CPD ACCREDITED ARTICLE
2 . Exudate An exudate forms due to increased vascular permeability caused by inflammation . The exudation of protein-rich fluid is accompanied by migration of inflammatory cells into the effusion :
• Dogs / cats : TP > 25 g / L , NCC > 5000 cells / µ L
• Exudates are hazy to cloudy , yellow , tan , cream , orange , and may have a putrid smell if bacteria are involved .
Neutrophils are the dominant cell present in most exudates . With inflammation due to bacterial infections , degenerate neutrophils will be the predominant cells present , unless the bacterial toxin is weak or produced in small amounts . Lack of bacteria and / or organisms does not rule out an infectious cause .
A septic exudate refers to the presence of intra- and extracellular bacteria , and a non-septic exudate refers to the absence of bacteria and a negative culture . The classification of an effusion as non-septic should be based on a negative culture . Non-septic exudates are caused by acute pancreatitis , necrosis associated with intracavitatory neoplasia or secondary to intracavitatory organ inflammation . Septic exudates are caused by disorders like GIT rupture or penetrating wounds . ( Figure 3 )
If acute pancreatitis is suspected to be the cause of a nonseptic exudate , fluid lipase may be helpful . A DGGR-lipase activity in fluid of > 500 U / L , or twice serum lipase ; or a SpecCPL of > 500 μg / L is highly specific for pancreatitis as the cause of the exudate .
Exception : FIP exudate : Caused by the FIP virus , has a very specific appearance – straw-coloured , viscous , TP > 25 g / L , NCC < 5000 cells / µ L . Cell population is a mixture of neutrophils and macrophages . ( The reason for the low cellularity is that although there is a vasculitis in FIP , the focus of inflammation is inside the blood vessels and not in the body cavity – so vessels are leaky to plasma proteins , but inflammatory cells remain in the blood vessel walls )
3 . Haemorrhagic Effusion Causes include haemostatic defects , trauma or neoplasia invading blood vessel walls . The fluid is red and bloody in appearance . Dominated by red blood cells . PCV > 1 %
• All species : TP > 25 g / L , NCC > 2000 cells / µ L
With haemorrhage of more than 24 hours duration or chronic persistent haemorrhage , erythrophagocytosis and / or haemosiderin or haematoidin should be present . With peracute haemorrhage or iatrogenic blood contamination , platelets could be present . If both erythrophagocytosis and platelets are present , chronic persistent haemorrhage or previous haemorrhage and iatrogenic blood contamination are present . A fluid PCV of > 1 % indicates that haemorrhage is contributing to the effusion . Inadvertent aspiration of the liver or spleen could also cause a cytological appearance similar to haemorrhage . The PCV of this fluid will then be higher or similar to the peripheral blood PCV .
The most common causes of haemoperitoneum in dogs is splenic disease , specifically haemangiosarcoma . However , fluid cytology has a very low sensitivity for detecting cells from haemangiosarcomas in haemorrhagic fluids , due to the dilution effect of the blood and poor exfoliation of cells from these tumours . In other words , neoplastic cells from haemangiosarcoma are rarely seen in haemoperitoneum caused by this tumour . The absence of neoplastic cells does not at all rule out a haemangiosarcoma .
In cats , the most common cause of haemorrhagic effusions is trauma , followed by various types of neoplasia .
4 . Uroperitoneum Caused by a ruptured bladder . TP and NCC are variable – both very low initially ( because urine has a very low protein and cell content ), then increasing with time as urine is irritant to the peritoneum and causes a low-grade inflammation , so that the fluid becomes an exudate with time . There may be a urine odour . If uroperitoneum is suspected , fluid creatinine concentrations must be measured .
Figure 3 : Sediment smear of a septic peritoneal exudate from a horse with caecal rupture . The dominant population consists of degenerate neutrophils , some of which contain intracellular bacteria . ( 1000x , Diff- Quick )
Two out of the following three criteria are diagnostic for uroperitoneum : - Fluid creatinine > 2x serum creatinine - Fluid creatinine > 4x normal serum creatinine
( upper reference limit ) - Fluid K + > 1.4 x serum K +
Issue 01 | MARCH 2018 | 23