Pediatric Wheezing and Stridor

One of the most frantic prehospital scenarios is one involving a child in respiratory distress. The pediatric patient is often difficult to examine, making it even more difficult to properly diagnose the condition and execute treatment. Anxious parents can add to the difficult situation and place the prehospital provider in a hectic predicament.

The ability to differentiate between the numerous types of respiratory sounds, especially stridor and wheezing, can be one of the most important skills perfected by the prehospital caregiver. Understanding pediatric airway anatomy and how to distinguish the sometimes-subtle upper and lower airway noises, and knowing how to treat the various etiologies of such noises, can all hasten swift and proper treatment of such patients. In addition, having the patient’s medical history and history of the presenting illness can be invaluable in determining the cause of the complaint and proper treatment.

Anatomy

When painting a mental picture of the pediatric airway, it is important to divide the entire path into separate areas. This is not only helpful for assessment, but it can help to explain the etiology of different airway noises. In order to better understand wheezing and stridor, divide the airway into two areas: that which is within the chest cavity (lower airway) and that which is out of it (upper airway). (See Figure 1.)

The distal portion of the trachea, the bronchi, bronchioles, smaller airways and the lungs themselves exist in an environment that is subject to varying pressures. Understanding the effects of these pressures on the anatomy of the lower airway can answer many questions that arise during the pediatric patient evaluation.

When the chest wall expands, it exerts a negative pressure on each component of the lower airway. This negative pressure can be thought of as a force that pulls on all sides of each component of the respiratory tract within the chest cavity. As an example, a bronchiole will actually increase its diameter due to the negative force exerted during inspiration. Conversely, during expiration, a positive pressure is exerted, decreasing the diameter of the bronchiole. So, during inspiration, air within the chest cavity experiences much less resistance than it does during expiration. In the normal patient, this explains why inspiration occurs in a smaller period of time than expiration.

The oral and nasal cavities, pharynx, larynx and proximal trachea are all outside the chest cavity. Because of this, they are subject to and react to different pressures during inspiration and expiration. When the chest wall expands during inspiration, the resulting influx of air through these structures pulls them inward. During expiration, the column of air being pushed from below “splints,” or opens, the passages of the upper airway tract. A simple experiment can demonstrate this. With your mouth closed, take a rapid breath in through the nostrils and observe their collapse. A forced expiration will cause them to dilate or “flare.” This occurs throughout the upper airway, except in the areas where complete cartilaginous rings prevent it.

Knowing how different locations of the pediatric airway react to the pressures produced by expansion and contraction of the chest wall helps to understand how the noises of stridor and wheezing are generated.

Stridor

Stridor is defined as a harsh, vibratory sound of varying pitch caused by turbulent airflow through an obstructed airway. Stridor is most commonly a result of obstruction in the portions of the airway that are outside the chest cavity. This is an important distinction, because obstruction of the airway within the chest cavity usually presents as wheezing.

As explained above, inspiration causes the upper airway (which is outside the chest cavity) to collapse. If there is an obstruction of this area, the lumen will further diminish during inspiration, worsening turbulence and resulting in stridor. During expiration, stridor will often disappear because the pushing column of air from below can open the upper airway, diminishing obstruction to flow. It is important to note that not all stridor is inspiratory. If the obstruction is severe enough or if it involves the portion of the trachea that is within the chest cavity, expiratory stridor can occur as well.

Patients with upper airway obstruction sometimes present with clinical clues that can help to distinguish them from patients with lower airway obstruction. Some patients exhibit “tripoding”—a position that opens the airway and makes breathing easier. These patients prefer the seated position with their elbows or hands on their knees, leaning forward with the neck extended and head tilted slightly backwards. This position gives the accessory muscles of respiration their most advantageous position and opens the upper airway. As the obstruction worsens, swallowing may become difficult, causing them to drool instead of swallow their oral secretions. Recognizing these sometimes-subtle clues can hasten the diagnosis and initiation of treatment.

The causes of upper airway obstruction and subsequent stridor are numerous (see Table I). The obstruction can range from a foreign body to tumor, from infection to inflammation, from injury to congenital abnormality. In the prehospital care setting, it is important to recognize a few key concepts relating to the treatment of stridor:

1. Patients with stridor should be considered as having a compromised airway. Expeditious transport is imperative, as many of the listed causes of stridor can have precipitous airway collapse and cardiopulmonary arrest.

2. Oxygen should be delivered without hesitation. Obstruction can cause hypoxemia, which can lead more quickly to complete respiratory arrest. Remember that 95% oxygen concentration can be delivered through pediatric non-rebreathing masks set at 10–12 liters/min.

3. Although it shouldn’t be avoided when emergently necessary, establishing a definitive airway should be deferred until arrival at a more controlled setting (i.e., the emergency department). Not only are these potentially the most difficult airways to establish, attempts may actually worsen the obstruction. It is important to remember that when the necessity for intubation is apparent, attempts to establish an airway should not be delayed.

Perhaps one of the most important determinations of the etiology of stridor in the pediatric patient is the history, both past medical and recent. Questions that yield information about a child’s or infant’s medical history will often point prehospital caregivers and other emergency personnel in the right direction when it comes to diagnosis and treatment. Table II demonstrates how historical information can highlight specific etiologies. Was the two-year-old playing with a small object just prior to developing stridor? Did the infant have any neck surgeries for congenital abnormalities? Was there a recent upper respiratory tract infection? Asking questions like these in the prehospital setting can expedite the care given in the ambulance and prepare ED staff for the next steps. Such questions may help save the life of an infant or child.

Wheezing

Like stridor, wheezing is an airway sound resulting from obstruction. Obstruction of lower airway tracts causes turbulent airflow that makes the characteristic sound most often heard in children with asthma. Most wheezing is heard in the chest cavity during the expiratory phase of respiration, when the positive/inward pressure exerted by the collapsing chest wall diminishes the diameter of the intrathoracic airways.

As in stridor, the causes of wheezing are numerous (Table III), varying from inflammation to infection, from neoplasms to cardiac, from congenital to traumatic in nature. The patient’s history can be helpful in determining the cause of abnormal lung sounds. Has the patient had valve replacement in the past? Is there a family history of asthma? Does the patient have known congenital defects? Has the patient ever had episodes of wheezing in the past? Just as in stridor, questions like these can elicit faster and more directed diagnosis and treatment.

In almost every case of stridor, prehospital care will consist of airway support and oxygenation alone. However, the wheezing patient’s prehospital treatment varies widely, depending on the cause of the wheeze. For example, if you give a particular wheezing pediatric patient nebulized beta2-agonist and oxygen prior to learning that she has a recent history of valve replacement, her condition will likely not improve. In this particular example, the child may be suffering from congestive heart failure (CHF), caused by a deficient or failing valve. In CHF, there is a leakage of fluid from pulmonary vessels, increasing the pressure around bronchioles and causing wheezing from the resultant narrowing of the lumens.

Despite the well-known mantra, “All that wheezes is not asthma,” most that wheezes is asthma where pediatric patients are concerned. Unless a child is known to be in CHF, the inflammatory causes of lower airway obstruction should be assumed and proper treatments administered. Asthma, the epitome of wheeze-inducing diseases, causes obstruction in the lower, small airways. Treatment is usually very effective and is aimed at both pharmacologically dilating the airways (beta2-agonists) and diminishing inflammation (steroids).

In general, prehospital treatment of pediatric wheezing is aimed at the most likely cause: asthma or bronchiolitis, an inflammatory condition usually caused by Respiratory Syncytial Virus (RSV) and seen most often in infants 2–9 months of age. Both are clinically indistinguishable and treated with beta2-agonists and oxygen if hypoxic. If a history of asthma is known, some EMS agencies also initiate oral or inhaled steroid treatments. As noted above, wheezing caused by CHF is best treated with diuretics and oxygen. Since most wheezing is caused by asthma or bronchiolitis, it should be treated as such initially. Whatever the cause, wheezing should cue the prehospital caregiver that something is causing obstruction of the lower airways and that the potential for rapid degradation of the patient’s status is possible.

Conclusion

Perhaps the most stressful patients that prehospital caregivers encounter are children in respiratory distress. The fretfulness of the parents, as well as the distress and usually uncooperative nature of the patient, all combine to create a situation laden with anxiety. By knowing the anatomy causing the respiratory noises, prehospital caregivers can discover the essence of the problem and quickly implement proper treatment. This will ease the anxiety of both patient and parents while helping the child’s condition improve en route to the hospital setting.

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