Sedation Airway Management

Introduction
Basic Airway Management
Airway Anatomy
Patient Assessment
Advanced Airway Management

Introduction

The drugs used for sedation and analgesia can interfere with a patient's ventilation both by relaxing the airway muscles and suppressing the urge to breathe. The primary risk related to sedation is respiratory complications.  Ability to maintain a patent airway is an essential prerequisite for administration of sedation. Airway obstruction can be either total or partial.

Symptoms of Partial Airway Obstruction
  • Snoring
  • Retraction of the sternum
  • Rocking motion of the chest not in sync with respiratory effort
  • Harsh, high-pitched sound upon inspiration (stridor)
  • Hypoxemia
  • Hypercarbia
  • Symptoms of Complete Airway Obstruction
    • Lack of any air movement perceived by feeling with the hand over the mouth or placing the ear over the mouth
    • Lack of breath sounds while listening with stethoscope to lung fields
    • Retraction of the sternum and rib cage
    • Rocking motion of the chest not in sync with respiratory effort
    • Hypoxemia
    • Hypercarbia

    Normal respiration relies on a series of structures that conduct air into and out of the lungs. An understanding of the functional anatomy of this region is critical to airway management.

    Basic airway management 

    Immediate action must be taken at the first signs of compromised respiratory function. If initial attempts to relieve airway obstruction through verbal and tactile stimulation are unsuccessful, the following techniques can be employed to restore effective ventilation

    Manual Maneuvers

    When the muscles of the tongue and mouth floor relax, the tongue lies close to or on the back wall of the oropharynx. The epiglottis may obstruct the glottic opening or seal against the back wall of the pharynx, as well. The following positioning maneuvers can be performed to relieve the soft tissue obstruction and improve airflow. 

    • Jaw thrust. This maneuver moves the tongue forward with the mandible which reduces the tongue's ability to obstruct the airway.  Standing at the head of the bed, the middle finger of the right hand is placed at the angle of the patient's jaw on the right. The middle finger of the left hand is similarly placed at the angle of the jaw on the left. An upward pressure is applied to elevate the mandible which will lift the tongue from the posterior pharynx.
    • Chin lift. The fingers of one hand are placed under the mandible, which is gently lifted upward to bring the chin anterior. The thumb of the same hand depresses the lower lip to open the mouth. 

    Pharmacologic Antagonists

    Specific antagonists are available to reverse the effects of opioids and benzodiazepinesNaloxone (for opioids) or flumazenil (for benzodiazepines) may be administered to improve patients spontaneous ventilatory efforts. 

    Artificial airway devices

    Once a patent airway is established, it is necessary to prevent it from becoming obstructed again. Either an oropharyngeal or a nasopharyngeal airway conduit may be used for this purpose. Both devices maintain a patent airway by preventing the tongue from resting against the posterior pharyngeal wall.

    • Oropharyngeal airway (OPA). The OPA is a curved, firm, hollow tube, usually plastic with a rectangular opening that is used to maintain a conduit between the mouth and the glottis and to prevent obstruction by the tongue and other soft tissue. OPAs come in sizes ranging from 50, 60, and 70 mm (nos. 0,1, and 2) for neonates and 80, 90, 100 mm (nos 3,4, and 5) for adults. All OPAs have a straight bite section that rests against the patient’s lips and a flange on the proximal end to prevent over-insertion.  Oropharyngeal airways should be used in unconscious (unresponsive) patients as they are quite stimulating and generate a gag reflex. In responsive patients OPAs can cause vomiting and aspiration. Incorrect insertion of an airway can push the tongue into the back of the throat causing airway obstruction.

      To select the proper size OPA, place it against the side of the face. When the tip of the OPA is at the corner of the mouth, the phalange is at the angle of the mandible.
    • Nasopharyngeal airway (NPA). The NPA, also called a "nasal trumpet," is a soft rubber or plastic hollow tube that is passed through the nose into the posterior pharynx just above the epiglottis. Because NPAs tend to provoke less airway irritations than oropharyngeal airways, NPAs are better tolerated by patients. NPAs  can be used when OPA placement is difficult, such as when the patient's jaw is clenched or the patient is semiconscious and cannot tolerate an OPA. NPAs come in sizes based on their external circumference that range in size from 28 to 34.

      The length of the NPA should be the same as the distance from the tip of the patient’s nose to the earlobe.

    Potential Hazards Involved in the Use of Airway Conduits
    Oropharyngeal airways   Nasopharyngeal airways
    • Increasing airway obstruction by pushing tongue backward
    • Using an incorrectly-sized devise. A device that is too small is ineffective and can be lost in the oropharynx. A device that is too large can press against the epiglottis and obstruct the larynx.
    • Causing trauma to soft tissue by catching the tongue or lips between the airway and the teeth.
    • Inducing vomiting by using the device in a patient with intact gag reflex.
     
    • Using an airway that is too long; this may cause the tip to enter the esophagus.
    • Injuring the nasal mucosa causing bleeding. This can lead to aspiration of blood or clots.
    • If nasal airway doesn’t have flange at the nasal end can lose airway in nose and the airway.

    Bag-mask ventilation

    Bag-mask ventilation is a basic but critical airway management skill. It enables clinicians to provide adequate ventilation for patients requiring airway support and allows enough time to establish a more controlled approach to airway management, such as endotracheal (ET) intubation. Because the technique can be difficult to perform correctly, clinicians performing the procedure should continually practice and monitor their technique.

    Successful bag-mask ventilation depends on three things: 

    • Patent airway. Airway patency can be established using airway maneuvers and airway conduits described above.
    • Adequate mask seal. In order to secure a good seal, the mask must be placed and held correctly. Disposable bag-mask units are often packaged with one large adult-sized mask. Even though facial anatomy differs for eachpatient, one sized face mask is usually sufficient for positive pressure ventilation with the bag mask.  The nasal portion of the mask should be spread slightly and placed on the bridge of the patient's nose. The body of the mask is then placed onto the patient's face covering the nose and mouth. The provider's wrists or the mask cushion should not rest on the patient's eyes during bag-mask ventilation. There are two methods for holding the mask in place. The two-hand mask hold is most effective, however it requires a second clinician. Therefore, the clinician should be comfortable with both techniques.
    • Proper ventilation (ie, proper volume, rate, and cadence). The three key errors to avoid when performing bag-mask ventilation are:
      • Excessive tidal volumes: A volume just large enough to cause chest rise (no more than 8 to 10 cc/kg) should be used. During cardiopulmonary resuscitation (CPR), even smaller tidal volumes are adequate (5 to 6 cc/kg) due to the reduced cardiac output of such patients.
      • Forcing air too quickly: The bag should not be squeezed explosively. It should be squeezed steadily over approximately one full second.
      • Ventilating too rapidly. The ventilatory rate should not exceed 10 to 12 breaths per minute.

     Airway Anatomy

    Upper airway

    The upper airway consists of the structures above the vocal cords. It is divided into the following regions:

    • Nose and oral cavity. Conduit for air entry into the pulmonary system. The nose, which is composed of bone cartilage, is the primary pathway for normal breathing. The resistance through the nasal passage accounts for more than 50% of the total respiratory resistance during normal breathing. This is more than twice the resistance during mouth breathing. The oral cavity consists of the upper and lower teeth, the tongue and floor of the mouth, the hard palate and the openings of the major salivary glands. The floor of the mouth is supported by the mylohyoid muscles.
    • Pharynx. In normal size adult males, an approximately 13-cm long muscular tube located behind the oral and nasal cavities. It conducts food to the esophagus and air to the larynx, trachea and lungs. The pharynx is divided into three sections:
      • Nasopharynx: extends from the back of the internal nasal cavity to the soft palate. Contains the adenoids.
      • Oropharynx: Begins at the soft palate and continues to the level of hyoid bone. Serves as both respiratory and food passage. Contains the tonsils. The tongue is the principal source of obstruction, usually because of decreased muscle tone related to sedation drugs such that the tongue falls backward in a supine patient.
      • Laryngopharynx:  Begins at the level of the hyoid bone and extends downward where it branches into two passages: the larynx at the front which leads to the lungs; the esophagus at the back which leads to the stomach.
    • Larynx. Enlargement at the top of the trachea which houses the vocal cords. The structure contains muscles, ligaments, and cartilages. The epiglottis is a fibrous leaf-like cartilage that hangs over the laryngeal inlet that closes during swallowing to prevent aspiration of gastric contents into the trachea.  The triangular opening between the vocal cords is called the glottic opening and is the entry point to the larynx, It is the adult airway’s narrowest point. Patency of the glottic opening is dependent upon muscle tone.

    Lower airway

    The lower airway encompasses the structures of the respiratory system below the larynx.

    • Trachea. Rigid tube approximately 10-15 cm length in the midline of the neck that provides a passage for air into the lungs.
    • Bronchial tree. Branched tree-like tube system leading from the trachea that conducts air into the lungs. It is made up of increasingly smaller tubes terminating in the alveoli.
    • Lungs. Paired organs consisting of millions of small sacs (alveoli) gas exchange occurs.  The lungs occupy most of the space of the thoracic cavity.

     Patient assessment 

    Before the initiation of sedation, patients should be evaluated for anatomical characteristics and relevant medical history that could increase the risk of airway management problems.

    Medical history

    The following factors may contribute to a potentially higher risk for airway difficulties. If any of these conditions are present, the clinician will determine the patient’s level of risk on an individual basis. 

    • Previous problems with anesthesia, sedation or airway management
    • Stridor, snoring, or sleep apnea 
    • Advanced rheumatoid arthritis
    • Abnormal anatomy in head/neck such as tumors
    • Obese patients
    • Congenital syndromes that involve the airway
    • Radiation therapy or previous surgery to head/neck may distort airway and complicate airway manipulations
    • Large beard such that mask ventilation is more difficult
    • A short, thick, muscular neck

    Physical assessment

    The pre-procedure physical examination should include the following assessments to evaluate the patient’s airway and uncover physical traits that could contribute to respiratory complications.

    • Oral cavity inspection. The patient's oral cavity should be carefully inspected for the following abnormalities prior to sedation. Findings should be documented in the patient's record.
      • Small mouth opening (less than 3 cm in an adult)
      • Protruding incisors
      • Loose or capped teeth
      • Missing teeth
      • Dental appliances such as crowns, bridges, and dentures
      • Enlarged tonsils
      • Non-visible faucial pillars, which are vertical folds of tissue created by muscles that surround the palatine tonsils (See Mallampati Class III and IV)
      • Non-visible uvula
      • Tumor that could obstruct air flow
    • Temporomandibular joint examination. Pain or limited range of motion in the temporomandibular joint can be assessed by palpating the joint while the patient's mouth is open to the widest point. In an adult, the normal mouth opening is 4 to 6 cm. Patients with temporomandibular joint disease who have an opening of less than 4 cm (approximately 2 finger breadths) may have limited airway mobility if mechanical devices are needed to treat respiratory distress.
    • Thyromental distance evaluation. The thyromental distance should be at least 5-7 cm as measured from the thyroid cartilage to the point of the chin when the neck is extended fully and the mouth closed. A distance less than 7 cm can indicate difficulty with intubation should the need develop.
    • Neck mobility. Assessment of the movement of the atlanto-occipital joint through flexion, extension, and side to side is necessary before sedation is initiated. Ability to align the oral, pharyngeal, and laryngeal axes is required for successful endotracheal intubation.
    • Physical characteristics. Patients should be examined for physical traits that can indicate a potential for airway complications.
      • Significant obesity especially in the region of the neck and face
      • High, arched palate
      • Enlarged tongue
      • Short, immobile neck
      • Protruding teeth
      • Recessed or protruding jaw
    • Mallampati Airway Classification System. This system is a method for quantifying the degree of difficulty of endotracheal intubation based on amount of posterior pharynx that can be visualized. The exam is performed with the patient sitting with the head in a neutral position and the mouth open as wide as possible

    Illustration with permission from UF Airway Evaluation Tutorial
    http://www.anest.ufl.edu/

    Class I: soft palate, fauces, uvula, pillars visible. No difficulty.
    Class II: soft palate, fauces, portion of the uvula visible. No difficulty.
    Class III: soft palate, base of uvula visible. Moderate difficulty.
    Class IV: hard palate only. Severe difficulty. 

    Advanced airway management  

    Cases where non-invasive means are insufficient to provide adequate oxygenation and ventilation, a clinician may need to use one of the following advanced airways.

    • Endotracheal tube (ETT). An endotracheal tube is indicated for airway protection in a comatose patient for example, for mechanical ventilation, and if pulmonary toilet is necessary. It is the definitive method to secure a compromised airway, prevent aspiration, and initiate mechanical ventilation. Placement typically requires laryngoscopy.
    • Laryngeal mask airway (LMA). A laryngeal mask airway can be inserted into the lower oropharynx after general anesthesia has been induced.  Some models also have a channel that can guide an endotracheal tube into the trachea. This device does not require laryngoscopy for insertion.

    Sources

    2005 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Part 4: Adult Basic Life Support. Circulation 2005;112: IV-19-IV-34 and Part 7.1: Adjuncts for Airway Control and Ventilation. Circulation 2005;112: IV-51-IV-57.

    Euliano TY, Gravenstein JS. Essential Anesthesia: From Science to Practice. Cambridge, UK. Cambridge University Press. 2004: 24-27

    Field, John M. Advanced Cardiovascular Life Support Provider Manual, American Heart Association 2006: 27-28.

    Kost M. Moderate Sedation/Analgesia: Core Competencies for Practice, 2nd Ed. St. Louis, MO: Saunders, St. Louis; 2004:171-184.