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

Choice A reason: Metabolic alkalosis is a condition where the pH and the HCO3- are both elevated, indicating a loss of acids or a gain of bases in the body. This is not the case for this patient, as his HCO3- is within the normal range of 22 to 26 mEq/L.

Choice B reason: Respiratory acidosis is a condition where the pH and the PaCO2 are both low, indicating a retention of carbon dioxide in the lungs due to hypoventilation. This is not the case for this patient, as his pH is high and his PaCO2 is low.

Choice C reason: Respiratory alkalosis is a condition where the pH and the PaCO2 are both high, indicating a loss of carbon dioxide in the lungs due to hyperventilation. This is the case for this patient, as his pH is above the normal range of 7.35 to 7.45 and his PaCO2 is below the normal range of 35 to 45 mm Hg. This condition is uncompensated, as his HCO3- is within the normal range and has not changed to counteract the pH imbalance.

Choice D reason: Metabolic acidosis is a condition where the pH and the HCO3- are both low, indicating a gain of acids or a loss of bases in the body. This is not the case for this patient, as his pH is high and his HCO3- is within the normal range.

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.