The laryngeal mask is undoubtedly one of the most famous inventions in the history of airway management. In 1981, British anesthesiologist Dr. Archie Brain designed the world's first laryngeal mask, which was successfully launched in the UK in 1988. Since then, the LMA brand alone has been used 500 million times, and Dr. Archie Brain received the Medical Future Innovation Award and the Lifetime Achievement Award in 2007.

The laryngeal mask, fully known as the laryngeal mask airway (LMA), is an artificial airway placed in the pharyngeal cavity, sealing the esophagus and pharyngeal cavity with an inflatable cuff, allowing ventilation through the laryngeal cavity. It avoids tracheal intubation but is more effective than using a face mask.

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Indications

1. Surgeries with no risk of vomiting or reflux, especially in patients with difficult tracheal intubation.

2. When intubation is difficult and the laryngeal mask (LMA) is used, it can serve as a guide for tracheal intubation.

3. Fiberoptic bronchoscopy can be performed through the laryngeal mask for laser ablation of small tumors in the vocal cords, trachea, or bronchi.

4. In patients with cervical spine instability who need to move their heads for intubation but have significant concerns, the laryngeal mask can be used.

5. The laryngeal mask is suitable for ophthalmic surgeries, as it causes less increase in intraocular pressure, less coughing and vomiting postoperatively, and has a milder response upon removal.

6. The laryngeal mask can be used in emergency resuscitation, as skilled operation can quickly establish effective ventilation with definite results.

7. Suitable for surface and limb surgeries under general anesthesia that do not require muscle relaxation.

Contraindications

(1) Absolute contraindications

1. Patients who have not fasted and have delayed gastric emptying.

2. Patients at risk of reflux and aspiration: such as those with esophageal hiatal hernia, pregnancy, intestinal obstruction, acute abdomen, thoracic injury, severe trauma, and a history of gastric content reflux.

3. Patients with tracheal compression and tracheomalacia may experience airway obstruction after anesthesia.

4. Obesity, oropharyngeal lesions, COPD, and pregnancy over 14 weeks.

5. Patients with limited mouth opening, where the laryngeal mask cannot pass.

(2) Relative contraindications

1. Patients with low lung compliance or high airway resistance: these patients often require positive pressure ventilation (25-30 cmH2O), and there is a frequent occurrence of leaks around the mask and anesthetic gas entering the stomach.

2. Lesions in the pharynx and larynx: patients with abscesses, hematomas, edema, tissue damage, and tumors in the pharynx and larynx. Laryngeal lesions may lead to upper airway obstruction.

3. Difficult access to the airway or certain special positions: such as when in the prone or lateral position, or when the anesthesiologist needs to be away from the operating table. If the LMA displaces or dislodges, and in cases of vomiting and reflux, the physician cannot immediately perform tracheal intubation or other interventions.

Structure of the laryngeal mask

The laryngeal mask consists of an inflatable cuff, a connecting tube, a connector, and a tube for inflating the cuff. It can be divided into straight and pre-curved types. The appropriate size of the laryngeal mask should be selected based on the patient's weight. Before placement, a 20-40 ml syringe (for inflating the cuff), lubricant, and tape should also be prepared.

Types of laryngeal masks

Based on their characteristics and uses, laryngeal masks can be divided into four categories: standard laryngeal masks (used to maintain spontaneous breathing during anesthesia), reinforced laryngeal masks (used for controlled ventilation), intubating laryngeal masks (to assist with tracheal intubation), and double-lumen laryngeal masks.

Standard laryngeal mask: available in 8 sizes (size 1, 1.5, 2, 2.5, 3, 4, 5, 6). Due to the risk of leaks during positive pressure ventilation, there is a danger of gastric distension, reflux, and aspiration, so long-term use is not recommended.

Reinforced laryngeal mask: the ventilation tube can be bent, and compared to the standard laryngeal mask, the airway is less likely to kink, thus reducing the risk of airway obstruction. It is mainly used for mechanical ventilation in eye, nose, throat, cranial, and oral surgeries. Currently, there are six sizes: 2, 2.5, 3, 4, 5, and 6, suitable for the same population as the standard laryngeal mask.

Intubating laryngeal mask: has a fixed curvature and a large inner diameter, allowing for the passage of a tracheal tube, and the size of the laryngeal mask determines the thickness of the tracheal tube that can be inserted. There are 3 sizes; sizes 3 and 4 can accommodate an ID 6.0 mm tracheal tube, and size 5 can accommodate an ID 7.0 mm tracheal tube, mainly used for patients with anticipated or unanticipated difficult intubation.

Double-lumen laryngeal mask: its main feature is the improvement of the ventilation mask and the addition of a drainage tube, forming two interconnected sealed chambers after insertion. One chamber seals the larynx and connects to the ventilation pathway, while the other seals the esophageal upper sphincter opening and connects to the drainage tube. Compared to the standard laryngeal mask, the insertion difficulty is similar, but it is safer and more effective during positive pressure ventilation, with a lower incidence of aspiration. It also allows for the placement of a suction catheter through the drainage pathway, making it easy to detect when positioned incorrectly. Therefore, its clinical application range is broader, suitable not only for surface surgeries of the limbs but also for laparoscopic abdominal surgeries.

　Selection of sizes

Neonates (<4 kg) size 1.0 laryngeal mask

Infants (5-10 kg) size 1.5 laryngeal mask

Children (10-20 kg) size 2.0 laryngeal mask

Children (20-30 kg) size 2.5 laryngeal mask

Adults (30-50 kg) size 3.0 laryngeal mask

Adult (50-70 kg) size 4.0 laryngeal mask

Adult (70-100 kg) size 5.0 laryngeal mask

Adult (>100 kg) size 6.0 laryngeal mask

Due to the relatively small volume of the oral and pharyngeal cavity in children, even a slight mistake can lead to airway obstruction and tissue damage. Therefore, before placing the LMA, the appropriate size should be selected based on age and weight (i.e., for newborns/infants <5 kg, infants 5-10 kg, infants 10-20 kg, children 20-30 kg, and children >30 kg, sizes 1.0, 1.5, 2.0, 2.5, and 3.0 LMA should be used respectively, with maximum inflation volumes of 4 ml, 7 ml, 10 ml, 14 ml, and 20 ml).

Alternatively, use the three-finger width method: the child's palm is opened, palm facing up, with the thumb and little finger separated, and the index, middle, and ring fingers together; different sizes of laryngeal masks are inflated to the standard maximum, and the front of the mask is pressed against the child's finger palm. The widest part of the mask is compared with the maximum width of the child's index, middle, and ring fingers to determine the most suitable size. This method is particularly useful in emergencies when the child's weight is unknown.

Insertion method

1. Conventional method

With the left hand, push the back of the patient's head to extend the neck and tilt the head back. With the right hand, hold the well-lubricated LMA with the index and thumb, orienting the opening of the mask towards the patient's chin. Press the front end of the LMA against the inner surface of the upper notch and insert it into the oral cavity, then push the LMA upwards against the hard palate. Use the index finger to push the LMA at the junction of the ventilation tube and the mask inward, pushing the LMA as far as possible into the hypopharynx, with the lower end entering the upper esophagus, tightly against the base of the epiglottis, and the ventilation port inside aligned with the glottis. When satisfactory depth is reached, resistance can be felt. Hold the ventilation tube with the left hand to stabilize the LMA, then withdraw the index finger, inflate, connect to the anesthesia machine, and assess ventilation function before adjusting and securing; in addition to using the index and middle fingers for guidance, the thumb can also be used to guide the insertion of the mask. This method is suitable when the operator cannot operate from the back of the patient for various reasons. The specific steps are as follows: the operator holds the mask with one hand, with the thumb at the junction of the mask body and airway tube, and the other fingers on the back side of the mask, facing the patient. The insertion process is similar to the index finger guidance method, except that during insertion, the thumb and the mask opening are always facing the mandible.

2. Inversion method

The insertion method is basically the same as the conventional method, except that the mask opening is first oriented towards the hard palate and inserted into the oral cavity until the base of the pharynx, then gently rotated 180 degrees (mask opening facing the larynx) before continuing to push the mask down until it cannot be pushed further.

3. Lateral position method

The mask is slid over the hard palate at a 45-degree angle, while the proximal end of the ventilation mask is pressed to one side and the distal end to the other side. During insertion, the distal side of the ventilation mask should be used as the contact edge with the hard palate, smoothly sliding the mask at a 45-degree angle over the hard palate and pushing it into the oropharynx. Once the ventilation mask reaches the laryngopharynx, it should be positioned correctly (opening facing the pharynx).

The ideal position for laryngeal mask insertion: the side of the mask cuff faces the piriform recess, and the anterior surface of the proximal end is behind the base of the tongue and below the level of the tonsils. The concave surface of the mask cuff is aligned with the aryepiglottic fold, and the back of the cuff is tightly against the posterior pharyngeal wall. Once the cuff around the mask is inflated, a closed circle can be formed at the larynx, ensuring effective ventilation. The average depth of laryngeal mask insertion for children under 10 years = 10.0 cm + 0.3 cm × age (years).

Operational methods

1. The recommended method is for the patient to be in a supine position, with the doctor standing at the patient's head side. Tilt the patient's head back, fully deflate the cuff, shape it, and insert it facing forward along the hard palate. The right index finger can help push the tongue aside. Applying a water-based lubricant to the distal surface can reduce insertion resistance. For patients suspected of having neck injuries, do not tilt their head back.

2. The cuff of the laryngeal mask can be partially inflated before insertion, with the mask facing the head end along the hard palate. Once it reaches the larynx, rotate it 180° and push down until resistance is met, then inflate.

3. The single-use Supreme laryngeal mask can be inserted without deflation. After inserting the laryngeal mask, perform positive pressure ventilation, observe the degree of chest wall movement, auscultate for symmetrical and clear breath sounds on both sides, and check for any leakage sounds in the anterior neck area.

4. The timing for withdrawing the laryngeal mask is divided into deep anesthesia extubation and light anesthesia extubation. Deep anesthesia extubation can avoid irritation that causes airway reflexes and laryngospasm, but there is a risk of aspiration and airway obstruction; light anesthesia extubation can ensure the recovery of protective reflexes, but there is a risk of excessive airway reactivity.

Using 2% lidocaine gel to lubricate the laryngeal mask cuff or administering opioids intravenously can reduce airway reflexes during awakening.

Advantages + Disadvantages

Advantages of the laryngeal mask

1. Easy to use, quickly establishes an artificial airway (spontaneous, controlled).

2. High success rate of intubation, with a first-attempt success rate of 87% for untrained individuals and a total success rate of 99.81% after two attempts.

3. Reliable ventilation, better than mask ventilation.

4. Can avoid damage to the pharynx, vocal cords, and trachea.

5. Minimal stimulation and cardiovascular response.

6. Emergency (urgent ventilation).

Disadvantages of the laryngeal mask

1. Poor sealing effect, can cause gastric distension (especially with IPPV), not suitable for high positive pressure ventilation.

2. The laryngeal mask is more prone to esophageal reflux than a mask, and should not be used in patients with a full stomach.

3. Increased oral secretions.

4. Some types of laryngeal masks cannot use standard suction catheters to aspirate secretions from the trachea through the mask.

Indications

1. Respiratory obstruction 1) Improper LMA positioning, folding or rotation of the ventilation mask, excessive inflation of the ventilation mask, increased content volume of the ventilation mask due to temperature rise or N2O diffusion, and glottis closure. 2) In children, the tongue is larger, the glottis is positioned higher and more anteriorly, and the epiglottis is large and soft, often covering the pharynx, leading to respiratory obstruction, which occurs nearly twice as often as in adults.

2. Reflux and aspiration 1) Anesthesia and surgery significantly reduce the tone of the upper and lower esophageal sphincters and normal physiological protective reflexes (coughing, breath-holding, etc.). 2) Children have relatively larger gastric juice volume, higher intragastric pressure, and lower pH, making the risk of reflux and aspiration during anesthesia relatively high. 3) LMA does not effectively isolate the esophagus and trachea, and factors such as shallow anesthesia, surgery, and coughing can easily induce reflux and aspiration.

3. Air leakage around the laryngeal mask 1) Poor alignment. 2) Inappropriate model selection of the laryngeal mask. 3) Excessive airway pressure. 4) Insertion too shallow or too deep.

4. Postoperative throat pain 1) The incidence of throat pain after using a laryngeal mask is very low, with literature reporting only 7%. 2) Endotracheal intubation can reach 47%. 3) Face mask and oropharyngeal airway can reach 10%.

5. Laryngeal spasm causes: Inserting or removing the laryngeal mask under shallow anesthesia can induce severe laryngeal spasm leading to airway negative pressure and lung injury; surgical or suction stimulation can also trigger laryngeal spasm.

Management: Generally, oxygen inhalation or deepening anesthesia can relieve it. For severe laryngeal spasm with difficulty in mask ventilation and oxygenation, succinylcholine should be used promptly, and re-intubation should be performed.

Precautions

1. Small tidal volume 6-8 ml/kg, respiratory rate 10-14 breaths/min.

2. Cuff pressure <60 cmH2O.

3. If using a silicone rubber cuff laryngeal mask, N2O can permeate through the silicone rubber into the cuff, increasing the cuff pressure, so cuff pressure should be monitored to avoid >60 cmH2O.

4. If using a double-lumen laryngeal mask, it is recommended to routinely place a gastric tube through the esophageal drainage tube, first actively aspirate, then open the gastric tube, without the need for continuous suction with a negative pressure suction device.

5. The principle of laryngeal mask insertion is to relax the temporomandibular joint, and whether to administer muscle relaxants should be determined based on the surgical needs. If muscle relaxants are not given, general anesthesia with preserved spontaneous breathing can be performed.

6. Apply lubricant to the underside of the laryngeal mask, and minimize or avoid applying it to the front to prevent coughing after insertion; the insertion of the laryngeal mask should be gentle to avoid airway injury caused by force.

7. Appropriate sedation, analgesia, and muscle relaxation are needed during anesthesia to avoid shallow anesthesia.

8. At the end of the surgery, adults can remove the laryngeal mask after waking up, while children can remove it in deep anesthesia and right lateral position.

9. Application of laryngeal mask in difficult airways

(1) The laryngeal mask, as a ventilation tool or intubation guiding tool, can be used for patients with various difficult airways such as cervical spondylosis, use of cervical collars, obstetrics, ankylosing spondylitis, sleep apnea, obesity, congenital diseases, and those at risk of reflux and aspiration. The Mallampati classification and Cormack-Lehane classification are not related to the difficulty of laryngeal mask insertion.

(2) When unable to intubate and unable to ventilate through a mask (CICV), first insert the laryngeal mask for ventilation, and then perform endotracheal intubation through the laryngeal mask.