Leicester Warwick Medical School

Tissue Fluid Formation and Oedema

Dr. Kevin Westkpw2@le.ac.uk

Department of Pathology

Tissue Fluid Formation - Objectives 1

Control of normal interstitial fluid formation

Definition of oedemaDefinition of pleural effusion, pericardial

effusion and ascitesDistinction 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 component60% male50% female3 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 pressureOncotic pressureEndothelial integrityLymphatic system

Interstitial Fluid

Fluid between cellsDerived from capillariesSolutes similar to plasma except for

protein content

Movement Of Fluid Across Capillaries

Capillary (hydrostatic) pressure Interstitial fluid (hydrostatic) pressurePlasma oncotic pressure Interstitial fluid oncotic pressure

Capillary Pressure

Forces fluid from capillary to interstitiumArterial end higher than venous endArterial approx. 30 mmHgVenous approx. 10 mm Hg

Interstitial Fluid Pressure

Maybe positive or negativeNegative - forces fluid into interstitiumPositive - forces fluid into capillaryApprox. minus 3 mm Hg in loose

connective tissueHigher 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 capillaryConcentration is approx 40 % of that in

plasmaApprox 8 mm Hg

Balance Sheet - Arterial

OutwardCap. pressure 30

Negative interstitial

fluid pressure 3

Interstitial oncotic

pressure 8

Total 41

InwardPlasma oncotic

pressure 28

Net out 13

(Filtration pressure)

Balance Sheet - Venous

OutwardCap. pressure 10

Negative interstitial

fluid pressure 3

Interstitial fluid

oncotic presure 8

Total 21

InwardPlasma oncotic

pressure 28

Net inward 7

(Reabsorption

pressure)

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 pressureEndothelial integrityLymphatic 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 pressureReduced oncotic pressureEndothelial 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 loss of albumin across glomerulus

Hepatic disease inadequate albumin synthesis

Malnutrition inadequate albumin synthesis

Lymphatic Obstruction

TumoursFibrosis InflammationSurgeryCongenital abnormality

Generalised Oedema

Congestive cardiac failureRight ventricular failureRenal diseaseLiver 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 diseaseCauses 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 heart failure, inflammation, tumour

Pericardial effusion 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