A child with severe anemia requires a unit of red blood cells (RBCs). The nurse explains to the child that the transfusion is necessary to:

D. A client's blood pressure changes from 112/60 mm Hg to 90/54 mm Hg when standing.
A significant drop in blood pressure when changing positions from lying to standing may indicate orthostatic hypotension, which can be a sign of dehydration, blood loss, or other underlying medical issues. This can be a cause for concern, especially if the client is an adolescent, as it may lead to decreased perfusion of vital organs and may require immediate medical attention.

The other options are as follows:
A. A client who has a burn injury to an estimated 5% of his leg and is crying - While it's essential to assess and address the client's pain and comfort, this finding does not indicate an immediate need for medical attention. Pain management and wound care can be addressed based on the severity of the burn and the client's pain level.
B. A client who has an ankle fracture reports a pain level increase from 3 to 5 after initial ambulation - This finding is concerning, and the nurse should notify the provider to reassess pain management and evaluate for potential complications related to the fracture. However, it may not require immediate medical attention unless there are signs of severe pain or complications.
C. A client who is 1 day postoperative and has a temperature of 37.5° C (99.5° F) - A slight increase in temperature in the immediate postoperative period may not be unusual and can be attributed to the normal inflammatory response after surgery. The nurse should continue monitoring the client's temperature and report any further changes or additional signs of infection or complications to the provider.
Overall, while all findings should be addressed and managed appropriately, the significant drop in blood pressure (option D) should be reported immediately due to the potential implications for the client's overall health and well-being.

To calculate the dose of acetaminophen for a child, the nurse needs to convert the child's weight from pounds to kilograms and then multiply it by the prescribed dose per kilogram. The formula is:

Weight in kg = Weight in lb / 2.2
Dose in mg = Weight in kg x Dose per kg
Dose in mL = Dose in mg / Concentration in mg/mL

Using the given information, the nurse can plug in the values and solve for the dose in mL:

Weight in kg = 28 / 2.2 = 12.73
Dose in mg = 12.73 x 10 = 127.3
Dose in mL = 127.3 / 120 x 5 = 5.3

Therefore, the nurse should administer 5.3 mL of acetaminophen to the child.