the right to override the study if there were low oxygen saturations (< 94%) or if there was any clinical or physiological indication of failure of patient well-being.
In addition several binary outcomes were measured. These were an end-tidal CO2 target > 3.5 kPa in 2 of the first 3 breaths, a tidal volume target > 250 ml in 2 of the first 3 breaths and all parameters had to be achieved within 2 attempts without the need for consultant assistance. These binary outcomes were chosen to reflect realistic requirements for BLS resuscitation as providing 16 breaths per minute of 250ml tidal volume delivering 4 l/min of Oxygen was considered to be a minimum provision to maintain the reasonable homeostasis of our anaesthetised patients, with a PCO2 of 3.5kPa being considered an reasonable relative reflection of ventilation in the presence of consistent gas flow settings.
The ease of airway insertion as measured on a 10 point scale (1 easy to 10 difficult) and the preference of airway used asked of the inexperienced user. Once the data was collected anaesthesia was completed according to the dictates of the anticipated surgery.
Immediate airway adverse effects (bronchospasm, gastric content regurgitation and vomiting) were recorded. Long term or post-operative complications were not recorded as these were outside the scope of the study and as all patients had both airway techniques no conclusions could be drawn as to the cause of any long term side effects.
Continuous outcomes were compared between methods using the paired t-test. Binary outcomes were compared between methods using the paired exact test and Prescott’s test was used to compare outcomes between methods used. Confidence interval analysis was performed where indicated [5,6]. Binary outcomes were compared between methods using the paired exact test. The primary comparison was between the Tulip and Guedel methods. Here the patients received the methods in a random order. In order to factor in the order of delivery, the analysis was performed using multilevel linear regression. Two-level models were used within individual measurements nested within patients. A term for the period in which the measurement was made (first or second method) was included, in addition to a term for the method used. It was not possible to use multilevel logistic regression for the binary outcomes, due to all (or almost all) of the patients taking the same the outcome for one or more methods. Instead Prescott’s test was used to compare these outcomes between methods. This method was used as it factors in the order in which the methods were given. A final analysis compared the patient preference, either Tulip or Guedel. A one-sample test of proportions was used to see if significantly more patients preferred one method or the other.
This study’s patient and user characteristics were as follows: 60 patients (19 male, 41 female), mean height 165 cm (SD 10), mean weight 80 kg (SD 22), with Mallampatti scores: 38 patients grade 1, 16 patients grade 2, 3 patients grade 3 and 3 unrecorded. The randomisation process gave 28 studies in which the Guedel airway was inserted before the Tulip GT® airway and 32 in which the Tulip GT airway was inserted before the Guedel airway. The BLS trained airway providers were as follows: 28 nurses, 16 medical students, 8 surgeons, 5 operating department practitioners and 2 paramedical trainees. A range of similarly sized Tulip GT and Guedel airways were used (2 red, 16 orange and 42 green) in the study.
The consultant anaesthetist was able to ventilate all patients lungs using a single handed facemask and bag technique. The consultant ventilation parameters were recorded and are presented as mean (standard deviation): end tidal CO2 3.9 (0.8) kPa, tidal volume 445 (114) ml, peak inspiratory pressure 19.4 (2.6) cm H20.
The average 3 breath ventilation parameters are shown in Table 1 with the statistical significance and confidence intervals of these results.
Translating the significant results in Tables 1 and 2 showed that when comparing the Tulip GT airway to the Guedel airway with facemask ventilation, in humans the BLS trained airway providers on average generated 77% bigger tidal volumes, 101% higher end-tidal CO2 readings and 36% higher ventilation pressures with the Tulip GT airway.
The analysis of the binary outcome data showed that the outcome of predefined adequate ventilation in less than 60 seconds and within 2 attempts was achieved with 35 out of 60 (58.3%) of Guedel and facemask users demonstrating 10 out of 60 (16.7%) total failures and 15 out of 60 (25%) inadequately ventilated patients. With the Tulip GT® airway 57 out of 60 (95%) of users achieved the required outcome variables with 0 out of 60 (0%) total failures and 3 out of 60 (5%) inadequately ventilated patients. This was statistically significant in favour of the Tulip GT airway at a p < 0.001 level. This study showed that when comparing the Tulip GT® airway to the Guedel airway with facemask ventilation the BLS trained user on average generated 77% bigger tidal volumes, 101% higher end-tidal CO2 readings, 36% higher ventilation pressures and fewer unresolvable ventilation leaks with the Tulip GT airway.
The BLS trained user asked for assistance and used a 2 handed mask technique with the Guedel airway in 13 out of 60 (21.7%) of patients and failed to adequately achieve the outcome variables in 25 out of 60 (41.7%) of cases. The same user was able to ventilate single handed in 60 out of 60 (100%) of cases but provided inadequate ventilation in 3 out of 60 (5%) patients with a Tulip GT that was directly connected to the anaesthetic breathing circuit. 10 out of 60 (16.7%) of users failed to ventilate the patient at all using the Guedel with a facemask technique which demonstrated an unresolvable leak in ventilation in 35 out of 60 times (58%) it was used. The Tulip GT airway initially leaked 14 out of 60 times (23%) but 10 out of 14 of these leaks (71% of leaks) were then sealed fully by the further inflation of the airway cuff with between 4-10 ml of air leaving 3 out of 60 events (5%) demonstrating a persistent leak, but any such leak was observed to make no significant difference to airway ventilation parameters or management.
of users favoured the Tulip GT airway.
The Tulip GT intra-cuff pressures and volumes were measured. There were 56 out of 60 recorded observations of intra-cuff pressure and 59 recordings for intra-cuff volumes. The results given as median (IQR [range]) are 74 (64 – 86 [30 – 120]) mm Hg for the intra-cuff pressures and 50 (50 – 60 [40 – 70]) ml for the intra-cuff volumes.
There were no immediate adverse effects noted and no patient experienced coughing, bronchospasm, gastric regurgitation or vomiting, only swallowing was noted.
Guedel airways are some of the most difficult airways to use for infrequent airway providers because of the facemask skills required yet they are relied upon by everyone including all emergency services and BLS trained airway providers as a first-line airway for Basic Life Support in all environments, including the home. This study shows that airway provision failure rates are high and studies show that survival rates from Out Of Hospital (OOH) cardio-respiratory arrest are low . We seek to investigate the role of alternative ventilating airways for less experienced and more infrequent airway providers such as nurses, paramedics and non-anaesthetic doctors for first-line airway provision and Basic Life Support in all environments.
For more experienced airway providers and anaesthetists, supraglottic airway devices (SAD’s) such as the Laryngeal Mask® and iGEL® cannot be used in semi-conscious patients because providers are limited by the presence of airway reflexes mandating the Guedel andfacemask as the only primary intervention for airway provision and support in semiconscious patients available at the moment. The Tulip GT® demonstrates low stimulation and tolerance with eyes open in the recovering patient like a Guedel airway whilst also being seen to be stable in-situ, hands-free and directly-connectable like a first generation SAD.
This statistically significant study shows that BLS trained airway providers perform ventilation on the unconscious patient with a Tulip GT airway better than with a Guedel/facemask despite greater familiarity and annual Basic Life Support training with the latter. Consideration should be given to the Tulip GT airway being amongst the first forms of airway intervention for airway management in the unconscious patient as it is small sized, easy to insert, has a low pressure cuff and is easily tolerated in semiconscious patients, eyes open upon recovery. With BLS trained airway providers there were no failures to ventilate with the Tulip GT airway despite this being a first contact, first use study. This clinical study confirms that people with Basic Life Support training may provide inadequate ventilation using a Guedel airway and facemask in unconscious patients. This confirms other manikin and human studies [7 – 11] with close correlation.
The Tulip GT is a small, retro-lingual, oropharyngeal cuffed device that comes as a multi-size GT (Guedel Type) and a one size fits all adults Tulip Advance (LMA/iGEL type). The Tulips offer softer, larger volume, inflatable cuffs placed in the oropharynx, rather than the laryngopharynx as with LMA and iGEL’s, demonstrating low stimulation for use in semiconscious patients in all environments. In this study the Tulip demonstrated the advantages of first generation supraglottic airway devices such as hands-free direct-connectability, airway stability and no mask. This was a ‘first contact’ Tulip GT airway study, as the BLS airway providers had never used a Tulip GT and most had never seen one before.
One perceived advantage of the Tulip GT airway is its ease of use and steep learning curve. This study confirms that manikin learning skills for the Tulip GT airway are easily transferred to the clinical environment which is in contrast to a recent study in this Journal of inexperienced users using the LMA-Supreme™ airway . They concluded that results in manikin studies cannot be easily transferred to the clinical situation but in our study manikin teaching was transferred to the clinical environment without any difficulty after a solitary manikin teaching session. Furthermore when we compared our human results to our previous manikin study  there was a close correlation between ventilation in man and manikin and if anything, manikins were found to be harder to ventilate than humans.
Both studies showed that the Tulip increased ventilation when compared to a Guedel/facemask, by 9% (p< 0.05) in the manikin study but by 77% (p< 0.001) in the Human version with both results being statistically significant. In both studies 100% of users were able to ventilate with a Tulip with the manikin study showing p< 0.0003 and the Human study demonstrating p< 0.001. Again, in both studies an identical number of Guedel users failed with 20% failing in the manikin study (p< 0.0003) and also 20% failing in the Human study but with p< 0.001. In the manikin study 77% of users preferred the Tulip with a near identical 78% of users preferring the Tulip in the Human study.
The results of both studies when compared suggest that not only are manikin studies of value, but that they are in fact an essential step in the research and development of new airway devices such as the Tulip airway and should be taken seriously for the development of pre-emptive data. Again we state that any results will only be as good as the simulation. In our experience manikins enable gross study with multiple introductions and the evaluation of extreme parameters such as high ventilation pressures with safety and ease preventing potential harm to patients in whom such evaluations may be well detrimental and most likely unethical.
A potential problem with this type of study is that one commonly used, familiar method (Guedel/face mask) is being compared to a previously unknown, ‘first contact’ technique (Tulip GT airway). The rationale and reasoning for using this as an acceptable study basis is that this is the reality of the clinical situation when a new device is introduced into clinical practice. Any new device is introduced without retraining on the current equipment in use. As this is a first contact study it is, in reality, the worst clinical scenario for a new device in that any bias is against the new device. Despite this user familiarity with the old device this study shows that a new device appears to work significantly better that the existing current equipment.
This study was part of a sequence of studies logically designed to assess a new airway . We have previously stressed the importance of manikin studies in supraglottic airway studies and this view has been recently supported . This study is an in-vivo reproduction of an identical manikin study , and to our knowledge, the first for a new airway device. The clinical study concurs with the results found in the manikin study so we can only conclude that manikin studies are effective in user training and in the evaluation of the Tulip GT airway.
This study shows that the Tulip GT performed well enough to be considered as a viable alternative to both oropharyngeal Guedel airways and supraglottic airway devices (SAD) such as the larger laryngopharyngeal Laryngeal Mask and the iGEL with its ease of use, high success rates, stable hands-free direct-connectability and low stimulation in semiconscious and recovering patients in whom these higher stimulation SAD devices cannot be used.
We previously suggested that future clinical trials were needed for the range of Tulip airways.This study answers the question as to whether ventilation is improved when the Tulip GT airway is compared to Guedel/facemask with BLS airway providers and demonstrates the relevance of manikin simulation in device development and user training. Nevertheless, further trials are needed to assess its place in clinical anaesthesia and to compare it with other supraglottic airways. Further studies investigating potential post operative side effects have been ethically approved and a comparative study with Laryngeal Masks and iGEL’s is intended in series. We welcome any similar investigations by other teams.
The devices were purchased by the North West London Hospitals NHS Trust and no funding for the study sought. Paul Bassett provided statistical input to the results of the study and thanks are due.
Dr. Shaikh is the inventor of the Tulip® airways and was not involved in the conduct of the clinical study but was involved in its planning and design. The airways used in the study were purchased by the Trust from Age of AquariusTM, UK, of which Dr. Shaikh is the owner and director. No other competing interests declared.
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Table 1. Ventilation parameters of the inexperienced users using both of the airway methods being studied. The data is presented as mean score (SD). The parameters measured are endtidal CO2 (ETCO2), tidal volume (VT), and peak inspiratory pressure (PIP). Statistical probability results as measured using paired t- test, paired exact test and Prescott’s test where appropriate. A p value < 0.05 is significant.
|Tulip GT® (T)||Guedel (G)||Significance|
|ETCO2 (kPa)||5.0 (0.7)||2.5 (1.5)||p < 0.001|
|VT (ml)||494 (175)||286 (186)||p < 0.001|
|IP (cm H2O)||18.3 (3.4)||13.6 (7)||p < 0.001|
Figure 1. Inflated frontal views of a green Tulip GT® airway with a size 3 (green) Guedel airway. Frontal views of the range of Tulip GT® airways and a size 4 (red) air way showing a version with an elasticated band which can secure the airway in position. The Tulip GT® airway has a central circular breathing tube of 10 mm internal diameter (ID) made of di-2-ethylhexyl phthalate free poly-vinyl chloride (DEHP Free PVC) with an oval internal diameter (ID) of 14 x 18 mm. The proximal end has a standard 15 mm diameter connector that connects to anaesthetic machine breathing tubing and resuscitation breathing devices.
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