In a term baby, functional closure of the ductus arteriosus occurs within?

MNS 2024

Applied Physiology

Easy

Appeared in: MNS 2024

Explanation

Functional closure of the ductus arteriosus refers to the constriction of its muscular wall, which stops the shunting of blood.
This process is triggered by increased arterial oxygen concentration (from breathing) and a drop in maternal prostaglandins after birth.
In full-term infants, this closure process begins within hours of birth.
While 90% of infants achieve closure by 48 hours, the process is considered complete for virtually all healthy term infants by 72 hours.
This makes 72 hours the correct upper limit for functional closure.

Option A: This is incorrect because although 90% of term infants have achieved functional closure by 48 hours, the process is not yet complete for all. About 10% of infants will complete closure between 48 and 72 hours.
Option C: This timeframe is incorrect as it relates to anatomical closure, not functional closure. Anatomical closure is the process where the ductus permanently turns into the ligamentum arteriosum.
Option D: This is the timeframe for the completion of anatomical closure, where the ductus arteriosus permanently becomes a fibrous ligament (ligamentum arteriosum). This is a much slower process than functional closure.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Physiology of neonatal circulatory transition as background academic context rather than a clinical decision trigger.
Failure of the ductus arteriosus to close results in a condition called Patent Ductus Arteriosus (PDA), a common congenital heart defect, especially in preterm infants.
Nurses assess for PDA by listening for a characteristic 'machinery-like' continuous murmur below the left clavicle and checking for bounding peripheral pulses and a wide pulse pressure.
What if? If the infant was preterm, the ductus arteriosus would be less responsive to oxygen, and functional closure would likely be delayed, increasing the risk of a symptomatic PDA requiring medical or surgical intervention.

How to Approach the Question

First, identify the key terms in the question: 'term baby', 'functional closure', and 'ductus arteriosus'.
Recall the critical difference between 'functional' closure (muscle constriction, rapid) and 'anatomical' closure (permanent tissue change, slow).
Recognize that functional closure is a rapid physiological event that occurs in the first few days of life, triggered by the first breaths.
Based on this, eliminate the longer timeframes (1 month and 3 months) as they relate to anatomical closure.
Between the remaining short timeframes (48 hrs and 72 hrs), choose the option that represents the point of completion for nearly all healthy term infants, which is 72 hours.

Concept Tested & Keywords

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E6 Anatomy Grays 43e Vol 1 Part 2 p. 60-62

E6 Nelson Textbook of Pediatrics(2024) — Volume 2 p. 524-526