The physiology of edema.The physiology of edema.

Edema:Edema:• The abnormal accumulation of fluid The abnormal accumulation of fluid

in a specific organ vs generalized.in a specific organ vs generalized.

• In capillary: Balance between In capillary: Balance between hydrostatic pressure hydrostatic pressure and and oncotic oncotic (colloid osmotic) pressure.(colloid osmotic) pressure.

Hydrostatic pressure:Hydrostatic pressure:• Intra-capillary vs interstitialIntra-capillary vs interstitial• Capillary pressures vary:Capillary pressures vary:• Nail bed capillaries: 32 mmHg at Nail bed capillaries: 32 mmHg at

arteriolar end and 15 mmHg at venous arteriolar end and 15 mmHg at venous end. Mean 25 mmHg.end. Mean 25 mmHg.

• Hydrostatic pressure gradient:Hydrostatic pressure gradient:• Intra-capillary hydrostatic pressure – Intra-capillary hydrostatic pressure –

interstitial fluid hydrostatic pressureinterstitial fluid hydrostatic pressure

Interstitial hydrostatic Interstitial hydrostatic pressure:pressure:• Varies from one organ to another:Varies from one organ to another:• Subcutaneous tissue: Subcutaneous tissue:

Subatmospheric (-2 mmHg)Subatmospheric (-2 mmHg)• Liver, kidney: +Liver, kidney: +• Brain: As high as 6 mmHgBrain: As high as 6 mmHg

Oncotic pressure:Oncotic pressure:• Capillary wall usually impermeable to Capillary wall usually impermeable to

plasma proteins and other colloids.plasma proteins and other colloids.• Only water and small solutes cross Only water and small solutes cross

capillary wall.capillary wall.• Crystalloids vs colloidsCrystalloids vs colloids

• These colloids exert an osmotic These colloids exert an osmotic pressure of about 25 mmHg.pressure of about 25 mmHg.

• The colloid osmotic pressure due to The colloid osmotic pressure due to the plasma colloids=oncotic the plasma colloids=oncotic pressure.pressure.

Edema:Edema:• Due to disturbance in hydrostatic Due to disturbance in hydrostatic

and/or oncotic pressure between and/or oncotic pressure between intra-capillary and interstitial intra-capillary and interstitial component.component.

Organ specific:Organ specific:• Brain: Cerebral edemaBrain: Cerebral edema

• Lung: Intra-alveolar=pulmonary edema, Lung: Intra-alveolar=pulmonary edema, intra-pleural=pleural effusionintra-pleural=pleural effusion

• Peritoneum=ascitesPeritoneum=ascites

• Severe generalized edema=anasarcaSevere generalized edema=anasarca

Reduced oncotic pressure:Reduced oncotic pressure:• Reduction in production of colloids--- Reduction in production of colloids---

plasma proteins.plasma proteins.

• Liver failureLiver failure• MalnutritionMalnutrition

• Increase in loss of colloids--- plasma Increase in loss of colloids--- plasma proteins.proteins.

• Nephrotic syndromeNephrotic syndrome• Catabolic statesCatabolic states

Increase capillary hydrostatic Increase capillary hydrostatic pressure:pressure:• Venous end: Heart failure, deep Venous end: Heart failure, deep

venous thrombosis, superior vena venous thrombosis, superior vena cava obstruction etc.cava obstruction etc.

• Arterial end: Pre-capillary dilatation. Arterial end: Pre-capillary dilatation. Calcium channel blockers.Calcium channel blockers.

Increased interstitial oncotic Increased interstitial oncotic pressure:pressure:• Lymphatic obstruction:Lymphatic obstruction:• Primary vs secondary group.Primary vs secondary group.

Capillary leaks:Capillary leaks:• Result of capillary damage:Result of capillary damage:• Pleura: Infections, tumorsPleura: Infections, tumors• Alveoli: Inhalation of noxious Alveoli: Inhalation of noxious

substance, eg chlorine gas etcsubstance, eg chlorine gas etc

Diverse causes of edema:Diverse causes of edema:• AnaemiaAnaemia• HypothyroidismHypothyroidism

Hormones involved in Hormones involved in edema:edema:• Renin angiotensin aldosterone Renin angiotensin aldosterone

system: system: secondary secondary hyperaldosteronismhyperaldosteronism

• ADH (Vasopressin)ADH (Vasopressin)

• ANPANP

Clinical physiological approach Clinical physiological approach to edema:to edema:• Hypervolemia:Hypervolemia:

• VsVs

• Normovolemia:Normovolemia:

Jugular venous pressure:Jugular venous pressure:• Elevated Elevated andand pulsating: pulsating:• =hypervolemia=hypervolemia• Then edema:Then edema:• Due to increased capillary hydrostatic Due to increased capillary hydrostatic

pressure:pressure:• Cardiac failure, or isolated RV (pulm HT)Cardiac failure, or isolated RV (pulm HT)• Hypervolemia caused by transfusionHypervolemia caused by transfusion

Normal JVP:Normal JVP:• UnilateralUnilateral• Unilateral increase in capillary pressureUnilateral increase in capillary pressure• Deep venous thrombosisDeep venous thrombosis• OR:OR:• Unilateral increase in interstitial colloid Unilateral increase in interstitial colloid

osmotic pressureosmotic pressure• Lymphatic obstruction (radiation, Lymphatic obstruction (radiation,

filariasis, congenital)filariasis, congenital)

• Edema due to capillary hypertension Edema due to capillary hypertension with normal venous pressure:with normal venous pressure:

• Pre-capillary dilatation:Pre-capillary dilatation:• Calcium channel blockersCalcium channel blockers

Generalized edema without Generalized edema without hypervolemia:hypervolemia:• Decreased capillary colloid oncotic pressure: Decreased capillary colloid oncotic pressure:

liver, kidney, catabolic states, malnutrition.liver, kidney, catabolic states, malnutrition.

• Increased interstitial colloid oncotic Increased interstitial colloid oncotic pressure: lymphatic.pressure: lymphatic.

• Increase in capillary permeability: Increase in capillary permeability: Inflammation, toxins, severe anaemiaInflammation, toxins, severe anaemia

Pressure changes in the Pressure changes in the heart:heart:• Atria: Study curve in Ganong: Atria: Study curve in Ganong:

jugular venous pressure curvejugular venous pressure curve, , also known as also known as flobogramflobogram, indicative , indicative of pressure changes in superior vena of pressure changes in superior vena cava/ right atrium.cava/ right atrium.

• 3 waves in the curve:3 waves in the curve:

• a-wave: atrial systolea-wave: atrial systole• c-wave: bulging of tricuspid valve into c-wave: bulging of tricuspid valve into

R atriumR atrium• v-wave: rise in atrial pressure, just v-wave: rise in atrial pressure, just

before tricuspid valve opens during before tricuspid valve opens during diastole.diastole.

•Clinical application of these 3 Clinical application of these 3 waves:waves:

• Sinus rhythm or not.Sinus rhythm or not.• Pulmonary hypertensionPulmonary hypertension• 3`rd degree heart block3`rd degree heart block• Patency between SVC and RAPatency between SVC and RA• Tricuspid regurgitation and stenosisTricuspid regurgitation and stenosis