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A Streamlined Pharynx Airway Liner: A Pilot Study in 22 Patients in Controlled and Spontaneous Ventilation

M. Miller, Donald, MB ChB, FFA(SA), PhD; Lavelle, Margie, MB ChB, DA

doi: 10.1097/00000539-200203000-00052
General Articles: Research Report

Department of Anaesthetics, Victoria Hospital, Alphen Hill, Wynberg, South Africa

Funding for this project was supplied by SLIPAmed SA Pty Ltd.

October 19, 2001.

Address correspondence and reprint requests to Donald M. Miller, MB ChB, PhD, GKT Department of Anaesthetics, NGH2, Guy’s Hospital, London, SE1 9RT. Address e-mail to

Donald M. Miller has a financial interest in the development of the SLIPA.

Two important reasons a new supraglottic airway device is needed are to minimize aspiration risk and to eliminate possible iatrogenic disease transmission related to reusable equipment.

Regurgitation and aspiration during positive pressure ventilation under general anesthesia is a small but real risk when the laryngeal mask airway (LMA) (Laryngeal Mask Company, Henley-on-Thames, UK) is used (1). To minimize the risk of regurgitation of stomach contents, the ProSeal LMA™ was developed (2).

The SLIPA™ airway is so named because it is both an acronym for Streamlined Liner of the Pharynx Airway and because it looks like a slipper. It is manufactured in South Africa (SLIPAmed SA Pty Ltd, Cape Town, South Africa). It was designed to provide an inexpensive single-use alternative to the LMA™ and to decrease the risk of aspiration if secretions and blood accumulate in the pharynx or if limited volume regurgitation should occur (3).

The SLIPA™ is an artificial airway device which lines the pharynx. (Figs. 1,2) It is shaped like a boot with “toe, bridge and heel” prominences. The SLIPA™ is a hollow, preformed, soft plastic, blow-molded, boot-shaped airway. No cuff is necessary for the device to seal in the pharynx because the shape of the SLIPA™ is similar to that of a pressurized pharynx. The dimensions of the airway need to match those of the patient, so it is anticipated that a large range of sizes will be required if this airway is to become reliable. This disadvantage is likely to be compensated for by other potential advantages relating to cost of production (no cuff mechanism required) and advantages relating to its hollow structure.

Figure 1

Figure 1

Figure 2

Figure 2

When inserting the SLIPA™, the hollow chamber can flatten to facilitate passing it between the teeth. As with the insertion of the LMA™, it is most helpful if an assistant lifts the jaw forward to negotiate the “toe” of the chamber past the bend in the pharynx at the base of the tongue. Without picking up the epiglottis, the toe of the chamber then slips very easily into the entrance to the esophagus where it seals the downward outlet of the pharynx against the cricopharyngeus muscle. Once in place, the SLIPA™ returns to its prior-to-insertion shape. The “bridge” with its two lateral bulges in the center of the chamber fits into the pyriform fossae sealing the upward outlet at the base of the tongue. The “heel” of the chamber anchors the SLIPA™ into position by sliding into the nasopharyngeal opening and soft palate. It may be appreciated that there is only one position for such a device. The need to manipulate and manage the airway after insertion is unlikely.

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The local hospital ethics committee gave approval and written consent was obtained to conduct this study using patients undergoing minor surgery under general anesthesia. Twenty-two fasted healthy adult patients with ASA status I–II and older than 17 yr were recruited. Exclusions included those at risk for pulmonary aspiration: diabetics, morbid obesity, gastroesophageal reflux, or pregnant patients.

This brief report relates to the first 22 uses of the SLIPA™. In addition, to limit failure on the grounds of there being only one size available meant that patients had to be selected carefully. The selection process was based on only one anatomical measurement. The investigators made the assumption that a direct indication of laryngeal diameters could be obtained by matching the width of the thyroid cartilage to that of the device in its widest dimension. If the measured diameters differed by more than an estimated 2 mm, the airway was excluded for use in that patient.

Mallampati scoring in all patients was recorded. General anesthesia was induced by preoxygenating with 100% oxygen, followed by the administration of midazolam 1 mg, followed 1–2 min later by fentanyl 1 μg/kg, followed 1 min later by propofol 2–3 mg/kg or more if required. One minute later the SLIPA™ was placed for airway management. If the SLIPA™ could not be placed and a clinically satisfactory airway achieved after the second attempt, it was recorded as a failure and an alternative airway used and recorded. Anesthesia was maintained with N2O, O2, and isoflurane in the usual way.

Ventilation was manually assisted and the peak airway pressures measured during gentle manual ventilation using a fresh gas flow delivery into a circle absorber system of 3 L/min. The patients were then allowed to breathe spontaneously throughout the procedure and no muscle relaxants were administered.

Ease of establishment of the airway was measured using the following criteria and scoring system: Scores were 0 for each of the following 5 criteria or

  • Time to insert the airway device: >10 s = 1;
  • Further manipulation of the device after insertion = 1;
  • More than one attempt = 1;
  • Lowest oxygen saturation <95% = 1;
  • Abandonment of technique on induction or loss of airway intraoperatively = 5.

A score of four or less was considered a success.

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Results are expressed in Table 1. No patients complained of sore throats, nor was blood noticed on any of the airways upon removal. Insertion of the airway proved to be no more difficult than inserting a LMA™. As with inserting a LMA™, lifting the jaw forward by an assistant was very helpful.

Table 1

Table 1

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The objective of this study was to determine whether the design of an uncuffed airway, such as the SLIPA™, could function in a similar way to the LMA™ or COPA™ (Mallinckrodt, St. Louis, MO), both of which have proved to provide satisfactory alternatives to the use of an endotracheal tube in many circumstances. A 90% success rate in the first-time use of a single-sized, nonexpandable prototype airway is a very promising result.

Provided more sizes are made available, we may conclude that use of the SLIPA™ airway could develop into a useful single-use means of noninvasive hands-free airway control with possible safety and cost advantages. Patents pending.

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1. Akhatar TM, Street MK. Risk of aspiration with the laryngeal mask. Br J Anaesth 1994; 72: 447–50.
2. Brain AI, Verghese C, Strube PJ. The LMA ‘ProSeal’–a laryngeal mask with an oesophageal vent. Br J Anaesth 2000; 84: 650–4.
© 2002 International Anesthesia Research Society