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 D
Explanation
The primary reason a small degree of inflammation in a child’s airway causes a disproportionately large increase in airway resistance is the significantly narrower airway diameter. According to Poiseuille’s law, resistance to airflow is inversely proportional to the fourth power of the radius, meaning even a slight reduction in airway size greatly increases resistance.
Rationale for correct answer:
4. A child’s airway is much narrower than an adult’s, so swelling or mucus buildup reduces the radius substantially, causing a dramatic increase in resistance and work of breathing. This makes conditions like croup or bronchiolitis more severe in young children.
Rationale for incorrect answers:
1. While children do have higher metabolic rates and oxygen demands, this is not the main reason for the exaggerated effect of inflammation on airway resistance.
2. The cartilaginous and flexible trachea in infants contributes to collapsibility but does not explain the disproportionate rise in resistance from swelling.
3. Greater diaphragmatic reliance affects breathing mechanics but not the mathematical relationship between airway narrowing and resistance.
Take home points
- Airway resistance is highly sensitive to changes in radius, especially in children due to their small baseline diameters.
- Even minor airway swelling (e.g., 1 mm circumferential edema) can reduce the cross-sectional area by more than half in a child.
- Rapid recognition and management of pediatric airway inflammation is critical to prevent respiratory distress and hypoxia.
Correct Answer is D
Explanation
Retractions are a clinical sign of increased work of breathing, often seen in infants and children. They occur when soft tissues around the chest wall are pulled inward during inspiration due to negative intrathoracic pressure, usually because the child is struggling to get enough air into the lungs.
Rationale for correct answer:
4. D: Substernal retractions are inward pulling of the soft tissue just beneath the sternum/xiphoid (subxiphoid/epigastric area). This reflects increased negative intrathoracic pressure and is common in moderate- severe respiratory distress.
Rationale for incorrect answers:
1. A: This represents suprasternal retractions, typically seen at the sternal notch with upper-airway obstruction (e.g., croup, laryngomalacia). Not “substernal.”
2. B: The xiphoid itself is the bony tip; retractions are named for the soft tissue below it (subxiphoid/substernal). At the xiphisternum isn’t the same as below the sternum.
3. C: Those are intercostal retractions along the lateral chest wall, not beneath the sternum.
Take home points
- Retractions are classified by location: suprasternal (above sternum), intercostal (between ribs), subcostal (below ribs), and substernal (below sternum).
- The more severe the respiratory distress, the more locations you may see retractions in simultaneously.
- Substernal retractions often point to lower airway or lung pathology (e.g., bronchiolitis, asthma, pneumonia).
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