A randomised comparison of the self-pressurised air-QTM intubating laryngeal airway with the LMA UniqueTM in children*

Authors

  • N. Jagannathan,

    1.  Attending Pediatric Anesthesiologist and Assistant Professor, Department of Pediatric Anesthesia, Ann & Robert H. Lurie Children’s Hospital of Chicago, Department of Pediatric Anesthesia and Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA
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  • L. E. Sohn,

    1.  Attending Pediatric Anesthesiologist and Assistant Professor, Department of Pediatric Anesthesia, Ann & Robert H. Lurie Children’s Hospital of Chicago, Department of Pediatric Anesthesia and Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA
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  • A. Sawardekar,

    1.  Attending Pediatric Anesthesiologist and Assistant Professor, Department of Pediatric Anesthesia, Ann & Robert H. Lurie Children’s Hospital of Chicago, Department of Pediatric Anesthesia and Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA
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  • R. Shah,

    1.  Attending Pediatric Anesthesiologist and Assistant Professor, Department of Pediatric Anesthesia, Ann & Robert H. Lurie Children’s Hospital of Chicago, Department of Pediatric Anesthesia and Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA
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  • K. Ryan,

    1.  Fellow in Pediatric Anesthesia
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  • R. Jagannathan,

    1.  Research Student
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  • K. Anderson

    1.  Anesthesia Technician, Department of Pediatric Anesthesia, Ann & Robert H. Lurie Children’s Hospital of Chicago, Chicago, Illinois, USA
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N. Jagannathan
Email: simjag2000@yahoo.com

Summary

We conducted a randomised trial comparing the self-pressurised air-QTM intubating laryngeal airway (air-Q SP) with the LMA-Unique in 60 children undergoing surgery. Outcomes measured were airway leak pressure, ease and time for insertion, fibreoptic examination, incidence of gastric insufflation and complications. Median (IQR [range]) time to successful device placement was faster with the air-Q SP (12 (10–15 [5–18])) s than with the LMA-Unique (14 (12–17 [6–22]) s; p = 0.05). There were no statistically significant differences between the air-Q SP and LMA-Unique in initial airway leak pressures (16 (14–18 [10–29]) compared with 18 (15–20 [10–30]) cmH2O, p = 0.12), an airway leak pressures at 10 min (19 (16–22 [12–30]) compared with 20 (16–22 [10–30]) cmH2O, p = 0.81); fibreoptic position, incidence of gastric insufflation, or complications. Both devices provided effective ventilation without the need for airway manipulation. The air-Q SP is an alternative to the LMA-Unique should the clinician prefer a device not requiring cuff monitoring during anaesthesia.

Several new supraglottic airway devices are available for use in paediatric patients. The laryngeal mask airway (LMA) UniqueTM (LMA North America, San Diego, CA) is a single-use supraglottic airway device with an established efficacy in both adults and children [1, 2]. The self-pressurised air-QTM intubating laryngeal airway (air-Q SP; Cookgas LLC, Mercury Medical, Clearwater, FL) is a new single-use device that may optimise the airway seal while reducing the potential for postoperative pharyngo-laryngeal morbidity. The overall structure of the air-Q SP is identical to the original air-Q, except with regard to the inflatable cuff. Instead, there is an inner aperture at the junction of the airway tube and the mask cuff, creating an open airspace between the two, and allowing the pressure to be self-regulated (Fig. 1). This feature of the air-Q SP may provide for easier device insertion, reduced risk for prolonged overinflation of the cuff and pressure-related injuries to the pharyngeal mucosa without the need for cuff pressure monitoring.

Figure 1.

 The self-pressurised air-Q intubating laryngeal airway (air-Q SP) size 2. (a) Frontal view. The air-Q SP lacks an inflatable cuff for its mask bowl. (b) View of the air-Q SP mask bowl. Note the inner aperture (arrow) at the junction of the airway tube and the mask cuff, creating an open airspace between the two that allows the intracuff pressure to be self-regulated. The proximal portion of the mask bowl has been cut to reveal its inner orifice.

Studies have shown the original air-Q to be an effective device for airway maintenance [3, 4], and as a conduit for tracheal intubation in both adults [5] and children [6]. To date, only one observational study has been reported using the air-Q SP in children [7], and there are no randomised studies using this device in either adults or children. The aim of this randomised trial was to evaluate the clinical performance of the air-Q SP compared with the LMA Unique. Ease and time for insertion, insertion success rate, airway leak pressures, incidence of gastric insufflation, fibreoptic laryngeal view, quality of airway during anaesthetic maintenance and complications were assessed.

Methods

This study was approved by the Children’s Memorial Hospital Research Center’s Institutional Review Board and written informed consent was obtained from the parents of all patients. Children weighing 20–30 kg, 3–9 years of age, of ASA physical status 1–3, scheduled for elective outpatient surgery in which airway management with a LMA would be appropriate, were enrolled in this study. Patients were excluded if they had active respiratory illness (cough, fever, rhinorrhoea) on the day of anaesthesia, inability to report (e.g. due to developmental delay) postoperative complaints such as sore throat, or a potentially difficult airway. Patients were screened and recruited consecutively based on eligibility criteria, and availability of the study investigators.

Sixty children were randomly allocated by a computer-generated list using Microsoft Excel (Redmond, WA, USA) to receive either a size-2 air-Q SP or 2.5 LMA Unique. The study investigator was only made aware of the allocation immediately before device insertion. The standardised anaesthetic protocol consisted of an inhalational induction with 8% sevoflurane in 70% nitrous oxide and oxygen followed by intravenous access, and administration of fentanyl 1 μ.kg−1. Manual ventilation of the lungs was continued until the heart rate was at least 20% lower than pre-fentanyl values with an end-tidal sevoflurane concentration of 2.5% maintained before device insertion. Adequate anaesthetic depth was confirmed by the lack of a motor response to jaw thrust [8]. A supplementary dose of 1 μ.kg−1 fentanyl was allowed if the depth of anaesthesia was considered insufficient for device placement. Each device was lubricated with a water-based agent before placement. A standard midline insertion technique was used for both devices, according to the manufacturer’s recommendations. All patients were maintained with at least 2% sevoflurane in 60% nitrous oxide and oxygen. No neuromuscular blocking drugs were administered. Three study investigators experienced with the use of both devices (over 500 insertions with the LMA Unique and at least 50 insertions with the air-Q SP) performed all the insertions. One investigator managed the airway, inserted the device and obtained the fibreoptic views for grading, while a second investigator recorded the airway leak pressures and assessed for gastric insufflation. An unblinded observer assisted with the measurement of time, recorded the fibreoptic views and ensured collection of all data.

The time for successful insertion was measured from the moment the facemask was removed until the first capnography upstroke after insertion. For patients receiving the LMA Unique, the intracuff pressure was standardised to 60 cmH2O using an aneroid cuff pressure gauge (Ambu® Inc., Glen Burnie, MD, USA). The ease of placement was assessed using a subjective scale of 1–4 (1 = no resistance, 2 = mild resistance, 3 = moderate resistance, 4 = inability to place the device). Insertion was recorded as a failure if the device could not be successfully placed within two attempts, lacked a square-wave capnograph tracing, resulted in airway obstruction (diagnosed by oxygen desaturation < 90%, abnormal thoraco-abdominal movements, or obstructive noises), or there was inadequate ventilation (an inability to generate 7–10 ml.kg−1 tidal volumes). The patient’s trachea was to be intubated should there be a failed insertion.

To determine the leak pressure, the expiratory valve was closed with a fresh gas flow of 3 l.min−1 until equilibrium was reached [9] (not allowed to exceed 40 cmH2O), and then released completely. Auscultation with a stethoscope was performed over the epigastrium during leak pressure testing to detect the occurrence of gastric insufflation [10]. A flexible fibreoptic scope (LF-V, 4.1 mm; Olympus America Inc., Melville, NY, USA) was used to view the anatomic alignment of the device to the larynx, 1 cm proximal to the airway orifice. The images were graded as follows [11]: Grade 1, larynx only seen; Grade 2, larynx and epiglottis posterior surface seen; Grade 3, larynx and epiglottis tip of anterior surface seen, less than 50% visual obstruction of epiglottis to larynx; Grade 4, epiglottis downfolded and its anterior surface seen, greater than 50% visual obstruction of epiglottis to larynx; Grade 5, epiglottis downfolded and larynx cannot be seen directly. A second airway leak pressure and a second fibreoptic view were both taken 10 min after the initial leak pressure and initial fibreoptic view to observe if there was a change in the airway seal.

The mode of ventilation for maintenance of anaesthesia (spontaneous, pressure support, or mechanical) was at the discretion of the anaesthetist, and recorded. Ventilation was adjusted to maintain the end-tidal carbon dioxide between 4.0 and 4.5 kPa during anaesthetic maintenance. The quality of the airway (clear, intermittent partial obstruction, intermittent complete obstruction, or complete obstruction) [12], and the number and type of airway manipulations (gentle advancement, withdrawal of device without removal, jaw thrust, or neck extension) required to maintain airway patency during the case were also recorded. Failure of the device during maintenance of anaesthesia was defined as inadequate ventilation (using the same criteria as above for device insertion, and/or end-tidal carbon dioxide > 5.9 kPa), airway obstruction that could not be corrected with airway manipulation, or the need for replacement of device with a tracheal tube. At the conclusion of the procedure, the intracuff pressure was checked and recorded for those patients who had received the LMA Unique.

All devices were removed under a deep plane of anaesthesia at the conclusion of the procedure. Complications with each device, such as airway reflex activation (coughing, laryngospasm, or bronchospasm), desaturation (SpO2 < 90%), gastric insufflation and bloodstaining on the device after removal, were also noted. All patients were seen in the postanaesthetic recovery ward by a blinded investigator. They also received a follow-up phone call the next day from a registered nurse who was not part of the study, to document any postoperative complications, such as sore throat, dysphonia, dysphagia, cough, or stridor, as reported by the child and/or the parents.

The primary outcome variable was airway leak pressure, and it was anticipated that with the air-Q SP these would be no less than 25% than that of the LMA Unique. Previous data with the air-Q SP suggested that the initial leak pressure with the size 2 was 17 (5) cmH2O in this patient population. After 10 min, the leak pressure was found 19 (5) cmH2O. A leak pressure difference of 4 cm H2O (the minimum difference considered to be clinically significant) on initial leak pressure testing, and/or at 10 min after placement, would be required to detect a significant difference between these two devices. Using this effect size, an alpha of 0.05, and a desired power of 0.9, we estimated that 27 patients would be required per device to demonstrate this difference in leak pressure between these two devices. This study enrolled 60 patients (30 in each group) to allow for the potential dropout of subjects.

Data were recorded intra-operatively using a standardised data collection sheet, and analysed using Microsoft Excel and the statistical software PASW Statistics 18 (SPSS Inc., Chicago, IL, USA). Statistical comparisons between devices were made using Student's t-test for continuous data, chi-squared test for categorical data and Mann–Whitney U-test for ordinal data. A p value < 0.05 was considered statistically significant.

Results

Eighty patients were screened for enrolment in the study. After the study was explained and the patient information was read, twenty parents declined to participate. No patients were excluded for violation in protocol or refusal to participate after consent was given. Patients' characteristics and surgical data are presented in Table 1 and comparative data between the air-Q SP and LMA Unique are seen in Table 2.

Table 1.   Patient and operative characteristics for the self-pressurised air-Q (air-Q SP) and LMA Unique. Values are median (IQR [range]) or number (proportion).
 air Q-SP (n = 30)LMA Unique (n = 30)
Age; years7.0 (4.8–8.6 [4.1–9.4])6.7 (5.9–7.9 [4.3–9.8])
Sex
 Male20 (67%)18 (60%)
 Female10 (33%)12 (40%)
Weight; kg25.5 (23.0–30.0 [20.1–30.5])24.8 (22.2–26.8 [20.0–30.8])
ASA physical status
 116 (53%)21 (70%)
 29 (30%)5 (17%)
 35 (17%)4 (13%)
Duration of procedure; min59 (43–78 [20–178])67 (45–85 [17–214])
Type of procedure
 Urology7 (23%)4 (13%)
 Imaging3 (10%)4 (13%)
 General9 (30%)13 (44%)
 Ophthalmology5 (17%)3 (10%)
 Orthopaedic6 (20)6 (20)
Table 2.   Comparative data for the self-pressurised air-Q (air-Q SP) and LMA Unique. Values are median (IQR [range]), number, or number (proportion).
 air-Q SP (n = 30)LMA Unique (n = 30)p value
  1. *Ease of device insertion as graded by the following subjective scale: 1 = no resistance; 2 = minimal resistance; 3 = moderate resistance; 4 = unable to place device.

  2. †Grade 1, larynx only seen; Grade 2, larynx and epiglottis posterior surface seen; Grade 3, larynx and epiglottis tip of anterior surface seen, less than 50% visual obstruction of epiglottis to larynx; Grade 4, epiglottis downfolded and its anterior surface seen, greater than 50% visual obstruction of epiglottis to larynx; Grade 5, epiglottis downfolded and larynx cannot be seen directly. [11]

  3. ‡Includes laryngospasm, bronchospasm, stridor and coughing.

Time to successful placement; s12 (10–15 [5–18])14 (12–17 [6–22])0.05
Ease of device placement*
 1/2/3/424/6/0/029/0/1/00.02
Single attempt required30 (100%)30 (100%)1.00
Leak pressure initial; cmH2O16 (14–18 [10–29])18 (15–20 [10–30])0.12
Leak pressure at 10 min; cmH2O19 (16–22 [12–30])20 (16–22 [10–30])0.81
Gastric insufflation
 No28 (93%)27 (90%)0.64
 Yes2 (7%)3 (10%)
Fiberoptic grade† initial
 1/2/3/4/510/12/3/3/24/15/5/4/20.47
Fiberoptic grade† at 10 min
 1/2/3/4/510/8/7/3/25/13/6/4/20.55
Airway quality
 Clear30 (100%)30 (100%)1.00
 Intermittent partial obstruction00
 Intermittent complete obstruction00
 Complete obstruction00
No airway manipulation required30 (100%)30 (100%)1.00
Intracuff pressure at end of case; cmH2O62 (55–66 [28–78])
Type of ventilation
 Controlled3 (10%)4 (13%)0.09
 Pressure support25 (83%)18 (60%)
 Spontaneous2 (7%)8 (27%)
Intra-operative complications
 None30 (100%)29 (97%)0.31
 Airway related‡00
 Blood on removal01 (3%)
Postoperative complications
 None30 (100%)25 (83%)0.07
 Dysphonia (sore throat)01 (3%)
 Dysphagia (sore throat)04 (14%)
 Cough00

There were no statistically significant differences with regard to success rates of device insertion, airway leak pressures (initial and at 10 min), gastric insufflation, fibreoptic grade of view (initial and at 10 min), quality of airway achieved, number of airway manipulations, and complications between the air-Q SP and LMA Unique. All devices in both groups were successfully placed at the first attempt. All patients in both groups had a clear airway without the need for airway manipulation. There were no instances of device failure during maintenance of anaesthesia, or conversion to a tracheal tube.

There were statistically significant differences for time to successful placement and subjective ease of placement between the devices (Table 2). Blood on the device was only seen with one patient, who received the LMA Unique, which had also been moderately difficult to place. Follow-up phone calls revealed five patients with postoperative complaints, all from the LMA Unique group: one with dysphonia and four children with dysphagia; all five children complained of a sore throat, including the child with bloodstaining on the LMA Unique. Children with a sore throat had intracuff pressures of 58, 63, 64, 73, 78 cmH2O. There were no episodes of gastric regurgitation, aspiration, laryngospasm, bronchospasm, or stridor in any of the patients.

Discussion

Our results suggest that the air-Q SP was faster to insert than the LMA Unique in children, although the clinical effect was marginal. The devices demonstrated similar airway leak pressures and overall clinical performance. The overall insertion success rates were similar to those reported by other randomised trials with the air-Q, LMA Unique, and classic LMA in children [4, 13, 14]. The airway tube of the air-Q SP is more flexible than the LMA Unique and could affect the subjective ease of placement, but insertion times were still faster with the air-Q SP. This is likely to be due to the elimination of the cuff inflation step for device placement, a finding also seen with the use of the i-gel in children [15]. The insertion times for the LMA Unique in this study are consistent with another randomised trial in children [16].

The airway leak pressures of the air-Q SP in this study were also similar to those reported with both the size-2 air-Q with an inflatable cuff [4, 6] and the size-2 air-Q SP [7] in children, but lower than in adult patients [3, 17]. The LMA Unique airway leak pressures at 10 min in this study were higher than with other randomised trials on the paediatric-sized classic LMA [14, 18, 19], and LMA Unique [13, 16]. An increase in airway leak pressure of both devices at 10 min may indicate some degree of moulding of the device in the posterior pharynx improving airway seal. Adjustments of the intracuff pressure are sometimes needed to maintain an adequate airway seal and prevent overinflation of the cuff when using supraglottic airways [20–22]. In this respect, the use of the air-Q SP may represent a benefit, as it may be more convenient than supraglottic airways with inflatable cuffs.

Fibreoptic examination through both the air-Q SP and the LMA Unique demonstrated similar anatomic alignment, and may not always correspond to the functional position of the device, as is often seen in children [23]. Even with some epiglottic downfolding present, both devices provided adequate ventilation parameters without evidence of airway obstruction, or need for airway manipulations. This suggests an adequate airway stability of both devices during anaesthetic maintenance. Although it has been shown that the air-Q gives more favourable fibreoptic views compared with the LMA Unique in smaller children [4], this finding was not observed in the current study. The hypopharyngeal seal, as evidenced by comparable rates of gastric insufflation, was similar with both devices and also consistent with the frequency seen in other studies with the air-Q and LMA Unique in children [4, 16].

There were no differences in the overall complication rates between the two devices, despite the air-Q SP’s theoretical advantages. Of note, we did not find an overall increased frequency of sore throat in the children from the LMA Unique group with intracuff pressures greater than 60 cmH2O at the end of the case. This increase in intracuff pressure may be attributed to the use of nitrous oxide, especially with longer anaesthetic duration, or changes in the LMA Unique position within the posterior pharynx, highlighting the importance of interval monitoring of intracuff pressures [22].

There are several limitations to this study. First, we only studied healthy children, and our results may not apply to children with poor lung compliance. Second, only one device size was studied. Third, data were collected by unblinded observers, which may have introduced bias. Fourth, our results may not apply to children receiving neuromuscular blockade. Finally, the mucosal pressure exerted on the posterior pharynx by the air-Q SP was not directly measured, and this could be a subject for future study, as has been done with the i-gel in adult patients [24].

Acknowledgements

The authors thank the anaesthesia attending staff at Children’s Memorial Hospital for allowing us to switch assignments and recruit patients and Grace Lee (Johns Hopkins Bloomberg School of Public Health) for statistical assistance. The air-Q SP was provided by Cookgas LLC and we thank Dr. Daniel J. Cook for this help, but no commercial financial support was granted either to our institution or to any of the listed authors.

Competing interests

No external funding or competing interests declared.

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