Endotracheal Tube Intubation Techniques

Anatomy and Physiology

The upper airway consists of the oral cavity and pharynx, including the nasopharynx, oropharynx, hypopharynx, and larynx. These structures humidify and warm the air and derive their blood supply from the external and internal carotid arteries. The trigeminal nerve provides sensory innervation to the mucous membranes of the nasopharynx, while the facial nerve and glossopharyngeal nerve innervate the oropharynx.

The trachea is soft and membranous posteriorly with cartilaginous rings anteriorly. Adult tracheal diameters vary between 15 mm and 20 mm. These features are important clinical markers that differentiate the trachea from the esophagus and allow for the utilization of a bougie for intubation. At the fifth thoracic spine, the trachea bifurcates into the right and left mainstem bronchi. The angle between the trachea and the left mainstem bronchus is more acute, making foreign object dislodgement into the left mainstem less likely. The obtuse angle between the trachea and the right mainstem bronchus makes it more prone to right mainstem intubation if the endotracheal tube is advanced too distally.

Superior to the vocal cords, the larynx is innervated by the superior laryngeal branch of the vagus nerve, which provides afferent innervation at the base of the tongue and vallecula. These vagal fibers contribute to circulatory changes with direct laryngoscopy. The cricoid cartilage is ring-shaped and sits inferior to the cricothyroid membrane, which is the landmark for emergent cricothyrotomy. Identification of the cricoid cartilage and manipulation of the airway often facilitates vocal cord visualization during intubation.[1]

The hyoepiglottic ligament attaches the hyoid bone to the larynx, and it inserts at the base of the vallecula. This ligament helps lift the epiglottis anteriorly during intubation to expose the vocal cords.

These anatomic landmarks can also be identified in a child with some special considerations. Compared to an adult, a child’s head is proportionally larger, leading to a flexed position of the neck when supine. Applying a shoulder roll to extend the head can overcome neck flexion. The larger tongue in children more easily obstructs the airway. The child’s larynx is also more cephalad and anterior compared to adults. These features contribute to the more acute angle between the epiglottis and glottis of children, which makes vocal cord visualization more difficult when using a laryngoscope. Children also have a shorter trachea, which makes right mainstem bronchus intubation more likely.[1]

Indications

The goal of endotracheal intubation in the emergency setting is to secure the patient’s airway and obtain first-pass success. There are many indications for endotracheal intubation, including poor respiratory drive, questionable airway patency, hypoxia, and hypercarbia. These indications are assessed by evaluating the patient’s mental status, conditions that may compromise the airway, level of consciousness, respiratory rate, respiratory acidosis, and level of oxygenation.[2] In the setting of trauma, a Glasgow Coma Scale of 8 or less is generally an indication for intubation.

Contraindications

The risks and benefits of endotracheal intubation should be assessed as would be done with any other procedure. Patients whose respiratory status might improve with less invasive methods should be tried on modalities such as non-invasive positive pressure ventilation or other modes of oxygenation. Severe orofacial trauma can obstruct oropharyngeal intubation due to significant bleeding or disruption of the facial and upper airway anatomy. Cervical spine manipulation during intubation can be harmful to patients with spine injury and immobility. In the setting of these clinical situations, other modes of ventilation and oxygenation should be undertaken if the clinical condition allows. If a definitive airway is required, providers should be prepared for the potential of a surgical airway. There are no absolute contraindications to intubation, and the decision to place a definitive airway should take into consideration each patient’s unique clinical condition.

Equipment

The following equipment may be needed for both direct and video laryngoscopy:

Preparation

• Intravenous access
• Hemodynamic monitoring 
• Stethoscope
• Pulse oximeter
• End-tidal carbon dioxide (EtCO2) monitor
• Suction catheter attached to continuous suction
• Cardiac arrest cart with resuscitation medications 
• Rapid sequence intubation medications (paralytic, sedative, and/or dissociative agent) 
• Defibrillator 

Pre-oxygenation

• Nasal cannula or high-flow nasal cannula (HFNC)
• Bag-valve mask with masks of various sizes
• Positive end-expiratory pressure (PEEP) valve
• Oral and nasal airways of various sizes 
• Non-rebreather mask 
• Supplemental oxygen 

Direct Laryngoscopy

• Laryngoscope handle with batteries 
• Laryngoscope blades of various sizes and shapes 
• Endotracheal tubes of various sizes+
• Malleable stylet+
• 10cc syringe+
• Tape+

Video Laryngoscopy

• Video laryngoscope connected to a power source
• Rigid or malleable stylet (dependent on the brand of video laryngoscope) 

Back up

• Laryngeal mask airway (LMA)
• Bougie
• Cricothyrotomy tray 
• Magill forceps

Personnel

The physician caring for the patient who decides to intubate is likely the person with the appropriate training to lead the team toward successful intubation. It is the physician’s role to delegate tasks to the other team members. The physician or another designated operator stands at the head of the bed. The nurse in charge of medication administration should be to the patient’s left or in proximity to the site of medication administration. The respiratory assistant is in charge of ventilating the patient, manipulating the airway if required, and handing the endotracheal tube to the operator. They should stand to the right of the patient. If in-line stabilization of the cervical spine is indicated, an additional assistant should be positioned to the left of the operator, ready to hold the neck in position.

Preparation

Airway Evaluation

Time permitting, the first step in preparation is to perform an airway evaluation, which includes a history of intubation and difficult intubations. Evaluation of the external anatomy may be predictive of a difficult airway. Patients with restricted cervical motion, obesity, and facial or neck trauma may present as difficult airways, and providers should anticipate alternative modes of intubation in these situations.

One commonly used mnemonic to evaluate the airway is “LEMON.” “Look” externally for signs of trauma, facial hair, neck masses, large tongue, or dentures. “Evaluate” the 3-3-2 rule. Less than three fingers between the incisors, three fingers between the hyoid bone and the mental protuberance, and two fingers between the hyoid bone and the thyroid cartilage (Adam’s Apple) may be representative of a difficult airway. “Mallampati” class greater than or equal to 3 is predictive of difficult intubation. “Obstruction” or obesity may restrict visualization of the vocal cords. “Neck” mobility and any restriction of it can contribute to difficulty passing the endotracheal tube.[3]

Positioning

Once the external evaluation of the patient is complete, the head position should be optimized to get the best possible view of the vocal cords. The “sniffing position” has traditionally been considered the optimal position for direct laryngoscopy as it aligns the oral, pharyngeal, and laryngeal axes. This position is achieved by elevating the patient’s head, extending the head at the neck, and aligning the ears horizontally with the sternal notch. In morbidly obese patients, rolls may be utilized to elevate the head until the external auditory meatus aligns with the sternal notch.

Endotracheal Tube

Traditionally, an endotracheal tube size of 7.0 is used for women, while an 8.0 is used for men. Variations in size depend on patients’ height and whether they will require bronchoscopy. Bronchoscopy requires at least a 7.5 or 8.0 tube. For children, endotracheal tube size is selected using the equations: size = [(Age/4) + 4] for uncuffed tubes and size = [(Age/4) +3.5] for cuffed tubes. Cuffed endotracheal tubes have become increasingly preferred for the pediatric population in recent years.[4] The endotracheal tube is prepared by placing the stylet inside, straightening the tube proximally, and creating a 35-degree angle proximal to the cuff. The cuff is inflated with air via a syringe connected to a side port and should be tested for leaks during preparation.[5]

Medications

Rapid sequence intubation (RSI) is often the method used by most physicians in emergency settings as it has been shown to improve the likelihood of first-pass success and minimize aspiration. RSI is accomplished by using medications that have a quick onset and short duration of action. Administration of these medications within a short period (e.g., <30 seconds) minimizes apnea time.[6] The components of RSI include a sedative along with a paralytic agent. Delayed sequence intubation (DSI) is an alternative method used in patients in which adequate pre-oxygenation is not possible due to combativeness and/or altered mental status.

A dissociative medication, such as ketamine, is used to allow patient compliance and adequate time for pre-oxygenation. A dissociative agent without respiratory depressant effects allows for the use of positive pressure ventilation in the pre-intubation period to optimize pre-oxygenation.[7] In patients with anticipated difficult intubation who do not require an immediate definitive airway, awake intubation is the method of choice. Awake intubation requires sufficient time for the preparation of an anticholinergic agent to decrease secretions, topical anesthetic, non-respiratory depressant sedative agent, and airway supplies.[8] The nurse in charge of medication administration should have these medications drawn up, labeled, and ready for administration with appropriate amounts of saline flushes.

Pre-Oxygenation

Once all instruments are prepared for intubation, the patient requires pre-oxygenation to increase alveolar oxygen and decrease alveolar nitrogen tension. Pre-oxygenation is accomplished by using a high fraction of inspired oxygen (FiO2) before the administration of sedative and paralytic medications. The goal of pre-oxygenation is to slow the decline of oxyhemoglobin during apnea. The preferred source of pre-oxygenation is a non-rebreather mask with 1-way valves that allow for delivery of close to 90% FiO2 and do not allow exhaled air to be re-inspired.

Other oxygen masks without 1-way valves can provide up to 70% FiO2 with a tight seal around the patient’s face, and bag valve masks can often deliver a higher than ambient air FiO2. Positive end-expiratory pressure (PEEP) using continuous positive airway pressure (CPAP) or non-invasive bilevel positive airway pressure (BiPAP) may be used in patients with pulmonary shunt pathologies as methods of pre-oxygenation. Patients with underlying conditions causing alveoli to be perfused but not ventilated may benefit from increased PEEP using these mechanisms. Pre-oxygenation should last 3 minutes and achieve end-tidal oxygenation (EtO2) greater than 90%.[9][10]

In emergency settings, where an EtO2 monitor is not readily available, a pulse oximeter may serve as a marker of arterial oxygen saturation. These methods of pre-oxygenation are employed in patients with a preserved respiratory drive. In apneic patients or patients with inadequate respiratory drive, bag-valve-mask ventilation with the highest possible level of FiO2 is the most appropriate method of pre-oxygenation. 

Apneic Oxygenation

Apneic oxygenation works by oxygen diffusion and helps prolong the safe duration of apnea during intubation. Efficient apneic oxygenation depends on airway patency and the patient’s functional residual capacity. This is achieved by providing oxygen via the nasopharyngeal or oropharyngeal route. Most commonly, this is done via nasal cannula at an oxygen rate of up to 15 L/min or high flow nasal cannula with 100% FiO2 during oropharyngeal intubation. These methods can provide approximately 10 minutes of adequate oxygenation during intubation attempts in patients without underlying lung pathology.[9]

Technique or Treatment

Appropriate preparation and positioning of the patient are essential to successful intubation. The operator should confirm that the light source of the laryngoscope is functioning and the blade is locked in place. The laryngoscope is held in the operator’s left hand. Next, the operator slides the laryngoscope into the right side of the patient’s mouth and advances inward while applying upward pressure at a 45-degree angle against the tongue. As the laryngoscope slides towards the back of the oropharynx, the operator can use the blade to push the tongue towards the left side of the mouth to make room for the advancement of the endotracheal tube. While keeping firm upward pressure on the laryngoscope with the left hand and avoiding bending the wrist, all the structures of the oropharynx are visualized until the vocal cords are exposed.

If using a curved laryngoscope, the operator should visualize the epiglottis and place the blade tip in the vallecula. Applying firm, steady upward pressure at a 45-degree angle, the curved laryngoscope is used to lift the epiglottis and expose the vocal cords. Once the glottis is visualized, the operator will ask the respiratory assistant to place the endotracheal tube with the malleable stylet on the operator’s right hand. The operator then inserts the endotracheal tube to the right of the laryngoscope blade and visualizes the passage through the vocal cords. Some brands of endotracheal tubes have a marking proximal to the cuff that indicates the relative level of insertion through the vocal cords.

If lifting of the epiglottis does not reveal the vocal cords, the operator may use her/his right hand to manipulate the airway. This technique often helps bring the glottis into view. Once the trachea’s optimal position is achieved, the operator should request that the respiratory assistant’s hand replace her/his hand to maintain that position while the operator slides the endotracheal tube into place.[11]

If intubating with a straight blade, the operator should insert the blade midline to reach the epiglottis. The straight blade lifts the mandible, tongue, and epiglottis as a unit. The straight blade tip goes underneath the epiglottis and is used to lift the epiglottis to expose the vocal cords. This is different from the curved blade technique in which the blade goes in the vallecula.[11]

In anticipated difficult intubations, operators should consider performing the first attempt with a video laryngoscope. Most video laryngoscopes have a curved blade, and some may require a rigid rather than a malleable stylet. The video laryngoscopy technique is similar to that of direct laryngoscopy with the special consideration that some video laryngoscope blades may obstruct endotracheal tube passage when a Cormack Lehane grade 1 view (full visualization of the glottis) is achieved. In these cases, the Cormack Lehane grade 2 view (partial visualization of the glottis) allows for easier passage of the endotracheal tube.

If the first intubation attempt is unsuccessful, operators must be ready to change their approach and method on subsequent attempts. A tracheal tube introducer, also called bougie, can be used if the initial attempt is unsuccessful. The bougie is a flexible device with an anteriorly angulated tip that is introduced in the airway when vocal cord visualization is poor. The introduction of the bougie allows for indirect identification of the cartilaginous ridges of the anterior airway. The endotracheal tube slides over the bougie and passes the vocal cords. Tracheal tube introducers may be considered for the first attempt in patients with an anticipated difficult airway.[12]

After the endotracheal tube is passed through the vocal cords, the cuff is inflated using a 5 cc or 10 cc syringe filled with air.  The stylet is removed, and the proximal end of the endotracheal tube is connected to the carbon dioxide monitor and the ventilation device. Traditionally, the desired depth from the incisors to the distal tip of the endotracheal tube is 21 and 23 cm in women and men, respectively. Although the preferred distance appears to correlate more with height than gender.[13]

Confirmation of Endotracheal Tube Position

After placing the endotracheal tube, it is essential to confirm its placement in the trachea and position proximal to the carina. End-tidal carbon dioxide monitor is the gold standard to confirm tracheal intubation. To rule out esophageal or hypopharyngeal intubation, an EtCO2 monitor measures the expired carbon dioxide with respiration. Extratracheal carbon dioxide waveform will read 0 mmHg, while endotracheal intubation correlates reliably with the patient’s arterial partial pressure of CO2.[14][15] The physician should also auscultate for symmetric bilateral breath sounds and the absence of breath sounds over the stomach. A post-intubation chest x-ray confirms the location of the endotracheal tube’s distal tip 2 to 4 cm proximal to the carina and rules out mainstem bronchus intubation.

Complications

Assessment for intubation should take into consideration potential complications. Hypoxemia is a feared complication of intubation that may be precipitated by multiple attempts with poor oxygenation between attempts, misplaced endotracheal tubes, and failed intubation. Oxygenation can be optimized by pre-oxygenation and apneic oxygenation. To avoid an unrecognized misplaced endotracheal tube, immediate confirmation of the tube position should take place. In cases of anticipated difficult airways, physicians should consider if RSI, DSI, or awake intubation using direct, video, or fiberoptic laryngoscopy is most appropriate for the patient.

Cardiovascular complications can arise as a result of direct pharyngeal manipulation as well as induction medications. Bradycardia can result from vagal stimulation during direct laryngoscopy. Some sedative medications can cause hypotension that can lead to hemodynamic compromise and cardiac arrest during the intubation of critically ill patients. Appropriate resuscitation before intubation can mitigate some of these risks. Patients should also have large-bore and reliable intravenous or intraosseous access to administer intubation and resuscitation medications if required.

Other complications include laceration to the oropharynx from direct manipulation, trauma to the teeth, and aspiration of vomit or objects from the oropharynx, such as dentures. Complications after intubation include uvular and mucosal necrosis from the pressure of the endotracheal tube against these anatomical structures. Tracheal rupture is extremely rare but can result from tracheal necrosis from cuff overinflation or direct trauma from the tube or stylet. Using manometry to inflate the cuff to a goal of 20-30cm water can prevent some of these complications.[16]

Clinical Significance

Endotracheal intubation is an essential skill for emergency medicine and critical care providers. Understanding the risks and complications of endotracheal intubation is as important as identifying appropriate candidates as early as possible. When preparing for endotracheal intubation, providers should optimize positioning, pre-oxygenation, equipment, and team preparation. They should also be ready to perform other methods of intubation if the initial attempt is unsuccessful. If starting with direct laryngoscopy, providers should have backup strategies such as video laryngoscopy, bougie, laryngeal mask airway (LMA), and cricothyrotomy tools immediately available. Preparation and practice are key to leading the team to successful intubation in the emergency setting.

Enhancing Healthcare Team Outcomes

All roles should be assigned by the physician or designated leader prior to the patient’s arrival if this information is available ahead of time.