Blood Loss

 

The clinical and morphologic reactions to blood loss depend on the rate of hemorrhage and whether bleeding is internal or external.

 

 

Acute Blood Loss

The effects of acute blood loss are mainly due to loss of intravascular volume, potentially leading to cardiovascular collapse, shock, and death.

% lost

symptoms

signs
< 20

+/- anxiety

+/- vasovagal reaction
20 - 30

anxiety, exercise intolerance, may faint on standing

orthostatic hypotension, exertional tachycardia
30 - 40

anxiety, syncope on sitting or standing

orthostatic hypotension, tachycardic at rest
> 40

anxiety, restlessness, often confused, may be short of breath

hypovolemic shock, fall in supine blood pressure, tachycardia, cool, clammy skin

 

Effect on CBC

Acute blood loss results in a normocytic anemia. Water moves from the interstitial compartment, lowering the hematocrit. Reduced oxygenation of renal juxtaglomerular cells increases the production of erythropoietin, which leads to increased production of RBCs. It takes about 5 days for differentiation to occur, heralded by increased numbers of reticulocytes in the blood. Reticulocyte count can reach 10-15% after 7 days of acute blood loss.

If bleeding is internal, iron can be recaptured. If it external, however, iron loss and possible deficiency will hamper the restoration of normal blood levels.

 

 

Patients with slower bleeds will present a more complex clinical and laboratory picture. Hemoglobin/hematocrit levels provide a measure of anemia severity, while reticulocyte count and RBC indices provide a good sense of RBC production and iron supplies.

 

 

Chronic Blood Loss

Gradual blood loss is compensated for by plasma volume expansion. Albumin is difficult to mobilize from extracellular tissues, and it can take 1-3 days to restore an acute volume loss of 1000-1500 ml. Normal individuals can easliy tolerate chronic losses of 1000 ml/week.

Gradual blood loss depletes iron stores and produce iron deficiency anemia.