Download Electrolytes

Water, Sodium, Potassium
The Balance
Douglas A. Stahura D.O.
8/29/2002
GOALS

Learner should be able to define:
– body fluid compartment components
– diffusion, osmosis
– hydrostatic pressure, oncotic pressure

Learner should be able to describe:
– Water regulation
– Volume regulation
GOALS

Learner should be able to identify
disorders and causes using history,
physical, laboratory data:
– Hypo/Hypernatremia
Why do you Care?


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Most common disorder of electrolytes in
hospitalized patients = hyponatremia
Responsible for delirium/change in
mental status, seizure activity
Life-threatening arrythmias
Commonly seen in DKA (diabetic
ketoacidosis)
Body Water


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Adult is 60% water
by weight
Intracellular 2/3rds
(40%)
Extracellular 1/3rd
(20%)
– Plasma (5%)
– Interstitial (15%)
Electrolytes

Intravascular
– Na+, Cl-, HCO3-

Interstitial
– Na+, Cl- , HCO3-

Intracellular
– K+ , PO43- , Proteins
Transcellular Transport

Passive
– diffusion
– co-transport

Active
– ion pumps-requires
energy (ATP)
Osmosis



Movement of WATER
between two
compartments
Osmotic pressure particles
Osmolarity –
milliosmoles of
SOLUTE per Liter
– Norm 275-295 mOsm/L
Fluid Shifts

Hydrostatic and
Oncotic pressures
in balance
Definitions



Na+ normal 135-145 meq/L
Osmolality normal 275-285 meq/L
Estimated serum osmolality:
– 2xNa+ + Glucose/18


Dehydration - loss of “free water”, I.e.
sweat
Hypotonic - loss of water and Na+ in
equal proportion
Case #1




You are hungry, and eat a bag of Salt ‘n
Vinegar chips, 3 dill pickles, and two
egg rolls smothered in soy sauce. You
wash it down with a ham sandwich.
What are the effects on osmolality?
How does the body respond?
You feel thirsty, and in the morning,
bloated
Regulation of Water Balance


Osmoreceptors in Hypothalmus can sense a
change of 1 mOsm/L
Brain responds with
– Thirst
– ADH (Anti diuretic hormone)

ADH
– adds water channels to cortical collecting ducts of
kidney
– Release stimulated by stress, nausea, nicotine,
morphine
Case #2



A 72 y/o AAM presents from XYZ
Nursing Home with Hx of CVA,
dementia presents with “change in
mental status” He is afebrile, BP
120/70, P-110, R-18. His UA is cloudy,
dark, +nitrites, +bacteria. Na+ = 169.
What is his ADH level?
What is his volume status?
Regulation of Volume

Sensors:
– body senses pressure/stretch
– Circulation: carotid bodies, Right Atrium
– Kidney: afferent arteriole

Effectors:
– Circulation: Sympathetic Nervous system
– Kidney: Renin-Angiotensin-Aldosterone
Regulation of Volume


Sympathetic Nervous system
“Increased Sympathetic Tone”
– Venous constriction
– Increased Myocardial contractility/Heart
Rate
– Arteriolar constriction
– e.g. Standing from a seated position
Regulation of Volume


Adrenal hormone (aldosterone) helps
regulate Volume through effects on
Sodium and Potassium.
(Mineralocorticoid)
Aldosterone:
– Increases Na+ reabsorption, K+ excretion
distal nephron
– Stimulated by:
• Decreased renal perfusion
• Decreased Na+ delivery to distal tubules
Renin-Angiotensin-Aldosterone
Case #3

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An 85 y/o WF with Hx of CHF and
Ejection Fraction of 20% eats the same
meal you had the night before!
How will she present in the ED?
Describe the osmolal regulation.
Describe the Volume regulation.
Case #4

A 37 y/o woman seen after several days
of severe diarrhea and poor oral intake.
PE shows moderate to severe volume
depletion. Lab data:
– Na+ = 142; K+ = 3.7.
– CL- = 114; HCO3- = 8.
– pH = 7.22; Urine (Na+) = 4.


What is the acid-base status?
Review signs of volume depletion.
Summary of Osmolality vs Volume


Osmolality is ratio of solutes to water
Volume determined by absolute amount
of Na+
– Exercising on a hot day leads to loss of
dilute fluid as sweat. The net effect is a
rise in the plasma osmolality and Na+
concentration but a fall in extracellular
volume.
Hypernatremia

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In the presence of a normal thirst
mechanism and access to water, is
uncommon.
DDx:
– Diabetes insipidus (Central/Nephrogenic)

Risk Factors:
– age (infant/elderly)
– disability(intubated/post-op/MRDD/CVA)
Case #5

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63 y/o AAM hx of Cerebral Palsy,
presents with GI bleed. Intubated,
bleeding stopped, Hbg = 11 and stable.
At 1400 on hospital day 4 begins
producing 400cc/hr of dilute urine. At
1800 BP 80/40. NS 500cc bolus given.
What will happen to his Na+?
What is the diagnosis?
Diabetes Insipidus

Disease of water regulation
– Central - lack of secretion of ADH
– Nephrogenic - lack of response by kidney
to ADH

Will result in increased sodium
Hyponatremia

Hyperosmotic
– Hyperglycemia
– Mannitol

Isoosmotic
– Hyperlidemia
– Hyperproteinemia

Hypoosmotic: most frequent
– Primary Na+ loss
– Primary water gain
– Primary Na+ gain exceeded by water gain
Work-Up of Hyponatremia

Labs:
– Posm
– Uosm
– UNA
Iso-osmotic Hyponatremia
Case #6

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A 40 y/o women is admitted to the hospital for
elective uterine ablation for dysfunctional bleeding
unresponsive to medical therapy. She is otherwise in
excellent health, and takes no medications. On
admission, weight = 60 kg, P-72, RR-12, BP-140/76.
The procedure is uneventful. Estimated blood loss
400ml. After 3 hours of anesthesia, she awakens
with headache, nausea, vomiting. HCT has fallen
from 37% to 24%. Na+ fallen from 140 to 100.
What is the most likely cause for this hyponatremia?
–
–
–
–
Severe hyperglycemia
Sorbitol administration
Severe hyperglobulinemia
Diuretic induced hyponatremia.
Bladder Irrigation with Sorbitol

This patient was irrigated with 16L of
Sorbitol 3%. She produced 11L of urine
outflow during that time. Additionally,
she was treated with aqueous
vasopressin(DDAVP) for persistent
bleeding.
Case # 7
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60 y/o Female, hospital day 3
Na+=118, K+=4.5, Cl-=88, HCO3-=22
Bun=5, Cr=0.5
Pt has myoclonus
Sosm=244, Uosm=255, UNa=92
TSH=3, Cortisol=0.9, Stim test: @ 30
min = 10
Case #7
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Conclusion: Adrenal Insufficiency
Tx:
– Hydrocortisone replacement
– Hypertonic saline (3% = 512Meq/L),
replace to sodium of 120-125
Summary

Reviewed basic definitions and
concepts
– body fluids, osmolality, transport


Reviewed Hormonal water and Volume
regulation
Reviewed examples of hypo/hyper
natremia