A nurse is assisting with the care of a client who is in the first stage of labor. The nurse observes the umbilical cord protruding from the vagina. Which of the following actions should the nurse take first?

Choice A rationale:
0.25 mL - The nurse should not administer 0.25 mL because the available concentration of vitamin K injection is 1 mg/0.5 mL. To achieve the prescribed dose of 1 mg, administering only 0.25 mL would be insufficient.
Choice B rationale:
0.5 mL - This is the correct choice. The nurse should administer 0.5 mL of the vitamin K injection to deliver 1 mg of vitamin K, as the concentration of the injection is 1 mg/0.5 mL. By giving the full 0.5 mL, the newborn will receive the appropriate 1 mg dose.
Choice C rationale:
0.75 mL - Administering 0.75 mL would be excessive for the prescribed 1 mg dose of vitamin K. It is unnecessary to give a higher volume than required, as it could lead to potential adverse effects or wastage.
Choice D rationale:
1 mL - Similarly, administering the entire 1 mL of the vitamin K injection would result in doubling the prescribed dose, leading to potential overdose and adverse reactions. The nurse should avoid administering more than the necessary 0.5 mL.

The correct answer is choice A: Respiratory rate of 16/min.

Choice A rationale:

A respiratory rate of 16/min is within the normal range for adults, which is typically between 12 to 20 breaths per minute. In the context of severe preeclampsia, maintaining a normal respiratory rate is crucial when administering magnesium sulfate IV, as one of the signs of magnesium toxicity is respiratory depression. Therefore, a respiratory rate of 16/min indicates that the client is not experiencing respiratory depression and it is safe to continue the magnesium sulfate infusion.

Choice B rationale:

A heart rate of 60/min is at the lower end of the normal range, which is 60 to 100 beats per minute for adults. However, bradycardia or a low heart rate can be a sign of magnesium sulfate toxicity, especially if accompanied by other symptoms such as hypotension or altered mental status. Without additional context, a heart rate of 60/min alone does not necessarily indicate it is unsafe to continue the infusion, but it would require further assessment.

Choice C rationale:

A urine output of 50 mL in 4 hours is significantly below the expected minimum of 30 mL/hour for adults. Adequate urine output is an important indicator of kidney function and is essential for the excretion of magnesium. In the case of magnesium sulfate infusion for severe preeclampsia, a low urine output could indicate renal insufficiency and an increased risk of magnesium toxicity. Therefore, a urine output of 50 mL in 4 hours is a contraindication for continuing the infusion without further evaluation.

Choice D rationale:

Diminished deep-tendon reflexes can be a sign of magnesium toxicity. Deep-tendon reflexes are assessed to monitor for signs of magnesium overdose during infusion, as magnesium acts as a central nervous system depressant at high levels. If deep-tendon reflexes are diminished, it may suggest that the serum magnesium levels are too high, and the infusion should be paused or discontinued to prevent further toxicity.

In summary, the only finding that clearly indicates it is safe to continue the magnesium sulfate infusion is a normal respiratory rate, as provided in choice A. The other options either require further assessment or are indicators of potential magnesium toxicity.