1.4 Call Processing Architecture: Parallel Dispatch, Fast Track & Shunts

1.4 Call Processing Architecture: Parallel Dispatch, Fast Track & Shunts

Quick Answer: The MPDS call processing architecture consists of four distinct stages: (1) Case Entry, (2) Key Questions, (3) Dispatch Life Support (DLS), and (4) Case Exit. Field units are mobilized using parallel processing, where the calltaker enters initial dispatch data into the Computer-Aided Dispatch (CAD) system immediately following Case Entry, allowing units to roll while Key Questions are interrogated. When cardiac arrest or agonal breathing is detected during Case Entry, the EMD activates the Fast Track protocol, bypassing Key Questions entirely to trigger an ECHO dispatch and begin immediate Telephone CPR. If interrogation uncovers a more severe medical condition or underlying etiology, the EMD executes a protocol shunt to transfer to the appropriate specialized protocol.

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The Four-Stage Architecture of MPDS Call Flow

Every medical call processed through the Medical Priority Dispatch System moves through a structured, four-stage sequential pipeline designed to balance diagnostic accuracy with rapid resource deployment:

Stage 1: Case Entry
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Stage 2: Key Questions
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Stage 3: Dispatch Life Support (DLS)
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Stage 4: Case Exit

Stage 1: Case Entry

As explored in Section 1.2, Case Entry is the universal intake module. It establishes the verified location, callback number, chief complaint description, and baseline patient stability (Age, Consciousness, Breathing). All calls begin here.

Stage 2: Key Questions (KQs)

Once Case Entry identifies the primary complaint, the EMD navigates to the specific Chief Complaint Protocol (Protocols 1 through 36). Key Questions are structured, protocol-specific interrogations that:

• Evaluate specific clinical discriminators (e.g., onset times, mechanisms of injury, secondary symptoms).
• Differentiate severity levels to calculate the final Determinant Code (OMEGA, ALPHA, BRAVO, CHARLIE, DELTA, or ECHO).
• Identify critical scene-safety hazards (e.g., violent assailants, toxic chemicals, electrical lines).

Stage 3: Dispatch Life Support (DLS)

Dispatch Life Support represents the active clinical treatment phase of emergency dispatch. DLS is divided into two distinct functional categories:

• Post-Dispatch Instructions (PDIs): Case-specific safety and preparation directives provided to the caller while responders are traveling (e.g., "Do not move him," "Unlock the front door," "Put away any family pets," "Gather his medications").
• Pre-Arrival Instructions (PAIs): Scripted, step-by-step life support protocols delivered in real time for critical medical crises (e.g., Adult/Child/Infant CPR, Choking Foreign Body Airway Obstruction, Emergency Childbirth, Severe Hemorrhage Control, Narcan Administration).

Stage 4: Case Exit

The formal closure sequence of the emergency call. The EMD provides standard closing instructions, reassesses the patient's condition, advises the caller to call back immediately if symptoms worsen, or maintains an open line until the physical arrival of EMS crews.

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Parallel Processing Mechanics: Dispatching While Interrogating

A persistent misconception among the public and inexperienced telecommunicators is that "asking questions delays the ambulance." Callers frequently shout: "Stop asking questions and just send someone!"

The Operational Reality of Parallel Processing

In modern public safety answering points (PSAPs) and emergency communications centers (ECCs), calltaking and radio dispatch are decoupled through parallel processing:

1. Case Entry Completion Point: As soon as the EMD completes Case Entry (establishing address, chief complaint, consciousness, and breathing), an initial CAD incident is generated.
2. The Dispatch Alert: In two-position systems, the CAD record instantaneously routes to a radio dispatcher, who alerts and mobilizes field units immediately. In single-position systems, the telecommunicator hits a "Quick Dispatch" key to alert crews.
3. Continuous Diagnostic Questioning: While field responders are starting their engines and navigating through traffic, the calltaker remains on the line asking Key Questions. The answers update the CAD screen in real time, refining the determinant code and alerting responders to vital clinical data (e.g., "Be advised, patient has history of angina and took one nitroglycerin 5 minutes ago").

No response is ever delayed by asking protocol Key Questions. The questioning occurs during the transit window that responders would spend driving anyway.

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The Fast Track Protocol: Cardiac Arrest Resuscitation

While parallel processing handles ordinary and severe medical calls, sudden cardiac arrest represents a hyper-acute category where every second counts. Brain tissue begins dying within 4 minutes, and survival declines by 7% to 10% for every minute without chest compressions.

Fast Track Mechanics

When Case Entry Question 5 ("Is s/he awake?") is NO, and Question 6 ("Is s/he breathing?") is NO (or breathing is described as agonal, gasping, snorting, or uncertain):

Case Entry: Unconscious & Not Breathing / Agonal
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[BYPASS STAGE 2: KEY QUESTIONS]
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IMMEDIATE ECHO DISPATCH (9-E-1)
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DIRECT TO DLS PROTOCOL A (TELEPHONE CPR)

The Three Steps of Fast Tracking

1. Immediate ECHO Trigger: The EMD instantly transmits an ECHO-level dispatch (e.g., Code 9-E-1: Expected Cardiac Arrest). ECHO mobilizes the closest available first responders (firefighters, law enforcement with AEDs) alongside ALS paramedics running maximum emergency transit.
2. Total Key Question Bypass: The EMD skips Stage 2 (Key Questions) entirely. Asking questions about cardiac history, medications, or symptom onset while a patient is in cardiac arrest is a fatal waste of time.
3. Direct Pipeline to DLS: The EMD shifts instantly to the MPDS DLS Link Protocol C: Airway/Arrest/Choking (Unconscious) or the age-appropriate resuscitation pathway, ordering the caller to place the patient flat on the floor, position their hands on the center of the chest, and begin hard and fast compressions at a cadence of 100 to 120 beats per minute.

Fast tracking compresses the time from call answer to first bystander compression to under 90 seconds, dramatically elevating neurologically intact survival rates.

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Protocol Shunts: Redirection Under Pressure

A shunt is an authorized, scripted protocol pathway that transfers the calltaker from their initially selected Chief Complaint protocol to a different, clinically appropriate protocol.

Why Shunts Are Necessary

Callers often frame the emergency around the final outcome or the most dramatic visual symptom. During structured Key Questions, the EMD may uncover that the underlying cause of the emergency is completely different from the initial complaint.

Primary Shunt Scenarios

1. The Medical-Preceding-Trauma Shunt (Fall vs. Medical Collapse)

A caller reports an elderly patient fell down the stairs (Protocol 17: Falls). During Key Questions, the EMD asks: "Did s/he fall because of a trip/slip, or did s/he faint, get dizzy, or have chest pain before falling?"

• Caller responds: "She told me she had sudden terrible chest pain and everything went black, then she collapsed."
• Action: The EMD shunts from Protocol 17 (Falls) to Protocol 10 (Chest Pain). The fall was secondary to cardiac ischemia. Treating this as a mechanical trauma call would withhold vital cardiac medications and response urgency.

2. The Unconsciousness Shunt

While interrogating a seemingly stable protocol (e.g., Protocol 23: Overdose/Poisoning or Protocol 28: Stroke), the caller suddenly screams: "He just stopped talking! His eyes rolled back and I can't wake him up!"

• Action: The EMD immediately halts the current protocol and shunts to Protocol 31 (Unconscious/Fainting) or Protocol 9 (Cardiac Arrest) depending on breathing status.

3. The Choking Airway Shunt

While processing Protocol 2 (Allergies/Envenomations) or Protocol 1 (Abdominal Pain), the patient develops severe laryngeal edema or aspirates food, producing complete foreign body airway obstruction.

• Action: Shunt directly to Protocol 11 (Choking) to deliver conscious or unconscious Heimlich instructions.

The Golden Rules of Shunting

1. Never Downgrade Without Re-Evaluation: When shunting, never reduce an established high-acuity response without thoroughly completing the new protocol's clinical assessment.
2. Log the Shunt Rationale in CAD: Immediately notify responders of the protocol shift (e.g., "Units advised: Call shunted from Fall to Chest Pain/Syncope").
3. Follow Destination Protocol Scripting: Once shunted, do not improvise; resume structured interrogation on the new protocol card.

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Comparative Table: The Four Stages of Call Flow

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Realistic Dispatch Transcript: Fast Track & Parallel Dispatch in Action

EMD: 9-1-1 Emergency, what's the address of the emergency? Caller: 314 West End Avenue, Apartment 4B. EMD: What's the phone number you're calling from? Caller: 555-2044. EMD: Okay, tell me exactly what happened. Caller: My brother collapsed on the kitchen floor! He's not moving! EMD: How old is he? Caller: He's 46. EMD: Is he awake? Caller: No! He is completely unresponsive! EMD: Is he breathing? Caller: He's making a weird groaning, gasping noise every few seconds, like a dry heave! EMD: (Identifies Agonal Breathing / Cardiac Arrest) EMD: (Silently enters 9-E-1 into CAD; sends ECHO alert to radio dispatcher in parallel; BYPASSES Key Questions) EMD: (Direct, urgent, authoritative tone) Listen to me carefully. Paramedics are already on the way with lights and sirens. I am going to help you do CPR right now. Do not hang up. Caller: Okay! What do I do?! EMD: Get him flat on his back on the floor. Take anything off his chest so it is bare. Caller: He's on the floor! EMD: Kneel by his side. Place the heel of your hand on the center of his chest, right between his nipples. Put your other hand on top of that hand. Interlock your fingers. Caller: Hands are in place! EMD: Lock your elbows straight. Lean directly over his chest. Push down HARD and FAST, at least two inches deep. Count out loud with me: 1, 2, 3, 4, 1, 2, 3, 4...