Laryngeal mask airway (LMA) insertion is a common rescue intervention for tracheal intubation in cases of difficult airway, and also in elective surgeries. Compared to endotracheal intubation, it allows appropriate airway management during controlled and spontaneous ventilation with lower doses of anesthetics and muscle relaxants. Therefore, it offers a reliable airway with minimum complications. However, there are some LMA-associated complications including sore throat, pharyngeal mucosal abrasions, dysphonia, dysphagia, and cranial nerve damage.
The classic model of LMA was designed by Archie Brain and it has been used in many clinical settings. In the original method of insertion, the device cuff is first deflated and a water-soluble lubricant is applied to the posterior surface of the mask, then it is held like a pen by the dominant hand and slid along the palate to enter the mouth, and its tip would be advanced toward the upper esophageal sphincter, which usually feels as a resistance. The reported success rates of insertion in the first attempt by this technique are estimated to be 76% to 96%. Many studies have been conducted to find more appropriate techniques for insertion, better drug regimens for easier placement, and their efficacy or complications. Some studies showed that LMA, when inserted by a semi or fully-inflated cuff the success rate of insertion was higher compared to the classical method. The success rate of LMA insertion with 180-degree rotation was reported to be 100% compared to 96% of classical techniques in the pediatric age group. Koay et al. reported that using a laryngoscope for LMA insertion did not increase the rate of successful insertion significantly, whereas it may increase the incidence of pharyngeal tissue damage. In the Yodfat technique, it was recommended to use a stylet with a 90-degree curve close to the laryngeal end of LMA with a semi-inflated cuff. Besides the mentioned techniques, there are many other maneuvers introduced such as using jaw thrust, removing the tongue out of the mouth and withdrawing a part of the mask and reinsertion that part again, and so on to facilitate the insertion.
Unsuccessful LMA insertion in the first attempt and reinsertion may increase the risk of oropharyngeal tissue damage, bleeding, and sore throat. Therefore, we tended to take initiative toward a novel technique of LMA insertion to increase the successful insertion rate and minimize the complications. In this study, we compared the success rate and complications of the classical LMA insertion with a semi-inflated cuff and our alternative technique using the index and middle fingers of the non-dominant hand to prevent retroversion of the LMA tip during the insertion, being assumed as a common factor of the insertion failure.
Materials and Methods
This double-blind randomized controlled trial was conducted on patients scheduled for elective ophthalmologic surgery (less than 1 h duration) at the university-affiliated, Khalili Hospital of Shiraz. It was approved by the Research Ethics Committees of the university (IR.SUMS.MED.REC.1379.142) and registered in IRCT (IRCT2018092204108N1). The sample size was calculated according to a pilot study on 30 patients using a comparison of proportions of success in the first LMA insertion attempts (86% in the classic method vs. 96% in the alternative method). One-hundred forty-two patients in each group were needed to detect a 10% difference in failure rate between the two groups with α of 0.05, power of 80%, and dropout of 10%. Patients were randomly allocated to two groups of LMA insertion either by classical technique (group C) or alternative technique (group A) using a blocked randomization list with the size of blocks 4.
Patients with ASA physical status I and II, aged 15 to 65 years were recruited. Exclusion criteria were sore throat, difficult airway, abnormalities in supraglottic anatomy, morbid obesity, pregnancy, NPO time less than 8 h, gastroesophageal reflux, consuming medication(s) that could delay gastric emptying, abnormalities in temporomandibular joints and mouth opening, abnormalities in cervical vertebrae and spinal cord, and limited neck motion.
All LMA placements were carried out by an anesthesiologist who had enough experience with both insertion techniques (more than 50 attempts with each method). The appropriate size of disposable classic LMA (Unique TM, The Laryngeal Mask Company Ltd., Singapore) was chosen according to the patients’ weights: size 3 for 30 to 49 kg, size 4 for 50 to 70 kg, and size 5 for more than 70 kg weight patients. After each patient entered the operating room and their general data were recorded, an IV line access was established and standard monitoring devices, including EKG, noninvasive blood pressure monitoring, and pulse oximeter, were applied. Pre-oxygenation was followed by a similar induction protocol of anesthesia in both groups with midazolam (15–30 μg.kg-1), remifentanil (0.5–25 μg.kg-1), and sodium thiopental (3–4 mg.kg-1). Then atracurium (0.4 mg.kg-1) was administered for muscle relaxation.
After 3 min of mask ventilation with 100% of oxygen, LMA was inserted as follows: the classical method with the semi-inflated cuff method (group C) and the alternative method (group A). In group C, the procedure was similar to that introduced originally by Dr. Archie Brain except that the size 3 masks were prefilled with 20 mL, size 4 with 30 mL, and size 5 with 35 mL of air before insertion. The posterior surface of the mask was lubricated by a water-soluble gel. The operator stood above the patient's head and held the device like a pen with his dominant hand and the assistant mildly extended the patient's head while keeping the mouth open with a jaw thrust maneuver. Then, the operator slid the mask toward the larynx as far as possible and pushed it back against the palate simultaneously. Finally, the distal end of the device was grasped by the non-dominant hand and it was pushed until a resistance did not let further advancement.
In the alternative group (group A), as in the first group, the procedure began first with emptying and then inflating the cuff with the above-mentioned volumes, LMA was lubricated by water-soluble gel, and the operator stood at the right or the left side of the patient and held the LMA like a pen while the assistant placed the patient's head in a suitable position and opened the patient's mouth by jaw thrust maneuver. Then, the operator inserted the mask, slid it down toward the pharynx, and pushed it upward to the patient's palate while simultaneously supporting the tip of the mask to prevent it to fold backward during the passage through the oropharynx with the aid of the index and middle fingers of his non-dominant hand as far as possible. At last, the operator grasped the distal end of the device and pushed it to its final position [Figure 1a-d].
A cuff pressure manometer was used to adjust the internal cuff pressure. Proper LMA location was confirmed by observing symmetrical chest excursions, auscultating bilateral breathing sound with a stethoscope, easy refilling of the ventilating bag, monitoring the arterial oxygen saturation, and detecting a normal capnography curve. Then, the LMA was fixed in place by a proper bandage in both groups.
All patients were connected to the ventilator of the anesthesia machine. Tidal volume and respiratory rate were adjusted to maintain eucapnia (EtCO2<45 mmHg) and airway pressure below 15 cm H2O. Any air leakage around the LMA cuff was diagnosed by placing a stethoscope diaphragm over the thyroid cartilage. If it occurred below 15 cm H2O pressure, first it is treated by mildly repositioning the patient's head in flexion or extension directions and then by inflating an additional 5 mL of air into the cuff. If it was not successful, the case was considered a trial failure. For those with the first attempt failed, the procedure was repeated two more times by the same method and if it was unsuccessful again the patient was intubated and considered a failure of insertion.
The maintenance phase of anesthesia was similar in both groups and was conducted with 1% isoflurane in 100% oxygen until the end of the operation. After the return of the gag reflex and the patient's ability to follow commands, the LMA cuff was deflated and the mask was removed. To prevent further tissue damage, oropharyngeal suctioning was limited to one gentle attempt with a small-size catheter just before deflating the cuff and removing LMA. If repeated suctioning was necessitated, the participant was excluded from the complication analysis. Data related to postoperative complications were gathered in the recovery room by a nurse who was blinded to the study group.
Patient characteristics (age, gender, and weight), and data related to oropharyngeal airway insertion including LMA insertion success rate, insertion time (from the beginning of insertion until proper placement was announced by the operator), number of insertion attempts, and the level of difficulty (easy, moderate difficulty, difficult) were documented. The incidences of laryngopharyngeal complications including bloody streaks on the mask surface or in oral secretions after LMA removal, and frequency of sore throat and its severity at the time of discharge from the recovery room based on the patient's report were also assessed.
Data are reported as mean with standard deviation for continuous variables and the differences between groups were analyzed by an independent sample t-test. Categorical variables are presented as numbers and percentages, and Chi-square and Fisher's exact tests were used to estimate the significant values. The data were analyzed using the statistical package for social science (SPSS Inc., Chicago, version 23), and a P value <0.05 was considered statistically significant.
A total of 284 patients who underwent elective ophthalmologic surgery participated in the study (142 patients in each group) [Figure 2].
There were no statistically significant differences in mean age, weight, and sex between the two groups [Table 1].
Table 2 shows the data related to LMA insertion. As can be seen, there is a statistically significant difference in the number of attempts, frequency of postoperative sore throat, and ease of insertion in favor of group A.
In the present investigation, the success rate and complications of two LMA insertion methods, the classic and the alternative techniques, were assessed. Although in the current study, we did not find any difference in insertion time among our study groups, we did find a greater number of LMA insertion attempts, a higher level of difficulty of LMA placement, and a less successful LMA insertion rate with classical technique.
The incidence of difficult LMA placement in our study was 3.7% (3% in the classic and 0.7 in the alternative groups) and the LMA failure rate was 6% (all in the classic group). Moreover, the incidence of failed LMA placement in our study is consistent with previous studies 9, 13, 18, 21, and 22, ranging from 0.19 to 4.7%.
In the present study, the successful placement rate of LMA by the first, second, and third attempts were 91.6%, 7.6%, and 0.8 in the classic and 98.6%, 1.4%, and 0% in the alternative method. The overall success rate of the classic insertion method by the first attempt was reported to vary between 76% and 96%. Walking et al. reported 97% success for LMA insertion with a semi-inflated cuff versus 94% of the classic method with a fully deflated cuff. Although the difference was not significant, they showed that the former technique was associated with lower tissue trauma and postoperative sore throat. Soh et al. found that the reverse or 180-degree rotation technique can lead to a 100% success rate comparing 90% for that the classic method in the pediatric age group. Mata compared the classic method with a technique using a semi-inflated cuff, which resulted in success rates of 75.4%, 84%, and 92% in the first, second, and third attempts by the former and 86.6%, 94.3%, and 97.7% with the latter technique. In the Wakeling study, the success rates with three consecutive attempts were 80%, 91%, and 94% by classic technique compared with 89%, 95%, and 97% by the semi-inflated cuff of LMA insertion.
Backward flexion of the mask tip during the passage from the oropharynx may be a cause of procedure failure in some cases proposed by Dingley. Hall and Kushins suggested that flexion of the cuff tip of a deflated mask before application may facilitate the insertion. Nevertheless, Brimacombe and Keller criticized the maneuver in their investigation. We showed that this phenomenon could be prevented if the operator's finger supports the mask tip until near the end of its path.
The discomfort caused by inserting a finger in the patient's mouth, especially in individuals with normal dentition, and hence the lack of enough space for the maneuver is one of the difficulties of alternative technique. Furthermore, the patient's sharp teeth or broken edges may cause harm to the operator's finger, although no such problem was reported in this study.
We found that the use of alternative techniques was associated with a lower incidence of sore throat and bleeding. Given that the presence of blood on LMA is a predictor for both the occurrence and the severity of sore throat, our findings suggest that the method may decrease the traumatic impact on the oropharyngeal structures during insertion.
The frequency of bloody streaks after removing LMA in Walking's study in the classic group was 15.3%, whereas it was zero in the semi-inflated group.
In the current study, these values in the semi-inflated and alternative groups were 18.3% and 14.3%, respectively. The insertion method in the control group of our study was similar to the Walking case group. Given the fact that in the Walking study, muscle relaxant has not been used, it seems that tissue damage in the semi-inflated group of the Walking study must not have such a difference from our case group (i.e., 14.3% against zero). The explanation of the issue does not seem easy, but we can say that some differences may be because of the different brands of the LMA, which have been used, or because of the difference in the mean age of participants of these two studies. The mean age of patients in the present study is about 10–15 years higher than in the Walking study and as we know according to the literature mucosal fragility and vulnerability increase with age.
The incidence of postoperative sore throat, although sought only at early stages, compared with that of Brimacombe (28.5%) and Dingley (30%) studies seems comparable.
There were some shortcomings in our study such as the inability to design it in a double-blinded manner and also the lack of muscle relaxation monitoring but generally, it can be concluded that this newly introduced technique can be considered as an alternative method when a difficult insertion situation is suspected or the classic technique insertion has failed.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
1. Hu LQ, Leavitt OS, Malwitz C, Kim H, Doty RA Jr, McCarthy RJ. Comparison of laryngeal mask airway insertion methods, including the external larynx lift with pre-inflated cuff, on postoperative pharyngolaryngeal complications: A randomised clinical trial Eur J Anaesthesiol. 2017;34:448–55
2. John R, Hill S, Hughes T. Airway protection by the laryngeal mask: A barrier to dye placed in the pharynx Anaesthesia. 1991;46:366–7
3. An J, Shin SK, Kim KJ. Laryngeal mask airway insertion in adults: Comparison between fully deflated and partially inflated technique Yonsei Med J. 2013;54:747–51
4. Wakeling HG, Butler PJ, Baxter PJ. The laryngeal mask airway: A comparison between two insertion techniques Anesth Analg. 1997;85:687–90
5. Matta BF, Marsh DS, Nevin M. Laryngeal mask airway: A more successful method of insertion JClin Anesth. 1995;7:132–5
6. Soh C, Ng A. Laryngeal mask airway insertion in paediatric anaesthesia: Comparison between the reverse and standard techniques Anaesth Intensive Care. 2001;29:515–9
7. Koay C, Yoong C, Kok P. A randomized trial comparing two laryngeal mask airway insertion techniques Anaesth Intensive Care. 2001;29:613–5
8. Yodfat UA. Modified technique for laryngeal mask airway insertion Anesth Analg. 1999;89:1327
9. Pennant J, White P. The laryngeal mask airway. Its uses in anesthesiology Anesthesiology. 1993;79:144–63
10. Dingley J, Baynham P, Swart M, Vaughan R. Ease of insertion of the laryngeal mask airway by inexperienced personnel when using an introducer Anaesthesia. 1997;52:756–60
11. Hall DB, Kushins LG. A laryngeal mask airway “tip” Anesth Analg. 1999;89:801
12. Brimacombe J, Keller C. Curling the tip anteriorly does not facilitate laryngeal mask insertion Anesth Analg. 2000;90:1247–8