Q:  What is "rule of 7" when writing orders for hemodialysis (HD)?

Answer: 

The "Rule of 7" is the rule of thumb for the choice of Potassium(K) bath concentration while writing orders for HD.

The patient's K plus the dialysate bath K should equal approximately 7.

For example, if somebody presents with a K of 5.1, put them on a 2 K bath; if they present with a K of 3.2, put them on a 4 K bath. The lowest K bath usually used is 1 K bath and the highest K bath is usually 4K bath - but these are used very judiciously.