Portal de Periódicos da CAPES

The Laryngeal Tube S: A Modified Simple Airway Device

2003; Lippincott Williams & Wilkins; Volume: 96; Issue: 2 Linguagem: Inglês

10.1097/00000539-200302000-00057

1526-7598

Volker Dörges, Hartmut Ocker, Volker Wenzel, Markus Steinfath, Klaus Gerlach,

Respiratory Support and Mechanisms

The recently introduced single-lumen Laryngeal Tube can be inserted without additional equipment, and was proven in bench models (1,2) and preliminary clinical trials, to effectively ventilate and oxygenate patients with respiratory arrest (3,4) undergoing routine induction of anesthesia. Thus, the Laryngeal Tube may be used as an alternative airway device during either routine or emergency airway management. Handling of the Laryngeal Tube was later simplified by blocking two cuffs with one catheter instead of two. This procedure secures inflation of the oropharyngeal cuff first, and then of the esophageal cuff because of the different resistance characteristics of the connected tubing. Unfortunately, because of the design of the Laryngeal Tube, it may not be the best airway device for spontaneously breathing patients (5). As discussed earlier, a second disadvantage of the Laryngeal Tube may be the blind ending in the esophageal inlet, which may provoke esophageal rupture in the case of vomiting (3). Accordingly, the Laryngeal Tube was fitted with a second lumen serving for suctioning and free gastric drainage (Laryngeal Tube S [LTS]), but not for ventilation, as with the Combitube. In the present study, our purpose was to assess whether the LTS could provide sufficient ventilation and adequate oxygenation in patients undergoing routine induction of anesthesia for minor surgery. Methods The LTS is a multiple usable, double-lumen, silicon tube with an oropharyngeal and esophageal low-pressure cuff and a ventilation outlet between these cuffs (Fig. 1). With the patient’s head in the neutral position, the tube is placed into the oropharynx until a distinct resistance is felt. Inflation of the oropharyngeal cuff closes the oropharynx and the esophageal inlet is closed by the lower cuff. Accordingly, the ventilation outlet of the LTS is placed in front of the vocal cords (Fig. 2). After approval of the IRB and written informed consent was obtained, 32 adult ASA physical status I and II patients (aged 26–82 yr; Mallampati status I–II) participated in our study, and underwent general anesthesia for routine surgery. After breathing oxygen for 3 min, the induction of anesthesia was initiated with IV alfentanil (15 μg/kg) and IV propofol (2.5 mg/kg; maintenance, 10–15 mg · kg−1 · h−1 IV). The LTS was always inserted by the same anesthesiologist, and cuff inflation was performed with a cuff pressure manometer up to 80 mm Hg. Ventilation (Fio2, 0.4; FiN2O, 0.6) was controlled with a tidal volume of 7 mL/kg, respiratory rate of 10/min, and monitored with a cardiorespiratory monitor. After 2, 5, and 10 min of ventilation, end-tidal carbon dioxide, expiratory tidal volume, and peak airway pressure were recorded. Additionally, two capillary blood gas samples were taken during room air breathing before the induction of anesthesia, and after 10 min of ventilation. Time of insertion was measured from loss of the eyelash reflex to delivering the first tidal lung volume. Oropharyngeal leak pressure and inflation volume were measured with the head in neutral position at a cuff inflation pressure of 80 mm Hg. The expiratory valve of the circle system was closed at a fixed gas flow of 3 L/min and noting the airway pressure at which the aneroid manometer reached equilibrium (6). To prevent lung barotrauma, the expiratory valve was opened as soon as peak airway pressure reached 40 mm Hg and occurrence of gastric inflation was assessed with a stethoscope placed on the epigastrium. Placement of the LTS was controlled with fiberoptic endoscopy.Figure 1: Image of the Laryngeal Tube S.Figure 2: Placement of the Laryngeal Tube S.Results For patients ranging from 153 to 194 cm, size 4 (153–175 cm) and size 5 (>175 cm) LTS were used. In all cases, the LTS was inserted successfully at the first attempt (range, 12–28 s; median, 21 s). Ventilation and blood gas variables 10 min after insertion revealed both sufficient ventilation and oxygenation (Fig. 3, Table 1), and no gastric inflation was noted in any patient. Fiberoptic endoscopy confirmed visualization of the epiglottis and/or the posterior pharyngeal wall, and correct placement of the LTS tip in the esophageal inlet. Airway leak pressure ranged from 20 to 40 (median, 27) cm H2O at an oropharyngeal cuff inflation pressure of 80 mm Hg (mean ± sd; cuff inflation volume, 82 ± 5 mL).Figure 3: Oxygen saturation and end-tidal carbon dioxide throughout the experiment with the Laryngeal Tube S. Data are given as mean ± sd. *P < 0.001 versus before induction, after 2, 5, and 10 min of ventilation. #P < 0.01 versus after 5 and 10 min of ventilation. §P < 0.01 versus after 10 min of ventilation.Table 1: Arterial Blood Gas Samples Before the Induction of Anesthesia, and After 10 min of Ventilation with the Laryngeal Tube SDiscussion Appropriate positioning of the LTS was verified with fiberoptic endoscopy in all patients. Hence, inflation of the lower cuff closed the esophagus and may have protected the airway from regurgitation, which is a major hazard when ventilating an unprotected airway (7,8). Insertion times for the LTS were comparable to those reported for the Laryngeal Tube (3) and laryngeal mask airways (9). After the induction of anesthesia, the LTS allowed immediate oxygenation of the patient with no prolonged lack of ventilation, because this might cause further oxygen desaturation in difficult conditions such as cardiopulmonary resuscitation without the possibility of preoxygenation. When using the LTS, our data show that sufficient ventilation and oxygenation could be achieved similar to the Laryngeal Tube, laryngeal mask airway (10,11), or Combitube (12). Simple handling of the LTS and aspiration protection might be a substantial advantage of this airway device in emergency airway management. Moreover, the possibility of introducing an esophageal catheter through the LTS enables evacuation of stomach contents. This feature may provide two advantages in one device, namely, the LTS can be inserted by health care personnel without intubation skills, and subsequent evacuation of stomach contents is possible. In contrast to the Combitube, the LTS has only one adapter that may be connected with a ventilation device, whereas the remaining connector can only be connected to a suction adapter. This may provide additional patient safety in order to prevent an inexperienced user inadvertently attaching the ventilator or bag-valve-mask device to the esophageal tubing, which could result in stomach inflation and subsequent ventilation-related complications. Accordingly, the LTS user is spared from the possibly difficult decision when employing the Combitube, which portion of the airway device is placed in either the esophageal or tracheal outlet. In our experiment, 80-mm Hg cuff pressure was sufficient to ensure a leak airway pressure of approximately 27 cm H2O, which is similar to the laryngeal mask (13). Even airway pressures of up to approximately 40 cm H2O would have been possible without gastric inflation. Because most patients can be safely ventilated with peak airway pressures of <20 cm H2O, a safety margin is incorporated with 80-mm Hg cuff pressure, allowing peak airway pressures up to 40 cm H2O. Limitations of this preliminary study are lack of comparison with the laryngeal mask and especially, the Combitube. Second, because of breathing oxygen before LTS insertion, our patients were not hypoxic and/or hypercarbic before the intervention. Third, there may be concerns that the LTS may induce possibly dangerous effects, similar to the Esophageal Obturator Airway. However, because of the technical design of the LTS, these adverse effects are, although theoretically possible, highly unlikely. Namely, the 125° angle of the LTS forces it automatically into the dorsal pharynx, and subsequently, into the esophageal inlet. This design feature ensures adequate placement, especially when not using laryngoscopy. Further, the width of the LTS (18 mm) is simply larger than the usual tracheal inlet, thus providing additional safety. In contrast, the Esophageal Obturator Airway does not have a given angle, thus providing a ≤10% chance of entering the tracheal inlet with possible subsequent catastrophes. Fourth, without doubt, a 100% success rate placing the LTS correctly in the esophageal inlet cannot be achieved. However, the LTS is not made for use without subsequent verification of ventilation efficacy. Furthermore, should the esophageal tip of the LTS be placed into the tracheal inlet, subsequent ventilation is not possible because the inflated cuffs would simply block air flow in all directions. Thus, the only theoretical safety leak is from a rescuer who inserts the esophageal inlet into the trachea, subsequently does not block the cuffs, and then fails to assess ventilation efficacy of the lungs. Even in this case, free flow of air into the stomach would not be possible because gas flow would likely be partially blocked by soft tissue in the pharynx. Fifth, in an emergency situation, the focus is ventilating the patient until personnel arrive at the scene who are able to perform endotracheal intubation. This indicates that an increased cuff pressure, which possibly may result in mucosal hypoperfusion, is only transient. However, cuff pressure with the silicone-made, low-pressure cuff of the LTS was approximately 80 cm H2O, which is significantly lower than the cuff pressure when using the Combitube. This is usually in the approximate range of 80–300 cm H2O, and 100–250 cm H2O, as was found for the laryngeal mask airway (14). In conclusion, the LTS might be a simple alternative device to secure the airway and to evacuate stomach contents of patients.