Pallor and approach to anaemia

19 Pallor and approach to anaemia



Pallor


Pallor of the mucous membranes is a common finding during major body system examination of dogs presenting as emergency patients. Pallor is harder to detect in cats but many of the points that follow are equally applicable. Pallor is most commonly the result of anaemia or vasoconstriction secondary to hypovolaemia and both processes may be present within the same patient. In addition, hypoperfusion due to cardiogenic or obstructive shock may also cause mucous membranes to appear pale, as can thermoregulatory vasoconstriction in hypothermia.


In many cases it will be possible on the basis of historical and physical examination findings to determine whether anaemia or hypovolaemia may be present. Concomitant hypovolaemia and anaemia are typically seen where anaemia is secondary to acute blood loss and the degree of pallor may be more severe than would otherwise be expected for the degree of hypovolaemia. It is important to remember that the packed cell volume may be normal for several hours following acute blood loss in dogs (but serum total solids should be low) (see Ch. 3).


Euvolaemic dogs with anaemia of sufficient severity are likely to show compensatory cardiovascular changes that may be distinguishable from hypovolaemia. In particular, capillary refill time (if detectable) is usually normal in euvolaemic anaemia. Euvolaemic dogs with acute anaemia may be distinguishable from chronically anaemic dogs as the former tend to be depressed or moribund while the latter are often remarkably bright (until a critical end-point is reached), having had time to adapt to the anaemia. In some cases anaemia is not identified until packed cell volume/haematocrit is measured.



Anaemia


A rational approach to the investigation of anaemia starts with classification of the anaemia as regenerative (due to red blood cell loss or destruction) or nonregenerative (due to reduced red blood cell production). In the emergency setting, this is done on the basis of peripheral blood smear examination, with regenerative anaemia being manifested as polychromasia, anisocytosis and a possible increase in nucleated red blood cells (see Figures 3.3 and 3.5). Regenerative anaemia occurs as a result of haemolysis or haemorrhage, and additional findings are used to determine which of these two processes is the likely cause (Figure 19.1).


image

Figure 19.1 Algorithm for pallor and approach to anaemia. CRT, capillary refill time; PCV, packed cell volume.



Clinical Tip



• There is a lag phase following red blood cell loss/destruction such that a regenerative erythrocyte response can take 3–5 (or even 7) days to be detectable on peripheral blood smear examination. Thus an apparently nonregenerative anaemia may in fact be preregenerative, i.e. if insufficient time has passed since the inciting event for the regenerative response to be detectable.


Regenerative anaemia


Causes of regenerative anaemia are listed in Box 19.1.



BOX 19.1 Causes of regenerative anaemia



Haemorrhage



• Trauma (e.g. haemoabdomen, bleeding in/around pelvis, external blood loss)

• Surgery

• Neoplastic rupture (e.g. splenic haemangiosarcoma)

• Coagulopathy (e.g. anticoagulant rodenticide intoxication, immune-mediated thrombocytopenia, angiostrongylosis, congenital disorders)

Related posts:

  1. Jaundice
  2. Shock and dehydration
  3. Pelvic limb paresis and paralysis
  4. Ocular emergencies

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Sep 3, 2016 | Posted by in SMALL ANIMAL | Comments Off on Pallor and approach to anaemia

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