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PEDIATRIC ANESTHESIA

The Size 1 ProSeal^TM Laryngeal Mask Airway in Infants: A Randomized, Crossover Investigation with the Classic^TM Laryngeal Mask Airway

Department of Anaesthesia and Intensive Care Therapy, Philipps University Marburg, Germany

Address correspondence and reprint requests to Kai Goldmann, MD, DEAA, Attending Anesthesiologist, Department of Anaesthesia and Intensive Care Therapy, Philipps University Marburg, 35033 Marburg, Germany. Address e-mail to Kaigoldmann1{at}aol.com.

	Abstract

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Many problems with the Classic^TM laryngeal mask airway (CLMA) in infants are believed to be related to its inadequate cuff design. One of the main limitations of the CLMA is that the resulting low-pressure seal can be inadequate for positive pressure ventilation (PPV). The ProSeal^TM LMA (PLMA), a new laryngeal mask airway with a modified cuff, has been shown to form a more effective seal than the CLMA in children. The first infant size PLMA, size 1, became available recently. We studied 30 anesthetized, nonparalyzed infants aged 15 mo (2–30 mo) and weighing 9 kg (5–12 kg). The CLMA and PLMA were inserted in random order into each patient. Airway leak pressure and maximum tidal volume were measured. Ease of insertion, quality of initial airway, and fiberoptic position were also determined. Gastric tube placement was assessed for the PLMA. The mean airway leak pressure in neutral head position (26.7 versus 18.9 cm H₂O), maximum flexion (35.6 versus 28.2 cm H₂O), and the mean maximum tidal volume (312 versus 260 mL) were significantly higher for the PLMA (P < 0.01). Air entered the stomach in eight patients with the CLMA but did not with the PLMA. Gastric tube placement was possible in all but one patient. In three patients, the use of the PLMA led to some degree of clinically relevant compression of the larynx. The size 1 PLMA seems to be a more suitable device for airway maintenance in infants than the same size CLMA. The ability to insert a gastric tube at the same time, and a significantly higher airway leak pressure than with the CLMA, may have important implications for its use for PPV in infants.

	Introduction

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Although the safety and efficacy of the Classic^TM laryngeal mask airway (CLMA) in children has been shown in several large observational studies (1–3), findings suggest that the smaller-sized CLMAs, in particular sizes 1 and 1, are less suitable for airway maintenance under general anesthesia (GA) in small infants (3–5) and that they may even be associated with more frequent complications than with the facemask (FM) and endotracheal tube (ETT) (6,7). Among the most frequently described complications are insertion difficulties, intraoperative dislodgement, poor airway sealing, ventilation difficulties, and airway obstruction secondary to laryngospasm (4–7). Whereas airway obstruction is most often caused by an inadequate level of anesthesia, many other problems are believed to be caused by inadequate cuff design, resulting in a suboptimal pharyngeal position of the mask in a large number of patients (8,9). An explanation might be that the pediatric size CLMAs are simply scaled-down versions of the adult sizes, and therefore, they do not match the pediatric airway anatomy as well as the adult sizes match the adult airway. As a consequence, less effective sealing, indicated by a lower leak airway pressure (P_leak), occurs in smaller children but not in older children and adults (10,11).

The low-pressure seal of the CLMA has always been one of the main limitations of its use in both adult and pediatric patients; however, because of the comparatively lower P_leak, this is particularly relevant in infants. One of the main concerns is that the low-pressure seal may be inadequate for positive pressure ventilation (PPV), resulting in a risk of gas leakage into the stomach with the subsequent risk of gastric distension and regurgitation. This could put the patient at risk of pulmonary aspiration.

The sizes 2 and 2 ProSeal^TM LMA (PLMA) (LMA North America, Inc., San Diego, California), a new LMA with a modified cuff and an esophageal drainage tube (DT), were shown to form a more effective seal, indicated by a higher P_leak, and allow a larger tidal volume (TV) than the CLMA, as well as enable gastric tube (g-tube) placement in children (12,13). The size 1 PLMA recently became available (Fig. 1). This randomized crossover study was designed to test the hypothesis that, in anesthetized infants, the size 1 PLMA forms a more effective seal and allows a larger TV than the same size CLMA and also facilitates g-tube placement.

View larger version (74K): [in this window] [in a new window]   Figure 1. Size 1 ProSealTM Laryngeal Mask Airway (PLMA) (ventral view [top] and dorsal view [bottom]).

	Methods

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After obtaining approval from the local ethics committee and written parental consent, 30 patients (ASA physical status I and II) scheduled for elective genitourinary, general, or orthopedic surgery were studied. Patients were excluded if their ASA physical status was more than II, were at risk of aspiration, or had a potentially difficult airway.

Infants younger than 6 mo were not premedicated; patients older than 6 mo were premedicated orally with 0.4–0.5 mg/kg of midazolam, and EMLA^TM cream (Astra Zeneca, Wilmington, Delaware) was applied to the back of both hands 30 min before the induction of anesthesia. Standard monitoring consisted of a precordial stethoscope, a temperature probe, an automated arterial blood pressure monitor, electrocardiography, pulse oximetry, and capnography. GA was induced by inhalation of 8% sevoflurane in 66% N₂O with oxygen in most patients (n = 18). After IV access was established, the level of anesthesia was deepened by an injection of 20–30 µg/kg of alfentanil followed by 2–3 mg/kg of propofol. GA was induced IV with 20–30 µg/kg of alfentanil followed by 4–5 mg/kg of propofol in older patients and patients in whom an IV line was in place before surgery (n = 12). Anesthesia maintenance was with 0.15–0.20 mg · kg^–1 · min^–1 of propofol and additional boluses of 20 µg/kg of alfentanil if required. No neuromuscular blocking drugs were used.

After cessation of spontaneous ventilation, the lungs of the patients were ventilated manually via a FM until a sufficient depth of anesthesia was reached, as indicated by a heart rate 20% less than the baseline value. The first LMA was then positioned, and measurements were made. After completion of measurements with the first mask, it was removed; the second mask was then positioned, and the same measurements made. The order of mask insertion in each patient was randomized by a departmental study nurse before commencement of the trial. The information on the order was kept in a sealed envelope opened before the induction of anesthesia by a study nurse not involved in the investigation. The envelopes were numbered from 1 to 30. Both types of mask were positioned using the standard technique recommended by Dr. Brain in Brimacombe et al. (14). The breathing tube was connected to the circle system of an anesthesia machine (Primus®; Draeger, Luebeck, Germany) and manual ventilation started after inflation of the cuff to an intracuff pressure (P_intracuff) of 60 cm H₂O (VBM Cuff Pressure Gauge; VBM Medizintechnik, Sulz a.N., Germany). Auscultation of the epigastrium and larynx was performed before the device was taped, as recommended by Dr. Brain in Brimacombe et al. (14). The head of the child was then placed in the neutral position, without a pillow to avoid any flexion of the neck. During the initial study period, the lungs were ventilated manually; once the measurements had been completed, pressure-controlled ventilation was used to ventilate the lungs throughout the procedure in most patients.

The total doses of propofol and alfentanil given throughout the period of measurement were recorded. The number of attempts to position each mask was recorded. A maximum of two attempts was allowed for each device. Removal of the mask from the mouth was considered a failed attempt. Ease of placement was recorded from 0 to 10 on a visual analog scale, with 0 indicating placement with one movement without interruption and no resistance felt and 10 indicating that placement was not possible. The quality of the initial airway was assessed during manual ventilation, with the pop-off valve set to limit peak airway pressure (PIP) to 20 cm H₂O. The initial airway was judged as follows: excellent = no audible leak; good = an audible leak with relevant loss of air but sufficient ventilation, as indicated by a PETCO₂ <40 mm Hg; and poor = clinically relevant loss of air and insufficient ventilation, requiring repositioning or replacement of the device. Air entry into the stomach and abnormal airway sounds over the larynx were noted by auscultation. After placement of the PLMA, a DT test, as described in the PLMA instruction manual (15), was conducted to confirm correct position of the distal end of the DT at the proximal end of the esophagus. A small amount of lubricant jelly was used to close the proximal end of the DT. A slight up and down movement of the lubricant bolus was judged a positive DT test, ejection of the lubricant bolus was judged a negative DT test, and no clear movement of the lubricant bolus was judged an inconclusive DT test. After confirming an adequate level of anesthesia again, the maximum TV and the P_leak were measured in three different head positions. The P_intracuff was checked before starting the measurements. If required, it was adjusted to 60 cm H₂O. Maximum TV was determined by squeezing the anesthesia circuit bag until an audible leak was noted in the mouth of the patient; the largest expired TV of three breaths, as indicated by the anesthesia machine, was recorded. P_leak was measured after the fresh gas flow was set to 3 L/min and the expiration valve closed (10). The airway pressure at which an audible leak in the mouth of the patient occurred was recorded as the P_leak. The expiration valve was opened if the P_leak reached 40 cm H₂O without an audible leak. The P_leak value on the monitor of the anesthesia machine was not visible to the observer of the audible leak. The order of the head position was neutral, maximum flexion, then maximum extension. The lungs of the child were manually ventilated between the consecutive measurements. Fiberoptic examination of the position of the LMA was performed thereafter (2.8-mm flexible endoscope; Karl Storz, Tuttlingen, Germany). The position of the LMA was graded in accordance with the fiberoptic scoring system described previously (16). When the PLMA was positioned first, a 10F gauge g-tube was then introduced and correct placement confirmed by auscultation of the epigastrium during injection of a small amount of air. Gastric fluid was aspirated using a syringe and the amount of fluid noted. The PLMA and g-tube were removed, and the same measurements were made for the CLMA, which was left in place for the rest of the procedure. When the PLMA was positioned second, the g-tube remained in place until surgery was over. It was removed under suction before the PLMA was removed once the child was fully awake. Both masks were inspected after removal for signs of blood. Any adverse events, apparent oropharyngeal injuries, or problems with the devices were documented. The patient was examined between 6 and 8 h after the end of the anesthetic.

The primary variable was P_leak. The mean P_leak values for different size CLMAs vary in the literature depending on the study population, size of the LMA, P_intracuff of the LMA, and fresh gas flow used during measurements (5,10,17). P_leak values for the size 1 PLMA have not been previously reported. Calculation of the required sample size was based on the finding of Gursoy et al.'s study (17). A 20% higher P_leak for the PLMA was considered to be clinically relevant; a sample size of 22 patients was therefore calculated to detect a projected difference of 20% between the groups with respect to P_leak for a type I error of 0.05 and a power of 0.9. Allowing for possible dropouts caused by and inability to position one of the masks in two attempts, we chose to examine 30 patients. The results were analyzed using the SPSS (SPSS Inc., Chicago, Illinois) computer program. Unless otherwise stated, data are expressed as mean ± sd (95% confidence intervals) or median values (range). The distribution of data was determined using Kolmogorov-Smirnov analyses. Statistical analysis was performed using the paired t-test, Wilcoxon test, and McNemar test. Results were considered statistically significant if the P value was <0.05.

	Results

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The study sample consisted of 26 male and 4 female patients (25 infants aged 12 mo (2–26 mo) and 5 former premature infants aged 29 mo (26–30 mo). Demographic and anesthetic data are presented in Table 1. No patients were excluded from the analysis.

All airway devices were positioned within two attempts (Table 2). Ease of insertion was similar for both devices; the initial quality of the airway was significantly better for the PLMA (P = 0.001); the PLMA had to be repositioned in one patient and the CLMA in seven patients because of a poor airway seal (Table 2). No LMAs had to be exchanged for ETTs. The size 1 PLMA was too large for two patients weighing 5.5 and 6 kg (bite block of mask 1 cm outside the mouth), respectively. Because the airway was patent and the P_leak sufficient enough for PPV, it was decided to leave the masks in place for the entire anesthetic session; however, in one of these patients, g-tube placement was not possible, even with three attempts. Air entry into the stomach was detected by auscultation in eight patients with the CLMA but not in any patients with the PLMA (P = 0.005). The PLMA DT test was positive in 21 patients and inconclusive in 9 patients. The maximum TV (P = 0.003) and P_leak in the neutral position (P < 0.001) and maximum flexion (P < 0.001) were significantly higher for the PLMA. The P_leak with maximum extension was also higher for the PLMA, but the difference was not significant (Table 3). Vocal cord visibility was significantly better for the PLMA (P = 0.012) (Table 4). Fiberoptic inspection revealed some degree of laryngeal compression, i.e., narrowing of the airway by supraglottic soft tissue bulging into the larynx and thereby obstructing the direct view onto the vocal cords, with the PLMA in five patients and with the CLMA in one patient, despite limiting the P_intracuff to 60 cm H₂O. In three patients, this resulted in a smaller maximum TV with the PLMA than with the CLMA. A g-tube was introduced without any difficulty in 29 patients at the first attempt. Gastric fluid was aspirated in 11 patients (volume, 2–14 mL). A trace of blood was seen after removal of the CLMA in two patients.

Adverse events were recorded in three patients during the anesthetic. One patient (PLMA in place) developed a degree of airway obstruction, indicated by an expiratory airway noise with an accompanying increase in end-tidal CO₂. The noise resolved, and the TV returned to normal, after a bolus injection of propofol and alfentanil, indicating an inadequate level of anesthesia as the underlying reason. One patient (CLMA in place, P_leak = 17 cm H₂O) had presented with a runny nose and a low preoperative (96% in room air) peripheral oxygen saturation (Spo₂) and began to wheeze during surgery. It was not possible to achieve normal ventilation, indicated by an increased end-tidal CO₂ (47–55 mm Hg), despite adjustment of the ventilator settings. It is most likely that this patient had a respiratory tract infection. Another child developed a clinically relevant opioid-induced respiratory insufficiency after a bolus injection of alfentanil during the induction procedure, resulting in a sudden increase in airway pressure and decrease in TV during FM ventilation. The Spo₂ decreased to a minimum of 87%, and the end-tidal CO₂ increased to a maximum of 62 mm Hg caused by the inability to ventilate the lungs of this patient adequately. Both variables were restored to normal within 15 min, and it was possible to take all measurements after this; however, the patient's lungs were ventilated manually until spontaneous ventilation resumed because controlled ventilation with an adequate TV (8–10 mL/kg) remained difficult, and the planned procedure lasted only 30 min. All cases continued without any further adverse events. All patients had an uneventful postoperative course.

	Discussion

Top Abstract Introduction Methods Results Discussion References

 
The PLMA has been shown to form a more effective seal than the CLMA and to facilitate g-tube placement in adults (18) and children (12,13). The results of this investigation indicate that this is also true for the size 1 PLMA in infants. We found that the P_leak for the size 1 PLMA was significantly higher than that of the CLMA in the neutral position and with maximum flexion of the neck. This, as well as the fact that the P_leak at maximum flexion was significantly higher and significantly lower at maximum extension than in the neutral position for both types of mask, agrees with our findings in larger children (12,13).

The PLMA can lead to some degree of upper airway obstruction (13,19,20). For this reason, we also determined the maximum TV to determine whether an increased P_leak is associated with a larger TV or might be associated with a reduced TV in some patients. Our results indicate that a higher P_leak actually allows a larger TV in most patients; however, in three of five patients, fiberoptically confirmed compression of the larynx during use of the PLMA led to a reduced maximum TV compared with the CLMA. This confirms our findings in older children (13) and, in our view, indicates that the PLMA might be a more invasive airway device than the CLMA. Anesthesiologists should be alerted to the potential of clinically relevant upper airway obstruction during use of the PLMA in infants, because this might require exchange of the PLMA for the CLMA or an ETT (in patients that are likely to require high PIP for PPV) before starting the surgical procedure.

The low-pressure seal of the CLMA has always been one of the main limitations of its use for PPV in both adult and pediatric patients. However, because of the comparatively lower P_leak (10,11), this limitation is particularly relevant to pediatric patients. An increased P_leak permits higher PIP during PPV. Therefore, the PLMA may be a better choice than the CLMA in pediatric patients requiring PPV, a mode of ventilation that is increasingly being used with the CLMA in children (17,21). Although our study was performed in infants without pulmonary disease, this might be particularly valuable in patients with low-lung compliance or high airway resistance requiring high PIP, such as patients with bronchopulmonary dysplasia or reactive airway disease. It has been clearly shown that these patients can benefit from the use of LMA, because supraglottic airway devices can be less irritating to the upper and lower airway than the ETT (22).

A further reason for using the PLMA relates to its ability to separate the respiratory and alimentary tracts. Gastric insufflation and the subsequent risk of aspiration with the CLMA is one of the main concerns when using it for PPV (23,24). Air entry into the stomach was not evident in any patient in our study on auscultation of the epigastrium after placement of the PLMA and during P_leak measurement but was detected in eight cases with the CLMA. These findings at the beginning of the GA, and our ability in all but one patient to place a g-tube in the stomach through the DT of the PLMA at the first attempt, suggest that the PLMA might provide a degree of protection against aspiration both by avoidance of gastric insufflation and by offering the possibility of emptying the stomach. This belief is supported by a cadaveric study (25) and clinical evidence from a number of case reports (26–29), where pulmonary aspiration of regurgitated gastric fluid under GA was prevented when the PLMA was used in adult and pediatric patients.

In contrast to studies in adult patients, we did not find that placement of the mask was more difficult or that positioning, as viewed fiberoptically, was worse for the PLMA than the CLMA. In fact, the incidence of an obstructed view of the larynx was less frequent with the PLMA. Brimacombe and Keller (18) speculated that the larger cuff of the PLMA is responsible for difficulties in placement and a higher likelihood of epiglottic downfolding. However, the design of the size 1 PLMA is not just a scaled-down version of the adult PLMA; it does not contain a large dorsal cuff so that the device is less bulky than the adult version. This might explain why placement of the PLMA was as easy as the CLMA and the fiberoptic view of the larynx was slightly better than with the CLMA. Another explanation might be that the authors have benefited from using the PLMA in children for more than three years, whereas Brimacombe and Keller (18) conducted their study in adults when the PLMA had just been released.

Some findings suggest that the smaller sized CLMAs, in particular sizes 1 and 1, might be less suitable for airway maintenance under GA in small infants (3–5) and might even be associated with more frequent complications than with the FM and ETT (6,7). The results of this investigation and our clinical experience do not support these findings. None of the adverse events reported was related to the device itself. We did not find frequent complications believed to be related to inadequate cuff design of the pediatric size CLMAs, such as placement difficulties, incorrect anatomical position, or intraoperative dislodgement. Here, in our opinion, the difference in the design of PLMA offers a further advantage over the CLMA. The DT, running parallel to the breathing tube, and the bite block help to stabilize the mask, whereas with the CLMA, particularly in children, there is the risk of mask rotation around the axis of the breathing tube, which can lead to an incorrect anatomical position or dislodgement of the LMA. However, because the use of the PLMA and CLMA was not compared with the use of the FM or ETT, no conclusion with respect to the incidence of airway-related adverse events in comparison to the FM or the ETT can be drawn.

According to the manufacturer's recommendations, the size 1 PLMA can be used in children weighing 5–10 kg; a size 1 PLMA is not available. Although the size 1 provided a patent airway in all of our patients weighing 5–6 kg, our results indicate that the size 1 might be too large for very small infants, indicating that a smaller size PLMA is required for neonates. Our results did, however, show that the size 1 PLMA can be used in older patients weighing more than 10 kg. The recommendations for size selection for the PLMA do not seem to be evidence based, but rather the same as for the CLMA; further research into this aspect of PLMA use, particularly in infants and children, seems desirable.

The main limitations of our investigation are the small number of patients studied, the lack of comorbid disease, and the role of PPV. We are unable to draw any conclusions about the feasibility of the PLMA for specific subgroups of patients or the safety of this device for PPV with respect to the risk of regurgitation and pulmonary aspiration. However, 21 patients were ventilated using pressure-controlled ventilation without any critical incidents or the need of exchanging the mask for an ETT, neither with the PLMA nor the CLMA. Another limitation of our study is the fact that assessment of initial quality of airway was nonblinded and therefore seems to be rather subjective.

In conclusion, we showed that the size 1 PLMA offers advantages over the same sized CLMA in this crossover investigation. We believe that this could have important implications for the management of infants undergoing GA if our findings are confirmed by others. The high reliability of g-tube placement and the better P_leak make the PLMA an attractive device for airway maintenance under GA in infants, particularly for PPV. The design of the size 1 PLMA seems to match the airway anatomy of infants better than the design of the CLMA, as indicated by the high P_leak, frequent first-placement success rate, frequent correct positioning, and infrequent of intraoperative complications such as dislodgement or inadequate ventilation.

	Footnotes

 
Accepted for publication September 20, 2005.

	References

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