Final answer:
Flaring nares in a newborn should alert the nurse to notify a practitioner as it can be a sign of respiratory distress. Other signs mentioned are within normal ranges. The Apgar score, which includes heart rate and respiration, helps assess the newborn's condition post-delivery.
Step-by-step explanation:
The sign that should alert a nurse to notify the practitioner when assessing a newborn of 33 weeks' gestation is flaring nares. This can indicate that the newborn is experiencing respiratory distress. The other signs listed are within normal ranges for a newborn: acrocyanosis (bluish discoloration of the hands and feet) is common in the first few hours after birth, a heartbeat of 140 per minute is within the normal range for a newborn, and respirations of 40 per minute are also within normal limits for a newborn.
According to the Apgar score, heart rate and respiration are critical measurements to assess the newborn's adaptation to life outside the womb. An Apgar score lower than 7 at the 5-minute mark indicates a need for medical assistance, and a total score below 5 indicates an emergency situation.