AIRWAY MANAGEMENT

AIRWAY MANAGEMENT

Final Objective: On completion of this module you will be able to evaluate and manage a patient's airway both in routine and difficult cases.

Enabling Objective: To achieve this goal, you should know how to:

Carefully evaluate a patient's airway to identify potential problems with intubation and mask ventilation.
Identify the indications for tracheal intubation.
Adequately bag-mask ventilate, intubate and insert a laryngeal mask into a patient.
Make decisions about the management of failed intubation for elective and emergency surgery using a difficult airway algorithm.
Perform alternative techniques of tracheal intubation such as the Intubating Laryngeal Mask and awake intubation under local anaesthesia
Establish an emergency airway for the patient who cannot be intubated nor ventilated.
Identify and manage the obstructed airway, inadequate ventilation, inadequate oxygenation and failed intubation.

Reference Reading:

Developing Anaesthesia Chapters 5, 19, 20, 27 & 40, (54, 55, 56 optional)
Oxford textbook of Anaesthesia. Chapter 36
Airway management seminar
Anaesthetists are airway experts. Every anaesthetist needs to be able to manage a patient's airway to ensure adequate oxygenation in both the elective and emergency setting. To achieve this, the anaesthetist needs to anticipate difficulties and to plan for the unexpected difficult or failed intubation. Alternative airway management techniques should be practiced regularly so they can be performed efficiently when there is an emergency.

AIRWAY ASSESSMENT

A difficult airway may present as difficult ventilation, difficult laryngoscopy, difficult intubation or a combination of these. 30 - 40% of anaesthetic related deaths are due to the inability to manage the airway, resulting in hypoxia. The definition of difficult intubation is greater than 3 attempts at intubation, or greater than 10 minutes of attempted intubation. The incidence of difficult intubation is about 0.5 - 16.6% (the rate varies depending on the definition). 15% of difficult intubations were also associated with difficult mask ventilation.

There are three broad categories of difficult intubation. They are the known or expected difficult airway, the potentially difficult airway and the unexpected difficult airway. Clearly, the ability to accurately predict a difficult intubation or ventilation is important in the ability to plan for alternative airway management. Unfortunately, the sensitivity and positive predictive value of preoperative tests is not high enough to predict all difficult intubations, however, when used in combination, the sensitivity and positive predictive value increases. Every patient for anaesthesia, regardless of the planned anaesthetic technique should have an airway assessment.

Evaluation of the airway includes a careful history and examination. Rarely, are any more detailed tests required.

A history of difficult intubation should alert the anaesthetist to a difficult airway, as physical examination may be unremarkable in some patients who have a difficult intubation. If there is an existing breathing problem, difficulty sleeping in the supine position or abnormal voice quality, the anaesthetist should be wary of a problem. Stridor at rest in an adult indicates a serious degree of airway obstruction with a cross sectional opening of less than 4 mm.

Potentially difficult intubation may be predicted with several bedside tests. These include:

Mouth opening (Inter-incisor distance should be greater than 3.5 cm)

Atlanto-occipital joint movement

Jaw movement (subluxation of the mandible, ability to protrude mandible forward)

Thyro-mental distance (should be greater than 6 cm)

Sterno-mental distance

Visualization of the oropharyngeal structures (Mallampati score)

It is useful to try to identify the cricothyroid membrane before anaesthesia in the event that an emergency surgical airway is required, remembering that 16.3% of difficult intubations will not be predicted.

Potentially difficult mask ventilation can be predicted in the presence of the following:

Presence of a beard BMI > 26 kg/m2 A lack of teeth Age > 55 years and a History of snoring

There are some physical and medical conditions that will increase the potential for difficult airway management. These include obesity, pregnancy, rheumatoid arthritis, congenital abnormalities, airway infection (which can cause major problems in children, especially peritonsillar abscess, retropharyngeal abscess and epiglottitis), trauma of the head and neck, tissue destruction (surgical scarring, burns, radiotherapy) and tumours.

When making any airway assessment and planning management, one should consider the following:

Is airway control necessary?
Is there a potential for difficult laryngoscopy?
Can the patient be ventilated without intubation?
Is there a risk of aspiration?
Will the patient tolerate a period of apnoea?
A predicted difficult intubation calls for an "awake" intubation technique if intubation is necessary.

AIRWAY MANAGEMENT TECHNIQUES

Successful airway management ensure adequate tissue oxygenation. Most airway related deaths and morbidity result from a failure to ventilate and oxygenate rather than a failure to intubate. It is important for the anaesthetist to be skilled at airway management without tracheal intubation.

Facemask ventilation

Anaesthetic facemasks are designed to fit the contours of the face with minimal pressure. They are cushioned to minimize the leakage of gases and come in different sizes. The correct size for the patient will minimize dead space and provide a good seal. Paediatric masks can be cushioned circular masks or the Rendell-Baker mask, which is designed to minimize dead space.

Once the patient loses consciousness in the supine position, the tongue and epiglottis fall towards the posterior pharyngeal wall tending to obstruct the upper airway. The anaesthetist can perform chin lift and jaw thrust manoeuvres to open the airway. The facemask is held onto the face using the thumb at the bridge of the nose, fifth finger behind the angle of the mandible and the rest of the fingers pull the mandible into the mask. The mask should not be pushed onto the face. Edentulous patients and beards will make it difficult to achieve an adequate seal with a facemask for positive pressure ventilation.

Pharyngeal airways

Pharyngeal airways relieve upper airway obstruction caused by soft tissue relaxation during unconsciousness. They are able to separate the soft tissues from the posterior pharyngeal wall. Insertion will require attenuation of the upper airway reflexes to prevent regurgitation, gagging and laryngospasm. Measuring the distance from the tragus of the ear to the corner of the mouth allow the anaesthetist to chose the correct size of an oral airway.

Laryngeal mask airway

Dr Archie Brain developed the laryngeal mask airway in the 1980s. It is a supraglottic airway device that allows the patient to breathe spontaneously under anaesthesia or be ventilated with positive pressure up to 20 cm of water safely. The LMA will not protect the patient from aspiration of regurgitated contents and will not be adequate for prolonged positive pressure ventilation.

The LMA consists of an elliptical bowl-shaped mask that sits over the laryngeal inlet surrounded by a cuffed rim. There is a tubular portion that sits in the oropharynx and mouth. It can be connected to the breathing circuit. It is available in adult and paediatric sizes and there is now a version with a gastric lumen that sits in the upper oesophagus to reduce the risk of regurgitation into the larynx (ProSeal). A reinforced version is also available.

The intubating LMA is used to enable the passage of an endotracheal tube and can be used as an alternative to direct laryngoscopy, particularly when direct laryngoscopy is difficult.

Insertion of the LMA requires the upper airway reflexes to be suppressed to prevent coughing and laryngospasm. The cuff is fully deflated and the mask is lubricated on the non-laryngeal side. The patient's head is tilted back and the mask is introduced into the mouth so that the tip of the mask follows the curve of the palate until it rests in the upper oesophagus. The index finger may be used to guide insertion. The cuff is inflated so that the tube is seen to move forward.

The LMA is well suited for the spontaneously breathing patient having a short procedure. It is comparable to face mask anaesthesia. Its benefits include the ability to ventilate when facemask ventilation has failed, the ability to facilitate blind or fiberoptic tracheal intubation and that it is easily learned. Limitations of LMA include difficultly achieving proper positioning; gas leak with airway pressures over 20 cm water and limited protection against aspiration and no protection against laryngeal spasm.

The ProSeal LMA has been designed with a gastric lumen and can be used with slightly higher positive airway pressures. The gastric drain tube will direct regurgitated fluid away from the larynx and can be used to establish rescue ventilation and decompress the stomach when there has been a failed intubation with gastric distension after attempts at facemask ventilation. Cricoid pressure will impede the insertion of a LMA so will need to be released to allow insertion.

TRACHEAL INTUBATION

Indications for tracheal intubation

Tracheal intubation allows the anaesthetist to control the airway and ventilation. It is indicated when there is a risk of aspiration and when there is a need to administer a muscle relaxant for surgical reasons, such as surgery in the abdomen or thorax.

The need for controlled ventilation over a prolonged period is best achieved with endotracheal intubation (the need for prolonged ventilation in an intensive care setting may eventually be better achieved with tracheostomy).

Intubation allows the patient to be positioned prone, sitting, lateral or head down, thereby minimizing concerns about loss of control of the airway. Surgery that positions the anaesthetist away from the airway is better managed with an endotracheal tube.

If adequate ventilation cannot be achieved using a facemask or laryngeal mask airway, intubation can allow for good control of the airway and ventilation.

Intubation during cardiopulmonary resuscitation allows for ventilation with 100% oxygen with no leaks, enables airway suction and is a route for the administration of some emergency medications.

Preparation

Skilled assistance is essential when intubation is planned. The assistant may be required to hand over equipment, apply cricoid pressure or provide external manipulation of the larynx to improve the view at laryngoscopy. The assistant may be called upon to call for help in the event of an airway emergency.

The equipment required for intubation includes:

Equipment for facemask ventilation

A source of positive pressure oxygen

· Self-inflating bag

· Anaesthesia machine

Oropharyngeal or nasopharyngeal airways

Laryngoscopes (preferably two with different sized blades)

Suction

Intubation stylet or introducers

Intubating (Magill) forceps

Backup equipment for the unanticipated difficult intubation is highly recommended.

Patient preparation includes information, intravenous access and positioning so as to optimise the view at laryngoscopy. Positioning with the head extended at the atlanto-occipital joint and slightly flexed at the lower cervical spine can be achieved with the use of a pillow under the head (sniffing position). More obese patients may require more than one pillow under the shoulders and head.

Monitoring of the patient includes blood pressure, oxygen saturation, electrocardiography and end-tidal carbon dioxide and oxygen monitoring.

Rigid Laryngoscopy

Rigid laryngoscopy is the simplest, most successful and frequently used method of visualizing the larynx for intubation. Once the patient is positioned in the "sniffing position", the left hand grasps the open laryngoscope with the fifth finger just above the blade. The blade is introduced into the right side of the mouth to sweep the tongue towards the left. When the blade of the laryngoscope passes the fauces, it is directed medially towards the epiglottis. The tip is the directed into the glossoepiglottic reflection for a curved blade or posterior to the epiglottis if a straight blade is in use. Pulling up and away from the anaesthetist (in the direction of the handle) elevates the tongue and epiglottis to expose the vocal cords. Levering on the teeth with the laryngoscope is to be avoided.

The view at laryngoscopy is graded according to the Cormak and Lehane classification. It describes how much of the larynx was visualized during laryngoscopy.

Cormack and Lehane classification:

Grade one – all of the vocal cords seen

Grade two – partial view of the vocal cords (posterior)

Grade three – epiglottis only

Grade four – no view

External manipulation of the larynx in an upward and rightward direction can bring the larynx into better view.

The common problems with direct laryngoscopy include inadequate positioning, inadequate mouth opening, selection of the wrong blade, allowing the tongue to hang over the right side of the blade and obscuring the line of vision with the endotracheal tube during insertion.

Rapid Sequence Intubation

Rapid sequence intubation is performed in the patient with a risk of regurgitation and pulmonary aspiration. The aim is to secure the airway with a cuffed endotracheal tube rapidly after the loss of consciousness. It is done in a careful and controlled manner.

Preoxygenation is performed in order to fill the patient's functional residual capacity with oxygen so as to allow for a longer period of apnoea. Upon loss of consciousness, cricoid pressure is applied to inhibit passive regurgitation of gastric contents into the oropharynx. A rapid acting muscle relaxant (suxamethonium) is used to provide good intubating conditions. Cricoid pressure is maintained until the endotracheal tube is inserted and its cuff is inflated and correct positioning is confirmed.

Intubation of the conscious patient

"Awake" intubation is performed in the patient who is at high risk for difficult intubation and is at risk of aspiration. Sedation is given, but verbal contact with the patient is maintained. It is important to avoid over sedation and apnoea. A drying agent such as glycopyrrolate is given to reduce secretions and to improve the effectiveness of topical anaesthetics. Topical anaesthesia is applied to the airway. This is usually achieved using lignocaine. It is possible to perform rigid laryngoscopy in the alert patient with adequate local and topical anaesthesia.

Intubation through a laryngeal mask airway

A size 6 endotracheal tube can be inserted through a size 3, 4 or 5 LMA. This is useful for intubating the patient who cannot be intubated in the conventional way. It is also possible to pass a guide such as the gum elastic bougie through the LMA into the trachea over which an endotracheal tube may then be inserted.

The intubating LMA is especially designed to allow for intubation in the patient who is difficult to intubate. It can also be useful in the "can't intubate, can't ventilate" situation, when the LMA portion is used to ventilate the patient before making further attempts to intubate.

Blind nasal intubation

The blind nasal intubation technique can be performed in the conscious or unconscious patient. In order to improve safety, it is usually performed in the conscious patient. It is useful if the patient cannot open the mouth. The nasal mucosa is anaesthetised with topical anaesthetic and a vasoconstrictor is applied to reduce the possibility of epistaxis. The patient should be breathing spontaneously.

The head is maintained in the "sniffing" position and a lubricated endotracheal tube is passed via the nostril into the oropharynx. If there is resistance to passage of the tube at this point, it is withdrawn 2 cm and rotated
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