Disorders of water balance

Outline Introduction of water and sodium balance Edema Alterations in isotonic fluid volume isotonic fluid volume deficit isotonic fluid volume excess Alterations in sodium concentration hyponatremia hypernatremia

Introduction of water and sodium balance

Water and sodium balance Total fluid volume and distribution Body fluid composition Osmolality of the body fluid Water balance Mechanisms of regulation of body fluid and sodium balance

Total fluid volume and distribution Total body fluid accounts for 60% of body mass in males. Total body fluid is mainly distributed in intracellular and extracellular compartments Intracellular fluid ( ICF) : 40% Extracellular fluid (ECF): 20% Interstitial fluid: 15% Plasma: 5%

Body fluid composition The ICF is separated from the ECF by a selective cell membrane that is only permeable to a limited number of substances such as water, oxygen and carbon dioxide, but not to most of the electrolytes in the body. The concentration of ions in the interstitial fluid and plasma are considered to be equal except for protein.

Osmolality of the body fluid The total osmolality is almost equal among plasma, the interstitial and intracellular fluids with a range from 280-310 mOsm/L, due to a free permeability of cell membrane to water. Nearly 80% of the osmolality of plasma and the interstitial fluid is induced by sodium and chloride ions. And approximately half of the intracellular osmolality is caused by potassium.

Water balance Water intake Water output Ingestion in the form of liquid and water in food: 2100ml/day Metabolism in the body following the oxidation of carbohydrates: 300ml/day Water output Insensible evaporation from respiratory tract and through the skin: 700ml/day Sweating: 100ml/day Feces: small amount Urine: 1500ml/day

Mechanisms of regulation of body fluid and electrolyte balance Sensation of thirst Antidiuretic hormone (ADH) Renin-angiotensin-aldosterone system Atrial natriuretic peptide (ANP)

ADH Main target sites: distal tubules and collecting ducts in kidney Function: to Promote the water reabsorption and cause increased ECF volume and decreased urinary output. Stimulating factors: Blood pressure↓ Plasma osmolality↑ Blood volume ↓

Renin-angiotensin-aldosterone system Arterial pressure ↓ Plasma sodium content↓ Sympathetic nerve ↑ Arterial pressure↑ ECF volume ↑ Glomerulus (juxtaglomerular cells) Renal retention of sodium Increase potassium secretion renin Angiotensin I Angiotensin II Adrenal gland aldosterone Angiotensin converting enzyme

ANP ANP is a hormone produced by specific cells of cardiac atrim in response to blood volume expansion. Function: ANP inhibits the reabsorption of sodium and water by the renal tubules, which in turn increases urinary excretion and helps to return blood volume back toward normal. ANP exerts a negative regulation against ADH in the central nervous system.

Edema

Definition of edema Edema can be defined as palpable swelling produced by expansion of the interstitial fluid volume. Edema is caused by excessive fluid in the interstitial compartment. Edema is not a special disease, it’s just a symptom that occurs in some other disease.

Causes and pathogenesis of edema Increased capillary filtration pressure Decreased capillary colloidal osmotic pressure Increased capillary permeability Obstruction to lymph flow

Increased capillary filtration pressure Increased vascular volume heart failure kidney disease pregnancy Venous obstruction liver disease with portal vein obstruction venous thrombosis

Decreased capillary colloidal osmotic pressure Increased loss of plasma proteins protein-losing kidney diseases extensive burns Decreased production of plasma proteins liver disease starvation malnutrition

Increased capillary permeability Inflammation Allergic reaction Malignancy Tissue injury and burns Increased capillary permeability leads to the leakage of proteins from C into interstitial compartment.

Obstruction to lymph flow Malignant obstruction of lymphatic structures Surgical removal of lymph nodes Lymphatic vessels take excessive fluid in the interstitial compartment back to blood vascular system. Obstruction of these vessels results in excessive fluid retention in the interstitial compartment.

Manifestations of edema Life threatening in some locations, such as brain, larynx, lungs. Interfering with movement and limiting joint motion. Increasing the distance for diffusion of oxygen, nutrients and wastes at the tissue level. Edema affects cellular metabolism.

Treatment of edema Correcting or controlling the cause , and preventing tissue injury Diuretic therapy Elastic support stockings and sleeves for patients with lymphatic or venous obstruction Administering albumin intravenously to raise the colloidal osmotic pressure when edema is caused by hypoalbuminemia.

Alterations in isotonic fluid volume

Alterations in isotonic fluid volume Isotonic fluid volume disorders represent an expansion or contraction of the ECF brought about by proportionate changes in both sodium and water. Two types: Isotonic fluid volume deficit Isotonic fluid volume excess They refer to an increase or decrease in the ECF resulting from proportionate changes in both sodium and water.

Isotonic fluid volume deficit Definition: Isotonic fluid volume deficit results when water and sodium are lost in isotonic proportions Causes: Inadequate fluid intake Excessive fluid losses

Inadequate fluid intake Oral trauma or inability to swallow Inability to obtain fluids Impaired thirst sensation Therapeutic withholding of fluids Unconsciousness or inability to express thirst

Excessive fluid losses Excessive gastrointestinal fluid losses vomiting, diarrhea, gastrointestinal suction Excessive renal losses diuretic therapy, osmotic diuresis, adrenal insufficiency Excessive skin losses fever, exposure to hot environment, burns and wounds that remove skin Third-space losses intestinal obstruction, edema, ascites Fluid can be lost through the following pathways

Manifestations of isotonic fluid volume deficit Acute weight loss Compensatory increase in ADH Decreased extracellular fluid volume Shock Symptoms and signs of shock appear, such as increase HR, cold and pale skin, decreased BP.

Treatment of isotonic fluid volume deficit Treating the underlying causes Using isotonic electrolyte solutions for replacement.

Isotonic fluid volume excess Definition: It represents an isotonic expansion of the extracellular fluid compartment. Water and sodium are increased in isotonic proportions. Causes: Inadequate sodium and water elimination Excessive sodium and water intake

Inadequate sodium and water elimination Congestive heart failure Renal failure Hyperaldosteronism Liver failure In heart failure, water and sodium retention usually occurs as a compensatory mechanism, which is caused by increased levels of ADH and aldosterone. In renal failure, GFR decreases. In hypersteronism, level of aldosterone increases, which may lead to water and sodium retention. Liver failure often leads to renal dysfunction.

Excessive sodium and water intake Excessive sodium intake Food, sodium containing medications or fluid Excessive fluid intake ingestion of fluid in excess of output administration of fluids or blood at an excessive rate excessive administration of sodium-containing

Manifestations of isotonic fluid volume excess Acute weight gain Increased interstitial fluid volume Dependent and generalized edema Increased vascular volume Increased vascular volume will increase the preload of heart. Within limits, increased preload results in increased cardiac output due to Frank-starling mechanism. But long-standing or excessive preload will impair the pumping ability of the heart.

Treatment of isotonic fluid volume excess Sodium-restricted diet Diuretic therapy is commonly used to increase sodium elimination. Restricting salt intake and using diuretics to increase sodium elimination.

Alterations of sodium concentration

Alterations of sodium concentration Hyponatremia Hypernatremia The normal range of sodium concentration in plasma is between

Hyponatremia Definition Hyponatremia represents a decrease in plasma sodium concentration below 135 mmol/L.

Causes of hyponatremia Excessive sodium losses and replacement with sodium-free water Excessive water intake in relation to output

Excessive sodium losses and replacement with sodium-free water Exercise- or heat-induced sweating Gastrointestinal losses Renal losses (some chronic renal diseases) Excessive sodium losses may occur through the following pathways.

Excessive Water Intake in Relation to Output Excessive administration of sodium-free solutions Repeated irrigation of body cavities with sodium-free solutions Irrigation of gastrointestinal tube with distilled water Kidney disorders that impair water elimination Increased ADH level

Manifestations of hyponatremia Signs Related to Hypo-osmolality of Extracellular Fluids and Movement of Water Into Brain Cells and Neuromuscular Tissue Muscle cramps, Weakness, Headache, Depression, Personality changes, Lethargy and coma Gastrointestinal Manifestations Anorexia, nausea, vomiting, Abdominal cramps, diarrhea Laboratory Values Serum sodium level below 135 mmol/L Decreased serum osmolality In hyponatremia, because of decreased osmolality in ECF, water moves into cells from EC compartment. Excessive water in brain cells and neuromuscular tissue can lead to the following symptoms and signs.

Treatment of hyponatremia water intoxication Limit water intake Administer diuretics sodium deficiency Administer saline solution orally or intravenously limiting water intake and administering diuretics to increase water elimination, when hyponatremia is caused by water intoxication. Administering saline solution orally or intravenously, when hyponatremia is caused by sodium deficiency.

Hypernatremia Definition Hypernatremia implies a plasma sodium level above 145 mmol/L.

Causes of hypernatremia Excessive Water Losses Decreased Water Intake Excessive Sodium Intake

Excessive water losses Watery diarrhea Excessive sweating Hyperventilation Decrease level of ADH

Decreased Water Intake Unavailability of water Oral trauma or inability to swallow Impaired thirst sensation Withholding water for therapeutic reasons Unconsciousness or inability to express thirst

Excessive Sodium Intake Rapid or excessive administration of sodium-containing solutions

Manifestations of hypernatremia Thirst and signs of increased ADH levels Oliguria or anuria Intracellular dehydration Dry skin and mucous membranes tongue rough and fissured decreased salivation Signs related to hyperosmolality of ECF and movement of water out of brain cells Headache, agitation and restlessness, seizure and coma Increased osmolality in ECF stimulates thirst , promotes the release of ADH and results in water movement out of the cells into ECF.