Fluid volume imbalances

FLUID VOLUME IMBALANCES

Prepared by Salman

NORMAL FLUID VOLUME•

• Approximately 60% of the weight of a

• typical adult consists of fluid

Third spacing • Loss of ECF into a space that does not contribute to

equilibrium between the ICF and the ECF is referred to as a third-space fluid shift, or “third spacing”

• Third spacing is the unusual accumulation of fluid in a transcellular space

REGULATION OF BODY FLUID COMPARTMENTS• OSMOSIS – movement of water from the low solute

concentration to a heigher solute concentration to lower concentration through a semipermeable membrane

• Tonicity- is the ability of all solutes to cause an osmotic driving force that promotes water movement from one compartment to another

• Osmotic pressure is the amount of hydrostatic pressure needed to stop the flow of water by osmosis. It is primarily determined by the concentration of solutes

• OSMOLALITY is the concentration of a solution in terms of osmoles of solute per kilogram of solvent . The number of dissolved particles contained in a unit of fluid determines the osmolality of a solution

• Diffusion – it is the natural tendency of a substance to move from an area of higher concentration to one of lower concentration

• FIILTRATION- Movement of water and solutes occurs from an area of high hydrostatic pressure to an area of low hydrostatic pressure

SODIUM-POTASSIUM PUMP

• The process of moving sodium and potassium ions across the cell membrance is an active transport process involving the hydrolysis of ATP to provide the necessary energy. It involves an enzyme referred to as Na+/K+-ATPase. This process is responsible for maintaining the large excessof Na+ outside the cell and the large excess of K+ ions on the inside.

SYSTEMIC ROUTES OF GAINS AND LOSSES

• Kidneys normal output is 1ml/kg/hr 1 -2 litres of urine per day

Skin fluid loss through sweating Actual sweat losses can vary from 0 to 1000ml or more

every hour, depending on factors such as the environmental temperature.

• LUNGS The lungs normally eliminate water vapor (insensible loss) at a rate of approximately 300 mL every day.

Gastrointestinal tract usual loss through the GI tract is 100 to 200 mL daily

HOMEOSTATIC MECHANISMS

• Kidneys• kidneys normally filter 180 L of plasma every day in the

adult and excrete 1 to 2 L of urinE• Regulation of ECF volume and osmolality by selective

retention and excretion of body fluids.• Regulation of normal electrolyte levels in the ECF by

selective electrolyte retention and excretion.• Regulation of pH of the ECF by retention of hydrogen

ions.• Excretion of metabolic wastes and toxic substances. 

 HYPOTHALAMIC REGULATION

Decrease in plasma volume

Sensed by osmoreceptors

stimulate thirst , impulses to the posterior pituitary

increases the release of ADH, which then travels in the blood to the kidneys

increased reabsorption of water and decreased urine output

• Pituitary functions stores ADH produced by hypothalamus , Functions of

ADH include maintaining the osmotic pressure of the cells by controlling the retention or excretion of water by the kidneys and by regulating blood volume.

Adrenal functions Aldosterone,- mineralocorticoid ↑ production - sodium retention, and potassium loss ↓ production - sodium and water loss and potassium

retention

Heart and blood vessel functions

• Atrial natriuretic peptide (ANP) IS PRODUCED BY atrial wall

• include increased atrial pressure, angiotensin11 stimulation, and sympathetic stimulation

• The action of ANP is the direct opposite of the rennin-angiotensin-aldosterone system; ANP decreases blood pressure and volume

Parathyroid • regulate calcium and phosphate balance by means of

parathyroid hormone(PTH)

Other mechanisms

• Baroreceptors • located in the left atrium and carotid and aortic arches. • receptors respond to changes in the circulating blood

volume and regulate sympathetic and parasympathetic neural activity as well as endocrine activities

• ↓in arterial pressure stimulate sympathetic nervous system and increase in cardiac rate, conduction and contractility and an increasing circulating blood volume

Rennin-Angiotensin-Aldosterone System(RAAS)

FLUID VOLUME IMBALANCES

• Iso-osmotic volume expansion• Iso-osmotic volume contraction• Hyperosmotic volume expansion • Hyperosmotic volume contraction • Hypo-osmotic volume expansion • Hypo-osmotic volume contraction •  

Iso-osmotic volume expansion

• Causes• Infusion of isotonic fluids eg; .9% Nacl solution

• Extracellular fluid volume increases• Extracellular fluid osmolality does not change .so water

does not shift between the ECF and icf• plasma protien concentration decreases because of

dilutional effect of additional fluid ,resulting in decresed plasma colloid osmotic pressure ,water moves out of blood vessel and disturbed in the interstitial compartment.

•

• Haematocrit decreases because of addition of fluid to ECF dilutes RBC. Because ECF osmolality is unchanged the RBC neither shrink or swell

• Arterial blood pressure increases because ECF volume increases

• corrective response • Change in plasma volume is sensed by vascular

volume receptors and brings about excretion of large volume of hypotonic urine(water diuresis) which gradually restores the plasma volume and osmolality to normal

ISO-OSMOTIC VOLUME CONTRACTION• Causes • Diarrhoea, vomiting• Haemorrhage • Ascitis and burns

• consequences • ECF volume decresed • ECF osmolality does not change ,so water does between not shift the ECF and ICF compartments

• Plasma protein concentration is increased because of loss of ECF concentrates .Due to presence of plasm protein ,the plasma volume is less reduced as compared to interstitial fluid.

• Haematocrit is increased because of loss of ECF concentrates the RBCs.because ECF osmolality is unchanged ,the RBC will neither shrink nor swell

• Arterial blood pressure is decresded because of decreased in ECF volume.

•  corrective response • Decreased plasma volume inhibits the vascular volume

sensors and reflexly restores the plasma volume by decreasing Na+ and water excretion .it is important to note that the thirst produced by volume receptors is quenched with isotonic salt solution instead of plain water.

HYPEROSMOTIC VOLUME EXPANSION

• Causes .• Administratio of excessive amount of hypertonic saline

• consequences• ECF osmolality is increased ,because osmoles (nacl)

have been added to ECF • Water shifts from ICF to ECF ,as a result of this shift ICF

osmolaity increases until it equals that of ECF • ECF volume increases because of addition of fluid as

well as shift from ICF to ECF ( volume expansion)• ICF volume is decreased due to fluid shift

• Plasma protein concentration decreases becauses of the increases in ECF volume

• Haematocrit decreases because of increase in ECF VOLUME .RBC shrink and ECF osmolality is increased

• Arterial blood pressure is increased because of increase in ECF volume

corrective response

• Increased plasma osmolality promotes water retention while increase in plasma volume inhibits the same

• .under such circumstances volume oversides tonicity .Therefore ,the increased plasma volume would suppress thirst and ADH leading to excretion of large volume of hypotonic urine which bring down the plasma volume.

• The natriuretic hormones ,which is secreted only ,in response to osmolality and not to volume changes,promotes na+ excretion and corrects osmolality.

HYPEROSMOTIC VOLUME CONTRACTION • CAUSES :• Decresed water intake• Diabetes mellitus • Diabetes insipidus • Excessive sweating in a desert • Alcoholism • In tracheostomy patients ,insensible loss of water upto

500ml occurs from lungs

CONSEQUENCES

• ECF volume is reduced because of loss of water • ECF osmolality increases because more water is lost• Water shifts from ICF ti ECF ,as a result of this shift ,ICF

osmolality increases until it equals that of ECF • ICF volume decreases because of shift of water • Plasma protein concentration increases becauses of the

decrease in ECF volume• Haematocrit is also expected to increase ,but it remains

unchanged because water shifts out of RBC s decreasing their volume and offsetting the concentrating effects of the decreased ECF volume

CORRECTIVE RESPONSE

• Increased ECF osmolality stimulates the osmoreceptors ,while reduced plasma volume inhibits the volume receptors .Either of them would relexly restore the plasma osmolality to normal level

ETIOLOGY AND RISK FACTORS

• Vomiting,• Diarrhea ,• GI suctioning,• Sweating, • Decreased intake as in nausea or inability to gain access to fluid

• Diabetes insipidus

• Adrenal insufficiency

• Osmotic dieresis

• Hemorrhage

• Coma

• Third-space fluid shifts or the movement of fluid from the vascular system to other body spaces (eg. With edema formation in burns,

• ascites with liver dysfunction also cause FVD.

CLINIAL MANIFESATIONS • Acute weight loss • Decreased skin turgor• Oliguria• Concentrated urine• Postural hypotension• A weak, rapid heart rate • Flattened neck veins• Increased temperature• Decreased central venous pressure• Cool, clammy skin• Thirst, Anorexia• Nausea, , Muscle weakness

DIAGNOSTIC FINDINGS• Health history and physical examination

• Blod investigations-Hematocrit value: hematocrit value is greater than normal because there is decreased plasma volume.

• Hypokalemia occurs with GI and renal losses.• Hyperkalemia occurs with adrenal insufficiency.• Hyponatremia occurs with increased thirst and ADH

release• Hypernatremia results from increased insensible losses

and diabetes insipidus.•

MANAGEMENTmedical

• FLUID RESTORATION• Oral rehydration . Oral glucose replacement solutions

• Intravenous rehydration isotonic fluids