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From the Department of Anaesthesia, Royal United Hospital, Bath, United Kingdom.
Address correspondence to: Dr. T.M. Cook, Department of Anaesthesia, Royal United Hospital, Combe Park, Bath, BA1 3NG, UK. Phone: +44 1225 825056/7; Fax: +44 1225 825061; E-mail timcook{at}ukgateway.net
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Source: Articles identified through Medline and EMBASE searches using keywords ‘Proseal’, ‘ProSeal’ and ‘PLMA’. Hand searches of these articles and major anesthetic journals from January 1998 to March 2005.
Principal findings: Searches identified 59 randomized controlled trials or clinical studies and 79 other publications. Compared to the cLMA, PLMA insertion takes a few seconds longer. First attempt insertion success for the PLMA is lower, but overall success is equivalent. Airway seal is improved by 50%. The DT enables early diagnosis of mask misplacement, allows gastric drainage, reduces gastric inflation and may vent regurgitated stomach contents. Evidence suggests, but does not prove, that the correctly placed PLMA reduces aspiration risk compared with the cLMA. PLMA use is associated with less coughing and less hemodynamic disturbance than use of a tracheal tube (TT). Comparative trials of the PLMA with other supraglottic airways favour the PLMA. Clinicians have extended the use of the PLMA inside and outside the operating theatre including use for difficult airway management and airway rescue.
Conclusions: The PLMA has similar insertion characteristics and complications to other laryngeal masks. The DT enables rapid diagnosis of misplacement. The PLMA offers significant benefits over both the cLMA and TT in some clinical circumstances. These and clinical experience with the PLMA are discussed.
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This is a pragmatic, descriptive review. Much source material consists of reports of new applications, as small trials or correspondence. The review assumes the reader is familiar with the design and performance of the cLMA.
There are 27 PLMA RCTs and sufficient summed data to compare insertion time, insertion success, and airway seal pressure, with the cLMA. There are insufficient data on other aspects of PLMA performance [risk of aspiration and safety compared to cLMA or tracheal tube (TT)] to analyze quantitatively.
The review is presented in three sections:
I. PLMA design, technical aspects, practicalities of use and performance
Design
Size selection, adjuncts and cost
Practicalities of use
Positioning and use of the DT to diagnose malposition
Performance
Use in children
Complications: actual and potential
II. Comparisons between the PLMA and other airway devices
Comparisons with the cLMA
Comparisons with the TT
Comparisons with other supraglottic airways
III. Clinical experience with the PLMA and use of the PLMA to extend the role of the supraglottic airway
Laparoscopic cholecystectomy
Gynecological laparoscopy
Obese patients
Difficult airway management
Intensive care
Trauma and resuscitation
Other
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). The airway tube is reinforced with similar calibre to an equivalent reinforced/flexible LMA (fLMA). Modifications compared to the cLMA are: 1) larger and deeper bowl with no grille; 2) posterior extension of the mask cuff; 3) drainage tube running parallel to the airway tube and exiting at the mask tip; 4) integral silicone bite block; 5) anterior pocket for seating an introducer or finger during insertion. The bowl lacks the ‘semi rigid shell’ of the cLMA.1
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Separation of the respiratory and gastrointestinal tracts
When the PLMA is positioned correctly, the airway orifice lies over the glottis and the DT tip lies behind the cricoid cartilage at the origin of the esophagus. Airway and DT each form uninterrupted routes from these sites to outside the mouth. This functional separation of the respiratory and gastrointestinal tracts is important in understanding potential advantages of the PLMA over the cLMA and other supraglottic airway devices (SADs). In this regard one might consider the PLMA to act as an ‘artificial larynx’, rather than simply an airway tube.
Size selection, practical aspects, adjuncts and cost
Sizes 3 to 5 were introduced in 2000 and sizes 1
- 2 in 2004. Sizes 1 - 2 have no dorsal cuff.
Device properties and recommendations for use are summarized in Table I. The manufacturer’s recommendations for size selection are identical to the cLMA.2 Two studies in Japanese patients reported identical performance and higher airway seal in males with size 5 (compared to size 4). In females, size 4 produced the best compromise between insertion ease and airway seal.3,4 No data on other size selection in other ethnic groups exist.
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The PLMA is accompanied by a cuff-deflator and insertion tool (Figures 2 and 3). The cuff deflator assists complete deflation and flattening the device tip before insertion to improve insertion success.
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Insertion
DEPTH OF ANESTHESIA
A 40% increase in plasma concentration of propofol (4.3 vs 3.1 µg·mL–1) and a 20% increase in end-tidal sevoflurane (2.8% vs 2.4%) was required for insertion of the PLMA compared to cLMA.6
INSERTION TECHNIQUE
Insertion is recommended with head extended and lower neck flexed, and may be performed with or without an introducer.
Insertion without an introducer is similar to cLMA insertion2 (Figure 4). The index finger is placed in the retaining strap (Figure 1
): this is made easier by lateral compression of the body of the mask to bow the strap outward. The PLMA is pressed against the hard palate and advanced into the hypopharynx until resistance is felt. The finger in the retaining strap is pushed towards the occiput, while the other hand exerts counter-pressure to maintain the ‘sniffing’ position.
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). The distal end locates in the retaining strap and the proximal end in the notch between airway tube and DT. The PLMA then resembles the intubating laryngeal mask airway (ILMA) and insertion technique is very similar,2 except ideal head and neck position is ‘sniffing’ for the PLMA insertion, and ‘neutral’ for the ILMA. The bowl is placed into the mouth, guided against the hard palate and advanced in a smooth arc with the handle, until resistance is encountered (Figure 5). The introducer is then removed, taking care to avoid dental damage.
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INSERTION WITH, OR WITHOUT, THE INTRODUCER AND ALTERNATIVE INSERTION TECHNIQUES
No studies have reported significant differences in insertion success between digital and introducer techniques.10–12
An alternative technique involves placing a gum elastic bougie (GEB) into the esophagus using a laryngoscope and railroading the PLMA DT over this. This technique prevents folding of the mask tip and increases correct placement of the PLMA13 (Figure 6). In 100 paralyzed patients first time insertion success, correct positioning (assessed clinically) and OGT passage were all 100% without evidence of increased complications or airway trauma.14
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AIRWAY MECHANICS
The airway tube of the PLMA is shorter than the cLMA, is wire-reinforced and of similar calibre to the fLMA. The bowl has no grills. Airway resistance is 20% greater than the cLMA and more like the fLMA.17
PASSAGE OF AN OGT
A (lubricated, not refrigerated) OGT can be passed through the DT when indicated (Table I). Slight resistance may be noted as the OGT negotiates the distal end of the DT and passes the UES. Inability to pass an OGT indicates mask misplacement.18
USE OF THE DT TO CONFIRM CORRECT POSITIONING
Gel placed over the exit of the DT enables detection of mask malposition. If the gel is ejected with airway pressure < 20 cm H2O the PLMA is probably misplaced.1 False negatives are minimized by using no more than 5 mm depth of gel or a meniscus of non-toxic liquid soap.
Positioning and use of the DT to diagnose misplacement
PLACEMENT AND MISPLACEMENT OF THE PLMA
When positioned correctly, the PLMA tip lies behind the cricoid cartilage (Figure 7a). There are three important misplacements:
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). ). Ventilation is ineffective, as ventilating gases pass directly out of the DT. ). Ventilation is obstructed, and DT function is compromised.
Identification of correct placement and diagnosis of misplacement is helped by organized placement checks (Table II and III).
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MISPLACEMENTS 2 AND 3
These are reduced by good insertion technique; ensuring full deflation and tip flattening before insertion, inserting fully8 and securing to avoid extrusion.9,21,22
Misplacement of the cLMA also occurs, though the frequency of misplacements of the cLMA is unclear.23 Misplacement impairs function of both cLMA and PLMA. The PLMA DT enables early diagnosis of misplacement: an advantage of the PLMA over the cLMA.
GEL AND ‘SOAP TESTS’ FOR MALPOSITION
One of the main reasons for addition of the DT in Brain’s design of the PLMA was to allow diagnosis of misplacement.1
The PLMA manufacturer advocates gel placed over the DT to diagnose misplacement, but this is unevaluated. Observation of a soapy film may be more sensitive in diagnosing misplacement: large changes in pressure within the DT lead to ballooning or rupture,24 small pressure changes cause bulging or indrawing of the film. If the PLMA tip is in the glottis or is too shallow (misplacements 2 and 3), positive pressure ventilation causes bubble formation. If the PLMA tip is in the glottis, minor movements of airway gases with the cardiac cycle may make the soap-film oscillate.25 Pressure on the chest causes bubble formation due to forced expiration.26
When the PLMA is folded (misplacement 1), the DT is obstructed so pressure changes at the distal end of the DT are not transmitted proximally. This is the basis of the suprasternal notch test.27 Firm tapping on the suprasternal notch is transmitted via the upper esophagus to the DT tip and causes a soapy film to bulge. If the tip has folded over, no bulging is seen. No formal evaluation of these tests is published: their reliability is unknown.18
The tests to identify correct positioning of the PLMA have been organized into an algorithm.18,27 We have modified this in Table II. Of note, adequate depth of anesthesia is essential before attempting insertion in non-paralyzed patients: the jaw must be fully relaxed, as indicated by no response to elevation of the angles of the jaw.28 Malposition may be diagnosed by further checks (Table III).
FURTHER USE OF THE DT OF THE PLMA
The DT has been used for a variety of esophageal tubes and catheters during anesthesia (Doppler probe, esophageal stethoscope, temperature probe). Partial occlusion of the DT with another tube may prevent it from functioning as designed.
Performance details
INSERTION SUCCESS
Overall insertion success, reported in 33 studies and 2,581 PLMA insertions ranged from 90 to 100%: mean 98.4% (Table IV).1,3,4,7,10–12,14,15,17,20,29–50
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).1,3,4,7,10–12,14,15,20,29–33,35–41,43–47,50
AIRWAY SEAL PRESSURE
Average airway seal pressure reported in 24 studies and 2,017 PLMA uses ranges from 23 cm H2O to 32 cm H2O, in 23 studies and is 47 cm H2O in one (Table IV).1,3,4,7,10–12,14,15,29–33,35,37,40,42,44–46,48–50
Several design factors contribute to the improved airway seal of the PLMA compared to the cLMA. The larger, softer wedge-shaped PLMA cuff enables the anterior cuff to adapt to the shape of the pharynx better. Secondly, the deeper PLMA bowl helps push the PLMA forward onto the periglottic tissues. The Hidrain is a prototype of the PLMA, which lacks the posterior cuff. Hidrain seal pressure is 28 cm H2O: between the cLMA and PLMA confirming this effect (unpublished data, T.M. Cook). Using strain gauge microchip sensors over multiple mask sites with PLMA and cLMA confirms that the principal cause of the improved airway seal is the device’s wedge shape with lesser contribution from the posterior cuff.7 The dorsal cuff makes the mask shape almost conical, pushing it towards the periglottic tissues and enabling adaptation to the contours of the hypopharynx. At low inflation pressures the PLMA traps gas pockets between cuff and pharyngeal mucosa, enabling matching of anatomical contours. With increased cuff inflation, gas pockets are displaced and the mask shape is dictated more by the mask structure, and less by the pharyngeal anatomy. Over-inflation may therefore reduce seal pressure: most increase in PLMA seal pressure occurs with the first 10 to 20 mL of cuff inflation.7 Further inflation increases pressure exerted on the mucosa without increasing seal pressure markedly.7
Average seal pressure without air in the cuff was 15, 15 and 18 cm H2O in three studies.7,10,42 General performance and safety of the PLMA without inflation of the cuff has not been evaluated.
USE OF THE DT TO CONFIRM CORRECT POSITION
In 150 patients with conventional PLMA insertion, ease of OGT insertion through the DT correlated with positioning of the airway over the larynx, assessed fibreoptically.20 It was concluded that easy OGT passage indicates correct positioning; difficulty passing an OGT suggests the mask should be repositioned even if ventilation is satisfactory.20
The GEB-guided technique ensures that the PLMA tip is optimally positioned and may be favoured when correct positioning is essential or other insertion techniques fail.14,15
VIEW OF THE GLOTTIS
Sixteen studies report the fibreoptic view of the larynx via the PLMA in 1,407 patients.3,4,10–12,17,20,29,31–34,41,44,50 Different scoring systems used make direct comparisons difficult, but the vocal cords were seen in > 80% of cases in 14 studies, mean 84.7%, (Table V). In contrast to the cLMA and ILMA, no bars or epiglottic elevator impedes the view or instrumentation of the glottis.
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).1,10–12,14,20,31–35,38–40,42,49,50 Higher success rates for OGT passage (up to 100%) are reported when efforts are made to eliminate folding of the mask tip.14–16
Whether the OGT tube should be left in place (to enable further gastric drainage) or removed (to enable the DT to act as a vent and drain) has not been examined, and probably depends on the clinical situation.
STABILITY OF THE PLMA WITH MOVEMENT OF THE HEAD AND NECK
The effect of altering head and neck position on airway seal and position of the PLMA is similar to reports with the cLMA and fLMA.29 Airway seal pressure increased approximately 25% with neck flexion and rotation, and decreased 25% with neck extension. The authors attributed this to differences in pharyngeal volume in these positions. Fibreoptic examination confirmed the airway and DT position did not alter with movement of head and neck. Seal pressure was higher with PLMA than cLMA in all positions.
HEMODYNAMIC RESPONSES TO INSERTION
Previous laryngeal mask studies indicate only minor hemodynamic responses to cLMA insertion with a 0 to 20% increase in heart rate and mean arterial blood pressure.23 Hemodynamic responses to PLMA insertion were similar to those of the cLMA in a randomized comparative trial of 280 patients anesthetized with a standard technique.33 Two non-randomized studies of 335 patients with varying anesthetic techniques reported hemodynamic variables change less than 10%.12,36 An abstract reports hemodynamic response to insertion/removal of the PLMA as significantly less than for tracheal intubation/extubation.47
PLMA use in children
There are limited clinical data on PLMA use in children. PLMA sizes 1- 2 do not have posterior cuffs and performance may differ from larger PLMAs. A lower seal pressure is unlikely to have major clinical implications due to the high compliance of most children’s lungs.
Two studies compared the size 2 PLMA with the cLMA. In 30 children weighing 10 to 21 kg first time insertion was always successful. The PLMA was associated with a higher seal pressure and maximum tidal volume, less gastric inflation and improved laryngeal view compared to the cLMA.51 In another study of 60 children: insertion, airway seal and fibreoptic view were all equivalent.52 OGT passage was successful in all patients in both studies. Type II errors are possible in these small studies.
Complications: actual and potential
1. MUCOSAL INJURY AND SORE THROAT
Mucosal injury, recognized by blood on the PLMA after removal, in 1,235 patients ranged from 3 to 28%: mean 10.2%.1,3,4,14,15,31–33,36–40 (Table VI). The incidence of sore throat after 1,586 PLMA uses ranged from 2 to 49%, mean 18%3,4,12,14,15,31,33,34,36–41,45,47 (Table VI).
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2. AIRWAY PROTECTION, GASTRIC INFLATION, REGURGITATION AND ASPIRATION
Design and performance features of the PLMA are expected to reduce gastric inflation, regurgitation and pulmonary aspiration compared to the cLMA.
In a bench study fluid was injected into a model esophagus: at 15 mL·sec–1 the PLMA prevented aspiration; at 30 mL·sec–1, or with the DT occluded, protection was reduced but better than the cLMA.51
In ten fresh cadavers with a PLMA in place and the DT open, incremental filling of the esophagus did not cause tracheal soiling.53 The PLMA provided better airway protection during ‘regurgitation’ than the cLMA. With the DT occluded the PLMA protected the airway from soiling at pressures up to 68 cm H2O. With the DT open no soiling occurred even with higher pressures. Passive regurgitation generates esophageal pressures < 12 cm H2O, and intragastric pressure is rarely above 34 cm H2O.53
In 103 paralyzed and non-paralyzed anesthetized adults the PLMA DT was filled with methylene blue (representing a pressure of 12 cm H2O) and kept filled throughout anesthesia.54 In 101 patients no soiling of the PLMA bowl was seen. In two patients soiling was attributed to intraoperative movement. It was concluded that a properly positioned PLMA isolates the airway from fluid within the hypopharynx.
If high ventilation pressures are used during PLMA use, gas leakage occurs, but less so than with the cLMA. Gas leaks into the oropharynx in 95% of cases7,12,32,35 similar to the cLMA.7,32 The DT of the PLMA (unlike the cLMA) enables venting of gas leaking to the esophagus, making gastric inflation less likely.
There are 15 reported cases of regurgitation without aspiration with the PLMA36,55–63 In all cases the DT vented liquid or solid gastric contents without airway soiling.
The PLMA should not be regarded as absolutely safe where there is an increased risk of regurgitation or aspiration. Importantly, the drainage tube tip must be positioned correctly for it to work correctly. There are three cases reported of definite aspiration41,64,65 and two of possible aspiration.49,66 Malposition was a recognized cause in one case of aspiration.64
UES PRESSURE AND FUNCTION
It has been suggested that the larger PLMA tip may mechanically open the UES1 contributing to regurgitation.22 The PLMA DT allows fibreoptic inspection of the UES during use. The UES was open in two cases of regurgitation57,59 and during routine use in 3 to 9% of cases (Table V).3,10,29,31,35 The UES should not be visible via a correctly positioned cLMA, but is seen in the mask bowl in 15% of routine cases.67
The effect of PLMA and cLMA on upper and lower esophageal sphincter (LES) performance was studied in awake patients, using topical oropharyngeal local anesthesia.68 Neither device altered sphincter pressures, while both increased deglutination rate. The authors concluded that any PLMA effect on the UES is similar to the cLMA. Whether the results are generalizable to performance during general anesthesia is unclear.
ASPIRATION RISK WITH CLMA AND PLMA COMPARED
Reported evidence suggests the PLMA reduces aspiration risk compared to the cLMA: proof is difficult. Meta-analysis of cLMA use estimates the incidence of clinically detectable regurgitation as 18 in 10,024 and aspiration one in four to 11,000.69 No large series of PLMA use exists to provide comparative data with the cLMA. In an estimated 1,000,000 uses of the PLMA (data on file LMA company) there are three cases of confirmed, and two of possible pulmonary aspiration (incidence one in 200,000–300,000).40,49,64–66 To have an 80% likelihood of detecting a genuine 50% reduction in aspiration with the PLMA would require a trial of 2,600,000 patients.
There is design, laboratory, cadaver and clinical evidence to support the view that the correctly placed PLMA is less likely to cause gastric inflation or allow aspiration than the cLMA. Both devices affect LES and UES similarly: however reduced aspiration risk with the PLMA has not, and probably cannot be, proven.
3. AIRWAY OBSTRUCTION
The PLMA may cause airway obstruction. Three mechanisms are: 1) the PLMA tip (and DT) enter the glottis leading to obstruction or failed ventilation through gas leak; 2) the sides of the PLMA bowl (larger and more pliable than the cLMA) fold inwards with partial or complete glottic occlusion by the device cuff; 3) the PLMA tip behind the larynx compresses the posterior larynx causing arytenoid malfunction or rotation and vocal cords shortening: paradoxical cord movement during spontaneous ventilation and mechanical closure during positive pressure ventilation might be observed. Notably, these problems also occur with the cLMA,23 but the larger size and softer material of the PLMA may increase their frequency.
Several cases of obstruction are reported.21,25,33,70,71 The soap test may help with detection and differential diagnosis.25
Two authors have quantified the frequency of PLMA-associated airway obstruction. Brimacombe reported 19 cases of partial obstruction during 6,321 PLMA uses (0.3%) in paralyzed patients.72
The maximal minute ventilation (MMV) test may be used to detect obstruction:73 during maximal attempted manual ventilation, supraglottic obstruction slows expiration, reduces anesthetic reservoir-bag refilling and limits MMV (independent of ventilation rate). MMV was measured in 317 patients. Fibreoptic examination confirmed supraglottic or glottic obstruction in 15 of 17 cases with MMV < 12 L·min–1. All devices were considered ‘correctly positioned’. The authors report partial obstruction in approximately 5% PLMA uses with removal required in 2%. There are several criticisms: the measurement of MMV appears prone to observer bias; no patients with normal MMV underwent fibreoptic examination; and observer bias might influence interpretation of fibrescopic findings. Obstruction in this study is higher than reported by other authors.
An algorithm for management of airway obstruction with the PLMA has recently been recommended.74
4. ESOPHAGEAL AND GASTRIC INFLATION
There are several reports of esophageal or gastric inflation during PLMA use from one author group.
Intermittent esophageal inflation was reported in two cases: partial glottic obstruction caused sub-atmospheric intrathoracic pressure during inspiration; air was drawn in via the DT during inspiration and expelled during expiration.21 No gastric inflation or complications occurred. Gastric inflation is unlikely without supranormal inspiratory effort. Paralysis, controlled ventilation, or repositioning the PLMA should resolve the problem. Similar effects can occur with the cLMA: without the DT, marked sub-atmospheric pressure may develop leading to risk of pulmonary edema.75 The PLMA DT likely limits negative intrathoracic pressure and therefore protects against further complication.75
Esophageal inflation with gastric inflation occurred during spontaneous ventilation.70 PLMA placement led to arytenoid dysfunction with glottic narrowing and paradoxical motion causing stridor. It is unclear whether LES dysfunction contributed to air advancing to the stomach. The authors suggest the ‘soap test’ to diagnose the problem: soap on the DT will be forcibly indrawn during inspiration. Once detected, OGT passage and controlled ventilation should resolve the problem. The PLMA is designed for use with controlled ventilation (with or without muscle relaxation), and the inventor, responding to these reports, advises use with controlled ventilation in preference to spontaneous ventilation.31,75
Finally, the same authors report esophageal inflation during controlled ventilation with a correctly placed PLMA.22 They concluded that during peak inspiratory pressure rise, the PLMA was distracted from the glottis, enabling leakage of gases via the pyriform fossa to the upper esophagus. The DT failed to vent this gas due to occlusion by the mucosa during inspiration. OGT passage vented the gas without gastric inflation. Seating and securing the PLMA correctly will minimize the likelihood of this problem; OGT passage may prevent or treat it.
The above complications may also occur with the cLMA (and other supraglottic airways). The PLMA DT enables early diagnosis of complications, and in many cases a route to resolve them. The incidence of these complications with other airways is unknown. Ability to diagnose these problems accurately with the PLMA may lead to reporting bias, without comparative data, and it would be wrong to assume these complications arise more (or less) frequently with the PLMA.
II. Comparisons between the PLMA and other airway devices
When considering studies comparing the PLMA with other devices (cLMA, TT and other supraglottic airways) it should be noted that some of these are small and measure multiple outcomes. Where ‘no difference’ is reported between devices this may arise because a study was too small (type II error): particularly when the study was not powered to examine that particular measure.
Comparisons between the PLMA and cLMA
Ten RCTs comparing PLMA and cLMA (1,150 patients, 753 PLMA uses) have been published.1,7,10,11,29–34
INSERTION SUCCESS
In direct comparison studies of 1,436 patients first time PLMA insertion ranged from 81 to 100% with summed success of 616/723 (85%), for the cLMA 89 to 100%, summed 662/713 (93%) (meta-analysis 
2 = 20.66, P < 0.0001),1,7,10,11,29–33 (Table VII).
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2 = 3.16, P 0.076),1,7,10,11,29–33 (Table VII).
PLMA insertion time is longer than the cLMA in three studies10,11,31 and equivalent in one.33 The difference is a few seconds (of negligible clinical importance) in all studies reporting a difference (Table VII).
PLMA insertion difficulty may be caused by the larger, deeper, softer bowl and the non-linear leading edge formed by the DT. A learning curve has not been studied, but it has been suggested the PLMA requires 20 to 30 insertions before achieving competence.11 Most comparisons of cLMA with PLMA involved operators with greater experience with cLMA than PLMA. After training by lecture and manikin, nurses naive to both devices (using digital insertion technique) achieved similar insertion time and success rates with both devices.4 Use of a GEB-guided technique, might increase this further.15
AIRWAY SEAL AND VENTILATION
Nine studies (1,470 adult patients) compare cLMA and PLMA seal pressures.1,7,10,11,29–33 Eight studies (858 comparisons) report significantly higher seal with PLMA than cLMA (Table VII). Results are similar in paralyzed1,7,10,29,32 and non-paralyzed patients.11,30,31,33 Median PLMA and cLMA seal pressures are approximately 30 cm H2O and 20 cm H2O respectively. In 20% of cases PLMA seal exceeds 40 cm H2O.11,30
VIEW OF THE GLOTTIS FROM THE PLMA
Fibreoptic view is equivalent in three1,11,17 and better with the cLMA in six7,10,29–31,33 studies. Differences are generally small with grading not showing statistically significant differences, but direct comparison in crossover trials favours the cLMA. No clinical importance of these differences has been established. Meta-analysis of the ability to see the vocal cords from the mask bowl shows no significant difference between devices (Table VIII).
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Incidence of sore throat in comparative studies is similar to the cLMA,11,31,32 or lower,33 ranging from 5 to 23% compared to 5.8% to 34%23 after cLMA use.
Comparisons between the PLMA and tracheal intubation
There are four reports comparing PLMA use with a TT: one during laparoscopic cholecystectomy,49 two during gynecological laparoscopy48,76 and one comparing hemodynamic changes during airway insertion/removal.47 In each study the PLMA caused less post-extubation coughing (TT 50%, 96%, 86% vs PLMA 0%, 4%, 15% respectively).47–49,76 In two studies the PLMA reduced hemodynamic changes at intubation and extubation.47,48
Comparisons between the PLMA and other SADs
The PLMA has been more thoroughly evaluated, by peer reviewed publication, than other new SADs introduced in the last five years. These include the Laryngeal Tube®, Laryngeal Tube Sonda®, Airway Management Device®, Pharyngeal Airway Xpress® and Cobra Perilaryngeal Airway®. Unlike these devices, many of which have been modified on several occasions since introduction, the PLMA has not. Comparative evaluations are only available with the Laryngeal Tube (LT) and Laryngeal Tube Sonda (LTS).
LT AND LTS
The LT is a reusable, SAD designed for use with controlled and spontaneous ventilation, with a higher airway seal than the cLMA.77
There is only one study comparing the currently available LT and the PLMA during controlled ventilation:44 airway seal and insertion were equivalent. The PLMA required fewer manipulations at insertion and during maintenance, enabled better ventilation and was sited over the glottis more frequently.
LT and PLMA were compared in 70 anesthetized patients breathing spontaneously.36 Insertion success and maneuvers required to maintain a clear airway favoured the PLMA. Spontaneous ventilation was unsuccessful in 37% with LT and 9% with PLMA. Repositioning the device corrected this in all PLMA cases and 46% of LT cases. This study might be criticized as neither device performs optimally during spontaneous ventilation44 and PLMA positioning appeared imperfect.
In a cadaver study pharyngeal mucosal pressures were higher with the LT than the PLMA, most markedly when airway seal pressures exceeded 25 cm H2O.78
The LTS is a modification of the LT with a DT running posterior to the airway tube. One study and three abstracts compare LTS and PLMA in 266 patients.40,45,46,50 Performance of the two devices was equivalent in three studies. Airway seal pressure did not vary between devices but varied between studies from 27 cm H2O45 to 47 cm H2O.45 A cross-over study of 32 patients found markedly different performance: insertion success, required manipulations, airway seal and positioning over the larynx all favouring the PLMA.50 The LTS had to be abandoned in 22% of cases. The explanation for the difference between study results is not clear. Of note the LTS was redesigned in late 2004 and replaced by the LTS II: extrapolation of results from the above studies may not be appropriate.
III. Clinical experience with the PLMA and use of the PLMA to extend the role of the supraglottic airway
Improved ventilation and the likelihood of increased airway protection, have led clinicians to extend the use of the PLMA into areas where SADs are not used routinely. These include during lower and upper abdominal laparoscopy, and open abdominal surgery, surgery in obese patients, those with gastroesophageal reflux, those with difficult airways, and for rescue after failed tracheal intubation. In one report73 the authors stated that 40% of 317 patients managed with a PLMA would previously have been intubated. Cases included hysterectomy, prostatectomy, laparotomy and major colonic resection. PLMA use outside the operating theatre is reported in the intensive care unit (ICU). Describing reports of PLMA use in the following circumstances does not imply endorsement by the authors of this review.
Laparoscopic surgery
Laparoscopic cholecystectomy
Use of a PLMA or TT was compared in 109 patients undergoing laparoscopic cholecystectomy.49 A surgeon blinded to the airway used, observed stomach distension. In non-obese patients [body mass index (BMI) < 30 kg·m–2] both devices provided equivalent ventilation. The PLMA provided smoother emergence (markedly reduced coughing). Four obese patients were crossed over from PLMA to a TT and their data excluded from analysis. Reasons for cross-over were: PLMA insertion failure with desaturation, high airway pressures and rhonchi in the lung fields (possible aspiration), sudden onset of gas leak, and sudden increase in airway pressure. These four cases may represent a learning curve, or may demonstrate genuine superiority of the TT for some obese patients.
Eighty paralyzed, non-obese patients were randomized to controlled ventilation via PLMA or cLMA during laparoscopic cholecystectomy.32 The PLMA required more insertion attempts but achieved higher seal pressures. OGT passage via the PLMA was 100% successful. Ventilation was successful before peritoneal inflation in both groups, but failed in 20% in the cLMA group during pneumoperitoneum. Gastric inflation occurred in three cases with the cLMA and none with the PLMA. The authors considered the PLMA (but not the cLMA) suitable for laparoscopic cholecystectomy.
At least one authority believes SADs should not be used for cholecystectomy because of bile reflux.79 One author reported three cases of regurgitation, without aspiration, after laparoscopic cholecystectomy using a PLMA.60 One possible case of aspiration during laparoscopic cholecystectomy is described above49 and one confirmed case occurred with unrecognized PLMA malposition.64 Whether laparoscopic cholecystectomy increases aspiration risk is not clear.
Although modest benefit has been demonstrated during emergence, unless further advantages are demonstrated, PLMA use during laparoscopic cholecystectomy will remain controversial.80
Gynecological laparoscopy
PLMA and cLMA were compared with tracheal intubation for gynecological laparoscopy in 209 paralyzed patients.48 A PLMA was used in the laryngeal mask group when BMI was > 30 kg·m–2 (17 patients) and a cLMA when BMI < 30 kg·m–2. Hiatus hernia and reflux were not considered contraindications. Ventilation and gastric inflation were equivalent between groups and there were no device failures. Use of a laryngeal mask reduced extubation coughing and sore throat. An accompanying editorial questioned the use of laryngeal masks for laparoscopic surgery.80 However, like a similar UK editorial,81 this focused only on the potential problems of laryngeal mask use, without considering problems of TT use. Up to 65% of cases of aspiration occur around the time of laryngoscopy, and difficult intubation (which is causally associated with multiple complications) occurs in nearly 2% of cases.
Obese patients
Several studies demonstrate clinical utility of the PLMA in this population. Whether the PLMA is safer for obese patients than the cLMA, is unknown: the very large studies required to test this hypothesis do not exist. Design features and performance characteristics make the PLMA intuitively a more appropriate and safer SAD for obese patients, who are at increased risk of gastric distension, regurgitation, low airway compliance and airway difficulties.
PLMA use is reported in patients with raised BMI: up to 47 kg·m–2,49 49 kg·m–2, 48 and 65 kg·m–2.8 Airway seal increased as BMI increased in Brain’s early study.1
In 60 morbidly obese patients (mean BMI 43 kg·m–2, range of 35–60 kg·m–2) undergoing abdominal surgery, a PLMA was inserted after induction without neuromuscular blockade.35 Ventilation without leak was achieved in 95%. Mean airway seal pressure was 32 cm H2O and OGT insertion was 100% successful.
PLMA efficacy was compared to the cLMA (with an OGT placed) in mild/moderately obese patients (BMI mean 33.5 kg·m–2, 97% < 40 kg·m–2).34 Airway cuffs were inflated to 60 cm H2O. Controlled ventilation with 10 cm H2O of positive end-expiratory pressure was applied. If leak fraction was > 15%, intracuff volume was increased (45% in the cLMA group, 13% in the PLMA group). Performance was equivalent, with minimal side effects. Leak fraction, 6%, was comparable to that with a TT. Limitations of the study were that peak airway pressure was generally < 30 cm H2O, up to 10% of PLMAs were probably malpositioned and OGT passage before cLMA use is not routine clinical practice.
Difficult airways
The PLMA has been used as a dedicated airway/conduit to the trachea in patients known (or predicted to be) difficult to intubate, and also for airway rescue after failed intubation. Theoretical advantages over other laryngeal masks include the large bowl and absence of a grille: both might improve laryngeal access. The glottis is visible from both PLMA and cLMA (Table VIII) more frequently than from the ILMA.23 The improved airway seal and DT offer potential benefits where ventilation proves difficult or when the stomach is full. Tracheal intubation via the PLMA requires a small long tube or a catheter exchange technique.82
ELECTIVE CASES OF KNOWN DIFFICULT AIRWAY
There are four reports of use of the PLMA to overcome known airway difficulties.82–85 In three cases the PLMA was used instead of tracheal intubation. In one case the PLMA was placed awake, using topical anesthesia.84
USE OF THE PLMA IN ‘AIRWAY RESCUE’
There are ten reports of PLMA use for airway rescue following failed or difficult intubation (Table IX).
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On six occasions the PLMA secured airway rescue after failed intubation at rapid sequence induction (RSI).90–94 Four were obstetric emergencies91–94 and two non-obstetric.90,91 Three cases were associated with difficult ventilation.90,91 In two cases rescue with a cLMA was attempted but failed before a PLMA was used.90,91 In all cases the PLMA was used uneventfully to completion of the case.
The PLMA has design features and performance evidence that support its use for airway rescue after failed intubation. Failed intubation with difficult ventilation after RSI is a particularly suitable application, as controlled ventilation and ability to drain the stomach are desirable. After successful airway rescue, the decision to continue surgery rather than awakening the patient will depend on clinical circumstance.
A novel approach to difficult RSI is described where the GEB facilitates passage of a TT if the vocal cords are partially visible and passage of a PLMA, as early ‘rescue’, when they are not.95
OBSTETRIC PRACTICE
Increased airway protection with the PLMA has aroused interest in its use in obstetric practice. The PLMA has not been reported for use during elective Cesarean section but a study is underway.96
THE ICU
There are four reports of PLMA use in ICU. These include use in patients with intubation difficulty: for eight hours ventilation after failed intubation,93 for securing the airway prior to immediate tracheostomy,88 and for airway rescue after accidental extubation and failed reintubation.89 The PLMA was used during bronchoscopic guided percutaneous tracheostomy in 25 patients.63 Potential advantages of the PLMA over other laryngeal masks include increased seal pressure (important in non-compliant lungs) and the absence of glottic aperture bars, enabling bronchoscopic tracheal access. A ‘leak test’ to identify supraglottic edema is recommended before PLMA insertion and tracheal extubation.97
The ability to ventilate with higher pressures than the cLMA, and the ability to access the stomach, infers advantages over other SADs in the event of difficulty or failure with primary airway devices. It is possible that short periods of lung ventilation on ICU via the PLMA might be suitable in selected patients.
Trauma and cardiopulmonary resuscitation (CPR)
There are no clinical case reports of the use of the PLMA in the trauma setting. During manual in-line stabilization of the neck, in 20 anesthetized volunteers, PLMA and cLMA insertion were compared using a cross-over technique.98 PLMA insertion was easier and seal pressures higher. The authors suggested the PLMA introducer improved ease of insertion. Neck movement was not measured. This study suggests a potential role for the PLMA during airway rescue in trauma.
During CPR, the PLMA has potential advantages over the cLMA of improved airway seal, ability to drain the stomach (and so reduce aspiration). A manikin study compared different laryngeal masks (cLMA, ILMA, PLMA, Unique LMA) with facemask or tracheal intubation during simulated CPR.99 During uninterrupted chest compressions the PLMA functioned as well as the TT and better than all other masks. In a similar manikin study the PLMA performed similarly to the LTS and the Combitube.100
After education and manikin practice, nurses naive to both cLMA and PLMA established an airway in anesthetized paralyzed patients equally rapidly with either device.43 Digital insertion enabled first attempt success within 45 sec in 85% of cases. The authors suggested that the introducer tool might increase PLMA insertion success further. These three studies offer support for clinical trials in resuscitation: as yet, none have been undertaken.
Other potential clinical uses
The PLMA has potential advantages over the cLMA and tracheal intubation in several other clinical areas. These include cardiac anesthesia (controlled ventilation is routine, reduced hemodynamic stimulation and smooth recovery are desirable), carotid endarterectomy (hemodynamic stability during airway manipulation is desirable), and neuroanesthesia (controlled ventilation is routine but vascular and intracranial hypertension might be minimized by avoiding tracheal intubation and extubation). To date, no studies have been reported in these areas.
MARKET SHARE OF THE PLMA
The PLMA has been available since 2000. In 2002, sales of the PLMA, as a fraction of sales of all laryngeal masks, (which may indicate trends in clinical practice), varied widely from 40% in Hong Kong to less than 1% in the UK.
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Conclusions |
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TOPAbstractIntroductionMethodsConclusionsConclusionsReferences |
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The PLMA has been used for laparoscopic and abdominal surgery, in increasingly obese patients, for management of anticipated or actual difficult airways, and after failed intubation in selected cases. Presently, the safety of these developments can neither be confirmed nor refuted: however, the PLMA is a welcome addition to the airway armory and is likely to increase the safety margin when using controlled ventilation via a laryngeal mask.
Before 1988, the airway was managed routinely during anesthesia with the facemask or TT. Use of a cLMA became increasingly widespread, but reservations remain about use during controlled ventilation and the risk of regurgitation. The PLMA offers an airway that bridges some of the gap between the cLMA and the TT (Figure 8).
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Footnotes |
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Accepted for publication October 18, 2004. Revision accepted March 31, 2005.
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References |
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2 LMA ProSeal® Instruction manual. Intavent Limited 2002.
3 Kihara S, Brimacombe J. Sex-based ProSealTM laryngeal mask airway size selection: a randomized crossover study of anesthetized, paralyzed male and female adult patients. Anesth Analg 2003; 97: 280–4.
4 Kihara S, Brimacombe JL, Yaguchi Y, Taguchi N, Watanabe S. A comparison of sex and weight-based ProSealTM laryngeal mask size selection criteria. A randomized study of healthy anesthetized, paralyzed adult patients. Anesthesiology 2004;101: 340–3.[Medline]
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7 Keller C, Brimacombe J. Mucosal pressure and oropharyngeal leak pressure with the ProSeal versus laryngeal mask airway in anaesthetized paralysed patients. Br J Anaesth 2000; 85: 262–6.
8 Stix MS, O’Connor CJ Jr. Depth of insertion of the ProSealTM laryngeal mask airway. Br J Anaesth 2003; 90: 235–7.
9 Brain AI, Verghese C. Correct fixation of the LMA ProSealTM (Letter). Anaesthesia 2003; 58: 922.
10 Brimacombe J, Keller C. The ProSeal laryngeal mask airway. A randomized crossover study with the standard laryngeal mask airway in paralyzed anesthetized patients. Anesthesiology 2000; 93: 104–9.[Medline]
11 Cook TM, Nolan JP, Verghese C, et al. Randomized crossover comparison of the ProSeal with the classic laryngeal mask airway in unparalysed anaesthetized patients. Br J Anaesth 2002; 88: 527–33.
12 Evans NR, Gardner SV, James MF, et al. The ProSeal laryngeal mask: results of a descriptive trial with experience of 300 cases. Br J Anaesth 2002; 88: 534–9.
13 Howath A, Brimacombe J, Keller C, Kihara S. Gum elastic bougie-guided placement of the ProSealTM laryngeal mask (Letter). Can J Anesth 2002; 49: 528–9.
represents variation in individual practice or ‘margin of disagreement’.