Water Balance and Electrolytes Flashcards
For clinical purposes, do we use osmolaity or osmolarity?
Osmolality
What is osmolality?
[solute] per kg of Solvent (mOsm/kg)
How are osmoles measured in plasma?
Freezing-point depression osometry
What is tonicity?
AKA effective osmolaity
Ability of a solution to initiate water movement
What type of solute is distributed equal through the total body water, causing no H20 movement
Permeant solute
Eg BUN
What type of solute does NOT readily distribute across cell membranes and will cause H20 movment
Impermeant solute
Eg Na, Glu, Mannitol
_____________ dieresis occurs when there is increased urine flow caused by excessive amounts of impermeant solutes within the renal tubules
Osmotic
What is the normal urine flow rate in dogs and cats?
> 1-2mL/kg/hr
__________ dieresis occurs when there is increased urine flow caused by decreased reabsorption of free water
Water
What is specific gravity?
Ratio of weight of a volume of liquid to the weight of an equal volume of distilled water
-estimate of osmolality
What is urine specific gravity dependent on?
Number of particles present
Molecular weight of those particles
________ regulates water balance and ___________ regulates sodium
ADH/vasopressin
Aldosterone
How do the osmoreeptors in the hypothalamus maintain water balance?
Hyperosmolality -> shrink -> ADH release -> H20 reabsorption in kidney and thirst response
Hypoosmolality -> swell -> inhibit ADH release -> increased water excretion
ADH responds to
Small increases in osmolality
Large decreases in plasma volume
ADH acts on which part of the nephron by increasing expression of ______
Collecting ducts; aquaporins
What electrolyte is the primary regulator of blood volume
Sodium
Blood volume regulated by sensing of??
Atrial stretch (ANP) Renal perfusion pressure (RAAS)
What effect does aldosterone have on sodium
Converse sodium (and water)
Secrete potassium
What is hypertonic dehydration?
Water loss > Na loss
What is isotonic dehydration?
Water loss = Na loss
What is hypotonic dehydration?
Water loss < Na loss
You have confirmed dehydration, Na is increased.
Type of dehydration?
Hypertonic
Dehydration confirmed, Na is normal.
Type of dehydration?
Isotonic
Dehydration is confirmed, Na is decreased
Type of dehydration
Hypotonic
What are your DDX for hypertonic dehydration?
Diabetes insipidus / mellitus
Osmotic dieresis
Osmotic diarrhea
Water deprivation
What is the DDX for isotonic dehydration
Renal disease
Diarrhea
What is the DDX for hypotonic dehydration ?
Secretory diarrhea
Vomiting
3rd space loss (effusions)
Heat stress and sweating in horse
T/F: in a hypotonic dehydration fluid shifts from vasculature and into cells and osmoreceptors will stimulate ADH release
False
Fluid into cells -> cell/osmoreceptor swelling -> ADH release is inhibited
Cerebral edema occurs when Na is < _________ mEq/L
115-120
When do we usually see overhydration?
Iatrogenic
Iv fluid admin with inappropriate elimination like heart failure, renal obstruction, or oliguria/anuria
Over hydration can cause ??
Cardiovascular overload
Pulmonary edema
Generalized edema
Will you see clinical signs if your plasma concentration of ineffective solutes is increased (eg uremia)
No
Urea is freely diffusible across cell membranes-> osmotic changes are negligible
Wil you see clinical signs associated with an increased plasma concentration of effective solutes (eg hpernateremia or hyperglycemia )
Yes
Cellular dehydration
-> cerebral cellular volume and neurological changes (depression, stupor, coma)
Decreased plasma concentration of effective solutes will have what clinical manifestations (eg hyponatremia)
Cellular swelling –> cerebral edema and cell lysis
Lethargy, weakness, altered mentation, obtundation, seizure, death
What is the normal plasma osmolality in dogs and cats?
Dog 300 mOsm/kg
Cat 310 mOsm/kg
In a chemistry panel, how is osmolality determined?
Calculated
2[Na] + [Glu]/18 + [BUN]/3
What is the osmole gap and what does an increase in this gap mean?
OG= measured osmolality - calculated osmolaity
Increase means there is an osmotically active molecule in blood that is not measured on the serum biochemical profile
Interpret:
Measured osmolality - increased
Calculated osmolality - increased
Osmole gap < 30
Increase in an osmole reported on the chemical
Eg Na, glu, or BUN
Usually represents sodium
Interpret:
Measured osmolality - decreased
Calculated osmolality - decreased
Osmol gap < 30
Hyponatremia
Even a marked decreased in BUN or GLU will only cause minor decreased in osmolality
Interpret:
Measured osmolality - increased
Calculated osmolality - normal
Osmole gap > 30(increased)
Probable toxin (or drug)
Eg ethylene glycol or mannitol
What is the major extracellular ion
Na
How is sodium regulated?
Adequate intake (esp herbivores)
Aldosterone - renal absorption
Intestinal absorption
ADH- indirectly influence Na
What are the 3 major mechanisms that alter sodium?
Change in intake
Redistribution
Changes in excretion
If water shifts from ICF -> ECF, what effect will this have on sodium?
Hyponatremia
T/F: hyponatremia can result due to an effusion?
True
Na shift from vasculature to the effusion - heart failure and liver fialure –> edematous states
What are sources of sodium loss that can result in a hyponatremia
Renal, GI, cutaneous
What 3rd space syndromes can result in a hyponaterima?
Peritonitis Ascities Uroabdomen Chylothorax GI sequestration
Hyperglycemia or mannitol administration can have what effect on sodium?
Hyponatremia -> redistribution
Water pulled by Glu or mannitol –> decreased concentration of Na
What is the most common cause of hyponatremia?
Hypovolemia
GI -vomiting, diarrhea, or saliva
Renal - hypoadrenocorticism, ketonuria, glucosuria, prolonged dieresis
Cutaneous - sweating, burns
What are the consequences of hyponatremia ?
Hyposmolality
Cellular and cerebral edema (cellular overhydration)
Hypernatremia can result form?
Increased intake of Na
Decreased H2o intake
H20 lost in excess of Na (GI, renal, insensible losses)
A diabetic patient is markedly hyperglycemia, what do you expect the sodium concentration to be?
Hyponatremia
A diabetic patient is markedly hyperglycemic. What is the mechanism that drives the change in Na+?
Water shifts from the ICF to the ECF
Is chloride a extracellular or intracellular ion?
Extracellular
BFFs with sodium
If the change in Cl- and Na+ are proportional, what should be your top differential?
Abnormalities in Na
DDX for hyper or hypo-natremia
If the change in Cl- concentration are greater than Na+, what should be your top DDX?
Acid-base abnormalities
How is chloride regulated?
Controlled by electrochemical gradients
Corresponds to active transport of sodium
What is the most common cause of selective chloride loss?
Hypochloremic metabolic alkalosis
Gastric HCl are NOT resorbed by small intestine
Monogastric- severe vomiting
Ruminant- abomasal disorder and high GI obstruction
Selective chloride loss in horse is likely due to?
Sweating
What is paradoxical aciduria associated with hypochloremia?
Metabolic alkalosis -> excrete HCO3- in kidney
Dehydration causes reabsorption Na and HCO3 (normally would be Cl- but we are lacking) –> exacerbated alkalosis
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
Albumin and globulin high => dehydration
Pre-renal azotemia
CL = 47 x 141/130 = 51
-> still below reference => selective chloride loss
What acid base abnormality accompanies a selective chloride loss?
Metabolic alkalosis
Causes of hyperchloremia?
Parallels increases with Na+
Hyperchloremic metabolic acidosis (GI loss of HCO3)
Alkalemia
How does an alkalemia cause a hyperchloremia?
HCO3- excreted in distal nephron
Generate H+
Cl- follows H+ into plasma
Is potassium an intracellular or extracellular ion?
Intracellular
What are clinical signs associated with abnormal serum K+ concentrations?
Cardiac dysfunction - can be life threatening
Skeletal muscle dysfunction -> change in posture
How is potassium regulated?
Intake
Renal excretion -promoted by aldosterone (K exchanged for Na)
GI loss
Sweat
What is the most common cause of hyperkalemia?
Failure of renal excretion
Eg oliguria/anuria/renal failure/obstruction
In what cases will you see hyperkalemia due to redistribution?
Inorganic acidosis
Insulin deficiency
Muscle trauma: rhabdomyolysis
Massive hemolysis
What endocrine abnormality can cause a hyperkalemia?
Hypoadrenocorticism
Decreased aldosterone -> Na is not reabsorbed and not exchanged for K
Pharm throw back…
What diuretics could cause a hyperkalemia?
Potassium sparing diuretics
Spirnolactone
Amiloride
What are causes of a redistribution hyperkalemia ??
Inorganic acidosis
Insulin deficiency
Massive cellular lysis
How does acidemia contribute to hyperkalemia ?
Preserve vascular pH, H+ moves into the ICF
To maintain electroneutrality, K+ will move into the ECF
How does an insulin deficiency cause hyperkalemia ?
Glucose pull water out of cells -> cell shrinks and increases K+ concentration –> K+ into the vasculature
What types of cellular lysis can lead to hyperkalemia?
Rhabdomyolysis
Acute tumor lysis syndrome
Severe hemolytic syndrome
K+ is released from lysed cells into vasculature
What are causes of a pseudo hyperkalemia?
EDTA contamination
Marked thrombocytosis
Hemolysis
Which animals have high RBC K+ concentrations and you can see a pseudohyperkalemia is serum is not separated quickly
Horse Pig Cattle Mice, rat Monkey
Akitas
some Japanese dog breeds
Clinical signs associated with hypokalemia
Weakness
Neurologic signs
EKG abnormalities: flattened T waves
(K < 2.5mmol/L)
How does diarrhea contribute to hypokalemia?
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
Alkalemia causes a hypokalemia. But how?
Maintain vascular pH by moving H+ (titrates with HCO3-) into the ECF -> K+ moves into the cell to maintain electroneutrality
T/F: insulin can cause a hyperkalemia
False
Hypokalemia because insulin up regulates Na/K ATPase –> K into cell
