ISSN 2398-2950      

Anemia: blood loss

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Synonym(s): Hemorrhagic anemia


Introduction

  • Cause: hemorrhagic (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 no signs.
  • Diagnosis: packed cell volume (PCV), total serum protein (TSP), reticulocyte count, cytology; evaluate homeostasis.
  • Treatment: depends on cause and rate of development.
  • Prognosis: can be good with appropriate treatment.

Pathogenesis

Etiology

  • Trauma (RTA/surgery) to major vessels or vascular organs   →   acute blood loss.
  • Surgery.
  • Any chronic hemorrhage:
  • Coagulophathies.

Pathophysiology

  • Signs usually triggered by blood loss > 20% total blood volume (50-70 ml in adult cat).

Acute blood loss

  • Inciting cause   →   proportional loss of all major blood components   →   PCV and TSP normal for first 12-24 hours.
  • Reflex splenic contraction   →   boosts red cell numbers (PCV) initially, so TSP drops before PCV.
  • Hypovolemia   →   recovery of volume expansion   →   dilutes PCV (12-24 hours after bleeding episode) and TSP (1-4 hours after bleeding).
  • Rapid increase in protein synthesis normalizes serum protein.
    Patients that survive hypovolemic shock are unlikely to have lost >30% of circulating red cells and will not be severely anemic unless bleeding continues.
  • 3-4 days later   →   erythrocyte regeneration   →   peaks 5-7 days.
    Do not see regenerative response immediately 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   →   to iron deficiency and non-regenerative anemia and microcytosis (small red blood cells).
    Kittens have poor iron stores and are therefore very susceptible to iron deficiency.
  • 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 (likely in unweaned kittens - rare in adult cats) and non-regenerative anemia Anemia: overview.

Timecourse

  • PCV normal within 2-3 weeks; TSP normal within 1 week.
  • Persistent anemia, 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 Practice 32, 184-189.
  • Helm J & Knottenbelt C (2010) Blood transfusions in dogs and cats. 2. Practicalities of blood collection and administration. In Practice 32, 231-237.
  • Raskin R E (2010) Haematological Disorders. In: Clinical Medicine of the Dog and Cat. 2nd edn. Ed Schaer M, Manson Publishing Ltd, London, pp 227-231.
  • Mills J (2000) Anaemia. In: Manual of Canie and Feline Haematology and Transfusion Medicine. 1st edn. Eds Day M J, Mackin A & Littlewood J D. BSAVA Publications, Gloucester, pp 29-42.

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