Background: This study compared two insertion techniques of ProSeal™ laryngeal mask airway.
Methods: A total of 160 female patients (American Society of Anesthesiologists physical status I or II; age 18–80 yrs) undergoing gynecologic surgery were randomly allocated to the standard or rotational technique groups. In the standard technique group (n = 80), ProSeal™ laryngeal mask airway insertion was performed by a single experienced user using digital manipulation. In the rotational technique group (n = 80), the ProSeal™ laryngeal mask airway was rotated counter clockwise through 90 degrees in the mouth and advanced until the resistance of the hypopharynx was felt, and then straightened out in the hypopharynx (n = 80). The ease of insertion was assessed by the success rate at the first attempt. Heart rate and mean blood pressure were recorded 1 min before and 1 min after insertion. Postoperative complications were noted.
Results: The success rate of insertion at the first attempt was higher for the rotational technique (100% vs. 85%, P < 0.001). The overall success rate, i.e., successful insertion within three attempts, was 94% for the standard technique versus 100% for the rotational technique. There was no significant change in heart rate, but mean blood pressure increased significantly with the standard technique (P = 0.001). The incidence of blood staining (9% vs. 36%, P < 0.001) and sore throat (8% vs. 25%, P = 0.005) was lower with the rotational technique.
Conclusion: The rotational technique is more successful than the standard technique and is associated with less pharyngeal mucosal trauma, as evidenced by a lower incidence of sore throat and mucosal bleeding.
THE ProSeal™ laryngeal mask airway (PLMA; Laryngeal Mask Co. Limited, Mahe, Seychelles) is a relatively new laryngeal mask device with an added dorsal cuff to improve the seal and a drainage tube to prevent aspiration and gastric insufflation. The PLMA is more difficult to insert at first attempt than the classic laryngeal mask airway, with success rates at first attempt varying between 82% and 100%.1–4
Several techniques have been described to improve the insertion success rate; Drolet and Girard5
described the use of a gastric tube, Brimacombe and Keller6
the use of fiberoscopy, Howarth et al.7
the use of a gum elastic bougie, and Garcia-Aguado et al.8
the use of a suction catheter. However, these techniques are only recommended to be used as backup when the digital or introducer tool techniques fail. The main cause of failed insertion is impaction at the back of the mouth,1
and a slight lateral approach has been used if tactile resistance was felt at the back of the mouth.9
We hypothesized that insertion of PLMA with 90-degree rotation would reduce the contact surface between the PLMA and the pharyngeal wall and make it easy to advance the PLMA over the smooth angle against the posterior pharyngeal wall. We compared the success rate and incidence of complications of the standard technique with the rotational technique.
Materials and Methods
This study was approved by the Institutional Review Board of Seoul National University Bundang Hospital, Seongnam, Korea. Written informed consent was obtained. This was a prospective, randomized comparison of the standard insertion technique of PLMA with a rotational insertion technique. A total of 160 female patients (age range 18–80 yr; American Society of Anesthesiologists physical status I–II) who were scheduled to undergo short gynecological procedures with general anesthesia using a PLMA were recruited for the study. Patients were excluded if they had a known or predicted difficult airway, recent sore throat, mouth opening less than 2.5 cm, or were at risk of aspiration (nonfasted or gastroesophageal reflux disease). Patients were allocated to the two insertion techniques by a nurse who was not involved in the study using a block (four patients per block) randomization technique. After randomization was determined using random number generator, the assignments were concealed in opaque envelopes until immediately before induction.
Midazolam 0.04 mg/kg was administered intravenously 15 min before induction. Anesthesia was given with the patient in the supine position, and all techniques were performed in the sniffing position. Anesthesia was induced with a plasma target concentration of propofol of 7 μg/ml and maintained with a plasma target concentration of propofol of 4 μg/ml and 67% nitrous oxide in 33% oxygen. Insertion was performed by a single experienced user (more than 500 uses of standard technique). A size 3 mask was used. Heart rate and mean blood pressure were recorded 1 min before and 1 min after insertion.
The standard technique was performed according to the manufacturer’s instructions.10
The posterior aspect of the deflated mask was coated with a water-based lubricant. The PLMA cuff was fully deflated and held like a pen and inserted while pressing up along the palatopharyngeal curve using the index finger. The PLMA was advanced into the hypopharynx until definite resistance was felt. The introducer tool was not used.
The rotational technique involved the following steps. The PLMA was lubricated on the posterior and both lateral aspects with the same water-based lubricant as in the standard technique group. The PLMA was inserted until the entire cuff was inside the mouth, rotated counter-clockwise through 90 degrees and advanced until the resistance of the hypopharynx was felt, and then straightened out in the hypopharynx.
For both techniques, once the PLMA had been inserted into the hypopharynx, the cuff was inflated with air until an effective airway was established. An effective airway was judged by a square-wave capnograph trace and no audible leak with peak airway pressures of 12 cm H2
O or greater during manual ventilation.4
Oropharyngeal leaks were detected by listening over the mouth. The PLMA was repositioned if air leaked up the drainage tube or if ventilation was ineffective (expired tidal volume less than 8 ml/kg). The following airway maneuvers were allowed: chin lift, jaw thrust, head extension, or flexion of the neck. Drainage tube leaks were detected by placing lubricant over the proximal end of the drain tube. Inspired and expired tidal volume was assessed using a spirometer. The requirement for manipulation during insertion was recorded. The number of insertion attempts was also recorded. If placement failed after three attempts, insertion was recorded as a failure. Insertion time was defined as the time from picking up the device to attaching it to the breathing system after inflation of the cuff. The ease of insertion was assessed by the success rate at the first attempt.
At the end of surgery, the PLMA was removed when protective upper airway reflexes returned. Nurses blind to the method of insertion recorded the presence or absence of blood on the laryngeal masks. When the patients were ready for discharge, the nurses asked them whether they had a sore throat.
The primary aim of the study was to compare the success rate of first attempts. Secondary outcome measures included insertion time, number of airway manipulations, and postoperative complications.
Sample size was determined on the basis of a published study4
in which the success rate for the first attempt at insertion of the PLMA using the standard technique was 82%. Accepting a 17% incremental improvement in success rate (i.e.
, 99% success with the rotational technique), we calculated a minimum sample size of 72 patients was required in each group, assuming a type 1 error (two-tailed) of 0.05 and a power of 0.9. Therefore, 80 patients per group were enrolled to compensate for possible dropouts. Student t
test was used to compare the demographic data and the time for insertion. The number of insertion attempts (success rates), the presence of the blood on the PLMA, and the occurrence of complications were compared using chi-square analysis and Fisher exact test. P
< 0.05 was considered significant.
There were no differences between groups with respect to age, weight, height, Mallampati class, or duration of surgery (table 1
). The success rate of insertion at the first attempt was higher for the rotational technique (100% vs.
< 0.001). The overall success rate of the standard technique was 94%. The standard technique failed in five patients after three attempts, and a single attempt with the rotational technique was successful in these patients. Insertion technique made no difference to insertion time. There was no significant change in heart rate, but mean blood pressure increased significantly with the standard technique (P
= 0.001). The incidence of blood staining (9% vs.
< 0.001) and sore throat (8% vs.
= 0.005) was lower with the rotational technique (table 2
We found that insertion of the PLMA was more successful with the rotational technique. Although both methods of insertion were satisfactory, the 90-degrees rotational technique improved the ease of insertion as assessed by the success rate at the first attempt. Our 85% success rate for the standard technique was similar to those in previous studies.3,4
The main cause of failed insertion is impaction with the back of the mouth.1
The rotational technique is more successful because the lateral edge reduces resistance between the PLMA and the posterior pharyngeal wall. Inserting the PLMA with its lumen rotated makes it easy to advance the PLMA over the smooth angle against the posterior pharyngeal wall. Further evidence of easier insertion with the rotational technique was the ability to insert the PLMA after previous failure to insert with the standard technique in five cases.
A rotational technique involving inserting the mask back-to-front like a Guedel airway and then rotating it 180 degrees as it is pushed into the hypopharynx has been used to improve the ease and success of laryngeal mask airway insertion in children11,12
However, this 180-degree rotational technique results in some residual rotation in the coronal plane in adults13
and did not improve the ease of insertion of PLMAs in children.14
We speculate that the 180-degree rotation of the PLMA in the hypopharynx is difficult because of the large cuff and that the 90-degrees rotational technique is a superior technique compared with the 180-degree rotational technique.
We used size 3 PLMAs, although size 4 masks are the most frequently selected size for female subjects in research and probably also in clinical practice. However, in nonparalyzed patients, a large-size sex-based strategy was associated with a higher incidence of sore throat than a small-size sex-based strategy.15
Moreover, leak pressures are less critical in spontaneously breathing patients. These might have altered the success rate and the incidence of postoperative complications. The leak pressure was assessed at only 12 cm H2
O, and spontaneous ventilation was maintained thereafter. This study may have failed to reveal differences in sealing pressure between the two techniques. This could be clinically relevant in a setting where positive pressure ventilation is used. Further research using the rotational technique for paralyzed patients is required.
A potential advantage of the rotational technique is that finger insertion into the oropharynx is not necessary for the rotational technique. PLMA insertion is more difficult than LMA insertion due to the large cuff,1
which is more difficult to place in the mouth and leaves less room for the index finger. The rotational technique also has the advantage of reducing the incidence of blood staining and sore throat, which may be related to reduced resistance between the lateral edge and the pharyngeal wall. We speculate that the reduction in sore throat is because the lateral edge causes less trauma. There was no significant increase in mean arterial pressure with the rotational technique, compared to a 10% increase with the standard technique (P
Our study has a number of limitations. First, we only studied female patients, so the results might not be applicable to male subjects. Second, we did not assess airway patency with a fiberoptic laryngoscope. However, fiberoptic assessment of position is not performed in the routine clinical setting, and perfect positioning is not necessary for maintaining satisfactory airway function.13
We studied the success rate of obtaining a clear airway, not the correct positioning, and a mask inserted into a suboptimal position is associated with a higher incidence of complications. Third, blinding was not possible for recording insertion time and number of attempts; the insertion technique could not be disguised, a potential source of bias. Fourth, we did not use the insertion tool provided by the manufacturer; however, there are no differences in the success rates and incidence of complications between digital and introducer tool techniques.9
We conclude that the rotational technique is more successful than the standard technique and is associated with less pharyngeal mucosal trauma, as evidenced by a lower incidence of sore throat and mucosal bleeding.
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10. LMA™ Airway Instruction Manual. San Diego, LMA North America, 2005
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© 2009 American Society of Anesthesiologists, Inc.