Emergency database interpretation

3 Emergency database interpretation

Together with an astute major body system examination, an immense amount of useful information can be derived from an emergency database. Traditionally the minimum emergency database consists of manual packed cell volume (PCV), plasma total solids (TS), blood glucose concentration and blood urea nitrogen (BUN) concentration. Where possible the author prefers to measure plasma creatinine concentration alongside BUN as creatinine is less prone to acute fluctuations. Gross plasma appearance may also provide valuable information.

In addition to the minimum emergency database, it is often appropriate to perform additional measurements or tests as part of the emergency database for specific patient populations. These include:

• Peripheral blood smear examination

• Plasma electrolytes (potassium, sodium, calcium)

• Urinalysis: gross appearance; specific gravity, dipstick analysis, sediment examination.

Depending on the facilities available, it may be possible to obtain all the blood required for the emergency database from an intravenous catheter at the time of placement.

Packed cell Volume and Plasma Total Solids

Manual PCV and TS should always be interpreted together and the changes identified will raise the index of suspicion for particular causes (see Table 3.1).

Table 3.1 Interpretation of manual packed cell volume and plasma total solids

Packed cell volume (%)	Plasma total solids (g/L)	Causes to consider
Decreased	Normal	Chronic anaemia Acute haemolytic anaemia
Decreased	Decreased	Haemorrhage Chronic anaemia + additional cause of hypoproteinaemia Aggressive fluid therapy
Normal	Increased	Hyperglobulinaemia Artefactual increase
Normal	Decreased	Acute haemorrhage Hypoproteinaemia Severe vasculitis
Increased	Normal	Breed-related normal variation Absolute polycythaemia Dehydration with concurrent protein loss
Increased	Increased	Dehydration

Clinical Tip

• In the majority of cases, reference ranges for normal plasma total protein concentration may be applied to plasma total solids. Synthetic colloid administration and hyperglycaemia may artefactually increase plasma total solids measured by refractometry.

Reduction in PCV and TS following haemorrhage is the result of dilution by fluid moving into the bloodstream from the interstitium. However, this decrease does not occur immediately as there is a lag for fluid movement to occur. Furthermore, in dogs, but not cats, splenic contraction occurs following acute haemorrhage to increase circulating red blood cell mass. Therefore PCV may be normal in the face of low TS following acute haemorrhage and these findings must be interpreted in light of the patient’s history and physical examination findings.

With the exception of haemorrhage and protein-losing enteropathy (PLE), most causes of hypoproteinaemia relate to hypoalbuminaemia. Causes of hypoalbuminaemia include protein-losing nephropathy (PLN), liver failure, malnutrition/malabsorption, chronic effusions and exudative skin lesions. Hyperglobulinaemia may occur secondary to dehydration but also inflammation, monoclonal gammopathy (e.g. due to plasma cell myeloma) and polyclonal gammopathy (e.g. due to chronic inflammatory disease, inflammatory bowel disease, feline infectious peritonitis).

When interpreting changes in all laboratory parameters, including PCV and TS, it is important to remember that normal ranges cited for adult dogs and cats may not be applicable to puppies and kittens (see Ch. 41).

Gross Plasma Appearance

Common abnormalities of plasma appearance and possible causes are listed in Table 3.2. In addition to plasma appearance, samples can be evaluated for the size of the buffy coat following centrifugation, with a large buffy coat suggestive of leukocytosis.

Table 3.2 Possible causes of abnormalities in gross plasma appearance

Plasma appearance	Possible causes
Haemolysed	Poor sampling technique Intravascular haemolysis
Icteric	Prehepatic causes, especially haemolytic anaemia Hepatic disorders causing intrahepatic cholestasis Posthepatic disorders (e.g. obstructive biliary tract disease)
Lipaemic	Postprandial lipaemia Pancreatitis Hyperadrenocorticism

Blood Glucose Concentration

Clinically significant hyperglycaemia requiring specific therapy is typically only associated with patients suffering from diabetes mellitus. Hyperglycaemia not requiring treatment may also be seen in other endocrine disorders (hyperadrenocorticism and acromegaly), secondary to stress (especially cats) and following seizures and head trauma.

Clinically significant hypoglycaemia requiring treatment is seen most commonly as a result of hyperinsulinism, iatrogenic causes or neoplasia, and in very young animals or toy breed dogs. Hypoglycaemia may also be identified in hypoadrenocorticism, liver failure, sepsis and heatstroke.

Azotaemia

The causes of azotaemia may be divided into prerenal, renal or postrenal.

Prerenal azotaemia

Prerenal azotaemia occurs as a result of reduced renal perfusion and a consequent functional decrease in glomerular filtration rate (GFR). Causes include dehydration, hypovolaemia and heart failure. Prerenal azotaemia is characterized by increased PCV, TS and urine specific gravity (USG), and is usually only mild. It is typically reversible but structural renal injury and renal azotaemia may develop if renal hypoperfusion is protracted.

Renal azotaemia

Renal azotaemia occurs as a result of reduced GFR secondary to structural renal changes. Urine specific gravity is isosthenuric (1.007–1.015) as the kidneys are no longer able to concentrate or dilute the urine and azotaemia may be mild, moderate or severe. Anaemia may be present with chronic renal insufficiency.

Clinical Tip

• Blood urea nitrogen (BUN) concentration may be affected by a number of extrarenal factors, being increased for example by increased dietary protein intake, gastrointestinal haemorrhage and increased protein catabolism. Thus BUN concentration should ideally be interpreted together with serum creatinine concentration as the latter is considered a more reliable indicator of renal function.

Postrenal azotaemia

Postrenal azotaemia occurs due to urinary tract obstruction or rupture which prevents excretion of urea and creatinine from the body. Azotaemia in these cases may be very severe but frequently will fully resolve with appropriate correction of the underlying disorder. Protracted urinary outflow obstruction can result in damage to the renal parenchyma and consequent intrinsic acute renal failure.

Peripheral Blood Smear Examination

Peripheral blood smear examination is recommended for the majority of emergency patients. Cytology allows cell morphology to be evaluated and abnormal cell populations to be identified; a degree of quantitative information can also be obtained. Red blood cells, white blood cells and platelets are evaluated (Figures 3.1 and 3.2).

Figure 3.1 Normal canine red blood cells, neutrophil, monocyte and platelets (×1000)

(Photograph courtesy of Kate English).

Figure 3.2 Normal feline red blood cells, neutrophil, monocyte and platelets (×1000)

(Photograph courtesy of Kate English).

Red blood cells

Red blood cells are examined for variability in size (anisocytosis) and colour (polychromasia) (Figure 3.3), both of which are suggestive of regenerative anaemia. When stained using a Romanowsky stain such as Diff-Quik, immature red blood cells (polychromatophils), which are larger than mature cells, have a purplish- or bluish-tinged appearance.

Figure 3.3 Peripheral blood smear from a dog showing regenerative anaemia (×1000). Marked polychromasia (large purplish-tinged red blood cells) and anisocytosis (variation in red blood cell size) is present; a neutrophil and two platelets can also be seen.

(Photograph courtesy of Kate English)

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Tags: Saunders Solutions in Veterinary Practice Small Animal Emergency

Sep 3, 2016 | Posted by admin in SMALL ANIMAL | Comments Off

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