Fluids

Fluid & Electrolytes

Distribution of Body Fluids Water is the largest single component

of the body 60% of adult’s weight is water

Healthy people can regulate balance

Compartments

Intracellular Within the cells

Contains dissolved solutes essential to balance

Extracellular Outside of the cell

Interstitial Between and around the cells

Intravascular Also lymph and organ fluids

Within the blood vessels Plasma

Composition of Body Fluids

Water Electrolytes

Separates into ions when dissolved Carries an electrical charge

Positive charge – CATIONS Sodium, Potassium, Calcium

Negative charge – ANION Bicarbonate, Chloride

Movement of Body Fluids Cell membranes are

selectively permeable Water passes through easily Most ions and molecules move

through much slower

Osmosis Moving a liquid through the

membrane from lesser to greater solute concentration Rate depends on concentration Temperature Electrical charges Differences between osmotic

pressures Works at equalizing concentration

Osmotic Pressure (Osmolarity) Pulling power for water

Depends on number of molecules in solution

Higher the concentration, greater pulling power

(higher osmotic pressure) Rate is quicker

Continues until equilibrium is reached

Osmolarity Hypertonic

Higher osmotic pressure than RBC’s Pulls fluid from cells

Shrinks cell Isotonic

Same osmotic pressure as RBC’s No fluid shift

Hypotonic Lower osmotic pressure than RBC’s

Fluid moves into cells Enlarges cell

Osmotic Pressure (cont) Affected by plasma proteins

Albumin Keeps fluid in intravascular compartment

using osmotic pressure Hydrostatic pressure draws fluid back

into capillaries Force of fluid pressure outward against

surface

Diffusion Moving a solid across the

semipermeable membrane From higher concentration to lower

To reach equilibrium Difference between the two is

concentration gradient

Filtration Both water and solids move

together in response to fluid pressure Seen in capillary beds ACTIVE Transport

Requires energy Moves against gradient

Sodium and potassium pump Uses carrier molecule

Glucose entering cell

Regulation of Body Fluids To maintain homeostasis, fluids

are regulated by: Fluid intake Hormonal controls Fluid output

Fluid Intake Regulated primarily by thirst

mechanism In the hypothalamus

Osmoreceptors monitor serum osmotic pressure Hypothalamus stimulated when osmolarlity

increases Thirst mechanism stimulated

With decreased oral intake Intake of hypertonic fluids Loss of excess fluid Stimulation of renin-angiotensisn-aldosterone

mechanism Potassium depletion Psychological factors Oropharyngeal dryness

Fluid Intake (cont) Average adult intake

2200-2700 cc/day Oral – 1100-1400 Solid foods – 800-1000 Oxidative metabolism – 300

By-product of cellular metabolism of ingested foods

Fluid Intake (cont) Must be alert Able to perceive mechanism Able to respond to mechanism **At risk for dehydration:

Elderly Very young Neurological disorders Psychological disorders

Hormonal regulation ADH

Stored in posterior pituitary gland Released in response to changes in blood

osmolarity Makes tubules and collecting ducts more

permeable to water Water returns the systemic circulation

Dilutes the blood Decreases urinary output

Hormonal regulation (cont) Aldosterone

Released by adrenal cortex In response to increased plasma potassium Or as part of renin-angiotensin-aldosterone

mechanism Acts on distal tubules to increase reabsorption

of sodium and water Excretion of potassium and hydrogen

Hormonal regulation (cont) Renin

Secreted by kidneys Responds to decreased renal perfusion Acts to produce angiotensin I

Causes vasoconstriction Converts to Angiotensin II

Massive selective vasoconstriction Relocates and increases the blood flow to

kidney, improving renal perfusion Stimulates release of aldosterone with low

sodium

Fluid Output Regulation Kidneys

Major regulatory organ Receive about 180 liters of blood/day to filter Produce 1200-1500 cc of urine

Skin Regulated by sympathetic nervous system

Activates sweat glands Sensible or insensible-500-600 cc/day

Directly related to stimulation of sweat glands Respiration

Insensible Increases with rate and depth of respirations, oxygen

delivery About 400 cc/day

Gastrointestinal tract In stool

Average about 100-200 GI disorders may increase or decrease it.

Regulation and Movement of Sodium

Most abundant cation in ECF Major contributor to maintaining

water balance By effect on serum osmolality, nerve

impulse transmission, regulation of acid-base balance and participation in chemical reactions

Regulated by dietary intake and aldosterone

Normal level : 135-145

normal osmolality290 mosm/ lWater deprivation,

solute ingestion,diarrhoea etc.



increased ECFosmolality




HYPOTHALAMIC OSMORECEPTORS

supraoptic &paraventricular

Nuclei

lateral preoptic

area






Nuclei

lateral preoptic

area

ADH releasefrom posterior pituitary






Nuclei

lateral preoptic

area


CD made water permeable






Nuclei

lateral preoptic

area



WATER RETENTION by Kidney






Nuclei

lateral preoptic

area


thirst

drink water



Regulation works in both directions

normal osmolality290 mosm/ l excessive

fluid ingestion

normal osmolality290 mosm/ l excessive

fluid ingestion

decreased ECF osmolality

normal osmolality290 mosm/ l



Nuclei

lateral preoptic

area

excessivefluid ingestion





Nuclei

lateral preoptic

area



ADH releasesuppressed




Nuclei

lateral preoptic

area




CD made waterimpermeable




Nuclei

lateral preoptic

area





WATER EXCRETION by Kidney




Nuclei

lateral preoptic

area




thirstsuppressed



Regulation works in both directions






Nuclei

lateral preoptic

area



Nuclei

lateral preoptic

area


thirst

drink water






thirstsuppressed



Osmoreceptors are the main controllers of ADH levels, but other factors include.. Alcohol (inhibits ADH) Nicotine (stimulates ADH)

Increased circulating volume(Atrial stretch, ANP release,ADH release inhibited)... seelater

Volume Regulation

Since the osmolarity (i.e. concentration) of ECF is tightly controlled,

the volume of the ECF is determined by the total quantity of solute (mainly NaCl),

so regulation of ECF volume is all about Sodium Balance

Volume Regulation .. The total amount of Sodium in ECF dictates volume of ECF

add 0.2gNaCl

“Osmo-regulation”

1.2g NaCl1.2 litre H2O

1g / l1g / l

1.2g NaCl1 litre H2O

1.2g / l1.2g / l

1g NaCl1 litre H2O

1g / l1g / l

The Sensor

... well, one of them

The Juxtaglomerular Apparatus


reninrenin

Renin may be released by:

sympathetic activity (n.b. baroreceptor response to low BP)

wall tension in afferent arteriole (? drop in mean or pulse pressure)

??? a fall in Sodium delivery to Macula Densa

i.e. Low Blood Volume (Hypovolemia)


SympatheticNerves

renin


renin

Low Pressure


Na

renin

Renin may be released by:

sympathetic activity (n.b. baroreceptor response to low BP)

wall tension in afferent arteriole (? drop in mean or pulse pressure)

??? a fall in Sodium delivery to Macula Densa

i.e. Low Blood Volume (Hypovolemia)

Plasma angiotensinogen

Angiotensin I (10 - peptide)

RENIN

Hypovolemia



Angiotensin II (8 - peptide)

RENIN

plasma ‘converting enzyme’ (ACE)Hypovolemia




Aldosterone released from adrenal cortex

RENIN

plasma ‘converting enzyme’Hypovolemia





Increased Sodium Reabsorption in DCT

RENIN







RENIN

plasma ‘converting enzyme’

osmoregulationVolume RegulationVolume Regulation

1g / l1g / l

add 0.2gNaCl

1.2g / l1.2g / l

1g NaCl1 litre H2O



1g / l1g / l


Hypovolemia






RENIN



1g / l1g / l

add 0.2gNaCl

1.2g / l1.2g / l

1g NaCl1 litre H2O



1g / l1g / l


Expansion of ECF






RENIN

plasma ‘converting enzyme’Restoration of Volume


1g / l1g / l

add 0.2gNaCl

1.2g / l1.2g / l

1g NaCl1 litre H2O



1g / l1g / l


Expansion of ECF

Aldosterone

Increases Na+ reabsorption in DCT as well as from :

gut sweat glands salivary glands

Aldosterone

Increases Na+ reabsorption in DCT as well as from :

gut sweat glands salivary glands

N

Na+

K+

H+

Na+

DCT cell

Lumen

BloodBlood

+

+

Another volume sensor.... The Atria

Atrial Natriuretic Peptide (ANP) released when atria stretched ( blood volume)causing:

Aldosterone secretion Renin release ADH release (emergency

response)

Regulation and Movement of Potassium

Major cation in intracellular compartments Regulates metabolic activities, necessary for

glycogen deposits in liver and skeletal muscle, transmission and conduction of nerve impulses, normal cardiac conduction and skeletal and smooth muscle contraction

Regulated by dietary intake and renal excretion

Normal level – 3.5-5.0 Body conserves potassium poorly

Increased urine output decreased serum potassium

Movement and Regulation of Calcium

Stored in bone, plasma and body cells (Cation) 90% in bones 1% in ECF

In plasma, binds with albumin Necessary for bone and teeth formation,

blood clotting, hormone secretion, cell membrane integrity, cardiac conduction, transmission of nerve impulses, and muscle contraction

Normal level – 4.5-5.5 Regulated by bone resorption

Movement and Regulation of Magnesium

Cation Normal 1.5-2.5 Regulated by dietary, renal and PTH

Movement and Regulation of Chloride

Major anion in ECF Normal level – 95-108

Follows sodium Regulated by dietary intake

and the kidneys

Movement and Regulation of Bicarbonate

Major chemical base buffer in the body Carbonic acid-Bicarbonate buffering

system Needed for acid-base balance

Normal level 22-26 Regulated by kidneys

Movement and Regulation of Phosphate

Buffer anion found mainly in ICF Assists in acid-base balance

Inversely proportional to calcium Helps maintain healthy bones and teeth,

neuromuscular activity, and CHO metabolism Absorbed through GI tract Normal level 2.5-4.5 Regulated by dietary intake, renal excretion,

intestinal absorption and PTH

Common Disturbances Electrolyte Balance

Sodium Hypernatremia (Na > 145, sp gravity < 1.010)

Caused by excess water loss or overall sodium excess Excess salt intake, hypertonic solutions, excess

aldosterone, diabetes insipidus, increased s water loss, water deprivation

S&S: thirst, dry, flushed skin, dry, stick tongue and mucous membranes

Hyponatremia (Na < 135, sp gravity > 1.030) Occurs with net loss of sodium or net water excess

Kidney disease with salt wasting, adrenal insufficiency, GI losses, increased sweating, diuretics, SIADH

S&S: personality change, postural hypotension, postural dizziness, abd cramping, n&v, diarrhea, tachycardia, convulsions and coma


Potassium Hyperkalemia (K > 5.3; EKG irregularities-

bradycardia, heart block, wide QRS pattern-cardiac arrest)

Primary cause: renal failure; major symptom: cardiac irregularity

Fluid volume deficit, massive cell damage, excess K+ given, adrenal insufficiency, acidosis, rapid infusion of stored blood, potassium-sparing diuretics

S&S: dysrhythmias, paresthesia Hypokalemia (K < 3.5; EKG irregularities-ventricular)

Most common electrolyte imbalance; affects cardiac conduction and function. Most common cause: potassium wasting diuretics

Diarrhea, vomiting, alkalosis, excess aldosterone secretion, polyruia, extreme sweating, insulin to treat diabetic ketoacidosis

S&S: weakness, ventricular dysrhythmias, irregular pulse


Calcium Hypercalcemia (Ca > 5; x-rays show calcium

loss, cardiac irregularities) Frequently symptom of underlying disease with

excess bond resorption and release of calcium Hyperparathyroidism, malignant neoplastic disease,

Paget’s disease, Osteoporosis, prolonged immobization, acidosis

S&S: anorexia, nausea and vomiting, weakness, kidney stones

Hypocalcemia (Ca < 4.0, EKG abnormalities) Seen in severe illness

Rapid blood transfusion with citrate, hypoalbuminemia, hypoparathyroidism, Vitamin D deficiency, Pancreatitis, Alkalosis

S&S: numbness and tingling, hyperactive reflexes, positive Trousseau’s sign (wrist), positive Chvostek’s sign (cheek), tetany, muscle cramps, pathological fracture


Chloride Usually seen with acid-base imbalance

Hyperchloremia (Na >145, Bicarb <22) Serum bicarbonate values fall or sodium rises

Hypochloremia (pH > 7.45) Excess vomiting or N/G drainage; loop of

thiazide diuretics because of sodium excretion Leads to metabolic alkalosis due to reabsorption of

bicarbonate to maintain electrical neutrality

Common Disturbances Fluid Balance

Isotonic imbalances When water and electrolytes are

gained or lost in equal proportions Osmolar imbalances

Loss or gain of only water Osmolality is affected

Isotonic imbalances Fluid volume deficit (Sp Gravity > 1.025, Hct >50%, BUN > 25)

GI losses, loss of plasma or whole blood, excess perspiration, fever, decreased intake, diuretics

S&S: postural hypotension, tachycardia, dry mucous membranes, poor skin turgor, thirst, confusion, rapid weight loss, slow vein filling, lethargy, oliguria, weak pulse, sunken, dry conjunctiva

Fluid volume excess (Hct < 38%, BUN < 10 Congestive heart failure, renal failure, cirrhosis, increased

aldosterone and steroid levels, excess sodium intake S&S: rapid weight gain, edema, hypertension, polyuria,

neck vein distention, increased venous pressure, crackles in lungs

Osmolar Imbalances Dehydration (Hyperosmolar imbalance)

(Na > 145) Diabetes insipidus, neurological damage to

block thirst drive, diabetic ketoacidosis, osmotic diuresis, hypertonic IV fluids of tube feedings

S&S: dry, sticky mucous membranes, flushed and dry skin, thirst, elevated temp

Water Excess (Hypoosmolar imbalance) (Na < 135)

SIADH, excess water intake S&S: decreased level of consciousness,

convulsions, coma

Variables Affecting Normal Fluid, Electrolyte and Acid-Base Imbalances

Age Orientation status Mobility level Prolonged illness

Cancer, CHF, endocrine disease, COPD Medications

Diuretics, steroids, IV therapy, TPN Gastrointestinal losses

Clinical Assessment for Fluid, Electrolyte and Acid-Base Imbalances

Pre-existing disease processes Cancer, cardiovascular, renal, GI

Age Infants have higher % water- loss felt faster Elderly –kidneys decreased filtration rate, less functioning

nephrons, don’t excrete mediations as fast, lung changes may lead to respiratory acidosis

Acute illness Surgery, burns, respiratory disorders, head injury

Environmental Vigorous exercise, temperature extremes

Diet Fluids and electrolytes gained through diet

Lifestyle Smoking or alcohol

Medications Side-effects may cause fluid and/or electrolyte imbalances

Medications Likely to Cause

F&E Imbalances Diuretics

Metabolic alkalosis, hyperkalemia, hypokalemia Steroids

Metabolic alkalosis Potassium supplements

GI disturbances Respiratory center depressants (narcotic analgesics)

Respiratory acidosis Antibiotics

Nephrotoxicity, hyperkalemia, hypernatremia Calcium carbonate (TUMS)

Metabolic alkalosis Magnesium hydroxide (Milk of Mag)

hypokalemia

References To be added

Fluids

Documents

water water

water balance

permeable water

cell osmotic pressure

rbc s fluid

water excretion of potassium

cell regulation of body

rbc s pulls fluid