ProSeal laryngeal mask protects against aspiration of fluid in the pharynx{dagger}

N. R. Evans*,1, S. V. Gardner1 and M. F. M. James1

1Department of Anaesthesia, University of Cape Town, Groote Schuur Hospital, Observatory,Cape Town 7925, South Africa*Corresponding author

{dagger}Declaration of interest. The authors wish to thank Chris Goslin of Olympus (SA). N.R.E. received funding from Marland Medical South Africa. Marland Medical South Africa also funded the salary of a research assistant and provided the masks. AstraZeneca (South Africa) provided the propofol used in this study.

Accepted for publication: November 27, 2000


    Abstract
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
Background. The ProSeal laryngeal mask airway (PLMA) is a new device designed to isolate the airway from the digestive tract.

Methods. We studied the ability of the PLMA to isolate the airway in 103 anaesthetized adults who were breathing spontaneously or given neuromuscular blocking agents, by filling the hypopharynx with methylene blue-dyed saline introduced down the drainage tube once the mask was in place. At the beginning and end of the procedure, a fibre-optic bronchoscope was passed down the airway tube to observe any dyed saline in the bowl of the mask.

Results. The PLMA was positioned correctly in all successful attempts (102 out of 103 attempts) and was able to isolate the glottis from fluid in the hypopharynx in all patients initially. Leakage of saline into the bowl of the mask occurred in two patients in whom displacement of the mask was caused by upper airway events during the procedure. In the remaining 100 patients, the glottis was isolated successfully for the duration of the procedure.

Conclusions. The PLMA can be positioned reliably. It can isolate the airway from fluid in the hypopharynx.

Br J Anaesth 2002; 88: 584–7

Keywords: equipment, masks anaesthesia; larynx, bronchoscopy fibreoptic; complications, aspiration; complications, regurgitation


    Introduction
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
The ProSeal laryngeal mask airway (PLMA; Intavent Orthofix, Maidenhead, UK) is a new device with features designed to isolate the airway from the digestive tract and prevent fluid aspiration.1 We investigated the ability of the PLMA to isolate the airway in anaesthetized adults. The hypopharynx was filled with methylene blue-dyed saline introduced down the drainage tube after the mask had been placed. At the beginning and end of the procedure, a fibre-optic bronchoscope was passed down the airway tube to detect any leakage of dyed saline into the bowl of the mask.


    Methods and results
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
One hundred and three adult patients were studied as part of a larger study.2 Ethics committee approval was obtained from the research ethics committee of the Faculty of Medicine of the University of Cape Town, and all patients gave informed written consent. We studied patients undergoing elective surgery in which a classic laryngeal mask airway would normally be used. Patients were excluded if they were at risk of aspiration. Anaesthesia was induced with fentanyl 1 µg kg–1 followed 2 min later by propofol 2–3 mg kg–1 until loss of eyelash reflex. In spontaneously breathing patients, the PLMA was inserted immediately after induction, when adequate jaw relaxation had been achieved. Patients to be ventilated were given a non-depolarizing neuromuscular blocking agent chosen at the discretion of the investigator at a dose appropriate for tracheal intubation. The PLMA was inserted 2–3 min later. Anaesthesia was maintained by isoflurane with nitrous oxide 66% in oxygen using a circle absorber system. A PLMA size 4 in females and size 5 in males was inserted using either the index finger or the introducer tool. The cuff was inflated to obtain an intracuff pressure of 60 cm H2O as measured by a calibrated aneroid manometer. The intracuff pressure was maintained at this pressure throughout the procedure by adjusting the air in the cuff if the intracuff pressure changed.

A fibre-optic bronchoscope (Olympus BF 240) was introduced down the airway to a position 1 cm proximal to the end of the tube. If the view showed that the mask was rotated or distorted without surrounding the glottis, the test was halted and the reason noted. Normal saline dyed with methylene blue was prepared by adding methylene blue 20 mg to normal saline 1 litre. The dyed saline was previously found to be easily visible through the bronchoscope when present within the bowl of the PLMA. The dyed saline was introduced down the drainage tube until the hypopharynx was filled and a column of saline flowed back up the drainage tube to form a meniscus outside the patient’s mouth at the level of the lips. In vitro testing found that the volume of methylene blue required to fill the drainage tube until the meniscus reached the level corresponding to the patient’s lips was 7 ml in a size 4 PLMA and 10 ml in a size 5 PLMA; the height of this column was found to be 12 cm above the tip of the mask. The presence or absence of a leak into the bowl of the mask was noted via the bronchoscope. If a leak was present, the process was halted, the saline suctioned from the tube and the case noted as a failure. The fluid in the hypopharynx and column of blue saline was then left in the drainage tube for the duration of the procedure, the meniscus being maintained by adding further amounts of methylene blue saline if necessary. The total amount of methylene blue saline used was recorded. In the event of any change in respiratory measurements combined with a drop in the level of the meniscus, airway endoscopy was repeated to see if a leak had occurred within the mask. If so, the saline was suctioned out and a failure noted. Otherwise, at the end of the procedure the bronchoscope was reintroduced and the bowl of the mask reinspected for any signs of leaked blue saline. The bronchoscope was then removed and the saline aspirated from the drainage tube.

The details of anaesthesia are shown in Table 1. Placement of the PLMA was unsuccessful in one patient.


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Table 1 Details of anaesthesia
 
Endoscopic airway inspection revealed no cases of mask malposition. Consequently, dyed saline was introduced down the drainage tube in all patients. The total volume of methylene blue-dyed saline introduced down the drainage tube during the procedure was 16.9 (6–30) ml for a size 4 and 28.4 (12–60) ml for a size 5. In every case, endoscopic inspection revealed an uninterrupted column of dyed saline within the distal portion of the drainage tube visible within the bowl of the mask. The oesophagus was not visible within the bowl of the mask in any cases. No incidences of leakage of saline into the bowl of the mask or oropharynx occurred on initial introduction of the saline down the drainage tube. No leakage of saline into the bowl of the mask or oropharynx occurred at any time in 100 patients (98%). Saline leaked into the bowl of the mask during the procedure in two patients (2%). One leak occurred in a 46-yr-old man undergoing an incision and drainage of a tibial abscess. A size 5 PLMA had been inserted easily on the first attempt and inflated with 35 ml of air. Gastric tube placement had been achieved easily. Total volume of dyed saline introduced down the drainage tube during the procedure was 35 ml. He had received fentanyl 1 µg kg–1 for analgesia and was breathing spontaneously when he coughed in response to surgical incision 7 min after induction of anaesthesia. On reintroduction of the bronchoscope, the mask was found to be displaced to the right with a small amount of dyed saline in the bowl of the mask. The saline was suctioned out and the anaesthetic continued uneventfully. Another leak occurred in a 72-yr-old male with chronic obstructive airway disease undergoing optical urethrotomy. A size 5 PLMA had been placed easily on the first attempt and inflated with 38 ml of air. Gastric tube placement had been achieved easily and the total volume of dyed saline introduced was 38 ml. He had received fentanyl 1 µg kg–1 for analgesia and was breathing spontaneously when he developed laryngospasm during the urethrotomy 20 min after induction. Dyed saline was seen leaking out of the mouth and on reintroduction of the scope the bowl of the mask was filled with dyed saline. The saline was suctioned out and anaesthesia deepened, but subsequently proceeded uneventfully.


    Comment
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
The PLMA was positioned correctly in all successful placements and at first isolated the glottis from fluid in the hypopharynx in all patients. A leak into the bowl of the mask occurred later in two of 102 patients during the procedure. In the remaining 100 patients the glottis was isolated successfully for the duration of the procedure.

In all but one case, the volume of dyed saline injected into the drainage tube was greater than the volume of the tube, indicating that the saline must have entered the hypopharynx. We presume that in the one case in which a smaller volume was injected an airlock must have occurred within the tube.

This study has shown that the properly positioned PLMA can isolate the airway from fluid contained within the hypopharynx in paralysed and non-paralysed patients, even when that fluid is present for a considerable period of time and the patient is in a variety of positions, including head-down. This study did not mimic the act of passive regurgitation, as the fluid did not travel up the oesophagus. However, the pressure attained in the drainage tube, and therefore, presumably, within the hypopharynx during this study (12 cm H2O) is greater than that normally associated with passive regurgitation, but less than the described maximum pressures of 30 cm H2O.3 The study by Brimacombe and colleagues in cadavers4 showed that, when the drainage tube was closed, the PLMA successfully protected the airway from fluid injected up the oesophagus until pressures of 63–68 cm H2O had been achieved. If the drainage tube was left open, no leaks occurred.

It is therefore reasonable to conclude that the PLMA is likely to provide better protection of the airway from passive regurgitation than either no airway protection device or the classic laryngeal mask airway.


    References
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
1 Brain AIJ, Verghese C, Strube PJ. The LMA ‘ProSeal’—a laryngeal mask with an oesophageal vent. Br J Anaesth 2000; 84: 650–4[Abstract]

2 Evans NR, Gardner SV, James MFM et al. The ProSeal laryngeal mask: results of a descriptive trial with experience of 300 cases. Br J Anaesth 2002; 88: 000–0

3 Holloway RH, Hongo M, Berger K, McCallum RW. Gastric distension: a mechanism for postprandial gastroesophageal reflux. Gastroenterology 1985; 89: 779–84[ISI][Medline]

4 Keller C, Brimacombe J, Kleinsasser A, Loeckinger A. Does the ProSeal laryngeal mask airway prevent aspiration of regurgitated fluid? Anesth Analg 2000; 91: 1017–20[Abstract/Free Full Text]