Anaemia in horses Flashcards
What is anaemia?
A reduction in the circulating red blood cell volume (PCV) or haemoglobin conc
How does anaemia affect tissues?
Oxygen carrying capacity of the blood is reduce so hypoxia occurs in tissues
Anaemia develops due to one or more of three patho-physiological mechanisms, what are they?
- Blood loss
- Increased RBC destruction
- Decreased RBC production
What is the role of the spleen in horses?
- important reservoir for erythrocytes
- also an important reservoir of platelets
When would it not be appropriate to measure a horses PCV?
During or after exercise
When excited
- produce splenic contractions
What are some clinical signs of anaemia?
- Tachypnoea, tachycardia
- Pallor
- Exercise intolerance
- Lethargy
What must you be aware of when looking for signs of chronic anaemia?
Chronic or slow onset of anaemia allows physiological compensation so signs may be less obvious
How many litres of blood can a 500kg horse lose before showing clinical signs of hypovolaemic shock?
- Blood volume = 8% of bodyweight = 40L
- 1/3 of that = 13L
What are some clinical signs of hypovolaemic shock
- tachycardia
- tachypnoea
- hypothermia
- pallor
- prolonged CRT
- weak pulse
- cold extremities
- weakness
What is the normal PCV range of:
- Thoroughbreds
- Ponies, warm bloods, donkeys
- 35-45%
- 26-35%
What steps are involved in diagnosing equine anaemia, what questions need to be asked?
- History and clinical exam
- Acute or chronic?
- External or internal blood loss?
- Evidence of a clotting disorder
- Evidence of haemolysis
- Lab assessment
An initial laboratory assessment to diagnose anaemia should include which tests?
- Complete blood count, including red cell morphology
- Total plasma protein
- Plasma fibrinogen (indicator of a chronic inflammatory disease)
- Lactate (levels of this increase when there is anaemia)
Reduction of total protein and PCV is indicative of?
Chronic blood loss
How does the spleen mask the extent of blood loss in the initial first hours following severe haemorrhage?
Injects a concentrated mass of stored erythrocytes into circulation
What is the role of catecholamines as a compensatory mechanism in anaemia?
Adrenaline and noradrenaline induce vasoconstriction and increase cardiac output to try and compensate the reduced circulating volume
What is the role of ADH as a compensatory mechanism in anaemia?
- Increases reabsorption of water in the renal tubules and GI tract, as fluid is withdrawn from the interstitium, plasma volume expands
Decrease in PCV is not usually seen until how long after haemorrhage?
12-24 hours
Small nuclear remnants called … are occasionally found in erythrocytes of normal horses and do not indicate increased erythropoiesis
Howell-Jolly bodies
What peripheral signs of regeneration are rarely seen in horses?
Reticulocytes
Polychromasia
What acts as an indicator of regenerative anaemia in horses?
-Immature RBCs are slightly larger than mature so the mean corpuscular volume goes up slightly
How would you test for severe intravascular haemolysis in horses?
- Take a blood sample
- Spin it
- Serum is pink – RBCs are being split open and Hb is leaking into the serum
Diagnostic evaluation of suspected haemolytic anaemia in horses should include which tests?
- Blood smear evaluation
- Urinalysis
- Coombs test
What does the Coombs test for?
Used to detect antibodies that act against the surface of your red blood cells
Will urine colour change to a pink colour in intravascular or extravascular haemolytic anaemia?
Intravascular
What is the most common cause of anaemia in horses?
Haemorrhage due to traumatic or surgical wounds
- acute blood loss anaemia
What are some other causes of acute blood loss anaemia in horses?
- Guttural pouch mycosis: fungal infection eats through the wall of the carotid artery
- Uterine artery rupture
- Epistaxis
- Tumours
- Renal haemorrhage
- Rib fracture => lung laceration
In chronic blood loss, when does anaemia develop?
- Allows the bone marrow to regenerate erythrocytes as they are lost
- Anaemia only develops once the rate of erythropoiesis is exceeded by the rate of haemorrhage
What are some causes of chronic blood loss in horses?
- Parasitic
- Neoplasia
- Gastric ulceration
- NSAID toxicosis
What are some causes of haemolytic anaemia in horses?
- Penicillin: Clostridium perfringes infection
- Injection site abscess
- Lymphoma
What is neonatal isoerythrolysis?
- Foal derives it antibodies from the mares colostrum, the mare has antibodies against the foals blood
- Mare has been exposed to blood that’s not her own
- Yellow colour and foal becomes anaemic
- A Coombs’ test will detect immune-mediated anaemia
How can you treat horses with anaemia?
- Identify and eliminate the cause
- Provide nursing care
- Ensure adequate tissue perfusion and minimise stress
- Stop any bleeding
When would a horse need to receive a blood transfusion?
Should be reserved for instances in which oxygen delivery to tissues is inadequate to support life
What must be done if you are unable to stop bleeding?
- ‘Permissive hypotension’: tolerating low blood pressure – as long as brain and heart are perfused
- Blood transfusion may be ideal
If the bleed has successfully been stopped, what are the next steps?
- Replace the lost circulating volume
- Hypertonic saline
- Crystalloids
- Colloids
- Blood transfusion
What % of blood loss from an animal would indicate a transfusion is needed?
more than 30%
