Clin Med II Exam 3 - RENAL (FLUID & ELECTROLYTE BALANCES)

gbalsam1

each nephron consists of

glomerulus and renal tubule

glomerulus

forms a protein-free filtrate from blood

tubule

processes the filtrate to form urine

each renal tubule consists of

- proximal convoluted tubule

- loop of Henle

- distal convoluted tubule

- collecting ducts

functions of the kidney

- secretions of hormones (erythropoietin, renin, vitamin D3)

- regulation of water, electrolyte balance, pH

- removal of waste from blood and excretion of urine

bloody urine

serious disease

colicky pain

ureteral obstruction

frequency and burning

lower UTI

nausea, weight loss, anorexia, GI, and neurologic symptoms

chronic renal failure

lack of urine formation, possibly N/V, progressively downhill course

AKI, cancer (kidney and prostate primary sites)

peripheral edema

nephrotic syndrome

flank pain and fever

acute pyelonephritis

serum/urine osmolarity

the concentration of a solute within a solution

how are changes in total body water content best evaluated?

documenting changes in body weight

measuring the effectiveness of the kidneys

fractional excretion (Fe) of an electrolyte X (FeX) calculated from a spot urine sample

renin angiotensin-aldosterone system (RAAS)

hormone system that regulates blood pressure and regulates water balance

renin

an enzyme secreted by the juxtaglomerular cells when blood pressure decreases; renin (angiotensinogenase) converts angiotensinogen to angiotensin I

angiotensin II

a potent vaso-active peptide which causes vasoconstriction resulting in increased blood pressure

what does the release of angiotensin II stimulate?

- the secretion of aldosterone

- the secretion of ADH

role of aldosterone in RAAS

- increases the reabsorption of sodium ions and, thereby, water

- increases the secretion of potassium ions in the collecting ducts for excretion

- increases blood volume (reabsorption of water), therefore increasing blood pressure

potassium-sparing diuretics used as antihypertensive medications

drugs that interfere with the secretion or action of aldosterone (i.e., spironolactone or eplerenone)

antidiuretic hormone (ADH)

- controls the reabsorption in the renal tubules by affecting the tissue's permeability (increases aquaporins)

- retains water from the collecting duct

- increases peripheral vascular resistance which then increases arterial blood pressure

overactive RAAS

results in high blood pressure

what is the most abundant compound in the body?

water

about how much of an adult's body weight is water?

about 60%

about how much of an elderly adult's body weight is water?

45-55%

about how much of an infant's body weight is water?

70-80%

natriuretic peptides

antagonists to the RAAS (include ANP and BNP) that are produced by cardiomyocytes in response to increased arterial pressure

GI regulation of fluid/electrolyte balance

- oral intake accounts for most water

- small amounts of water are eliminated by the GI tract in feces

- diarrhea and vomiting can lead to significant fluid and electrolyte loss

intracellular fluid

aka "ICF;" water inside the cells, and the largest of the 3 volumes

extracellular fluid

aka "ECF;" water outside the cells including plasma and interstitial spaces

first spacing

normal distribution of fluid in ICF and ECF

second spacing

abnormal accumulation of interstitial fluid (think of edema)

third spacing

fluid accumulation in part of body where it is not easily exchanged with ECF (i.e., pleural spaces, pericardial spaces, peritoneal spaces, etc.)

gerontologic considerations of fluid/electrolyte balance

- structural changes in kidneys decrease ability to conserve water

- hormonal changes lead to decrease in ADH and ANP

- loss of subcutaneous tissue leads to increased loss of moisture

- reduced thirst mechanism results in decreased fluid intake

fluid intake

what we drink (beverages), water in foods we eat, and water formed by catabolism of food

fluid output

via kidneys, lungs, skin, and intestines

insensible fluid loss

fluid lost from the skin, lungs, and GI tract

obligatory water loss

minimal amount of fluid loss from the body that includes insensible and minimal amount of fluid necessary to excrete wastes through the kidneys

regulation of water intake

governed by thirst which is provoked by increased plasma osmolarity and blood loss

thirst center

area located in the hypothalamus that responds to signs of dehydration (i.e., signals from osmocenters or reduced BP) and inhibits salivation

regulation of water intake by inhibited salivation

- dry mouth

- sense of thirst

- ingestion of water cools and moistens mouth, distends stomach and intestines, rehydrates blood

- thirst inhibited

regulation of water output

controlled via alterations in urine volume

what is urine volume affected by?

- sodium reabsorption

- ADH

action of ADH

- if blood volume is decreased and sodium increased, osmoreceptors are stimulated, and the pituitary releases ADH

- aquaporins increase their production in kidney's collecting ducts (i.e., increases ways for water to be reabsorbed)

- facilities reabsorption

examples of insensible water loss

- expired air

- cutaneous transpiration

- sweat

- fecal moisture

- minimum urine output (~400 mmL/day)

about how much water is lost through the lungs and the skin daily?

600-900 ml/day

fluid deficiency

hypovolemia and dehydration

volume depletion (hypovolemia)

caused by a proportionate loss of water and sodium without replacement

characteristics of hypovolemia

- total body water decreased

- osmolarity unchanged

- caused by hemorrhage, severe burns, chronic vomiting or diarrhea

dehydration

losing more water than electrolytes

characteristics of dehydration

- total body water decreased

- ECF osmolarity increased

- caused by lack of drinking water, diabetes mellitus, ADH hyposecretion, profuse sweating, or overuse of diuretics

why are infants more vulnerable to dehydration than adults?

- higher metabolisms lead to more wastes and more urine volume

- immature kidneys lead to urine being less concentrated

- greater surface area-to-volume ratio leading to greater water loss by evaporation

fluid excess

volume excess and hypotonic hydration

volume excess

caused by proportionate retention of excess water and sodium

characteristics of volume excess

- total body water increased

- osmolarity unchanged

- caused by aldosterone hypersecretion or renal failure

what might volume excess lead to?

second spacing

hypotonic hydration

aka "water intoxication;" caused by retention of more water than sodium

characteristics of hypotonic hydration

- total body water increased

- ECF osmolarity decreased

- caused by replacement of water and salt with water (lack of proportionate intake of electrolytes)

fluid sequestration

excess fluid accumulates in a particular location

characteristics of fluid sequestration

- total body water may be normal

- circulating volume may drop

examples of fluid sequestration

- edema

- hemorrhage

- pleural or pericardial effusion

- ascites

effects of fluid deficiency

- circulatory shock due to loss of blood volume

- neurological dysfunction due to dehydration of brain cells

- infant mortality from diarrhea

effects of fluid excess

- less common due to the kidneys' ability to excrete more urine

- pulmonary or cerebral edema

lower extremity edema

presence of an abnormally large amount of fluid in the intercellular spaces

causes of lower extremity edema

- retention of electrolytes, especially sodium (increased capillary BP pushes fluid out of the blood and into the IF) which is common during heart failure due to venous congestion

- plasma proteins act as a water holding force, and if the concentration of blood proteins decrease, the less water moves from the blood into the IF resulting in water accumulation

pitting edema

edema that retains an imprint when touched; an example of fluid overload

purposes of IV fluids

maintenance and replacement

maintenance IV fluids

when oral intake is not adequate to maintain

calculation of maintenance fluids

follow the 4, 2, 1 rule:

- 4 ml/kg/hour for first 10 kg of body mass

- 2 ml/kg/hour for second kg of body mass

- 1 ml/kg/hour for body mass above 20 kg

replacement IV fluids

when fluid losses have occurred (an increased requirement compared to maintenance fluids)

crystalloid IV fluids

- dextrose in water

- saline

- combo

- ringer's lactate

colloid IV fluids

- albumin

- dextrans

- hetastarch

hypotonic IV fluids

- more water than electrolytes (pure water lyses RBCs)

- water moves from the ECF to ICF by osmosis

- usually maintenance fluids

isotonic IV fluids

- expands only the ECF

- no net loss or gain from the ICF

hypertonic IV fluids

- initially expands and raises the osmolality of ECF

- requires frequent monitoring of vital signs, Na+, and lungs

D5W (5% dextrose in water)

- isotonic

- provides 170 cal/L

- free water that moves into ICF and increases renal solute excretion

- does not provide electrolytes

uses of D5W

replace water losses and treat hypernatremia

normal saline

- isotonic

- no calories

- more NaCl than ECF

- 30% stays in IV

- does not change ICF volume

- compatible with most medications

uses of normal saline

expands IV volume and is the preferred fluid for immediate response

lactated ringer's

- isotonic

- more similar to plasma than normal saline (has less NaCl but has potassium, calcium, phosphate, and lactate)

- expands ECF

D5 1/2 normal saline

- hypertonic

- KCl added for maintenance or replacement

uses for D5 1/2 normal saline

common maintenance fluid

D10W (10% dextrose in water)

- hypertonic

- provides 340 kcal/L

- limit of dextrose concentration may be infused peripherally

uses of D10W

provides free water (mostly used in hypoglycemic patients)

plasma expander

- stays in vascular space and increases osmotic pressure

- colloids (protein solutions)

- packed RBCs

- albumin

- plasma

electrolytes

chemicals that dissolve in water and dissociate into positive and negative ions (including inorganic salts, acids and bases)

osmosis

water will move from a compartment with a low concentration of electrolytes to one with a high concentration

cations

positive ions

sodium (Na+)

- most abundant cation in the ECF

- essential for electrical activity of nerve and muscle cells

- the level is regulated primarily by the kidneys

potassium (K+)

- most abundant cation in the ICF

- essential for electrical activity of nerve and muscle cells

calcium (Ca2+)

- mostly in bones and teeth

- essential for blood clotting

- maintains normal nerve and muscle cell function

magnesium (Mg2+)

- more abundant in ICF than ECF

- essential for ATP production and activity of nerve and muscle cells

anions

negatively charged ions

chloride (Cl-)

most abundant anion in ECF

bicarbonate (HCO3-)

- part of bicarbonate buffer system

- participates in acid-base balance

phosphate (H2PO4-)

most prevalent anion in ICF

proteins

- negatively charged proteins inside the cell and in plasma regulate water in those compartments

- play a role in regulating electrolyte distribution

signs and symptoms of excess sodium

- hypernatremia

- thirst

- CNS deterioration

- increased interstitial fluid (edema)

signs and symptoms of deficient sodium

- hyponatremia

- CNS deterioration