Water, Sodium, PotassiumThe 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?

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

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+ , PO4

3- , 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

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 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 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 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

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

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