Clinical Projects old
Dr P N Robinson
Northwick Park Hospital
Middlesex HA1 3UJ
The Tulip® airway: the first in-vivo study.
P.N. Robinson1, A. Shaikh2, N.M. Sabir3, D.J.A. Vaughan3, M. Kynoch4 and M. Hasan5
1 Consultant Anaesthetist, Department of Anaesthesia, Northwick Park Hospital, Middlesex,UK.
2 Honorary Research Fellow, Department of Anaesthesia, Northwick Park Hospital,Middlesex, UK and General Practitioner, Norfolk, UK.
3 Consultant Anaesthetists, Department of Anaesthesia, Northwick Park Hospital, Middlesex,UK.
4 Specialist Trainee in Anaesthesia, Imperial School of Anaesthesia, London, UK.
5 Consultant Anaesthetist, University College Hospital, London, UK.
Correspondence to: P N Robinson
Oropharyngeal airways and supraglottic airways are commonly used both inside and outside hospital and have become the mainstay of airway management, especially in inexperienced practitioners’ hands. The Tulip® airway is a new disposable, one-size-fits-all-adults, hands free, directly connectable oropharyngeal airway that is designed for both experienced and inexperienced users by being one adult size and smaller than other supraglottic devices that perform similar functions. This clinical study was undertaken to assess the performance of the new Tulip® airway, after induction of anaesthesia, on 75 consented patients and this is the first use report of the Tulip’s function in-situ. The ease of insertion, manual ventilation parameters, intra-cuff pressure, three breath end tidal carbon dioxide levels, airway pressure, tidal volume and ease of removal were measured. Any complications were noted. The results showed a successful airway was achieved in 74/75 patients. In 60 patients the Tulip® airway provided a patent airway immediately. In 15 patients adjunct procedures such as jaw thrust and head extension were required to provide a patent airway secondary to under inflation of the Tulip® cuff (<50cmH2O cuff pressure). The device worked effectively as a high volume, low pressure airway in 74/75 patients, with the final patient demonstrating lingual tonsils on bronchoscopy which obstructed both other contemporary devices. Further studies of the airway are indicated to establish its potential role in anaesthesia and resuscitation, especially for inexperienced practitioners.
The Tulip® airway (Figures 1 and 2) is a single sized disposable oropharyngeal airway. It has a central circular breathing tube of 10mm internal diameter (ID) made of di-2-ethylhexyl phthalate free poly-vinyl chloride (DEHP Free PVC) with an external diameter (ED) of 14mm. The proximal end has a standard 15mm diameter connector that connects to anaesthetic machine breathing tubing and resuscitation breathing devices. The distal end is surrounded by a single bevelled, high volume, low pressure, anatomically shaped polyhedral cuff which may be inflated to a recommended 50cmH2O intra-cuff pressure (range 40-60cmH2O), or up to a maximum recommended volume of 60mls (range 40-60mls) according to patient size for the one size adult Tulip®. This cuff inflation increases Tulip® cuff size insitu and provides an oropharyngeal seal, pushes away obstructive anatomical structures such as the tongue and secures the Tulip® airway in the oropharynx. It is sterilised by ethylene oxide (ETO) and has three posterior coloured markings. These different coloured markings on the proximal convex surface of the airway provide a guide to the appropriate insertion length of the airway. This visual colour scheme corresponds to the length of the equivalent Guedel airway and its known colour coding of sizes. The green, orange and red markings correspond to the sizes of the small (size 2), medium (size 3) and large (size 4) Guedel airways.
The Tulip® airway can be inserted in the midline in a semi-inflated manner (40mls), after lubrication, and passed behind the tongue until a ‘give’ is felt as it passes into the wider space of the oropharynx. More air can be added to increase the size of the cuff to affect a seal if there is a leak and secure the airway in place. The Tulip® is insert-to-fit and inflate-to-fit, thus offering one size for all adults.
The philosophy behind the development of the Tulip® airway is improvement on the current standard supraglottic and oropharyngeal airway equipment. For example, the Guedel airway is cumbersome when used as an adjunct to facemask ventilation which requires a two handed technique, is difficult for inexperienced non-anaesthetic personnel to use and cannot be directly connected to an anaesthetic breathing circuit or a ventilator. Several different sizes of airway must be stocked and also kept immediately to hand and is far from ideal in acute resuscitation [1-6]. The same is true of supraglottic airway devices . The Tulip® airway is designed in an attempt to remove these difficulties from clinical practice by providing a disposable airway that is small, easy to introduce quickly and designed for inexperienced users with a one-size-fits-all-adults philosophy. The Tulip® aims to provide an airway that is hands-free, directly connectable and one that may be secured to provide positive pressure ventilation without a leak suitable for starved elective surgical anaesthesia. The Tulip® is designed to provide a first-line interventional airway for use from the first moment an airway is required in semi-conscious states right up to the point where endotracheal intubation is required without interruption or change. The oropharynx was chosen as the site of cuff location because it is the only site of the upper airway which is not in immediate proximity to another anatomical structure. In theory, an inflatable anatomical cuff external to a single oropharyngeal tube allows a device to be invented which fits all sizes of the oropharyngeal anatomy. The size of the device in question can then be easily adjusted using incremental increases or decreases in the cuff volume to fit each patient individually. The length variations between patients’ airways can be addressed by increasing the length of the breathing tube inserted into each patient assisted by guides and this is addressed by the coloured markings on the airway. A ‘one-size-fits-all-adults’ airway can thus be created using this insert-to-fit and inflate-to-fit ability. The low intra-cuff pressures and expected advantages including cost may be beneficial in anaesthesia and acute resuscitation. Complications of contemporary supraglottic airways, such as sore throat, may also be minimised but this study does not observe post operative morbidity.
The Tulip® airway has been through multiple component testing and manikin studies. It has undergone bench testing to destruction (MeDEC, Wales School of Medicine, 2007), manikin testing (AMBU Intubation Trainer 2006, TRUCORP AirSim Multi 2007 , Laerdal 2008, TRUCORP AirSim Advance 2012 ), received MHRA (Medical Healthcare Regulatory Authority 2007) approval and is C.E. (Conformité Européene 2010) marked. It has undergone component testing in-vivo and has been available for clinical practice for some 3 years. Manikin studies have shown it to work, be easy to insert for even inexperienced users and have a steep learning curve . This suggests that it may have a place in initial resuscitation and airway management in the unconscious patient, especially in inexperienced hands. This is the first use clinical trial of the Tulip® airway and this study is aimed at investigating whether the new device provides a competent airway, seals the oropharynx, delivers adequate tidal volumes and whether the Tulip® really is a one size for all adults airway device that functions with low cuff pressures whilst delivering manageable ventilation pressures and easy, non-obstructed removal upon recovery in patients as measured after the induction of anaesthesia.
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. The primary outcome variable was the ability of the Tulip® airway device to achieve an oropharyngeal seal and reproduce three times intermittent positive pressure ventilation (IPPV) breaths of 15-20cmH2O peak, expired pCO2 capnography readings >3.5kPa to indicate adequate ventilation and tidal volumes of >6ml/kg threshold (6-8ml/kg target) without leakage. Failure to produce a peak IPPV pressure of >15cmH2O, an expired capnography reading of <3.5kPa or tidal volumes <6ml/kg was considered a failure to ventilate. This ventilation ability was also measured subjectively by the user and by using the on-going capnography trace to reveal any obstruction during the respiratory cycle.
It was anticipated that 90% of patients undergoing the procedure would achieve a successful outcome so it was felt necessary to be confident that the estimated proportion of success from the trial should be within 10% of the true population value. Therefore, it was calculated that a sample size of 62 patients completing the procedure would be required, which gave a 95% exact binomial confidence interval of (80-96%). It was estimated that around 20% of patients who were consented into the trial may not complete the procedure. Therefore the numbers required were inflated to allow for this, giving a total sample size of 75 subjects. Statistical advice, suggested by the R and D department, also powered (80%) the study at 75 patients.
The devices were purchased by the Trust and no funding for the study sought. All studies were carried out by one of three consultant anaesthetists (NR, DV or NS). All patients provided written informed consent for the study.
The inclusion criteria were as follows: age 18 to 70 years (inclusive), ASA physical status 1 or 2, scheduled surgery not involving the head or neck under general anaesthesia with or without neuromuscular paralysis. Patients were excluded if they were considered at risk of bronchospasm, regurgitation or aspiration.
General anaesthesia was standardized for all patients. Anaesthesia was induced with an intravenous combination of fentanyl, ondansetron, and propofol and muscle relaxation was given if the nature of the potential surgery demanded it. A standardized 3 minutes preoxygenation was performed after the introduction of 100mcg’s Fentanyl I.V., and the instigation of full monitoring. The starved, elective patient was then induced with 2mg/kg Propofol I.V., or to a sleep dose. At this time the 100% oxygen available to the patient through the anaesthetic circuitry was changed to a 50%:50% mix with nitrous oxide and supplemented with the appropriate anaesthetic dose of volatile agent Sevoflurane to standardize the experiment. After induction of anaesthesia the patient underwent face mask ventilation until deemed clinically suitable for the insertion of a supraglottic airway. The Tulip® airway was then inserted and positioned within the oropharynx. The measurements of the study were then undertaken. After these recordings the anaesthetist was then free to continue the anaesthetic in any manner whether it was by intubation, with the Tulip® airway or with another supraglottic airway. A bronchoscope was used to view the anatomical location of the Tulip® airway in-situ.
The Tulip® airway was assessed after induction of anaesthesia. Whether the airway was inserted in a ventilated or spontaneous breathing and paralysed or non-paralysed patient was recorded. The ease of insertion of the airway with 40 ml air in-situ (semi-inflated) and manual ventilation ease were assessed on a 10 point scale (1 hard to 10 easy) and the initial cuff pressure (cmH2O) measured once the airway was placed in the oropharynx. Selfretention of the airway was assessed on a 10 point scale (1 bad to 10 good) and the total cuff volume at seal (no audible leak heard) measured and the volume and pressure of the cuff recorded if additional air was added to the cuff to achieve a leak free seal. Any airway manoeuvres to assist with the achievement of a patent airway such as jaw thrust or lift, head turn, head extension or pillow adjustment were recorded. Three consecutive ventilation breath measurements were recorded: capnography (end-tidal CO2 greater than 3.5kPa); peak airway pressure; the presence of an audible leak and the tidal volume of the breaths. The airway was then removed. The removal ease was measured on a 10 point scale (1 hard to 10 easy) and any tube obstruction, blood or secretions within the tube noted. Any suction of secretions required for the patient was recorded and the cuff volume on removal was noted. The quality (1 poor to 10 good) and the success or not of the airway (1 unsuccessful to 10 successful) were recorded on a 10 point scale.
The following patient demographic details were recorded: age, sex, BMI, Mallampatti score, ASA status and the potential nature of the surgery.
In 74 of the 75 patients an airway was achieved satisfactorily. The Tulip was considered easy to insert with a study mean of 8 in a study population with a mean age of 44.25years and an average BMI of 27.72. Of the 75 patient cohort, 55 were not paralyzed and 52 were female. No differences were noted between sexes or between paralyzed and no-paralyzed patients.
In one patient the airway was nearly impossible to site and required both head thrust and jaw lift to ventilate. This patient, a 45 year old, ASA 2, oriental lady with a Mallampatti score of 1 and a BMI of 19 was also found to be difficult to ventilate when the Tulip® airway was substituted for both laryngeal mask and i-gel® airways. The Tulip® fitted this patient and achieved a hands free, directly connected ventilating airway without an audible leak but it was not optimal. In this case the performance of an i-gel® and a laryngeal mask was worse than with the Tulip® for ventilation and airway management. Bronchoscopy was carried out through the Tulip® airway in this patient but visualisation was difficult. It was thought that the obstruction was secondary to the presence of tonsillar tissue as the obstructive mass was made of tissue that appeared polypoid and easily friable in nature. This suggests that this patient may have had lingual tonsils but this was not confirmed.
The patient demographics are shown in Table 1.
The insertion and removal parameters are shown in Table 2.
Tulip® mean intra-cuff pressures were lower than contemporary devices at seal without audible leak. The mean intra-cuff pressure was 33cmH2O (SD 10cmH2O) at introduction, with 40mls in-situ, and 34cmH2O (SD 9cmH2O) at seal. The volume of the Tulip® cuff at seal was measured with 65 patients sealing at insertion (40mls air in-situ). The remaining 10 patients required the addition of between 5 and 20mls to obliterate audible leak. The Tulips ventilation ability was unaffected by the presence of a leak in any patient. The results of any adjunct airway manoeuvres in assisting with the provision of a patent airway following insertion of the Tulip® airway were recorded. A seal without further cuff inflation was achieved in 65 patients immediately. A non-obstructed or patent airway was achieved in 60 patients without the need for airway procedures but adjunct procedures were required in 15 patients. Of those that required intervention there was an incidence of jaw lift in 8, head extension in 2, tube adjustment in 3, and in 2 patients it was withdrawn and re-sited successfully at the second attempt.
In reviewing the subjective assessments in Table 2 we feel it is important to record the results if there was a score less than 6 on the 1 to 10 scale as this may be indicative of device difficulty. In 69 cases there was no recorded score of less than 6. Of the other six cases: in case A insertion ease and manual ventilation ease were scored as 5 each and a jaw lift was required to maintain the airway with the subsequent quality and success of the airway scored as 5, case B required the Tulip® airway to be pulled back and the quality and success was scored as 4, case C was the similar to case B with the Tulip being pulled back to secure the airway and scored 5 on quality and success, case D required insertion of the airway to the limit and was described in terms of quality as a score of 5, case E required both head extension and Tulip® airway readjustment to stop obstruction and the quality and success of the airway scored 5. Case F is described above and scored 5 on quality and success. In all of these cases there were intra-cuff pressures of < 30cmH2O (recommended cuff pressure is 50cmH2O). The Tulip® intra-cuff pressures of the cases listed above were case A 24cmH20, case B 20cmH2O, case C 28cmH2O, case D 24cmH2O, case E 28cmH2O and case F 30cmH2O. Analysis of the results revealed that the incidence of adjunct airway manoeuvres was higher in devices that were under-inflated. Fifteen patients out of 75 required adjunct airway manoeuvres, but 11 (73%) demonstrated intra-cuff pressures of < 40cmH2O. Low intra-cuff pressures increased the incidence of adjunct airway manoeuvres, particularly if intra-cuff pressures were < 30cmH2O (9 of 15 patients, 60%).
Removal of the tube was considered easy in 71 cases (score > 7). Four patients scored 6, 5, 5 and 5 on this scale. There was minimal obstruction upon removal in 72 patients but 3 patients were observed to have partial obstruction. Secretions were observed on the cuff of the airway in 7/75 patients and only one patient who had a fractured mandible was noted to have traces of blood on the cuff of the airway. All other Tulip’s were free of blood upon removal and there was no other evidence of trauma. Neither sex or neuromuscular paralysis was shown to make a significant difference to the Tulip’s function in this study. Sore throat and other post operative side effects were not observed.
The volume of the device at seal was measured with 65 cases sealing at insertion (40mls air). The remaining 10 required the addition of between 5 and 20mls to affect a seal. One patient required 60mls volume to affect a seal. The device worked as expected in terms of volume required to effectively seal the oropharynx. In 72 of the 75 patients the cuff pressure was
below 50cmH2O at seal. Three patients had a seal pressure greater than recommended by the manufacturer (50cmH2O). These were 59, 57 and 62cmH2O.
The measured ventilation parameters are shown in Table 3.
In 64 patients there was no audible leak to manual ventilation. Two patients had no recorded results and there was a minimal audible leak in 9 patients. Peak airway pressure was 15mmHg with a SD of 3mmHg in all breaths. Of the 219 breaths recorded 212 had a peak ventilation pressure under 20cmH2O. There were 5 with 21cmH2O, one with 24cmH2O and one with 25cmH2O.
Tidal volumes (Tv) were considered adequate if >6ml/kg, with the range 6-8ml/kg being considered optimal. Tidal volumes greater than this were reduced by reducing ventilating pressure to minimize patient risk. Three intermittent positive pressure ventilation (IPPV) breaths were recorded in each case. The first IPPV breath recorded a mean Tv of 457mls at a ventilating pressure of 14.8cmH2O , the second a mean of 493mls at 14.9cmH2O and the third a mean Tv of 484.93mls at a ventilating pressure also of 14.9cmH2O. Audible leaks did not affect the Tulip’s ability to ventilate any patient.
Seventy five healthy ASA 1 and 2 patients undergoing scheduled surgery were recruited to the study. These results confirm that the Tulip® airway is successful in the management of the airway in the unconscious patient as tested after the induction of general anaesthesia and can be considered as a successful ‘one size fits all adults’ airway, as an airway was achieved in all 75 of the adult patients with the single size of Tulip®. However, the airway management was considered inadequate in one patient with the Tulip® and 2 other contemporary supraglottic airways. We accept that this is the first use report of the Tulip’s function in experienced hands, but this is unavoidable in the first use report of a new technology, so we recommend further studies of this device at other sites and in other hands, both experienced and inexperienced.
The measured parameters were both subjective and factual. The subjective measurements such as ease of insertion and quality of the airway were felt to be important as much of the airway skills that anaesthetists use incorporates a tactile component. There is no guidance on how these subjective components should be measured but we considered a 10 point scale a good and adequate way to perform these measurements.
In 60 patients the airway sited and ventilated well immediately, in 13 cases minor adjustments (jaw thrust, head extension) were used to achieve a successful airway and in 2 patients the Tulip® airway required a second insertion before a patent airway was achieved. In one patient an airway was achieved but with difficulty. In 11 of the 15 patients (73%) requiring adjunct airway procedures we found low intra-cuff pressures (< 40cmH2O) despite these patients having no ventilating airway leak. The highest incidence of adjunct airway manoeuvres was seen in those with intra-cuff pressures of < 30cmH2O (60%). In the complete study there was only a 5% incidence (4 patients) of adjunct airway manoeuvres in those with intra-cuff pressures of >40cmH2O. The role of adequate inflation is now better understood as previously we postulated that under-inflation would be indicated by an audible, leak. However, the study makes apparent that under-inflation of the Tulip® cuff does not cause a leak but causes inadequate displacement of anatomical structures in proximity to the breathing tube causing partial obstruction of the ventilating airway which necessitates adjunct airway manoeuvres. This is particularly apparent with intra-cuff pressures < 40cmH2O and deteriorates further if intra-cuff pressures are < 30cmH2O as the Tulip® cuff volume, and hence cuff size, is inadequate to fulfil its function of forming a seal and pushing away obstructive anatomy at these intra-cuff pressures and volumes. Adequate inflation of the centrally placed balloon cuff pushes the local anatomical structures out of the way in all 3 dimensions and clears a ventilating airway for use. If adjunct airway manoeuvers are required we postulate that the Tulip® airway be further inflated up to a recommended intra-cuff pressure of 50cmH2O. We consider that this will minimise adjunct airway procedures and help secure the Tulip® in-situ.
The maximum recommended Tulip® airway intra-cuff pressure of 50cmH2O is deliberately less than the accepted mucosal perfusion pressure within the oropharyngeal mucosa (mucosal perfusion pressure is 40 mmHg which is equivalent to 54.38cmH2O). The intra-cuff pressure intra-cuff volume relationship shows that the maximum inflation volume of 60mls was required in one patient out of 75, and that the maximum pressure of 50cmH2O intra-cuff pressure or lower was achieved in 72 patients. We believe that the three patients with cuff pressures greater than 50cmH2O could have had the intra-cuff pressures reduced to less than 50cmH2O by the simple removal of 1 – 5mls of air from the cuff, bringing them below our 50cmH2O intra-cuff pressure target. Such deflation is unlikely to have caused any loss of airway control as the volume required to reduce the Tulip cuff pressure from 60cmH2O to 50cmH2O in-situ was found to be only 3 – 4mls at these cuff pressures. We suspect this may not have altered the function of the device but further studies are needed to substantiate this. This may not be an issue in clinical practice as the Laryngeal Mask Airway (LMA®) has a recommendation of a maximum inflation pressure of less than 60cmH2O.
The mean intra-cuff pressure at introduction and at seal was low (33cmH2O, SD 10cmH2O and 34cmH2O SD 9cmH2O respectively) confirming the device as an effective large volume, low pressure cuffed airway in clinical practice. The volume of the device at seal was measured with 65 patients sealing at insertion (40mls air). The remaining 10 patients required the addition of between 5 and 20mls to affect a seal. We feel this is an advantage of the Tulip® airway as the consequences of such low cuff pressures are expected to be reflected in both a low level of airway stimulation and a reduction of potential post-operative side effects, such as sore throat and dysphagia. This needs to be studied in further trials but is considered to be likely from our unpublished data collection.
We measured the ventilation parameters of the first 3 breaths once the airway was secured. At acceptable airway pressures of 15(SD 3) cmH2O there was no audible leak in 64 of the 73 recorded results and a minimal leak in 9 patients was observed. The ventilation was considered successful if the tidal volume (Tv) recorded was greater than a 6ml/kg threshold value that was used to define adequate ventilation, with a target range of 6-8ml/kg. The Tv was reduced if higher than 8mls/kg for patient safety by reducing IPPV pressure. The recorded Tv’s were between a minimum of 250mls at 11cmHO2 IPPV in a female patient with a BMI of 29.39 and 1040mls at 19cmH2O IPPV in another female with a BMI of 24, both without an audible leak. The patient who revealed polypoid lingual tissue on bronchoscopy that caused obstruction to the Tulip® as well as an i-gel® and a laryngeal mask, was ventilateable with Tv’s of 250mls, 270mls and 260mls respectively at an IPPV pressure of 4cmH2O without a leak, but required a constant jaw lift in order to do so. A hands free, directly connected airway for IPPV was achieved but it was not suitable for longer term ventilation and was removed.
Of the three recorded IPPV breaths in each case, the first recorded a study mean Tv of 457mls at a ventilating pressure of 14.8cmH2O , the second a mean of 493mls at 14.9cmH2O and the third a mean Tv of 485mls at a ventilating pressure also of 14.9cmH2O, indicating adequate ventilation. Audible leaks did not affect the Tulip’s ability to ventilate as it generated reasonable Tv’s with low cuff pressures and normal IPPV pressures, irrespective of any audible leaks.
The volume of the expired gas recorded was, on average, consistently +/- 50mls less than the inspired gas overall which is not easily explained. As with all supraglottic devices there is more compliance in the ventilation system, in some patients there was a leak, and the monitor (Datex-Ohmeda Cardiocap/5) occasionally recorded aberrant results in which the inspired tidal volumes were less than the expired volumes. We believe error was present within the gas flow instrumentation as there was great disparity in these measurements, so this aspect of the study was frustrating in that we feel that it is difficult to assess a meaning to these results and that in the future it may be better for such studies to utilise the expired CO2 as an acceptable indicator of adequate ventilation.
There was no clinical evidence of gastric insufflation or regurgitation in our study, either through clinical use or bronchoscopy. Bronchoscopy through the Tulip® in-situ revealed a fully closed oesophagus when visualized. The Tulip® sits 1-3cms above the oesophageal entrance and does not open it in order to seat itself, as do other contemporary supraglottic devices. This may be beneficial as a review of the published literature suggests that laryngeal masks have a higher incidence of methylene blue dye regurgitation when compared to Guedel airways with facemask ventilation in-vivo . Measurements of the lower oesophageal sphincter tone for both the laryngeal masks and Guedel airways with facemask ventilation showed that the laryngeal masks demonstrated a mean decrease in barrier pressure compared with a rise in pressure with the Guedel airway facemask group (p <0.005) . Do laryngeal mask airway devices attenuate liquid flow between the oesophagus and pharynx? In a clinical human study, with an active sphincter, such placement may open the oesophagus and reduce lower oesophageal sphincter tone, thus increasing the regurgitation of trace dye [11-14].
The Tulip® airway is designed to sit 1 – 3cms deeper into the oropharynx than an equivalent Guedel or cuffed oropharyngeal (COPA®) airways but 2 – 5cms higher than an equivalent laryngeal mask whose tip lies within the opening of the oesophagus. The evidence would suggest that gastric insufflation is unlikely at normal ventilation pressures (< 20cmH2O) using the Tulip® airway but this needs further study. There is conflict in the evidence but we feel it reasonable to conclude that 20cmH2O is a safe maximum airway pressure for the Tulip® to be used in clinical anaesthesia. Higher airway ventilating pressures may be as best avoided for this device as they are for all supraglottic airways.
Which is the best site to attempt a seal of the airway above the trachea? Current airway devices, such as the laryngeal mask and i-gel® airways, seek to seal the trachea as it branches off of the laryngo-oropharynx at the point where the three tubes of the oropharynx, trachea and oesophagus meet. In order to do this both devices are ‘circumferentio-glottic’ as well as being ‘supra-glottic’ and form elliptical seals around the oval entrance of the trachea. The seal is formed around the epiglottis above, around the glottic opening bilaterally and into the oesophagus below, much as the facemask seals around the nose and mouth externally. The historical COPA® also attempted to seal the junction of three tubes; the nose, the mouth and the oropharynx. The COPA® cuff started in the mouth (mid-way) and attempted to push the soft palate against the back wall of the naso-oropharynx to seal the mouth from the nose, whilst simultaneously attempting to seal around the upper part of the oropharynx in an attempt to seal that part of the anatomical structure [15-18]. The COPA® was not a ‘one size fits all adults’ airway, had an inflatable cuff volume of 25 – 35 ml according to size. The COPA® and its inflatable cuff were located in a higher anatomical space than the Tulip® airway which sits strictly within the oropharynx approximately 3 – 5 cm lower than the COPA® and its cuff is not in the mouth. We propose that the best seal is not provided by attempting to seal at the junction of multiple connecting tubes but by providing a seal at one point from within the upper airway, for example, the oropharynx. Provision of a seal within this single tube by an inflatable balloon cuff theoretically allows that single oropharyngeal tube to be sealed completely by a large volume, low pressure cuff which may be inflated to any volume or pressure within that oropharyngeal tube. The theory of an inflatable cuff within the single oropharyngeal tube then extends to the ability of the device being created to fit all sizes with a single inflatable cuff, provided that the patient in question is able to tolerate the size of the breathing tube provided for gaseous exchange through that inflatable cuff. The size of the device in question could then be easily adjusted using incremental increases or decreases in the cuff volume to fit each patient individually. Theoretically the cuff is then the perfect fit for each patient. The length variations between patients and sizes are then be addressed by adjusting the length of the breathing tube inserted into each patient as marked by colour-coded measurements and guides, with a longer length being used for larger, longer patients and a shorter length of insertion for smaller, shorter patients. Thus one device could fit all adults with one size. All the intended design abilities of the Tulip® airway are achieved by this anatomical location of the inflatable balloon cuff.
How should airway studies with new devices be carried out? The existing method of presenting a new device on the clinical market without a logical sequence of testing has been addressed by this Journal [19, 20]. Bench testing, manikin studies, and in-vivo testing have shown that this airway is worthy of further study in accordance with the Difficult Airway Society ‘ADEPT’ guidance. There are no comparative studies with other supraglottic airways being introduced into clinical practice as all other devices ‘appeared’ on the market and there was no regulation or control over their initial clinical trials (many of which had none). The role of manikin studies has been questioned but we believe that clinical studies should follow manikin studies because our manikin studies have shown similar results to our clinical study [21-23]. This further supports our view that the quality of the results depends on the quality of the simulation. We have performed a manikin study on the airway skills of inexperienced users when comparing the Tulip® airway to Guedel airway and facemask ventilation technique. This study showed statistical significance. With the Guedel and facemask method the inexperienced users required help in 20% of cases, whilst with the Tulip 0% assistance was requested. The Tulip® was used correctly first time in 93.3% of cases, and correctly 100% by the second attempt (p = 0.00026). The Tulip® airway provided hands-free 100% O2 via a directly-connected breathing circuit, whilst the Guedel and facemask provided 40% O2 and was two-hands-on. The average tidal volume generated, when used as a single-operator technique, was significantly greater with the Tulip (397mls) compared with the same inexperienced users using the Guedel and facemask technique (364mls, p = 0.0423). Each tidal volume supplied by the Tulip® airway was on average 9% greater than that provided by the Guedel and facemask method and 46 out of 60 inexperienced users preferred the Tulip® airway (one-sample z scores of – 4.15 to 4.15, p = 0.05) . This study was carried out after manikin studies suggested a role for the Tulip airway in acute hospital and outside hospital resuscitation. Our reported study results compare well with initial studies from other contemporary devices.
Recommendations state that the Tulip® airway should be securely fixed at the mouth. There is discussion about the best way of inserting this airway. The recommended method is to insert the Tulip® airway uninflated up to the colour and size markings on the tube that are appropriate for the individual patient size, and then inflate the cuff as appropriate, but this study utilised the insertion of the airway with a 40mls semi-inflated cuff (the airway is packaged with some 40mls air in the cuff) that was passed behind the tongue until a ‘give’ was felt. Visualisation of the colour scale assisted with confirmation of the correct siting and placement. The use of the semi-inflated cuff allowed the operator to get greater “feel” as the semi-inflated cuff slid behind the tongue and into the oropharynx but this technique may place the Tulip® airway 1 – 2cms further down the oropharynx than designed. However the results of this study show that the airway functions are perfectly acceptable in this marginally deeper location as this is still within the single tubular oropharynx. A third technique of inserting the Tulip® airway is to pass the airway into the oropharynx fully deflated, inflating the cuff with 40mls of air and then pulling the breathing tube back until it feels ‘tight’. With this final method the opposition of the airway cuff and the tongue may be better and may assist first time users. We feel inflating air into the cuff using a pressure manometer set at 50cmH2O may be a better method for Tulip® airway use rather than filling the airway with 40mls of air and then adding more intra-cuff volume, if indicated, to secure a seal. A 50cmH2O pressure release valve (PRV®) is to be added to the Tulip® to fulfil this role and assist inexperienced and experienced users alike. A leak around the cuff is not considered a major problem as ventilation is adequate with a small leak. It is well recognise that all supraglottic airways can leak in the clinical situation. A leak was found to have minimal effects upon the user ability to ventilate the patient to acceptable pressures. This effect was not altered by the presence of neuromuscular paralysis.
The Tulip® has worked adequately in its first use clinical trial. It has demonstrated ease of insertion and use, very low cuff pressures at seal without an audible leak, adequate IPPV pressures with good tidal volumes, an easy removal with minimal trauma or obstruction and has done so with a confirmed single sized adult device in this study. These abilities suggest that the Tulip may be of benefit, particularly if the device is studied in the hands of inexperienced practitioners. This inexperienced element is currently the subject of a subsequent study. The Tulip® needs to be further evaluated to assess its role in airway management, resuscitation and anaesthesia at other sites and in other hands, both experienced and inexperienced.
Dr. Shaikh is the inventor of the Tulip® airway. Dr. Shaikh was not involved in the conduct of the clinical study but was involved in the planning of the clinical study and in the ethical committee application process. The airways used in the study were purchased from The Age of AquariusTM, UK.
1. Alexander R, Hodgson P, Lomax D, Bullen C. A comparison of the laryngeal mask airway and Guedel airway, bag and facemask for manual ventilation following formal training. Anaesthesia 1993; 48: 231-4.
2. Tolley PM, Watts AD, Hickman JA. Comparison of the use of the laryngeal mask and face mask by inexperienced personnel. British Journal of Anaesthesia 1992; 69: 320-1.
3. Martin PD, Cyna AM, Hunter WA, Henry J, Ramayya GP. Training nursing staff in airway management for resuscitation. A clinical comparison of the facemask and laryngeal mask. Anaesthesia 1993; 48: 33-7.
4. Vogel C. Dental injuries during general anaesthesia and their forensic consequences. Anaesthetist 1979; 28: 347-9.
5. Harrison S, Robinson NP, Shaikh A, Yentis SM. Manikin evaluation of the Tulip – a new supraglottic airway. Anaesthesia 2009; 64: 807.
6. Kynoch M, Saini R, Robinson PN, Shaikh A, Hasan M, Vaughan D. Randomised crossover comparison of the Tulip airway compared with the Guedel airway for inexperienced users in a manikin. Anaesthesia 2013; in press.
7. Hasegawa K, Hiraide A, Chang Y, Brown DFM. Association of pre-hospital advanced airway management with neurologic outcome and survival in patients with out of hospital cardiac arrest. Journal of the American Medical Association 2013; 309(3): 257-266.
8. Murashima K, Ozaki M. New supraglottic airway device Tulip is easy to insert: a manikin study. Anesthesia and Analgesia 2011; 112: S05.
9. Barker P, Langton JA, Murphy PJ, Rowbotham DJ. Reurgitation of gastric contents during general anaesthesia using the laryngeal mask airway. British Journal of Anaesthesia 1992; 69: 314-5.
10. Rabey PG, Murphy PJ, Langton JA, Barker P, Rowbotham DJ. Effect of the laryngeal mask airway on lower oesophageal sphincter pressure in patients during generalanaesthesia. British Journal of Anaesthesia 1992; 69: 346-8.
11. Keller C, Brimacombe J, Radler C, Puhringer F. Do laryngeal mask airway devices attenuate liquid flow between the oesophagus and the pharynx? A randomized, controlled cadaver study. Anesthesia and Analgesia 1999; 88; 904-7.
12. Schmidbauer W, Genzwurker H, Ahlers O, Proquitte H, Kerner T. Cadaver study of oesophageal insufflation with supraglottic airway devices during positive pressure ventilation in an obstructed airway. British Journal of Anaesthesia 2012; 109: 454-8.
13. Ho-Tai LM, Devitt JH, Noel AG, O’Donnell MP. Gas leak and gastric insufflation during controlled ventilation: face mask versus laryngeal mask airway. Canadian Journal of Anaesthesia 1998; 45: 206-11.
14. Helmy AM, Atef HM, Wl-Taher EM, Henidak AM. Comparative study between I-gel, a new supraglottic airway device, and classic laryngeal mask airway in anaesthetised spontaneously ventilated patients. Saudi Journal of Anaesthesia 2010; 4: 131-6.
15. Hsu YW, Pan MH, Huang CJ, Cheng CR, Wu KH, Wei TT, Chen CT. Comparison of the cuffed oropharyngeal airway and laryngeal mask airway in spontaneously breathing anaesthesia. Acta Anaesthesiologica Sinica 1998; 36: 187-92.
16. Pusch F, Wildling E, Freitag H, Goll V, Hoerauf K, Weinstabl C. A prospective randomized trial comparing the cuffed oropharyngeal airway (COPA) with the laryngeal mask for elective minor surgery in female patients. Wiener Klinische Wochenschrift 2001; 113: 33-7.
17. Brimacombe J, Berry A. The cuffed oropharyngeal airway for spontaneous ventilation anaesthesia. Clinical appraisal in 100 patients. Anaesthesia 1998; 53: 1074-9.
18. Greenberg RS, Brimacombe J, Berry A, Gouze V, Piantadosi S, Dake EM. A randomized controlled trial comparing the cuffed oropharyngeal airway and the laryngeal mask in spontaneously breathing anaesthetized adults. Anesthesiology 1998; 88: 970-7.
19. Pandit JJ, Popat MT, Cook TM, Wilkes AR, Groom P, Cooke H, Kapila A, O’Sullivan E. The Difficult Airway Society ‘ADEPT’ guidance on selecting airway devices: the basis of a strategy for equipment evaluation. Anaesthesia 2011; 66: 726-37.
20. Shaikh A, Robinson PN. An ADEPT apology. Anaesthesia 2012; 67: 432-3.
21. Jackson K, Cook T. Evaluation of four airway training manikins as patient simulators for the insertion of eight types of supraglottic airway devices. Anaesthesia 2007; 62: 388-93.
22. Popat MT, Rai MR. Evaluation of airway equipment: man or manikin? Anaesthesia 2011; 66: 1-3.
23. Shaikh A, Robinson PN. Manikin studies are essential in airway research. Anaesthesia 2011. www.respond2articles.com/ANA/forums/909/ShowThread.aspx#909 (accessed 20/11/1012).
Figure 1. Inflated and deflated adult Tulip® airway showing the tri-colour size markings with
a size 4 (red) Guedel airway.
Figure 2. Tulip® airways showing the bevelled front ends relative to a size 4 laryngeal mask
(Genesis LMPRV®; The Age of AquariusTM, UK) illustrating the additional yellow pressure
release valve (PRV®) on the pilot balloon.
Table 1. Demographics of patients tested. Age and BMI are given as mean (SD).
|Age (years):||mean 44, SD 15|
|Sex:||male 23, female 52|
|Mallampatti scores:||1 – 50 patients,|
|2 – 23 patients|
|3 – 2 patients|
|4 – 0 patients|
|BMI status:||mean 28, SD 6|
|ASA status:||I – 35 patients|
|II – 40 patients|
Operations proposed: general surgery 39, gynaecological 28, other 8
Ventilation status at Tulip® insertion: ventilated 67 patients, non-ventilated 8 patients
Muscle relaxants usage: paralysed 12 patients, non-paralysed 63 patients
Table 2. Tulip® airway assessment parameters including cuff pressures at seal. Results are given as median (IQR) or mean (SD)
|Insertion ease (1 hard – 10 easy)||median 8, IQR 7 -9|
|Manual ventilation ease (1 hard – 10 easy)||median 10, IQR 9 – 10|
|Self-retention (1 bad – 10 good)||median 7, IQR 6 – 8|
|Quality of airway (1 poor – 10 good)||median 9, IQR 8 – 10|
|Successful airway (1 unsuccessful – 10 successful)||median 10, IQR 8 – 10|
|Initial cuff pressure at 40 ml air inflation (cmH2O)||mean 33, SD 10|
|Cuff pressure at seal (cmH2O)||mean 34, SD 9|
Table 3. Ventilation results and airway pressures for 3 tested breaths. Results are given as mean (SD).
|Capnography: mean (SD)||5.3 (0.5)||5.7 (4.0)||5.3 (0.6)|
|Peak ventilation pressure mm Hg: mean (SD)||15 (3)||15 (3)||15 (3)|
|Audible leak (patient numbers)|
|Inspired tidal volume (ml): mean (SD)||457 (145)||493 (125)||485 (126)|
|Expired tidal volume (ml): mean (SD)||411 (133)||441 (112)||436 (114)|
|Mean difference (ml): mean (SD)||46 (72)||52 (64)||49 (65)|