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 Cardiac failure, or isolated RV (pulm HT)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 c-wave: bulging of tricuspid valve into R atriuminto R 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