April 21, 2023

Dear colleagues:

In this installment of UH EMS-I’s Pharmacy Phriday, we review Nitroglycerine (NTG), a common vasodilator that is supplied in our drug boxes for use in acute coronary syndromes (ACS) and CHF/Pulmonary Edema. 

Nitroglycerine is probably thought of most for its use in ACS, chest pain, and STEMIs.  The medication can be administered by all providers (EMT basics must first receive online medical direction) via the sublingual (SL) route.  The SL tablet is placed under the tongue, and the medication diffuses into the blood through tissues under the tongue. The adult dose of 0.4 mg (400mcg) can be repeated every 5 minutes, up to three total doses. In UH protocols, the use of NTG for the pediatric patient is not recommended.  Remember to ask the patient if they had self-administered NTG prior to EMS’s arrival and about the effectiveness of the medication.

As NTG can cause vasodilation and resulting hypotension, the provider must first check the patient’s blood pressure.  Protocol guidelines indicate NTG only be administered if the systolic is > 120 without an IV or > 110 with an IV.  Although a right-sided infarct does not preclude the use of NTG, a 12-lead ECG should also be completed before administration.  An IV should be established if the patient exhibits signs of a right-sided infarct, as these patients are often dependent on pre-load for adequate perfusion.  In cases of hypotension following NTG, place the patient in the Trendelenburg position and administer a Normal Saline bolus.

Other than hypotension, an additional contraindication is the use of erectile dysfunction (ED) or pulmonary hypertension medications within the last 48 hours.  Most providers are familiar with the contraindication associated with the ED medications like Viagra, Sildenafil, etc., but may not be as aware of the contraindication associated with the pulmonary hypertension medications.

In cases of pulmonary hypertension, the blood vessels in the lungs narrow, causing the blood pressure in the arteries to rise above normal limits. It causes a strain on the right side of the heart and can be life-threatening. Medications, one of which is phosphodiesterase type 5 inhibitor like Sildenafil, Tadalafil, etc. are prescribed to promote selective smooth-muscle relaxation in the lungs.  This results in mild vasodilation and an associated small, generally insignificant, decrease in blood pressure. However, because of the synergistic decrease in blood pressure with the use of nitrates like NTG, severe hypotension can result.  Note that these medications are not just prescribed for the male ED patient but also for both males and females with the diagnoses of pulmonary hypertension.  Be sure to ask all patients about these diagnoses and medication usage.

An additional indication for the use of NTG within the protocols is for the patient in CHF/pulmonary edema. The patient with acute pulmonary edema experiences a rapid filling of the lung’s interstitial and alveolar spaces and can present with a dramatic onset and rapid progression of symptoms (sometimes called flash pulmonary edema).  These patients have a narrow time window where the provider can intervene, prevent possible intubation, and improve patient outcomes significantly.  The early use of non-invasive ventilation, such as CPAP, combined with NTG, is often seen as a cornerstone in the treatment of these patients.

These patients need the excess fluid removed from the lungs as quickly as possible. This can be accomplished by applying a positive airway pressure with CPAP and creating vasodilation with the use of NTG.  The effects of the NTG cause a reduction in arteriole pressure which will decrease hydrostatic pressure in the capillary bed, thereby reducing the fluid being forced out of the capillary. The exception to using this combination of treatments of NTG and CPAP in the pulmonary edema patient is the presence of hypotension. In those cases, the provider is directed to the Cardiogenic Shock Protocol and the use of Push Dose Epi.

Some guidelines reference the use of IV NTG in the continued care of these patients.  Within the UH drug boxes, NTG is only provided in the sublingual tablet form.  Therefore, dosing is the same for CHF/pulmonary edema cases and the ACS cases, except that the maximum dose does not apply to the CHF/pulmonary edema patient.  The continued administration of the NTG every five minutes, along with the use of CPAP, can be lifesaving for patients in extreme distress. The NTG would be discontinued once the desired effect is achieved, i.e., improved respirations and perfusion, or a contraindication such as hypotension is applicable.

Side effects from the administration of NTG are secondary to the hypotensive effects of the medication. Patients may complain of dizziness, weakness, palpitations, and syncope. Profound hypotension may occur in patients with preload-dependent conditions, as mentioned above.  The patient may also complain of a persistent, throbbing headache.  This common side effect, which is often encountered by the provider, is due to venous pooling in the cranial space, resulting in increased intracranial pressures.  Be sure to monitor your patient and document your findings.

Till the next installment, stay safe!

Sincerely,



The UH EMS-I Team

University Hospitals