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The declared aim of airway management is to secure a patient’s airways so that he/she can breathe spontaneously during an emergency case or an operation, or may be mechanically ventilated. Thus, supplying the organism with oxygen can be ensured. A prior assessment of respiratory conditions, the decision which technique should be applied and, of course, the professional handling of instruments and scrupulous implementation are all important elements in the management of the respiratory tract. The time pressure of falling oxygen saturation presents a challenge for the anesthetist, making every minute count. Even so, intubation and its related procedures require a calm and accurate approach.
Assessment of the Respiratory Tract
To be able to detect difficult intubation conditions before induction of anesthesia, the attending anesthetist must examine a patient’s airway during premedication visit. This is important as in the case of foreseeable difficulties, it will help planning ventilation accordingly and relocating suitable equipment (a video laryngoscope) and staff, for example, an experienced anesthetist from the start. Thus, the following parameters should be enquired and analyzed under a fixed scheme: medical history, the Mallampati score, the size of mandibular space, reclination of the head and dental status.
In the medical history, we may initially gather information on potentially difficult intubation from the previous operations if a patient has experienced intubation problems before. Often a patient does not have detailed knowledge on this matter. Information is provided in the patient passport with anesthesia history. This little yellow document, similar to a vaccination certificate, will be issued by anesthetists when complications or problems occurred during the initiation or anesthesia.
At the same time, a premedical doctor should enquire about and examine malformations and tumors in the mouth and throat area: everything which could constrict or constrain airways must be recorded. In addition, it is important how wide the mouth can be opened. Whether it is 2, 3, 4 or 6 centimeters: the wider it opens, the more “space” remains for the anesthetist to do his/her work. A restricted mouth opening makes it difficult, for example, to view the larynx with the laryngoscope during intubation.
Clinical scores help assessing the airways. Their documentation is also used for standardized disclosure of information to colleagues, because a premedical doctor may not always take part in anesthesia. This includes, for example, the Mallampati score. We judge with the Mallampati score which pharynx structures are visible when a patient opens his/her mouth wide and sticks his/her tongue out as far as possible. In this case, he/she sits upright, with a neutral head position, phonation is not applicable. Depending on the visible structures, we choose a score of intubation difficulty under Mallampati classification (Class I-IV). The goal is to determine whether the laryngeal inlet is visible with direct laryngoscopy.
|Class I||Uvula completely visible||The glottis is usually fully adjustable laryngoscopically|
|Class II||Uvula partially visible||Varying good glottal adjustability|
|Glass III||Soft and hard palate visible||Varying good glottal adjustability|
|Glass IV||Only hard palate visible||Usually only epiglottis or the base of the tongue|
Cormack and Lehane
During the intubation procedure the glottis is adjusted and its visible structures are directly evaluated using the laryngoscope. This index is called classification by Cormack and Lehane. It divides the invisible portion of the larynx in Class I, II, III and IV. The higher the class, the more difficulty of intubation increases.
Cormack and Lehane:
|Class I||Total glottis is visible|
|Class II||Glottis is only partially visible (at the rear commissure)|
|Class III||Glottis is not adjustable. Only epiglottis is visible.|
|Class IV||Larynx structures and epiglottis cannot be adjusted. Only soft palate visible.|
The size of mandibular space is another object of examination. Mandibular space includes the oral cavity and upper throat, thus focusing on the space in front of the larynx. In this case, we estimate the distance between the chin and jaw line. The throat is usually clearly visible at a distance of > 9 cm (adults) (the Mallampati score).
Reclination of the head
In addition, the reclination ability of the head must be checked. How far the patient’s head can be extended in the reclination position is important in the introduction of the laryngoscope. In this case, the patient’s head is hyperextended in order to reach a common axis of the mouth, the pharynx and the larynx. Measures for dealing with difficult airways must be taken (see below) if this is not possible, e.g. in the case of the cervical spine stiffness in the context of ankylosing spondylitis, or it is only possible to a limited extent, for instance, due to cervical spine injuries. Normal hyperextensibility of the head is approximately 35 degrees. In order to fix this angle, after seating the patient upright with his/her head straight ahead, he/she is asked to overstretch it.
Last but not least, the dental status also plays an important role in airway management. Are there prostheses which must be removed before the procedure, or loose front teeth? Caution should be exercised when intubating: a loose tooth is already annoying enough as it may fall in the oral cavity of the patient during anesthesia. It also poses a risk of aspiration and swallowing. Dental status is exceptionally important for the patient and doctor in order to be able to provide evidence that an injury of the patient has not occured due to intubation.
At a glance: Assessment of the respiratory tract
If these criteria which are easy to comprehend are considered, intubation difficulties are expected to be relatively simple to assess!
- Medical history and examination
- Mallampati score
- Size of mandibular space
- Reclination of the head
- Dental status
In fact, securing the patient’s airways can be carried out via supraglottic procedures such as a face mask and a laryngeal mask, or through endotracheal intubation using infraglottic techniques.
With the induction of anesthetic drug, the patient loses his/her consciousness which is also accompanied by respiratory arrest. Therefore, in all anesthesia cases, the patient is initially ventilated with a face mask manually until intubated or until a laryngeal mask is introduced to obtain sufficient oxygen saturation of blood during the application of instruments.
During mouth and nose mask ventilation, tightly enclosed face masks made of antistatic rubber are used. Face masks are anatomically correctly shaped in different sizes for children and adults. Masks have an elbow which inspiration and expiration tubes are connected to.
Mask ventilation techniques
When carrying out the mask ventilation, you need to consider a few things: as a rule, the mask must be firmly fixed on the patient’s face with the left hand. While the mask is kept on top and in the bottom part of its elbow with a thumb and a forefinger, a middle finger, a ring finger and a little finger should embrace the patient’s lower jaw and stretch his/her head posteriorly. Using the so-called C-grip, named after the position of the thumb and the forefinger during this procedure, the mask can be fixed so that no air can escape. At the same time, the reclination of the head should prevent misplacement of the airways by the tongue falling back. The physician can now use the ventilation bag with a free hand.
Guedel and spiral tube
The additional use of nasopharyngeal tubes or oropharyngeal tubes prevents the falling back of the tongue to the epiglottis. Keeping the airway open can be ensured during mask ventilation. In this case, the Guedel tube is the method of choice. The Wendl tube introduced through the nose triggers a gag reflex and it is generally used in the case of non-tolerance of the Guedel tube. Although both the tubes keep the airway free, but offer no protection against aspiration, the laryngeal inlet remains open with the mask ventilation. This is an important disadvantage compared to intubation!
When performing mask ventilation, it is important to keep the lowest possible ventilation pressure. At a pressure of more than 20 mbar, the closing pressure of the oesophageal sphincter is exceeded and the air volume compresses into the stomach. On the one hand, you should avoid it, because it can overinflate the patient’s stomach. Additionally, even more important, the air should get into the lungs, in order to provide the patient with oxygen. This fact is often asked during exams.
The use of a laryngeal mask is something more invasive than the face mask, but there are some advantages. The laryngeal mask offers the possibility to keep the upper respiratory tract free, without the risks of tracheal intubation being taken into account. A laryngeal mask consists of a silicone tube with a connector. An elliptically shaped mask is attached at its distal end. Its beaded-edge can be inflated via a supply line and, thus, block the airstream. The empty mask is introduced into the hypopharynx blindly, without laryngoscope. If the laryngeal mask is in its place, it cannot be further advanced, and the funnel is located at the entrance of the larynx, the bead is inflated which seals the larynx.
If air escapes during respiration despite adaptation attempts, you may try again with a mask of a different size. The shaft of the laryngeal mask can be fixed on the patient’s face with an adhesive tape in order to prevent an intraoperative slipping after successful placement.
Contraindications for a laryngeal mask include pharyngeal abscess or obstructions and restrictive lung diseases that require a high inspiratory pressure (> 30 cm H2O). A non-fasting patient also represents a contraindication, as the laryngeal mask closes the entry to the oesophagus and trachea not against each other, and therefore does not protect against aspiration in regurgitation.
Advantages and disadvantages
Advantages of the laryngeal mask against the face mask include the reduced trauma risk of facial structures, such as the facial nerve and the eyes. The airway is easier to keep open and this method is best suited for bearded patients because a mask would often close not completely airtight. A holding hand is not required. However, the placement requires a deeper anesthesia than the face mask to minimize the gag and cough reflex. It is a purely mechanical invasive method.
Compared to intubation, the laryngeal mask is naturally less invasive. It causes fewer teeth- and larynx traumas. For the introduction, no muscle relaxant is required; the risk of laryngeal and bronchial spasm is lower. At the same time, there is no risk of accidental esophageal or endobronchial intubation.
In patients with difficult airways, especially in the “cannot ventilate, cannot intubate situation”, due to its relatively easy placement, the laryngeal mask as a lifesaving temporary measure is an important tool for securing the airway. Generally, however, the laryngeal mask is used only during small, uncomplicated operations. With non-fasting patients and the increased risk of aspiration, it offers no adequate aspiration protection. In this case, endotracheal intubation is preferred.
The endotracheal intubation is one of the most essential topics of anesthesia and is an indispensable tool. You should familiarize yourself with the instruments, the clinical implementation, their advantages and disadvantages as well as the indications for their application. Endotracheal intubation describes the insertion of a tube (a hose, Latin “pipe”’) through the glottis into the trachea, which allows the patient either to breathe by himself/herself or provides artificial ventilation.
Also, an introduction of a tube through the nose, the so-called nasotracheal intubation is possible. By means of sealing with a balloon (cuff), airways are protected against the ingress of liquids, such as gastric fluid or blood. So, ventilation becomes possible. In addition to this aspiration protection, the suction of endobronchial secretion is possible via the tube. Besides, the secure aspiration of all anesthetic gases is possible, which consequently allows medical staff to be less burdened with escaping gases.
When is there an indication for endotracheal intubation? On the one hand, during operations in the neck and facial area, where supraglottic airway aids such as facial or laryngeal mask are unfavorable: with non-fasting patients like emergency patients whose fasting is impossible to state, or with pregnant women from the 14th week of pregnancy due to the increased intra-abdominal pressure. There is also an indication for tracheal intubation in the case of abdominal and thoracic surgery, too overweight patients, and in difficult surgery positions such as sitting, and operations in lateral or prone position.
The intubation requires that a treating physician should have good knowledge of larynx anatomy. In order to insert the tube under direct vision, the laryngeal aperture is presented with a laryngoscope. Since the glottis is the narrowest point of the larynx, the tube size and its diameter are dependent on the glottis size. With children, the narrowest point is located just below the glottis in the area of the cricoid cartilage. If you push the tube after passing through the glottis with resistance, it must be replaced by a model with a smaller diameter. Under no circumstances should it be forcefully pressed inside.
We can distinguish between several tube types. They are important to know, because they are a favorite topic in exams. There is the Magill tube, the Murphy tube and the Woodbridge tube. The Magill tube is made of plastic (PVC) and represents the standard tube. The slightly curved tubes with normalized radius of curvature are generally intended for single use only.
The Murphy tube has an additional hole, the so-called “Murphy eye” just in front of the tube tip. The ventilation can be performed via this lateral Murphy eye, if the main lumen of the tracheal mucous membrane sits closely or if an atypically arising right main bronchus is to be ventilated.
The Woodbridge tube is particularly suitable for operations in the prone position and other OP positions where the tube has to be bent much. The latex spiral tube reinforced with metal is extremely flexible and cannot be bent. Thus, a stylet is used in order to stabilize it during insertion.
Safe and unsafe intubation signs
Immediate control is important for each intubation. You should check if the tube is correctly placed in the trachea or if misintubation is present. Only in this way, a reliable supply of the patient’s both lungs with air is assured. Due to anatomical proximity to the larynx, the tube may well land in the esophagus (oesophageal intubation). In this case, despite established respiration, oxygen saturation of the patient continuously falls, because the air arrives in the stomach instead of the lungs. Even a one-sided ventilation of only one lung is possible if the tube is too far advanced. Anatomically, due to the steeper angle mostly to the right, the tube may land in one of the main bronchi. Here we deal with (endobronchial intubation).
Intubation signs for checking the tube placement are therefore a popular examination topic. With a little logical thinking, they can be quickly memorized. Secure intubation signs include the direct inspection of the tube pass through the vocal cords, a bronchoscopic view of the intra-tracheal position of the tube and the CO2 detection in the exhaled air with the capnometer (tidal volume 4-5 % = 35-40 mmHg). Insecure intubation signs are chest rise, fogging of the tube inner walls with breath moisture, auscultatory breathing sound (particularly in children), as well as a constant pulse oximetric saturation over longer periods of time.
At one glance – endotracheal intubation:
- Endobronchial suction via the tube is possible
- Secure aspiration of all anesthetic gases
- Operations in face, neck and chest area
- Regurgitation threat
- Surgical positions: sitting, lateral position, prone position
Important tube types
- Magill tube – standard tube
- Murphy tube – “Murphy eye“
- Woodbridge tube – very flexible
Problems during ventilation, i.e. when keeping the airway open and sufficient ventilation of the respiratory tract are not possible, describe approximately 50 % of anesthesia-related complications. If you have difficulties with mask ventilation or intubation, in fact, there is a distinction between expected and unexpected types in the context of induction of anesthesia (acute). Among the expected difficult airway, there are things that have already been recognized during the premedication visit, e.g. changes through tumors or injuries.
With the expected airway difficulties, there are basically two types of procedures: intubation using video laryngoscope or conducting awake fiberoptic intubation. Both methods allow the anesthesiologist to conduct visual inspection of the tube position by means of a video camera.
“Can’t ventilate, can’t intubate situation”
If mask ventilation is not sufficient or not possible with an already anesthetized patient, even after such measures as stronger hyperextension of the head, an intubation must be conducted without muscle relaxation. However, with less than 0.02 % of patients, neither mask ventilation nor subsequent intubation is possible. When this situation arises, we may describe the “can’t ventilate, can’t intubate” situation as an absolute emergency.
Due to the administered anesthetic, the anesthetized patient is temporarily no longer able to breathe independently: oxygen saturation drops rapidly. Escalation of this situation may lead to a hypoxic brain damage. Therefore, the very first measure is to call an experienced anesthesiologist to help. If the situation permits, anesthesia recovery with evocation of the patient can bring him/her back to spontaneous breathing.
Often, as a first measure, you may successfully place a laryngeal mask, which can be then ventilated or intubated fiberoptically. If this attempt fails, you may apply cricothyrotomy (you can read more about cricothyrotomy in our article “Anatomy of the Lower Respiratory Tract”) or a transtracheal jet ventilation in emergency cases, in order to re-open the patient’s airway and secure his/her vital supply of oxygen.
At one glance: airway difficulties
Procedures for the “can’t ventilate, can’t intubate situation”
- Place a laryngeal mask
- Ventilation or awake fiberoptic intubation
- Cricothyrotomy (emergency)
- Transtracheal jet ventilation
Popular Exam Questions Regarding Airway Management
The correct answers can be found below the references.
1. What is determined by the Mallampati Score?
- Dental status
- Mouth opening
- Reclination of the head in degrees
- Visibility of pharynx structures with an open mouth and a protruded tongue
- Complications of the previous anesthesia
2. Which measure is NOT used in the “can’t intubate, can’t ventilate” situation?
- Laryngeal mask
- Transtracheal jet ventilation
- Endotracheal intubation
- Get experienced anesthesiologists to help
3. Which one of the following belongs to secure intubation signs?
- CO2 detection in the exhaled air
- Thorax excursion
- Constant pulse oximetric saturation
- Auscultatory breathing sound
- Fogging of tube inner walls with respiratory moisture