What is the difference between hypotension and hypovolemia?

From the Guidelines

Hypotension and hypovolemia are distinct medical conditions that require different treatment approaches, with hypotension referring to abnormally low blood pressure and hypovolemia referring to a state of decreased blood volume or fluid volume in the body. Hypotension is typically defined as a systolic pressure below 90 mmHg or a diastolic pressure below 60 mmHg, and can occur due to various factors such as certain medications, heart problems, or neurological conditions 1. On the other hand, hypovolemia results from fluid loss through bleeding, vomiting, diarrhea, excessive sweating, or inadequate fluid intake, and is characterized by symptoms like thirst, dry mucous membranes, decreased urine output, and poor skin turgor in addition to possible hypotension.

Some key differences between hypotension and hypovolemia include:

• Causes: Hypotension can be caused by a variety of factors, including medications, heart problems, and neurological conditions, while hypovolemia is typically caused by fluid loss or inadequate fluid intake.
• Symptoms: Hypovolemia is often characterized by symptoms such as thirst, dry mucous membranes, and decreased urine output, in addition to possible hypotension.
• Treatment: Hypotension management depends on the underlying cause and may include medications like vasopressors to increase blood pressure, while hypovolemia treatment focuses on fluid replacement with intravenous fluids to restore blood volume 1.

According to a recent study published in the British Journal of Anaesthesia, the most appropriate management for hypotensive, haemodynamically unstable patients is to perform a bedside assessment to define the cause and then treat accordingly 1. The study found that an increase in cardiac output after passive leg raise (PLR) strongly predicted fluid responsiveness, and that no increase in cardiac output after PLR classified patients who most likely would not respond to fluid. This suggests that a PLR test should be considered for patients with postoperative hypotension to determine the underlying cause and guide treatment.

In terms of treatment, hypotension should be treated immediately in the symptomatic patient, with intravenous fluid being appropriate in many instances, particularly if the patient is fluid responsive 1. However, if preload augmentation is not needed, vasopressor or inotropic support is indicated. The side-effect profile of drugs used in the treatment of hypotension must be taken into account, and phenylephrine is best used in situations where the hypotension is accompanied by tachycardia because it can result in a reflex bradycardia, especially in the preload independent state 1.

From the FDA Drug Label

Blood volume depletion should always be corrected as fully as possible before any vasopressor is administered. When, as an emergency measure, intraaortic pressures must be maintained to prevent cerebral or coronary artery ischemia, LEVOPHED can be administered before and concurrently with blood volume replacement Prolonged administration of any potent vasopressor may result in plasma volume depletion which should be continuously corrected by appropriate fluid and electrolyte replacement therapy

The main difference between hypotension and hypovolemia is that:

• Hypotension refers to low blood pressure
• Hypovolemia refers to low blood volume It is essential to correct hypovolemia before administering a vasopressor to treat hypotension, as uncorrected hypovolemia can lead to severe peripheral and visceral vasoconstriction, decreased renal perfusion, and tissue hypoxia when the vasopressor is discontinued 2 2.

From the Research

Definition and Difference

• Hypotension refers to low blood pressure, which can be caused by various factors such as dehydration, blood loss, or certain medical conditions 3.
• Hypovolemia, on the other hand, refers to a state of decreased blood volume, which can lead to hypotension 4, 5.
• The key difference between the two is that hypotension is a symptom, while hypovolemia is a condition that can cause hypotension.

Causes and Symptoms

• Hypovolemia can be caused by loss of extracellular fluid volume or blood, and its indicators include supine or postural hypotension, increased heart rate, and decreased central venous pressure 6.
• Hypotension, particularly sepsis-induced hypotension, can be treated with fluid resuscitation using lactated Ringer's solution or 0.9% saline 3.
• It is essential to determine the intravascular volume status of patients in shock to categorize and inform treatment decisions 5.

Diagnosis and Assessment

• The physical examination can be used to assess for hypovolemia, with indicators such as dry axilla, dry oral mucosa, and a decrease in central venous pressure 6.
• Point-of-care ultrasonography is also an important adjunct to physical assessment in estimating volume status 7.
• Laboratory testing, such as serum lactate levels, and imaging can be used to diagnose and manage hypovolemia and hypotension 5.