Canis ISSN: 2398-2942

Anemia: blood loss

Synonym(s): Hemorrhagic anemia

Contributor(s): Prof Bernard Feldman, Yvonne McGrotty

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.

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.
Chronic blood loss
  • 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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Outcomes

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Further Reading

Publications

Refereed papers

Other sources of information

  • Helm J & Knottenbelt C (2010)Blood transfusions in dogs and cats. 1.Indications.In Practice32, 184-189.
  • Helm J & Knottenbelt C (2010)Blood transfusions in dogs and cats. 2.Practicalities of blood collection adn administration.In Practice32, 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 Practice23, 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.


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