Article

Comparison of 2 cuff inflation methods of laryngeal mask airway Classic for safe use without cuff manometer in adults

a b s t r a c t

Purpose: This single-center, prospective, randomized, double-blind, 2-arm, parallel group comparison trial was performed to establish whether the adult-sized laryngeal mask airway (LMA) Classic (The Laryngeal Mask Company Ltd, Henley-on-Thames, UK) could be used safely without any consideration of cuff hyperinflation when a cuff of the LMA Classic was inflated using half the maximum inflation volume or the resting volume before insertion of device.

Basic procedures: Eighty patients aged 20 to 70 years scheduled for general anesthesia using the LMA Classic were included. Before insertion, the cuff was partially filled with half the maximum inflation volume in the half volume group or the resting volume created by opening the pilot balloon valve to equalize with atmospheric pressure in the resting volume group. Several parameters regarding insertion, intracuff pressure, airway leak pressure, and leakage volume/fraction were collected after LMA insertion.

Major findings: The LMA Classic with a partially inflated cuff was successfully inserted in all enrolled patients. Both groups had the same success rate of 95% at the first insertion attempt. The half volume group had a lower mean intracuff pressure compared with the resting volume group (54.5 +- 16.1 cm H₂O vs 61.8 +- 16.1 cm H₂O; P = .047). There was no difference in airway leak pressure or leakage volume/fraction between the 2 groups under mechanical ventilation.

Conclusions: The partially inflated cuff method using half the maximum recommended inflation volume or the resting volume is feasible with the adult-sized LMA Classic, resulting in a high success rate of insertion and adequate range of intracuff pressures.

Introduction

Since the laryngeal mask airway (LMA) Classic (The Laryngeal Mask Company Ltd, UK) was introduced into clinical practice as the first Supraglottic airway device, it has achieved popularity for airway management in anesthesia as well as emergency situations [1-5]. Recently, the LMA Classic has been used as an alternative to endotracheal intubation in the prehospital setting because its use may more reliably secure the airway by Prehospital personnel when compared with endotracheal intubation [6-8].

Although the LMA Classic was originally intended to be inserted with the cuff completely deflated, numerous previous studies showed the LMA Classic could be more easily placed with a higher success rate when the cuff is partially inflated before insertion [1,5,9]. In particular, this method using a partially inflated cuff may be more useful for occasional users, such as Prehospital providers or

? Financial support/conflict of interest: Nothing to declare.

* Corresponding author. Tel.: +82 41 570 2721; fax: +82 41 573 3559.

E-mail address: [email protected] (K.R. Ahn).

nursing staff [5,9,10]. However, there is still no consensus regarding the amount of air to add in the cuff before insertion despite many studies involving partially inflated cuffs. In addition, high intracuff pressure after LMA Classic insertion due to incorrect cuff inflation can result in several complications such as deterioration of sealing function, nerve injuries, or sore throat [11-13]. In spite of these issues associated with cuff hyperinflation, the intracuff pressure is not routinely monitored with a cuff manometer in many institutions. Emergency care providers may have some difficulties in obtaining an adequate intracuff pressure without the use of cuff manometer [8,12-15]. Hence, it would be very useful in a busy clinical setting if the cuff was partially inflated using a certain amount of air or a standardized inflation method before insertion, and this inflated cuff can resolve the need to monitor or adjust excessive intracuff pressure after insertion.

Through a review of companion articles and our clinical experi- ence, we hypothesized that the half maximum inflation volume determined by the manufacturer according to the size of LMA Classic or the resting volume using equilibrium with atmospheric pressure could be easily applied to inflate the cuff before insertion and ensure a high success rate of insertion with a clinically acceptable range of

intracuff pressure [1,5,9,16-18]. To test our hypothesis, this clinical study was aimed to investigate and compare the efficacy and safety of the half maximum inflation and the resting volume as partial LMA Classic cuff inflation methods.

Methods

Participants

This single-center, prospective, randomized, double-blind, 2- arm, parallel group comparison clinical trial was approved by the Institutional Review Board of Severance Hospital, Yonsei University Health System in Seoul, Republic of Korea (ref: 1-2012-0012). It was also registered in ClinicalTrials.gov (ref: NCT01606956). This study was performed at Severance Hospital, Yonsei University Health System.

Eighty adult patients aged 20 to 70 years who were undergoing elective operations under general anesthesia using the LMA Classic and who provided written informed consent were included in the present study. Patients having abnormal airway anatomy, reactive airway disease, or aspiration risks such as gastroesophageal reflux were excluded from this study.

All patients included in this study were randomly allocated to 1 of 2 groups according to a predetermined allocation sequence: the half volume group and the resting volume group. Patients were unaware of their allocation. The random allocation sequence was created without dividing blocks using a random sequence generator program (http://www.random.org/) and concealed by keeping the paper with this sequence in an opaque-sealed envelope. The envelope was opened to determine the sequence just before the preparation of the LMA Classic.

Intervention

The size of the LMA Classic was selected according to the manufacturer’s guidelines (size 3 for 30-50 kg, size 4 for 50-70 kg, and size 5 for 70-100 kg). Before insertion of the LMA Classic, the cuff was checked and prepared depending on the allocation group by a researcher who was not participating in anesthesia or data collection. In the half volume group, the cuff was deflated completely and then inflated with half the maximum inflation volume (10 mL for size 3, 15 mL for size 4, and 20 mL for size 5) in accordance with the manufacturer’s guidelines (Fig. 1A). In the resting volume group, the valve of the pilot balloon was connected to a syringe without a piston to assure the valve remained open to the atmosphere and to naturally achieve equilibrium between cuff pressure and atmospheric pressure (Fig. 1B). The syringe was removed from the valve of the pilot balloon, and the cuff was maintained in the state of the resting

volume before insertion. A water-based lubricant was applied on the back plate of the prepared LMA Classic before insertion.

Anesthesia and insertion of the LMA Classic

Premedication was not administered to any patients. The position for inserting the LMA Classic was achieved by putting a pillow under the occiput while the patient laid in the supine position. Routine anesthetic monitoring was applied, including electrocardiography, pulse oximetry, noninvasive arterial blood pressure, and capnogra- phy. Induction of anesthesia was established using propofol 2 mg/kg and remifentanil 1 ug/kg. Rocuronium bromide 0.3 mg/kg was administered intravenously as a Neuromuscular blocking agent. The appropriate depth of anesthesia to insert the LMA Classic was judged by confirming no response to jaw thrust. The prepared LMA Classic was inserted by a single anesthesiologist with sufficient experience regarding Supraglottic airway devices. The insertion of the LMA Classic was performed as follows: while holding the distal portion of the airway tube of the LMA Classic, the leading tip of the inflated cuff was inserted into the mouth along the hard palate and then advanced downward and backward with a continuous and smooth push until resistance was apparent. Successful insertion of the LMA Classic was confirmed by observation of chest wall movement and the square wave pattern on the capnograph during manual ventilation. If effective ventilation could not be achieved, the following manipula- tions were performed: gentle adjustment of insertion depth, Chin lift, jaw thrust, or extension/flexion of head position. If insertion failed after 2 attempts, the airway was secured properly in accordance with the attending anesthesiologist’s preference, and these patients were withdrawn from the current study. After confirmation of successful insertion, the lung was mechanically ventilated with a tidal volume of 8 mL/kg, and the respiratory rate was adjusted to maintain an end- tidal carbon dioxide volume of 35 to 40 mm Hg during the operation. General anesthesia was maintained using a 0.7 to 1 minimum alveolar concentration of sevoflurane in a 50% oxygen/air mixture without the use of Nitrous oxide or intravenous administration of remifentanil

0.05 to 0.2 ug/kg per minute. At the end of the surgical procedure, the

attending anesthesiologist removed the LMA Classic when the patient could breathe unassisted and consciousness returned. The patient was then moved to the post anesthesia care unit (PACU).

Measurements

In this study, the primary end point was the intracuff pressure measured after insertion of the LMA Classic, and the secondary end points were insertion parameters, efficacy of the airway sealing, final cuff position determined by fiber-optic view of the vocal cords, and adverse events during anesthesia maintenance and recovery.

Fig. 1. The half volume group (A) and the resting volume group (B) as simple methods for the partially inflated cuff method using the LMA Classic.

The intracuff pressure was assessed using cuff pressure manom- eter (Mallinckrodt Medical, Athlone, Ireland) after final placement of the LMA Classic. Insertion parameters consisted of time and ease of insertion, success rate of first attempt, and manipulations used. These parameters were recorded during the insertion of the LMA Classic. Time of successful insertion was defined as the time from the attending anesthesiologist holding the airway tube of the LMA Classic until the confirmation of an adequate capnograph trace. Ease of insertion was evaluated by an attending anesthesiologist using a 4-point grading scale: 1, no resistance; 2, mild resistance; 3, moderate resistance; 4, inability to place the device [5].

The efficacy of airway sealing was evaluated by determining the airway leak pressure and leakage volume/fraction without any additional adjustment of the initial intracuff pressure. The airway leak pressure was assessed by closing the adjustable pressure- limiting valve of the breathing circle to 30 cm H₂O at a fresh gas flow fixed at 3 L/min and recording the airway pressure displayed on the monitor of the anesthesia machine at the moment when equilibrium of airway pressure was reached. Peak airway pressures were not allowed to exceed 30 cm H₂O to avoid any Possible complications. During measurement of the airway leak pressure, auscultation over the epigastrium using a stethoscope was conducted to confirm gastric insufflation. The leakage volume was obtained from the difference of 5 corresponding inspiratory and expiratory tidal volumes measured by the spirometry sensor of the Primus anesthetic workstation (Drager, Lubeck, Germany) during mechan- ical ventilation at 8 mL/kg tidal volume. To obtain the leakage fraction, the leakage volume was divided by the inspiratory tidal volume. In addition, peak airway pressure during mechanical ventilation was recorded.

The anatomical position of the LMA Classic was investigated by introduction of a fiber-optic bronchoscope (Olympus Optical Co, Tokyo, Japan) through the airway tube of the LMA Classic. Broncho- scopic views of the vocal cord were evaluated using a 4-point grading scale: 1, vocal cords not visible; 2, vocal cord with anterior epiglottis visible; 3, vocal cord with posterior epiglottis visible; 4, only vocal cords visible [19].

Complications including airway obstruction, hypoxia (SpO₂ b 90%) [20], coughing, and gastric insufflation were recorded during anesthesia maintenance and recovery. After removal of the LMA Classic, blood on the device and any injuries of lips, tongue, or teeth were observed. In the PACU, a registered nurse who was indepen- dent of the study reported postoperative pharyngolaryngeal compli- cations such as sore throat, dysphagia, and dysphonia. Twenty-four hours after surgery, a researcher who was not aware of the group allocation underwent a ward visit or telephone interview to investigate the presence of possible postoperative pharyngolaryngeal adverse events.

Statistical analysis

The sample size was calculated based on the primary end point. In a previous study comparing the half volume and the resting volume when using the pediatric LMA Classic, the mean values of the intracuff pressure were 49.6 +- 12.1 cm H₂O and 58.1 +- 13.8 cm H₂O, respectively [5]. Assuming a type I error of 0.05 and a power of 0.9, 35 patients in each group would be needed to detect an intracuff pressure difference of 10 cm H₂O between the 2 groups. Finally, 40 patients in each group participated to secure against patient dropouts and increase the Power of the study.

Statistical analysis of data between the 2 groups was performed with SPSS version 18 (SPSS, Inc, Chicago, IL). Data were presented as mean +- SD (range or 95% confidence interval [CI]), number (percentage), or numbers according to the characteristics of each variable. Comparisons of continuous data were established using 2- tailed Student t test. The comparisons of categorical data were

achieved using ?² or Fisher exact test. In addition, Mann-Whitney U test was used to compare ordinal data. Statistical significance was set as P b .05.

Results

Between June 2012 and July 2013, 80 patients were enrolled without exclusion through screening processes, and all enrolled patients were included without withdrawal in the current study (Fig. 2). Patient characteristics are presented in Table 1.

The half volume group demonstrated statistically lower mean intracuff pressure than the resting volume group (54.5 +- 16.1 [95% CI, 49.4-59.4] vs 61.8 +- 16.1 [95% CI, 56.7-67.0] cm H₂O; P = .047)

(Fig. 3). There were fewer patients with an intracuff pressure greater than 60 cm H₂O in the half volume group compared with the resting volume group (30% vs 57.5%; P = .013). However, the maximum value of intracuff pressure was 90 cm H₂O in the half volume group and 89 cm H₂O in the resting volume group.

The results of insertion parameters and fiber-optic viewing of vocal cord are summarized in Table 2. There were no failed insertions among all enrolled patients, although 2 patients in the half volume group and 2 patients in the resting volume group required a second attempt for successful insertion. There were no differences of insertion time or frequency of manipulation to obtain adequate ventilation between the 2 groups. The most common type of manipulation was withdrawal of the LMA Classic after insertion. Both groups generally had acceptable fiber-optic view scores of 3 or 4. Table 3 demonstrates results regarding the efficacy of airway sealing. The airway leak pressure and the leakage volume/fraction during mechanical ventilation did not differ between the 2 groups

despite the significant differences in intracuff pressure.

No complications were observed during anesthesia maintenance or recovery. Blood staining was observed on the removed LMA Classic in 1 patient in half volume group and 3 patients in the resting volume group. The postoperative pharyngolaryngeal complications are reported in Table 4. During recovery in the PACU and 24 hours after surgery, the incidence of these complications did not differ between the 2 groups.

Discussion

In the current study, we investigated the feasibility of using half the maximum recommended inflation volume and the resting volume as partial cuff inflation methods before insertion of the LMA Classic. Half the maximum inflation volume had a lower range of intracuff pressures than the resting volume, but both methods were comparable in other parameters regarding sealing efficacy and complications.

The adequate volume of air to inflate the cuff before insertion has not been established despite various studies introducing the partial cuff inflation method [1,9,18,21]. The most important reason why the cuff should be inflated using an adequate volume is prevention of cuff hyperinflation after insertion, which is an important cause of postoperative pharyngolaryngeal adverse events and increased leakage around the LMA Classic due to reduction of sealing function [11,12,14]. Seet et al [11] reported that strict regulation of intracuff pressure using a cuff manometer could reduce the incidence of the postoperative pharyngolaryngeal morbidity. In addition, the mean value of the intracuff pressure (114.57 +- 57 mm Hg) was significantly higher in the routine care group that was measured without any interventions after insertion of the LMA Classic by experienced anesthesiologists in that report [11]. Other previous reports have warned that the maximum recommended volume or clinical end point using inflation methods previously used frequently by anesthe- siologists could result in serious cuff hyperinflation if adjustment of intracuff pressure was not performed [12,16,22]. In the study of Keller

Fig. 2. CONSORT flow diagram.

et al [17] about the relationship between inflation volume and intracuff pressure, the best sealing capacity was observed with intracuff pressures of 55 and 88 cm H₂O, and the sealing capacity was decreased with an intracuff pressure greater than 100 cm H₂O. Therefore, there is a need to establish the inflation volumes or methods, which can ensure the proper range of the intracuff pressures without additional need for pressure adjustment or monitoring in emergency situations.

Clues regarding the appropriate inflation volumes or methods before insertion for partially inflated cuff have been provided by several investigations. It has been demonstrated that a partially inflated cuff with half the maximum recommended volume resulted in a significantly higher success rate of insertion compared with a fully deflated cuff [19]. Cuff inflation using half the maximum recom- mended volume after insertion also yielded adequate intracuff pressure, airway leak pressure, and fiber-optic view in adults [9]. In

Table 1

Demographic data of all enrolled patients

Patients	Half volume group (n = 40)	Resting volume group (n = 40)
Males/females	5/35 (12.5/87.5)	8/32 (20/80)
Age (y)	41.8 +- 11.6	40.0 +- 11.6
Weight (kg)	60.2 +- 10.8	57.4 +- 9.8
Height (cm)	158.5 +- 17.7	162.4 +- 7.4
LMA Classic size 3/4/5	6/29/5 (21/70/9)	11/27/2 (27.5/67.5/5)
anesthesia time (min)	55.9 +- 20.7	62.4 +- 22.1
operation time (min)	34.2 +- 17.7	37.3 +- 19.6

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

No differences were observed between the 2 groups.

addition, half the maximum recommended volume produced intra- cuff pressures around approximately 60 cm H₂O on the pressure- volume curves of LMAs in children [12]. With the pediatric LMA Classic, cuff inflation using the resting volume guaranteed a reliable range of the intracuff pressures after insertion [23]. In adult-sized Portex LMA, the resting volume also provided a mean intracuff pressure of 40 cm H₂O with a high success rate of insertion [18]. Both methods are likely to be standardized and easily applied because half

Fig. 3. Mean values of intracuff pressures in the half volume group and the resting volume group. Black circle represents the mean value of intracuff pressure. Error bars represent the 95% CI.

Table 2

Insertion data and fiber-optic view of vocal cord for the half volume group and the resting volume group

Table 4

Postoperative pharyngolaryngeal complications

Patients Half volume group (n = 40) Resting volume group (n = 40)

	Half volume group (n = 40)	Resting volume group (n = 40)	P	Recovery room Sore throat	3 (7.5)	4 (10)
Ease of insertion 1/2/3/4^a	24/14/2/0	24/14/2/0	1.000	Dysphagia	1 (2.5)	2 (5)
Success at first attempt	38 (95)	38 (95)	1.000	Dysphonia	0 (0)	0 (0)
Insertion time (s) (95% CI	21.4 +- 8.1 (15-53)	22.0 +- 10.5 (14-65)	.794	After 24 h
for mean)	(19.2-24.2)	(19.2-25.6)		Sore throat	3 (7.5)	3 (7.5)
Manipulation necessary	5 (12.5)	3 (7.5)	.712	Dysphagia	0 (0)	0 (0)
Fiber-optic view 1/2/3/4^b	0/3/14/23	0/4/9/27	.461	Dysphonia	0 (0)	1 (0)

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

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

^b Fiber-optic view was graded as follows: 1, vocal cords not visible; 2, vocal cord with anterior epiglottis; 3, vocal cord with posterior epiglottis; 4, only vocal cords.

the recommended inflation volume can be identified by dividing the value printed on the airway tube of LMA Classic in half, and the resting volume can be obtained by connecting a piston-free syringe to the pilot balloon valve of LMA Classic. In addition, previous research supported the feasibility of the 2 methods for ensuring adequate intracuff pressures and sealing function with the pediatric LMA Classic [5].

From the results of our study, the ranges of intracuff pressures were less than 90 cm H₂O in both groups, and the intracuff pressures in the resting volume group were significantly higher than those in the half volume group, which was similar to the results of the study using the pediatric LMA Classic [5]. Maino et al

[24] revealed that the resting volume was slightly larger than half the maximum volume in the LMA Classic of the same size. For these reasons, safety should be assessed due to the high intracuff pressures of 60 to 90 cm H₂O, especially in the resting volume group. Wong et al [22] demonstrated that intracuff pressures of 60 to 100 cm H₂O were not clearly associated with sore throat compared with intracuff pressures less than 60 cm H₂O. In a study investigating sealing function and complications of the LMA Supreme at different intracuff pressures of 40, 60, and 80 cm H₂O in adults, the best sealing function was observed at an intracuff pressure of 80 cm H₂O without an increase of complications [25]. The results of our study similarly showed no difference in the incidence of complications between the 2 groups. Therefore, ranges of intracuff pressures including 60 to 90 cmH₂O were considered to be reasonable without requiring pressure adjustment.

The success rate of insertion is a significant parameter for evaluation of devices and insertion methods. Matta et al [9] reported that the success rate of insertion of the LMA Classic with cuff partial inflated (97.7%) was higher than that with the cuff fully deflated (92%), and in 14 patients, the LMA Classic was easily inserted using cuff partially inflated after its insertion failure with the cuff fully

Table 3

Data related to airway sealing and ventilation in the half volume group and the resting group

No differences were observed between the 2 groups.

deflated. In our study, an overall success rate of 100% and a first attempt success rate of 95% were observed in both groups. These favorable outcomes related to the partially inflated cuff may stem from softness and less prominence of the semi-inflated cuff, which allows the LMA to more easily slide over the surface of the tongue [9].

The main concern when applying the partially inflated cuff method is the possibility of pushing the epiglottis backward, causing airway obstruction [9]. In this study, an adequate fiber-optic view was seen in most enrolled patients, and no incidents of airway obstruction were observed during anesthesia maintenance or recovery. Thus, the partially inflated cuff method can be useful to insert the LMA Classic without consideration of airway obstruction.

There are some limitations to the interpretation of our results. First, our study verified the 2 methods using only the LMA Classic. So, it may be difficult to apply the results of our study to other supraglottic airway devices with an inflating cuff. Further studies should be conducted using these methods with other types of supraglottic airway devices. Second, in both groups, the number of female patients was larger than the number of male patients, and a size 4 LMA Classic was most commonly used. Additional evaluation should be conducted using the LMA Classic in other sizes.

We concluded that, in various clinical situations without a cuff manometer, the partially inflated cuff method using half the maximum recommended inflation volume or the resting volume could be feasible with the LMA Classic, resulting in a high success rate of insertion and adequate range of intracuff pressures.

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AJEM

Comparison of 2 cuff inflation methods of laryngeal mask airway Classic for safe use without cuff manometer in adults

a b s t r a c t

Introduction

Methods