Lecture 2 - Fluids & Electrolytes

Question 0

…so how is it different from Osmolarity

Answer 0

Osmolarity meas’s solute conc.;

Unit: Osm/L sol’n

Question 1

Osmolarity is…

Answer 1

# of dissolved particles in solution
In Osm/kg H2O

Question 2

So how is Osmolality maintained in plasma?

Answer 2

OSMORCPs from Hypothalamus quickly responds to fluctuations

Question 3

…and between Osmolality and Osmolarity, which is preferred? and Why?

Answer 3

Osmolality. Because unlike Osmolarity, it is

Not affected by INCREASE in LIPIDS and PLASMA, ALCOHOL or changes in TEMP

Question 4

So how does Osmoreceptors regulate it?

Answer 4

1-2% Osm. increase = 4x Increase of Circu. ADH

1-2% Osm decrease = Turn off ADH

Question 5

How do you measure Plasma Osmolality?

Answer 5

Two ways:

1. Meas’d (Using Osmometer)
2. Calculated (refer to Index Card for formula)

Question 6

What are 5 important things to know about the Osmometer?

Answer 6

1) Measured like Clin. Mic’s Urinometer.
2) Specimen: Serum, Urine
3) NEVER PLASMA (Acoags interfere)
4) Uses freeze-point depression
5) Not commonly used –> OBSOLETE

Question 7

What are contributors of Calculated Osmolality?

Answer 7

Major: Na+ (90%, more signi)
Minor: Glucose and Urea

Question 8

Differentiate Hypoosmolality from Hyperosmolality.

Answer 8

HypoOsm HyperOsm
–>More water. –>Less water => Hypernatremia
–>Less solutes –>More solutes
–>ADH and thirst is inhi’d. –>ADH and thirst stim’d
–>concern for unconscious px, elderly,
w/ decr’d mental status, infants

Question 9

Differentiate Hypoosmolality from Hyperosmolality.

Answer 9

HypoOsm HyperOsm
Cs: Imp’d Renal Excre Cs: SIADH
Polydispsia Hypovolemia
Diabetes Insipidus
(Inad. ADH)

Question 10

What is Osmolal gap?

Answer 10

Osmolal gap indicates presence of osmotically actv parts other than Na, BUN, Glc

Question 11

So what are examples of these osmotically actv particles detected by Osmolal gap?

Answer 11

Methanol, Ethanol, Ethylene glycol, Lactate, beta-Hydroxybutyrate

Question 12

So, what is Osmolal gap’s clinical significance?

Answer 12

> 10 mOsm/kg >30 mOsm/kg

• • (+) Ing’d OHs – (+) Ing’d OH in High amts
    - - Inds grave prognosis

Question 13

Give an overview of Na+

Answer 13

• • Major EC Cation
• • Maintained, along with K+ thru Na+-K+ pump
• • Can be excreted 100% into the urine