The Medical Priority Dispatch System (MPDS) is a medically-approved, unified system used to dispatch appropriate aid to medical emergencies including systematized caller interrogation and pre-arrival instructions. Priority Dispatch Corporation is licensed to design and publish MPDS and its various products.

MPDS was developed by Dr. Jeff Clawson from 1976 to 1979. Dr. Clawson worked as an Emergency Medical Technician

Emergency medical technician

Emergency Medical Technician or Ambulance Technician are terms used in some countries to denote a healthcare provider of emergency medical services...

and dispatcher prior to medical school: he designed a set of standardized protocols to triage patients via the telephone and thus improve the emergency response system. Dr. Clawson states the main objective of MPDS is to "send the right thing to the right person in the right way at the right time." Cards were first alphabetized by chief complaint that included key questions to ask the caller, pre-arrival instructions, and dispatch priorities. After many revisions, these simple cards have evolved into MPDS.

MPDS today still starts with the dispatcher asking the caller key questions. These questions allow the dispatchers to categorize the call by chief complaint and set a determinant level ranging from A (Minor) to E (Immediately Life Threatening) relating to the severity of the patient's condition. Some systems also use the determinant O which may be a referral to another service or obvious death. Another sub-category code is used to further categorize the patient. For instance, a suspected cardiac or respiratory arrest where the patient is not breathing is given the MPDS code 9-E-1, whereas a superficial animal bite has the code 3-A-3. The MPDS codes allow emergency medical systems to determine the appropriate response mode (i.e. routine or "lights and sirens") and resources to be assigned to the event.

Dispatch Determinants

Each dispatch determinant is made up of three pieces of information, which builds the determinant in a Number-Letter-Number format. The first component, a number from 1 to 36, indicates a broad category or specific "Card" from the MPDS: the selection of this card is based on the initial questions asked by the emergency dispatcher. The second component, a letter A through E (including the Greek character Ω), is the response determinant indicating the potential severity of injury or illness based on information provided by the caller. The third and final component, a number, is the sub-determinant and provides more specific information about the patient's specific condition.

Cards

Card	Category	Card	Category
1	Abdominal Pain/Problems	20	Heat/Cold Exposure
2	Allergic Reactions/Animal Stings/Envenomation	21	Hemorrhage/Lacerations
3	Animal Bites/Attacks	22	Inaccessible Incident/Entrapments
4	Assault/Sexual Assault	23	Overdose/Poisoning (Ingestion)
5	Back Pain (Non-Traumatic/Non-Recent)	24	Pregnancy/Childbirth/Miscarriage
6	Breathing Problems	25	Psychiatric/Suicide Attempt
7	Burns/Explosions	26	Sick Person
8	Carbon Monoxide/Inhalation/HazMat	27	Stab/Gunshot/Penetrating Trauma
9	Cardiac or Respiratory Arrest/Death	28	Stroke (C.V.A.)
10	Chest Pain	29	Traffic/Transportation Accidents
11	Choking	30	Traumatic Injuries
12	Convulsions/Seizures	31	Unconscious (Near)
13	Diabetic Problems	32	Unknown Problem (Man Down)
14	Drowning/Diving/SCUBA Accident	33	Inter-Facility Transfer/Palliative Care
15	Electrocution/Lightning	34	Automatic Crash Notification (A.C.N.)
16	Eye Problems/Injuries	35	HCP (Health-Care Practitioner) Referral
17	Falls	36	Flu-Like Symptoms (Possible H1N1)
18	Headache	37	Inter-Facility Transfer specific to medically-trained callers
19	Heart Problems/A.I.C.D.

Card 36

This card was created to handle the influx of emergency calls during the H1N1 pandemic: it directed that Standard EMS Resources be delayed until patients could be assessed by a Flu Response Unit (FRU), a single provider that could attend a patient and determine what additional resources were required for patient care to reduce the risk of pandemic exposure to EMS Personnel.

Response Determinant

Letter	Severity	Resources	Response
Alpha	Non Life-Threatening	Basic Life Support	Non Emergency
Bravo	Possibly Life-Threatening	Basic Life Support	Emergency
Charlie	Life-Threatening	Advanced Life Support	Emergency
Delta	Serious Life Threat	Advanced Life Support	Emergency
Echo	Life Status Questionable	Closest Available (Multiple Resources Sent)	Emergency
Omega "Ω"	Public Assist Only	Basic Life Support	Non Emergency