Praise be to Allah.
Allah, may He be exalted, has limited spending of zakaah funds to the eight categories mentioned in the verse in which He says (interpretation of the meaning):
“As-Sadaqat (here it means Zakat) are only for the Fuqara (poor), and Al-Masakin (the poor) and those employed to collect (the funds); and for to attract the hearts of those who have been inclined (towards Islam); and to free the captives; and for those in debt; and for Allah’s Cause (i.e. for Mujahidoon - those fighting in the holy wars), and for the wayfarer (a traveller who is cut off from everything)”
Based on that, it is not permissible to use zakaah funds to purchase dialysis equipment, because this is not one of the categories mentioned, and because the benefit of such equipment is not only for the poor; rather all patients will benefit from it, poor and rich alike.
But if a poor person needs treatment in a local hospital in order to undergo dialysis or other kinds of treatment, because it is not possible to do it in a free hospital, then it is permissible to give him zakaah for this purpose.
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was asked:
What is the ruling on giving zakaah to some charitable organisations for the purchase of dialysis equipment?
That is not valid; it must be given to the poor person to keep as his property on the basis that he is poor, apart from the view of those who expand the meaning of “for Allah’s cause” to include all kinds of charity, which is a less strong view.
End quote from Thamaraat at-Tadween, no. 236, 7/2/1420 AH
However, the matter of spending to buy this equipment should not be connected only to the obligatory zakaah for which there are very specific categories of recipients; there are also funds from charitable donations that Muslims are encouraged to give, and there are also charitable endowments (awqaaf, sing. waqf) that the founders should devote to such beneficial causes.
And Allah knows best.