1.Preparation before insertion
Choose the appropriate type and model of mask according to the patient’s physical condition, concomitant diseases and the type of surgery, routinely check carefully whether the mask air sac is leaking, and then apply a small amount of water-based lubricant on its dorsal side (note that silicone based lubricant should not be used because it will react with the silicon-containing components of the mask and affect the safe use of the mask, and lubricants containing lidocaine should also be avoided.
Because it will delay the recovery of protective reflexes, cause allergy and affect the surrounding tissues including vocal cords) to reduce the resistance of the mask during insertion, but when applying the lubricant, care should be taken that the lubricant is applied in the right amount, and the lubricant should not be applied on the front side of the air sac to avoid sliding between the mask and the laryngeal tissues after mask insertion, which will affect the positioning of the mask, in addition the lubricant should not be applied at the mask opening to prevent the lubricant from entering The lubricant should not be applied to the opening of the mask to prevent the lubricant from entering the larynx and inducing laryngospasm.
There are many opinions about the state of the airbag when the mask is inserted. It has been reported in the literature that the gas in the airbag should be completely pumped out by a syringe before the mask is inserted (because the airbag of the mask is very likely to curl during the pumping process, so the tip of the airbag can be pinched and pulled forward with the fingers while pumping, which will ensure the shape of the airbag to a certain extent. This step can also be performed with a special mask airbag shaping clip, which ensures that the airbag of the mask maintains its flat shape during the process of pumping), but the airbag is prone to folding if the mask is not compressed in the direction of the hard palate or if there is insufficient lubrication.
It is also believed that keeping the balloon partially inflated during mask insertion can help prevent the balloon from folding during insertion and that the success rate of mask insertion using the partial balloon inflation method is higher than mask insertion with the balloon fully deflated. It must be noted, however, that the use of partial inflation of the balloon requires good mouth opening and complete muscle relaxation, and should be used with caution in patients with stiff jaws and small mouths.
It has also been reported that inserting a core into the mask to facilitate mask insertion (for one generation of plain masks only) can definitively improve the one-time success rate of mask insertion, especially in the less experienced patient, and that bending the mask with the core to 90 degrees so that its curvature is similar to that of an intubated laryngeal mask (ILMA) can also improve the success rate of one-time insertion. It must be noted that when the laryngoscope is guiding the mask insertion, it is easier to operate the mask with the core inside, but if the finger guidance method is used, the addition of the core inside the mask affects the operation.
After making the above preparations, the mask should be set aside for use (at the same time, a suitable tracheal tube should be prepared in case of mask insertion failure).
2.Method of laryngeal mask insertion
(1) Blind probe method
①Finger guidance method.
This method is the most traditional and most commonly used method of mask insertion in clinical practice and is applicable to all types of masks. The specific operation method is as follows: the operator wears gloves and pushes the patient’s head gently with the right hand to make the patient’s head tilt back slightly (such a position is favorable for mask insertion. It has been reported that if the angle between the oral axis and the laryngeal axis is too small, such as the restricted head tilt caused by ankylosing spondylitis or severe rheumatoid arthritis, the mask insertion may fail even if the method is correct.
Therefore, the axis of the mouth and the axis of the larynx must be greater than 90 degrees for the mask to be successfully placed. The operator probes the patient’s mouth with the thumb of the left hand and pulls the patient’s jaw to widen the oral space, the right hand holds the mask in the pen style, and to facilitate the force, the fingertips of the index and middle fingers can be placed against the connection between the mask body and the ventilation tube. The mouth of the mask should be oriented toward the jaw (or toward the palate, and then twisted 180 degrees after the mask is inserted into the bottom of the mouth), and the position of the patient’s lips and tongue should be noted during this process, which should be avoided to be stuck between the teeth and the mask to avoid various injuries.
After the position of the mask is determined to be in the middle of the mouth and the balloon is flat, the mask is placed along the midline of the tongue against the hard palate, the soft palate, and the posterior pharyngeal wall in sequence until it cannot be advanced any further (some male patients can see the laryngeal nodes moving up and down with the mask), and finally the balloon is inflated. 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 for cases where, for various reasons, the operator cannot operate from the posterior side of the patient.
The procedure is as follows: the operator holds the mask in one hand, the thumb is located at the connection between the mask and the airway tube, and the other four fingers are located on the dorsal side of the mask, with the operator facing the patient. When inserting the mask using the finger guidance method, it should be noted that the guiding finger should keep the mask body pressed against the patient’s hard palate during the mask insertion process, which can reduce the possibility of the mask tip folding and help the mask to be placed in the correct position.
This method of insertion is simple and easy to learn, and does not require specialized procedures such as laryngoscopy and revealing the vocal cords, and can be used easily and effectively by inexperienced physicians after simple training. For some patients with small mouth opening, large tongue or abnormally enlarged tonsils, it is difficult to use.
②Using the guiding tool method.
This method is limited to third generation esophageal drainage type laryngeal mask. It is a bendable and ductile metal sheet device (the inner surface and the bent head are coated with a layer of transparent dimethylsilicone oil, which can reduce the damage caused during insertion), and has a control handle.
Its specific use is as follows: In addition to the usual preparation before use, the guidance tool and esophageal drainage mask should be assembled together as follows: first, insert the end of the guidance tool into the locking ring of the mask, then bend the airway tube and drainage tube of the mask so that it is attached to the protruding curved surface of the guidance tool, and snap the outer end of the airway tube in the corresponding slot of the guidance tool to be used.
When inserting the mask, the patient’s head and neck should be adjusted first, and then the mask should be placed in the mouth with the guiding tool assembled, with the mouth of the mask facing the jaw, and placed sequentially along the midline of the tongue against the hard palate, the soft palate, and the posterior pharyngeal wall until it can no longer be advanced. Once the position of the mask is determined with the other hand, the airway tube can be moved out of the slot and then the guiding tool is rotated and moved out of the oral cavity.
The advantage of this insertion method is that it can be inserted without finger guidance and the curvature of the guiding tool is well suited to the flexion of the human oral cavity to the pharynx, making insertion smoother. On the other hand, this method can help the operator insert the mask in certain positions that are not very conventional, such as when it is located on the front and side of the patient.
This is of great importance in the placement of laryngeal mask in patients with respiratory infectious diseases (such as SARS patients), which can reduce the chance of infection of medical personnel.
(2) Visualization method
(1) Laryngoscopy-assisted visualization method.
It is applicable to all types of laryngeal mask, and the specific operation method is as follows: place the laryngoscope according to the conventional method, revealing or not revealing the voice box, hold the mask with the right hand by holding the pencil, with the mouth of the mask facing the jaw, and place the mask along the midline of the tongue against the hard palate, the soft palate, and the posterior pharyngeal wall in the downward sequence. In this method, the patient’s mouth is fully exposed and there is a large operating space when inserting the mask, which reduces the possibility of collapse of the balloon in the oral cavity and makes it easier to reach the correct position of the mask, but on the other hand, because of the need to insert the laryngoscope, the mechanical stimulation of the patient is greater, and the patient must be under a certain depth of anesthesia compared with the blind exploration method, otherwise it may cause greater hemodynamic changes.
②GEB (rubber elastic probe) and gastric tube guidance method.
(GEB is an elastic probe that has been put into clinical use in recent years, with a diameter of about 2 to 3 mm and a length of about 45 to 50 cm, with rounded ends and good elasticity). This method is only applicable to the third generation of esophageal drainage type laryngeal mask. Since this type of mask is designed with an esophageal drainage tube parallel to the tracheal ventilation tube, it makes it possible to insert the GEB into the esophagus and then use this as a track to introduce the esophageal drainage type laryngeal mask.
This approach was used in 2002 as follows: The lubricated GEB is first inserted into the esophageal drainage tube of the laryngeal mask and should extend some distance beyond its medial port to facilitate its insertion into the esophagus by the operator, and the lateral end of the GEB should extend some distance beyond the lateral port of the laryngeal mask to facilitate grip by the operator. The insertion procedure is to first gently place the laryngoscope (without having to see the voice box as in tracheal intubation), see the esophageal opening, the operator grasps the laryngeal mask and the lateral end of the GEB, places the medial end of the GEB into the esophagus about 5-10 cm, carefully removes the laryngoscope, and introduces the esophageal drainage type laryngeal mask using a finger-guided technique while ensuring that the GEB does not move forward in the esophagus.
An assistant helps to pump up the air bag and connect the ventilation system. Do not take out the GEB until it is secured. In case the mask is displaced, it can be reinserted using the GEB as a guide. The advantage of this method is that the lower part of the mask can be accurately placed in the hypopharynx with minimal damage to the posterior aspect of the oral cavity. It also avoids folding of the lower portion of the mask.
Moreover, the incorrect insertion position rarely occurs in the case of using this method, so there is no need to check the position of the mask and the patency of the drainage tube after insertion. However, the biggest disadvantage of this method is the possibility of damaging the upper esophagus, so it is required that the GEB be inserted as gently as possible. (Although the GEB guidance method is highly accurate, it has not been in clinical use for a long time, and there is not yet a large amount of clinical trial data to support its safety, so it should still be used with caution.)
In 2001 and 2002, a gastric tube was used to guide the insertion of the esophageal drainage mask, and the specific procedure was the same as that of the GEB guidance method. Although injury to the upper esophagus does not occur with the use of the gastric tube, the gastric tube is soft, which sometimes leads to its inability to guide the mask well to a good position.
(iii) Fiberoptic endoscopic guidance method.
The light-guided endoscope was rarely used during the insertion of the first-generation laryngeal mask and was generally used only to determine whether the mask was correctly positioned. In the use of second-generation trans-intubated laryngeal mask, fiberoptic endoscope is mostly used to guide the insertion of tracheal intubation, especially in patients with head and neck injuries or lesions resulting in limited head and neck mobility or fixed position. The endoscope can be inserted into the esophagus without laryngoscopic guidance, thus guiding the insertion of the mask.
This insertion method allows a clear view of the larynx through the fiberoptic endoscope, and the position of the mask insertion is more accurate.
④Using video laryngoscope to assist insertion.
Video laryngoscope is a new type of laryngoscope put into clinical use in recent years. The difference between it and the ordinary laryngoscope is that a camera system is added under the laryngoscope lens, and there are wires leading out to a specific monitor, so that the situation at the front of the laryngoscope is like on the monitor. The biggest advantage is that the operator does not need to see through the mouth, but only needs to observe the monitor image to guide the operation, and can check whether the various parts of the mask are in the correct position by the video laryngoscope image. This method allows the anesthesiologist to insert the mask in relatively difficult positions, and for infectious patients (e.g. SARS patients), the video laryngoscope can be used to facilitate the procedure without fear of infection.
If one insertion method fails, other methods can be tried until the mask is successfully inserted.
With the advent and improvement of various mask insertion methods, physicians will become more comfortable with the use of the mask, and it will be used more and more widely as an adjunct to both the definitive airway and other airway devices, playing a greater role in emergency airway opening.