When the newborn's crib was moved suddenly, the nurse noticed that his legs flexed and the arms fanned out, and then both came back toward the midline. The nurse would interpret this behavior as:

Injecting the medication into the vastus lateralis. This is because the vastus lateralis is a large muscle in the thigh that is suitable for intramuscular injections in newborns³. The vitamin K injection helps prevent vitamin K deficiency bleeding, which is a rare but serious condition that can cause bleeding in the brain or other organs¹. The American Academy of Pediatrics recommends that all newborns receive a single intramuscular dose of 0.5 to 1 mg of vitamin K within one hour of birth².

Choice A is wrong because a 21 gauge needle is too large for a newborn's muscle. A 25 or 27 gauge needle is more appropriate.

Choice B is wrong because injecting at a 45-degree angle may not reach the muscle tissue. A 90-degree angle is more appropriate.

Choice C is wrong because injecting 1cc of medication is too much for a newborn's muscle. The recommended dose of vitamin K is 0.5 to 1 mg, which is equivalent to 0.05 to 0.1 mL.

Sternal or chest retractions. This is because sternal or chest retractions are a sign of respiratory distress in newborns, which means they are having difficulty breathing. Chest retractions occur when the baby's chest pulls in with each breath, indicating that they are using extra muscles to breathe. This can be caused by various conditions that affect the lungs, such as respiratory distress syndrome (RDS), transient tachypnea of the newborn (TTN), meconium aspiration syndrome (MAS), pneumonia, or congenital heart defects.

Choice A is not correct because mucus draining from the nose is not a symptom of respiratory distress in newborns. It is normal for newborns to have some mucus in their nose and mouth after birth, which can be cleared by suctioning or wiping.

Mucus drainage does not interfere with breathing unless it is excessive or thick.

Choice B is not correct because cyanosis of the hands and feet is not a symptom of respiratory distress in newborns. It is normal for newborns to have bluish discoloration of their hands and feet, called acrocyanosis, for the first few days after birth. This is due to immature circulation and does not indicate a lack of oxygen. Cyanosis of the central parts of the body, such as the face, lips, and tongue, is more concerning and should be reported.

Choice C is not correct because irregular heart rate is not a symptom of respiratory distress in newborns. It is normal for newborns to have some variations in their heart rate, especially during sleep cycles. The normal heart rate range for newborns is 100 to 160 beats per minute. A heart rate that is too fast (tachycardia) or too slow (bradycardia) may indicate a problem with the heart or other organs³.