Categorized | Features

A Tight Squeeze

Posted on 22 November 2011

EMS providers can use certain mnemoincs to assess a patient’s airway for difficulty. Photo JEMS

Michael F. Murphy, MD, & Fred Ellinger Jr., NREMT-P

Objectives
>> Recognize the importance of classifying the limited-access patient as a difficult airway.
>> Identify the steps that need to be taken when assessing a patient’s airway for difficulty.
>> Review the process for rapid sequence intubation.
>> Identify helpful mnemonics for assessment of the difficult airway.

On a dreary morning in 2006, EMS providers from Gilbertsville (Pa.) Area Community Ambulance Service were dispatched for a multi-system trauma patient. Initial reports suggested a single motor-vehicle collision with a tree. Additional reports indicated a male subject bleeding from the head with a branch sticking out of his eye.

Several minutes after dispatch, police arrived and confirmed the reports. They also discovered the patient was entrapped and would require hydraulic extrication by fire department rescue companies. Additional fire and EMS resources were immediately dispatched, and the ALS unit en route was advised of the updated reports. Considering the confirmed report of entrapment and extended ground transport time to the nearest trauma center, Hahnemann University Hospital’s MedEvac 3 helicopter based out of Montgomery County, Pa., was placed on standby by the responding ALS unit.

On arrival of the first ALS unit, the young male subject was found entrapped in the driver’s seat. The mechanism of injury (MOI) was suggestive of a single vehicle that struck a large tree broadside between the A and B posts of the driver’s door. The lead ground paramedic reported the patient to be awake and confused with a GCS of 11 (E3, M4, V4) and positive radial pulses. His airway was patent, and circulatory status was intact.

When the rescue companies arrived, work began on disentangling the driver. After a brief scene survey, the helicopter EMS (HEMS) unit was requested to fly by the ground providers due to the MOI—an approximately 6? branch impaled in his eye.

MedEvac 3 arrived on scene 21 minutes after being requested. As per protocol, the crew immediately located the incident commander for accountability check-in and to determine the rescue status. The HEMS crew completed a global scene assessment and began formulating a care plan.

At the same time, the rescue chief reported that the patient was “about to come out.” However, when attempting to extricate the patient via a vertical move to a long spine board, it was quickly discovered that the patient was still pinned by his hips and legs. Extrication now focused on freeing the patient from the secondary entrapping mechanism. The time to complete extrication still remained unknown. The HEMS crew then established a treatment plan that included airway assessment, oxygen administration as permitted by access, pain management by fentanyl, airway management in the vehicle in the event of decompensation, and rapid extrication.

Limited access to the patient permitted only a primary assessment from the exterior of the vehicle. The assessment was negative with the exception of the impaled ocular object. The patient complained of pain and required physical restraint to prevent him from pulling out the impaled object. Initial treatment had been limited to C-collar placement and IV initiation of 14 g at the antecubital fossa. Because of the ongoing rescue attempt and limited PPE for the HEMS crew, the ground providers remained closest to the patient and offered details concerning the patient status as needed.

Patient Status Changes
A sharp decline in the patient’s mental status occurred 52 minutes into the incident. Extrication was paused to allow for reassessment of the patient. The patient was now unresponsive with a GCS of 5 (E1, M1, V3), indicating the need for advanced airway management. An airway assessment was performed, and no anatomical difficult airway indicators were present. Physical access to the patient was considered as a potential difficult airway indicator. Passive ventilations were continued with oxygen at 15 lpm via non-rebreather mask because the patient’s minute volume was still adequate.

Because of the potential for difficult intubation, the MedEvac 3 crew opted to proceed with their non-paralytic rapid sequence intubation (RSI) Difficult Airway Algorithm. Confident the patient could be managed with bag-mask ventilation (BMV), the MedEvac 3 crew utilized a pharmacologically assisted intubation (PAI) via etomidate because of its known cerebroprotective properties.

After all medications and equipment were readied, including rescue airway devices (Laryngeal Mask Airway [LMA] and Melker cricothyrotomy kit), advanced airway management began. Manual C-spine stabilization was maintained from behind the patient, and etomidate 24 mg was administered via IV push for deep sedation. Sellick’s maneuver was initiated pending successful intubation.

Almost immediately after the administration of etomidate, the patient was noted to have masseter muscle spasm with associated decline in oxygen saturations. Two-rescuer BMV was initiated on the upright, trapped patient with poor gas exchange being appreciated. The masseter muscle spasm failed to resolve in a timely manner, requiring succinylcholine 120 mg via IV push to mitigate its effects. Within seconds of the administration of succinylcholine, the masseter muscle spasm resolved, and BMV resumed easily. (For more on succinylcholine, read “Paralysis Analysis” in October JEMS or at www.jems.com.)

Once the oxygen saturation level was raised, a face-to-face intubation attempt was made. On insertion of the laryngoscope, a Grade 3 airway view was appreciated, but a styletted 7.5 mm inner diameter (ID) endotracheal tube couldn’t be passed into the glottis. The intubation attempt was aborted, BMV was re-initiated and a smaller tube was chosen. Another intubation was attempted and again revealed a Grade 3 view. A 7.0 ID tube was placed and tracheal position confirmed carbon dioxide detection, presence of bilateral breath sounds and absent epigastric sounds. Post-intubation management included Versed for continued sedation, vecuronium for long-term neuromuscular blockade and fentanyl for analgesia.

Approximately 10 minutes after intubation, the patient was successfully freed from the entrapping mechanism, extricated and secured to a long spine board. The patient was taken by ambulance to the awaiting helicopter and safely transported to a Level 1 trauma center. He was diagnosed with pneumocephalus, ventricular hemorrhage with midline shift, left frontal lobe hemorrhage, right temporal lobe hemorrhage, left orbital fractures, impalement of the left eye by an approximately 6? wooden object and fractured left superior pubis ramus. After a 16-day hospitalization, the patient was discharged with intact vision in his left eye and no appreciable neurological deficits.

Prep for Intubation
This case demonstrates how airway management in a limited-access situation can pose unique problems for EMS providers. As an added element of complexity, the physical task of performing BLS and ALS airway maneuvers may become burdensome or near impossible using conventional approaches.

Working in a methodical fashion, the EMS provider must thoroughly assess the airway for suspected difficulty and then choose the correct approach and tools, keeping in mind that access may be the only difficulty present. The EMS provider should be extremely familiar with all of the tools and medications at their disposal. This is especially true when performing PAI.

During the planning phase, it’s extremely important that the airway manager adequately assess the airway for suspected difficulty, choose the appropriate approach (i.e., Airway Management Algorithm) and prepare all needed equipment and medications. If they decide to employ RSI techniques or a PAI, the need to assess for a difficult airway increases to prevent a “can’t intubate, can’t ventilate” failed airway. In this age of adequate training, skills maintenance and intense quality oversight, it’s reasonable to anticipate that RSI will emerge as a cornerstone of EMS airway management.

Assessment Mnemonics
Most EMS providers have heard of the “LEMON Law” theory of assessing a patient for difficult laryngoscopy and intubation. However, this is only one of four important steps in assessing a patient’s airway for difficulty. The four “Dimensions of Difficulty” are: 1) difficult BMV; 2) difficult orotracheal intubation/laryngoscopy; 3) difficult extraglottic device (EGD) placement; and 4) difficult cricothyrotomy. This assessment is a systematic and simple approach to ensure all areas of concern have been looked at for suspected difficulty. Four mnemonics, or memory aids, will help you thoroughly assess a patient for difficult airway management identifiers: MOANS, LEMONS, RODS and SHORT.

‘MOANS’
Difficult BMV may be identified by the mnemonic MOANS. The “M” represents “mask” to indicate difficult mask seal. Blood, facial injuries and beards are several examples of situations that may make BMV difficult or impossible.

“O” refers to “obesity” and “obstruction.” Obese and pregnant patients are inherently more difficult to bag-mask ventilate.

“A” refers to aged patients (older than 55 years) who may be more difficult to bag-mask ventilate due to physiological conditions that decrease compliance and promote loss of muscle tone in the upper airway, leading to collapse and obstruction to gas flow.

“N,” or “no teeth,” may cause difficult BMV due to missing supporting structures needed to properly seat and seal the mask.

Lastly, the “S” in MOANS refers to “stiff lungs” or “stiff chest wall.” Patients who require increased ventilatory pressure, such as the patient with chronic obstructive pulmonary disease, acute respiratory distress syndrome or pulmonary edema, may be difficult to ventilate because sufficient positive pressure may be difficult to achieve. Failure to complete this assessment prior to the administration of airway medications may lead to disastrous results, particularly in the event of a failed intubation. When employing an RSI technique or a PAI, the provider must have confidence that BMV will be successful. The provider should never take away something from a patient they’re not confident they can replace.

‘LEMONS’
This assessment assists in predicting whether a difficult laryngoscopy and intubation will be encountered. The “L” stands for “look externally.” These signs include a thick beard, bull neck or large tongue.

“E,” or “evaluate the 3-3-2 rule,” is an effective exam to reveal both the location of the larynx in relationship to the base of the tongue and whether the oral cavity will provide sufficient room to accommodate the intubation tools. (For more on the 3-3-2 rule, visit jems.com/airway.)

The “M” in LEMONS refers to the Mallampati scale. This assessment of the awake, seated patient “classes” the view of anatomical structures seen when the patient opens their mouth, protrudes the tongue and doesn’t phonate. A Class 1 airway is the least threatening; conversely, a Class 4 airway is considered to predict a difficult intubation.

“O” refers to “obstruction.” Signs of anatomical obstruction include a hoarse or “hot potato” voice, stridor, or painful or difficulty swallowing.

The “N” is for “neck mobility.” Patients with limited neck mobility secondary to musculoskeletal diseases or injuries may be unable to assume the sniffing position, making the alignment of the airway structures and oral access difficult. Patients in C-collars aren’t immediately considered to be difficult intubations because of the collar alone. With proper manual cervical spine stabilization, it’s acceptable to remove the front of the collar during intubation.

Finally, the “S” refers to “space,” “scene” and “skill” of the intubator. Common problems associated with space and scene include confined spaces, limited physical access to the patient or their airway, unique patient presentation and extremely high- or low-light conditions. When placed in a unique or new situation, the intubator must assess their skill and comfort level before embarking on advanced airway management, especially RSI or a PAI.

‘RODS’
EGDs have emerged as an invaluable rescue airway management resource in addition to their role in routine airway management in the operating room. Airway devices, such as the LMA (Fastrach), the Esophageal Tracheal Combitube (ETC or Combitube) and the King LT airway, have a substantial volume of literature attesting to their efficacy as rescue devices in EMS, the critical care unit and anesthesia.

Studies have identified factors that predict difficulty in placing an EGD and providing adequate gas exchange. These can be assessed using the mnemonic RODS.

The “R” stands for “restricted mouth opening.” Depending on the EGD to be employed, more or less oral access may be needed.

The “O” represents “obstruction” of the upper airway at the level of the larynx or below. An EGD won’t bypass this obstruction.

The “D” stands for “disrupted” or “distorted” airway that leads to a compromised seat and seal of the EGD. Seal may be exceedingly difficult or impossible to achieve in the face of a fixed flexion deformity of the neck or with the upper airway distortion of angioedema.

Lastly, the “S” refers to “stiff lungs” or “cervical spine.” Ventilation with an EGD may be difficult or impossible in the face of substantial increases in airway resistance (e.g., deadly asthma) or decreases in pulmonary compliance (e.g., pulmonary edema). There are reports of difficult LMA insertion in patients with limited neck movement.

‘SHORT’
This evaluation identifies potentially difficult surgical cricothyrotomy should intubation fail on three attempts and the airway manager be faced with a “can’t intubate, can’t ventilate” scenario. The “S” identifies patients with previous neck surgery. Surgical scars of the neck should warn the operator of suspected distorted anatomy.

“H” refers to “hematoma/infection.” Expanding neck hematomas and infectious processes, such as Ludwig’s angina, may make correct neck landmark identification difficult or impossible.

“O” is for “obese.” Obviously, it may be difficult to find landmarks in the obese patient. Furthermore, these patients have redundant tissue, making access difficult.

“R” stands for “previous radiation therapy” and “T” for “tumor.” Either of these conditions may also make surgical cricothyrotomy difficult due to anatomy distortion.

Failure to predict difficult BMV, intubation, EGD and/or cricothyroidotomy may lead to the use of an inappropriate algorithm and may result in airway management failure.

Mind Your Ps
The “Seven Ps of RSI,” as described by Ron Walls, MD, in the companion textbook to The Difficult Airway Course: EMS, Manual of Emergency Airway Management, has been recited ad nauseam. However, the process should never be discounted or underestimated. This memory aid, when applied appropriately, is extremely useful in preventing the accidental omission of one of the many important steps in paralytic and non-paralytic RSI.

The first and undoubtedly most important step in this seven-“P” process is the “preparation” phase. The intubator must prepare their equipment, medications and, especially, themselves.

The second “P” is “pre-oxygenation” prior to the placement of the laryngoscope. The goal of the pre-oxygenation phase is to provide as near 100% oxygen for as long as possible prior to the attempt. A pulse oximetry reading of at least 94% is desirable.

The “pretreatment” phase of RSI is the third step and is designed to administer medications that may assist in mitigating the untoward effects of laryngoscopy and intubation. The most important adverse responses include increased intracranial pressure, increased airway resistance (bronchospastic response), tachycardia and hypertension, and “shear” pressure associated with an increased cardiac ejection velocity.

The fourth “P” stands for “paralysis with induction.” Prior to chemically paralyzing the patient, they must be “induced” with a potent sedative agent. In prehospital care, the use of etomidate has been demonstrated to be a reliable and safe induction agent with few untoward effects.

Should a non-paralytic approach be used, the “P” in this step may be used to remember to “push” the induction agent. When using etomidate alone in a PAI approach, deliver it via slow IV push because it has been documented to cause masseter muscle spasm if pushed too rapidly.

The fifth “P” is for “protection and positioning.” As consciousness fades, Sellick’s maneuver is applied and maintained until the patient is intubated. At this time, the patient is also properly positioned for the intubation attempt.

The sixth “P” refers to “placement with proof.” The endotracheal tube is placed, and the position in the trachea confirmed by several techniques. Although visualization of the tube passing the vocal cords has been considered a reliable method of determining tracheal placement, end-tidal carbon dioxide (EtCO2) monitoring has superseded it as the gold standard.

The final “P” is for “post-intubation management.” Immediately following successful intubation, it’s necessary to properly secure the endotracheal tube, sedate the patient, administer long-term chemical paralysis and provide adequate oxygenation and mechanical ventilation when possible.

The Case at Hand
Utilizing the Difficult Airway Algorithm approach, the crew of MedEvac 3 opted for a non-paralytic approach, using the potent hypnotic agent etomidate. The patient was able to be pre-oxygenated and successful BMV was predicted using the MOANS assessment; however, using the LEMONS mnemonic, intubation was predicted to be difficult secondary to physical access issues alone. The etomidate-only approach was attempted but had to be rescued by the administration of succinylcholine to eliminate the etomidate-induced masseter muscle spasm.

Although not addressed in the Difficult Airway Algorithm, succinylcholine had to be administered in an attempt to avoid hypoxemia and the need for a surgical airway secondary to not being able to place a rescue airway device. Once successfully intubated, the transition back to a universal algorithm was seamless and appropriate.

A variation of conventional laryngoscopy was discussed in this case. This method is referred to as a face-to-face intubation, the “pick” method or the “tomahawk” method. (For more, visit jems.com/airway.)

It’s important to note that a non-medication approach would have been taken if successful BMV wasn’t predicted during the preparation phase of the airway management sequence. All providers who decide on PAI, whether paralytic or non-paralytic, should bear in mind that a ventilatory and oxygenation airway emergency may be created should BMV, an EGD or endotracheal intubation not be successful.

Few options exist for intubation of the limited-access patient, including face-to-face intubation, fiber-optic intubation using rigid or flexible devices, digital intubation, retrograde intubation, and possibly a light wand technique. Although conventional laryngoscopy may be utilized, situations like the one presented don’t usually allow for it. Successful airway management requires a broad knowledge base, sound clinical judgment, and the decisiveness and authority to act when indicated. Control the airway; don’t let the airway control you!

Review Questions
Test your comprehension with this post-article quiz. Answers are provided at the end.

1.You’re called to the scene of a rollover MVC. When you arrive, you see a tractor trailer with its cab upside down. The driver is still in his seat belt, and his legs appear to be pinned. Your initial rapid trauma assessment reveals he’s unresponsive with shallow respirations of six per minute. Which of the following factors indicate this patient’s airway may be difficult to manage?
a.his position in the vehicle

b.his level of consciousness and respiratory effort

c.an inexperienced paramedic as his primary provider

d.both a and c

2.You’re dispatched to a residence where bystander CPR is being performed. While en route, the dispatcher advises you that your patient weighs approximately 400 lbs. You anticipate airway management may be challenging because in obese patients:
a.it’s difficult to get a good mask seal for BMV

b.there’s an increased horizontal length of the submandibular space

c.the Mallampati classification is usually a Class 3 or 4

d.the mouth opening is typically restricted

3.As you ventilate a deteriorating patient with a bag-valve mask, your partner is preparing to intubate. He says he’s concerned he may not be able to visualize the glottis because the patient has less than two finger breadths between the chin-neck junction and thyroid cartilage notch. Seeing your puzzled look, he explains that this indicates the:
a.glottis is further down in the neck and out of view

b.glottis is high and the tongue may hide its view

c.mouth won’t be able to accommodate the intubation equipment

d.airway structures are out of alignment

4.Your next call is to an unconscious 36-year-old female whose husband says she complained of a severe headache this morning. You now find her responding only to painful stimuli with decorticate posturing. Her respirations are 10 and shallow. You prepare for a pharmacologically assisted intubation. You want your inexperienced partner to give the etomidate, but first ask him if he recalls how to give the medication and why. He correctly tells you:
a.IV drip to avoid hypotension

b.endotracheal to avoid hypoxemia

c.rapid IV push to promote immediate paralysis

d.slow IV push to minimize masseter muscle spasms

5.You’ve decided to perform a rapid sequence intubation on a patient with 85% full-thickness burns and airway involvement. Which of the following is the single most important step in the RSI process for a successful outcome?
a.pre-oxygenation

b.preparation

c.pretreatment

d.positioning

1. D, 2. A, 3. B, 4. D, 5. B

Acknowledgement
The authors thank Tessa Fisler, RN, CCRN, PHRN, for her contribution and patient care of the case presented.

References
Walls RM , Murphy MF . Manual of Emergency Airway Management . Third Edition. Philadelphia: Lippincott, Williams and Wilkins; 2008;

Glossary Terms
Extraglottic -Occurring outside the glottis.
Laryngoscopy -Examination of the larynx using a laryngoscope.
Mallampati scale -Four classifications based on the ease of visualization of oral cavity anatomy; used to predict difficulty in oral endotracheal intubations.
Masseter muscle -One of the muscles used in mastication, or chewing. Spasm of this muscle makes intubation difficult.
Pneumocephalus -Presence of air or gas within the cranial cavity.
Sellick’s maneuver -Method of applying pressure to the cricoid cartilage in order to prevent regurgitation during endotracheal intubation. Also known as cricoid pressure.

Michael F. Murphy, MD, is the professor and chair of anesthesiology and a professor of emergency medicine at Dalhousie University, Halifax, Nova Scotia, Canada. He’s also the district chief of anesthesiology for the Capital District Health Authority and an attending physician in emergency medicine at Queen Elizabeth II Health Sciences Centre in Nova Scotia. Contact him at murphymf1@gmail.com.

Fred Ellinger Jr., NREMT-P, is the ALS program manager at Em-Star Ambulance Service, Philadelphia, Pa. He also serves as a flight paramedic for MidAtlantic MedEvac, Hahnemann University Hospital, Philadelphia. Contact him at fred.ellinger@difficultairway.net.

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One Response to “A Tight Squeeze”

  1. Derek says:

    I use the King LTS as my primary device. It works excellent. Blind intubation, speed, and success rates are great.


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