01-03 Sodium and Water IIa: Water Disorders

Question 1

What is the principal determinant of intravascular fluid volume?

Answer 1

[Na+]

—∆s in Na+ balance/regulation lead to hypo- or hyper-volemia

Question 2

What are renal causes of sodium wasting?

Answer 2

—DIURETICS* - no. 1 most common cause
—osmotic diuresis (i.e. w/ hyperglycemia)
—Bartter’s or Gitelman’s

*Aside from diuretics, most hypovolemia is due to NON-renal causes

Question 3

Renal response to hypovolemia?
Effective on:
—urine [Na+]
—urine osmolarity
—FENa

Answer 3

RESPONSES
—Renin → A-I → A-II → PT Na+ reabs + aldo release
—Aldo → Na+ reabs in CT
—ADH: water reabs + thirst

CHEMISTRIES
—‪↓‬ urine [Na+] (<1%)

Question 4

What are some possible consequences of Aldosterone secretion triggered by hypovolemia?

Answer 4

—hypokalemia

—metabolic acidosis

Question 5

Equation for FENa

Answer 5

FENa = U_[Na] X S_Cr / S_[Na] X U_Cr

Question 6

DDx for edematous states

Answer 6

—CHF
—cirrhosis
—nephrotic syndrome
—SIRS (Systemic Inflamm Response Syn)

Question 7

CHF
—mechanism that causes fluid retention/edema
—UA findings
—mech behind “cardiorenal syndrome”

Answer 7

EDEMA MECHANISM

1. Impaired forward flow → ↑ venous P
2. macula densa/baroreceptors/L-sided atrial stretch sense low CO → aldosterone → water retention

UA
—low urine [Na+]
—high urine Osm

CARDIORENAL
—low ECV → hypoperfusion of kidney → renal failure

*Hyponatremia is poor prognosis in CHF

Question 8

Cirrhosis
—Pathophys
—Hepatorenal syndrome

Answer 8

—Architecture ∆s in liver blocks venous return leading to ‪↓‬ ECV on arterial side

1. ↑ venous P → ascites & LE edema
2. liver makes less albumin → ‪↓‬ P_oncotic
3. art side see ↓ BP → ‪Aldo and ADH release

HEPATORENAL SYNDROME
—‪↓‬ perfusion 2° to ‪↓‬ ECV from liver dz → ‪RF

Question 9

Nephrotic Syndrome

Answer 9

—leaky capillaries → proteinuria & leaching of water and albumin into interstitium → ‪↓‬ ECV
—high aldo and ADH result

Question 10

SIRS

Answer 10

—inflamm → leaky caps in criticaly il
—usually b/c of sepsis (also drug rxn/anaphyl)
—fluid extravasation & venous pooling → ↓‬ ECV
—anasarca = severe, diffuse edema