The Scary Airway Series Part II: Mastering Obesity, Peds, and Burns
Author: Francesca Civitarese, DO (EM Attending Physician, UTSW / Parkland Memorial Hospital) // Edited by: Alex Koyfman, MD (@EMHighAK) & Justin Bright, MD (@JBright2021)
We’ve all heard it at one point or another: “Man, I’d HATE to have to intubate THAT!” Typically, this sentence is used to describe a patient in an ominous, sphincter-tightening situation, or the patient with the obviously suboptimal airway.
You walk by the door to the Resuscitation Bay or Trauma Bay, see that the patient is in respiratory distress, and rapidly breeze through your airway mnemonics and ultimately come to the conclusion that this would be a scary airway. The airways of myths and legends, and where heroes are made.
In the previous article, we discussed some of the airways that I, and many colleagues, find very challenging. We touched on emergent cricothyrotomy and discussed possibilities and arguments for/against the use of a primary surgical option for an airway. Below, I’d like to submit to you some more “special situations” to consider in the scary airway series.
-The Obese Airway –
Why It’s Scary
The obese airway is one that is consistently challenging. Also, when you talk about the obese patient, you also have to consider that it is estimated that 60-90% of obese patients also suffer from obstructive sleep apnea, another beast challenging to airway management.
Patients who are obese are difficult at times to adequately sedate, to obtain good airway seals on your BVM, to get a strong chin lift/jaw thrust to assist with ventilation, and can be hard to bag in general due to excess adipose weight on the neck/chest wall/abdomen.
They tend to have lower start values when considering their functional reserve capacity and increased oxygen consumption, and will de-saturate quickly. Add to this a patient who is in extremis, hypoxic, and may or may not be easily laid flat for intubation and you have yourself a scary airway.
Anatomical and Physiological differences
Obesity affects nearly every aspect of what you’d expect with normal physiology.
The most concerning things to remember are that patients who are morbidly obese desaturate quickly, they often will have medical comorbidities that can affect airway control, and airway management with BVM as well as visualization of the airway is profoundly affected due to adipose tissue. Obese patients have a higher percentage of comorbid conditions like diabetes, hyperlipidemia, hypertension, cardiac disease or heart failure, and obstructive sleep apnea.
Obesity is often categorized via body mass index (BMI), with overweight being considered at or greater than 25, obese at or greater than 30, and morbid obesity at or greater than 40.
Problem: Obese People Have Abnormal Airway Physiology
Morbidly obese patients also have decreased chest wall compliance (due to fat), and thus increased airway resistance. They consume more oxygen stores at baseline than their non-obese counterparts simply due to size and increase in body tissues demanding oxygen. When your patient is in distress, imagine them being on a treadmill. Therefore, their baseline CO2 production will be higher than a patient who is smaller.1,2
They often will have baseline hypoxemia with widened A-a gradients, due to VQ mismatching from alveolar collapse. This has been attributed to decreased motion of the diaphragm due to abdominal and chest adipose. In the obese patient, a heavier pannus and chest prevents adequate movement of the respiratory mechanisms of the body, resulting in long term restrictive lung disease patterns, all of which worsens when you lie the patient flat. Functional residual capacity can be decreased up to 30% in the morbidly obese, and up to 50% in the super-morbid categories. 1,2
As BMI increases, functional residual capacity decreases resulting in lower oxygen reserves. This decreased functional residual capacity and increased oxygen consumption = desaturation during RSI in the apneic period.
How Do I Fix This?
You can’t. But you can improve your chances of successful intubation.
1. Anticipate the difficult airway.
In addition to your usual assessment, another tool in the toolbox for the obese patient can be neck circumference. Anything greater than 43cm at the level of the thyroid cartilage is associated with increased likelihood of difficult intubation.2,3
2. Make sure you have adequate IV access.
Morbidly obese patients often will have difficult IV access simply secondary to body size and increased subcutaneous tissue. Often, peripheral IVs in the morbidly obese patient will fail. The worst time for this to happen is mid-intubation of a critical patient. Prior to intubation, have at least TWO reliable IVs. If you need to, look for an EJ, or place an I.O. for reliable, stable IV access.
- Preoxygenate the patient
Ideally, this will occur in the upright position to improve and maximize the already compromised respiratory mechanics, with both simultaneous high flow nasal cannula and non-rebreather, for as long as possible prior to intubation. Maintain passive oxygenation with high flow nasal cannula throughout your intubation attempts. At a minimum, keep the patient at a 25 degree head up position.2,4
- Ramp the Patient
This technique will help support the weight of the pannus and the chest to facilitate BMV and intubation, and align the anatomical axis gods in your favor.
Look at your patient from the side. Ideally, you would be able to draw a horizontal line from the ear to the angle of Louis.2
You can place pillows or folded blankets to achieve this angle, essentially from the midpoint of the back (between shoulder blades) and to the head/neck. The blanket stack under the head/neck may be higher than that between the shoulder blades. This is in contrast to pediatric airways, where there is a shoulder roll placed, but nothing under the head/neck.
- Improve your Mechanics
During BVM, a way to mitigate and improve respiratory mechanics that are impaired from a heavy pannus or abdomen burden/chest weight (read: breasts) is to place the patient semi-upright, or in the reverse Trendelenburg position. This drops the “weight” lower, enabling easier bagging and easier motion of the diaphragm.
Use a two-person technique for bagging, so one person can obtain an adequate seal and jaw-lift.
Another way to improve your BVM is to use a PEEP valve, maintaining 5-15cm H20 during bagging in the upper airway, as RSI will cause collapse of the obese patient’s pharynx (which has an increased percentage of extra adipose). Read: extra weight requires extra pressure (PEEP) to maintain patency.
Also remember that adjuncts like oral or nasal airways can be very beneficial in bagging your obese patient.
If you are having trouble with BVM oxygenation, you can consider placing an LMA (preferably an intubating LMA).
- Awake Versus Asleep/Approach
In the ideal situation, an awake flexible endoscopy or fiberoptic intubation is preferred in the morbidly obese patient with an anticipated difficult airway, particularly in patients with a BMI greater than 40.4
However, if it reassures you at all, in a study of 150 patients in the operative theater (read: non-emergent, controlled situation) for the super morbidly obese category undergoing bariatric surgery, only about 7% required awake fiberoptic intubation, with 93-94% of patients able to be successfully intubated with RSI in the ramped position, using propofol (2-3mg/kg IBW) or thiopentone (3-5mg/kg TBW), followed by succinylcholine at 1.5mg/kg TBW.5
If awake fiberoptics are not available or you are on a time-crunch, video laryngoscopy is preferred.
If video laryngoscopy is not available, a MAC blade or a short handled laryngoscope may give you a better view.6 Longer handled blades may be difficult to manipulate because the handle will run into the chest wall during intubation attempts.
Special Circumstances: Approach to Meds
Sedation/anesthesia/induction medications are dosed in several different ways, and is of particular importance in obese patients: Ideal Body Weight (IBW), Total Body Weight (TBW), and Lean Body Weight (LBW).
Total Body Weight: estimated or actual
Ideal Body Weight: nomogram based on patient’s height
Lean Body Weight: IBW + 20-30% of the difference between TBW and IBW
In the obese patient, anesthesia is challenging in that their baseline pharmacodynamics are different, as well has having altered physiology at baseline. They have an increase in adipose, and approximately an increase of 30% over normal of lean body mass. However, the adipose to lean body mass ratio is increased compared to normal-weight patients. Many sedation medications have varying lipophilicity, which changes duration, distribution, and bioavailability.
Additionally, metabolism of meds through the renal system will be increased in obese patients due to their inherently increased GFR. Despite the high frequency of fatty liver in obese patients, hepatic metabolism of meds seems to be relatively unchanged.
Distribution and metabolism of your meds is altered in the obese patient, and is also markedly affected by the lipophilicity of the drug being administered (i.e. how much of the drug is effective vs being trapped in the patient’s body fat). Some meds may have increased free plasma distribution in obese patients if lipids limit the binding of the drug. Lipophilicity can prolong effects of a medication. Generally speaking, highly lipophilic drugs will require increased dosages of the meds (due to the increased volume of distribution required).
All of the Above Summarized from: 2, 7-11
How to dose your meds:
Ideal Body Weight Drugs:
*There is conflicting data on how to administer benzos as an induction agent, with some sources advocating strictly by total body weight for a single dose, versus others by ideal body weight or at some point between TBW and IBW (to prevent prolonged sedation from prolonged half life in obese patients).
All of the Above Summarized from: 2, 7-11
Lean Body Weight Drugs:
**although still being investigated, some evidence supports administering ketamine at Lean Body Mass (estimated in obese patients at approx. 20-30% greater than ideal body weight)
All of the Above Summarized from: 2, 7-11
Total Body Weight Drugs:
Benzodiazepines* (see above)
Other Great Airway Reads Used for This Section: sources #12-17
-The Pediatric Airway-
Why It’s Scary
Most ED practitioners rarely will see a critically ill kid requiring an emergent airway. Kids are typically petri dishes for bacterial/viral infections, however thankfully pediatric respiratory failure is not an every day diagnosis in the ED. Don’t get me wrong, it happens – kids wander in, parents rush in with a sick child in their arms – but unless you work in a Children’s ED, an ED with heavy peds traffic, or a facility without Peds EM trained docs, you may not see this stuff often.
If you don’t see it that often, obviously you will be less comfortable with its management. Add this to the dosage and equipment mental exercises that come with pediatric patients, coupled with a hysterical parent or family, and the anxiety level that increases with a sick child in general. It’s a recipe for a disaster. Hopefully below will be a review on how to make this easier on everyone and successful in the ED if one of these scary airways crosses your path.
Anatomical and Physiological Differences
In your EM career you’ll hear it a million times “kids are not little adults”.
For this reason, if you have a kid who looks like they may potentially require an airway, unless you are one of those people who is great with memorizing equations, and numbers and emergency dosages for every single age group and weight class, get out your Broselow pediatric tape early.
This will relieve you of some of the mental anguish and acrobatics required during the intubation of the pediatric patient. It will give length based (and therefore project the appropriate weight based) dosing of critical medications, Mac or Miller blade sizes, airway adjunct information, and ETT sizes.
It can alleviate some of the mental anxiety out of the pediatric code and pediatric airway management.
If your facility does not have one, buy one.
Also, it is never a bad idea to call in the troops and to get some help. A respiratory therapist and a pharmacist can be your best friends during a pediatric respiratory code, or an anesthesia specialist if they are available.
The times “kids are not little adults” rings the most true and becomes most apparent is during airway management, particularly between the neonate and 1 year age groups, when the airway is most unlike the adults.
By about age 8, the pediatric airway becomes more like the adult airway. The topic of the pediatric airway management is obviously broad, but some specific anatomical and physiological differences can lead to “scary airway” feelings in practitioners, so let’s run through some of them, and how to manage these issues.
The head is huge, with a much bigger occiput than the adult, which throws off the alignment of the upper airway because the neck flexes when the patient lays flat, and predisposes them to anatomical airway obstruction.
How Do I Fix this?
Place a shoulder roll (ie folded towel under the shoulders) to optimize alignment. Try to place your patient in the “sniffing” position, which can be accomplished by aligning the patient with the neck slightly extended and chin lifted.
- The infants tongue is larger and mandible is shorter.
- Infants are mostly nasal breathers up until about 6 months, and it can even persist through toddler-age group
- Preschoolers tend to have larger tonsils and adenoids
How Do I Fix this?
All of the above factors can lead to difficulty with BVM and loss of the airway after administration of medications, due to relaxation of the natural airway reflexes. This can be mitigated with a 2 person BVM technique, using the “EC clamp” technique taught in PALS over the bag valve mask, decreasing pressure during bagging (i.e. don’t press DOWN on the face, this will collapse some of the softer kiddie airway structures, particularly when they don’t have the support of fully formed tracheal rings yet) and ideal positioning as described above.
Don’t forget that you can also use oral airways or nasal airway adjuncts in children to help eliminate obstruction from a large tongue during BVM. Use this in the comatose patient, or the patient without gag reflexes, or the paralyzed patient.
Measure oral airways by placing the end of the airway along the side of the face with the base at the corner of the lip, the tip extending to the angle of the mandible.
Nasal airways can be placed in the awake or semi awake patient, but be careful placing them in the very young, as they can cause the enlarged tonsils and adenoids to bleed. Measure the size with the nasal trumpet end from the nostril with the bevel extending to the tragus of the ear. The width of the tube should be less than the patient’s nostril.
Finally, LMAs as a supraglottic device in children have been found to have a 95-98% success rate in various studies for adequate ventilation in children and there is good data supporting their safety. If you cannot pass an ETT or are having BVM/ventilation issues, and if all else fails, throw an LMA down there. 18,19
- The larynx is higher than in adults. In neonates, it sits at about the C4 level, at C5 in toddlers, and C6 in adults. This makes for a more “anterior” airway.
- Additionally, the epiglottis is more U shaped in kids, larger, and can lie directly across the glottic opening.
How Do I Fix This?
By using a Miller blade, which is the semi straight blade of choice in pediatrics, you may mitigate this issue. It enables better views of an anterior airway with a large floppy epiglottis. Many practitioners use this as their “blade of choice” in children under 5.
Mac blades rely on the ligamentous structures of the upper airway that connect vallecula with the epiglottis in order to enable lifting of the epiglottis indirectly to view the airway. In peds, this ligamentous connection may not be fully formed or matured. After age 5-6 semi curved Mac Blades with sizes adapted for children may be used with success.
- infants have about 40% the functional residual capacity of adults, meaning there is less oxygen available stored up in the lungs during periods of apnea
- infants have an overall lower percentage of type I or slow twitch muscle fibers, particularly in the intercostal muscles and diaphragm, ie. a lower percentage of respiratory fibers that are less prone to fatigue
- infants have lower glycogen and fat stores in their respiratory muscles, predisposing the pediatric patient to respiratory fatigue faster than the adult
- infants have a higher metabolic rate than adults (metabolizing 6mL of O2 per minute compared to an adult at 3mL of O2 per minute)
All of this results in a tendency of your pediatric patient to desaturate faster during periods of apnea than your adult patient. You are approaching a patient whose compensatory capacity is low.
How do I fix this?
Try to optimize the oxygenation. Take note of the patients’ respiratory pattern. Watch for signs of difficulty breathing such as increased respiratory rates (which are age dependent), abdominal accessory muscle use, or retractions.
Remember that paradoxical breathing (chest retraction during inspiration while abdomen bulges out) and then the opposite occurs during exhalation. This is referred to as “seesaw breathing” and can result in rapid respiratory muscle tiring and fatigue. Take note if the patient is grunting, typically a bad sign of the patient attempting to exhale against a partially closed glottis and increased end-expiratory pressure by the patient.
As kids, particularly below age 5, are typically obligatory nose breathers, make sure that secretions are cleared from the nares in the hypoxic patient.
Provide oxygen. Nasal cannula can be attempted, but often is poorly tolerated in peds, and the distressed child uses up oxygen and reserve stores faster than the non distressed child. Put the child in the parent’s arms if possible, keep a calm environment, and try instead to give blow-by oxygen if nasal cannula is not tolerated. In severe distress, place child on a non-rebreather to preoxygenate as much as possible prior to intubation.
Other notes on management
The Failed Peds Airway
Troubleshooting a “failed” peds airway is difficult, and there are many articles detailing proposed algorithms. Below is a brief outline.
Picture the scenario: Not only are you intubating a kid, but now it’s not going well. You’ve sedated. The Kid is out. You can’t intubate or oxygenate. Try to trouble shoot with the below thoughts….
- Call for help
- Check for foreign bodies in the airway.
- Check for anatomic obstruction. Place an oral or nasal airway. Use your jaw thrust/chin lift. Check your shoulder roll.
- Check for adequate sedation and consider the possibility of laryngospasm. If you recognize this early and fix it, you can facilitate a successful intubation.
- If you cannot intubate, place an LMA or other supraglottic device to attempt oxygenation/ventilation.
- You can attempt adjuncts such as the gum elastic bougie if appropriate pediatric supplies are available to you. You will need either a size 5F or 10F in peds. There are also other available malleable stylets in size 2F and 5F.
- If you have anesthesia available, a fiberoptic intubation after inability to visualize the cords on direct laryngoscopy may be needed. It is considered the “gold standard” in pediatric failed airway management.
- Finally, in a last case, rescue, emergent “can’t intubate, can’t oxygenate” scenario, a surgical airway may be indicated.
Cuffed Versus Uncuffed ETT?
Historically, it has been the practice to use uncuffed tubes in pediatric patients in an effort to minimize trauma to the delicate pediatric subglottic structures during intubation. In the past, the concern in placing cuffed ETT in children less than 8 years old was concern for ischemic damage to the tracheal mucosa by the cuff. In pediatrics, the narrowest portion of the airway has been identified at the cricoid ring, where in the adult, it is at the glottis.
What does this mean for you? An ETT that passes through the cords in a kid may not pass easily through the cricoid ring, which is also more elliptical in shape than in the adult. These important anatomic differences can affect the seal and functionality of cuffed vs uncuffed ETT.
Cuffed ETT are becoming more frequently used in peds EDs and pediatric ICUs, with improved designs for high volume and low pressure seals, and now with good data that they may have lower rates of aspiration without higher rates of reintubation or post intubation stridor. 20
Also, uncuffed tubes are showing higher rates of laryngospasm and that even with an acceptable air leak in the uncuffed ETT, it can still cause pressure trauma to the subglottic mucosa.2,21-25
Other Great Airway Reads: sources #23-28
-The Burn Airway-
Why It’s Scary
Caring for inhalational injuries in the emergency department can be particularly challenging because the airways can be dynamic and can gradually deteriorate, and the patient that “looked great when they came in with a little soot in the nose” can progress to a dyspneic, tachypneic, and hypoxic patient.
Inhalational injuries and upper airway tissue burns can lead to the primary concerning pathology; swelling. Swelling can equal narrowing of the airway – sometimes to the point of total occlusion of the airway. Airway swelling can ultimately be a harbinger of badness due to its potential for progression over time, and it can complicate your life when it comes to acutely managing your burn patient. This lands it square in the middle of the “scary airway” category.
Important Points about Inhalational Injuries and Evaluation of Your Patient
One of the top 3 causes of morbidity and mortality in a burn patient is inhalational injury, coupled with age of the patient and total body surface area of the burn.
Important physical exam and history findings in your suspected inhalational injury patient include burns sustained in a closed space, which may have included hot steams or liquids, aspiration of hot liquids (more frequent in children)29,soot in the airway or singed hairs (nares, oropharynx), mucosal erythema/edema, carbonaceous sputum, or erosions/intraoral burns. These, however, have little predictive value with regards to potential for respiratory failure.
Take note of stridor, management of secretions, rales/rhonchi on exam, cough, sensation of throat swelling, or voice changes in your patient. They all can indicate airway edema and potential for progression to obstruction. Stridor should mandate intubation.30
Remember that many patients, even with severe inhalational injuries, may not exhibit pulmonary dysfunction initially, and the first chest Xray is often normal.
Also of importance to note are circumferential burns, particularly of the thorax, but also of the neck and abdomen. Burns that encircle the patient can decrease thoracic compliance and your ability to ventilate the patient. In select cases with decreased thoracic compliance, escharotomies may be indicated.31
A common lab test is carboxyhemoglobin (COHb) in evaluation of the burn patient when attempting to assess for inhalational injuries. Remember though, that in patients who are smokers, or who live in urban areas, COHb levels can be as high as 10% at baseline. The half-life of COHb is approximately 3-4 hours, and this can be expedited to around 30-40minutes when the patient is on 100% oxygen, and hyperbarics can drop this to around 20 minutes, so if your burn patient is a smoker who showed up on supplemental oxygen, the COHb level may not necessarily reflect the extent of injury.32
Predicting relative hypoxemia in your burn patient can be simplified by evaluating the PaO2/FiO2 (P/F) ratio. A low P/F ratio demonstrates VQ mismatches, diffusion issues, ventilation disturbances, and shunting. In some studies done in children, a P/F ratio <300mmHg after volume resuscitation has been found to be predictive of mortality.
Unfortunately, this ratio is mostly useful after completion of burn resuscitation for predicting survival, with lower ratios correlating with higher morbidity/mortality.33,34
Diagnosing inhalational injury is an inexact science, and currently the ‘gold standard” for evaluating extent of injury is bronchoscopy, but even bronchoscopy isn’t great for predicting anticipated respiratory failure.35-37
Inhalational airway injuries can be classified and separated based on location:
Upper airway thermal damage (oropharynx/larynx/mouth): In this zone, superheated gases and steam create direct thermal burns to the upper airway, ultimately resulting in edema and the potential for airway obstruction. Pair this with diffuse capillary leaks associated with cutaneous burns and you have a recipe for disaster.37
Lower airway and parenchymal damage(tracheal, bronchial, or alveolar injuries): can result from smoke, irritating gases, end products of burning synthetic substances, and particulate matter and creates the potential for bronchospasm (usually in the first 24-4 hours), impaired ciliary transport, necrotic bronchial mucosa with sloughing and increased secretions., as well as disruption of the alveolar surfaces from the residue/end products of burning synthetic substances, which can trash your diffusion potential by flooding or collapsing alveoli .37
Finally, you can have metabolic injury to the patient, where carbon monoxide or HCN impair oxygen delivery or oxygen consumption in the body tissues.37
WHEN DO I INTUBATE?
One of the more difficult decisions in your burn patient is when to consider intubation. Some literature suggests several potential intubating criteria, but there are no hard and fast rules:37,38
- Mental status changes resulting from inhalation injuries
- High risk for airway obstruction resulting from post burn edema
- Pulmonary failure/hypoxia resulting from subglottic injury
- Large TBSA burns (>40%)
- History of syncope at the scene
Patients with inhalational injuries and evidence of upper airway edema resulting from direct thermal injury on initial presentation should probably be prophylactically intubated, as these burns can progress over time, resulting in complete airway obstruction with edema progression. If total airway obstruction or near total obstruction is present, a surgical airway is indicated.
There are no definite rules as to when to intubate based on total body surface area. Some sources suggest that prophylactic intubation in patients with >40% TBSA burns is useful and indicated during the first 48 hours of resuscitation.38
Remember that if available, fiberoptic intubations can be a great adjunct in a burn airway, particularly if you are prophylactically intubating someone for airway protection and have some time to intubate in this way.
After securing a burn airway, MAKE SURE YOU SECURE THE TUBE WELL. Communicate to your team that preservation of the tube is paramount, as accidental extubation can result in a catastrophic loss of the airway if edema has progressed.38
WHAT MEDS SHOULD I USE?
Patients who have evidence of significant airway injury or post burn facial/oropharyngeal swelling should have careful sedation selection. If possible, attempt to avoid paralytics, or to use them with extreme caution, in order to escape the dreaded “can’t intubate, can’t oxygenate” scenario. This is not to say that you cannot or should not use RSI in these patients, but proceed with caution and have all available back up airway devices at your side, including surgical options.
Some viable alternatives to RSI and paralytics for intubation of your burn patient include fentanyl, versed, ketamine, and propofol.38
Happy Airway Management, Kids!
References / Further Reading
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