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RUSVM Clinical Pathology > Water Balance and Electrolytes > Flashcards

Water Balance and Electrolytes Flashcards

1
Q

For clinical purposes, do we use osmolaity or osmolarity?

A

Osmolality

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2
Q

What is osmolality?

A

[solute] per kg of Solvent (mOsm/kg)

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3
Q

How are osmoles measured in plasma?

A

Freezing-point depression osometry

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4
Q

What is tonicity?

A

AKA effective osmolaity

Ability of a solution to initiate water movement

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5
Q

What type of solute is distributed equal through the total body water, causing no H20 movement

A

Permeant solute

Eg BUN

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6
Q

What type of solute does NOT readily distribute across cell membranes and will cause H20 movment

A

Impermeant solute

Eg Na, Glu, Mannitol

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7
Q

_____________ dieresis occurs when there is increased urine flow caused by excessive amounts of impermeant solutes within the renal tubules

A

Osmotic

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8
Q

What is the normal urine flow rate in dogs and cats?

A

> 1-2mL/kg/hr

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9
Q

__________ dieresis occurs when there is increased urine flow caused by decreased reabsorption of free water

A

Water

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10
Q

What is specific gravity?

A

Ratio of weight of a volume of liquid to the weight of an equal volume of distilled water

-estimate of osmolality

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11
Q

What is urine specific gravity dependent on?

A

Number of particles present

Molecular weight of those particles

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12
Q

________ regulates water balance and ___________ regulates sodium

A

ADH/vasopressin

Aldosterone

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13
Q

How do the osmoreeptors in the hypothalamus maintain water balance?

A

Hyperosmolality -> shrink -> ADH release -> H20 reabsorption in kidney and thirst response

Hypoosmolality -> swell -> inhibit ADH release -> increased water excretion

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14
Q

ADH responds to

A

Small increases in osmolality

Large decreases in plasma volume

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15
Q

ADH acts on which part of the nephron by increasing expression of ______

A

Collecting ducts; aquaporins

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16
Q

What electrolyte is the primary regulator of blood volume

A

Sodium

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17
Q

Blood volume regulated by sensing of??

A 
Atrial stretch (ANP)
Renal perfusion pressure (RAAS)
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18
Q

What effect does aldosterone have on sodium

A

Converse sodium (and water)

Secrete potassium

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19
Q

What is hypertonic dehydration?

A

Water loss > Na loss

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20
Q

What is isotonic dehydration?

A

Water loss = Na loss

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21
Q

What is hypotonic dehydration?

A

Water loss < Na loss

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22
Q

You have confirmed dehydration, Na is increased.

Type of dehydration?

A

Hypertonic

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23
Q

Dehydration confirmed, Na is normal.

Type of dehydration?

A

Isotonic

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24
Q

Dehydration is confirmed, Na is decreased

Type of dehydration

A

Hypotonic

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25
Q

What are your DDX for hypertonic dehydration?

A

Diabetes insipidus / mellitus
Osmotic dieresis
Osmotic diarrhea
Water deprivation

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26
Q

What is the DDX for isotonic dehydration

A

Renal disease

Diarrhea

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27
Q

What is the DDX for hypotonic dehydration ?

A

Secretory diarrhea
Vomiting
3rd space loss (effusions)
Heat stress and sweating in horse

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28
Q

T/F: in a hypotonic dehydration fluid shifts from vasculature and into cells and osmoreceptors will stimulate ADH release

A

False

Fluid into cells -> cell/osmoreceptor swelling -> ADH release is inhibited

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29
Q

Cerebral edema occurs when Na is < _________ mEq/L

A

115-120

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30
Q

When do we usually see overhydration?

A

Iatrogenic

Iv fluid admin with inappropriate elimination like heart failure, renal obstruction, or oliguria/anuria

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31
Q

Over hydration can cause ??

A

Cardiovascular overload
Pulmonary edema
Generalized edema

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32
Q

Will you see clinical signs if your plasma concentration of ineffective solutes is increased (eg uremia)

A

No

Urea is freely diffusible across cell membranes-> osmotic changes are negligible

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33
Q

Wil you see clinical signs associated with an increased plasma concentration of effective solutes (eg hpernateremia or hyperglycemia )

A

Yes

Cellular dehydration
-> cerebral cellular volume and neurological changes (depression, stupor, coma)

34
Q

Decreased plasma concentration of effective solutes will have what clinical manifestations (eg hyponatremia)

A

Cellular swelling –> cerebral edema and cell lysis

Lethargy, weakness, altered mentation, obtundation, seizure, death

35
Q

What is the normal plasma osmolality in dogs and cats?

A

Dog 300 mOsm/kg

Cat 310 mOsm/kg

36
Q

In a chemistry panel, how is osmolality determined?

A

Calculated

2[Na] + [Glu]/18 + [BUN]/3

37
Q

What is the osmole gap and what does an increase in this gap mean?

A

OG= measured osmolality - calculated osmolaity

Increase means there is an osmotically active molecule in blood that is not measured on the serum biochemical profile

38
Q

Interpret:

Measured osmolality - increased
Calculated osmolality - increased
Osmole gap < 30

A

Increase in an osmole reported on the chemical

Eg Na, glu, or BUN

Usually represents sodium

39
Q

Interpret:

Measured osmolality - decreased
Calculated osmolality - decreased
Osmol gap < 30

A

Hyponatremia

Even a marked decreased in BUN or GLU will only cause minor decreased in osmolality

40
Q

Interpret:

Measured osmolality - increased
Calculated osmolality - normal
Osmole gap > 30(increased)

A

Probable toxin (or drug)

Eg ethylene glycol or mannitol

41
Q

What is the major extracellular ion

A

Na

42
Q

How is sodium regulated?

A

Adequate intake (esp herbivores)
Aldosterone - renal absorption
Intestinal absorption
ADH- indirectly influence Na

43
Q

What are the 3 major mechanisms that alter sodium?

A

Change in intake
Redistribution
Changes in excretion

44
Q

If water shifts from ICF -> ECF, what effect will this have on sodium?

A

Hyponatremia

45
Q

T/F: hyponatremia can result due to an effusion?

A

True

Na shift from vasculature to the effusion - heart failure and liver fialure –> edematous states

46
Q

What are sources of sodium loss that can result in a hyponatremia

A

Renal, GI, cutaneous

47
Q

What 3rd space syndromes can result in a hyponaterima?

A 
Peritonitis 
Ascities 
Uroabdomen 
Chylothorax 
GI sequestration
48
Q

Hyperglycemia or mannitol administration can have what effect on sodium?

A

Hyponatremia -> redistribution

Water pulled by Glu or mannitol –> decreased concentration of Na

49
Q

What is the most common cause of hyponatremia?

A

Hypovolemia

GI -vomiting, diarrhea, or saliva
Renal - hypoadrenocorticism, ketonuria, glucosuria, prolonged dieresis
Cutaneous - sweating, burns

50
Q

What are the consequences of hyponatremia ?

A

Hyposmolality

Cellular and cerebral edema (cellular overhydration)

51
Q

Hypernatremia can result form?

A

Increased intake of Na
Decreased H2o intake

H20 lost in excess of Na (GI, renal, insensible losses)

52
Q

A diabetic patient is markedly hyperglycemia, what do you expect the sodium concentration to be?

A

Hyponatremia

53
Q

A diabetic patient is markedly hyperglycemic. What is the mechanism that drives the change in Na+?

A

Water shifts from the ICF to the ECF

54
Q

Is chloride a extracellular or intracellular ion?

A

Extracellular

BFFs with sodium

55
Q

If the change in Cl- and Na+ are proportional, what should be your top differential?

A

Abnormalities in Na

DDX for hyper or hypo-natremia

56
Q

If the change in Cl- concentration are greater than Na+, what should be your top DDX?

A

Acid-base abnormalities

57
Q

How is chloride regulated?

A

Controlled by electrochemical gradients

Corresponds to active transport of sodium

58
Q

What is the most common cause of selective chloride loss?

A

Hypochloremic metabolic alkalosis

Gastric HCl are NOT resorbed by small intestine

Monogastric- severe vomiting
Ruminant- abomasal disorder and high GI obstruction

59
Q

Selective chloride loss in horse is likely due to?

A

Sweating

60
Q

What is paradoxical aciduria associated with hypochloremia?

A

Metabolic alkalosis -> excrete HCO3- in kidney

Dehydration causes reabsorption Na and HCO3 (normally would be Cl- but we are lacking) –> exacerbated alkalosis

61
Q 
Glu H 545
BUN H 70
CREA H 7.1 
ALB H 4.7 
GLOB H 5.6

Na L 130 (136-147)
Cl L 47 (95-105)

Interpret

A

Albumin and globulin high => dehydration
Pre-renal azotemia

CL = 47 x 141/130 = 51
-> still below reference => selective chloride loss

62
Q

What acid base abnormality accompanies a selective chloride loss?

A

Metabolic alkalosis

63
Q

Causes of hyperchloremia?

A

Parallels increases with Na+
Hyperchloremic metabolic acidosis (GI loss of HCO3)
Alkalemia

64
Q

How does an alkalemia cause a hyperchloremia?

A

HCO3- excreted in distal nephron
Generate H+
Cl- follows H+ into plasma

65
Q

Is potassium an intracellular or extracellular ion?

A

Intracellular

66
Q

What are clinical signs associated with abnormal serum K+ concentrations?

A

Cardiac dysfunction - can be life threatening

Skeletal muscle dysfunction -> change in posture

67
Q

How is potassium regulated?

A

Intake
Renal excretion -promoted by aldosterone (K exchanged for Na)
GI loss
Sweat

68
Q

What is the most common cause of hyperkalemia?

A

Failure of renal excretion

Eg oliguria/anuria/renal failure/obstruction

69
Q

In what cases will you see hyperkalemia due to redistribution?

A

Inorganic acidosis
Insulin deficiency
Muscle trauma: rhabdomyolysis
Massive hemolysis

70
Q

What endocrine abnormality can cause a hyperkalemia?

A

Hypoadrenocorticism

Decreased aldosterone -> Na is not reabsorbed and not exchanged for K

71
Q

Pharm throw back…

What diuretics could cause a hyperkalemia?

A

Potassium sparing diuretics

Spirnolactone
Amiloride

72
Q

What are causes of a redistribution hyperkalemia ??

A

Inorganic acidosis
Insulin deficiency
Massive cellular lysis

73
Q

How does acidemia contribute to hyperkalemia ?

A

Preserve vascular pH, H+ moves into the ICF

To maintain electroneutrality, K+ will move into the ECF

74
Q

How does an insulin deficiency cause hyperkalemia ?

A

Glucose pull water out of cells -> cell shrinks and increases K+ concentration –> K+ into the vasculature

75
Q

What types of cellular lysis can lead to hyperkalemia?

A

Rhabdomyolysis
Acute tumor lysis syndrome
Severe hemolytic syndrome

K+ is released from lysed cells into vasculature

76
Q

What are causes of a pseudo hyperkalemia?

A

EDTA contamination
Marked thrombocytosis
Hemolysis

77
Q

Which animals have high RBC K+ concentrations and you can see a pseudohyperkalemia is serum is not separated quickly

A 
Horse
Pig 
Cattle 
Mice, rat
Monkey

Akitas
some Japanese dog breeds

78
Q

Clinical signs associated with hypokalemia

A

Weakness
Neurologic signs
EKG abnormalities: flattened T waves

(K < 2.5mmol/L)

79
Q

How does diarrhea contribute to hypokalemia?

A

Losss of K+ and HCO3-

Bicarbonate lost via GI causes metabolic acidosis
-> H+ is exchanged for K+ -> serum K may appear normal even but there is a total body K deficiency

80
Q

Alkalemia causes a hypokalemia. But how?

A

Maintain vascular pH by moving H+ (titrates with HCO3-) into the ECF -> K+ moves into the cell to maintain electroneutrality

81
Q

T/F: insulin can cause a hyperkalemia

A

False

Hypokalemia because insulin up regulates Na/K ATPase –> K into cell

RUSVM Clinical Pathology (18 decks)

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