Na+ Chap 50

Question 1

Patients with hypernatremia or hyponatremia that require intravascular volume expansion should be treated with intravenous fluids that contain:

Answer 1

similar sodium concentration as the patient’s plasma

Question 2

in critically ill people even sodium concentration changes within the reference interval have been associated with:

Answer 2

increased mortality risk

Question 3

mmol/L to mEq/L

1 mmol Ca++ to mEq

Answer 3

x valence

1mmol Ca++ = 2 mEq Ca++

Question 4

what % TBW is intravascular

Answer 4

8.3%

83 m/1000ml (25% of 333 ml) will be distributed to the intravascular compartment

Question 5

Osmolality

Osmolarity

Answer 5

concentration of osmoles in a mass of solvent
mOsm/kg - measured using an osmometer

concentration of osmoles in a volume of solvent
mOsm/L of water

Question 6

Calculation of Serum Osmolality

divided by 2.8 and 18 why:

Answer 6

= 2[Na] + [BUN/2.8] + [Gluc./18]

convert them from mg/dl to mmol/L

Question 7

Regulation of Plasma Osmolality
snsed:
regulation 2 mech.:

Answer 7

hypothalamic osmoreceptors
2 to 3 mOsm/kg
ADH (secreted post. pituit.) and thirst

Question 8

describe pathway of hypothalmic osmoreceptor sensing increased osmolality:

barorecept:

Answer 8

hypothalamus osmoreceptors shrink - send impulses to posterior pituitary - ADH release

low effective circulating volume - decreased firing baroreceptor cells in the aortic arch and carotid bodies - neural impulses to the pituitary gland that stimulate ADH release

Question 9

V2 and ADH depends on:

.:. doesn’t work in:

Answer 9

hyperosmolar renal medulla down their osmotic gradient

medullary wash out
diuretic therapy

Question 10

explain hypoNa and hypoOsm. in CHF

Answer 10

maintenance ECV prioritized over maintenance of normal plasma osmolality

increased thirst and ADH release regardless of their osmolality = increased free water intake (from drinking) and water retention

Question 11

why is hydration misnomer:

difference bw. total body Na and H2O:Na ratio:

Answer 11

Total body sodium content refers to the total number of sodium molecules in the body, regardless of the ratio of sodium to water.

Na content determines the hydration status of the animal. hydration is a misnomer, because findings such as skin tenting determined by both the sodium content and the H2O:Na ratio in interstitial space

doesn’t accurately reflect TBNa

Question 12

can patients be hypernatremic an overhydrated?

THM total body sodium reflect hydration NOT plasma Na

Answer 12

sodium/water ratio is independent of the total body sodium

patients may be normally hydrated, dehydrated, or overhydrated (normal, decreased, or increased total body sodium content) and have a normal plasma sodium concentration, hypernatremia, or hyponatremia.

Question 13

ddx for free water deficit (5):

Answer 13

1. V/D
2. DI
3. toxic - charcoal, salt tox.
4. mannitol
5. water deprivation

syndrome of hypodipsic hypernatremia has been reported in Miniature Schnauzers

Question 14

All cells that have Na+/K+-ATPase pumps ___ as a result of hypernatremia

Answer 14

shrink

Question 15

Physiologic Adaptation to Hypernatremia

minutes - hrs.:

Answer 15

hyperosmolal state, as neuronal water is lost to the hypernatremic circulation, lowered interstitial hydraulic pressure draws fluid from the cerebrospinal fluid (CSF) into the brain interstitium
(CSF hydraulic shift into brain cells)

as plasma osmolality rises, sodium and chloride also appear to move rapidly from the CSF into cerebral tissue
(e- shifts into brain cells)

Question 16

Physiologic Adaptation to Hypernatremia

hrs. - days (complete 2-7d):

Answer 16

idiogenic osmoles:
glutamate
glutamine
inositol

Question 17

Treatment of the Normovolemic, Hypernatremic Patient:

should be treated, even if no CS

cases of ongoing free water loss:

Answer 17

Free water loss = 0.6 x kg x (currNa - normNa/normNa)

inadequate but safe starting point

Question 18

Why is free water replacement alone will not correct clinical dehydration or hypovolemia

Answer 18

because free water replacement = Total Body Sodium Content NOT Plasma Sodium Concentration

Question 19

complication of therapy for hypernatremia:

Next 3 steps:

Treatment:

Answer 19

CS of cerebral edema: obtundation, head pressing, coma, seizures

1. immediately stop the administration of any fluid that has a lower sodium concentration than the patient
2. disallow drinking
3. measure

mannitol at 0.5 to 1 g/kg
or consider a dose of 7.2% sodium chloride

Question 20

Hyponatremia ddx (5):

Decreased effective circulating volume =

Answer 20

free water retention

Decreased ECV common cause of hyponatremia which causes ADH release

1. congestive heart failure
2. excessive gastrointestinal losses
3. excessive urinary losses
4. body cavity effusions
5. edematous states
6. Addisons
7. Diuretics
8. SIADH
9. GI parasites
10. polydipsia

Question 21

CHF hydration status vs

GI loss hypoNa

Answer 21

patient has increased total body sodium (is “overhydrated”) bc activation of RAAS
-yet is hyponatremic because of increased water retention in excess of sodium retention

excessive salt and water losses from the GI or urinary tract, the patient is total body sodium depleted (is “dehydrated”) and is hyponatremic as a result of compensatory water drinking and retention to maintain effective circulating volume

Question 22

HypoNa and Addisons

Answer 22

decreased sodium retention (caused by hypoaldosteronism) + increased water drinking and retention in ADH defense of ECV

atypical - low circulating cortisol concentration leads to increased ADH release and resultant water retention regardless of intravascular volume status

Question 23

HypoNa and diuretics

Answer 23

Thiazide
loop diuretics

1. via induction of hypovolemia, hypokalemia that causes an intracellular shift of sodium in exchange for potassium
2. and the inability to dilute urine

Renal failure can cause hyponatremia by similar mechanisms

Question 24

HypoNa and SIADH

Answer 24

Syndrome of inappropriate ADH secretion (SIADH) causes hyponatremia via:

1. water retention in response to improperly high circulating concentrations of ADH
2. will be euvolemic/hypervolemic

Question 25

C/S at what level:

ATPase cells:

Answer 25

<120 mEq/L obtundation, head pressing, seizures, com

all cells that have Na+/K+-ATPase pumps swell

Question 26

Physiologic Adaptation to Hyponatremia

Answer 26

1. Interstitial and intracellular CNS edema increases intracranial tissue hydrostatic pressure - enhances fluid movement into the cerebrospinal fluid - flows out of the cranium through subarachnoid space, central canal into venous circulation
2. swollen neurons also expel solutes such as sodium, potassium, and organic osmolytes
3. organic osmolytes requires hours to days

Question 27

Tx

Answer 27

[Na+]p ≥ 130 mEq/) and usually self-corre

Question 28

Tx of symptomatic hyponatremia
best management approach is controversial

why furosemide too

amount increase

Answer 28

mannitol with furosemide (0.5 to 1 mg/kg IV) to ensure that electrolyte-free water is excreted along with the mannitol.

Fluid loss should be replaced with standard replacement intravenous fluids, unless the patient is overhydrated and the fluid loss desired

no more than 10 mEq/L 24 hours
no more than 18 mEq/L 48 hours of treatmen
never to exceed the low RI
limit of 10 mEq/L during the first day of treatment is more important than the rate over specific period w.in that day

Question 29

alternate approach to tx

Answer 29

hypertonic saline
human medicine recommendation is to raise by 10% to 15% in the first day of treatment
rate of correction may be as high as 2 mEq/L/hr initially
no more than 15 mEq/L in the first 24 hours

sodium deficit calculated to target plasma sodium concentration of no more than 10% to 15% higher
infused to raise plasma sodium no faster than 2 mEq/L/

Question 30

major complication of treatment for hyponatremia is:

manifest:

Myelinolysis lesions in dogs are commonly seen in

Answer 30

myelinolysis

many days after intervention

thalamus, rather than the pons as in humans

Question 31

Volume Expansion in the Hypovolemic, Hyponatremic, or Hypernatremic Patient

23.4% NaCl to the bag- product contains ____ NaCl/ml solution

Answer 31

should be resuscitated with a fluid that has a sodium concentration that matches that of the patient (±6 mEq/L)

4mEqNaCL/ml

Question 32

100 mg/dl increase in blood glucose, sodium concentration drops

Answer 32

by approximately 1.6 mEq/L