Stridor Mnemonic – BEST USMLE Step 2 CS Mnemonics

Stridor Mnemonic THUMBNAIL - Child With Noisy Breathing - BEST USMLE Step 2 CS Mnemonics -
Stridor Mnemonic USMLE
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Stridor Mnemonic USMLE

Stridor describes a high-pitched, monophonic sound made when breathing that is best heard over the anterior neck. These characteristics distinguish stridor from typical wheezing due to diffuse airflow limitation (asthma or bronchiolitis), which tends to consist of multiple sounds that start and stop at different times. The term is derived from the Latin verb stridere, meaning to make a harsh noise or shrill sound, as to creak.

Stridor is caused by the oscillation of a narrowed airway, and its presence suggests significant obstruction of the large airways. The acoustics of stridor may be explained as a result of Bernoulli’s principle, which states that as the speed of a moving fluid increases, the pressure within the fluid decreases. When airflow is forced through a narrowed tube, a local area of low pressure creates a vacuum effect distal to the narrowing. The focal area of low pressure distal to a narrowed airway causes the airway walls to collapse and vibrate, generating the high-pitched squeaking sound that is characteristic of stridor [1].

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Physical Examination

  • No child will be present during your USMLE Step 2 CS examination encounter.
  • Instead of a child, there will be a family member who will either be present in the exam room or will be communicating with you through a phone call [Telehealth (virtual visit) may also be a possibility in the near future].
  • You have TWO very important goals here:
    1. Ask pertinent questions so you can narrow down your differential diagnosis and come up with an appropriate assessment and plan.
    2. To determine whether the case that is being presented to you is either an emergency or a non-emergency.
  • Based on what the case is, you must instruct the family member to either bring their child to the clinic or to take their child to emergency department for further evaluation.
  • You may give simple advice such as making sure to monitor the child’s breathing/pulse or attempting oral hydration and monitoring the urine output but NEVER prescribe any medications, especially antibiotics without seeing the patient first. 
  • Ultimately the child has to be seen soon and you need to determine WHEN and WHERE the family member must take them.

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Differential Diagnosis Stridor Mnemonic

  • FOREIGN BODY ASPIRATION:  should always be suspected in an infant or toddler who presents with sudden or intermittent onset of stridor, with or without respiratory distress, and without other physical findings. Its incidence peaks around 2 to 3 years of age. If an infant is in an environment with older children, foreign body aspiration can occur at an earlier age. A history of a witnessed choking episode is common but may not be recalled by the caregiver, because it appeared to resolve.
  • CROUP (Laryngotracheitis): Croup accounts for more than 90% of all cases of stridor in children.
    • Epidemiology: It typically occurs in young children (typically between ages 6 months to 3 years)
    • Microbiology: Commonly caused by Parainfluenza virus.
    • Symptoms: The onset of symptoms is usually gradual, beginning with nasal irritation, congestion, and coryza and progressing to inspiratory and sometimes expiratory stridor. Symptoms generally progress over 12 to 48 hours to include fever, hoarseness, barking cough, and stridor.
    • Diagnosis:  The diagnosis of croup is clinical, based on the presence of a barking cough and stridor, especially during a typical community epidemic of one of the causative viruses.
      • Neither radiographs nor laboratory tests are necessary to make the diagnosis. However, radiographs may be helpful in excluding other causes if the diagnosis is in question.
      • Neck X-ray if obtained is commonly associated with ‘steeple sign‘.
Steeple Sign on Neck X-ray seen in a patient with croup

The anteroposterior (AP) view showing the narrowing of the upper trachea, AKA the “steeple sign” of croup. Wikipedia ©

    • Treatment: Depends whether it is mild or  moderate to severe.  
      • MILD: should be treated symptomatically with humidity, fever reduction, and oral fluids. 
        • Supplemental oxygen: should be humidified and administered to children who are hypoxemic (O2 saturation of <92% in room air)
        • Glucocorticoids: should be given to all patients with moderate to severe croup. Decreases edema in the laryngeal mucosa of children with croup. Decreases length of stay in the emergency department (ED) or hospital, and reduce unscheduled medical visits.
        • Nebulized epinephrine: should be given to all patients with moderate to severe croup.
        • Supportive care, including humidified air or oxygen, antipyretics, and encouragement of fluid intake.
    • Microbiology: Haemophilus influenzae type b (Hib) was the most common infectious cause of epiglottitis in children but the incidence declined after Hib vaccine was added to routine immunization schedule in U.S. Hib epiglottitis still occurs, primarily in unvaccinated children. This is why it is very important to always ask about the immunization history of the child.
      • Additional causes of epiglottitis in children include other H. influenzae (types A, F, and nontypeable), streptococci (including group A streptococcus), and Staphylococcus aureus, including methicillin-resistant strains.
    • Symptoms: Sudden onset of high fever (between 38.8 and 40.0°C), severe sore throat, odynophagia, and drooling is common. 
      • Young children classically present with respiratory distress, anxiety, and the characteristic “tripod” or “sniffing” posture to maximize the diameter of the obstructed airway so they can breath.
      • Abrupt onset and rapid progression (within hours) of Dysphagia, Drooling, and Distress (“the three D’s“) are hallmarks of epiglottitis in children.
    • Diagnosis: Epiglottitis should be suspected in young children, especially those who are un- or under-immunized against Haemophilus influenzae, type b (Hib) and who present with the following characteristic clinical features as follows: “Tripod” position, Anxiety, Sore throat, Stridor, Drooling, Dysphagia and Respiratory distress.
      • Direct visualization of an erythematous, edematous epiglottis via laryngoscopy, nasolaryngoscopy or oropharyngeal examination confirms the diagnosis.
      • Lateral Neck X-ray: can provide the diagnosis by showing the ‘thumb sign‘, which is the swelling epiglottis. X-ray is obtained in cases when direct visualization is not readily available or oropharyngeal examination is non-revealing.
Epiglottis Neck X-ray showing "thumb sign"

Lateral neck x-ray showing the “thumb sign”; the swollen epiglottis (→) aryepiglottic folds (*) in a child with epiglottitis. UpToDate ©

    • Treatment: The approach to airway management is determined by whether the patient is able to maintain their airway and by the patient’s age.
      • This is an EMERGENCY . The airway must be immediately secured in the operating room.
      • Once intubated, blood culture and an epiglottic culture should be obtained prior to antibiotic administration.
      • After airway management is complete, patients with infectious epiglottitis should receive empiric antimicrobial therapy directed toward the most likely organisms. 
    • Epidemiology: Most retropharyngeal abscesses occur in children between two and four years of age.
    • Microbiology: is often a polymicrobial infection commonly caused by Streptococcus pyogenes (group A streptococcus [GAS]), Staphylococcus aureus (including MRSA)
    • Symptoms: Children with retropharyngeal abscess generally appear ill with moderate fever.
      • Additional symptoms may include; dysphagia [difficulty swallowing’, odynophagia [pain with swallowing], drooling, decreased oral intake, neck stiffness, muffled or “hot potato” voice, neck swelling, neck mass or lymphadenopathy.
    • Diagnosis
      • Laboratory evaluation: The initial laboratory evaluation of a child with suspected retropharyngeal infection should include a complete blood count  (CBC) and blood culture.
      • Imaging:  The radiographic evaluation for retropharyngeal infection may include lateral neck radiographs and/or computed tomography (CT) with contrast of the neck.
      • Lateral neck radiograph may be the obtained first, if there are no signs of airway compromise and the suspicion is low.
      • Neck CT with contrast is the preferred is the suspicion for airway compromise is high.
Retropharyngeal abscess Lateral neck xray

Lateral neck radiograph demonstrating widening of the retropharyngeal space and reversal of the normal cervical spine curvature. The epiglottis and subglottic area in this radiograph are normal. UpToDate ©

    • Treatment:
      • Supportive care: for the child with retropharyngeal infection includes maintenance of the airway, adequate hydration, provision of analgesia, and monitoring for complications. Patients with an unstable airway should be monitored in the intensive care unit; endotracheal intubation may be necessary for airway maintenance.
      • Empiric Antibiotic Therapy: should include coverage for group A Streptococcus, S. aureus, and respiratory anaerobes.
        • Either Ampicillin-sulbactam (Unasyn) or Clindamycin combined with either vancomycin or linezolid t provide optima coverage for potentially resistant Gram-positive cocci.
      • Parenteral treatment is maintained until the patient is afebrile and clinically improved. Oral therapy should be continued to complete a 14-day course.
        • Appropriate oral regimens for continuation of therapy include either Amoxicillin-clavulanate (Augmentin) or Clindamycin.
  • PERITONSILLAR ABSCESS: Commonly caused by Strep Pneumonia or Staph Aureus. Patient has a “hot potato voice” and is usually drooling cause they cannot swallow. On exam the tonsil is shifted to the side. No imaging is needed and its often diagnosed by visualization. Treatment is incision and drainage and antibiotics.
  • LARYNGITIS: is the inflammation of the larynx (voice box) from overuse, irritation or infection.
    • Patients usually presents with sore throat, drooling, dry cough and hoarseness.
    • Diagnosis is usually made with laryngoscopy.
    • Treatment for acute laryngitis is self-care since it is usually due to a viral infection and resolves within a few days.
  • ANGIOEDEMA: is often the result of an allergic reaction and can be triggered by an allergic reaction to certain types of food, medications, latex or insect bites and stings. 
    • This is an EMERGENCY and must be treated immediately by administration of epinephrine (EpiPen). Other medications include antihistamines and corticosteroids.

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Stridor Mnemonic USMLE - Child With Noisy Breathing Mnemonic - BEST USMLE Step 2 CS Mnemonics -

Stridor Mnemonic USMLE Step 2 CS Mnemonics

Telephone Triage:

When assessing patients by phone, the health care provider must distinguish children who need immediate medical attention or further evaluation from those who can be managed at home. Children who need further evaluation include those who have:

  • Stridor at rest
  • Rapid progression of symptoms (ie, symptoms of upper airway obstruction after less than 12 hours of illness)
  • Inability to tolerate oral fluids
  • Underlying known airway abnormality (eg, subglottic stenosis, subglottic hemangioma, previous intubation)
  • Previous moderate to severe episodes 
  • Medical conditions that predispose to respiratory failure (eg, neuromuscular disorders or bronchopulmonary dysplasia)
  • Parental concern that cannot be relieved by reassurance
  • Prolonged symptoms (more than three to seven days) or an atypical course (perhaps indicating an alternative diagnosis)

Stridor Mnemonic USMLE

Diagnostic Work-up

  • Neck X-ray: usually nonspecific but may reveal changes associated with retropharyngeal abscess, epiglottitis, croup, or a radiopaque foreign body. 
  • Chest X-ray: in cases where an intrathoracic problem is suspected, a plain chest radiograph should be obtained, because it can demonstrate mediastinal lymphadenopathy, masses, atelectasis, or the actual foreign body, if it is radiopaque.
  • Laryngoscopy &/or Bronchoscopy: can visualize the airways and allow definitive diagnosis of the cause of stridor in children. They are appropriate for the patient with an unstable airway such as those with epiglottitis or for those with suspected foreign body aspiration. These procedures should be performed in the operating room, with anesthesia, sedation, and continuous monitoring.
  • Complete Blood Count (CBC): to look for signs of infection, specially those who look very sick and/or septic
  • ABG (Arterial Blood Gases): to assess the arterial gases to determine whether patient is in respiratory acidosis/hypercapnic respiratory failure.

Stridor Mnemonic USMLE

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