Direct Laryngoscopy

Article Author:
Francisca Valenzuela
Article Editor:
Nilmarie Guzman
Updated:
10/27/2018 12:31:32 PM
PubMed Link:
Direct Laryngoscopy

Introduction

A direct laryngoscopy allows visualization of the larynx. It is used during general anesthesia, surgical procedures around the larynx, and resuscitation. This tool is useful in multiple hospital settings, from the emergency department to the intensive care unit and the operating room. By visualizing the larynx, endotracheal intubation is facilitated. This is an important step for a range of patients who are unable to secure their own airway, including those with altered mental status and those who are undergoing a surgical procedure. One must be well acquainted with the anatomy, indications, contraindications, equipment, and personnel for successful use of direct laryngoscopy. The preparation, technique, and potential complications are also topics that are of use. 

Anatomy

The larynx is situated just below the pharynx. It is comprised of three paired smaller cartilages, three unpaired cartilages, and the intrinsic muscles. The three paired cartilages include the arytenoids, corniculate, and cuneiform. The three unpaired cartilages include the cricoid, thyroid, and epiglottis. The cricoid cartilage is the only cartilage that completely goes around the trachea. The epiglottis is an important landmark in laryngoscopy usage. The epiglottis is located at the base of the tongue and goes over the glottis to form a lid over it. It protects the larynx from any aspiration of food or liquids. At the base of the tongue and right next to the epiglottis is an area called the vallecula. This is where a laryngoscope blade can be placed. The blade will be pressed up against the hyoepiglottic ligament, which is what suspends the epiglottis from the hyoid bone.

Indications

Indications include patients who require endotracheal intubation. Patients requiring emergent intubation include those who are experience acute respiratory failure, an altered mental status that needs airway protection, and inadequate oxygenation and ventilation. Non-emergent intubation occurs in the perioperative setting as patients may require general anesthesia.

Contraindications

Absolute contraindication to laryngoscopy would include patients who have supraglottic or glottic pathology. This type of pathology would not allow an endotracheal tube to be advanced successfully into the trachea or the placement of an endotracheal tube might cause further damage to the area. Patients with blunt trauma to the larynx area also would be excluded from direct laryngoscopy as this would further aggravate the injury. A patient with this injury would be more suited for surgical intervention such as cricothyrotomy for securing an airway.

A relative contraindication to laryngoscopy includes difficulties in performing the procedure, such as patients with anatomy that does not allow successful laryngoscopy use, injuries to the area,  or physiologic status that is not conducive to the procedure.

Equipment

Direct laryngoscopy requires a laryngoscope handle and blades. The laryngoscope will usually have a light attached. One should always check to make sure the blade is attached to the handle properly, and if it has a light source, that the light is working properly. Endotracheal tubes and a stylet also are required. Having a laryngeal mask airway also is helpful to have available as a rescue airway in the event that the endotracheal intubation is unsuccessful.

The two types of blades are the Macintosh and the Miller. The Macintosh is the curved blade that was created to decrease the amount of stimulation of the posterior epiglottis. The curvature of the blade was created to mimic the curvature of the tongue. The Miller is the straight blade that is meant to directly lift the epiglottis as it is placed right beneath it. There are certain anatomical instances when the Miller blade is more beneficial. The anatomical instances include a long epiglottis, prominent upper incisors, or a deep or anterior glottis.

Personnel

The personnel involved in direct laryngoscopy can come from multiple departments within the hospital. The emergency department physicians can use it for intubating critical patients. Anesthesiologists regularly use this technique in the operating room during endotracheal intubations. Critical care physicians also use this method when they need to protect the airways of their patients.

Preparation

In preparation for the procedure, one must first assess the patient. Some patients may prove to be more difficult candidates for a successful endotracheal intubation with direct laryngoscopy. The following traits all can lead to more difficult visualization of the larynx with direct laryngoscopy, making a patient a less than ideal candidate:

  • Interincisor gap of less than 4 centimeters
  • Thyromental distance of less than 6 centimeters
  • Sternomental distance of less than 12 centimeters
  • Head and neck extension of less than 30 degrees from neutral
  • Mallampati class 3 or 4
  • Mandibular protrusion
  • Neck circumference of greater than 40 centimeters
  • Submental compliance

Once the patient is adequately assessed, the patient must be pre-oxygenated. If a patient is a difficult intubation or at risk for rapidly desaturating, one can pre-oxygenate by using apneic oxygenation. Apneic oxygenation is achieved by using passive oxygen insufflation via nasal cannula at 15 liters per minute. Another important part of the preparation is to keep a functioning suction device and bag-valve mask nearby. Monitoring devices such as blood pressure, pulse oximetry, continuous cardiac monitoring, and capnography should be appropriately connected to the patient. Next, intravenous access should be established. A final preparation step is to ensure that induction agents, neuromuscular blocking agents, adjunctive medications, and emergency medications are prepared.

Technique

Successful direct laryngoscopy involves multiple steps. 

  1. One must first properly position the patient. The classic position is the “sniffing” position where the atlanto-occipital extension with a head elevation of three to seven centimeters; however, patients with cervical spine injury should not have head and neck manipulation performed.
  2. Next one must open the patient’s mouth by using the right hand. An effective method is by using the scissor technique. This is performed by flexing the thumb and middle finger past each other.
  3. The laryngoscope is then inserted using the left hand either midline or along the right side of the mouth.
  4. It is then placed until it reaches the vallecula. 

Complications

As in many procedures, complications may arise. The laryngoscope may cause blunt or penetrating trauma to the oropharynx, larynx, and trachea. Direct laryngoscopy involves the possibility of vocal cord damage as well as arytenoid cartilage dislocation.

Clinical Significance

Direct laryngoscopy is a useful tool to gain mastery of for use in various settings of the hospital. Its application ranges from emergent scenarios requiring airway protection to routine use in the operating room.