The following requests are available for passengers with special needs. These are an IATA standard, and apply to pretty much all airlines. They are entered into your flight reservation by your travel agent, tour operator or airline, depending who actually made the booking on those flights.
WCBD - Wheelchair - Dry Cell Battery (N. Amer.)
WCMP - Wheelchair - Manual Power
WCHR - Wheelchair (Can Climb Stairs)
WCHS - Wheelchair (Cannot Climb Stairs)
WCHC - Wheelchair (Carry-on)
WCOB - Wheelchair Required on Board
BLND - Blind Passenger
DEAF - Deaf Passenger
DEPU - Deportee (Unaccompanied)
LANG - Language Assistance
MEDA - Medical Case
MAAS - Meet and Assist
STCR - Stretcher
UMNR - Unaccompanied Minor
Many of these special assistance codes allow free form texts, giving the booking agent to option to provide more detail on the pax condition or requirements.
These will NOT appear on your ticket. They will appear on your itinerary.
I hope this helps, and the only thing I can suggest is making sure your agent puts the request in, never assume. It is your holiday, not your agents. And unlike me, not all agents are perfect.