Ottawa's new ambulance dispatch system launches today, bringing changes to the way paramedics prioritize emergency calls.

Under the Medical Priority Dispatch System, or MPDS, ambulances will be dispatched based on answers to detailed questions, and according to five colour-based levels based on the “acuity” of the situation.

Top-priority calls are now marked as “purple,” which indicates there are immediate life-threatening conditions, where time is critical. This accounts for about two per cent of calls.

Next on the priority list is “red,” which means emergent and potentially life-threatening, representing about 38 per cent of calls. Time is sensitive in these cases.

“Orange” is urgent and potentially life-threatening. Time may be a factor. This accounts for 17 per cent of calls.

“Yellow” is non-urgent, but potentially serious. Time is sensitive. It’s about 19 per cent of calls.

“Green” is non-urgent and not serious, with no immediate threat to life, and it may be deferred without detriment to the patient’s outcome. This is about 24 per cent of calls.