Comparison of Different Methods in Determining the Laryngeal Mask Airway (LMA) Size in Adult Patients

Abstract

Purpose

In this study, we aimed to compare the effects of different LMA size selection methods on successful LMA application, perioperative ventilation parameters and postoperative airway complications in determining the appropriate size of LMA used for elective surgery in adult patients in our operating room.

Methods

All data obtained from records of ASA group I-II patients between ages 18 and 70, who were anesthetized by using LMA and had elective surgery. Cases were classified according to methods used for deciding appropriate LMA size, and retrospectively successful LMA application, perioperative ventilation parameters and postoperative complications were recorded.

Results

A total of 190 patients were included in our study grouped in 5 different ways. For the 51 cases, the LMA size was chosen according to the body weight of the patients in LMA size selection guided weight according to the body weight of the manufacturer. For the thirty-three cases, the size of the LMA, approximately equal to the width of the external auditory canal auricula, was used. The size of the LMA selected for thirty-eight cases was the LMA dimensions corresponding to the language width of the cases. In thirty-six cases, the size of the LMA that corresponds to the width of the fingers, while the thumb, and the small finger were opened to the outside, and the second, third and fourth fingers were adjacent, were preferred. In thirty-two cases, it was found that the appropriate LMA was chosen to correspond to this distance by looking at the thyromental distances of the cases. The best score in terms of LMA insertion score was found out to be in Group Ear. The best group in terms of the number of attempts to place the LMA in the cases was found out as Group Ear. Group Ear was the best group for the complications of sore throat in terms of postoperative complications.

Conclusion

The results of our study showed that the ear size measurement method was one of the effective methods to decide the appropriate LMA size. Therefore, it can be said that the ear size can be used as a guide for the selection of the appropriate LMA size. This method may be an addition to the methods currently in use and can save users from remembering formulas and tables based on body weight / gender.

1 Introduction

Airway management is one of the important subjects of anesthesia practice. Although usage of face masks and endotracheal tubes for adequate ventilation is accepted as standard practice for many years, search for new more convenient options continued in terms of efficiency, safety and side effects, and supraglottic airway devices (SGAs) have been developed [1]. Supraglottic airway device is a term used to describe the family of various medical devices placed into the pharynx blindly [2]. The most important advantage of SGAs is the ability of securing airway where both tracheal intubation and ventilation with face mask are hard to manage. Moreover, no need for muscle relaxant during application and usability in numerous daily surgical interventions are also some of the reasons for their preferability [1, 3]. Application of LMA is easy and atraumatic, and it induces minimal somatic and autonomic reactions in the patient. Hearth rate and blood pressure increases during insertion and removal but this increases are significantly lower than tracheal intubation and extubation [4, 5]. Usage of LMA is increasing in elective surgeries, resuscitation and hard airway management cases [6, 7].

Successful utilization of LMA depends on appropriate size selection, insertion technique, cuff inflation amount. Selecting and placing an LMA with unsuitable size may cause malposition and problems during ventilation [8]. Different methods are defined for proper LMA size selection [8, 9]. The most frequently used method, which is also defined in the LMA operating manuals prepared by the manufacturers, is the size selection by only using the patient’s body weight. However, we frequently face with cases in which size of the airway anatomy cannot be closely correlated with body weight such as obese or malnutrition cases. Especially in some emergency cases, lack of reliable anamnesis about the patient’s body weight makes LMA size selection with respect to body weight inappropriate [8].

Brimacombe et.al. [10] addressed that deciding correct laryngeal mask size can be difficult since relationship between the gender, body weight, height and upper airway geometry shows inconsistency. They claim that appropriately sized LMA selection with respect to body weight is a widely accepted method in daily applications but, LMA size selection with respect to the body weight may not be appropriate for every condition. In many previous studies different selection methods were designed to achieve more successful LMA insertion rates [8]. Bery et.al. [11] on the other hand, showed that there is no meaningful correlation between body weight, gender or any other anatomical measurement in their studies.

In our study, for determination of appropriate LMA size used in elective surgery on adults, we aimed to compare different LMA size selection methods in terms of successful LMA application, effect on perioperative ventilation parameters and postoperative airway complications.

2 Materials And Methods

3 Results

A total of 190 cases were found to be conform with the inclusion criteria of our study. There was no significant statistical difference in the demographic and anthropometric data of the included cases (Table 1) (p > 0.05). No significant difference acquired between the groups when evaluated with initial tidal volume (TV) values after LMA insertion (Table 2) (p > 0.05). No statistically significant difference in average Peripheral Oxygen Saturation (S_PO₂) values and average Oropharyngeal Leak Pressure (OLP) values acquired in cases with successful LMA insertion (p > 0.05).

Statistically significant difference acquired between Group Ear and Group Weight (p = 0.045), Group Tongue (p = 0.023) and Group Finger (p = 0.003) when End-Tidal Carbon dioxide Pressure (P_ETCO2) values between the groups are evaluated. Statistically significant difference acquired between Group Weight (p = 0.045) and Group Finger (p = 0.022) and between Group Tongue, Group Weight (p = 0.041) and Group Finger (p = 0.020) in terms of difference related to Peak Inspiratory Pressure (P_IP) values (Table 3).

When LMA insertion score defined as easy (no maneuver required), moderate (single maneuver required), hard (multiple maneuvers required) evaluated statistically significant difference acquired between Group Ear and Group Weight (p = 0.004), Group Tongue (p = 0.036), Group Finger (p = 0.009) and Group Thyromental (p = 0.012). It is seen that in Group Ear LMA insertion is easier than other groups (Table 4).

Significant difference acquired in terms of number of trials for successful LMA insertion between the groups (p = 0.025). In terms of comparison of average trial number statistically significant difference acquired between Group Ear and Group Weight (p = 0.028), Group Finger (p = 0.002) and Group Thyromental (p = 0.019) (Table 5).

Statistically significant difference acquired between Group Weight and Group Ear (p < 0.001), Group Tongue (p = 0.010) and Group Finger (p = 0.010), and between Group Thyromental and Group Ear (p = 0.010), Group Tongue (p = 0.040) and Group Finger (p = 0.040) (Table 6).

No statistically significant difference acquired between the groups when average values for LMA insertion duration, operation duration, anesthesia duration and LMA usage duration are evaluated (Table 7-) (p > 0.05).

When complications in the cases are evaluated no statistically significant difference for blood stain, laryngospasm, hoarseness and dysphagia between the groups acquired (p > 0.05). On the other hand statistically significant difference acquired for throat pain complications between the groups (p = 0.008). Group Ear and Group Weight (p = 0.009), and Group Thyromental (p = 0.004), and between Group Tongue and Group Thyromental (p = 0.023) (Table 8).

No statistically significant difference was present between the groups in terms of experience of LMA operators (p > 0.05).

4 Discussion

Successful application of LMA often depends on appropriate size selection, insertion technique, cuff inflation amount. Insertion and selection of inappropriate LMA may cause malposition during intraoperative period and problems during ventilation, throat pain, hoarseness, aglutition, bleeding, laryngospasm and nerve damage in postoperative period [8]. Generally size of the LMA is, as suggested by manufacturers, decided by the formula for body weight which is obtained by previous studies on adults [8, 9]. However, we frequently face with cases in which size of the airway anatomy cannot be closely correlated with body weight such as obese or malnutrition cases. Especially in some emergency cases, lack of reliable anamnesis about the patient’s body weight makes LMA size selection with respect to body weight inappropriate. Because of this, sometimes, LMA size selection can be complicated in adults [11, 12]. Different methods such as selection according to gender, height and BMI are also suggested as alternatives for body weight method [13]. Nevertheless no factor or method that can easily measure potential pharyngeal volume correlated with appropriate laryngeal mask is defined yet [14]. Brimacombe et.al. [15] addressed that deciding correct laryngeal mask size can be difficult since relationship between the gender, body weight, height and upper airway geometry shows inconsistency. Voyagis et.al. [16–17] also in their studies on this subject claimed that appropriately sized LMA selection with respect to body weight is a widely accepted method in daily applications but, LMA size selection with respect to the body weight may not be appropriate for every condition. Different methods for LMA size selection had been defined. In many previous studies different selection methods depending on anatomy were designed for more successful LMA insertion rates [8, 9].

During mechanical ventilation airway pressures must be kept limited in order to prevent gastric insufflation [18]. In our study, statistically significant difference between Group Ear, Group Weight and Group Finger, and between Group Tongue, Group Weight and Group Finger acquired for P_IP values. However, in all groups, values were within limits required for preventing regurgitation and aspiration [19, 20]. Similar to our study Haliloğlu et.al. [21] found out that in their LMA size selection study on 197 pediatric cases Group Ear and Group Weight had similar P_IP values.

Oropharyngeal Leak Pressure (OLP) indicates success of LMA insertion, applicability of positive ventilation and level of securing airway [19]. Oropharyngeal leak pressure must exceed posterior pharyngeal wall liquid pressure, approximately 10 cmH₂O, to prevent pharyngeal secretion and gas leak [22]. In our study it is identified that average OLP values of cases for all groups are over 10 cmH₂O. Similar to our study Haliloğlu et.al. [21] found out that in their appropriate LMA size selection study on 197 pediatric cases found out that average OLP values of cases were 28.6 ± 1.4. Huang et.al. [23] found out that average OLP as 15.14 ± 3.15 cmH₂O in their study on 21 cases where appropriate LMA selection is done by tongue size and concluded that OLP is lower in case group with selection by tongue size than the case group with selection by body weight. Weng et.al. [8] could not find a statistically significant result in terms of OLP between their groups in their study on 80 cases in which appropriate LMA size selection decided by thyromental distance and body weight. Also in our study no statistically significant difference is found between the groups in terms of OLP values of cases. However, the study by Keller et.al. where LMA compared for different head and neck positions showed that OLP can differ with respect to head and neck positions [24]. In our study, it is conceivable that one of the constraints in our study was no data have been obtained for head and neck positions.

In our study, when number of trials for LMA insertion is evaluated, it is found that there is significant difference in number of average trials between groups. Results of our study makes us think that LMA size selection by ear size method may result in faster successful LMA insertion with a smaller number of trials than selection methods used in other groups. Similar to our study, Zahoor et.al. [17] found out that LMA selected by ear size was successfully placed in 93.3% of cases on first trial, in 6.7% of case after second trial in their study on 210 pediatric cases. Haliloğlu et.al. [21] found out that LMA selected by ear size was successfully placed in 93.9% of cases on first trial, in 6.1% of case after second trial in their study on 197 pediatric cases. LMA selected by tongue size was successfully placed in 90% of cases on first trial in Huang et.al.’s study on 21 cases. Weng et.al. [8] obtained similar LMA insertion success rate results in first trial for selection by thyromental distance and selection by body weight in their LMA selection study on 80 cases. Cook et.al. [25] also reported that rate of successful LMA insertion in first trial changes between 76–100% in their review study on 28 research studies [26]. Whereas in our study it is found out that apart from Group ear (93.9%), rate of successful LMA insertion in first trial was low for other groups; for Group Weight – 77.1%, for Group Tongue – 73%, for Group Finger – 61.8% and for Group Thyromental – 71.0%. Eschertzhuber et.al. [27] found out that insertion success frequency is higher with guided tool (GEB) technique than other techniques in their study on 19–68 years of age female cases where three LMA insertion techniques (standard technique, introducer tool technique, gum elastic bougie (GEB) tool technique) is used in difficult intubation scenarios created by cervical collar usage. First insertion success rate is found to be 100% for insertion with guided tool whereas 64% with standard technique and 61%. In our study it is identified that LMA insertion was done with standard technique in all cases. This might have affected first trial success rates for all groups.

In our study statistically significant difference acquired in LMA insertion scores between Group Ear and Group Weight, Group Tongue, Group Finger, Group Thyromental. It is found out that LMA insertion is easier in Group Ear than other groups. Janakiraman et.al. [28] in one of their studies with LMA, graded insertion easiness by “easy-moderate-hard” and reported 80% insertion success rate for classic LMA as “easy”. In their study Alexiev et.al. [29] reported maneuver requirement for classic LMA as 4%. Whereas in our study these values are obtained only for Group Ear and it is found that in 78.8% of cases in Group Ear LMA was inserted easily. In other groups additional maneuver requirement found to be higher than Group Ear at statistically significant level. In the study of Weng et.al. [8], where LMA selection carried out on 80 cases, they concluded that LMA insertion is easier for LMA selection according to thyromental distance than LMA selection according to body weight, in 9 cases with LMA selected according to body weight required additional maneuver, whereas LMA selected according to thyromental distance required no additional maneuver. Also in our study insertion was more successful in Group Thyromental than Group Weight, and it is found out that in 50% of Group Thyromental and in 43.1% of Group Weight LMA was inserted easily without requiring additional maneuver. Nevertheless, when all groups are evaluated except for Group Ear in all groups rate of LMA insertion without any additional maneuver found to be very lower than previous studies. In our study LMA was inserted in all groups by standard technique with partially deflated cuff. This technique may have affected our success rates. Inflating the cuff slightly may be beneficial in some cases [30]. In our study, when LMA sizes preferred for all cases are evaluated, it is found that there is statistically significant difference between Group Weight and Group Ear, Group Tongue, Group Finger, and between Group Thyromental and Group Ear, Group Tongue, Group Finger. Zahoor et.al. [17] in a study they conducted on 210 pediatric cases where LMA selection was according to ear size, concluded that LMA size decided according to the ear size were smaller than LMA size suitable for body weight. Also in our study LMA sizes chosen in Group Ear found to be significantly smaller than sizes chosen for Group Weight cases. Huang et.al. [23] found out that LMA sizes selected according to tongue width were smaller than LMA sizes selected according to body weight in their LMA selection according to tongue width study on 21 cases. Gallart et.al. [31] concluded that in 78% of cases LMA sizes according to finger width were the same with LMA sizes according to body weight, whereas in 22% of cases LMA sizes according to body weight were bigger than LMA sizes according to finger width in their LMA size selection study on 183 pediatric cases. Also in our study it is found out that LMA sizes chosen in Group Weight were bigger than LMA size according to Group Tongue and Group Finger cases at statistically significant level. Weng et.al. [8] found out that in cases which LMA size chosen according to thyromental distance no.4 size and no.3 size were used mostly, in cases which LMA size chosen according to body weight no.4 size and no.5 size were used mostly in their LMA selection study on 80 cases. We can indicate in our study that as shown in previous studies biggest LMA sizes were preferred in Group Weight and Group Thyromental.

Incidence rate of laryngopharyngeal complaints can be between 0–50% as reported in various studies [32]. Chauhan et.al. [33] emphasized that multiple insertions during placement and pressure exerted by cuff on pharyngeal mucosa were held responsible for postoperative complications. Throat pain is seen almost in all LMA studies on laryngopharyngeal morbidity evaluations, with incidence rates ranging between 0–43%, as a symptom [34]. Grady et.al. [35] found relation between large size LMA usage and increased throat pain in their study on importance of LMA size number in less than 2 hours daily 258 ASA 1–3 cases, but no difference found out between the cases in terms of nausea, vomiting, dysphagia, blood stain. Researchers showed trauma during LMA insertion and pressure exerted by large cuff on pharyngeal mucosa as causes of high airway morbidity [36, 37]. Also in our study the difference between the groups in terms of postoperative throat pain found as statistically significant. Statistically significant difference detected between Group Ear and Group Weight, Group Thyromental, and between Group Tongue and Group Thyromental. Higher occurrence of throat pain in Group Weight and Group Thyromental was an expected result since most of the LMA sizes selected in Group Weight and Group Thyromental was bigger than LMA sizes chosen in other groups. Moreover, in Group Thyromental and Group Weight required additional maneuvers may led to the increase in incidence rates of throat pain in our studies. We think that the reason behind the significantly lower throat pain in Group Ear is the smaller LMA sizes chosen with respect to other groups, and increased rate of proper LMA insertion at first trial decreased the incidence rate of complications.

Weng et.al. [8] found out that there was blood stain on LMA after removal in 20% of cases with LMA selection by thyromental distance and 10% of cases with LMA selection by body weight, and they concluded that also throat pain incidence rate is significantly higher in selection by thyromental distance than selection by body weight in their LMA selection study on 80 cases. No difference had been found between group with LMA selection by body weight and group with LMA selection by thyromental distance in terms of other complications. Whereas in our study no significant difference between Group Thyromental and Group Weight in terms of all complications has been found. We think that, for our study, this result between these two groups is due to the similarity between chosen LMA sizes, number of trials for proper LMA insertion and similar additional maneuvers. Bikramjit et.al. [38] detected blood stain on the tool after extubation in two cases at their LMA study on pediatric cases. In the same study parents are questioned for discomfortable complications after postoperative 24th our such as throat pain and change in voice; the researchers found no statistically significant difference between the answers. Also in our study no statistically significant difference detected between the groups in terms of all complications except for throat pain. Ostergaard M et.al. [39] reported that in one case, where anesthesia duration was 2 hours 20 minutes and Classic LMA was used, taste hypesthesia due to one-sided lingual nerve paralysis occurred after 1 week, and it continued at check-up after 6 months. In our study operation times did not exceeded 2 hours for all groups and no statistically significant difference has been found between the groups in terms of average operation duration. We think that another reason for no statistically significant difference for other complications between the groups except for the throat pain is short waiting time of the tools inside the mouth due to short operation durations. In literature, generally, it looks like that increase in the cuff volume increases incidence of postoperative complications [40]. In our study LMA cuffs were inflated such that cuff volume was 60 cmH₂O for all groups, and this gives rise to the thought that this is another reason for no significant difference between the groups in terms of complications.

Our study being not prospective, data obtained from the files being limited, differences between LMA operators and the fact that high body mass index, abnormal airway anatomy, difficult ventilation and intubation, ASA III and IV class cases were excluded constitutes the limitations of our study.

As a result, data obtained in our study shows that proper LMA size estimation by ear size can be an efficient and fast decision method. This method can be an addition to the methods still used and can save operators from remembering formulae and tables for body weight/gender.

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