What Causes Difficult Intubation?

What Causes Difficult Intubation Unexpected difficulties in intubation are more common than one might think, with an incidence rate that varies from 0.1% to 10.1%

They pose a higher risk of injury, with repeated attempts leading to severe complications that include edema, increased gastric sufflation, increased blood and secretions in the airway, and trauma to the posterior pharynx. As expected, it leads to suboptimal performance in subsequent procedures. 

Moreover, a study suggests that 93% of difficult intubations are unanticipated, making them challenging to manage. To ensure clinicians are prepared for such instances, Hospital Procedures Consultants offers a detailed guide into the likelihood of difficult intubation, indications, clinical factors, processes, techniques, and more.

How To Predict Difficult Airways 

Difficulty in intubation can be predicted with the RODS mnemonic:

  • R: Restricted mouth opening
  • O: Obstruction (upper airway)
  • D: Disrupted or distorted oropharynx
  • S: Stiff lungs or cervical spine

Other strategies that highlight anatomical or physiological predictors for difficult intubation consider the:

  • 3-3-2 rule
  • Age, specifically if patients are more than 55 years old
  • Head and neck radiation
  • Mallampati score III & IV
  • Post-operative hematoma
  • Presence of intraoral cavity mass
  • Obesity (incidence of 11% compared to the normal 7% level)

This due diligence is crucial for achieving first‐pass success. It can also help avoid “cannot intubate, cannot ventilate” scenarios.

Understanding the Process 

Difficult or failed intubation is a common cause of mortality and morbidity. Hence, it’s important to minimize complications by becoming familiar with the systematic preparation for the procedure. 

Step 1: Prepare the Patient 

Establish IO/IV access for drug therapy, choose the right position (head elevated in a 20° to 45° upright position), assess the airway to predict difficult intubation, and screen for allergies to ensure the safety of anesthesia and other drugs. 

Ensure optimal preoxygenation to broaden the safe apnea period and maintain oxygenation in the absence of patient respiratory effort. Then, insert a nasogastric tube to decrease the risk of aspiration.

Step 2: Gather the Equipment

Familiarize yourself with recent trends in airway management for more informed decisions. Intubation requires:

  • A bag-valve-mask
  • A bougie or Eschmann stylet 
  • A carbon dioxide detector
  • Extracorporeal membrane oxygenation (ECMO)
  • Flexible intubation scopes for navigating anatomically difficult airways
  • Nasopharyngeal airways  
  • Oropharyngeal airways
  • A high-flow nasal cannula
  • A laryngoscope (use VL for improved laryngeal visualization)
  • A suction catheter
  • A syringe
  • Tracheal tubes or narrow-diameter catheters (Ventrain system)

There should also be a FONA (front of neck airway) or cricothyroidotomy set on standby for emergencies. 

Step 3: Check Medications

Essential drugs for effective intubation include:

  • Sedatives like etomidate and ketamine. Propofol can also be used.
  • Neuromuscular blocking agents: succinylcholine and rocuronium.
  • Push dose pressors: epinephrine and phenylephrine for hypotension. 

Check for contraindications before administration to minimize risk.

Step 4: Get All Hands on Deck 

Assemble the necessary personnel for intubation, ensuring a detailed division of labor. This is crucial for progressing through the airway pathway at an appropriate pace and without the undue repetition of failed techniques.

Step 5: Prepare for Complications 

Difficult intubations can result in adverse events, such as cardiovascular instability, severe hypoxemia, and cardiac arrest. It’s thus important to have a plan for peri-intubation as secondary outcomes can lead to mortality.

Likelihood of Adverse Events Increases With Intubation Attempts 

An observational study demonstrated that multiple intubation attempts were independently associated with higher odds of adverse events (AEs). Patients who underwent 3 or more intubation attempts exhibited a 35% incidence of AEs compared to 9% of parents who experienced 2 or fewer attempts.

This has been established across medical literature, even in the field of pediatrics.  

For example, a 2022 study by Hiraku Funakoshi and colleagues found that among 279 children with first-pass success, 9% had an adverse event. In contrast, only 31% of 160 children who underwent 2 or more attempts experienced an adverse event.

The findings remain consistent after adjusting for potential confounders.

Using the Right Adjuncts and Techniques 

Difficult intubations are complex procedures, but they can be easier and more successful. The key is to execute them with research-backed approaches like: 

Research also recommends the use of ultrasonography. It can be used to evaluate the thickness of the skin at the epiglottis and hyoid levels, the hyomental distance, the hyomental distance ratio, and the airway size. 

Is Due Diligence Enough?

Many postoperative complications can be avoided with good patient selection, training, and surgical planning. However, this may not be possible in emergency situations where physicians may not have enough time to obtain a patient’s medical history or assess their airway due to the urgency of the situation. 

For urgent cases that do not allow thorough evaluations, the upper lip bite test can be used. It can raise the probability of difficult intubation from 10% to more than 60% for patients with average risk. However, critically ill patients in the emergency room are frequently unable to follow commands.

When intubation is hard to achieve, the American College of Surgeons recommends a rescue surgical intubation via cricothyroidotomy

Improve Your Airway Management Skills With Hospital Procedures Consultants

Airway management is an essential skill in restoring a patient’s breathing. Clinicians must thus develop and maintain their airway management skills to avoid the most common adverse event, severe hypoxemia.

Their knowledge should extend to children even if unanticipated difficult intubations are rare among this patient group (0.03%).

Master airway management even in the face of difficult intubation cases. Hospital Procedures Consultants has comprehensive courses that range from  Endotracheal Intubation to Glidescope Intubation. These offer valuable insights into the predictors of and pearls for difficult intubation along with the knowledge and experience to troubleshoot them. 


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Goto, T. Goto, Y. Hagiwara, Y. Okamoto, H. Watase, H. Hasegawa, K. Advancing emergency airway management practice and research. Review Acute Med Surg. 2019 May 21;6(4):336-351. doi: 10.1002
Foley, L. J. Urdaneta, F. Berkow, L. Aziz, M. F. Baker, P. A. Jagannathan, N. Rosenblatt, W. Straker, T. M. Wong, D. T. Hagberg, C. A. Difficult Airway Management in Adult Coronavirus Disease 2019 Patients: Statement by the Society of Airway Management. Review Anesth Analg. 2021 Oct 1;133(4):876-890. doi: 10.1213
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