Peak figure attending hospital (6)
I believe the answer is:
Here is my best explanation:
'peak' is the definition.
('height' can be a synonym of 'peak')
'figure attending hospital' is the subsidiary indication.
'figure' becomes 'eight' (I've seen this in other clues**).
'attending' means one lot of letters go next to another.
'hospital' becomes 'h'.
'eight' put after 'h' is 'height'.
(Other definitions for height that I've seen before include "Vertical dimension", "Measurement from top to bottom", "Dimension upwards", "Distance above ground or sea", "Vertical extent", "Loftiness", "Stature", "Hill, elevation", "Measurement from base to top" and "Vertical extension".)