What Is Endotracheal Intubation Used For?

Endotracheal intubation is used for people who can't breathe on their own, whether because of an illness, accident or planned anesthesia for surgery.

Endotracheal intubation is the procedure to insert a flexible tube into the airway (trachea) through the mouth or the nose. The endotracheal tube is most often placed through the mouth, especially in emergencies. Endotracheal intubation is usually performed prior to surgeries with general anesthesia or in patients under critical care.

Intubation procedure can cause discomfort, stress and pain for patients, so sedation and painkillers (analgesics) are usually mandatory during intubation. A rapid-acting, short-duration sedative is administered along with other medications to block pain and reflex actions like gagging.

The tip of the epiglottis is the anatomical landmark doctors look for when performing tracheal intubation. The epiglottis is a flap of cartilage located below the root of the tongue, on top of the voice box (larynx). The epiglottis covers the tracheal opening while swallowing food or drink to prevent them from getting into the trachea. The epiglottis remains open at other times to allow breathing.

Endotracheal intubation may be performed for the following reasons:

• Keeping the airway open and preventing inhalation of gastric contents (aspiration) during surgeries with general anesthesia
• Providing a pure oxygen supply to the lungs (as opposed to the mixed-gas ratios in the general atmosphere)
• Administration of anesthesia and certain medications
• Clearing blockage in the airway
• Supporting breathing in critically ill patients who are unable to breathe or have difficulty breathing because of illness or trauma
• Many people with severe COVID-19, the respiratory conditions caused by the pandemic coronavirus, must spend weeks intubated and receiving oxygen via ventilation machines.

Endotracheal intubation before a planned surgery may be performed with sedation alone. Patients should fast in preparation to reduce the risk of vomiting and aspiration. 

Mechanical ventilation with an oxygen mask (bag-valve-mask) is started before anesthesia and paralysis are induced.

When endotracheal intubation is performed in an emergency, preparatory fasting is not possible. A protocol known as rapid sequence intubation is followed, which induces unconsciousness and paralysis rapidly.

Bag-valve-mask ventilation is avoided after induction of anesthesia and paralysis, in order to prevent aspiration and stomach insufflation (filling with air). 

Mechanical ventilation starts only after completion of the intubation procedure.

Rapid sequence intubation is not performed if the patient is already unconscious or not breathing. The patient is intubated with immediate bag-valve-mask ventilation.

Procedure

An anesthetic team performs the tracheal intubation, coordinating with the physician/surgeon and nurse. The intubation steps are as follows:

• Administer anesthesia and muscle relaxant.
• Apply pressure on the cricoid cartilage located in the throat to block the esophagus and prevent the tube’s entry into it.
• Use a laryngoscope to see the epiglottis and the opening to the trachea.
• Gently insert the tube into the trachea and secure the tube in place.

Rapid sequence intubation involves administration of specific medications in three stages before the tube insertion.

Stage 1: Pretreatment

Preoxygenation

Preoxygenation is performed to maximize the oxygen saturation levels in the blood and create an oxygen reservoir in the lungs. Preoxygenation provides continued oxygen for circulation for the duration of intubation procedure, when the patient remains in a state of anesthetic paralysis and cannot breathe for themselves.

Preoxygenation is accomplished by delivering high-flow oxygen for three minutes using a face mask. Nitrogen constitutes about 80% of ambient air in the general atmosphere. Preoxygenation replaces the nitrogen in the lung’s air sacs (alveoli) with oxygen.

Preoxygenation allows eight minutes to complete tracheal intubation before the oxygen blood saturation starts to fall below 90%. Oxygen desaturation may be more rapid in children and acutely ill patients with respiratory problems. If oxygen saturation falls below 90%, start bag-valve-mask ventilation.

Premedication

Premedication involves preventive administration of medications two to three minutes prior to intubation to prevent pain (analgesia) and control physiological responses induced by the insertion of the laryngoscope into the airway.

Intubation can induce:

• Pressor response: Pressor response is the sympathetic nervous system’s reflex to the insertion of laryngoscope. The laryngoscope’s edge stimulates the pharynx, larynx and the trachea, inducing stress response and release of stress hormones, which leads to elevation of blood pressure and heart rate. The pressor effects may last for about five minutes, and may be unsafe for critically ill patients.
• Intracranial hypertension: Intracranial hypertension is elevated pressure in the cerebrospinal fluid around the brain, which can result in cerebral edema or reduced blood supply (ischemia) to the brain. In addition to the pressor response the laryngoscope causes reflexes such as coughing and gagging, which together can lead to transient intracranial hypertension. 

Stage 2: Induction

The induction phase of intubation involves the administration of an anesthetic agent. A rapid-acting, short duration sedative is administered intravenously to induce unconsciousness and unresponsiveness.

Stage 3: Paralysis

The final step before tracheal intubation is to induce temporary paralysis in the muscles to prevent them from contracting and hindering the procedure. After the induction of anesthesia, a paralytic agent is used to relax the skeletal muscles.

The motor function of the muscles is controlled by the brain through transmission of signals through the nerves. The nerve endings, where they join with the muscles, release a neurotransmitter known as acetylcholine which activates the muscles.

Paralytic medications are neuromuscular blockade agents which interfere with acetylcholine’s activity and prevent muscular activation. Paralytic agents prevent gagging and coughing reflexes during intubation.