Anesthesiology, Article

Comparison of 2 cuff inflation methods before insertion of laryngeal mask airway for safe use without cuff manometer in children

Unlabelled imageAmerican Journal of Emergency Medicine (2013) 31, 346-352

Original Contribution

Comparison of 2 cuff inflation methods before insertion of laryngeal mask airway for safe use without cuff manometer in children?

Min-Soo Kim MD a, Sun-Joon Bai MD, PhD a, Jung-Tak Oh MD, PhD b,

Seung-Mok Youm MD a, Jeong-Rim Lee MD, PhD a,?

aDepartment of Anesthesiology and pain medicine, Anesthesia and Pain Research Institute, Yonsei University College of Medicine, 50 Yonsei-ro, Seodaemun-gu, Seoul 120752, Republic of Korea

bDepartment of Pediatric Surgery, Severance Children’s Hospital, Yonsei University College of Medicine, 50 Yonsei-ro, Seodaemun-gu, Seoul 120752, Republic of Korea

Received 9 August 2012; revised 20 August 2012; accepted 22 August 2012

Abstract

Purpose: This prospective, randomized trial was conducted to establish whether the pediatric laryngeal mask airway (LMA) could be used without any concerns for abnormally high intra-cuff pressure when a cuff of the LMA was inflated with half the maximum recommended inflation volume or the resting volume before insertion.

Basic procedures: Eighty children 0 to 9 years of age and weighing of 5 to 30 kg scheduled for general anesthesia were included. Before insertion, the cuff of the LMA was filled with half the maximum recommended inflation volume in the Half volume group, or the resting volume by opening the pilot balloon valve to atmospheric pressure in the Resting volume group. After insertion of the LMA, intra- cuff pressure, Oropharyngeal leak pressure, and leakage volume were investigated.

Major findings: The Half volume group showed lower mean intra-cuff pressure than the Resting volume group (49.6 +- 12.1 cm H2O vs 58.1 +- 13.8 cm H2O, P = .005). There was no difference in oropharyngeal leak pressure (22.1 +- 5.8 vs 21.7 +- 5.1 cm H2O, P = .757) or leakage volume between the Half volume group and the Resting volume group (0.13 +- 0.13 ml/kg vs 0.11 +- 0.12 ml/kg, P = .494) under spontaneous respiration. Conclusions: Both methods of the LMA cuff inflation before insertion provided an acceptable range of intra- cuff pressure with adequate pharyngeal sealing without any intervention after insertion.

(C) 2013

Introduction

The pediatric laryngeal mask airway (LMA) is frequently used for airway management in both the operating room and the

? Presented at the European Society of Anaesthesiology annual meeting, Paris, France, June, 2012.

* Corresponding author. Tel.: +82 2 2227 3840; fax: +82 2 2227 7897.

E-mail address: [email protected] (J.-R. Lee).

emergency setting [1,2]. Recently, the use of the pediatric LMA instead of endotracheal intubation has been attempted in the prehospital setting because it may be associated with ease of training, prompt establishment of adequate ventilation, and fewer complications when inserted by Prehospital providers [1]. Because of difference in the airway anatomy of children compared to adults, clinicians are uncomfortable with insertion and safe maintenance of the pediatric LMA [3]. In this regard, though originally LMA is introduced to be

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inserted with complete cuff depletion, the pediatric LMA is known to be more easily inserted with higher success rate when the cuff is partially inflated beforehand than fully depleted. There are large volume of literatures related to the insertion method with cuff partially inflated, while there is still no recommended standard for how much the cuff should be inflated before insertion [3-6].

Intra-cuff pressure after insertion of the LMA is a major concern in terms of complications and function [7,8]. High intra-cuff pressure can be a cause of several complications such as sore throat, dysphasia, or nerve damage [5,9-11], and the possibility of airway complications related to high intra- cuff pressure is presumably higher in children as a child’s airway is more prone to mucosal damage and swelling than that of an adult [12]. In addition, higher intra-cuff pressure results in poor oropharyngeal sealing with increased leakage around the LMA cuff [8]. For these reasons, inattentive inflation of the cuff before insertion accompanied with indifference of intra-cuff pressure after insertion can cause complications and deteriorate the performance [11-13]. However, several reports demonstrated that intra-cuff pressure is not routinely monitored in many institutions. Emergency providers are no exception; they may have some difficulties in inflating cuff with adequate pressure without routine use of manometer [2,13,14]. In addition, the use of maximum recommended inflation volume or clinical end- points to inflate LMA cuffs can result in significant hyperinflation in most pediatric patients [8,15]. Therefore, it would be extremely useful in the busy clinical setting if the cuff is inflated with a certain standardized and convenient method before insertion and this status can eliminate any need to check or adjust intra-cuff pressure after insertion.

Through a review of relevant literatures and our clinical experience, we hypothesized that half the maximum recommended inflation volume for each size of LMA introduced by the manufacturer or the resting volume of the cuff could simply be used for partial inflation of the cuff before insertion. We hypothesized that if the cuff is inflated with these 2 methods, intra-cuff pressure after insertion would be in a clinically tolerable range [4,6,12,16,17].

The purpose of this prospective, randomized, controlled trial was to confirm that intra-cuff pressure is within clinically acceptable range without adjustment when the

cuff of LMA is inflated with half the maximal inflation volume or the resting volume before insertion in children.

Methods

This study was approved by the Institutional Review Board of Severance Hospital, Yonsei University Health system. Written informed consent was obtained from the guardians of all participants. Eighty children, who were American Society of Anesthesiologists (ASA) Physical Status I or II, aged 0-9 yrs, weighing between 5 and 30 kg, and scheduled for inguinal hernia repair under general sevoflurane anesthesia were prospectively included in this study. Children with abnormal airway anatomy, reactive airway disease, a history of upper respiratory tract infection in the preceding six-week period, or gastroesophageal reflux disease were excluded. All of the children enrolled in this study were randomly assigned to one of 2 groups: the Half volume group and the Resting volume group. The groups were assigned by random numbers generated by an internet site program (http://www.random.org/).

The LMAs used in this study were the LMA-classic (LMATM, The Laryngeal Mask Company Ltd., UK). The LMA size was determined by the manufacturer’s guidelines, which suggested a size 1.5 for 5-10 kg, size 2 for 10-20 kg, and size 2.5 for 20-30 kg. Prior to use of the LMA, the cuff was checked by the attending anesthesiologist for any potential damage. The cuff was then completely deflated. Preparation of the cuff before insertion was performed according to the assigned group conditions. In the Half volume group, the cuff of the LMA was filled with half the maximum inflation volume for each LMA according to the manufacturer’s guidelines (3.5 ml for size 1.5, 5 ml for size 2, 7 ml for size 2.5; Fig. 1A). In the Resting volume group, the pilot balloon valve was connected to a piston-free syringe in order to keep the valve open to the atmosphere and allowing the pressure within the cuff to equalize with atmospheric pressure (Fig. 1B). Before insertion, the syringe was disconnected from the pilot balloon valve, and the cuff was permitted to remain at its resting volume. The LMA was lubricated with saline before insertion.

Fig. 1 Preparation of the Half volume group (A) and the Resting volume group (B) as a simple method for partial inflation of the LMA cuff.

No premedication was provided to any child. Upon arrival at the operating room, the patients were monitored with pulse oximetry, capnography, noninvasive arterial blood pressure, electrocardiography, and assessment of inhaled and exhaled sevoflurane concentrations. Anesthetic induction was achieved with an inhalation technique using 8% sevoflurane in 100% oxygen. After loss of consciousness, intravenous cannulation was performed in all the patients. The concentration of sevoflurane was adjusted to 3-3.5% [18,19], and maintained for several minutes until adequate jaw relaxation was attained for LMA insertion. A neuro- muscular blocking agent was not administered.

The insertion of LMA previously inflated according to the assigned group conditions was achieved using a rotational technique, which was associated with the highest rate of insertion success and the lowest incidence of complications among techniques with the cuff partially inflated [3]. The LMA was inserted with its lumen facing backwards and then rotating through 180? when the resistance of the posterior pharyngeal wall was felt and then passed downwards into position behind larynx by one anesthesiologist who had extensive experience performing more than 100 LMA insertions. Successful insertion was confirmed by observing symmetric movement of the chest wall and the presence of a stable square wave on the capnograph trace during sponta- neous ventilation or gentle squeezing of the reservoir bag. insertion time and ease of insertion were recorded during the LMA insertion. Insertion time was defined as the time from the attending anesthesiologist picking up the LMA until the confirmation on capnography. Ease of insertion was graded from 1 to 4 (1, no resistance; 2, mild resistance; 3, moderate resistance; 4, inability to place the device) [20]. In grade 4 insertions, the airway was managed properly at the discretion of the attending anesthesiologist, and those cases were withdrawn from the study. Manipulation of the LMA such as adjusting the head or neck position, changing the depth of the insertion or repositioning of the pillow was also recorded.

After 5 min from final positioning of the LMA, the intra- cuff pressures were measured using a cuff pressure manometer (Mallinckrodt Medical, Athlone, Ireland). Then, without any modification of the cuff pressure, the oropharyngeal sealing efficacy was investigated by measur- ing the airway leak pressure and leakage volume/fraction. First, the leakage volume was measured using the spirometry sensor of the Primus anesthetic workstation (Drager, Lubeck, Germany); 5 corresponding inspiratory and expiratory tidal volumes during spontaneous and mechanical ventilation at a

10 ml/kg tidal volume were recorded, respectively. The difference between these volumes was defined as the leakage volume. The leakage fraction was defined as the leakage volume divided by the inspiratory tidal volume, and was recorded. After measuring the leakage volume under spontaneous ventilation, mechanical ventilation was achieved through the control of anesthetic depth and leakage volume under mechanical ventilation was measured. Second, airway leak pressure was measured by closing the pop-off

valve of the breathing circuit to 30 cm H2O at a fixed fresh gas flow of 3 l/min and recording the airway pressure at which equilibrium was reached. The airway pressure displayed on the monitor of the anesthesia machine was not allowed to exceed 30 cm H2O for safety reasons. During leak pressure testing, auscultation over the epigastrium with a stethoscope was performed to detect gastric insufflation.

After collecting the data, the intra-cuff pressure was adjusted to below 60 cm H2O if the cuff pressure was more than 60 cm H2O. On the contrary, if the intra-cuff pressure was less than 40 cm H2O, it was adjusted between 40 and 60 cm H2O only when ventilation was inadequate. A caudal block was performed or fentanyl was administered intrave- nously for perioperative analgesia, and anesthesia was maintained with sevoflurane 1.5-2.5% with approximately 50% oxygen in a total inflow of 2 L/min [21,22].

When the operation was finished, the LMA was removed after adequate consciousness and spontaneous respiration were restored. Complications with each method such as bronchospasm, laryngospasm, hypoxia, gastric insufflation during anesthetic maintenance, blood staining from the removal of the LMA, and any injuries to the tongue, lips or teeth were noted. The patient was then transferred to the post anesthesia care unit (PACU), and a registered nurse who did not take part in this study investigated any postoperative complications such as sore throat, dysphagia, or dysphonia. A previous study showed that mean and standard deviation of intra-cuff pressure after LMA insertion in children was 50 cm H2O and 12.9 [23]. Assuming a 5% 2- tailed significance level (? = 0.05) and power of 90% (? = 0.10), a sample size of 35 patients in each group would be required to detect 10 cm H2O between the Half volume group and the Resting volume group. Forty patients in each

group were included to compensate for possible dropout.

We analyzed the data with SPSS version 18 (SPSS Inc, Chicago, IL). Continuous variables were reported as mean +- SD and were analyzed using an independent Student t test. Categorical variables were reported as numbers and percentages, and were analyzed using the chi-square test or Fisher exact test. Ordinal variables were reported as numbers, and were analyzed using the Mann-Whitney t test. P b .05 was considered statistically significant.

Results

Of the 85 patients screened, 80 were enrolled in the present study. Among the enrolled patients, 1 patient was dropped from the Half volume group due to flooding rhinorrhea at induction, and 1 patient was dropped from the Resting volume group due to a change of surgical plan. Finally, 39 patients in the Half volume group and 39 patients in the Resting volume group were included in this study (Fig. 2). Patient characteristics are presented in Table 1 and were not different between the 2 groups.

Fig. 2 CONSORT flow diagram.

The insertion characteristics are shown in Table 2. There was no insertion failure in any patients, although only one patient in the Resting volume group required a second attempt for insertion. The ease of insertion, success on first attempt, and insertion time were not different between the 2 groups. However, manipulation was more frequently required in the Half volume group than that in the Resting volume group (23% vs 3%, P = .007).

The Half volume group had a statistically lower mean intra- cuff pressure than the Resting volume group (49.6 +- 12.1 cm H2O vs 58.1 +- 13.8 cm H2O, P = .005) (Fig. 3). There were also fewer patients with an intra-cuff pressure greater than 60

Table 1 Patient characteristics

Table 2 Insertion data for the Half volume group and the Resting volume group

cm H2O in the Half volume group than in the Resting volume group (18% vs 39%, P = .044). In addition, the maximum value of intra-cuff pressure was 77 cm H2O in the Half volume group and 90 cm H2O in the Resting volume group.

Despite the difference in intra-cuff pressure, the airway leak pressure and the frequency of gastric insufflations did not differ between the 2 groups. The leakage volume was not different between the Half volume group and the Resting volume group during spontaneous ventilation (0.13 +- 0.13 ml/kg vs 0.11 +- 0.12 ml/kg, P = .494), although it was significantly lower in the Resting volume group (0.13 +- 0.24 ml/kg vs 0.41 +- 0.62 ml/kg,

Patients The Half volume The Resting volume group (n = 39) group (n = 39)

Males/Females 25/14 (64/36) 23/16 (59/41) Age (y) 3.6 +- 2.4 3.5 +- 2.4

Weight (kg) 15.6 +- 6.1 15.0 +- 5.5

Height (cm) 98.5 +- 19.6 96.4 +- 19.4

ASA status 1/2 31/8 (80/20) 33/6 (85/15) LMA size 1.5/2/2.5 7/25/7 7/24/8 anesthesia time (min) 64.1 +- 14.1 60.5 +- 11.1

operation time (min) 33.8 +- 13.4 30.4 +- 7.7

Data are given as mean +- SD or number (%).

No differences were observed between the 2 groups.

ASA status, American Society of Anesthesiologists physical status.

The Half volume The Resting volume P

group (n = 39) group (n = 39)

Ease of insertion 34/5/0/0 37/1/1/0 .150 1/2/3/4 ?

Success at first 39 (100) 38 (97) .314 attempt

Insertion time 17.8 +- 3.2 17.5 +- 2.6 .672 (s)

Manipulation 9 (23) 1 (3) .007 necessary

Data are given as mean +- SD (range) or number (%).

* Ease of insertion was graded as 1: no resistance, 2: mild resistance, 3: moderate resistance, 4: inability to place the device.

Fig. 3 The distributions of intra-cuff pressures in both the Half volume group and Resting volume group. The box contains the middle 50% of the data, and the line in the box indicates the median value of the data. The upper edge of the box indicates the 75th percentile of the data set, and the lower edge indicates the 25th percentile. The range of the middle 2 quartiles is known as the inter- quartile range. The ends of the vertical lines indicate the minimum and maximum data values.

P = .013) during mechanical ventilation. The same results were also observed in the comparison of the leakage fraction between the 2 groups (Table 3).

There were no serious complications during the intrao- perative period and emergence with either method. One patient who had an intraoperative laryngospasm in the Half volume group also suffered an airway obstruction during emergence. All spasm and airway obstruction were resolved immediately by the attending anesthesiologist who main- tained adequate ventilation. Blood staining of the LMA on removal occurred in one case in the Resting volume group. postoperative complications such as sore throat, dysphagia, or dysphonia were not observed in any of the patients during recovery in the PACU.

Patients The Half volume The Resting P

group (n = 39) volume group

(n = 39)

Leakage volume (ml/kg)

Spontaneous 0.13 +- 0.13 0.11 +- 0.12 .494

ventilation (0-0.47) (0-0.53)

Mechanical 0.41 +- 0.62 0.13 +- 0.24 .013

ventilation (0-2.32) (0-1.37) Leakage fraction (%)

Spontaneous 2.1 +- 2.2 1.8 +- 2.1 .560

ventilation (0-8) (0-10)

Mechanical 3.7 +- 5.6 1.2 +- 2.2 .011

ventilation (0-20) (0-12)

Data are given as mean +- SD (range).

Discussion

In this study, we evaluated half the maximum recom- mended inflation volume and the resting volume as a standardized cuff inflation method before insertion of a pediatric LMA; half the maximum volume technique guaranteed a safer range of intra-cuff pressure, and the resting volume was beneficial in that less manipulation was required during insertion and better sealing was achieved during mechanical ventilation.

Despite the superiority of insertion ease with the cuff partially inflated [16], routine practice for LMA cuff inflation varies by attending clinicians. How much the cuff has to be inflated before insertion and whether the cuff is inflated or deflated after insertion has rarely been discussed. According to one survey, a number of anesthesiologists use the maximal recommended volume for inflating the cuff of a LMA without checking the intra-cuff pressure after insertion, though the maximal recommended volume can induce high pressure greater than 120 cm H2O [15]. Another technique addressed in the literatures was the use of a clinical end-point, that is, inflating the cuff after insertion until a slight outward shift of the device is noted [8]. However, this method also resulted in a mean cuff pressure of 106.2 +- 19.2 mmHg [24], and the lowest cuff pressure of 92 cm H2O [8]. Thus, the maximum recommended volume or clinical end-point method should not be used as the standard of cuff inflation in LMA, and alternative means of ensuring a safe range of cuff inflation are needed for application in a busy clinical setting.

Several investigations have provided clues as to the adequate amount of volume to inflate the cuff prior to insertion in order to assure reliable cuff pressure after insertion and lessen the need for continuous inspection of cuff pressure. It has been reported that half the maximum recommended volume yielded a significantly higher rate of insertion success than cuff that was fully deflated (97.7% vs 92%) and provided optimal oropharyngeal leak pressure and fiberoptic position in adults [6,16]. Approximately half the maximum recommended volume resulted in intra-cuff pressures around 60 cm H2O on the pressure-volume curves of pediatric laryngeal mask airways [12]. Another study utilized the resting volume, which resulted in a mean intra-cuff pressure of 40 cm H2O after insertion of the Portex LMA with cuff inflated [17]. In children, cuff inflated with the resting volume provided acceptable range of intra-cuff pressure after insertion [23]. Both methods appear to be easy to standardize and apply because half the recommended inflation volume can be recognized through just reading the value printed on the stem of LMA and the resting volume can be obtained through simply connecting a piston-free syringe to the pilot balloon valve of LMA. Therefore, we supposed that in children, half the maximum recommended volume or the resting volume would be sufficient for the partially inflated cuff, which can be used in the absence of a manometer.

Table 3 Leakage volume and fraction of the Half volume group and the Resting volume group

The verification point of priority in this study was to prove that the 2 methods of cuff inflation before insertion can

guarantee a clinically acceptable range of intra-cuff pressure after insertion. According to the study by Maino et al, cuff inflation volume with half the maximum recommended volume was slightly lower than that with the resting volume [15]. In the present study, half the maximum recommended inflation volume resulted in less than 60 cm H2O in more than 80% of children while the resting volume resulted in an average pressure of 60 cm H2O. However, it is questionable if the intra-cuff pressure of 60 to 90 cm H2O noted in 39% patients in the Resting volume group is critically dangerous. Seet et al [7] revealed that tight regulation of the LMA cuff pressure at 44 mmHg reduces postoperative pharyngolar- yngeal adverse events by 70%. In Seet’s study, the intra-cuff pressure of the comparison group was much higher, 114 +- 57 mmHg. In another study of the association between cuff pressure and sore throat in children, a cuff pressure exceeding 100 cm H2O significantly increased the incidence of sore throat and that less than 60 cm H2O mostly prevented sore throat when using a LMA made with silicone (such as LMA classic). However, a cuff pressure of 60-100 cm H2O was not distinctly related with sore throat [25]. Slightly high intra-cuff pressure in itself does not necessarily mean that the pressure on the pharynx is excessively high because there is no proportional relationship between intra-cuff pressure and pressure on the pharynx [26]. In addition, most studies of pharyngeal complications related to the LMA used the maximal recommended volume for cuff inflation or used N2O during anesthetic maintenance, and failed to interpret the intra-cuff pressure [5,9-11,27]. Furthermore, fewer patients in the resting volume group in our study required manipulation during insertion, which may be related to pharyngeal complications. Therefore, it does not seem that a slightly higher intra-cuff pressure by resting volume cuff inflation induces significant morbidity compared with half volume inflation. Because we adjusted the cuff pressure to 60 cm H2O if it was over 60 cm H2O after obtaining the data, the complication results in the present study fail to illustrate the safety of a mildly elevated intra-cuff pressure in the Resting volume group. However, half volume inflation at least guaranteed a safer range of intra-cuff pressure, and resting volume inflation seems to be safer than using the clinical end-point or the maximum volume method.

An additional consideration for choosing the inflation technique is functional differences. The Resting volume group and the Half volume group did not differ in term of oropharyngeal leakage or leak volume during spontaneous respiration. Several studies have already reported that a cuff pressure of 60 cm H2O resulted in better oropharyngeal sealing than higher cuff pressures [8,16]. Under spontaneous ventilation, 40 cm H2O of cuff pressure may be better than 60 cm H2O [13]. The better sealing around the LMA cuff at a lower intra-cuff pressure could be explained by the ability of a soft cuff with lower pressure to mold to the variable contours of the pharyngeal space compared to a stiff cuff with higher pressure [13,16]. In the present study, the mean intra-cuff pressures of the 2 methods were less than 60 cm

H2O, and inflation by half the maximal volume and the resting volume showed comparable sealing efficacy.

There are some limitations and considerations in this study. First, only the LMA-classic was investigated. It may be difficult to generalize the results of this study to other types of LMA or disposable LMAs. Additional studies will be needed to apply these methods to other types of LMA. Second, the number of patients according to the LMA size was not similar, and the size 2 of the LMA was the most common in the both groups. This dissimilarity might be considered a limiting factor in the interpretation of these study results.

In clinical situations without a cuff manometer, such as the prehospital and emergency setting, an acceptable range of intra-cuff pressure with adequate pharyngeal sealing can be guaranteed without needing any adjustment after insertion if the cuff of the pediatric LMA is inflated with half the maximum recommended inflation volume or the resting volume before insertion.

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