The Tulip GT® Airway: Man and Manikin
The Tulip GT® Airway: Man and Manikin;
Dr. A. Shaikh
Northwick Park Hospital
Middlesex HA1 3UJ
The Tulip GT® Airway: Man and Manikin; the first comparison of randomised, controlled trial results in both humans and manikins.
A. Shaikh,1 P.N. Robinson2 and M. Hasan3
1 General Practitioner; Old Catton Surgery, Norwich; 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, Department of Anaesthesia, University College Hospital, London, UK.
Dr. A. Shaikh
Honorary Research Fellow
Northwick Park Hospital
Middlesex HA1 3UJ
Two randomised, controlled, cross-over trials (RCTs) using Basic Life Support (BLS) airway providers, defined as inexperienced users (IU’s), with annually trained Guedel airway and Facemask skills, compared ventilation using either the Tulip GT® airway or a Guedel airway with Facemask in 60 subjects, first in manikins and then in humans after the induction of anaesthesia, using identical protocols but within the limitations of equipment that prevented the estimation of end expiratory CO2 in manikins.
The manikin study showed that the Tulip GT® airway increased ventilation by 9.1% (p < 0.0423) in the manikin study but by 76.6% (p < 0.0002) in the human study. In both man and manikin 100% of IU’s were able to ventilate with a Tulip GT® airway on their first ever encounter with the device, with 0% requiring assistance in either man or manikin. 20% of IU’s using a Guedel airway and Facemask required assistance in the manikin study (p<0.0003) and 25% in the human study. There were no significant differences in the number of attempts made to insert each airway device in either trial, with manikin results revealing 98.3% (59/60) IU’s introducing the Guedel first time and 93.3% (56/60) introducing the Tulip GT® first time, whilst the human study showed 78.3% (47/60) for the Guedel and 96.7% (59/60) for the Tulip GT®. The Tulip GT® was considered easier to use in both studies (man p < 0.005, manikin p < 0.05), with the manikin study 76.7% (46/60) of IU’s preferred the Tulip® with a near identical 78.3% (47/60) of IU’s preferring the Tulip GT® in the human study.
Our twin RCTs revealed both similarities and differences in man and manikin results, revealing the actual worth of manikins by replicating the same protocol in both sets of test subjects.
The Tulip GT® airway device has been specifically designed for everyone, including hospital, theatre and anaesthetic use, but especially for inexperienced users both inside and outside hospital and for home use as a hands-free, directly-connectable, first-line, low stimulation oropharyngeal airway to replace the Guedel and Facemask technique, hence twin RCT’s to investigate its viability in use.
In response to the editorial by Ward and Irwin “Man vs. manikin revisited” last month , we wish to forward another view that challenges the conclusions proposed relating to the role of manikins in anaesthetic research. Whilst manikins may understandably not be accurate in the simulation of difficult airways due to the stiffness of plastic and the softness of mucosal tissue, we have found that they do have a significant role in airway research. We now compare the results of a manikin and a human study to reveal the close correlation of the two studies and their results when the same protocol is applied within the limitations of manikins.
New anaesthetic airway equipment and the pathway to introduction has been a topic of debate and is a conversation in which we have participated [2, 3, 4]. The 2012 ADEPT recommendations [4, 5] were noted to reflect the Tulip® airway process through which the airway had been developed, tested and researched starting with bench testing in 2007, manikin studies in 2007 and 2012 [6, 7] and ultimately producing level 1 evidence with a human randomised controlled trial  in 2014. The Tulip® is the first airway to utilize this method of introduction.
The discussion included the role of simulation and manikins in initial research, with some suggesting that they were of little value and that research should only involve humans . This was not our finding, as our studies in manikins and humans showed a close correlation between the two types of study. It was suggested that there was no record of the same study being done in manikins and in
humans, so to that end we did so using identical protocols. Both studies have been peer reviewed and published in Anaesthesia [7, 8] previously.
A randomised crossover manikin study comparing the Tulip GT® (Guedel Type) airway and the Guedel with Facemask in the hands of BLS (Basic Life Support) trained IU’s was conducted  in 2012 with a follow on randomised controlled crossover human study  in 2014. The results of both studies, when compared showed close correlation, suggesting that not only are manikin studies of value, they are an essential and safe step in the research and development of new airway devices such as the Tulip® airway. Manikins are not good at simulating everything but certain aspects of study make them worthwhile in data collection and study.
For both RCT’s sixty IU’s, who were defined as being a BLS provider, were recruited and consented to participate on the day of assessment. For both manikin and human studies this was the first contact the IU’s had with a Tulip GT® airway as the BLS trained airway providers had not previously used a Tulip GT® and most had never seen one before. We recruited from non-anaesthetic doctors, recovery room nurses, operating department assistants, medical students, ward nurses and scrub nurses. Study participants were randomised into one of two groups, using computer generated random numbers. This established which of the two devices they were to use first. Both airway adjuncts were inserted by the same IU in the same manikin or human subject to cancel out any sequential bias that may occur in the statistical results. Training was given to all participants of the study in the form of a written information sheet, accompanied by a one minute training video and step-by-step demonstration accompanied by verbal instruction for the manikin study. A resuscitation scenario was prepared, with a manikin simulating a patient in cardiorespiratory arrest. The IU was instructed to start giving airway and ventilatory support using a Tulip GT® or a Guedel airway with a Bag Valve Mask (BVM). The supervising anaesthetist intervened if requested, to assist with a two-operator technique for BVM ventilation. A separate anaesthetic observer recorded outcome data.
For the human study, the IU’s were given a written information sheet and trained once in a manikin with a step-by-step demonstration accompanied by verbal instruction. The supervising anaesthetist intervened if requested, to assist with a two-operator technique for ventilation. A separate anaesthetic observer recorded outcome data also.
Regional ethics committee approval and North West London Hospitals NHS Trust Research and Development sponsorship for the study to be carried out within an NHS institution was sought and granted for the human study . 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 same protocol in both the manikin and human study . All study observations were performed by a single anaesthetist in each study. It was considered unethical to allow the first use on a patient without training so all human users were shown how to use a Tulip GT® in a in a TRUCORP™ manikin once. The BLS trained airway providers were asked to use both the Guedel and Facemask and the Tulip GT® in a randomised order in the test manikin or the human subject.
For human use  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 oropharyngeal 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.
For the human study 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 BLS guidelines. The technique applied was recorded along with the presence of a facemask leak or not.
For both studies the order of the crossover 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 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.
Further volumes of air were added to the cuff until there was no leak around the cuff for both studies, if this was required. The intra-cuff volumes and pressures of the Tulip GT® airway were measured in the human study. 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 in humans but CO2 readings were not taken in manikins.
For safety reasons the BLS trained airway providers were given a maximum of 60 seconds to achieve ventilation of the human 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) in both studies and the preference of airway used asked of the IU. Once the data was collected anaesthesia was completed according to the dictates of the anticipated surgery in humans.
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 [9, 10]. Binary outcomes were compared between methods using the paired exact test. The primary comparison was between the Tulip GT® and Guedel methods. 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 subjects taking the same 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 GT® or Guedel. A one-sample test of proportions was used to see if significantly more patients preferred one method or the other.
The manikin study showed that the Tulip GT® airway increased ventilation by 9.1% (p < 0.0423) in the manikin study but by 76.6% (p < 0.0002) in the human study. This was the biggest difference between the man and manikin study, with the remainder of the results being remarkably similar. The studies suggested manikins, if anything, are harder to ventilate than humans, which raises the bar for training through added difficulty.
In both studies 100% of IU’s were able to ventilate with a Tulip GT® airway on their first ever contact with the device, with 0% requiring assistance in man or manikin but 25% (15/60) of Guedel airway and Facemask users required assistance in the human study and 20% (12/60) required assistance in the manikin study (p < 0.0003). 5% (3/60) of Tulip GT® users failed to achieve the required ventilation parameters in humans with 41.7% (25/60) of Guedel users failing to achieve adequate ventilation parameters in the same study.
There were no significant differences in the number of attempts made to insert each airway device in either trial, with manikin results revealing 98.3% (59/60) IU’s introducing the Guedel first time and 93.3% (56/60) IU’s introducing the Tulip GT® first time, whilst the human study showed 78.3% (47/60) for the Guedel and 96.7% (59/60) for the Tulip GT®.
In the manikin study 76.7% (46/60) of users preferred the Tulip® with a near identical 78.3% (47/60) of users preferring the Tulip GT® in the human study, with no significant difference in the number of attempts made to insert each airway device and the Tulip GT® being considered easier to use in both studies (man p < 0.005, manikin p < 0.05).
Interestingly, whilst 25% (15/60) of IU’s requested assistance in the human study, an additional 16.7% (10/60) of Guedel airway and Facemask users failed to ventilate at all but did not ask for assistance, showing high combined failure rates of 41.7% (25/60) in BLS Guedel and Facemask airway management by IU’s in real patients.
In the manikin study  20% (12/60) IU’s required assistance to generate satisfactory tidal volumes using a Guedel and BVM, which was significantly more than when using the Tulip GT® (0% assistance requested, p < 0.0003). The average tidal volumes generated, when used as a single-operator technique, was significantly greater with the Tulip GT® and BVM (397ml) compared with the same IU’s using the Guedel and BVM (364ml, p = 0.0423). There was no significant difference noted between the number of attempts to insert either device first time, 93% (56/60) for the Tulip GT® and 98.3% (59/60) for the Guedel. There was a significant difference noted when the IU’s were asked to state which device they found easier to use. 76.6% (46/60) stated that they preferred using the Tulip and only 23.3% (14/60) preferred using the Guedel (one-sample z scores of -4.15 to 4.15, p < 0.05).
In humans the 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. 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® is the first airway device to be introduced using this method of testing and study.
A potential problem with this type of study is that one commonly used familiar method (Guedel and Facemask) is being compared to a previously unknown piece of equipment and technique such as the Tulip GT® airway. The rationale and reasoning for using this method 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.
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. Furthermore, the Tulip® airway is capable of generating >100cmH2O ventilation pressure without a leak in manikins, which is clearly undesirable in humans, so manikins in our experience enable gross study and the evaluation of extreme parameters such as ventilation
pressure with safety and ease preventing potential harm to patients in whom such evaluations may be detrimental, if not unethical.
These studies raise the question as to why BLS airway management using the Guedel and Facemask is still performed when failure rates are as high as 41.7%, despite annual BLS training with the Guedel and Facemask and out of hospital cardiac arrest survival without neurological deficit is approximately 1.25-2.5% . It should be noted that a significant number of IU’s failed to ventilate at all in humans (16.7%) with a Guedel and Facemask but still did not ask for assistance, perhaps due to the NHS requirement of competency for airway management in BLS.
“Anaesthesia is the airway” and as a subject is responsible for evaluation and recommendation of airway devices for medicine as a whole, and as such should consider airway management for everyone, including inexperienced users who find current Guedel and Facemask management difficult with high failure rates, yet these users have had no other alternative until now.
Regurgitation is an issue which is raised commonly but evidence has existed for some time that regurgitation is actually more frequent with Laryngeal Masks than Guedels due to the forced opening of the upper oesophagus by these supraglottic devices [18, 19, 20] and that gastric insufflation is uncommon when ventilation pressures are maintained below 20cmH20 . Our studies revealed that whilst ventilation pressures are increased when IU’s use the Tulip® airway (17.5cmH2O) when compared to a Guedel and Facemask combination (13.4cmH2O), this is because the high failure rate of IU’s to form a Facemask seal is the primary cause. Ventilation pressures whilst raised by IU’s using a Tulip GT® (17.5cmH2O), they are actually lower than when a Consultant Anaesthetist uses a Guedel and Facemask (19.4 cmH2O), yet the IU’s provide a higher tidal volume with a Tulip GT® (501mls) than the Consultant using a Guedel and Facemask combination (420.6mls), so the Tulip GT® actually provides higher tidal volumes for lower ventilation pressures, increasing ventilation and reducing the likelihood of reflux and regurgitation by maintain low ventilation pressures <20cmH2O.
Additionally, ease of use, higher ventilation volumes, lower ventilation pressures and a higher inspired O2% (estimated at >200% more O2 per breath) is further assisted by the hands-free, directly connectable design of a Tulip®, which has lower dead space and rebreathing volumes than a Guedel and Facemask combination. As such the Tulip® can be directly connected to a ventilator and secured through head-ties or optional headband assemblies (see picture). The Tulip Advance®, which is a one-size-fits-all adults version is also available for more experienced users who are able to estimate depth of insertion and volume of cuff inflation, allowing an “insert to fit” and “inflate to fit” method to form a airtight seal for all adults using a single airway device  for cost benefits.
Many airway interventions are required in semi-conscious patients who may tolerate an oropharyngeal Guedel airway but are simply too awake to tolerate an iGEL or LMA type supraglottic airway, but until recently no other oropharyngeal alternative has been available. Intervention at this earlier stage with a hands-free, directly connectable, low stimulation device that does not cause gagging, coughing, vomiting [8, 22], is tolerated in the semi-conscious state and one that provides higher success rates, higher inspired O2%’s may well reduce deterioration of these patients clinical condition to their benefit by replacing the difficult Guedel and Facemask combination.
Both studies showed that the Tulip increased ventilation when compared to a Guedel and 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 a similar number of Guedel users required assistance with 20% requiring assistance in the manikin study (p < 0.0003) and 25% requiring assistance in the Human study but with p < 0.001. In the manikin study 76.6% of users preferred the Tulip with a near identical 78.3% of users preferring
the Tulip in the human study. Not all results are similar in man and manikin but we believe the correlation to be of note.
The Tulip GT® airway have been shown to be easier to use and more effective with our combined studies suggesting that the Tulip GT® should be used for initial airway management, especially by inexperienced users for BLS both inside hospital, outside hospital and operating theatre settings . These studies were conducted by the team at Northwick Park Hospital, Harrow, and with the assistance of the inventor, so it may now be time for others to investigate the efficacy of the Tulip® airway range, with consideration given for assistance by the ADEPT  policy of exclusion of weaker devices whilst assisting the most promising new equipment by fast-tracking research and use, in this case investigating whether the Tulip GT® should replace the 83 year old Guedel airway, as what else of such age do we still use in current clinical practice?
Our studies suggest that this should be considered as the Tulip GT® is the only alternative low stimulation airway to a Guedel available and offers significant results, despite the inexperienced users being annually trained with a Guedel and Facemask combination and these studies being the first contact the IU’s had with the Tulip GT® airway device. It is well documented that IU’s have difficulty with the Guedel and Facemask combination [14, 15, 16, 17] but how much better would the results be if the IU’s were annually trained in Tulip GT® use as well as the Guedel and Facemask combination used in these studies by the IU’s? Practice makes more perfect in all things.
With previous publications [9, 10] highlighting the need for randomized controlled trials (RCT) rather than observational studies to observe new airway devices we have now provided multiple confirmed statistically significant results with trials conducted as RCT’s in both man and manikin, which do provide parallel control groups and have demonstrated ventilation failure rates below 1%. This then raises the question, how good can the Tulip® actually be? .
These studies were 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 . The human study  is an in-vivo reproduction of an identical manikin study  and to our knowledge, the first for any airway device, in keeping with ADEPT guidelines .
With confirmation from an observational human study  and an independent manikin study , we conclude that manikin studies are effective in the evaluation of new airway devices such as the Tulip® airway and should be taken seriously for the development of pre-emptive data but again we state that the results will only as good as the manikin and the simulation. Ventilation seems to be harder in manikins but airway management and Facemask seal formation seems to be harder in humans, suggesting that difficult airway simulation may well be suboptimal in manikins.
Through these twin studies we found that it isn’t man or manikin, it is man and manikin, especially when studying new devices such as the Tulip® airway. Manikins form part of a logical pathway by minimizing potential harm and accelerating both study and development of new airway devices and as such the Tulip® airway pathway and process is thus the first to confirm both the benefits and reliability of manikins and the ADEPT  process of introduction of new airway devices.
The Tulip GT® and Tulip Advance® devices were purchased by the North West London Hospitals NHS Trust and no funding for the study was sought. Paul Bassett provided statistical input to the results of both studies.
Dr. Amer Shaikh is the inventor of the Tulip® airway and was not involved in the conduct of the clinical study but was involved in its writing, 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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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) airway showing a version with an elasticated band to 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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