The nurse caring for a frail 92-year-old dehydrated patient should add to the plan of care:

Choice A reason: This is incorrect because over-hydration is unlikely in a dehydrated patient. Over-hydration is a condition where the body has too much water, which can cause hyponatremia, edema, and cerebral swelling.

Choice B reason: This is incorrect because diarrhea is a cause, not a consequence, of dehydration. Diarrhea is the frequent and watery passage of stool, which can lead to fluid and electrolyte loss.

Choice C reason: This is incorrect because pulmonary congestion is also unlikely in a dehydrated patient. Pulmonary congestion is a condition where the lungs are filled with fluid, which can cause dyspnea, cough, and crackles.

Choice D reason: This is correct because fall is a potential complication of dehydration. Dehydration can cause confusion, dizziness, weakness, and hypotension, which can increase the risk of falling and injuring oneself.

Choice A reason: This is incorrect because low HCO3- and high PaCO2 are signs of metabolic acidosis, not alkalosis. Metabolic acidosis is a condition where the blood pH is lower than the normal range of 7.35 to 7.45, due to an excess of acids or a loss of bases in the body.

Choice B reason: This is incorrect because low PaCO2 and low HCO3- are signs of respiratory acidosis, not alkalosis. Respiratory acidosis is a condition where the blood pH is lower than the normal range of 7.35 to 7.45, due to impaired gas exchange or hypoventilation, which causes carbon dioxide to accumulate in the blood.

Choice C reason: This is correct because low PaCO2 and high HCO3- are signs of alkalosis. Alkalosis is a condition where the blood pH is higher than the normal range of 7.35 to 7.45, due to a loss of acids or an excess of bases in the body. There are two types of alkalosis: respiratory and metabolic. Respiratory alkalosis is caused by hyperventilation, which lowers the PaCO2 in the blood. Metabolic alkalosis is caused by vomiting, diuretics, or excessive intake of antacids, which raises the HCO3- in the blood.

Choice D reason: This is incorrect because high PaCO2 and high HCO3- are signs of compensation, not alkalosis. Compensation is a process where the body tries to restore the normal pH by adjusting the levels of PaCO2 and HCO3- in the opposite direction of the primary disorder. For example, if the patient has metabolic alkalosis, the respiratory system will try to compensate by retaining carbon dioxide and lowering the PaCO2. If the patient has respiratory alkalosis, the renal system will try to compensate by excreting bicarbonate and lowering the HCO3-.