Cobra-PLA provides higher oropharyngeal leak pressure than LMA-Classic and LMA-Unique: A meta-analysis with 22 studies.

Cobra Perilaryngeal Airway (Cobra-PLA) is a relatively new single-use supraglottic device employed during general anesthesia. This meta-analysis includes randomized controlled trials (RCTs) yielding extensive comparison results among Cobra-PLA, Laryngeal Mask Airway (LMA)-Classic, and LMA-Unique.Two authors performed searches in EMBASE, CENTRAL, PubMed, and ScienceDirect to identify RCTs that compared Cobra-PLA with LMA-Classic and with LMA-Unique in patients undergoing general anesthesia. Both random- and fixed-effects models were used. Begg's funnel plot was used to evaluate publication bias.Twenty-two RCTs with a total of 1845 patients were included. Cobra-PLA offered significantly higher oropharyngeal leak pressure than LMA-Classic [mean difference (MD) = 3.56 (1.56, 5.55), P = .0005] and LMA-Unique [MD = 4.44 (2.12, 6.76), P = .0002]. First-insertion success rate, ease of insertion, insertion time, and reported complications among Cobra-PLA, LMA-Classic, and LMA-Unique were similar.Compared with the commonly used LMA-Classic and LMA-Unique, Cobra-PLA provides superior airway sealing.

Introduction

Since its inception by Archie Brain in 1981, the Classic Laryngeal Mask Airway (LMA) have shown unexpectedly high popularity among anesthetists.[ In the past decades, new airway devices, such as Cobra Perilaryngeal Airway (PLA) and LMA-Unique, have been fabricated by modifying the LMA-Classic.

Cobra-PLA contains a polycarbonate transparent breathing tube, a high volume low-pressure cuff, and a far end cobra-shaped head. The soft pointed end of the cobra head is devised to provide passage of the device into the hypopharynx via crooking in the direction of the glottis. At the time of insertion, the distal head keeps the throat soft tissue and the epiglottis in place and connects to the throat inlet, allowing spontaneous or controlled breathing through the slotted opening.[

Oropharyngeal leak pressure (OLP) is used to quantify the efficacy of airway sealing in devices and indicates airway protection, successful placement, and positive pressure ventilation.[ Several randomized controlled trials (RCTs) compared Cobra-PLA with LMA-Classic and LMA-Unique. Four RCTs[ found higher OLP values in Cobra-PLA compared with LMA-Classic, whereas 3 other studies[ found no difference. Comparison with LMA-Unique also provides contested results across studies. Therefore, RCTs alone cannot sufficiently provide a clear evaluation of the Cobra-PLA.

To solve this problem, we conducted a meta-analysis including 22 RCTs that compared the supraglottic devices during general anesthesia. OLP was the primary outcome, and rate of first-insertion success, ease of airway insertion, insertion time, and reported complications associated with the device were the secondary outcomes. And furthermore, subgroups analysis were performed considering confounding factors, such as age, surgery type, neuromuscular blocker (NMB) use, and the possible effect of the measurement method on the OLP.

Materials and methods

This meta-analysis was performed based upon the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statements.[

Literrature search

Electronic databases EMBASE, CENTRAL, and PubMed, as well the ScienceDirect, were searched for eligible studies. All researches were conducted in May 2018. The search items were as follows:

Cobra Perilaryngeal Airway, CPLA, or Cobra-PLA;

Laryngeal Mask Airway Classic (CLMA), LMA-Classic, Laryngeal Mask Airway-Unique (LMAU), or LMA-Unique; and

randomized controlled trial, randomly, or randomized. The key words were linked using “AND” (for “Cobra-PLA,” “LMA Classic,” and “randomized”) and “OR” (for “Cobra Perilaryngeal Airway,” “Cobra-PLA,” and “CPLA”).

The search was performed across English language content.

Study selection

We included only published prospective RCTs comparing Cobra-PLA with other 2 LMAs during general anesthesia. The exclusion criteria included correspondence, case reports, reviews, animal studies, and non-English papers.

Data collection

The following data were collected: name of the first author, publication year, age, patients’ number, surgical type, premedication, neuromuscular blocker use, type of ventilation, OLP and its measurement method, the rate of first-insertion success, insertion ease, insertion time, and complications associated with the devices (sore throat, laryngospasm, dysphagia, blood-soiled device, or other rare complications). Two independent authors gathered the data. Disagreements were resolved by discussion.

Risk of bias assessment

Cochrane Collaboration standards were used to evaluate the risk of bias in RCTs. The standards were as follows: randomization, allocation concealment, blinding, incomplete outcome data, selective reporting, and other bias. A judgment of high, unclear, or low risk of material bias was assigned for each item.

Statistical analysis

Review Manger 5.3 software was used to count data. Weighted mean differences (MD), relative ratio (RR), and associated 95% confidence intervals were applied to pool data. An I2 >50% denotes heterogeneity, and the random-effects model was used. Sensitivity analysis was used to search for possible explanations for significant heterogeneity. Subgroups were analyzed considering confounding factors, such as age, surgery type, NMB use, and the possible effect of the measurement method on the OLP.

If 1 trial contained more than 1 intervention group, each group was regarded as a study. Publication bias of eligible studies was tested by visual inspection of funnel plots (if the number exceeded 10).

Results

Figure 1 described detailed steps and study selection. Electronic database search revealed that 15 trials where Cobra-PLA was compared with LMA-Classic[ and 8 trials containing a comparison between Cobra-PLA and LMA-Unique.[ The characteristics and methodological quality of RCTs are shown in Tables 1 and 2, respectively.

Figure 1

Flow chart of meta-analysis.

Table 1

Characterristics of included trials.

Table 2

Risk of bias assessment for evaluation the quality of each included trials.

Cobra-PLA versus LMA-Classic

OLP

A pooled analysis of data from 8 trials[ revealed that Cobra-PLA provided significantly higher OLP than LMA-Classic [MD = 3.56 (1.56, 5.55), I2 = 88%, P = .0005] (Fig. 2). Sensitivity analysis certified that the pooled outcome was not changed by a single study. Given substantial heterogeneity, we used subgroup analysis to determine the impact of confounding factors (Table 3). On the basis of age subgroup analysis, the pooled results showed that Cobra-PLA provided slightly higher OLP in the child subgroup despite the lack of significant difference [MD = 2.36 (−0.02, 4.74), I2 = 0%, P = .05] and higher OLP in the adult subgroup [MD = 3.90 (1.56, 6.23), I2 = 91%, P = .001] compared with LMA-Classic. Five trials[ that did not use NMB were included, and the combinative result was higher for Cobra-PLA than for LMA-Classic [MD = 3.92 (2.77, 5.07), I2 = 0%, P <.0001]. With NMB, the combinative result was not significantly different between the 2 groups [MD = 2.95 (−2.74, 8.63), I2 = 98%, P = .31]. When the pooled analysis was restricted to the subgroup analysis of surgery type, Cobra-PLA also provided higher OLP than LMA-Classic in non-laparoscopic surgery [MD = 3.41 (1.25, 5.57), I2 = 90%, P = .002]. Data on laparoscopic surgery in only 1 trial[ were not counted. Studies[ using the measurement of audible noise found that Cobra-PLA exhibited comparatively high OLP [MD = 2.70 (0.86, 4.54), I2 = 65%, P = .004].

Figure 2

Forest plot for comparison of Cobra-PLA and LMA-Classic for OLP (cmH2O); insertion success rate at the first attempt; ease of insertion; and insertion time (s). CI = confidence interval, Cobra-PLA = Perilaryngeal Airway, I2 = I-square heterogeneity statistic, IV = inverse variance, LMA = Laryngeal Mask Airway, OLP = Oropharyngeal leak pressure.

Table 3

Subgroup meta-analysis for OLP with Cobra-PLA and LMA-Classic.

Rate of first-insertion success, insertion ease, and insertion time

Thirteen trials[ examined the rate of insertion success at the first attempt and found no significant difference between the 2 devices [RR = 1.03 (0.95, 1.12), I2 = 62%, P = .45]. Heterogeneity was significantly decreased (I2 = 0%, P = .10) upon the removal of 5 studies[ that used NMB. The funnel plot of first-insertion success rate did not indicate evident substantial asymmetry (Fig. 3). Insertion ease and insertion time were similar between the 2 devices [RR = 1.10 (0.95, 1.27), I2 = 30%, P = .22; MD = 2.80 (−0.68, 6.28), I2 = 71%, P = .11, respectively]. When we removed individual studies, the heterogeneity of insertion ease and insertion time was not markedly decreased. Figure 2 lists the forest plot of this analysis.

Figure 3

Funnel plots for comparison of Cobra-PLA and LMA-Classic for insertion success rate at the first attempt and blood staining. Cobra-PLA = Perilaryngeal Airway, LMA = Laryngeal Mask Airway.

Complications

The incidence of reported complications was assessed: blood staining on the device was reported in 10 studies,[ sore throat was found in 7 studies,[ and laryngospasm was observed in 5 studies.[ The 2 groups exhibited a similar incidence of blood staining, sore throat, and laryngospasm [RR = 1.45 (0.75, 2.80), I2 = 78%, P = .27; RR = 0.90 (0.65, 1.26), I2 = 56%, P = .54; RR = 1.01 (0.24, 4.22), I2 = 0%, P = .99, respectively] (Fig. 4). The funnel plot of blood staining indicated possible asymmetry (Fig. 3). None of the serious complications were reported in any included studies.

Figure 4

Forest plot for comparison of Cobra-PLA and LMA-Classic for blood staining; sore throat; and dysphagia. CI = confidence interval, Cobra-PLA = Perilaryngeal Airway, I2 = I-square heterogeneity statistic, IV = inverse variance, LMA = Laryngeal Mask Airway.

Cobra-PLA versus LMA-Unique

A combined result from 6 trials[ demonstrated that Cobra-PLA offered significantly higher OLP than LMA-Unique [MD = 4.44 (2.12, 6.76), I2 = 91%, P = .0002] (Fig. 4). Based on age subgroup analysis, the pooled results showed that Cobra-PLA provided higher OLP in child and adult subgroups than LMA-Unique [MD = 2.79 (0.25, 5.34), I2 = 89%, P = .03; MD = 7.85 (3.44, 12.26), I2 = 90%, P = .0005, respectively]. Regardless of the presence or absence of NMB during anesthesia induction, pooled data showed that Cobra-PLA presented higher OLP compared with LMA-Unique [MD = 9.45 (2.76, 16.14), I2 = 93%, P = .006; MD = 3.05 (0.95, 5.16), I2 = 85%, P = .004, respectively]. All trials involved non-laparoscopic surgery. Four trials[ measured manometric stability, and Cobra-PLA yielded higher combined result in comparison with LMA-Unique [MD = 4.73 (1.90, 7.56), I2 = 92%, P = .001]. However, the result was not significantly different between the 2 groups [MD = 3.42 (−2.32, 9.16), I2 = 90%, P = .24] (Table 4) when audible noise measurement was used.

Table 4

Subgroup meta-analysis for OLP with Cobra-PLA and LMA-Unique.

First-insertion success rate, insertion ease, and insertion time

Six studies[ investigated the insertion success rate at the first attempt, and no significant difference was observed between the 2 devices [RR = 0.98 (0.94, 1.02), I2 = 0%, P = .31]. Ease of insertion is similar between 2 devices [RR = 0.94 (0.73, 1.22), I2 = 87%, P = .67]. Insertion time is also similar [MD = 0.37 (−1.35, 2.08), I2 = 67%, P = .68]. Figure 5 lists the forest plot of these analyses.

Figure 5

Forest plot for comparison of Cobra-PLA and LMA-Unique for OLP (cmH2O); insertion success rate at the first attempt; ease of insertion; and insertion time (s).CI = confidence interval, Cobra-PLA = Perilaryngeal Airway, I2 = I-square heterogeneity statistic, IV = inverse variance, LMA = Laryngeal Mask Airway.

The incidence of reported complications was assessed: blood staining on the device, sore throat, and laryngospasm were reported in 4,[ 4,[ and 3 studies,[ respectively. The 2 groups showed similar incidence of blood staining, sore throat, and laryngospasm [RR = 0.71 (0.42, 1.20), I2 = 26%, P = .20; RR = 1.10 (0.76, 1.60), I2 = 0%, P = .60; RR = 0.49 (0.12, 1.95), I2 = 0%, P = .31, respectively] (Fig. 6). None of the serious complications were reported in any of the included studies.

Figure 6

Forest plot for comparison of Cobra-PLA and LMA-Unique for blood staining; laryngospasm; and sore throat. CI = confidence interval, Cobra-PLA = Perilaryngeal Airway, I2 = I-square heterogeneity statistic, IV = inverse variance, LMA = Laryngeal Mask Airway.

Discussion

The main finding of the present meta-analysis is that Cobra-PLA offers significantly higher OLP than LMA-Classic and LMA-Unique undergoing general anesthesia. First-insertion success rate, ease of insertion, insertion time, and reported complications were similar among 3 devices.

Airway sealing pressure or airway leak pressure is also referred to OLP, which is the most important indicator for assessing the safety and efficacy of airway devices.[ OLP decides the practicability of degree of airway protection and safe positive pressure ventilation and is determined by the strength of the seal between the cuff of the mask and the surrounding soft tissue of the neck.[

Several studies showed that LMA-Classic can provide safe and effective airway management.[ However, certain limitations were found in this reusable device, especially its low-pressure seal, which may be insufficient for positive pressure ventilation.[ Gastric distention with a risk of regurgitation may be caused by leaks in certain cases.[ In the present meta-analysis, we found significantly higher OLP with Cobra-PLA than LMA-Classic. The higher OLP in the Cobra-PLA group compared with those of other groups may be due to the larger cuff structure compared with those of the other devices. Increased OLP offers particular advantage in obese patients, lithotomy position, restrictive lung diseases, and pneumo-peritoneum patients.[ Thus, Cobra-PLA may be considered as an alternative to LMA-Classic during general anesthesia.

Other factors that may affect OLP include age, the use of NBM, intra-abdominal pressure during surgery, measurement method, and LMA size selection criteria.[ In our meta-analysis, substantial overall heterogeneity (I2 = 88%) was reduced by subgroup analysis based on pediatric patients (I2 = 0%) and non-use of NMB (I2 = 0%). A polled data of 8 trials, which did not use NMB, showed similar device insertion time between Cobra-PLA and LMA-Classic. Furthermore, the high heterogeneity (I2 = 61%) of insertion time was possibly relative to the measurement standards among the studies included in our analysis.

LMA-Unique is the 1-off version of the LMA-Classic and is currently used for both adult and pediatric patients.[ We also found a significantly higher OLP with Cobra-PLA compared with LMA-Unique. The difference in OLP between the 2 groups may be due to the different structure designs.[ A bowl-shaped cuff of LMA-Unique surrounding the larynx decides the sealing mechanism. The device may tilt to 1 side or the other owing to the posterior placement of the exiting breathing tube from the center of the posterior wall. However, Cobra-PLA can provide evident stability with its wide and flat distal head, which is sufficiently rigid to prevent movement of the device.[

Evident data heterogeneity in the combined OLP result is one limitation in our finding. High heterogeneity (I2 = 91%) cannot be decreased despite the use of various subgroup analyses. This finding is probably due to the use of different size of devices in the trials. In 1 trial,[ sizes 1.5, 2, and 3 of Cobra-PLA and sizes 1.5, 2, and 2.5 of LMA-Unique were compared; 1 trial[ compared sizes 0.5, 1, 1.5, 2, and 3 of Cobra-PLA and size 1.5, 2, 2.5, 3, 4, and 5 of LMA-Unique; and another study[ compared sizes 0.5, 1, 1.5, and 2 of Cobra-PLA and sizes 1, 1.5, 2, and 2.5 of LMA-Unique. Notably, larger-sized (1.5, 2) Cobra-PLA possesses the dorsal cuff, which may provide higher OLP than the smaller variants (0.5, 1). In addition, a study comparing Cobra-PLA and LMA-Unique in adult patients found that the former presented higher OLP.[ The ease of insertion was the same for 2 devices with high heterogeneity (I2 = 87%). Considering that only 2 trials were included in the analysis, further studies are required to validate the conclusion.

Compared with the Xu’ meta-analysis,[ our study presented different findings. First, 5 eligible RCTs[ were not included in the Xu’ study, and we included these RCTs in our study. Second, this work was the first study to show that Cobra-PLA can provide higher OLP than LMA-Classic regardless of age group (children or adults), surgical type (laparoscopic or non-laparoscopic), use of 3 OLP measurement methods, and lack of NMB. Third, Cobra-PLA also offers higher OLP than LMA-Unique regardless of age group (children or adults), with or without NMB, and use of manometric stability of measurement method, Fourth, we also first find that Cobra-PLA did not exhibit higher OLP in comparison with LMA-Classic and LMA-Unique under conditions of NMB and audible noise measurement method. Lastly, significant heterogeneity (I2 = 91%) was found when the studies were pooled to evaluate the OLP between Cobra-PLA and LMA-Classic in the Xu’ meta-analysis, but the study didn’t explore the possible causes of such heterogeneity. On the contrary, the heterogeneity seen in our study can be explained by the difference in age and the use of NMB between studies.

Several limitations were found in present work. First, in addition to high heterogeneity discussed above, differences in induction, maintenance, depth of anesthesia, and patient population studied may contribute to the evident data heterogeneity. Although we conducted subgroup and sensitivity analyses in an attempt to control several factors, we cannot account for all possible confounding factors. Second, we comprehensively searched the published studies, but potential publication bias may still exist due to failure to include ongoing or unpublished trials. Finally, several included studies were of poor quality. Two studies[ did not blind the participants, and some included studies did not describe the details of binding the outcome assessment. Therefore, additional high-quality studies are required to certify our results.

In conclusion, our findings show that Cobra-PLA provides significantly higher OLP than both LMA-Classic and LMA-Unique and a similar clinical performance to both devices during general anesthesia.

Author contributions

Study design: Yuan T. Data collection and Wring the draft: Yuan T, Qin C, Feng C. Data interpretation, discussion and preparation of the final manuscript: Yuan T, Guangyou D, Hong L. All authors have read and approved the final manuscript.