What weight person can nurse comfortably push in wheelchair?

Your question needs more refinement. What degree slope is the nurse pushing the wheelchair? Up hill or down hill? What type of terrain? dirt, gravel, cement... has the cement set? Inside or Outside? What the present temperature outside? Barometric pressure? Altitude? What type of wheelchair? standard or performance? What mood is the nurse in? Do they feel like just pushing the wheelchair over a cliff or in a lake?