Abstract

Objective

Supraglottic airways (SGA) through which blind endotracheal intubation is made possible is an area of considerable interest. Our study aimed at comparing the Cobra Perilaryngeal Airway (CPLA) with the Intubating Laryngeal Mask Airway (ILMA) with regard to the performance of the former as a conduit for facilitating blind endotracheal intubation.

Methods

American Society of Anesthesiologists (ASA) I–II patients consenting to the study, with no predictors of difficult airway, scheduled for elective surgery were randomized into two groups of 30 each. Anesthesia was induced with fentanyl, propofol and vecuronium. CPLA was inserted in Group I and ILMA in Group II. Fibreoptic scoring of the laryngeal view was done through the SGA. Blind intubation through either CPLA or ILMA was then carried out with cuffed polyvinyl chloride (PVC) tube in Group I and ILMA-tracheal tube in Group II.

Results

Demographic and surgical data were comparable between the two groups. The success rate of intubation (87% through CPLA and 90% through ILMA) (p value 1), number of attempts made and the fibreoptic scores (p value 0.12) were comparable between the two groups. Insertion time was significantly longer in Group I as compared with Group II (9 s vs. 4 s; p value 0.004). Trauma and sore throat were more common in Group I (p value −0.1, 0.19 respectively). Hemodynamic monitoring showed more tachycardia during CPLA insertion as compared with ILMA (p value 0.006).

Conclusion

We conclude that CPLA can be used as an effective conduit for blind endotracheal intubation with cuffed PVC tube and has comparable efficacy in tracheal intubation as that with ILMA.

Keywords

laryngeal masks; supraglottic airway devices: Cobra perilaryngeal airways; intubation, intratracheal;

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1. Introduction

The use of supraglottic airway (SGA) devices as a guide to endotracheal intubation has been the subject of considerable interest and the theme of research in the last two decades. These devices offer the advantage of ventilating the lungs in case intubation fails in difficult airway situations. The Intubating Laryngeal Mask Airway (ILMA) has stood the trial of time to be the gold standard for SGA guided endotracheal intubation and has been recognized in the American Society of Anesthesiologists (ASA) difficult airway algorithm as a rescue device in the emergency limb.1, 2

The Cobra Perilaryngeal Airway (CPLA) is one of such SGA devices introduced in 2003, which came with a promise of easy insertion, good airway seal and wide bore breathing tube. The ventilatory performance of CPLA and LMA have been mentioned in a report to be comparable, whose authors also mentioned that intubation through a CPLA should be at least as easy as through a LMA.³ This suggestion was made after reviewing the fiberoptic scoring of the laryngeal view in their study. They did not however evaluate the ease of intubation through either device. Similar comments regarding the possible ease of intubation through CPLA were made in another study.⁴ These observations prompted us to evaluate the role of CPLA as a conduit to facilitate blind endotracheal intubation and compare it with tracheal intubation by means of ILMA.

2. Methods

After obtainment of formal approval from institutional ethics committee, a prospective randomized study was planned in 60 ASA grade I–II patients, scheduled for elective surgery under general anesthesia. Written informed consents for the participation in the study were obtained from the patients. The criteria of inclusion for study were patients more than 15 years of age, 3 kg in weight and having modified mallampati (MMP) of grade I or II. Patients with predictors of difficult airway, gastroesophageal reflux disorder, diaphragmatic hernia, having inadequate fasting time or undergoing upper airway surgery were excluded from the study.

Patients were randomly divided into two groups according to a computer generated random number table. In Group I endotracheal intubation was attempted blindly through CPLA and in Group II, trachea was intubated through ILMA.

After submitting written informed consents the patients were premedicated with oral diazepam (0.1–0.2 mg/kg) and ranitidine (150 mg) the night before and on the morning of surgery. General anesthesia was induced with intravenous fentanyl (2 μg/kg), propofol (2 mg/kg) and neuromuscular blockade was achieved with vecuronium (0.1 mg/kg), to facilitate tracheal intubation.

In Group I, CPLA of appropriate size (Cobra PLA^®, Palmodyne, Indianapolis IN 46241, USA) was selected and the gap between the two medial most bars of the epiglottic grill was dilated by passing a lubricated appropriately sized polyvinyl chloride (PVC) cuffed endotracheal tube (ETT) (Portex^® Tracheal tube, Smiths Medical International Ltd, Keene, NH 03431, USA) which was kept in situ for 5–7 minutes (Fig. 1). The CPLA cuff and dorsal surface of the hood was adequately smeared with lubricating jelly, after which it was inserted with the patient’s head in the neutral position. When the tip reached the back of the mouth, it was advanced into the hypopharynx until moderate resistance was felt. The cuff was inflated with air to ensure sealing of airway. Proper placement of the airway was confirmed by auscultation, end-tidal carbondioxide (EtCO₂) tracing and visible chest rise. Another experienced anesthesiologist, not involved in the study, was asked to do a fibreoptic scoring of the laryngeal view through the CPLA and grade the view (Table 1). The score was not disclosed to the investigators before intubation. After proper lubrication, size 6.5 cuffed PVC ETT (for size 3 CPLA) or size 7 cuffed PVC ETT (for size 4 CPLA) was selected and blind tracheal intubation was attempted through the CPLA after removal of the 15 mm male connector of the CPLA. The proper placement of the ETT in the trachea was checked by ventilation (visible chest expansion) and confirmed by adequate EtCO₂ tracing. The CPLA was deflated, fixed to the ETT with tape and left in situ. Both the CPLA and the ETT were removed during extubation at the end of surgery.

In Group II, an ILMA of appropriate size (LMA Fastrach, LMA™, The Laryngeal Mask Company Limited, LMA North America Inc, San Diego CA 921222, USA) was inserted with the patient’s head placed in the neutral position and its cuff was inflated. Proper placement of the airway was confirmed as in Group I. The ILMA was stabilized by holding the steel handle and fiberscope guided scoring of the laryngeal view was done as in Group I. A silicon wire reinforced ETT (Intubating Laryngeal Mask Airway Tracheal tube, ILMA-TT) of size 7 was passed through the ILMA of size 3 or 4. The proper placement of the ETT was checked as in Group I. The ILMA was removed and the ETT was left in place.

The hemodynamic variables (heart rate and blood pressures) were monitored at 1 minutes interval in both the groups. All patients were followed for any airway morbidity as evidenced by sore throat, dysphonia or dysphagia 6 hours and 24 hours after surgery.

We compared Group I and Group II for immediate assessment with regard to the following points:

 

 Success rate of tracheal intubation by means of CPLA and ILMA.

 

 Fibreoptic score (FOB) by means of the CPLA or ILMA.

 

 Insertion time (s) (defined as the time taken from the moment the ETT was inserted into the SGA device till an adequate EtCO₂ trace was obtained).

 

 Number of attempts for tracheal intubation by means of CPLA or ILMA.

 

 Complications – air leak during ventilation by means of CPLA or ILMA, laryngospasm, trauma (blood staining of the CPLA/ILMA cuff or hood).

In case of failure to intubate the trachea even after 3 attempts through ILMA or CPLA, laryngoscope guided intubation was done and the case was considered as failure.

2.1. Statistical analysis

The SPSS 15 software for Windows was used for the statistical analysis. Chi-square test/Fisher’s exact test was used to compare the categorical data (sex, MMP score, fibreoptic score, success of intubation, correlation between fibreoptic score and success of intubation, number of attempts required, trauma, and sore throat at 6 hours). We used two-sided independent Student t-test to compare the parametric data (age, weight, baseline and subsequent changes in heart rate and blood pressure at various time points during the procedure). Mann–Whitney U-test was used to compare the duration of surgery and the insertion time between the two groups as some values were “off the scale” and hence the population was unfit for parametric tests. p value < 0.05 is taken as statistically significant.

3. Results

The demographical and surgical data including age, sex, weight, duration of surgery, MMP score, baseline heart rate and blood pressure were comparable between Groups I and II (Table 2).

Twenty six patients in Group I and 27 patients in Group II were intubated successfully (p value 1) (Table 3). Endotracheal intubation was possible in the first attempt in 19 patients in Group I and 21 patients in Group II (p value 0.779) (Table 3).

The fibreoptic scores were comparable in the two groups (p value 0.126) (Table 3). There was a high degree of correlation between the fibreoptic scores and successful intubation (p value 0.001) (Table 4).

The time to insertion of the ETT varied from a minimum of 3 s in both groups to a maximum of 106 s in Group I and 90 s in Group II. The median insertion time was significantly higher in Group 1 (9 s) as compared with Group 2 (4 s) (p value 0.004) (Table 3).

Trauma, as judged by the presence of blood stain on the SGA device, was more in Group 1 (n = 6) as compared with Group II (n = 1) (p value 0.103). Five patients in the Group I were found to develop sore throat and only one patient in Group II was so post-operative follow-up carried out some 6 hours after surgery (p value 0.19). No patient reported any dysphonia or dysphagia 6 hours and 24 hours postoperatively (Table 3).

There was no air leak during ventilation and no incidence of laryngospasm. There was no statistically significant difference in systolic or diastolic blood pressure at various time points during the procedure (Table 5). However, there was statistically significant increase in heart rate at the time of insertion of the SGA device (p value 0.006), during the second (p value 0.03) and the third attempts (p value 0.039) of endotracheal intubation in Group I as compared with Group II (Table 5). However, increase in heart rate was not clinically significant.

4. Discussion

In our study, we found that CPLA was comparable to ILMA for tracheal intubation. The fiberoptic scores through both the SGA devices were comparable. Though the time taken for tracheal intubation was statistically more in CPLA group as compared with ILMA group, yet it appeared to be clinically insignificant. The complication rates were comparable in both groups.

Because of the introduction of LMA, a number of modifications has been made to suit various purposes, one of which was the ILMA introduced in 1997 for endotracheal intubation. Since then the ILMA stood the trial of time as a SGA device to facilitate intubation. However, CPLA does have certain advantages over ILMA, if blind endotracheal intubation is possible and it is revealed that ILMA could achieve equal or even more success than ILMA as suggested by some earlier studies. The advantages of CPLA include easy of insertion with good airway seal, disposable single use device as compared with ILMA, no need for a delicate ILMA-ETT, small distal aperture and devoid of proneness to damage.² Furthermore, CPLA is primarily a ventilatory device which need not be removed after intubation like ILMA which is heavy and exerts high pressure in the hypopharynx even when the cuff is deflated.⁵

Our study revealed that CPLA can be used as a device for facilitating blind endotracheal intubation with standard PVC cuffed endotracheal tube. The high success rate of blind endotracheal intubation (87%) in contrast with low success rate (36%) as reported by J.J. Lee and colleagues⁶ may be because of various factors. First, in case the openings of the anterior grill of the CPLA were inadequate, excessive force applied to the ETT to overcome the resistance might deflect the ETT into the perilaryngeal space or esophagus. We realized this problem during a series of 10 pilot cases with CPLA. The technique was modified by dilating the space between the two medial most bars of the CPLA with lubricated PVC ETT before inserting the SGA so that the ETT takes the path of least resistance and remains in midline. Secondly, removal of the 15 mm male connector of the CPLA just before inserting the ETT through it gives us more room to maneuver the ETT and also makes the effective length of the breathing tube shorter (by around 2 cm).

The size of PVC ETT chosen for intubation by means of CPLA in our study was the same as proposed in earlier studies.3, 6 Although manufacturers claim that up to 8 mm ID ETT can pass through size 4 CPLA, we found that negotiating high volume cuff of the PVC ETT more than 6.5 mm ID or 7.0 mm ID through CPLA size 3 and 4 respectively becomes difficult. We found that CPLA is an equally effective device (success rate of 87%) to facilitate blind intubation as compared with ILMA (success rate of 90%). This success rate of blind intubation with ILMA corroborates well with previous trials which all showed an intubation success of around 95.7%.7, 8, 9, 10 The success rate at first attempt with these trials was 66% and 22% at second attempt, which is in agreement with our study (first attempt 70% and 16.67% at the second attempt). In comparison, the success rate through CPLA in our study at first attempt was 63.33% and 16.67% at the second attempt. The number of attempts taken to facilitate endotracheal intubation through ILMA or CPLA were comparable (p value 0.779).

It took longer time for insertion of the ETT through the Cobra PLA (9 s) in comparison with the ILMA (4 s) (p value 0.004). However, this time difference of 5 s may be clinically insignificant. The elongation of time may be because of the high-volume cuff of the PVC tube which takes more time to negotiate through the grilled epiglottic bars of the CPLA as compared with the low-volume cuff of the ILMA-TT. Secondly, while passing through the grills, the PVC tube may be deflected from the centre thus consuming more time. Lastly, maneuvering the ILMA is easier since it has a stainless steel handle to hold and stabilize the device, and this advantage is absent in CPLA. So the device should be fixed firmly in place with adhesive tape after inserting and checking adequacy of ventilation is mandatory.

There was no statistically significant difference in the fibreoptic scores obtained between the two groups, thus confirming the anatomic fitness of the two SGAs. This is in agreement with the previous study comparing CPLA and classic LMA.³ In our study the best view (score 4) was obtained in 14 patients with CPLA as compared with 20 in the ILMA group. The poorest view (score 1) was found in 2 patients belonging to Group I and none in Group II. While doing fibreoptic scoring it was found that the score is best judged behind the anterior epiglottic grills of the CPLA, which are transparent. This is probably because that the CPLA abuts upon the glottis and it becomes difficult to appreciate the scoring if the fiberscope is passed through the grills, in which case the fiberscope almost enters the larynx. However, in case of the ILMA, there is a definite gap between the distal aperture of the ILMA and the glottis.

There was no difficulty with insertion of the ILMA and CPLA or inability to ventilate the patients. So, our study revealed that the insertion and ease of ventilation with both the SGA devices were comparable although no objective data was collected. It was stated in a case report that it might be easier to insert the CPLA as compared with the LMA even in patients with restricted mouth opening.¹¹ These hint that CPLA insertion does not need a lot of head and neck manipulation or a large mouth opening.

A higher incidence of trauma was found in Group I. The probable reason is that Cobra head of the CPLA is stiffer than the ILMA cuff which may hit against the periglottic structures if it is inadvertently pushed. Furthermore, as previously mentioned, while maneuvering the PVC ETT through the CPLA, it could be deflected from the grills and hits against the pyriform fossa. The PVC tube is traumatic as the soft tuohy tipped ILMA-TT while performing a blind procedure. Our observation correlates well with previous studies in which it was reported that more blood staining and airway trauma were found with CPLA insertion as compared with other SGA devices.12, 13, 14

The hemodynamic variables were recorded throughout the procedure in both groups. It was revealed that a steady increase in heart rate and blood pressure in the procedure, starting from the insertion of the SGA device and also with each attempt of endotracheal intubation. A statistically significant (p value 0.006) increase in heart rate was found while inserting the CPLA inside the mouth as compared with the insertion of ILMA. This was not clinically significant as increase of heart rate on both occasions were within the normal physiological range.

Limitation of our study was that it was conducted in patients with predicted easy airway although these devices are more useful in difficult airway situations. Hence further studies are necessary to further clarify the role of CPLA as a guide to blind endotracheal intubation in difficult airway situations. In our study, the sample size was not rational for conclusively commenting on the complications and a study of larger scale is required to compare the complications in two groups.

Our study concludes that the CPLA can be used as a conduit for blind endotracheal intubation with cuffed PVC endotracheal tube and its performance is comparable to that of ILMA. The anatomic fitness of two supraglottic devices were comparable, and the time required for inserting the ETT through the CPLA is significantly more than that required through the ILMA but this time difference appears to be clinically insignificant. The incidence of trauma or sore throat is higher with CPLA than with ILMA although the difference is not statistically significant.