From the Guidelines
Intravenous (IV) fluids effectively counteract nitrate-induced hypotension by increasing preload. When nitrates like nitroglycerin cause hypotension, administering IV fluids, typically normal saline or lactated Ringer's solution, rapidly expands intravascular volume, directly increasing venous return to the heart, enhancing left ventricular end-diastolic volume (preload) and subsequently improving cardiac output and blood pressure 1. The mechanism works because nitrates primarily cause hypotension through venodilation, which reduces venous return to the heart, as stated in the 2014 AHA/ACC guideline for the management of patients with non-ST-elevation acute coronary syndromes 1.
Key Points to Consider
- Nitrates are endothelium-independent vasodilators with peripheral and coronary vascular effects, which decrease cardiac preload and reduce ventricular wall tension 1.
- The decision to administer nitrates should not preclude therapy with other proven mortality-reducing interventions such as beta blockers 1.
- IV fluids counteract the effect of nitrates on preload by filling the expanded venous capacity, thereby improving cardiac output and blood pressure.
- For optimal management, administer fluids while monitoring vital signs, especially in patients with heart failure or renal impairment who may not tolerate volume expansion.
Management Approach
- Administer IV fluids, typically normal saline or lactated Ringer's solution, at 500-1000 mL bolus to rapidly expand intravascular volume.
- Monitor vital signs, especially in patients with heart failure or renal impairment.
- In severe cases, positioning the patient supine with legs elevated can augment venous return while fluid therapy takes effect.
- Consider the use of other anti-ischemic therapies with proven benefits, such as beta blockers, in conjunction with nitrates and IV fluids 1.
From the Research
Preload and IV Fluids in Nitrate-Induced Hypotension
- The administration of IV fluids is a common intervention in the management of hypotension, including nitrate-induced hypotension 2.
- However, the optimal fluid management strategy in this context is not well established, and the effects of IV fluids on preload and cardiac output are complex and depend on various factors, including the type and amount of fluid administered, as well as the patient's underlying cardiac function and volume status 3, 4.
- Some studies suggest that the use of balanced crystalloids, such as lactated Ringer's solution, may be associated with improved outcomes in patients with sepsis-induced hypotension, potentially due to their ability to maintain a more stable acid-base balance and reduce the risk of hyperchloremic acidosis 5, 6.
- In the context of nitrate-induced hypotension, the use of IV fluids to support preload and cardiac output may be beneficial, but the optimal fluid management strategy should be individualized based on the patient's specific needs and clinical context 2, 4.
- The effects of IV fluids on preload can be monitored using various hemodynamic parameters, including central venous pressure, pulmonary capillary wedge pressure, and cardiac output, although the reliability of these parameters can be limited in certain situations 4.