Effectiveness of the Streamlined Liner of the Pharynx Airway (SLIPA[TM]) in allowing positive pressure ventilation during gynaecological laparoscopic surgery.
The aim of this study was to assess whether the Streamlined Liner
of the Pharynx Airway (SLIPA[TM]) performed as well as an endotracheal
tube for positive pressure ventilation in gynaecological laparoscopic
surgery in the Trendelenburg position. Forty patients (American Society
of Anesthesiologists physical status I to III) were randomly divided
into two groups: SLIPA (n=20) or endotracheal tube group (n=20). Lung
mechanics and severity of postoperative sore throat were assessed in
both groups. In the SLIPA group, the oropharyngeal leak pressure was
There were no significant differences between groups in the lung mechanics. In the SLIPA group, oropharyngeal leak pressure and peak inspiratory pressure increased significantly after gas insufflation compared to 10 minutes after patient positioning in the lithotomy position (P <0.05). The difference between oropharyngeal leak pressure and peak inspiratory pressure (approximately 10 cm[H.sub.2]O throughout the procedure) remained suitable for airway maintenance. The incidence of sore throat was similar in both groups but the severity was less in the SLIPA group 24 hours after surgery (P <0.05). There were no other complications such as regurgitation noted in either group. In the study population, the SLIPA performed as well as an endotracheal tube in allowing positive pressure ventilation without gas leak during gynaecological laparoscopy. The way in which the SLIPA increases its resistance to gas leak as the inspiratory pressure rises may account for this.
Key Words: laryngeal mask airway, SLIPA[TM], positive pressure ventilation
|Article Type:||Clinical report|
Positive pressure respiration (Research)
Gynecology, Operative (Research)
|Publication:||Name: Anaesthesia and Intensive Care Publisher: Australian Society of Anaesthetists Audience: Academic Format: Magazine/Journal Subject: Health Copyright: COPYRIGHT 2011 Australian Society of Anaesthetists ISSN: 0310-057X|
|Issue:||Date: July, 2011 Source Volume: 39 Source Issue: 4|
|Topic:||Event Code: 310 Science & research|
|Product:||SIC Code: 3069 Fabricated rubber products, not elsewhere classified|
The laryngeal mask airway (LMA), developed as an alternative to the
endotracheal tube (ETT), is a supraglottic airway device initially used
for elective operations and later also for emergency airway management
(1,2). However, in positive-pressure ventilation during general
anaesthesia, the low airway sealing pressures of the LMA can result in
inadequate ventilation and gastric air insufflation (3-6) followed by
pulmonary aspiration (7,8). Doyle et al commented that the LMA is an
inappropriate airway device for an operation performed under the
conditions of pneumoperitoneum (9). There is also debate about its cost,
the time-consuming process of cleaning and autoclaving re-usable devices
and the risk of cross-infection.
The Steamlined Liner of the Pharynx Airway (SLIPA[TM], Medical Limited, Douglas, Isle of Man, Great Britain) is a more recently released supraglottic airway, designed to fit the hypopharynx. It is made from moulded plastic without an inflatable Cuff (10). This device is an inexpensive, disposable, hands-free airway that requires minimal expertise for insertion and is claimed to have a lower risk for aspiration in the event of regurgitation or collection of pharyngeal secretions. A hollow sump-like section is specially designed to prevent aspiration of gastric contents to some degree (11-13). During gynaecological laparoscopic surgery, insufflation of carbon dioxide (C[O.sub.2]) gas and changes in patient position result in increased peak inspiratory pressures (PIP) and changes in compliance of the chest and lung, the airway resistance and the functional residual capacity (14).
The SLIPA is designed to completely close the pharynx, without a cuff inflated in the hypopharynx, so the oropharyngeal leak pressure (OLP) must remain higher than PIP to adequately ventilate, without a leakage of gas. We hypothesised that the SLIPA would provide satisfactory conditions for positive pressure ventilation and be comparable to a standard ETT in gynaecological laparoscopic surgery in the Trendelenburg position. We assessed lung mechanics, OLP-PIP difference, severity of postoperative sore throat and other complications in both groups.
MATERIALS AND METHODS
The study protocol was approved by the Institutional Review Board of our hospital and all patients gave written informed consent. The 40 patients (American Society of Anesthesiologists physical status I to III) recruited to this study were between the ages of 18 and 75 years and were scheduled for gynaecological laparoscopic operations under general anaesthesia. They were randomly divided into two groups: those who underwent endotracheal tube insertion (ETT group, n=20) and those who underwent SLIPA insertion (SLIPA group, n=20). The following patients were excluded from the study: 1) body mass index [greater than or equal to] 30 kg/[m.sup.2]; 2) current sore throat and dysphagia; 3) a history of gastroesophageal reflux; or 4) at risk of pulmonary aspiration. To evaluate postoperative sore throat, the patients were informed of sore throat accompanied by ETT and SLIPA insertion and asked to report its severity using a 0 to 10 numerical rating scale.
An intramuscular injection of glycopyrrolate 0.2 mg was given one hour preoperatively. In the operating room, noninvasive arterial blood pressure, electrocardiogram, pulse oximeter, neuromuscular block, end-tidal C[O.sub.2] (EtC[O.sub.2]) and anaesthetic gas concentration were continuously monitored with the Datex-Ohmeda S/5[TM] Anesthesia Monitor. Bispectral index (BIS) was monitored with a BIS monitor (BIS[R], Aspect Medical System, Norwood, MA, USA). Three minutes after administration of fentanyl 1.0 [micro]-g/kg, anaesthetic induction was achieved with lignocaine 1.0 mg/kg and propofol 2.0 mg/kg, followed by rocuronium 1.0 mg/kg. The patients were manually ventilated through a facemask with 100% [O.sub.2] until the SLIPA or ETT had been inserted by a single experienced anaesthetist. If the first attempt at insertion failed, the patient was excluded from the study and the surgery was performed after ETT intubation. The size of the SLIPA was 47 or 49, according to the patient height, and the ETT was 7.0 mm with a medium-sized cuff (SIMS Portex Inc., UK). All patients were maintained with oxygen ([O.sub.2]), nitrous oxide ([N.sub.2]O) and sevoflurane with semi-closed circuit anaesthesia. The flow of [O.sub.2] and [N.sub.2]O was 2 l/minute each, and sevoflurane 1.2 to 3.0 vol% was used to maintain BIS values between 40 and 65. Ventilation was performed at tidal volumes ([V.sub.T]) of 8 to 10 ml/kg and respiratory rate of 12 to 18 /minutes, to maintain EtC[O.sub.2] concentration near 35 mmHg. The inspiratory to expiratory ratio was 1:2 and the train-of-four value was maintained at 0. Body temperature was maintained above 36[degrees]C.
All vital signs, preset [V.sub.T], measured [V.sub.T], EtC[O.sub.2], oxygen saturation, BIS, PIP and OLP were recorded one minute before and after the insertion of the airway device, 10 minutes after patient positioning in the lithotomy position, 10 and 30 minutes after gas insufflation, 10 minutes before the completion of the surgery and immediately after extubation. The times for pneumoperitoneum, the operation and anaesthesia were recorded. All patients were asked to report the severity of sore throat according to a numerical rating scale at one and 24 hours after surgery. The OLP was measured by closing the expiratory valve of the breathing circuit and noting the pressure at which a leak developed at a fixed fresh gas flow of 3 l/minute (15). The OLP was measured in the lithotomy position, 10 minutes after assuming the Trendelenburg position, 10 and 30 minutes after gas insufflation and 10 minutes before the completion of surgery. We compared the difference between OLP and PIP in the SLIPA group. Data for lung mechanics and severity of postoperative sore throat were noted.
We used data from previous studies to calculate the sample size required for this study (15,16), based on an [alpha]-error of 5% and [beta]-error of 20%. The required sample size per group was 20. Normally distributed data were compared between the two groups by unpaired t-tests and presented as mean [+ or -] standard deviation (SD). Descriptive variables were analysed using the chi-square test or Fisher's exact test when appropriate. The differences in lung mechanics were compared using two-way repeated measures analysis of variance. Within each group, comparisons with baseline data were made using one-way repeated measures analysis of variance. P values less than 0.05 were considered statistically significant and statistical analysis was performed with SPSS version 17.0 (SPSS Inc., Chicago, IL, USA).
There were no exclusions or significant differences in age, weight, height, pneumoperitoneum or operation time between the two groups (Table 1). No regurgitation of gastric contents was observed in either group. Changes in lung mechanics data are shown in Table 2. There were no significant differences between the two groups in preset [V.sub.T] and measured [V.sub.T] . The PIP was higher in the ETT group than in the SLIPA group at 1 minute after intubation (P <0.05), but no significant difference was found thereafter.
Changes in PIP, OLP, and the difference between OLP and PIP in the SLIPA group are shown in Figure 1. The OLP significantly increased at 10 and 30 minutes after gas insufflation and at 10 minutes before the completion of surgery, compared to that at 10 minutes after placement in the lithotomy position (P <0.05). PIP showed a significant increase until 30 minutes after commencing gas insufflation, but decreased 10 minutes before the completion of surgery (P <0.05). The difference between OLP and PIP showed a significant decrease at 10 and 30 minutes after commencing gas insufflation, compared to 10 minutes after patient positioning in the lithotomy position (P <0.05). The difference increased again 10 minutes before the completion of surgery, but was not significantly different from that at 10 minutes after placement in the lithotomy position.
The incidence of sore throat was 35% (n=7) in the ETT group and 30% (n=6) in the SLIPA group (P=NS). The severity of sore throat did not differ between the two groups at one hour but was lower in the SLIPA group at 24 hours after surgery (P <0.05) (Table 3).
[FIGURE 1 OMITTED]
Values for 0 to 10 numeric rating scale scores are expressed as mean [+ or -] SD. ETT=endotracheal tube, SLIPA=streamlined liner of pharynx airway. * significantly different from the ETT group at 24 hours (P <0.05).
Although the LMA has increasingly replaced the ETT for airway control, its use for laparoscopic operations is controversial because of the possibility of inadequate ventilation due to gas leak and gastric regurgitation leading to aspiration pneumonia after gastric insufflation for pneumoperitoneum. While the possibility of these complications is present, Miller et al have demonstrated that, unlike devices with an inflatable cuff in the pharynx, the soft plastic of the SLIPA lines the pharynx and the resilience of the plastic maintains a seal pressure gradient that is supported by the airway pressure itself as the latter increases (17).
The SLIPA is composed of toe, bridge and heel. When the toe of the chamber passes the base of tongue, it easily advances to the pharynx aided by a jaw thrust by an assistant, and seals the entrance of the oesophagus without lifting the epiglottis. The bridge fits into the pyriform fossae, sealing the upward outlet at the base of the tongue. The heel of the chamber is fixed at the entrance of the nasopharynx and soft palate tightly enough to be connected to the corrugated tube without securing using other measures such as adhesive strapping or a bite-block. SLIPA insertion is simpler than insertion of an LMA because the SLIPA can be inserted without cuff insufflation or use of a bite-block. Hein et al reported in a trial with medical students that the SLIPA could be used for primary airway management because it is more easily inserted than a SoftSeal[TM] laryngeal airway (18).
In this study, OLP or maximum sealing pressure was measured to evaluate the stability of the SLIPA for airway maintenance. The OLP was originally identified by listening for gas leak into the oral cavity. Keller et al defined OLP as the point where slowly increased pressure, within a mechanical ventilator, peaks and is maintained. If the OLP is equal to or lower than PIP, gas leakage around the SLIPA can occur and trigger inadequate ventilation or gastric distension, heightening the risk of regurgitation and aspiration3. In the SLIPA group, the OLP increased more significantly after gas insufflation than after patient positioning in lithotomy or Trendelenburg and this was the case in both groups for PIP. These increases in PIP appear due to the intra-abdominal pressure of 10 to 14 mmHg maintained by C[O.sub.2]. In the SLIPA group, the difference in the values between OLP and PIP (approximately 10 cm[H.sub.2]O throughout the procedure) was suitable for airway maintenance, despite the marked increases in OLP and PIP observed immediately before and after the creation of a pneumoperitoneum. Miller et al described three main sealing mechanisms for supralgottic airways (17). The SLIPA is a cuffless, anatomically pre-shaped sealer and the mechanism by which the outlet from the pharynx at the base of the tongue is sealed is by virtue of the resilience of the walls of the shaped airway. The pressure inside the airway assists in keeping the airway shape as the pressure increases, making it a very stable airway once in position.
The risk of pulmonary aspiration is a major concern when using supraglottic airway devices. Lange et al conducted a comparative study of the SLIPA and an LMA in patients undergoing ophthalmic surgery and reported that gastric insufflation occurred more often with the SLIPA, but no regurgitation was observed in either group (19). In this study, although gastric air insufflation was not monitored by auscultation using a stethoscope, gastric distension was not observed and clear surgical fields were provided throughout the operation in both groups. No regurgitation of gastric contents occurred, possibly in part due to adequate neuromuscular block.
The incidence of sore throat was not significantly different. The SLIPA is made of stiff plastic material and of fixed shape and causes direct trauma to the oral mucosa. Brimacombe et al reported that although the SLIPA caused more damage to pharyngeal tissue due to its rough surface compared with the LMA, the incidence of sore throat was markedly decreased by the SLIPA (20). In this study, compared to the ETT group, the SLIPA group showed no significant difference in sore throat in the recovery room but less severe symptoms at 24 hours, possibly because of the inflatable cuff of the ETT or the use of a laryngoscope in the ETT group. No additional analgesics were needed to treat sore throat in either group, so we do not think the finding has clinical significance.
In conclusion, the SLIPA, a new supraglottic airway device, performed as well as an endotracheal tube in allowing positive pressure ventilation, without gas leakage, during gynaecological laparoscopy. There were no differences in airway maintenance or ventilatory efficiency and we speculate that the way in which the SLIPA increased its resistance to leak, as the inspiratory pressure rose, might account for the similar performance.
Accepted for publication on February 21, 2011.
(1.) Wilkins CJ, Cramp PG, Staples J, Stevens WC. Comparison of the anesthetic requirement for tolerance of laryngeal mask airway and endotracheal tube. Anesth Analg 1992; 75:794-797.
(2.) Pennant JH, White PF. The laryngeal mask airway. Its uses in anesthesiology. Anesthesiology 1993; 79:144-163.
(3.) Weiler N, Latorre F, Eberle B, Goedecke R, Heinrichs W. Respiratory mechanics, gastric insufflation pressure, and air leakage of the laryngeal mask airway. Anesth Analg 1997; 84:1025-1028.
(4.) Ho-Tai LM, Devitt JH, Noel AG, O'Donnell MP. Gas leak and gastric insufflation during controlled ventilation: face mask versus laryngeal mask airway. Can J Anaesth 1998; 45:206-211.
(5.) Devitt JH, Wenstone R, Noel AG, O'Donnell MP. The laryngeal mask airway and positive pressure ventilation. Anesthesiology 1994; 80:550-555.
(6.) Fullekrug B, Pothmann W, Werner C, Schults am Esch J. The laryngeal mask airway: anesthetic gas leakage and fiberoptic control of positioning. J Clin Anesth 1993; 5:357-363.
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(8.) Koehli N. Aspiration and the laryngeal mask airway. Anaesthesia 1991; 46:419.
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(10.) Puri GD, Hegde HV, Jayant A, Bhukal I. Haemodynamic and Bispectral index response to insertion of the Streamlined Liner of the Pharynx Airway (SLIPA): comparison with the laryngeal mask airway. Anaesth Intensive Care 2008; 36:404-410.
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(14.) Pelosi P, Foti G, Cereda M, Vicardi P, Gattinoni L. Effects of carbon dioxide insufflation for laparoscopic cholecystectomy on the respiratory system. Anaesthesia 1996; 51:744-749.
(15.) 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; 85:262-266.
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(17.) Miller DM. A proposed classification and scoring system for supraglottic sealing airways: a brief review. Anesth Analg 2004; 99:1553-1559.
(18.) Hein C, Owen H, Plummer J. Randomized comparison of the SLIPA (Streamlined Liner of the Pharynx Airway) and the SS-LM (Soft Seal Laryngeal Mask) by medical students. Emerg Med Australas 2006; 18:478-483.
(19.) Lange M, Smul T, Zimmermann P, Kohlenberger R, Roewer N, Kehl F. The effectiveness and patient comfort of the novel streamlined pharynx airway liner (SLIPA) compared with the conventional laryngeal mask airway in ophthalmic surgery. Anesth Analg 2007; 104:431-434.
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S. J. HONG*, K. M. KO [dagger], J. H. PARK [double dagger], I. S. KIM [double dagger], S. M. HWANG [section], K. M. SHIN**, Y. J. YOON**, S. S. KANG [dagger]
Department of Anesthesiology and Pain Medicine, Kang-Dong Sacred Heart Hospital, Seoul, Republic of Korea
* M.D., Ph.D., Assistant Professor.
[dagger] M.D., Resident.
[double dagger] M.D., Assistant Professor.
[section] M.D., Ph.D., Assistant Professor, Department of Anesthesiology and Pain Medicine, Hallym University, College of Medicine, Chuncheon.
**M.D., Ph.D., Professor.
Address for correspondence: Dr S. S. Kang, Department of Anesthesiology and Pain Medicine, Kang-Dong Sacred Heart Hospital, Hallym University Medical Center, 445, Gildong, Kangdong-gu, Seoul 134-701, Republic of Korea Email: firstname.lastname@example.org
Table 1 Demographic data ETT group, SLIPA group, (n=20) (n=20) Age, y 42.3 [+ or -] 11.3 43.3 [+ or -] 7.9 Weight, kg 58.4 [+ or -] 5.5 56.3 [+ or -] 5.6 Height, cm 160.1 [+ or -] 6.6 158.6 [+ or -] 5.3 BMI, kg/[m.sup.2] 22.9 [+ or -] 3.2 22.4 [+ or -] 2.1 Operation time, min 114.5 [+ or -] 48.7 99.5 [+ or -] 35.5 Anaesthesia time, min 127.8 [+ or -] 49.2 116.3 [+ or -] 35.3 Pneumoperitoneum time, min 96.3 [+ or -] 46.4 91.3 [+ or -] 36.8 Values are expressed as mean [+ or -] SD. ETT=endotracheal tube, SLIPA=Streamlined Liner of Pharynx Airway, BMI=body mass index. Table 2 Changes in lung mechanics T1 EtC[O.sub.2], mmHg ETT 34.1 [+ or -] 3.3 SLIPA 35.2 [+ or -] 5.6 Preset [V.sub.T], ml ETT 516.3 [+ or -] 50.2 SLIPA 502.5 [+ or -] 25.5 Measured [V.sub.T], ml ETT 66.4 [+ or -] 66.8 SLIPA 463.0 [+ or -] 25.5 RR ETT 13.5 [+ or -] 0.9 SLIPA 13.6 [+ or -] 1.0 PIP (cm[H.sub.2]O) ETT 15.3 [+ or -] 1.9 SLIPA 13.7 [+ or -] 2.3 * T2 EtC[O.sub.2], mmHg ETT 27.6 [+ or -] 2.1 SLIPA 31.7 [+ or -] 2.3 Preset [V.sub.T], ml ETT 517.5 [+ or -] 51.4 SLIPA 507.5 [+ or -] 29.3 Measured [V.sub.T], ml ETT 486.0 [+ or -] 56.1 SLIPA 476.7 [+ or -] 29.4 RR ETT 13.4 [+ or -] 0.9 SLIPA 13.7 [+ or -] 1.0 PIP (cm[H.sub.2]O) ETT 16.5 [+ or -] 1.7 SLIPA 15.5 [+ or -] 2.6 T3 EtC[O.sub.2], mmHg ETT 35.2 [+ or -] 3.0 SLIPA 35.2 [+ or -] 2.8 Preset [V.sub.T], ml ETT 516.3 [+ or -] 49.5 SLIPA 512.5 [+ or -] 31.9 Measured [V.sub.T], ml ETT 489.5 [+ or -] 54.6 SLIPA 491.2 [+ or -] 40.0 RR ETT 13.4 [+ or -] 0.9 SLIPA 13.6 [+ or -] 1.1 PIP (cm[H.sub.2]O) ETT 23.7 [+ or -] 3.4 SLIPA 22.8 [+ or -] 2.9 T4 EtC[O.sub.2], mmHg ETT 34.8 [+ or -] 3.1 SLIPA 35.7 [+ or -] 2.6 Preset [V.sub.T], ml ETT 492.0 [+ or -] 55.8 SLIPA 510.0 [+ or -] 38.4 Measured [V.sub.T], ml ETT 465.5 [+ or -] 56.5 SLIPA 499.0 [+ or -] 38.4 RR ETT 13.9 [+ or -] 1.0 SLIPA 14.3 [+ or -] 1.7 PIP (cm[H.sub.2]O) ETT 22.9 [+ or -] 3.3 SLIPA 23.0 [+ or -] 2.9 T5 EtC[O.sub.2], mmHg ETT 34.8 [+ or -] 3.2 SLIPA 36.4 [+ or -] 2.9 Preset [V.sub.T], ml ETT 486.3 [+ or -] 43.3 SLIPA 507.5 [+ or -] 33.5 Measured [V.sub.T], ml ETT 475.2 [+ or -] 57.2 SLIPA 496.0 [+ or -] 33.5 RR ETT 14.4 [+ or -] 1.7 SLIPA 14.7 [+ or -] 2.0 PIP (cm[H.sub.2]O) ETT 19.1 [+ or -] 2.6 SLIPA 19.3 [+ or -] 3.4 Values are expressed as mean [+ or -] SD. T1 = 1 minute after induction, T2=10 minutes after lithotomy position, T3 = 10 minutes after pneumoperitoneum, T4=30 minutes after pneumoperitoneum, T5 = 10 minutes before the end of procedure, EtC[O.sub.2]=end-tidal carbon dioxide, ETT=endotracheal tube, SLIPA=Streamlined Liner of Pharynx Airway, [V.sub.T]=tidal volume, RR=respiratory rate, PIP=peak inspiratory pressure. * significantly different from the ETT group (P <0.05). Table 3 Complications ETT group, SLIPA group, (n=20) (n=20) Blood staining 0 1 Regurgitation or aspiration 0 0 Sore throat, n 7 6 Severity of postoperative sore throat 1 h 0.9 [+ or -] 1.3 0.6 [+ or -] 0.9 24 h 1.35 [+ or -] 1.6 0.4 [+ or -] 0.8 *
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