Ease of Endotracheal Intubation with the Conventional Polyvinyl Chloride Endotracheal Tube versus Wire-reinforced Flexometallic Tube through the Intubating Laryngeal Mask Airway: A Comparative Study

Abstract

Background:

The I-LMA ventilates while providing a port for blind insertion of an endotracheal tube. The ILMA Fastrach is used especially for intubating in a difficult airway scenario. Its accompanying endotracheal tube is not economical nor readily available. In comparison, two alternative endotracheal tubes – polyvinyl chloride and wire-reinforced tubes were used for tracheal intubation through the ILMA.

Aims and Objectives:

The aim of our study was to compare the ease of intubation when using conventional PVC tubes versus the wire-reinforced flexometallic tubes with the ILMA-FastrachTM. The number of attempts, time taken and additional maneuvers were noted. Intra-operative hemodynamic changes, post-operative sore throat, bleeding and hoarseness of voice was recorded over a period of 24 hours.

Methodology:

After informed consent, 60 ASA I-II patients undergoing elective surgeries under general anesthesia were allocated to undergo blind intubation with the PVC tube or the wire-reinforced flexometallic tube.

Results:

More attempts were required for successful intubation using the wire-reinforced tube than the PVC tube with 76.7% passing in the first attempt in the PVC, and 53.3% passing in the first attempt in the flexometallic group. (P = 0.4). Average time for intubation in the PVC group: 28.24 ± 7.22 seconds. Average time for intubation in the flexometallic tube: 45.8 ± 15.78 sec. Occurrence of post-operative sore throat was 13.3% in the PVC group and 26.6% in the flexometallic group, with minimal hoarseness of voice 3.3% in the PVC group and 10% in the flexometallic group. There was also a slightly higher hemodynamic response in those who were intubated with the flexometallic tube than a PVC tube.

Conclusion:

Intubating via the ILMA-Fastrach with the PVC tube offered better intubating conditions with regards to lesser time taken, lesser attempts, less manipulation, and less hemodynamic variations as compared to the patients who were intubated using the wire-reinforced tube.

INTRODUCTION

The American Society of Anesthesiologists (ASA) defines a difficult airway as one where a conventionally trained anesthesiologist experiences difficulty with facemask ventilation of the upper airway, difficulty with tracheal intubation, or both.[1] Despite newer airway adjuncts and technological advancements, definitive tracheal intubation is the safest for the patient. The intubating laryngeal mask airway Fastrach™, (ILMA-Fastrach) invented by Dr. Brain et al., in 1997, is specifically designed to allow tracheal intubation while maintaining a patent airway and providing ventilation.[2]

Although the ILMA has greatly improved intubation, the dedicated wire-reinforced silicone endotracheal tube (ETT) that is designed specifically for the ILMA may not be readily available. It is reusable up to 40 times after sterilization; however, it is not the most cost-effective option, especially in a setting of patients of low socioeconomic status. Moreover, it may not be readily available in case of an emergency intubation.” The cuff is a high-pressure low-volume cuff which makes it unsuitable for prolonged intubation due to the risk of tracheal mucosa necrosis. In patients with difficult airway where tube exchange may not be possible, the usage of this silicone tube is detrimental. Another disadvantage is its reinforced nature. The Fastrach tube is prone to permanently kink if a patient bites it, leading to tube occlusion.

In contrast, the conventional polyvinyl chloride (PVC) tube has a “high-volume low-pressure cuff.” It is of a much lower cost, is disposable, and is easily available for emergency situations. It also has a preformed curvature that matches the anatomical curvature of the palate. The flexometallic wire-reinforced tube is more flexible than the standard ETTs and is less likely to kink or occlude.

In this study, we compared the ease of insertion of a conventional PVC tube [Figure 1] with a regular wire-reinforced flexometallic tube [Figure 2] for blind intubation through the Fastrach™ ILMA. The aim of our study was to compare the ease of intubation when using conventional PVC tubes versus the wire-reinforced flexometallic tubes with the ILMA-Fastrach^™. The number of attempts, time taken, and additional maneuvers were noted. Intraoperative hemodynamic changes, postoperative sore throat, bleeding, and hoarseness of voice were recorded for 24 h.

Figure 1.

Polyvinyl chloride endotracheal tube insertion through intubating laryngeal mask airway

Figure 2.

Wire-reinforced flexometallic tube insertion through intubating laryngeal mask airway

METHODOLOGY

After obtaining approval from the Institute’s Ethical Committee, 60 adult patients of ASA Physical Status of I/II of either sex, scheduled for elective surgery requiring general anesthesia, were enrolled for the study. The study was a prospective comparative study between the PVC group and the flexometallic group using the ILMA. The patients were randomized into two groups using a simple random sampling technique.

The primary objectives of the study were to assess the ease of intubation in terms of number of attempts, time taken for intubation, and any manipulations required. The secondary objectives were to measure the airway morbidity in terms of sore throat, hoarseness of voice, and bleeding. Hemodynamics were also noted at 0, 3, 5, 10, and 15 min of intubation.

Inclusion criteria for the study were patients of ASA Physical Class I/II, aged 18–70 years of either sex, who are willing to be a part of the study and give consent, with Mallampatti grade I and II, and interdental distance of >3.5 cm.

Patients who were excluded were those with removable dentures, hypertrophied tonsils (grades 3 and 4), thyroid enlargement, morbid obesity, pregnancy, previous upper gastrointestinal surgery, and those with a predicted difficult airway – Mallampati grades III and IV, short neck, large neck circumference, limited mouth opening, short thyromental distance, large tongue, and any other airway pathology.

A thorough preanesthetic evaluation was performed 24 h before the scheduled procedure. Written informed consent was obtained from the patient. Patients were kept in an nil per mouth (NPO) status overnight after taking tablet alprazolam 0.5 mg and tablet ranitidine 150 mg the night before the surgery.

In the operating room, an intravenous infusion was started, and patients were randomly allocated to one of the two groups – Group I – intubation with cuffed PVC ETT, Group II – intubation with the flexometallic tube by opaque sealed envelope technique. Standard monitors were applied, and baseline parameters were recorded, including heart rate, arterial oxygen saturation, and noninvasive blood pressure recording.

Patients were premedicated with injection ondansetron 4 mg, injection midazolam 1 mg, and injection glycopyrrolate 0.2 mg. They were then preoxygenated for 3 min with 100% oxygen. Injection fentanyl 1.5 µg/kg was given. The patients were induced with injection propofol 2 mg/kg, and a muscle relaxant injection vecuronium 0.1 mg/kg was given. Face-mask ventilation was done until complete relaxation.

After complete relaxation, with the head in a neutral position, an appropriate-sized ILMA was inserted. Proper positioning of ILMA was confirmed with equal bilateral air entry. If air entry was found to be unequal or if resistance felt in the reservoir bag was high, optimization maneuvers were done. Extension of the ILMA handle (up/down movement), head–neck maneuver, rotation in the sagittal plane, or lifting away from the posterior pharyngeal wall was done. Time taken for laryngeal mask airway insertion was defined as the time from cessation of face-mask ventilation until successful ILMA placement and confirmation with bilateral air entry and capnography.

Then, a well-lubricated cuffed PVC tube/flexometallic tube was passed through the ILMA until 16 cm (the epiglottis elevating bar). The tube was advanced into the trachea, and confirmation was based on square-wave capnography and the presence of bilateral breath sounds. The ILMA was then deflated and removed using the stabilizing rod (red rubber ETT or smaller cuffed ETT) to maintain the tube in place. The ETT tube cuff was inflated, and the patient was connected to a closed circuit. The time taken for intubation was defined as the time from disconnection of the breathing circuit from the ILMA up to successful tracheal intubation. A maximum of three attempts were tried; in case of failure, the airway was secured with direct laryngoscopy alternatively, and such patients were excluded from the study.

After endotracheal intubation and confirmation of correct placement with auscultation and square-wave capnography, heart rate, arterial oxygen saturation, noninvasive blood pressure, and end-tidal CO₂ were monitored.

Thereafter, hemodynamic parameters were recorded at 0 min, 3 min, 5 min, 10 min, and 15 min after successful intubation. After extubation, all patients were evaluated for sore throat, bleeding, and hoarseness of voice during the first 24 h at 2, 6, 18, and 24 h postextubation.

After intubation, anesthesia was maintained with isoflurane 0.6%–1% and a mixture of oxygen and nitrous oxide at 34% and 66% with closed circuit and controlled ventilation as per standard practice.

Following ILMA removal and extubation, trauma or any amount of blood seen on the ILMA, on the ETT, on the lips, gums, oropharynx, and tongue, and any loosening of teeth were all considered airway morbidity. At the end of the procedure, the patients were reversed, extubated, and shifted to the postoperative ward for further monitoring.

Statistical analysis

Data were analyzed with IBM SPSS version 21 – Trial version. Demographic data and the time taken for tracheal intubation were presented as mean ± standard deviation and analyzed using the Student’s t-test. The Chi-square analysis was used for comparing nominal data. P ≤ 0.05 was considered statistically significant. The sample size was determined through power analysis (α = 0.05, β = 0.08) to detect a difference in the overall success rate between the two groups, which indicated a sample size of 30 patients in each group.

RESULTS

Demographic criteria such as the mean age and gender distribution were similar in both groups [Table 1]. ASA physical status and body mass index of the patients were also similar in both groups [Table 2]. The difference between the preoperative hemodynamic parameters of the patients in both groups was clinically insignificant.

Table 1.

Gender and American Society of Anesthesiologists physical status distribution between the two groups

	Type of ETT
	PVC		Flexometallic
	Count	N %	Count	N %
Sex
Female	18	60.0	13	43.0
Male	12	40.0	17	57.0
ASA physical status
I	14	46.7	17	56.7
II	16	53.3	13	43.3

ASA=American Society of Anesthesiologists, ETT=Endotracheal tube, PVC=Polyvinyl chloride

Table 2.

Demographic data between both groups

	Type of ETT, mean±SD
	PVC	Flexometallic
Age (years)	45.7±13.8	41.1±15.3
BMI	26.95±5.46	4.69±0.3
LMA insertion (s)	27.8±6.07	31.7±9.15

P=0.23, (age), P=0.3 (BMI), P=0.06 (LMA insertion). BMI=Body mass index, LMA=Laryngeal mask airway, SD=Standard deviation, ETT=Endotracheal tube, PVC=Polyvinyl chloride

In the PVC group, the first attempt at intubation was successful in 76.7% of patients, 16.7% of patients were successful in the second attempt, and 6.7% of patients required a third attempt for successful endotracheal intubation. In the flexometallic group, only 53.3% of patients were successfully intubated on the first attempt, 33.3% of patients were successfully intubated on the second attempt, and 13.3% of patients were successfully intubated on the third attempt. Repeated attempts were either due to esophageal intubation or inability to pass the tube.

The PVC group required an average time of 28.24 ± 7.22 s for intubation, whereas the flexometallic group required 45.8 ± 15.78 s for intubation. P =0.04 is significant [Table 3]. The longer time for intubation required by the flexometallic group could be explained by a higher number of attempts and a higher number of maneuvers required for successful intubation. In the PVC group, 83.3% of patients required no manipulation, and 73.3% of patients required no manipulation in the flexometallic group (P = 0.05). The flexometallic group required more maneuvers in 26.7% of patients versus 16.6% in the PVC group [Table 4]. Hemodynamic variations were slightly higher in the flexometallic group, most likely due to more attempts at manipulation and insertion [Table 5]. The occurrence of postoperative sore throat was more in the flexometallic group (26.7%) [Table 6].

Table 3.

Average time taken for intubation among the two groups

	Type of ETT, mean±SD		P
	PVC	Flexometallic
Average time for intubation (s)	28.24±7.22	45.8±15.78	0.04

SD=Standard deviation, ETT=Endotracheal tube, PVC=Polyvinyl chloride

Table 4.

Maneuvers required to achieve successful intubation

Maneuvers used	Type of ETT				P
	PVC		Flexometallic
	Count	N %	Count	N %
Nil	25	83.3	22	73.3	0.05
Neck extension	1	3.3	3	10
Optimization	2	6.7	1	3.3
Sagittal	1	3.3	2	6.7
Up–down maneuver	1	3.3	2	6.7

ETT=Endotracheal tube, PVC=Polyvinyl chloride

Table 5.

Pre- and postinduction hemodynamic parameters recorded among the two groups

	Type of ETT, mean±SD
	PVC	Flexometallic
Preinduction HR	85.13±12.16	95.13±17.16
Preinduction SBP	137.90±20.52	127.90±21.37
Preinduction DBP	80.20±10.82	79.20±9.91
Postinduction HR	81.7±15.48	71.70±14.28
Postinduction SBP	123.60±23.57	119.60±24.59
Postinduction DBP	82.77±9.27	62.77±11.25

ETT=Endotracheal tube, PVC=Polyvinyl chloride, SD=Standard deviation, HR=Heart rate, SBP=Systolic blood pressure, DBP=Diastolic blood pressure

Table 6.

Postoperative airway morbidity in the form of sore throat, hoarseness of voice, or bleeding observed over 24 h in the two groups

Postoperative complications	Type of ETT
	PVC		Flexometallic		P
	Count	N %	Count	N %
Sore throat
No	26	86.6	22	73.3	0.196
Yes	4	13.4	8	26.7
Hoarseness
No	29	96.7	27	90.0	0.3
Yes	1	3.3	3	10.0
Bleeding (ETT blood stain)
Yes	2	6.7	4	13.3	0.28
No	28	93.3	26	86.7

ETT=Endotracheal tube, PVC=Polyvinyl chloride

DISCUSSION

The current rationale for the design of the ILMA-Fastrach has been described by Brain. Initial testing demonstrated the importance of a 30° angle, which is formed by the tube that emerges from the ILMA. This makes it so the tube accurately reaches the laryngeal inlet.[3] A soft flexible reinforced silicone tube design was chosen for this very reason. Joo and Rose demonstrated that a curved, PVC ETT could emerge from the ILMA close to this ideal 30° angle if inserted with its curve in relation to the curvature of the ILMA.[4] We also found similar results with regard to the PVC tube. The ILMA has a preformed curvature mimicking the hard and soft palates. When the flexometallic tube is inserted, it follows the same curvature. However, as it emerges from the epiglottic bar, there is no firm support to guide the tube into the larynx. This may be the reason why a higher number of intubation attempts were required for the flexometallic tube.

In our study, initial unsuccessful attempts were due to the learning curve; insertion of the ILMA and practicing the insertion of the ETT was required. We required a trial of seven cases where we identified either improper placement of the ILMA or unsuccessful intubation occurred. Baskett et al. suggest that a learning curve of 20 ILMA insertions and intubations is required before becoming proficient with the device and achieving higher intubation success rates.[5] The data from Chan et al. support this conclusion. In their study, three failures to intubate happened within the first 20 attempts.[6]

Our study’s primary objective was to study the ease of intubation in each of the tubes by measuring the number of attempts, time taken, and additional maneuvers required to achieve successful endotracheal intubation. Our results were comparable to that of Kundra et al.[7] who found that tracheal intubation on the first attempt was successful 96% of the time with the Fastrach tube and 86% of the time with the PVC tube. Even though our comparison was between the PVC and the flexometallic tube, we found similar results regarding the first- and second-attempt success rates between the two ETTs. Kundra et al.[7] also found that esophageal placement was significantly more frequent with the flexometallic tube (29.7%) when compared with the PVC tube and ILMA-Fastrach tube (1.8% and 7.4%, respectively).

Sharma et al. conducted a similar study in 2013 with a larger sample size of 200 patients of ASA I/II. They found that the time taken for tracheal intubation and maneuvers required was greater for the PVC tube than the Fastrach tube (14.71 ± 6.21 s and 10.04 ± 4.49 s), respectively (P = 0.001).[8] Hemodynamic stability was comparable between both groups. The first-attempt success rate at tracheal intubation was higher in the Fastrach group compared to the PVC tube, similar to the study performed by Kundra et al.[7] We found similar results with the PVC tube.

Shah et al. compared the clinical performance of ILMA-Fastrach with conventional PVC tubes for tracheal intubation through ILMA in a study with 60 patients of ASA I/II, which is nearly similar to our study. The overall success rate with the ILMA-Fastrach was 96.63% and 93.33% with the PVC endotracheal tube.[9]

Korula et al. have found that the stabilizer rod that is supplied with the ILMA-Fastrach is prone to disconnection due to its short length compared to the ETT. They have used a small cuffed ETT instead of the custom stabilizer rod.[10] As we used PVC or flexometallic tubes for our study, we did not have the stabilizer rod designed for the ILMA-Fastrach. We used a red rubber tube or a smaller PVC tube that was one size smaller than the tube used for endotracheal intubation, and the ILMA was then deflated and removed. We did not find any difficulty, nor was the tube dislodged after removal of the ILMA. However, we did find that the ETT was significantly pushed further down on removal of the ILMA; hence, confirmation of bilateral air entry after pulling out the tube was required after all the cases.

Damage to other structures in the pharynx and the larynx is another potential problem of blind intubation through the ILMA, which we have studied as part of the secondary objective of our study. Takenaka et al. reported epiglottic edema as a consequence of down-folding of the epiglottis during blind intubation.[11] Kihara et al. reported the incidence of sore throat with the ILMA alone when left in situ for the duration of the procedure due to pressure exerted by the ILMA on the pharyngeal mucosa.[12] In our study, postoperative sore throat, hoarseness of voice, and evidence of traumatic intubation were observed more frequently in those intubated with the flexometallic tube than the PVC tube. The incidence of sore throat and hoarseness in the present study was more in the patients who required more number of attempts, which is consistent with the observations of Lu et al.[13] and Kundra et al.[7]

CONCLUSION

To conclude, a suitable alternative for intubation through the ILMA-Fastrach™ is the polyvinyl ETT than the flexometallic wire-reinforced ETT, as it is easier to insert, more economical, readily available, and causes lesser airway morbidity. Overall, we have found that the time required for intubation through the ILMA was less in the PVC group compared to the flexometallic group. Lesser manipulation was required, and lesser incidence of postoperative airway morbidity comparatively, there was not much of a hemodynamic response between the two groups even though the flexometallic group had a slightly higher response.

Although there is a learning curve associated with ILMA use, it can be considered an alternative to tackle the normal airway and the difficult airway with the use of a PVC ETT.

Limitations

A larger sample size comprising patients with an anticipated difficult airway would yield more conclusive results. Proper fitting seal of the ILMA over the laryngeal inlet was checked with bilateral air entry clinically and not with fiberoptic scope which could be attributed to the relatively longer intubation time and slightly higher number of attempts required in our study. We also have not identified esophageal intubation by auscultation over the fundus; if bilateral air entry was not present, the ETT was immediately removed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.