The ProSeal laryngeal mask airway
Section snippets
Design and development
Archie Brain never regarded the Classic LMA as the best form of the device [2]. He knew that increasing the force against the periglottic tissues or increasing the surface area over which this force is applied would produce a more effective seal. He also knew that a drainage tube, or groove, could be incorporated to divert regurgitated fluid away from the respiratory tract. Between 1981 and 1996, a variety of prototypes were constructed and tested that proved the feasibility of these concepts,
Device description
The ProSeal LMA is made from medical-grade silicone and is reusable (Fig. 1). The different or modified features compared with the Classic LMA are listed in Table 1. The mask and inflation lines are identical to the Classic LMA. The ProSeal LMA is currently available in sizes 3 to 5. The cuff has identical proportions but different dimensions among sizes. The introducer tool is a reusable clip-on/clip-off device that comprises a thin, curved, malleable, metal blade with a guiding handle similar
Anatomy
The anatomic position occupied by the ProSeal LMA is similar to but more extensive than the Classic LMA (Fig. 2). The larger, conical-shaped distal cuff fills the hypopharynx more completely, and the larger, wedge-shaped proximal cuff fills the proximal laryngopharynx more completely, both to form a better seal with their respective tracts. Epiglottic downfolding is more common with the ProSeal than the Classic LMA (68%–88% versus 31%–66%), probably because the larger proximal cuff is more
Cardiovascular system
The influence of the ProSeal LMA on pharyngeal perfusion has not been measured directly, but mucosal pressures [13] are usually below pharyngeal perfusion pressure [14]. There are no published data about the influence of the ProSeal LMA on the carotid artery or internal jugular vein, but in principle, the larger cuff may cause more distortion or compression. Cardiovascular responses seem to be similar to the Classic LMA [11] and the laryngeal tube airway [15]. Howath et al [16] detected no
Function
The function of the ProSeal LMA is to form a seal with and provide a conduit to the respiratory and gastrointestinal tracts. Most of the studies conducted to date provide information about these functions.
Indications and contraindications
The indications are the same as for the Classic LMA, but the ProSeal LMA is preferable whenever a better seal, better airway protection, and access to the gastrointestinal tract are required (Table 6). Some experts consider that these advantages are desirable in all patients and that the ProSeal therefore should replace the Classic LMA. The ProSeal LMA is contraindicated in patients who are at risk of aspiration before induction of anesthesia (other than for airway rescue) and in patients with
Depth of anesthesia and size selection
There are no studies specifically determining the depth of anesthesia or drug dosage required for insertion and subsequent tolerance of the ProSeal, but two studies of nonparalyzed patients suggest that requirements are similar [11], [16]. Size selection is similar to the Classic LMA and can be either weight-based (size 3 for adults and children, 30–50 kg; size 4 for normal adults, 50–70 kg; and size 5 for large adults, 70–100 kg) or gender-based (size 4 for female patients; size 5 for male
Emergency medicine
There are no reports of the ProSeal LMA being used for emergency medicine, but the improved seal, the potential to protect against regurgitation, easy gastric tube insertion, and the option of finger-free insertion offer advantages over the Classic and Disposable LMAs. Potential limitations are that it is more complex to use and more difficult to insert; however, Coulson et al [43], in crossover study of 60 anesthetized, paralyzed adults by inexperienced personnel following manikin-only
Intensive care medicine
There are no reports of the ProSeal LMA being used in the intensive care unit, but the same advantages it offers for resuscitation also apply for intensive care. Additional advantages include access to the gastrointestinal tract for monitoring and the potential for reduced pharyngeal morbidity owing to lower mucosal pressure for a given seal pressure [13].
Difficult airway
There are no reports of the ProSeal LMA being used in the difficult airway scenario, but Keller et al [23], in a prospective study of grossly or morbidly obese patients, found that the ProSeal was successful in 11 of 11 patients who were either difficult or impossible to intubate with a laryngoscope. Insertion success seems to be independent of Mallampati or Cormack and Lehane scoring [23]. In principle, cricoid pressure might interfere with insertion more than the Classic LMA because the
Pediatrics
The smallest ProSeal LMA currently available is the size 3. Although it is recommended for children weighing 30 to 50 kg or greater, there are no reports of its use in the pediatric population. There is, however, one report of a prototype ProSeal LMA being used successfully in the pediatric population. A seal greater than 40 cm H2O was obtained in 49 of 50 patients [44]. Unlike the Classic LMA, the smaller sizes may not be scaled-down versions of the adult sizes.
Coexisting diseases
The ProSeal LMA is suitable for patients with a similar range of coexisting diseases to the Classic LMA, but the improved seal allows its use in patients with diseases causing a reduction in pulmonary compliance, and the drainage tube allows its use in patients with some increased risk of regurgitation. The only study in which the ProSeal LMA has been used in a population of patients with a specific coexisting disease is gross or morbid obesity, in which case it was used successfully as a
Surgery
The ProSeal LMA extends the range of surgical procedures for which the LMA can be used. It is more appropriate than the Classic LMA for surgical procedures in which a better seal is required or when there is a risk of regurgitation arising during the procedure. The ProSeal LMA, like the Classic LMA, can be used for most head and neck and ENT procedures, but the tube is too rigid for oropharyngeal procedures and the cuff is too large for pharyngeal procedures. The ProSeal LMA is more appropriate
Airway morbidity and trauma
There are three studies providing information about airway morbidity and trauma: one comparing the ProSeal with the Classic LMA [11], one comparing the ProSeal LMA with the laryngeal tube airway [15], and one describing airway morbidity after gum elastic bougie-guided insertion [16]. In both comparative studies, the incidence and severity of airway morbidity and trauma were similar. The frequency of airway morbidity and blood staining for the gum elastic bougie-guided technique is probably
Summary
The ProSeal LMA is a major advance over the Classic LMA because of the following reasons: it allows ventilation at much higher airway pressures; it protects the lungs from aspiration and the stomach from gastric insufflation; it facilitates passage of a gastric tube and monitoring devices into the esophagus; it can be inserted like the Classic or Intubating LMA; it has its own built-in bite block; malposition is detected more readily; and, through use of techniques such as gum elastic
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