#@1 Yeees ... with reservations. "OT" may be used as an abbreviation if it has been defined as such:
"In addition to their technical expertise, members of an operating theatre (OT)
team will use a range of ‘non-technical’ skills. These are the cognitive and social skills that complement technical skills to achieve safe and efficient practice."http://www.abdn.ac.uk/iprc/documents/JAN_lit_...
or if it's absolutely clear from context:
"The patient is booked for an urgent laparotomy, and arrives in theatre
15 minutes later.
On arrival in the OT
her BP is 65/45 mmHg and her HR is 125 bpm." http://www.frca.co.uk/Documents/136%20Managem...
But I think you are still more likely to hear " ... in theatre" than "... in the OT" in the UK. This may be partly because "OT" is also used for "operating time" and especially for "occupational therapy" - without any context, "OT staff" are more likely to be "occupational therapists" than "(operating) theatre staff".
@wmw #2, I think the [Amer.] flag is needed for OR.
As the *OP* said: Within the Commonwealth nations, the term
[operating theatre] is used synonymously with operating room (OR) or operating suite, the modern facility within a hospital where surgical operations are carried out in a sterile environment.http://en.wikipedia.org/wiki/Operating_theater