What is the primary muscle of respiration in a newborn infant, and why is this significant?
The sternocleidomastoid muscles; because they are accessory muscles that are heavily used for quiet breathing.
The intercostal muscles; because they are highly developed and provide a stable chest wall.
The diaphragm; because it is the main driver of breathing and fatigue of this muscle can lead to respiratory distress.
The abdominal muscles; because they are used to force air out of the lungs during exhalation.
The Correct Answer is C
The diaphragm is the primary muscle of respiration in newborn infants. This is significant because their intercostal muscles are underdeveloped, and their rib cages are highly compliant, so they rely almost entirely on diaphragmatic movement for ventilation.
Rationale for correct answer:
3. In newborns, diaphragmatic contraction creates negative pressure to draw air into the lungs. If the diaphragm tires due to illness, hypoxia, or increased work of breathing, ventilation can rapidly deteriorate since accessory muscle use is limited.
Rationale for incorrect answers:
1. Sternocleidomastoid muscles are accessory muscles used during respiratory distress, not for quiet breathing in healthy infants.
2. Intercostal muscles are not fully developed in newborns and provide minimal contribution to chest wall stability or ventilation.
4. Abdominal muscles assist in forced exhalation and coughing but are not the primary drivers of quiet respiration.
Take home points
- Infants’ dependence on the diaphragm makes them vulnerable to respiratory fatigue in prolonged distress.
- Conditions that impair diaphragmatic function (e.g., sepsis, neuromuscular disorders, fatigue from tachypnea) can cause rapid deterioration.
- Early recognition of increased work of breathing is essential, as infants have limited reserves.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
Infants and young children have anatomical and physiological differences in their upper airways compared to adults that increase their risk for airway obstruction. These differences include a smaller and more flexible airway structure and narrower passages, which make them more vulnerable to swelling and obstruction.
Rationale for correct answer:
1. Underdeveloped cricoid cartilage and narrow nasal passages contribute significantly to the increased risk of upper airway obstruction in infants and children. The cricoid cartilage is the narrowest part of a child’s airway and is less rigid than in adults, making it more prone to collapse or swelling. Narrow nasal passages can become easily blocked by secretions or inflammation, further compromising airflow.
Rationale for incorrect answers:
2. Tonsils in children tend to be relatively large, not small, and can contribute to obstruction. The nasal passages are narrow, but this option misses the critical role of cricoid cartilage development.
3. The child’s larynx is funnel-shaped, not cylindrical, with the narrowest point at the cricoid cartilage. While sinuses develop over time, their underdevelopment doesn’t directly increase risk of upper airway obstruction.
4. Children actually have proportionally larger tongues relative to their oral cavity, which can contribute to obstruction, so “smaller tongue” is inaccurate.
Take home points
- Infants and children have a funnel-shaped, narrower airway with a less rigid cricoid cartilage, making them more susceptible to airway obstruction.
- Narrow nasal passages add to the risk by limiting airflow, especially during inflammation.
- Understanding these anatomical differences is critical when assessing respiratory distress in pediatric patients.
Correct Answer is B
Explanation
Lymphoid tissues such as the tonsils and adenoids form part of the Waldeyer’s ring and play a vital role in local immune surveillance of the upper respiratory tract, detecting and responding to inhaled or ingested pathogens.
Rationale for correct answer:
2. Lymphoid tissue like tonsils and adenoids provide local immune surveillance and defense. These structures contain immune cells (B and T lymphocytes) that detect antigens entering through the nose and mouth, initiating immune responses to help prevent infection spread.
Rationale for incorrect answers:
1. Alveolar macrophages are part of the innate immune system, not adaptive immunity. They engulf and destroy pathogens and debris but do not produce specific antibodies.
3. Infants’ cough and sneeze reflexes are actually less forceful and less coordinated than adults’, making clearance of secretions less efficient.
4. Secretory Immunoglobulin A (sIgA) is part of the active mucosal immune system, not passive immunity. Passive immunity is typically acquired via maternal antibodies (e.g., IgG via placenta, IgA via breast milk).
Take home points
- The pediatric respiratory tract uses multiple defense layers: mechanical (mucociliary clearance), reflexive (cough/sneeze), and immune (lymphoid tissue, sIgA, macrophages).
- Tonsils and adenoids are particularly important in early childhood but can also be a site of chronic infection or hypertrophy leading to obstruction.
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