Anemia: blood loss
Synonym(s): Hemorrhagic anemia
Introduction
- Cause: hemorrhage (acute or chronic) or hemolysis (see Anemia: immune-mediated Anemia: immune mediated hemolytic ).
- Signs: hypovolemic shock (acute), signs of anemia (chronic), eg pale mucous membranes, lethargy, tachypnea, tachycardia, exercise intolerance, may be asymptomatic.
- Diagnosis: packed cell volume (PCV), total serum protein (TSP), reticulocyte count, cytology; evaluate hemostasis.
- Treatment: depends on cause and rate of development.
- Prognosis: may be good but depends on severity of blood loss, source of hemorrhage and if bleeding continues.
Presenting signs
- Lethargy.
- Depression.
- Collapse.
- Pallor.
Acute presentation
- Death - loss of >30% blood volume can cause death due to hypovolemic shock.
Pathogenesis
Etiology
- Trauma (RTA/surgery) to major vessels or vascular organs → acute blood loss.
- Surgery.
- Any chronic hemorrhage:
- Refractory epistaxis Epistaxis.
- Bleeding neoplasms Hemangiosarcoma , eg splenic hemangiosarcoma, intestinal neoplasm.
- Unilateral renal hemorrhage.
- Gastrointestinal ulceration Gastric ulceration.
- Endoparasitism (rare).
- Ectoparasitism - fleas Ctenocephalides canis , especially in neonatal animals.
- Hemostatic dysfunction.
Pathophysiology
Acute blood loss- Inciting cause → proportional loss of all major blood components → PCV Hematology: packed cell volume 24 h.
- Reflex splenic contraction → boosts red cell numbers (PCV) initially, so TSP Blood biochemistry: total protein drops before PCV.
- Hypovolemia → recovery of volume expansion → dilutes PCV (12-24 h after bleeding episode) and TSP (1-4 h after bleeding).
- Rapid increase in protein synthesis normalizes TSP. Patients that survive hypovolemic shock are unlikely to have lost >30% of circulating red cells and will not be severely anemic unless bleeding continues.
- 3-5 days later → erythrocyte regeneration → peaks 5-7 days.
- Do not see regenerative response for 3-5 days following hemorrhage.
- Initially see regenerative response with anisocytosis, polychromasia (new red blood cells are bigger and stain slightly darker blue) but continued blood loss leads to iron deficiency and non-regenerative anemia and microcytosis (small red blood cells).
- Continued blood loss → reduced oxygenation of kidneys → erythropoietin release → bone marrow increases RBC production and release.
- Also, increased levels of erythrocyte 2,3-diphosphoglycerate (2,3-DPG) → improves release of oxygen from hemoglobin into tissues.
- Insufficient circulating hemoglobin → tissue hypoxia → pale mucous membranes, lethargy and weakness, and compensatory responses of the sympathetic nervous system, ie tachypnea, tachycardia, bounding pulse.
- Chronic external blood loss → iron-deficiency and non-regenerative anemia Anemia: non-regenerative.
Timecourse
- PCV normal within 2-3 weeks; TSP normal within 1 week.
- Persistent anemia with hypoproteinemia Hypoproteinemia suggests persistent blood loss.
Diagnosis
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Treatment
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Prevention
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Outcomes
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Further Reading
Publications
Refereed papers
- Recent references from PubMed and VetMedResource.
Other sources of information
- Helm J & Knottenbelt C (2010) Blood transfusions in dogs and cats. 1. Indications. In Practice 32, 184-189.
- Helm J & Knottenbelt C (2010) Blood transfusions in dogs and cats. 2. Practicalities of blood collection adn administration. In Practice 32, 231-237.
- Raskin R E (2010) Haematologic Disorders. In:Clinical Medicine of the Dog and Cat. 2nd edn. Schaer M, Manson Publishing Ltd, London, pp 227-231.
- Selting K A (2007) Cancer of the Gastrointestinal Tract- Intestinal Tumors. In: Small Animal Clinical Oncology. Withrow S J & Vail D M (eds). 4th edn, Saunders, pp 491-503.
- Knottenbelt C (2001) Investigation of anaemia in dogs. In Practice 23, 306-314.
- Abrams-Ogg A (2000) Practical Blood Transfusion. In: Manual of Canine and Feline Haematology and Transfusion Medicine.1st edn. Day M J, Mackin A & Littlewood J D (eds). BSAVA Publications, Gloucester, pp 263-303.
- Mills J (2000) Anaemia. In: Manual of Canine and Feline Haematology and Transfusion Medicine.1st edn. Day M J, Mackin A & Littlewood J D (eds), BSAVA Publications, Gloucester, pp 29-42.