Problems with airway management during anaesthesia are a leading cause of complications,1,2 and this has prompted extensive research and education to improve standards. Children are often bypassed by these efforts, a fact that is of particular concern as most anaesthesiologists lack experience in managing the paediatric airway. Not only is the anatomy of children different, but their physiology also. They are less tolerant of apnoea with earlier haemoglobin desaturation, with the result that inadequate ventilation resulting in brain damage or death is more common in children than in adults.3
Airway management guidelines for adults4,5 and children6 both emphasise supraglottic airway devices (SGAs) as the immediate ‘plan B’ in case of failed mask ventilation and intubation. Once oxygenation is secured, tracheal intubation is often still desirable and can be carried out through several forms of SGA. In adults, blind rescue intubation through SGA is a standard procedure with high success rates.7–9 The paediatric SGA Air-Q and AmbuAura-i are two disposable SGAs that have been specifically designed to serve as conduits for tracheal intubation (Fig. 1). Although there are data regarding fibreoptic-guided intubation via SGA in children,10–12 clinical studies of blind intubation are lacking. When a paediatric fibrescope is unavailable or when secretions and bleeding hinder its use, an SGA with a high blind intubation success rate is desirable to ensure patient safety.13
The Air-Q Intubating Laryngeal Airway (Cookgas LLC, St. Louis, USA, Fig. 1a) is a single-use SGA with an inflatable cuff. Two paediatric studies report a 97 to 98% first attempt success rate with fibreoptic-guided intubation.10,12 The paediatric AmbuAura-i (Ambu A/S, Ballerup, Denmark, Fig. 1b) is a similarly shaped SGA, and one paediatric study found a 95% first attempt success rate for fibreoptic-guided intubation.10
This trial evaluates the possibility of blind intubation through the Air-Q or the AmbuAura-i in children anaesthetised for elective surgery. On the basis of data regarding the fibreoptic view of the vocal cords through the SGA,12,14 we hypothesised that the success rate of the AmbuAura-i would be higher than the success rate of the Air-Q.
Materials and methods
This randomised, controlled, patient-blinded trial was performed at the Inselspital, University Hospital Bern, Switzerland, between September 2012 and July 2014 with written informed consent of parents. Ethical approval for this study was provided by the Ethical Committee of Bern (Kantonale Ethikkommission, Bern, Switzerland, approval number 093/12) on 17 July 2012. The study was registered through the registry ClinicalTrials.gov (identifier NCT01692522). Primary outcome was the success rate of visualised blind intubation (without fibreoptic guidance).
Participants, inclusion and exclusion criteria
We included children of both sexes, 0 to 16 years, weighing 5 to 50 kg, with American Society of Anesthesiologists’ physical status I to III, scheduled for elective surgery with tracheal intubation. Exclusion criteria were risk of aspiration, known difficult airway, cervical spine disease, malformations of the respiratory tract, upper respiratory tract symptoms in the previous 14 days and preoperative sore throat.
The SGA AirQ and AmbuAura-i are designed for management of difficult airways and for intubation. They were inserted according to manufacturers’ recommendations. SGA size was determined by patient's weight, and tracheal tube size (Microcuff GmbH, Weinheim, Germany) by patient's age, following the manufacturers’ recommendations.
Oral premedication with midazolam 0.5 mg kg−1 was given 30 to 40 min before induction of anaesthesia. After preoxygenation, anaesthesia was induced with sevoflurane, propofol or thiopental. The type of induction depended on the ease of establishing intravenous (i.v.) access and the decision of the anaesthesiologist. Induction by inhalation was performed with sevoflurane with an end-tidal sevoflurane concentration of 6% with or without nitrous oxide. For i.v. induction, propofol 4 mg kg−1 or thiopental 6 mg kg−1 was used. Fentanyl or alfentanil was given and, after insertion of the SGA, atracurium.
Children were randomly assigned to the Air-Q or AmbuAura-i group by computer-generated randomisation numbers in sealed, opaque envelopes. To assure that smaller and bigger children would be equally distributed between groups, we randomised in blocks of 10, according to body weight in blocks of 5 kg (5 to 9.9 kg, 10 to 14.9 kg, up to 45 to 50 kg). The seal of the envelope was broken by trained study personnel after successful facemask ventilation.
Senior anaesthesiologists from the paediatric anaesthesia division performed all airway interventions. Trained study personnel not involved in the clinical procedure performed all measurements.
Supraglottic airway device placement
Adequate depth of anaesthesia was verified clinically by confirmation of the absence of mydriasis, divergent gaze, tachycardia and haemodynamic or motor response to the jaw thrust manoeuvre.14 SGA were lubricated with K-Y Lubricating Jelly (Johnson & Johnson Medical Limited, Gargrave, Skipton, UK), and inserted according to allocation. The jaw thrust manoeuvre facilitated insertion of the SGA. The cuff was inflated and pressure set to 60 cmH2O using a digital manometer to obtain standardised, comparable conditions for all patients (VBM GmbH, Sulz, Germany, or Rüsch GmbH, Kernen, Germany).10 If ventilation was adequate, the SGA was secured and measurements related to the SGA performed as described below. To improve ventilation, up to three minor airway manoeuvres (adjusting head/neck position and changing depth of insertion) could be performed.15 A maximum of three SGA insertion attempts were allowed.
Visualised blind intubation attempt without fibreoptic guidance
A paediatric fibrescope was primed with a Microcuff tracheal tube. The tracheal tube and fibrescope were prepared so that the tip of the fibrescope did not extend beyond the tube (Fig. 2).8 The tube was taped to the fibrescope to keep this position, as the tube and fibrescope were advanced simultaneously. Thus, the fibrescope did not guide, but followed the progress of the tube.8 This allowed well tolerated ‘visualised blind’ intubation with the option to abort if the tube deviated into extra-laryngeal structures. Only smooth intubation without force together with manoeuvres necessary to correct the position of SGA or tracheal tube were allowed. A second person stabilised the SGA in the set position in order to prevent unintentional movement during the intubation procedure. The operator advanced the tracheal tube and the fibrescope simultaneously without rotational or other correctional movements. When the tube entered the trachea, the fibrescope was withdrawn and the breathing circuit reconnected.
Supraglottic airway device removal
To remove the SGA after successful intubation, the breathing circuit was disconnected, and the laryngeal mask withdrawn with the aid of a stylet in a continuous push-pull movement. The time necessary for this manoeuvre was measured from disconnection to reconnection of the breathing circuit.
Three insertion attempts of the SGA with three minor airway interventions were allowed.15 One visualised blind intubation attempt of 2 min was allowed.16 If the trachea could not be intubated, the patient was intubated by fibreoptic guidance or by conventional laryngoscopy. If saturation fell below 92%, or if facemask ventilation or ventilation via the SGA began to fail, the airway was secured according to the choice of the anaesthesiologist.
Data were checked for accuracy and plausibility by two members of the research team. Recorded data included sex, age, weight, ASA class and the type of anaesthesia induction.
The primary outcome was the success rate of first pass visualised blind intubation.
First attempt and overall success rate of the SGA were secondary outcomes. Success was defined as the ability to introduce the SGA and provide sufficient ventilation, defined as a minimal tidal volume of 6 ml kg−1.14,15 A failed attempt was defined as removal of the device from the mouth or three failed minor airway interventions.15 The ease of insertion was subjectively graded by the anaesthesiologist as very easy, easy, difficult or impossible. Time necessary to insert the SGA was measured from removal of the facemask from the face until appearance of end-tidal CO2 on the monitor after connection of the breathing circuit to the SGA. Airway leak pressure of the SGA was measured by closing the circle system's expiratory valve at a fresh gas flow of 3 l min−1, and detecting the airway pressure (max allowed 30 cmH2O) at which equilibrium was reached or audible air was leaking.17 Air entering the stomach was detected by auscultation over the epigastrium.18 The best fibreoptic view from the opening of the SGA was recorded.19 Scoring was as follows: grade 1: full view of the glottis, grade 2: partial view of the glottis, grade 3: only epiglottic structures seen, and grade 4: no glottic/epiglottic structures visible.19 Also, epiglottic downfolding and rotation of the SGA were recorded.
Time necessary for successful blind intubation and the time necessary to remove the SGA were measured from disconnection of the breathing circuit to appearance of end-tidal CO2 on the monitor. In case of blind intubation failure, the direction of the tracheal tube was noted: posteriorly to the arytenoids, anteriorly to the epiglottic cartilage, to the left or to the right. Also, the means by which the airway was secured were noted. Any problems during SGA removal were recorded.
Adverse events were recorded, such as suspicion of aspiration or regurgitation, hypoxia, bronchospasm, laryngospasm and coughing. Staining of blood on the SGA was recorded, as well as dental, tongue or lip trauma. Twenty-four hours after surgery, a structured interview about side effects was performed with the child and the parents. The postoperative investigator was blind to randomisation and device performance. Enquiry included the occurrence of postoperative nausea and vomiting (PONV), hoarseness, numbness of the tongue, dysphagia and sore throat.
Hypothesis and sample size calculation
No data regarding blind intubation through paediatric SGA were available so that sample size calculations could not be based on published data. We assumed that the success of blind intubation would be related to the alignment of the SGA with pharyngeal and laryngeal structures as evaluated by the fibreoptic view of laryngeal structures from the opening of the SGA. For the Air-Q, a study described complete sight of the vocal cords in 31%.12 No data were available for the AmbuAura-i, but for the similarly shaped AmbuAura Once, a full view of the vocal cords had been described in 87%.14 We thus hypothesised that the success rate of blind intubation through the AmbuAura-i would be at least 50% higher than the success rate of blind intubation through the Air-Q.
On the basis of the expected success rates, χ2 power analysis with a two-sided alpha level of 0.05 and a power of 0.9 calculated that 36 patients were needed. As this calculation was based on a surrogate (fibreoptic view vs. intubation success), and on data from a previous version (AmbuAuraOnce) of the SGA (AmbuAura-i) used, we increased the number of study participants to 80.
Normality distribution for continuous data was tested using Shapiro–Wilk W test. Nonparametric data are presented as median with 25th and 75th percentiles. Binary data are given as number and percentage. Nonparametric data were analysed using Mann–Whitney U test. Binary data were analysed using χ2, or Fisher's exact test if more than 20% of expected values were below 5. Ninety-five percent confidence intervals (95% CIs) were computed as exact binominal confidence intervals for binary data. Subgroup analysis was carried out for four predefined groups according to body weight: Subgroup 1: 5 to 9.9 kg, subgroup 2: 10 to 19.9 kg, subgroup 3: 20 to 29.9 kg and subgroup 4: 30 to 50 kg. For the comparison of the four subgroups, nonparametric data were analysed using Kruskal–Wallis test. A probability of 0.05 or less was considered as statistically significant. Data were analysed using Stata V.13.1 (StataCorp, College Station, Texas, USA).
Eighty children of both sexes were included (40 Air-Q, 40 AmbuAura-i). There were no drop-outs after randomisation (Fig. 3). Personal characteristics were similar between groups (Table 1). Nine anaesthesiologists participated. Both devices were equally distributed among them (P = 0.72, Fisher's exact test).
Primary outcome: blind intubation success rates
Visualised blind intubation was possible in 15% with the Air-Q and in 3% with the AmbuAura-i (P = 0.057, Table 2). The 95% CI was 6–31 for the Air-Q and 0–13 for the AmbuAura-i. The hypothesis that the success rate of blind intubation through the AmbuAura-i would be at least 50% higher than that of the Air-Q was rejected.
Secondary outcomes related to the supraglottic airway device
Ventilation by facemask was easy and oxygenation remained stable throughout the procedure in all 80 cases. SGA insertion was successful in 79 cases and was graded as very easy or easy in all of these cases (Table 2). Insertion was slower with the Air-Q than with the AmbuAura-i (median 27 vs. 19 s, P < 0.001). Median leak pressures were 18 cmH2O (Air-Q) and 17 cmH2O (AmbuAura-i; interquartile range 14 to 18 vs. 14 to 19 cmH2O; P = 0.66). The airway seal enabled positive pressure ventilation in all successful cases. There was no difference between the devices regarding fibreoptic view, epiglottic downfolding or SGA rotation (Table 2). A full fibreoptic view of the vocal cords was present in only 21% of Air-Q and 10% of AmbuAura-i cases.
Secondary outcomes related to blind intubation and supraglottic airway device removal
As intubation success was low, the numbers of intubation times and SGA removal were also low, but intubation times were similar between groups. Most failed blind intubations were managed by direct laryngoscopy. In one of the seven cases in which blind intubation was possible, the tube dislocated during SGA removal and the child was intubated by direct laryngoscopy (Air-Q size 1.5, tube size 3.5).
Adverse events and side effects
In one case with the Air-Q, bronchospasm occurred during insertion. The Air-Q was removed and the child was uneventfully intubated by conventional laryngoscopy. There were no other complications during SGA insertion or anaesthesia. One Air-Q was stained with blood at removal. PONV did not differ between the Air-Q and the AmbuAura-i (38 vs. 24%, respectively, P = 0.27, χ2). The same was true for hoarseness (23 vs. 40%, P = 0.19, χ2), numbness of the tongue (0 vs. 0%), dysphagia (8 vs. 28%, P = 0.08, Fisher's exact test) and sore throat (23 vs. 40%, P = 0.19, χ2), but unfortunately one-third of the patients could not be reached for the postoperative interview (Air-Q 35%, AmbuAura-i 38%).
Analysis according to body weight (Table 3) revealed a statistically significant difference between the AmbuAura-i subgroups for airway leak pressure, with higher airway leak pressures in bigger children (median leak pressure in subgroups 5 to 9.9 kg: 15 cmH2O; 10 to 19.9 kg: 17 cmH2O; 20 to 29.9 kg: 18 cmH2O; 30 to 50 kg: 21 cmH2O; P = 0.04). Also, there was a statistically significant difference in insertion difficulty between the subgroups of the AmbuAura-i (insertion ‘very easy’ in subgroups 5 to 9.9 kg: 100%; 10 to 19.9 kg: 93%; 20 to 29.9 kg: 50%; 30 to 50 kg: 100%; P = 0.01). There were no statistically significant differences between the first attempt success rate, the overall success rate, insertion difficulty, airway leak pressure, insertion time, fibreoptic view or blind intubation success rate between the different subgroups of the Air-Q. Apart from the described differences, there were also no other statistically significant differences for these outcomes between the different subgroups of the AmbuAura-i.
For children weighing 20 to 29.9 kg, insertion was easier with the Air-Q (100% very easy) than with the AmbuAura-i (50% very easy, P = 0.03). For children weighing 10 to 19.9 kg, insertion was faster with the AmbuAura-i than with the Air-Q (median insertion time 19 vs. 25 s; P = 0.02). The same was true for children weighing 30 to 50 kg (median insertion time 17 vs. 27 s; P = 0.004). There was no significant difference in any subgroup regarding blind intubation success rate, SGA success at first attempt, overall SGA success, airway leak pressure or fibreoptic view between the AmbuAura-i and the Air-Q (Table 3).
For adults, blind intubation through an SGA has been a cornerstone in difficult airway management for years.7,9 Depending on the SGA, success rates vary widely. Although first pass blind intubation success rate through the ILMA Fastrach reaches 80% or more, it is as low as 15% for the i-gel.8 Results from adult studies cannot be extended to paediatric anaesthesia, and SGA tend to perform worse in smaller children.14 Although some paediatric SGA have been validated for fibreoptic-guided intubation,10,12 they have not been evaluated for blind intubation. Thus, manufacturers recommend the Air-Q and AmbuAura-i for fibreoptic-guided, but not for blind intubation. Some authors argue that because of epiglottic downfolding and potential injury to the epiglottis or the glottis, blind intubation through SGA should not be attempted.20,21 However, blind rescue intubation through paediatric SGA continues to be performed.13 If the paediatric fibreoptic scope is unavailable or fails due to airway bleeding, the clinician needs to know which paediatric SGA will perform best for blind intubation.
We postulated that a full fibreoptic view of the vocal cords would facilitate blind intubation. On the basis of results of the fibreoptic view, we expected success rates of approximately 31% with the Air-Q12 and of approximately 87% with the AmbuAura-i.14 A more recent study that was unavailable before the present study reported a full view of the vocal cords in only 17% for the Air-Q and in 15% for the AmbuAura-i.10 Success rates of blind intubation in this study were much lower than originally expected and, at least for the Air-Q, closely resembled the results of full fibreoptic view described by Jagannathan et al.10 In contrast, a study in adults showed a 58% first pass blind intubation success with the Air-Q,22 confirming that caution is needed when extrapolating adult data to the paediatric setting.
The low blind intubation success rates in the present study are probably due to a combination of factors. First, the fibreoptic view was optimal (full view of the vocal cords) in only 10% with the AmbuAura-i and in 21% with the Air-Q. It has been shown that a full fibreoptic view is not necessary for fibreoptic-guided intubation,10,23 but it seems that it is an essential criterion for successful blind intubation.
Second, in this study, we performed visualised blind intubation attempts and not ‘true’ blind intubation (Fig. 2). Whenever the tube struck the epiglottis or glottic structures, the attempt was abandoned to prevent injury to the child's airway.8 It is possible that without visualisation, the application of a little force would have led to intubation success in additional cases, but this could also have resulted in airway trauma20,21 or oesophageal intubation. Blind intubation failure was frequently due to a deviation of the tracheal tube towards the oesophagus. It is possible that rotating the tracheal tube by 180° (reverse loading),24 or manoeuvres such as anterior laryngeal pressure, the use of a bougie or head extension and flexion could have improved success rates, but this remains speculative. Also, reverse loading may direct the tracheal tube towards the arytenoids or the epiglottis, potentially leading to airway injury. As blind intubation was rarely successful, data about intubation times cannot be interpreted.
One child was accidentally extubated when removing the SGA. To avoid accidental extubation, an airway exchange catheter could be beneficial,25 but this also implies extra costs and additional manipulation with the risk of airway injury by the exchange catheter.
With regard to ventilation with SGA, we have defined 90% as the minimal acceptable lower limit for the success rate of SGA.26 The measured first attempt success rates were 95 and 100% for the Air-Q and AmbuAura-i, respectively, and success rates were similar to a previous study.10 Although our rates were above 90%, the calculated 95% CI was above 90% only for the AmbuAura-i. With a higher sample size, the true value might indeed be above 90% for both SGA. Airway leak pressures ranged around 16 to 17 cmH2O for both devices, and were also similar to two previous studies.10,27 Although the measured leak pressures were lower than those described for SGA in adults,8,28 the seal was sufficient for positive pressure ventilation.
This study evaluated visualised blind intubation (Fig. 2) and not ‘true’ blind intubation. Although we cannot per se exclude that the fibrescope altered the path of the tracheal tube, we consider this the only acceptable way to study blind intubation, especially in paediatrics. With ‘true’ blind intubation, deviations of the tracheal tube cannot be assessed and airway injury may occur. Also, as the tracheal tube often deviated towards the oesophagus, ‘true’ blind intubation could have resulted in oesophageal intubation.
The fibreoptic view was worse than expected and statistical significance for our primary outcome was not achieved. All in all, the very low success rate of blind intubation renders this technique unusable.
Induction was either i.v. or by inhalation. For both techniques, a strict clinical protocol was in force to ensure adequate depth of anaesthesia. We did not consider that the choice of induction technique would influence the insertion success rate of SGA.14 Before intubation, propofol, opioid and muscle relaxant were administered in all children.
Finally, we studied children with a large weight range. Variation of the upper airway between weight groups could have influenced visualised blind intubation success, but subgroup analysis did not reveal differences. Also, we performed an additional logistic regression analysis and found that weight did not influence blind intubation success rate (AmbuAura-i: OR 1.04, P = 0.43, Air-Q: OR 1.03, P = 0.25). Numbers were very limited for some subgroups, as the study was not powered for a subgroup analysis, and thus, results should be interpreted with caution.
In conclusion, both SGAs are efficient for ventilation. In contrast to our hypothesis, blind intubation success rate with the AmbuAura-i was not higher than with the Air-Q, and success rates with both devices were unacceptably low. Given this evidence, blind intubation through either device cannot be recommended.
Acknowledgements relating to this article
Assistance with the study: the authors would like to thank Christine Riggenbach, RN, Yves Charriere, MD, and Marco Enderlin, MD (all Department of Anaesthesiology and Pain Medicine, Inselspital, Bern University Hospital, Switzerland) for their help with the clinical part of the study and data acquisition.
Financial support and sponsorship: this work was funded by an institutional research grant of the Department of Anaesthesiology and Pain Medicine, Inselspital, Bern University Hospital, Switzerland. The AmbuAura-i and the Air-Q were provided by the manufacturers free of charge.
Conflicts of interest: none.
Presentation: this report was previously presented, in part, at the 2013 ASA Annual Meeting in San Francisco, USA, and at the 2013 Swiss Society of Anaesthesiology and Reanimation Annual Meeting in Lausanne, Switzerland.
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