Anatomic and Physiologic Considerations: Special Issues in Pediatric Patients
Pediatric Update
Anatomic and Physiologic Considerations: Special Issues in Pediatric Patients
by Leonard Friedland, MD
The adage "the child is not a small adult" is one that emergency physicians know well and practice. The anatomic and physiologic differences apply across all spectrums of care from the approach to the ABCs to fluid and pharmacological management. In this review, I compare the child with the adult, looking at anatomic and physiologic considerations along with the clinical consequences in the areas of airway, breathing, and circulation. (See Table on page 5.)
Table | ||
Anatomic and Physiologic Considerations: Child vs. Adult | ||
ANATOMY AND PHYSIOLOGY | CLINICAL CONSEQUENCES | |
Airway and Breathing | • Infant and child upper airway is smaller | • Small amounts of mucus and airway swelling can occlude the small airway diameter and greatly increase the work of breathing |
• Infant tongue is disproportionately larger | • The tongue can displace posteriorly, occlude the airway, and interfere with tracheal intubation | |
• Infant and child head is larger in proportion to body size | • Difficult to expose the vocal cords during tracheal intubation | |
• Infant and child epiglottis is short, narrow, and thick | • Difficult to control the epiglottis with a curved laryngoscope blade | |
• Vocal cords attach lower anteriorly | • Difficult to expose the vocal cords during tracheal intubation | |
• Infant and child larynx is positioned higher | • Difficult to control the line of vision between the tongue and vocal cords with a curved laryngoscope blade | |
• Infant and child larynx is funnel shaped (compared with cylinder shape); therefore, the narrowest portion of the airway is at the nondistensible cricoid cartilage | • Cuffed endotracheal tubes are not used in children younger than 8 years of age | |
• Infant ribs and intercostal cartilage are highly compliant | • If the airway is obstructed, the ribs and intercostal cartilage may not support the lungs, and the sternum and intercostal areas may move during respiration rather than the chest and lungs (paradoxical respiration)
• Upper airway obstruction (croup, extrathoracic foreign bodies) may cause tracheal collapse during inspiration • Intrathoracic foreign bodies and lower airway disease (bronchiolitis, asthma) may cause lower airway obstruction during expiration • Opposing these dynamics with positive end-expiratory pressure (PEEP) may improve gas exchange |
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• Oxygen demand in child is 6-8 mL/kg/minute (3-4 mL/kg/min in the adult)
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• Hypoxemia develops more rapidly in the setting of inadequate ventilation
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Circulation | • In children and adults, the normal hemodynamic response to blood loss is tachycardia and vasoconstriction early, with hypotension occurring as a late sign of shock | • Assess indirect signs of cardiac output and systemic vascular resistance
Pulses: Weak peripheral pulses may indicate low cardiac output; bounding peripheral pulses may be a sign of decreased systemic vascular resistance |
• Infants and children have higher resting HR than adults | • Important to recognize normal values, as sinus tachycardia commonly occurs as a response to anxiety, pain, fever, hypoxemia, hypovolemia, and, thus, the presence of true tachycardia merits further investigation | |
• Infant and child normal blood pressure values vary by age | • Median systolic blood pressure estimated as:
90 mmHg + [(2) (age in years)] • Lower limit systolic blood pressure can be estimated as:
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• Cardiac output in the infant and child is affected more by heart rate than stroke volume | • The development of bradycardia in children with cardiorespiratory distress signifies decreasing cardiac output | |
• Circulating blood volume in infant is 80 mL/kg, children 75 mL/kg, and adults 70 mL/kg | • Hypotension is usually not observed until 25% of blood volume is acutely lost |
Anatomic differences in the infant’s airway, coupled with the small size of the glottic aperture, make endotracheal intubation of the infant a difficult procedure. The Table highlights these differences, along with the signs of low cardiac output in children. Familiarity with these signs will enhance the emergency physician’s ability to recognize the early signs of shock in the pediatric patient.
References
1. Pediatric Advanced Life Support Course—1997-1999. Dallas, TX: American Heart Association; 1997.
2. Fleischer GR, Ludwig S (eds). Textbook of Pediatric Emergency Medicine, 3rd edition. Maryland: Williams and Wilkens; 1993.
3. Barkin RM, ed. Pediatric Emergency Medicine: Concepts and Clinical Practice. St. Louis: Mosby Year Book; 1992.
4. Behrman RE, Kleigman RM, Arvin AM, eds. Textbook of Pediatrics, 15th edition. Philadelphia: W.B. Saunders; 1996.
Which of the following statements regarding differences between pediatric and adult airway is false?
a. The epiglottis in an infant may be more difficult to control with a straight blade than with a curved blade.
b. Cuffed endotracheal tubes should not be used in children younger than 8 years old.
c. Tracheal collapse may occur in children with severe croup.
d. The infant tongue is disproportionately larger.
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