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Pediatric airways: Nightmares on baby street

EMS1.com News

January 1, 2013


Firemedically
by Mike McEvoy

Pediatric airways: Nightmares on baby street

The anatomic differences between adult and pediatric airways are well described in EMT and paramedic courses

By Mike McEvoy

Bound Tree University

You've heard it time and time again: "Kids are not little adults." Their anatomy differs markedly from older patients. Children are normally healthy and rarely have medical emergencies. When they do, unfamiliarity and inexperience with their unique physiology can make healthcare providers very nervous.

Pediatric airway emergencies create extreme angst in experienced healthcare providers for several reasons.

In a child, airway is king. Adults have oxygen reserves they can draw upon in crises, kids do not; their oxygen supply and demand are closely matched even at rest.

Kids are vagal machines; even minor vagus nerve stimulation can trigger the parasympathetic nervous system to induce profound bradycardia. Finally, we all expect kids to grow up and live long and productive lives.

Mistakes that cut into those hopes can require expensive, lifelong care that our legal system will seek to recover from responsible parties. All of these considerations mandate a thorough understanding and no nonsense approach to management of the pediatric airway.

The anatomic differences between adult and pediatric airways are well described in EMT and paramedic courses. When supine, their proportionally larger heads lead to varying degrees of neck flexion that can lead to airway obstruction or difficulty seeing the glottic opening during intubation.

Placing a rolled towel under a child's shoulders will allow proper alignment1. Infants and small children also have proportionately larger tongues for the size of their oral cavities. Their tongue then, becomes a common source of anatomic airway obstruction.

Placement of an oropharyngeal (OPA) or nasopharyngeal (NPA) in pediatric patients with diminished level of consciousness is imperative. Gentle insertion and generous lubrication of the artificial airway are also important owing to larger tonsils and adenoids that bleed easily when traumatized.

The pediatric larynx is much more superiorly positioned than adults, with a considerably weaker hyoepiglottic ligament and larger, more floppy epiglottis. This makes endotracheal intubation more challenging: straight blades are preferred over curved blades that may not adequately lift or control the epiglottis.

Challenges for intubation
The shorter, more narrow and funnel shaped trachea pose challenges for intubation2. Tube misplacement leading to extubation or right mainstem intubation can occur easily from small movements, including head movement. Securing the tube, preventing head movement and continuous monitoring with waveform capnography is imperative. With the cricoid ring is the most narrow part of the pediatric airway (as opposed to the cords in adults); very small decreases in the airway lumen from swelling, secretions or external compression will dramatically increase resistance to airflow.

Choking is more common in children for this same reason. The pediatric anatomy also makes needle cricothyroidotomy virtually impossible. Simple observation of a child's chest wall will warn you when airway resistance increases: intercostal retractions quickly become evident with inspiration. Always make a point to look under clothing directly at a child's chest. Retractions are not evident through clothing.

It is no secret that most pediatric cardiac arrests begin with respiratory arrest. The differences between adult and pediatric physiology can explain this sequence and significantly impact airway management decisions.

Infants are commonly believed to be obligate nose breathers, although more recent studies suggest some infants can mouth breath when nasal airflow is obstructed. In most infants, the nose accounts for almost half the total airway resistance; obstruction from secretions, compression or a non-flowing nasal cannula can seriously increase the work of breathing, leading to exhaustion1.

Tidal volume in kids is relatively fixed at about 6 to 8 mL per kilogram. As a result, any need for increased minute volume will be met by increased respiratory rate (unlike adults who can increase respiratory depth). This leads children to tire more quickly. The fixed tidal volumes also make them much more susceptible to trauma (such as pneumothoraces) from positive pressure ventilation. Be extremely cautious never to over ventilate a child.

Metabolism is higher in younger patients. Infants consume oxygen at twice the rate of adults and have a much lower lung functional residual capacity (FRC). With considerably less lung and blood oxygen stores, children will desaturate very quickly when apneic or under breathing. Oxygenation and preoxygenation are imperative in kids1.

Monitoring oxygen saturation provides a wealth of information about the balance of oxygen supply and demand. Low saturations tell you that the child's oxygen supply is inadequate.

The skeletal structure in a child's chest is primarily made of cartilage, requiring more muscle tone to breath. Unfortunately, skeletal muscle efficiency is not as developed as adults. As a result, kids are much more likely to tire and progress to respiratory failure3.

Aside from assessment of chest wall movement and level of consciousness, the best monitoring device for adequacy of respirations is end-tidal carbon dioxide (EtCO2).

Finally, the higher vagal tone found in children makes them very susceptible to bradycardia from stimulation of the airways (intubation, manipulation, suctioning) as well as hypoxia induced bradycardia1.

Monitor heart rate
Be very suspicious of bradycardia; immediately evaluate the adequacy of breathing and oxygenation in any bradycardic child. Always monitor heart rate when suctioning, intubating or placing an airway. Don't hesitate to ventilate in the face of bradycardia and begin chest compressions any time that ventilation alone fails to increase heart rate.

Basic pediatric airway management incorporates an understanding of anatomy and physiology. Children in respiratory arrest resuscitated by prehospital providers have survival rates between 43 percent and 82 percent while only 4 percent to 14 percent of those who progress to develop cardiac arrest survive4.

Aggressive airway management is key to good outcomes. Good management begins with positioning. If the head is not aligned, place a rolled towel under the child's shoulders. Eliminate any anatomic or mechanical obstruction by opening the airway using a chin lift (or jaw thrust if trauma is suspected).

Maintain this opening with an OPA or NPA, well lubricated and cautiously inserted. Assess breathing and pulse and do not hesitate to ventilate. Carry a reference of age related normal respiratory rates. Be very cautious about over distending the lungs; immediately stop positive pressure at the first sign of chest rise. If the heart rate is below 60, hypoxia is profound and chest compressions are needed5.

There are conflicting data on prehospital pediatric advanced airway management strategies. Given the potential for rapid decline leading to cardiopulmonary arrest, prehospital providers should advance to more invasive techniques only when a pediatric airway cannot be managed with less invasive maneuvers.

Definitive advanced airway management may well be at a local hospital where the environment is more controlled and more sophisticated equipment is available.

As with adults, any thoughts of advanced airway management require a contingency plan in case they fail. "Failure" is not well defined but three attempts using three different blade types or lengths once each or any drop in oxygen saturation below 90 percent during an intubation attempt meet most published definitions of a failed attempt.

These suggest an alternative provider or device be used6. Obviously, any field intubation of a child should be attempted by the most experienced provider using the best equipment available7 (i.e., video laryngoscope, bougie, etc.).

The laryngeal mask airway (LMA) is a supraglottic airway (SGA) device that can be inserted blindly and is probably the most available and likely rescue device to be employed in a failed pediatric intubation attempt.

Different sizes
LMA devices come in sizes that will fit virtually any pediatric patient. LMA use, especially in pediatric patients, requires training and frequent practice. When providers are well trained, successful first attempt placement can be as high as 94 percemt6.

There are some special considerations with pediatric LMA use. Firstly, pediatric anatomy can sometimes cause the LMA to catch on the epiglottis or vallecula, effectively occluding the airway. In cases involving significant obstruction as seen in croup or refractory asthma, it will not be possible to obtain a seal owing to the very high airway pressures6.

The Combitube™, used by some EMS services as a rescue device, is only available in sizes down to patients taller than 48" and has been associated with more complications than the LMA including esophageal rupture, pyriform sinus perforation, tongue engorgement and mucosal ischemia8.

Several manufacturers make laryngotracheal airways (for example, the King LT-D™), which come in smaller sizes than the Combitube and are softer, making them less likely to injure the esophagus. While these will not fit the smallest pediatric patients, they are a reasonable rescue device for larger kids.

Advanced airway management for adults emphasizes risk assessment. Recognizing a problem airway might be more important in kids, given their lack of reserve and higher likelihood of progressing to cardiopulmonary arrest if they become hypoxic during a failed intubation attempt.

Some congenital conditions that spell trouble include misshapen head, facial abnormalities, abnormal neck mobility (frequently seen with Down syndrome), small mouth opening, small oral cavity (often associated with cleft palate), large tongue (also seen in Down syndrome), and neck masses7.

Evaluation tools used to identify difficult airways in adult patients have not been systematically evaluated in children. Nonetheless, pediatric anesthesiologists find some adult tools predictive and suggest a reasonable approach to assessing pediatric airways7.

The interincisor gap, or distance between upper and lower front teeth with the mouth open as widely as possible is considered adequate for laryngoscopy when it is at least the width of three of the patient's fingers.

The same seems true for kids. Likewise, the thyromental distance (between the chin tip and notch of the thyroid), considered normal when not longer or shorter than three of the patient's fingers, also seems a good predictor of ability to visualize the glottis in kids.

The Mallampati score, when used by itself, has limited utility in predicting a difficult airway in any aged patient. There are certainly a variety of congenital and acquired conditions that can create major difficulties for bag valve mask ventilation. If it is impossible to obtain a seal with a bag valve mask, advanced airway management may be the only viable alternative.

If kids were just little adults, then pediatricians would probably be little doctors. This article has provided a review of the anatomical and physiological differences between the adult and pediatric airway with an eye towards forming a step-wise strategy for successfully managing pediatric airway emergencies.

In many cases, the best management is calming the child and closely observing them for signs of increased airway resistance or exhaustion. Keep in mind that secretions or objects obstructing airflow through the nose can dramatically increase airflow resistance and lead to respiratory failure.

Always be concerned about oxygenation in children with respiratory distress. A step-wise approach to managing pediatric airways will help you to confidently improve outcomes in this uncommon but extremely stressful emergency.

References:

1. Nagler, J. Emergency airway management in children: Unique pediatric considerations. In: UpToDate, Stack, AM (Ed), UpToDate, Waltham, MA 2012.

2. Kleinman ME, Chameides L, Schexnayder SM, et al. Part 14: Pediatric advanced life support: 2010 Cardiovascular Care. Circulation 2010; 122:S876.

3. Keens TG, Btyan AC, Levison H, Ianuzzo CD. Developmental pattern of muscle fiber types in human ventilator muscles. J Appl Physiol. 1978; 44:909.

4.      Lopez-Herce J, Garcia C, Dominguez P, et al. Outcome of out-of-hospital cardiorespiratory arrest in children. Pediatr Emerg Care. 2005; 21:807.

5. Bailey P. Basic airway management in children. In: UpToDate, Torrey, SB (Ed), UpToDate, Waltham, MA 2012.

6. King, BR. Emergency rescue devices for difficult pediatric airway management. In: UpToDate, Stack, AM (Ed), UpToDate, Waltham, MA 2012.

7. Mick, NW. The difficult pediatric airway. In: UpToDate, Torrey, SB (Ed), UpToDate, Waltham, MA 2012.

8. Oczenski W, Krenn H, Dahaba AA, et al. Complications following use of the Combitube, tracheal tube and laryngeal mask airway. Anesthesia. 1999; 54:1161.

About the author

Mike McEvoy, PhD, NRP, RN, CCRN is the EMS Coordinator for Saratoga County, New York and a paramedic supervisor with Clifton Park & Halfmoon Ambulance. He is a nurse clinician in cardiothoracic surgical intensive care at Albany Medical Center where he also Chairs the Resuscitation Committee and teaches critical care medicine. He is a lead author of the “Critical Care Transport” textbook and Informed® Emergency & Critical Care guides published by Jones & Bartlett Learning. Mike is a frequent contributor to EMS1.com and a popular speaker at EMS, Fire, and medical conferences worldwide.Contact Mike at mike.mcevoy@ems1.com.
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