Final answer:
The priority nursing intervention for a patient with a critically high potassium level of 9.0 meq/L is to prepare for dialysis and to monitor cardiac activity closely due to the risks of fatal cardiac dysrhythmias associated with hyperkalemia.
Step-by-step explanation:
A patient with a potassium level of 9.0 meq/L is critically hyperkalemic, which is a potentially life-threatening condition and must be treated as a medical emergency. The priority nursing intervention for a patient with such a high potassium level would be A. Prepare the patient for dialysis and place the patient on a cardiac monitor. This is because hyperkalemia can lead to serious cardiac complications, and the rapid reduction of serum potassium via dialysis is paramount. Additionally, placing the patient on a cardiac monitor allows for continuous monitoring of cardiac electrical activity, as hyperkalemia can cause fatal cardiac dysrhythmias.
Other interventions like administering Spironolactone, a potassium-sparing diuretic, placing the patient on a potassium restrictive diet, or administering a laxative are not immediate lifesaving measures and, therefore, are not the priority in such a critical situation.