Pathophysiology: Fluid and Electrolytes

Intracellular fluid

Fluid inside the cells; 2/3

What is the major cation in the ICF?

Potassium

Extracellular fluid

Any fluid that remains outside the cells which includes interstitial and intravascular fluid; 1/3

What is the major cation in the ECF?

Sodium

Fluid movement

What serves as a primary barrier to movement inside/outside the cell?

Cell membrane

Edema

general term for too much fluid

Dehydration

general term for too little fluid

Fluid homeostasis

Composition of body fluids including electrolytes, acid/base balance and regulation of fluid (both intake and output) volume

Who are the major players of fluid homeostasis?

- kidneys

- RAA system

- osmoreceptors

- thirst sensation

- baroreceptors

- antidiuretic hormone

- natriuretic peptides

Renin-angiotensin-aldosterone system

signaling pathway responsible for regulating the body's blood pressure - stimulated by low pressure causing the kidneys to release an enzyme called renin (vasoconstriction)

What signals the RAAS?

- hypotension

- hypovolemia

- low cardiac output due to low circulation

- dehydration

Baroreceptors signal the secretion of....

renin from the kidneys

Renin releases....

aldosterone

Aldosterone causes sodium and water ____ and potassium ___

retention; excretion

Spironolactone

aldosterone antagonist; potassium sparing

Spirolactone releases ___ and ___ and holds onto ____

sodium and water; potassium

Angiotensin converting enzyme inhibitor

inhibits movement through the RAAS causing high pressure and vasodilation to lower the blood pressure

Osmoreceptors

located in the hypothalamus which respond to changes in the extracellular tonicity; monitor and respond to distribution of water between intracellular and extracellular fluid; concentration

Baroreceptors

detect pressure changes in the blood vessels to help maintain blood pressure at a constant level

Which receptors signal pressure?

Baroreceptors

Which receptors signal fluid concentration?

Osmoreceptors

Anti-diuretic hormone

another term for vasopressin, released from the posterior pituitary gland to keep up the volume in the bloodstream at all times - decrease in urine production

If pressure is low what system is kicked in?

Sympathetic nervous system - vasoconstrictor - causing pressure to increase

Anti-diuretic hormone - decreased urine output to hold onto fluid

Where are pressure sensitive receptors located?

Kidneys or afferent arterioles

What do the kidneys release?

Renin to activate RAAS to stimulate sympathetic nervous system

What do the osmoreceptors tell the body to do in time of thirst?

drink water

What is another term for antidiuretic hormone?

vasopressin

Where is vaspopressin released?

posterior pituitary

Syndrome of inappropriate antidiuretic hormone (SIADH)

too much ADH

What happens when there is too much ADH?

- fluid overload

- decreased urine output

- urine concentration increases (dark)

- blood osmolality decreases

Diabetes insipidus

too little ADH

What happens when there is too little ADH?

- fluid loss

- increased urine output

- urine concentration decreases (clear)

- blood osmolality increases

Osmosis

passage of liquid through a semi-permeable membrane from an area of low concentration to an area of high concentration of solute

Capillary-interstitial fluid exchange

Capillary hydrostatic pressure

pressure exerted by the capillaries causing water to move out of the capillary and into the interstitial space

Capillary osmotic pressure

the pressure applied to the capillaries preventing it from passing to into a given solution by osmosis - pulls the water into the capillaries

Who is a major contributor to capillary osmotic pressure?

Albumin

Interstitial hydrostatic pressure

pressure exerted within the interstitial space opposing water from leaving the capillaries - water build up in the capillaries

Interstitial osmotic pressure

pressure applied to the interstitial space pulling water out of the capillary and into the surrounding tissue

What is the lymphatic systems importance?

accessory route for the fluid in the interstitial space

What happens to the proteins that have leaked in the interstitial space?

they get picked up from the lymphatic system

What happens when the lymphatic system doesnt work properly?

excess fluids accumulate in the interstitial space

Increased capillary filtration pressure

Edema

What disease processes cause increased vascular volume?

- heart disease

- kidney disease

- pregnancy

- venous obstruction (fluid shifting in places it shouldnt)

What disease processes cause venous obstruction?

- liver disease

- acute pulmonary edema

- venous thrombosis

What causes a decreased capillary osmotic pressure?

- increased loss of plasma proteins

- decreased production of plasma protein

What happens when capillary osmotic pressure is decreased?

pulling power is lost - lack of additional force pulling water into the blood vessel

increased loss of plasma proteins or decreased production of plasma protein

Which way does water get pulled?

water moves from areas of low osmotic pressure to high osmotic pressure

water moves from areas of high concentration to low concentration

What disease processes cause an increased loss of plasma proteins?

- protein-losing kidney diseases

- excessive burns

What disease processes cause a decreased production of plasma protein?

- liver disease

- starvation

- malnutrition

Number one player of capillary osmotic pressure

Albumin

Increased capillary permeability causes?

edema

What causes an increase in capillary permeability?

- inflammation

- allergic reactions

- malignancy

- tissue injury

- burns

Obstruction of lymphatic flow causes?

edema

What causes an obstruction of lymphatic flow?

- malignant obstruction of lymph structures

- surgical removal of lymph nodes

Third spacing

trapping of extracellular fluid in the transcellular spaces - spaces that have the capacity to hold fluid but shouldnt

Areas with continual movement are closely related to the....

lymphatic system

Which organs are closely related to the lymphatic system?

heart, abdomen and lungs

Examples of third spacing

pleural effusion, abdominal ascites, pericardial effusion

Dehydration

state of diminished water volume in the body either occurring vascularly or cellular

Vascular dehydration

diminished water volume within the vascular space

Cellular dehydration

diminished water volume within the cells

What do the osmoreceptors signal during dehydration?

thirst

What do the baroreceptors signal during dehydration?

stimulate the sympathetic nervous system causing vasoconstriction of the arterial vessel and increased HR

What happens when dehydration occurs and there isnt enough blood volume getting to the kidneys?

the RAAS is initiated causing water and sodium to be retained

RAAS signals ____ as a vasoconstrictor

Angiotensin II

Natriuretic peptide

released when baroreceptors sense too much volume - signaling the body to pee

If you have diarrhea what is your bodies response?

anti-diuretic hormone will increase to hold onto fluid

If a heart failure patient has edema what will increase?

capillary pressure to get rid of fluid

What ions influence neurotransmission and muscular contraction?

sodium, potassium and calcium

Sodium influx

depolarizes skeletal muscles

Calcium influx

cardiac muscle contractions through voltage gate channels

Normal sodium range

135 - 145 mEq/L

Sodium is the primary _____ cation

extracellular fluid

How does sodium effect hormone regulation?

- aldosterone

- natriuretic peptides

Aldosterone

hormone that signals the kidney for sodium to follow water back into the blood

Atrial natriuretic peptide and brain natriuretic peptide

natriuretic peptides released by the heart (atrial) and brain in response to high pressure and volumes

Urodilatin

natriuretic peptide released by the kidney

Normal chloride level

96 - 106 mEq/L

Hypovolemia

decreased volume of circulating blood in the body

Causes of hypovolemia

- inadequate fluid intake

- excess GI losses

- excess renal losses

- excessive skin losses

- third spacing

What effect does hypovolemia have on the cells?

none, cells do not change shape

What would a patient present with if they have hypovolemia?

- increased HR

- decreased BP

- weak, thready pulse

- thirst

- sunken eyes

- poor skin turgor

Hypervolemia

increased volume of circulating blood in the body

Causes of hypervolemia

- decreased sodium

- decreased water elimination

- heart failure

- renal function

- corticosteroid excess

What affect does hypervolemia have on the cells?

none; cells do not change shape

What would a patient present with hypervolemia?

- edema

- full bounding pulse

- weight gain

- decreased BUN

- decreased creatinine

- dilutional effects

What is the most common electrolyte disorder?

hyponatremia

Hyponatremia

too little sodium circulating in the blood causing cells to swell altering de/repolarization

<135 mEq/L

Causes of hyponatremia

- diuretics

- extrarenal losses

- vomiting

- diarrhea

- GI suctioning

- burns

- use of excess hypotonic saline

What is an example of a hypotonic solution?

0.45% NaCl

Hypervolemia in combination with hyponatremia

water excess and decreased sodium as a response to water intoxication (psychogenic disorder)

decreased urine formation

What are symptoms of hyponatremia?

- cramping

- weakness

- fatigue

- GI cramps

- lethargy

What are the serious effects of hyponatremia?

- seizures

- cerebral edema

- loss of deep tendon reflexes

Serious effects of hyponatremia is correlated with....

a release of ADH

Hypernatremia

excess sodium circulating in the blood usually due to free water loss causing cells to become dehydrated altering membrane potentials

> 147 mEq/L

What causes the body to retain sodium?

- inappropriate administration of hypertonic saline solution

- over-secretion of aldosterone

What would cause the body to over-secrete aldosterone?

excess secretion of adrenocorticotropic hormone (ACTH)

What is an example of a hypertonic solution?

D5 1/2 NS, Lactated Ringers (LR),