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Aspirin (ASA)

Category: Pharmacology Sources: raw/supplemental/emt-b-pharmacology.md Last updated: 2026-04-03

Overview

Aspirin (acetylsalicylic acid, ASA) is administered prehospital for suspected acute coronary syndrome (ACS) — cardiac chest pain. It is an antiplatelet agent that inhibits thromboxane A2, reducing platelet aggregation and limiting the growth of a coronary clot. Early aspirin administration in ACS has demonstrated mortality benefit. It is one of the highest-impact interventions an EMT-B can deliver.

Key Points

  • Indications: Suspected cardiac chest pain (ACS) — chest pain with a cardiac quality (pressure, tightness, crushing) especially with associated symptoms (diaphoresis, radiation to left arm/jaw, nausea)
  • Dose: 162–324 mg, chewed (not swallowed whole). Chewing speeds absorption.
  • Typical field presentation: two 81 mg baby aspirin = 162 mg, or one 325 mg tablet = 325 mg
  • Patient chews and swallows — do not give with water to swallow whole
  • Contraindications:
  • Known allergy to aspirin or NSAIDs
  • Active bleeding or recent significant GI bleeding
  • Patient has already taken their aspirin dose today (risk of stacking)
  • Some protocols also list: bleeding disorders, recent surgery (check NM protocol)
  • Authorization: Requires standing order or online medical direction.
  • Reassess: Monitor for allergic reaction after administration; reassess chest pain and vitals.

Assessment Relevance

The aspirin trigger is found during history-taking (OPQRST + SAMPLE). Key assessment findings pointing toward ACS:

  • OPQRST: Chest pain — pressure quality, onset with exertion or at rest, radiation to left arm/jaw/back, associated with diaphoresis, nausea, shortness of breath
  • SAMPLE: Cardiac history, hypertension, diabetes, smoking, medications (nitrates, beta-blockers suggest known cardiac disease), allergies (specifically ask about aspirin and NSAIDs)
  • Vitals: BP, pulse, SpO2 — SBP <100 with chest pain is a priority patient indicator
  • Skin: Pale, cool, diaphoretic skin suggests poor perfusion and a higher-acuity cardiac event

The field differential between musculoskeletal chest pain and ACS often isn't possible — when in doubt and contraindications are absent, aspirin administration is appropriate if the mechanism could be cardiac.

Procedures

  1. Identify chest pain with plausible cardiac mechanism via OPQRST.
  2. Screen for contraindications via SAMPLE (allergy, bleeding history, already took ASA today).
  3. Obtain authorization (standing order or online medical direction contact).
  4. Confirm the patient can chew and swallow.
  5. Administer 162–324 mg; instruct patient to chew thoroughly before swallowing.
  6. Document: time, dose, authorization source, patient response.
  7. Reassess chest pain at next reassessment interval; monitor for adverse reaction.
  8. Inform receiving hospital — "aspirin administered at [time]" is part of the hand-off report.

NM Protocol Notes

  • NM EMT-B scope includes aspirin administration for suspected ACS under standing order in most EMS systems.
  • Confirm San Juan Basin EMS protocols for standing order specifics — some systems require online medical direction contact.
  • NM protocols may list specific BP thresholds (e.g., SBP >90) as an additional criterion — check current protocol.
  • Document the authorization method on the PCR.

NREMT Relevance

Aspirin is a high-frequency topic on the NREMT cognitive exam. Common question angles: - "A 58-year-old male has crushing chest pain radiating to his left arm. He is diaphoretic. He has no aspirin allergy and has not taken aspirin today. What medication do you administer?" → Aspirin 162–324 mg chewed - Contraindication recognition: patient with known aspirin allergy, or patient who already took their daily aspirin - Administration method: chewed, not swallowed whole - Dose range: 162–324 mg (know both ends of the range) - "Chewed" is the critical word — appears frequently in exam questions

  • history-taking — OPQRST and SAMPLE findings trigger aspirin consideration
  • primary-assessment — chest pain with signs of shock detected here; aspirin considered after ABCs stabilized
  • reassessment — reassess chest pain and vital signs after administration
  • oxygen — oxygen is co-administered with aspirin in ACS management
  • oxygen-administration — delivery procedure for supplemental O2 in chest pain

Sources

  • raw/supplemental/emt-b-pharmacology.md — Aspirin section and General Medication Administration Rules