What is the single most appropriate next step for a 44-year-old man with acute renal failure and tall tented T waves on ECG?

In the context of acute renal failure accompanied by tall tented T waves on an ECG, the most appropriate next step is administration of intravenous calcium chloride. Tall tented T waves are classic signs of hyperkalemia, a potentially life-threatening condition where elevated potassium levels can lead to serious cardiac complications like arrhythmias.

When potassium levels are high, as seen in acute renal failure where the kidneys can no longer efficiently excrete potassium, there is an immediate risk to cardiac function. Calcium acts to stabilize the cardiac cell membrane and mitigate the effects of high potassium on the heart. IV calcium chloride helps protect the heart from the excitatory effects of excess potassium, effectively buying time while other treatments for hyperkalemia can take effect.

While dialysis, insulin with dextrose, and calcium resonium can also be effective management strategies for hyperkalemia, they are not immediate interventions. Dialysis would be appropriate for long-term management, especially in the setting of acute renal failure, but may not address the immediate cardiac risk. Insulin with dextrose shifts potassium intracellularly, but this is a secondary measure and may take time to act. Calcium resonium is a resin that can help lower potassium levels but is not an immediate action for cardiac stabilization.

Thus,