3-3-2 Rule


Article Author:
Sandeep Sharma
Roshan Patel
Muhammad Hashmi


Article Editor:
Rotem Friede


Editors In Chief:
Yvonne Carter
Jason Wallen


Managing Editors:
Avais Raja
Orawan Chaigasame
Carrie Smith
Abdul Waheed
Khalid Alsayouri
Kyle Blair
Trevor Nezwek
Radia Jamil
Erin Hughes
Patrick Le
Anoosh Zafar Gondal
Saad Nazir
William Gossman
Hassam Zulfiqar
Navid Mahabadi
Hussain Sajjad
Steve Bhimji
Muhammad Hashmi
John Shell
Matthew Varacallo
Heba Mahdy
Ahmad Malik
Abbey Smiley
Sarosh Vaqar
Mark Pellegrini
James Hughes
Beata Beatty
Daniyal Ameen
Altif Muneeb
Beenish Sohail
Nazia Sadiq
Hajira Basit
Phillip Hynes
Komal Shaheen
Sandeep Sekhon


Updated:
9/19/2019 8:19:22 AM

Introduction

The airway is one of the most important components in the body to be protected regardless of why a patient is in a hospital, whether for outpatient surgery or admission to the intensive care unit (ICU) for observation and therapy. For this reason, when a physician considers intubation, they must evaluate the risk of failure to intubate and optimize variables for success. One percent to 3% of the patient population that requires endotracheal intubation has difficult airways. Recognizing these patients is crucial as it allows the clinician to prepare accordingly to minimize complications. The 3-3-2 rule is an assessment tool for the prediction of difficult intubations in the unexpected difficult airway.[1][2][3]

According to the American Society of Anesthesiologists, intubation is determined to be difficult to secure when an appropriately trained and experienced anesthesiologist requires more than three attempts or longer than 10 minutes for successful endotracheal intubation. Similarly, ventilation is determined to be difficult when a trained clinician is unable to maintain an oxygen saturation of more than 90% when using a facemask for ventilation, and 100% fraction of inspired oxygen (FIO2) is in use for oxygenation.

The airway should be managed in a very time-sensitive way as poor oxygenation or ventilation can lead to hypoxia and hypercapnic abnormalities; this can be detrimental at the cellular level. Hypoxic brain injury can lead to permanent neuronal damage and acidosis due to hypoxia and hypercapnia, which together can lead to cardiac arrest or death.

Function

The 3-3-2 rule functions to estimate whether the anatomy of the neck will allow for appropriate opening of the throat and larynx. It serves to roughly estimate if the alignment of the openings for direct visualization of the larynx is possible given anatomical findings.[3]

3: A measurement of three fingers between the upper and lower teeth of the open mouth of a patient indicates the ease of access to the airway through the oral opening. A typical patient can open their mouth sufficiently to permit placement of three of their fingers between the incisors. Adequate mouth opening facilitates both insertions of the laryngoscope and obtaining a direct view of the glottis.

3: A measurement of 3 fingers from the anterior tip of the mandible to the anterior neck provides an estimate of the volume of the submandibular space. A typical patient can place three fingers on the floor of the mandible between the mental angle and the neck near the hyoid bone. Normally this distance should measure close to 7 cm. If this distance is less than three finger-widths, the laryngeal axis will be at a more acute angle with the pharyngeal axis, indicating that alignment of the oral opening to the pharyngeal opening will be difficult. It also indicates that there will be less space to displace the tongue within the throat. The rule has limitations as the distance can vary according to height and ethnicity. For this reason, an alternative in the form of a ratio of height to thyromental distance (RHTMD) has been suggested.

2: A measurement of 2 fingers between the floor of the mandible to the thyroid notch on the anterior neck identifies the location of the larynx relative to the base of the tongue. A typical patient can place two fingers in the superior laryngeal notch. If the larynx is too high in the neck, measuring less than two fingers, direct laryngoscopy will be difficult and potentially impossible; this is because the angle between the base of the tongue to the larynx is too acute to be negotiated for direct visualization of the larynx easily.

A likely indication of difficult intubation is present if the inter-incisor or hyoid-mental distance is less than three fingers or the hyoid-thyroid cartilage distance is less than two fingers. Depending on the patient population, reports of difficult intubation occur in 1.5% to 13% of patients. When combined with the Mallampati score in evaluating an airway, the positive predictive value for determining a difficult airway increases.

Additional estimations to be considered in preparing for intubation of a patient should include:

Assessment of atlanto-occipital extension is performed by asking the patient to look at the floor and the wall after fully flexing and fixing the neck.  Flexion movement of the cervical spine is assessed by asking the patient to touch the manubrium sterni with the chin. If successful, this indicates that the flexion and extension range of motion is sufficient to help in aligning the oral pharyngeal and laryngeal axis in a straight line, thus indicating easier intubation.

A combined assessment of the mandibular space with the 3-3-2 rule and atlanto-occipital extension will further determine how easily the laryngeal and pharyngeal axis will fall in line with the atlantoaxial joint during extension of the neck.

The Warning sign of delicate is performed by placing the index finger of each hand, one submental, under the chin, and the other under the inferior occipital prominence with the head in the neutral position. The patient is then asked to extend their head and neck fully. If the submental finger is seen to be higher than the inferior occipital prominence finger, there should be no difficulty with intubation. If the finger on the inferior occipital prominence is still higher than the submental finger, the clinician can anticipate a difficult airway.

Prayer sign is positive when the patient cannot approximate the palmar surfaces of the phalangeal joints while pressing the hands together. This sign presents in advanced diabetes and has a very high positive predictive value for cervical spine immobility and thus difficult endotracheal intubation.

Clinical Significance

Recognizing that a patient’s airway will be difficult allows the clinician to plan for and minimize the risks of airway-related morbidity. A prospective observational study of 156 patients undergoing intubation in the emergency department found the LEMON scale evaluation accurately stratified patients according to the risk of difficult intubation. The 3-3-2 rule plays a crucial role in planning as a component of the LEMON scale.[4] LEMON stands for:

L: Look externally

Look for external indicators of difficult endotracheal intubation. Which can include the abnormal shape of the face, extreme cachexia, poor dentition, edentulous mouth, morbid obesity, high arching palate, short neck, large front teeth, surgical scar indicating previous tracheostomy scar, indicating patient might have tracheomalacia, narrow mouth, face, or neck pathology.

E: Evaluate 

This is where the 3-3-2 rule is important. It is the estimated measurement of 3 separate distances on the patient using the examiner's fingers.

3: Measurement of the Inter-incisor space, which should be greater than three fingers distance between the upper and lower teeth of the open mouth of a patient.

3: Measurement of the hyoid-mental distance, which should be greater than three fingers from the anterior tip of the mandible to the anterior neck on the hyoid bone.

2: Measurement of the hyoid-thyroid cartilage distance, which should be greater than two fingers between the floor of the mandible at the hyoid bone to the thyroid notch on the anterior neck.

M: Mallampati Scoring

Mallampati scoring is a system based on the anatomy of the mouth and the view of various anatomical structures when one opens his or her mouth as wide as possible. The scoring is done in a sitting position and is not performable in an emergency. A class I score is interpreted as easy, and class IV is the most difficult.[5][6][7]

Class I: Structures visualized- soft palate, uvula, fauces, anterior and posterior pillars

Class II: Structures visualized- soft palate fauces and uvula 

Class III: Structures visualized- soft palate and the base of the uvula

Class IV: Soft palate is not visible

O: Obstruction

One should assess if the airway could be obstructed with the foreign body, abscess, tumor, soft tissue swelling such as in a burn victim or expanding hematoma in a trauma patient.

N: Neck Mobility

In alert and awake patients, see if the patient can place their chin on their chest and how far back are they able to tilt their head. Decreased neck mobility is a negative predictor of intubation complication.

Other Issues

Pearls

  • It is essential to anticipate when a difficult airway may occur. Many patients that otherwise appear normal/easy to intubate may prove difficult. The 3-3-2 rule can help to anticipate complications.
  • The 3-3-2 rule is useful, but its significance is greater when combined with the Mallampati score.
  • The 3-3-2 rule, along with other estimations, does not play a role in emergent intubations.

Enhancing Healthcare Team Outcomes

The airway is one of the most critical components in the body to be protected regardless of whether a patient is in a hospital, undergoing outpatient surgery or has admission to the (ICU) intensive care unit for observation and therapy. While most intubations are straight forward, there are some difficult airways which if not handled appropriately can lead to the death of the patient.

For this reason, when a clinician considers intubation, they must evaluate the risk of failure to intubate and optimize variables for success. Besides anesthesiologists, physicians in many specialties and nurse anesthetists, as well as the clinical pharmacist, are often called upon to assist in the preparation and intubation of a patient, but they should be fully aware of the 3-3-2 rule. Difficult airway cart should be kept at bedside when intubating difficult airway. All physicians with intubation skill in the hospital should be informed as a backup before difficult intubation. The reversal agent of sedation and paralytics should be kept at bedside in case if the physician is not able to intubate the patient. 

ED nurses are often called upon to secure the tubes, or assist in their placement, as well as monitoring patient vitals following intubation, and communicate any concerns to the physician on duty. Failure to intubate on a timely basis is a very common cause of cardiac arrest. Given this, an anesthesiologist consult is always in order if anticipating a difficult airway. Sometimes, oral intubation may not be possible, and an emergent tracheostomy may be required. The nursing staff should be prepared to assist the clinician in this procedure, often assisting with patient alignment and control of the head position. [8][9][10] The nursing staff should monitor the patient and immediately report any changes in oxygen saturation or evidence of breathing difficulty to the clinician after intubation. Nurses should place sign outside of room "difficult intubation" This keeps medical team aware of it in case of self-extubation.

Employing the 3-3-2 rule is not the purview of any single healthcare discipline; all members of the interprofessional team with exposure to intubation should know the rule, how to employ it, and communicate openly with other interprofessional team members if issues arise. This collaborative approach is essential for advancing patient outcomes in cases of intubation. [Level V]


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3-3-2 Rule - Questions

Take a quiz of the questions on this article.

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An 82-year-old male presents to the emergency department with severe shortness of breath. His vitals are temperature 38.5 C, pulse 120, respirations 36, BP 100/60 mmHg, and oxygen saturation 82% on 15 L nonrebreather mask. Chest auscultation reveals a silent chest. There is a concern for impending respiratory failure and preparations are made for endotracheal intubation. Using the 3-3-2 rule, which of the following measured distances will most likely predict difficult intubation?



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A 66-year-old female with a history of obstructive sleep apnea, hypertension, diabetes mellitus, extreme obesity, and asthma presents with 5 days of worsening shortness of breath associated with wheezing and cough. Her vital signs on presentation show a blood pressure of 168/70 mmHg, oxygen saturation 85% on room air, respiratory rate 32/min, and pulse 110/min. On exam, she has diffuse expiratory wheezing. Her chest x-ray does not show any major infiltrates. Her labs are grossly normal except her ABG shows a pH of 7.2 with pCO2 56 mmHg, pO2 55 mmHg and bicarbonate of 21 mmol/L. She is started on nebulizations, corticosteroids, and antibiotics. She is placed on a BiPAP and transferred to a step-down unit. Repeat ABG shows a pH of 7.1 with pCO2 of 70 mmHg. She is prepared to be intubated and moved to the ICU. Rapid sequence intubation is attempted but failed after 4 attempts. The patient goes into bradycardia and codes. Which of the following would have best prevented the patient coding?



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A 72-year-old male with COPD, congestive heart failure, diabetes mellitus, and hypothyroidism presents to the emergency department with cough and shortness of breath. The patient is found to have acute on chronic hypercapnic respiratory failure. His pH on arterial blood gas is 7.1, pCO2 90 mmHg, and pO2 100 mmHg on a nonrebreather mask. Upon evaluating his mouth, the clinician is unable to pass more than two fingers between upper and lower teeth. Because of the possibility of a difficult airway, the patient is intubated with a video laryngoscope after giving intravenous etomidate and rocuronium. The patient is now transferred to ICU. Which of the following is the next best step in the management of this patient?



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A 42-year-old woman with no past medical history is scheduled for elective repair of her femoral hernia. A newly trained anesthetist on duty attempts intubation for airway protection during surgery. He uses fentanyl 100 micrograms intravenous for sedation during the first attempt at 8:00 am. The patient coughs when attempting intubation, so he takes laryngoscope out. After the first failed attempt, he uses midazolam 2 mg intravenous for sedation and attempts intubation. Again he fails to intubate the patient. The pulse oximeter shows a reading of 85%, so the patient is placed on bag and mask ventilation for about 5 mins. Now pulse oximeter shows a reading of 99%. The patient is given 30 mg of intravenous rocuronium, and she is successfully intubated on the third attempt at 8:15 am. Which of the following best defines difficult intubation as per the American Society of Anesthesiology?



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A 72-year-old woman with a history of dementia is scheduled for elective abdominal hernia repair. She has a history of anaphylaxis to penicillin. She takes alprazolam for insomnia at night. The patient was given alprazolam at 11 pm night prior to surgery by mistake by nursing home staff even after giving NPO order. The patient is somnolent. The patient is asked to open her mouth. The anesthetist cannot see the soft palate. He thinks that the patient is not following command because of her mentation, so he asks the patient again to open mouth as wide as possible. Now he can see soft palate and base of uvula. Which of the following puts her at the highest risk for difficult intubation?



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3-3-2 Rule - References

References

Sankar D,Krishnan R,Veerabahu M,Vikraman BP,Nathan JA, Retrospective evaluation of airway management with blind awake intubation in temporomandibular joint ankylosis patients: A review of 48 cases. Annals of maxillofacial surgery. 2016 Jan-Jun     [PubMed]
Yu T,Wang B,Jin XJ,Wu RR,Wu H,He JJ,Yao WD,Li YH, Predicting difficult airways: 3-3-2 rule or 3-3 rule? Irish journal of medical science. 2015 Sep     [PubMed]
Mahmoodpoor A,Soleimanpour H,Nia KS,Panahi JR,Afhami M,Golzari SE,Majani K, Sensitivity of palm print, modified mallampati score and 3-3-2 rule in prediction of difficult intubation. International journal of preventive medicine. 2013 Sep     [PubMed]
Ji SM,Moon EJ,Kim TJ,Yi JW,Seo H,Lee BJ, Correlation between modified LEMON score and intubation difficulty in adult trauma patients undergoing emergency surgery. World journal of emergency surgery : WJES. 2018     [PubMed]
Ilper H,Franz-Jäger C,Byhahn C,Klages M,Ackermann HH,Zacharowski K,Kunz T, [Update Mallampati : Theoretical and practical knowledge of European anesthetists on basic evaluation of airways]. Der Anaesthesist. 2018 Oct     [PubMed]
Rao KVN,Dhatchinamoorthi D,Nandhakumar A,Selvarajan N,Akula HR,Thiruvenkatarajan V, Validity of thyromental height test as a predictor of difficult laryngoscopy: A prospective evaluation comparing modified Mallampati score, interincisor gap, thyromental distance, neck circumference, and neck extension. Indian journal of anaesthesia. 2018 Aug     [PubMed]
Siriussawakul A,Maboonyanon P,Kueprakone S,Samankatiwat S,Komoltri C,Thanakiattiwibun C, Predictive performance of a multivariable difficult intubation model for obese patients. PloS one. 2018     [PubMed]
Ahmad I,Onwochei DN,Muldoon S,Keane O,El-Boghdadly K, Airway management research: a systematic review. Anaesthesia. 2018 Nov 20     [PubMed]
Gosavi K,Dey P,Swami S, Airway Management in Case of Diffuse Idiopathic Skeletal Hyperostosis. Asian journal of neurosurgery. 2018 Oct-Dec     [PubMed]
Tsukamoto M,Hitosugi T,Yokoyama T, Awake fiberoptic nasotracheal intubation for patients with difficult airway. Journal of dental anesthesia and pain medicine. 2018 Oct     [PubMed]

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