The Role of Nitroglycerin in Prehospital Care
Nitroglycerin (NTG) is a rapid-acting vasodilator used by Emergency Medical Services (EMS) to treat chest pain or discomfort associated with suspected angina pectoris or acute myocardial infarction (heart attack). By relaxing smooth muscles in the vascular walls, NTG decreases myocardial oxygen demand and increases coronary blood flow, helping to alleviate pain and reduce the heart's workload. However, its powerful effect on blood pressure requires strict adherence to established protocols, particularly regarding the number and frequency of doses that can be given.
Nitroglycerin Administration Limits
Standard protocol for Basic Life Support (BLS) and Advanced Life Support (ALS) providers involves administering or assisting with a maximum number of sublingual doses of nitroglycerin. This total includes any doses the patient may have taken prior to EMS arrival. These doses are typically administered at specific intervals, based on the patient's ongoing symptoms and vital signs.
Dose Timing and Repetition Guidelines
- Initial Dose: Perform a full assessment and administer the first dose if indications are present and no contraindications are found.
- Follow-Up Doses: Reassess the patient's chest pain and vital signs at a specific interval after the first dose. If chest pain persists and the systolic blood pressure remains above the minimum threshold (typically 90–100 mmHg, depending on local protocol), additional doses may be given.
- Subsequent Doses: If chest pain continues and vital signs remain stable after subsequent doses, further administration may be permitted up to the maximum limit. At this point, contact with medical control is often required, and transport to the hospital is imperative.
Assessment and Contraindications
Before administering any dose of nitroglycerin, a thorough patient assessment is critical. Providing NTG to a patient with certain conditions can cause a dangerous and rapid drop in blood pressure.
Essential Pre-Administration Checks
- Confirm Indication: Is the patient experiencing chest pain or discomfort consistent with cardiac ischemia?
- Check Vital Signs: Obtain a baseline set of vital signs, with particular attention to blood pressure. The systolic blood pressure must be above the system's threshold, typically 90 or 100 mmHg.
- Assess Medication History: Ask the patient if they have taken any medications for erectile dysfunction, such as sildenafil (Viagra), tadalafil (Cialis), or vardenafil (Levitra), within a specific timeframe. The combination of these drugs with NTG can cause a life-threatening drop in blood pressure.
- Confirm Prescription and Expiration: When assisting a patient with their own prescribed NTG, verify that the medication belongs to them and has not expired.
- Check Patient Alertness and Consent: Ensure the patient is alert and able to consent to the medication assist.
Relative and Absolute Contraindications
- Hypotension: The most critical contraindication is hypotension. Administering NTG to a patient who is already hypotensive can further decrease blood pressure, potentially leading to inadequate tissue perfusion.
- Phosphodiesterase (PDE-5) Inhibitor Use: The use of medications like sildenafil, tadalafil, or vardenafil within a specific recent timeframe is an absolute contraindication due to the risk of severe hypotension.
- Right Ventricular Infarction: Patients with a suspected right ventricular (RV) infarction are highly sensitive to preload reduction. Giving NTG to these patients is generally contraindicated or requires extreme caution, as it can worsen their condition.
Comparison of EMT and Paramedic Protocol
While the basic principles of nitroglycerin administration are consistent across provider levels, the scope of practice and available resources differ. The following table highlights some of the key differences and similarities.
| Feature | EMT | Paramedic |
|---|---|---|
| Administration Authority | Can assist the patient with their own prescribed NTG based on local protocol and medical direction. | Can administer NTG from the ambulance drug box and has a broader scope. |
| Available Forms | Typically sublingual tablets or sprays prescribed to the patient. | Sublingual tablets, sprays, paste, and potentially intravenous (IV) infusions in some systems. |
| Max Sublingual Doses | Standard maximum number of doses, including any taken before EMS arrival. | Standard maximum number of doses; however, can also initiate IV drips under medical control. |
| Special Circumstances | Protocol may require contact with medical control if the patient's prescribed NTG is expired or not readily available. | Can administer higher concentrations of NTG or initiate infusions for specific conditions like hypertensive pulmonary edema under medical control. |
Step-by-Step Administration Guide for the EMT
- Patient and Scene Safety: Ensure the scene is safe and your patient is in a position of comfort, preferably sitting or lying down, to minimize the effects of hypotension.
- Assessment and Vitals: Perform a full primary and secondary assessment. Confirm blood pressure meets the protocol threshold and ask about contraindications, especially recent PDE-5 inhibitor use.
- The Six Rights: Before administering, verify the 'six rights' of medication administration: right patient, right medication, right dose, right route, right time, and right documentation.
- Administer First Dose: Place one prescribed tablet or spray sublingually (under the tongue). Ensure the patient keeps their mouth closed and does not swallow the medication.
- Reassess Patient Condition: Recheck vital signs within the protocol-specified timeframe and monitor for changes in the patient's condition, including chest pain level, dizziness, or headache.
- Repeat Doses (if necessary): If chest pain persists and blood pressure is stable (above protocol threshold), you can repeat the dose at the specified interval, up to the maximum number of total doses.
Conclusion
Understanding how many doses of nitroglycerin can you give as an EMT is foundational to safe and effective emergency cardiac care. The standard maximum number of sublingual doses, administered at specific intervals, is not an arbitrary limit but a critical safety measure. This rule, combined with mandatory vital sign checks and a thorough assessment for contraindications, protects the patient from the risk of dangerous hypotension. By strictly following protocols and continuously monitoring patient response, EMTs can confidently provide this vital medication and improve patient outcomes during suspected cardiac events.
For additional training resources and detailed protocols, please consult authoritative EMS publications and your local medical direction. The article by EMS1.com provides further insights into the actions and misconceptions of nitroglycerin administration for prehospital providers.
