Supraglottic airway devices [Laryngeal Mask Airway (LMA); Teleflex Medical, Athlone, Ireland] are specific airway devices now used commonly for airway maintenance during general anaesthesia for different elective procedures. Airway management guidelines suggest their use for rescue ventilation during difficult airway management.1–3
In addition, they are used as an airway conduit for endotracheal intubation either blindly or preferably with fibreoptic assistance. The first, and probably most commonly used, supraglottic airway device is the laryngeal mask airway, consisting of a hollow tube connected to an anatomically shaped cuff designed to fit the hypopharynx facing the glottis, with its tip sealing the upper oesophageal sphincter.
Further evolutions have been provided over the years, including the intubating laryngeal mask (iLMA – Fastrach; Teleflex Medical), and so-called second-generation devices, allowing gastric access and increased sealing capabilities, and newer devices with advanced airway protection features and intubation possibility.3 The LMA Supreme (LMA-S; Teleflex Medical) is a second generation polyvinyl chloride (PVC) single-use device with gastric access and not primarily designed for intubation, and has been shown to be particularly safe, easy to use and effective.4
Recently, a new supraglottic airway device, the Spritztube tracheal cannula (Med Europe s. r. l, Aulla, Italy) was developed in our centre at the Department of Anaesthesia and Intensive Care, San Bortolo Hospital, Vicenza, with specific features combining the ability to perform both supraglottic airway device ventilation and fibreoptic-guided tracheal intubation using the same device.5 The Spritztube consists of a silicone cannula with two low-pressure cuffs: a proximal cuff, designed to seal the pharynx cranially in respect of the epiglottis, and a distal cuff designed to seal the oesophagus. The positioning of this device requires the aid of a dedicated stilette, designed to align the two cuffs while stiffening the Spritztube so as to allow passage through the oropharynx down to the hypopharynx. The Spritztube can be inserted blindly or with the aid of direct or indirect laryngoscopy or rigid or flexible endoscopes (Figs. 1 and 2). More information about the device and the insertion technique can be accessed at http://www.spritztube.eu/en/details.
To date, the Spritztube is not commercially available and is only for experimental use. The only published report on the Spritztube is a recent mannequin-based study demonstrating a higher successful insertion rate and ease of use compared with the LMA Fastrach.5
We designed a randomised controlled trial to compare the LMA-S and Spritztube performance in a cohort of mechanically ventilated patients undergoing elective surgery in the supine position. We hypothesised that the Spritztube is as effective as the LMA-S in maintaining the airway.
The current study was approved by the ethics committee of St. Bortolo Hospital, Vicenza, Italy (29/16) in accordance with the principles outlined in the Declaration of Helsinki and registered (NCT03443219). We obtained written informed consent from all patients enrolled in the study.
American Society of Anesthesiologists’ (ASA) physical status classification 1, 2 or 3 patients scheduled for elective surgery in the supine position were considered eligible.
Before arrival in the operating room, and after the collection of written informed consent, patients were randomly assigned to LMA-S or Spritztube group by opening an opaque sealed envelope with their number of randomisation order, provided by an independent physician blinded to the patient's allocation, who also recorded successful placement, time taken for insertion and complications at insertion or removal.
The general anaesthesia protocol, intra-operative monitoring and postoperative care performed for all patients was standardised and managed by an independent anaesthetist not directly involved in the study, and included HR, peripheral oxygen saturation and continuous electrocardiography. All patients received premedication with midazolam 0.03 mg kg−1 followed by fentanyl 2 μg kg−1 and propofol 2 mg kg−1 for induction of anaesthesia. Anaesthesia was maintained with propofol (continuous infusion 6 to 8 mg kg−1 h−1) and remifentanil (continuous infusion 0.25 to 0.75 μg kg−1 min−1). Neither nitrous oxide nor a neuromuscular blocking agent were given, and depth of anaesthesia was monitored with the bispectral index (BIS monitor; Covidien Medical, Louisville, Colorado, USA), targeting the range 40 to 60. Both the LMA-S and the Spritztube were inserted by trained anaesthesiologists with at least 5 years of experience. The size of the LMA-S was chosen according to the patient's weight and ranged from size 3 (30 to 50 kg) through 4 (50 to 70 kg) to 5 (70 to 100 kg). The Spritztube is available in a unique adult size.
The Spritztube was inserted blindly into the oropharynx using the following method. Before insertion, the cuffs were deflated and a water-soluble lubricant was applied to the cuffs. The patient's neck was extended to the ‘sniffing position’. Held as a pen, the device was inserted into the oral cavity following the soft palate, stopping introduction once the black marker on the Spritztube (teeth mark) reached the upper incisors. Then, distal and proximal cuffs were inflated with 20 and 60 ml of air, respectively. The stilette was then removed and the tube was connected to the breathing circuit or to a bag-valve assembly.5
The LMA-S was inserted completely deflated and lubricated using the recommended technique.4–7
The insertion time was measured with a stopwatch by an independent observer, from the start of insertion of the device into the patient's mouth until connecting the breathing circuit; the cuff pressure was set at 60 cmH2O once the device was inserted. Successful placement was defined as adequate patient ventilation after supraglottic airway device placement and was assessed considering the presence of regular and repeated end-tidal carbon dioxide waveforms and chest movement without audible leaks after gently squeezing the reservoir bag. In the event of supraglottic airway device placement failure, two more attempts at insertion of the device were allowed, then the supraglottic airway device placement was considered to have failed and the patient's trachea was intubated. A bubble-test was performed and a gastric tube was placed through the gastric port of the LMA-S, as correct position confirmatory tests (drain tube leak test and gastric tube placement).4 Mechanical ventilation was in volume control mode with a fraction of inspired oxygen = 0.35, an inspiratory–expiratory ratio of 1 : 2, a targeted tidal volume of 6 to 8 ml kg−1, a positive end-expiratory pressure of 4 to 8 cmH2O, and a frequency set to keep the end-tidal carbon dioxide tension between 4.0 and 4.7 kPa (30 and 35 mmHg). The presence or absence of gastric insufflation was then detected by auscultation over the epigastrium, and through air leak evaluation on a ventilator spirometer (FLOW-i; Maquet, Solna, Sweden), and determined by the difference between the inspired and expired tidal volumes on an average of three mandatory breaths (the presence of air leak was considered if there were differences >20% of the preset tidal volume).8 Expiratory tidal volume, and peak and plateau inspiratory pressures, were also collected at baseline (skin incision), 15, 30, 45 and 60 min directly from data displayed on the ventilator screen. The anaesthetic procedure was then completed with the LMA-S or Spritztube.
The sample size was calculated considering the reported incidence of successful insertion of the LMA-S (92%) and the expected rate of successful insertion of the Spritztube (99%). Starting from these data and considering an A/Z test (or χ2 test) for comparison of proportions from independent samples with a ratio M/N = 1/1, the sample size resulted in at least 137 patients in each group for two-sided tests with type I error of 5% and power of 80%.
The primary outcome was the successful placement rate of the airway device. Secondary outcomes were insertion time, number of attempts, subjective assessment of ease of insertion, the number of complications at insertion (air leak, laryngospasm, obstruction after induction, blood-staining, gastric insufflation device failure) and symptoms after removal (dysphagia, hoarseness and sore throat). We also investigated the presence of a relationship between predefined variables [age; BMI; BSA; thyromental distance (TMD); inter-incisor distance (IID); Mallampati score; El-Ganzouri risk index; neck mobility; ASA physical status; presence of prognathism; any previously reported difficult intubation] and two separate dependent variables (the presence of at least one complication and the time needed to perform the device placement). Respiratory parameters (expiratory tidal volume, peak inspiratory pressure and plateau inspiratory pressure) were also collected at predefined time-points during anaesthesia.
Data distribution was evaluated by means of the one-sample Kolmogorov–Smirnov test. Continuous variables are presented as mean ± SD or median [IQR] as appropriate. The primary outcome was ascertained by means of the comparison between the percentage of successful placements of the LMA-S vs. the Spritztube using the χ2 test. Secondary outcomes were evaluated according to variable type as following: differences between the LMA-S and Spritztube groups for continuous variables were assessed using Student's t test or Mann–Whitney U test according to normal or nonnormal distribution, respectively; for dichotomous or categorical variables, the χ2 test for comparison of proportions was applied. Four different stepwise logistic regression analyses (backward stepwise method based on likelihood) were also calculated to investigate a potential relationship between the presence of at least one complication (dependent variable 1) or time for device placement (dependent variable 2) separately both for LMA-S and Spritztube. The predefined variables included in the model as independent variables for both devices and both dependent variables were: age, BMI, BSA, TMD, IID, Mallampati score, El-Ganzouri risk index, neck mobility, ASA physical status, presence of prognathism and any previously reported difficult intubation. All the nondichotomous variables were computed as dichotomous according to the following cut-off points: for categorical variables based on clinical indication (BMI > 25 kg m−2, Mallampati score > 2, El Ganzouri risk index ≥ 4, neck mobility > 1, ASA physical status > 2); for continuous variables (time for device placement, age, BSA, TMD, IID) based on the median value of the study population. The results were reported as the odds ratio (OR) and 95% confidence intervals. For all tests, the null hypothesis was rejected for P values less than 0.05. Data were analysed using MedCalc Statistical Software version 13.0 (MedCalc Software bvba, Ostend, Belgium).
Of the 355 enrolled patients, 334 were randomised to either the LMA-S or Spritztube group (Fig. 3). Demographic, anaesthesiological and surgical characteristics are shown in Table 1.
The Spritztube was placed correctly in all the patients enrolled (100%), while the LMA-S was correctly placed in 94.6% of patients (P = 0.006).
Insertion time was not significantly different between LMA-S and Spritztube groups (10 [10 to 20] vs. 10 [10 to 15] s, respectively; P = 0.06). Subgroup and single complication data are shown in Table 2. Overall, the rate of complications was higher in the LMA-S group compared with the Spritztube (19.1 vs. 6.0%; P < 0.001). In the subgroup analyses, the LMA-S was associated with a higher rate of complications at anaesthesia induction (18.0 vs. 5.3%, P < 0.001), but not at removal (1.2 vs. 0.6%, P = 0.99). Device failure and blood-staining were observed more often in the LMA-S group than the Spritztube group (5.4 vs. 0%, P = 0.006 and 3.6 vs. 0%, P = 0.04). No differences were found in volume or pressure variables during anaesthesia between the LMA-S and Spritztube groups.
In both LMA-S and Spritztube groups, none of the variables included in the logistic regression model was associated with complications. In the LMA-S group, age (directly) and prognathism (inversely) were associated with longer time of insertion [OR 1.04 (1.01 to 1.06), P = 0.003, and 0.42 (0.18 to 0.98), P = 0.04, respectively]. Conversely, in the Spritztube group, the TMD was related inversely to longer time of insertion [OR 0.30 (0.11 to 0.82) P = 0.02].
This is the first randomised prospective study comparing the Spritztube and LMA-S in anaesthetised adult patients. Our study showed that the Spritztube was as effective as the LMA-S in maintaining the airway with all patients’ lungs being ventilated safely and successfully. The success rate of achieving a patent airway was comparable between the groups (LMA-S 94.6% vs. Spritztube 100%), with less complications in the Spritztube group (10.6 vs. 19.1%; P < 0.001). The success rate of the LMA-S was in line with data from the literature9,10 and the two groups enrolled were basically comparable because difficult airway management was excluded by screening according to SIAARTI (Italian Society of Anaesthesiology, Analgesia Reanimation and Intensive Care) 2005 guidelines.6
Overall, there were no significant differences between the groups at baseline. Although TMD, uncorrectable maxillary prognathism and duration of anaesthesia were different in the two groups, these differences appear to have low clinical relevance in consideration of the study's objective. The same consideration applies to differences in the type of surgery. In our study, the time necessary for Spritztube insertion was not significantly shorter when compared with the LMA-S. Nevertheless, both insertion times were shorter and faster than reported in other studies,9,11 probably because all physicians involved in the study had considerable experience of supraglottic airway device placement. In addition, the first attempt and overall insertion success rates for the Spritztube were significantly higher than for the LMA-S (P = 0.0007). We do not believe that our results indicate a significant clinical difference in terms of time of positioning between the Spritztube and the LMA-S, whereas our data might suggest that the Spritztube might be useful as a rescue device in emergency conditions.
The LMA-S and Spritztube reflect two different approaches to supraglottic airway device placement. As for the original LMA Classic and LMA-like devices,3 LMA-S insertion requires sliding of the supraglottic airway device along the anatomical curve of the oropharynx and hypopharynx. The ease of insertion and insertion time may be influenced, given the same experience of the operators, by lubrication, tongue/oropharynx ratio and correct size choice. There is still debate as to whether the weight-based sizing policy is suitable or correct,2 and any data on insertion time and perceived ease should be interpreted cautiously. Insertion of the Spritztube is similar to that of the ‘Combi’-like devices,3 with a (generally) stiffer and smaller diameter device pushed blindly towards the oesophagus with minor need to adapt to physiological upper airway curves, compared with LMA-like devices. This concept should make the Spritztube and ‘Combi’-like device insertion faster, whereas data from the literature express contradictory results.12–14 However, subjective perception of ease of insertion seems to be generally higher for ‘Combi’-like devices.
In our study, participating physicians were advanced Spritztube users, obtaining fast insertion times also in patients in whom logistic regression showed a higher incidence of anatomical factors potentially making the Spritztube group airways more difficult than in the LMA-S group.
There was a significant difference between the two groups in respect of the patients’ characteristics (Table 1) concerning the Mallampati class, TMD, uncorrectable maxillary prognathism and El-Ganzouri index, which were significantly higher in the Spritztube group. The logistic regression analysis showed that increased time of insertion of the LMA-S was directly related to the age of the patient and the presence of prognathism. A recently published retrospective study on almost 20 000 cases of supraglottic airway device placement found a global supraglottic airway device failure rate of 1.9%15 and identified different factors associated with supraglottic airway device failure. Our study showed a higher failure rate for the LMA-S, even though none of the factors indicated by Vannucci et al.15 was observed in our patient sample. Conversely, in the Spritztube group, increased time for insertion was directly related only to a large TMD. A possible explanation for this finding is that a longer time is necessary to reach the final oesophageal position of the Spritztube tip in a longer neck, considering that the LMA-S has been demonstrated to penetrate deeper than other supraglottic airway devices in the upper oesophageal sphincter.16
In our study, we assessed intra-operative and postoperative complications. Concerning complications at insertion, the occurrences of blood-staining and device failure were significantly higher in the LMA-S group. The incidence of these two complications is quite common after LMA-S insertion, as shown in other studies.17,18 Compared with the Spritztube, the LMA-S is somewhat bulkier, has a different insertion technique and a certain tendency for the tip to flip,9 all factors which might increase the risk of insertion-related minor trauma to the upper airway. In the Spritztube group, the lower occurrence of blood-staining could be attributed to different elasticity of the constructive material (silicone) of the Spritztube compared with the stiffer PVC of the LMA-S; the silicone elastomer cuff probably allows better oropharyngeal adaptability, thus minimising tissue trauma. Finally, there might be a different pattern of eventual bleeding deposition, as the larger cuff of the LMA-S positioned in the hypopharynx, could collect more blood than the rounded (and deflated) cuff of the Spritztube (which remains located more cranially) at the time of removal.
The incidences of dysphagia, hoarseness and sore throat at removal were comparable in the two groups. The LMA-S and the Spritztube cuffs lie in different positions in the upper airway, and despite a longer mean duration of anaesthesia in the LMA-S group, no oropharyngeal symptoms were observed. This might also be due to the cuff pressure monitoring policy which was adopted in the study, and to the experience of the investigators, as these have been shown to be factors involved in the genesis of oropharyngeal symptoms.19
There are a number of limitations of our study. First, our patients were anaesthetised, and volume control ventilation was used without paralysis. Although we monitored the depth of anaesthesia with a BIS monitor, the absence of neuromuscular blocking agents might also affect the ease of insertion and eventual oropharyngeal symptoms because of cricopharyngeal muscle and upper oesophageal sphincter activity.19 Second, the oropharyngeal leak pressure was not measured at the start of the procedure and over time, meaning that we might have a snapshot of the devices’ performance but not an overall evaluation. Third, we did not perform fibreoptic inspection through the airway device to visualise the laryngeal inlet and the device positioning, as other studies have done.14 In addition, we included patients undergoing many different surgical procedures, but we considered that because the study's endpoints were successful insertion, safety and complication rates, this was only a potential bias while it allowed faster and wider sample population enrolment. A further bias in our study could be the extensive of the Spritztube at our centre, and our results might not be reproduced elsewhere until after an adequate learning curve with the device.
In this clinical randomised trial comparing the LMA-S and Spritztube tracheal cannula, the new device seems to be a safe, effective and easy-to-use disposable supraglottic airway device, showing performance and reliability not less than the LMA-S. Further studies, to be conducted on larger numbers of patients and comparing with different supraglottic airway devices, are necessary to assess efficacy and performance of the Spritztube and to define an adequate learning curve.
Acknowledgements relating to this article
Assistance with the study: The authors wish to thank Fiorenza Ferrari for statistical assistance and sample size calculation at the beginning of study protocol. In addition, the authors thank Saher Abd Elghani, Desiderio Bonaventura, Elisa Boni, Vito Cirillo, Fiorenza Ferrari, Cecilia Maietti, Pierluigi Marranconi, William Miglioranza and Mirco Primadei, Maurizio Scollo from the Department of Anaesthesiology and Intensive Care, San Bortolo Hospital, Vicenza, Italy for valuable support, participation, advice and help.
Financial support and sponsorship: none.
Conflicts of interest: SCC is the inventor of the Spritztube that is marked CE. There is no financial or personal relationship with people or organisations that could inappropriately influence the work. MS participated at research, development and preclinical testing of the LMAProtector, and has paid consultancies with Teleflex Medical, Dublin, Ireland and DEAS, Castelbolognese, Italy.
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