What is a common physiological response when a patient loses 20% of their blood volume?

When a patient experiences a loss of approximately 20% of their blood volume, commonly referred to as a class II hemorrhage, the body initiates several compensatory physiological responses to maintain adequate perfusion and blood pressure. Tachycardia, or an increased heart rate, is one of the primary responses.

The heart rate increases as the body attempts to compensate for the reduced blood volume and maintain cardiac output. This response helps to ensure that vital organs continue to receive an adequate supply of oxygenated blood despite the decreased circulating volume. During this stage of fluid loss, the body releases catecholamines such as epinephrine and norepinephrine, which further stimulate the heart to beat faster.

In contrast, other options do not primarily serve as immediate responses to this level of blood volume loss. Oliguria (decreased urine output) may occur later as the kidneys experience decreased perfusion, confusion might manifest in more severe cases or when blood loss is much greater, and hypotension might not present until blood volume is decreased significantly beyond 20%. Therefore, the increase in heart rate, or tachycardia, is the most immediate and characteristic response to a significant decrease in blood volume.