At birth, what triggers the initial breath in a neonate?

• A Surfactant release reduces surface tension, automatically expanding alveoli without a neurological trigger
• B Cold environment, tactile stimulation, rising PaCO2, and falling PaO2 stimulate medullary respiratory centers ✓
• C The neonate inhales in response to the mother's oxytocin surge
• D Clamping of the umbilical cord raises fetal blood pressure, triggering the Hering-Breuer reflex

Explanation

The first breath is triggered by multiple converging stimuli: (1) sudden drop in temperature stimulates skin cold receptors; (2) tactile stimulation during delivery; (3) rising PaCO2 and falling PaO2 (due to placental separation) stimulate peripheral and central chemoreceptors; and (4) the distress of the birth process itself. The medullary respiratory center integrates these signals to fire the first inspiratory effort. Surfactant reduces surface tension but does not initiate breathing — it only facilitates alveolar stability thereafter.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.