Patho: Fluid and Electrolyte Management Flashcards
what percent of the body weight is water?
45-75% of body weight is water
what influences the amount of water in a body?
age, gender, body mass composition
The average man has with % of body water
55%
the average women has what % of water?
45%
an infant has what percent of body water?
80%
why do infants have so much more water?
o Greater body surface area – can lose more water through evaporation
o When they sweat, they lose more water
o Higher metabolic rate
< renal function. Do not have reabsorption capacities, urinate a lot. Must keep hydrated!
do obese people have more or less water?
Less
____have the highest water
____ have the lowest amount of water
Highest in lean and young
Lowest in eldery and obese
(muscle contains > H2O), why males have more water than female. Lowest in elderly/obese.
Distribution of total body water
Intracellular is 2/3, Extracellular is 1/3
Of the Extracellular fluid:Extravascular is ¾ and Intravascular is ¼
how much water does a typical man that is 70 kg have
70 kg x .6 (average body % water) → 42L of water
28L is intracellular, 14 L is extracellular
11L is interstitial, 3 L is intravascular → Normal person has 5-6 L in intravascular space of blood cells and water, so 3L water, 2-3 blood cells.
Composition of Fluid Compartments
-what determines water movement
Osmolarity determines water movement
Na: ____mEq/L extracellular, ____ mEq/L intracellular
K: ____ mEq/L extracellular, ____ mEq/L intracellular
Calcium:____ mEq/L extracellular, ____ mEq/L intracellular
HCO3: ____ mEq/L extracellular, ____ mEq/L intracellular
Na: 140mEq/L extracellular, 10 mEq/L intracellular
K: 5 mEq/L extracellular, 141 mEq/L intracellular
Calcium: 5 mEq/L extracellular,
If potassium lab comes back and is 10 & pt is asymptomatic what do you think?
lysis of RBC where cells lysed and released potassium. If this high, pt normally would be symptomatic
If intracellular is 300mOsm and extracellular is 350mOsm, water shifts where?
outside of cell
If intracellular is 300mOsm and extracellular is 250mOsm, water shifts?
inside of cell
Shifting is based on mOsm
OUTSIDE of cell, ONLY measure OUTSIDE
Composition of Fluid Compartments
o Composition maintained by:
o Movement of water is determined by:
o Solute concentration expressed as :
o Normal plasma osmolarity is:
o Composition maintained by selective permeability of cellular membranes
o Movement of water is determined by solute concentration
o Solute concentration expressed as milliosmoles (mOsm)
o Normal plasma osmolarity is 270-300mOsm/L
Calculate osmolarity
2(Na + K) + Glucose/16 + BUN/2.8
Explain Potassium levels if they are high or low
-First, know that Na is in charge of _______ and water movement and K is in charge of
Na: osmolarity
K: resting membrane potential
if K is high, RMP will be:
What will increase K+ Levels?
what are symptoms of high K?
high, more excitable and easier to reach threshold leading to muscle twitches and increased heartbeat.
Spironolactone increases K – pee out more Na, reabsorb more K
-Monitor K often
muscle cramps
If K is low, RMP will be
Where low K+ is Important with the heart, when K is low:
low and you need a stronger stimulus to reach threshold.
conduction in AV node is delayed resulting in slow heart rate.
People with heart failure are often of Dig and Lasix why is this a bad combination?
oDigitoxin works by:
o Those with CHF also on diuretic such as Lasix that also does what to K+ levels?
Digoxin: Increase contractibility of the heart and slowing conduction through AV node decreasing HR → CHF
decrease K levels by bulk flow – double wammy, could have complete heart block. MONITOR K OFTEN IN THESE PATIENTS because you can put them in a complete heart block
-
-
o kayexalate – bind up K and excrete through feces
o Insulin + glucose- push the K into the cells
o Calcium gluconate – works by increasing threshold levels so nerves and muscles are hyperexcitable. Normal stimulus needed now.
What are ways to regulate volume?
o Antidiuretic Hormone (Arginine-Vasopressin) regulates plasma osmolarity
o Renin/angiotensin/aldosterone system
o Baroreceptors (aortic arch, carotid bodies)
o Stretch receptors (atrium, juxtaglomerular apparatus)
o Cortisol
Explain how ADH regulates Volume (Arginine-Vasopressin)
- how does ADH work?
- ADH if high osmolarity?
- ADH if low osmolarity ?
•ADH comes from neurons from the hypothalamic area in the brain – neurons in hypothalamus send axon down and ADH released from Pit gland into the bloodstream
- Neurons in brain sense osmolarity.
- If high osmolarity, releases ADH so you reabsorb H2O bringing OSM down
oADH goes to distal tubule collecting duct allowing production of more water channels so H2O can be reabsorbed based on OSM of distal tubule
•If low osmolarity, no action potentials or ADH released, do not reabsorb H2O
Explain how the Renin/angiotensin/aldosterone system works to regulate Volume
You have low volume so low GFR, since the fluid is moving so slow alot of Na+ is able to be reabsorbed in the proximal tubule, so by the time the fluid gets to the distal tubule the low Na+ levels are sensed by the macula densa cells (so it thinks GFR is low, so it needs to do something to increase filtration)
1: sends signal to afferet arterole to dilate to increase blood flow to increase GFR
2: produces prostalandins that go the JG and cause the release of renin
Renin
will do all that it can to get pressure and volume back up to perfuse the kidney:angitoteninofent –> angiotensin I–> Angiotensin II ( in the lungs) direct vascular effects and causes aldosterone release, (tubules of kidney > reabsorption of Na and H20 to increase bp
JG apparatus: Contains the macula densa and Juxtrartiral cells
When BP bottoms out the Barro receptors sence that and send info up to the brainstem and causes
1: SNS activation to increase Vasoconstriction
2: JG cells to increase Renin
• JG cells under regulation of baroreceptors in the SNS
oDo not need Macula densa to play a role for renin release
why is it important that the kidney regulates flow when pressure is low?
to regulate perfusion to the nephron
Fluid and electrolyte replacement considerations- when it comes to Sxr
Maintenance:
Resuscitation:
Replacement:
o Maintenance: Amount of fluid/ions you need to maintain homeostasis when not eating
Could be through urinating, sweating, defecating
o Resuscitation: Repair imbalances that are already present
•When they hit ER, if NPO or vomiting for 12 hrs prior to sx must be caught up
•Take bowel prep into consideration here
oReplacement: Provide for ongoing loss that occur during surgery
2 major things:
1:Blood loss (measurable)
2: third space loss (extreme swelling after major surgery from tissue and vascular damage where vessels become leaky). Fluid accumulates into interstitial space.
how to determine Maintenance
In adults: approximaently ___ is maintenace
•In adults: Approximately 1.5ml/kg/hr
o Maintenance requirements (4-2-1 rule) PER HOUR
•4ml/kg/hr for first 10kg
•2ml/kg/hr for the second 10kg
•1ml/kg/hr for the remaining kg
o Maintenance requirements (100-50-20 rule) PER 24 HOURS
•100ml/kg for first 10kg
•50ml/kg for next 10kg
•20ml/kg for each remaining kg
If a patient has a fever what happeneds to maintenance value?
•Must adjust for fever and high ambient temperatures, fever may often require an additional 500ml of salt free water per day
