Leicester Warwick Medical School
Tissue Fluid Formation
and Oedema
Dr. Kevin West
kpw2@le.ac.uk
Department of Pathology
Tissue Fluid Formation - Objectives 1
Control of normal interstitial fluid
formation
 Definition of oedema
 Definition of pleural effusion, pericardial
effusion and ascites
 Distinction between transudate and
exudate

Tissue Fluid Formation - Objectives 2
Common causes and mechanisms of
development of oedema
 Pulmonary oedema - causes and
effects
 Cerebral oedema - causes and effects

Water
Major body component
 60% male
50% female
 3 compartments




intracellular
extracellular interstitial
extracellular intravascular
Osmolality
Osmotic pressure related to number of
particles of solute
 Oncotic pressure describes osmotic
pressure exerted by proteins
 Effect of oncotic pressure small but
significant across capillaries

Control of Interstitial Fluid
Hydrostatic pressure
 Oncotic pressure
 Endothelial integrity
 Lymphatic system

Interstitial Fluid
Fluid between cells
 Derived from capillaries
 Solutes similar to plasma except for
protein content

Movement Of Fluid Across Capillaries
Capillary (hydrostatic) pressure
 Interstitial fluid (hydrostatic) pressure
 Plasma oncotic pressure
 Interstitial fluid oncotic pressure

Capillary Pressure
Forces fluid from capillary to interstitium
 Arterial end higher than venous end
 Arterial approx. 30 mmHg
 Venous approx. 10 mm Hg

Interstitial Fluid Pressure
Maybe positive or negative
 Negative - forces fluid into interstitium
 Positive - forces fluid into capillary
 Approx. minus 3 mm Hg in loose
connective tissue
 Higher in denser connective tissue

Plasma Oncotic Pressure




Proteins are the only solutes which do not
pass freely between plasma and interstitium
Thus it is only proteins which exert a
significant osmotic effect across capillary
walls
Albumin is the most abundant plasma protein
Approx 28 mm Hg (Albumin = 21.8)
Interstitial Oncotic Pressure
A small amount of protein is present in
the interstitium
 Tends to force fluid out of capillary
 Concentration is approx 40 % of that in
plasma
 Approx 8 mm Hg

Balance Sheet - Arterial

Outward

Inward
Cap. pressure
30
Negative interstitial
fluid pressure
3
Interstitial oncotic
pressure
8
Plasma oncotic
pressure
Total
Net out
13
(Filtration pressure)
41
28
Balance Sheet - Venous

Outward

Cap. pressure
10
Negative interstitial
fluid pressure
3
Interstitial fluid
oncotic presure
8
Total
21
Inward
Plasma oncotic
pressure
Net inward
(Reabsorption
pressure)
28
7
Lymphatic System
The lymphatic system provides a route
for the transport of fluids and protein
away from the interstitium
 System of fine lymphatic channels
throughout the body passing via lymph
nodes to thoracic duct
 Valves ensure one-way flow

Oedema
Hydrostatic pressure
 Oncotic pressure
 Endothelial integrity
 Lymphatic integrity

Oedema

Definition
An increased volume of interstitial fluid
in a tissue or organ
May be localised or generalised
(systemic)
Causes of Oedema
Raised capillary pressure
 Reduced oncotic pressure
 Endothelial damage (inflammation)
 Impaired lymphatic drainage

Raised Capillary Pressure

Cardiac failure




right ventricular failure - systemic oedema
left ventricular failure - pulmonary oedema
congestive cardiac failure - both
Local venous obstruction



deep vein thrombosis
external compression
SVC obstruction
Reduced Oncotic Pressure

Renal disease


Hepatic disease


loss of albumin across glomerulus
inadequate albumin synthesis
Malnutrition

inadequate albumin synthesis
Lymphatic Obstruction
Tumours
 Fibrosis
 Inflammation
 Surgery
 Congenital abnormality

Generalised Oedema
Congestive cardiac failure
 Right ventricular failure
 Renal disease
 Liver disease

Generalised Oedema



Commonly causes
swelling of ankles
Swelling may extend
higher
Sacral oedema in
recumbent patients
Right Ventricular Failure


Raised jugular
venous pressure
also seen
Enlarged liver also
common due to
congestion (nutmeg
liver)
Pulmonary Oedema




Usually caused by LVF
Raised pressure across
pulmonary capillaries
Causes shortness of
breath
Due to ischaemic heart
disease or hypertension
Pulmonary Oedema
Congestive Cardiac Failure
Combination of left and right ventricular
failure
 Common in ischaemic heart disease
 Causes systemic and pulmonary
oedema

Cerebral Oedema




Causes increased
intracranial pressure
Fatal if left untreated
Generalised in
hypoxia, injury
Surrounding other
lesions eg tumour,
abscess
Fluid in Body Cavities

Pleural effusion


Pericardial effusion


heart failure, inflammation, tumour
inflammation, tumour
Ascites (peritoneal effusion)

cirrhosis, heart failure, tumour
Pleural Effusion
Pericardial Effusion
Ascites

Most severe cases
associated with


cirrhosis of the liver
intra-abdominal
malignancy
Superior Vena Cava Obstruction