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From the Department of Anaesthesia and Critical Care, University of Würzburg, Würzburg, Germany.
Address correspondence and reprint requests to Franz Kehl, MD, PhD, DEAA, Universität Würzburg, Klinik und Poliklinik für Anästhesiologie, Zentrum Operative Medizin, Oberdürrbacher St. 6, 97080 Würzburg, Germany. Address e-mail to franz.kehl{at}mail.uni-wuerzburg.de.
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Abstract |
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METHODS: We compared the SLIPA® with the conventional laryngeal mask airway (LMA®) regarding handling, safety, sealing of the pharynx, and patient comfort in 124 adult patients (ASA I–III) undergoing ophthalmic surgery under general anesthesia.
RESULTS: Insertion of the SLIPA® was straightforward in 88%, slightly difficult in 10%, and obviously difficult in 0% of cases. The SLIPA® could not be inserted in 2% of patients. In the LMA® group, insertion was straightforward in 90%, slightly difficult in 8%, obviously difficult in 2%, and a failure in 0% of patients. Maximum seal pressure was 24 ± 6 mm H2O with the SLIPA® and 24 ± 4 mm H2O with the LMA®. Gastric air insufflation was noticed in 19% of patients in the SLIPA® group and 3% in the LMA® group (P < 0.05). No regurgitation of gastric contents was observed. Removal of the airway was uneventful in all cases. Blood traces were noted on the surface of the device in 20% in the SLIPA® versus 11% (n.s.) in the LMA® group. Complaints of a sore throat were recorded in 2% vs. 14% in the SLIPA® and the LMA® group, respectively.
CONCLUSION: The SLIPA® is a useful alternative to the conventional LMA® in patients undergoing minor surgery. However, it is associated with a higher incidence of gastric air insufflation, which may increase the risk of aspiration.
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Introduction |
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METHODS |
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18 yr of age, ASA physical status I–III, with a body mass index less than or equal to 35 kg/m2. Exclusion criteria were contraindications for the use of a laryngeal airway device, a history of gastroesophageal reflux, current sore throat, dysphagia, and pregnancy. All physicians inserting the supraglottic airway devices had a minimum of 3 yr experience in anesthesia and airway management with LMAs. Patients were randomly assigned to receive either the SLIPA® (Teleflex Medical, Kernen, Germany) or a conventional LMA® (LMA Deutschland, Bonn, Germany). Choice of the appropriate size of the airway device used was left to the anesthesiologist's discretion. Sizes of the SLIPA® and the LMA® used ranged from 47 to 57 and from 4 to 6, respectively. After standard monitoring (electrocardiogram, noninvasive arterial blood pressure measurement, and pulse oximetry) had been established and administration of 100% oxygen was accomplished, anesthesia was induced with propofol 2–3 mg/kg and remifentanil 0.5 µg/kg IV and maintained by continuous infusion of propofol 4–6 mg · kg–1 · h–1 and remifentanil 0.2 µg · kg–1 · min–1. Neuromuscular blockade was not used in any study patient. Adequate depth of anesthesia was verified by clinical assessment. Additional bolus injections of propofol were administered as required to achieve a sufficient depth of anesthesia.
The airway device was introduced into the pharynx approximately 2 min after induction of anesthesia. Normal saline solution was used as a lubricant for both devices. Insertion was rated as "straightforward" (insertion succeeded on the first attempt, and within 15 s), "slightly difficult" (insertion success on first attempt, but required longer than 15 s), "obviously difficult" (more than one attempt before successful insertion), or "failure" (insertion not possible despite multiple attempts). If failure occurred, a single attempt to introduce the alternative supraglottic airway device into the pharynx was performed. If this attempt failed, endotracheal intubation was performed. Insertion time was the time from jaw opening to successful placement of the airway device, verified by sufficient ventilation (6 mL/kg) and normal capnogram.
If a LMA® was used, the cuff was inflated with 20 mL of air after successful placement. If substantial leakage occurred despite optimal placement of the LMA®, another 10 mL of air was added. The cuff pressure was then maintained constantly at 20 cm H2O by manometric control. If the chosen size of the SLIPA® or the LMA® proved too small to attain an adequate seal, the airway device was replaced by a different size. Exchange of the airway was noted and insertion time of the correctly sized airway device was included in the evaluation.
Maximum airway sealing pressure was measured by closing the expiratory valve of the breathing circuit and noting the pressure at which a leak developed with a fixed fresh gas flow of 3l/min (7). Patients' lungs were ventilated using pressure-controlled mode below maximum sealing pressure with a minute ventilation of 80 mL · kg–1 · min–1. Controlled ventilation was performed in all patients throughout the operation. Gastric air insufflation was monitored repeatedly by auscultation using a stethoscope positioned over the patient's stomach, immediately after insertion of the airway, after positioning, and at the end of surgery. All surgical procedures were performed with the patients in the supine position. At the end of surgery, patients were allowed to breathe spontaneously, and the airway device was removed when tidal volume reached 8 mL/kg and the patient responded to simple verbal commands. Removal of airway devices was graded as easy or difficult. Patients were interviewed by an independent investigator 30 min after arrival in the postanesthesia care unit to determine if they had a sore throat. A visual analog scale was used to rate soreness of the throat from 0 to 10.
Continuous data were tested for normal distribution and analyzed by Student's t-test. Noncontinuous data were analyzed by 
2 test and Mann–Whitney U-test test, where appropriate. Data are expressed as mean ± sem where applicable. P < 0.05 was considered statistically significant.
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RESULTS |
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The rate of successful insertion was 98% (n = 58) and 100% (n = 65) in the SLIPA® and the LMA® groups, respectively. In the SLIPA® group, insertion of the airway device was rated straight forward in 88% (n = 52), slightly difficult in 10% (n = 6), obviously difficult in 0%, and failure in 2% of patients (n = 1). In the LMA® group, insertion was straightforward in 90% (n = 59), slightly difficult in 8% (n = 5), obviously difficult in 2% (n = 1), and failure in 0% of patients. In the single failure case in the SLIPA® group, the SLIPA® was replaced by a LMA®. No patients required endotracheal intubation. The airway was replaced by a smaller device in three patients in the SLIPA® group and in two patients in the LMA® group. The airway was replaced by a larger device in two patients in the SLIPA® group and in one patient in the LMA® group. Maximum airway sealing pressure was 24 ± 6 mm H2O and 24 ± 4 mm H2O in the SLIPA® and the LMA® groups, respectively. Gastric air insufflation occurred significantly more often in the SLIPA® group (19%, n = 11) than in the LMA® group (3%, n = 2). No regurgitation of gastric contents was observed in any patient. Removal of the SLIPA® or the LMA® was uneventful in all cases. Blood traces were noticed on the surface of the device in 20% (n = 12) of the SLIPA® group and in 11% (n = 7) of the LMA® group. Complaints of a sore throat were noticed at a significantly higher rate in the LMA® group (14%, n = 9) than in the SLIPA® group (2%, n = 1).
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DISCUSSIONS |
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The current study is the first investigation to compare the current version of the SLIPA®, intended for commercial distribution, with the classic LMA® in the clinical setting. In the study by Miller and Light (6), an experimental version of the SLIPA® was used that differed markedly from the current device. Another study compared SLIPA® with the ProSeal LMA® and with endotracheal intubation, but not with the conventional LMA® (8).
Airway sealing pressures were similar in the SLIPA® and LMA® groups, in accordance with prior reports (6). This suggests that the risk of aspiration should be comparable for the two airway devices. The ProSeal LMA®, a modified version of the classic LMA® with an additional channel for gastric tube placement and a superior cuff, may provide airway sealing pressures that are higher than those of the conventional LMA® (9,10). Theoretically a supraglottic airway device with higher sealing pressures should better protect the airway from aspiration.
Pulmonary aspiration of gastric contents remains a major concern when using supraglottic airway devices (11). Although gastric air insufflation did occur at a higher rate in the SLIPA® group, no regurgitation of gastric contents was observed in either group. Whether this difference translates into a higher risk of gas extension of the stomach and higher risk of aspiration cannot be determined with the small number of patients in the available studies. The fluid collection chamber of the SLIPA® might provide some protection from aspiration of gastric contents.
The inflatable cuff of the LMA® exerts pressure on the pharyngeal structures. Several reports associate the use of the LMA® with injuries of the lingual, hypoglossal, and recurrent laryngeal nerves (12,13) and to sore throat (9,10). Blood traces on the airway device, reflecting direct trauma to pharyngeal mucosa or other structures, were found at the same rate in both groups. Although the SLIPA® is made of stiffer material than the conventional LMA®, it appears to be traumatic to the pharynx to the same degree as the LMA®.
A significantly higher rate of sore throat was noticed in the LMA® group. This might have been due to the pressure exerted on the pharynx by the inflatable cuff of the conventional LMA® (14). Soreness was predominantly mild, with only one patient in the LMA® group rating soreness >3. The incidence of sore throat is in line with other studies reporting an incidence of sore throats of 11% (15) and 27% (16) using the conventional LMA®. Interestingly, Miller and Light (6) found no difference in the rate of sore throats between the classic LMA® and the SLIPA®. However, they reported an unusually high rate of sore throats when compared with our study.
In conclusion, the SLIPA® is a useful alternative to the classic LMA® in patients undergoing minor surgery. Management of the airway with the SLIPA® was as simple as using the conventional LMA®. Although no signs of aspiration were noted in any study patient, the significantly higher rate of gastric insufflation in the SLIPA® group may have put patients at increased risk for aspiration. Fewer patients in the SLIPA® group complained of a sore throat, suggesting that the SLIPA® might increase patient comfort after minor surgery.
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Footnotes |
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This article has been cited by other articles:
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  D. Miller Laryngeal Mask Airway Classic and Streamlined Pharynx Airway Liner Airway Comparison Anesth. Analg., November 1, 2007; 105(5): 1508 - 1508. [Full Text] [PDF]
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M. Lange, N. Roewer, and F. Kehl The Conventional LMA(R): Benchmark for Assessing Supralaryngeal Airway Efficacy? Anesth. Analg., November 1, 2007; 105(5): 1509 - 1509. [Full Text] [PDF]
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S. Vamadevan and A. Diba The Conventional LMA(R): Benchmark for Assessing Supralaryngeal Airway Efficacy? Anesth. Analg., November 1, 2007; 105(5): 1508 - 1509. [Full Text] [PDF]
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