Acid Base & Electrolyte Balance Clinical Pathology

Front 1

True or false. PO2 can be interpreted on venous and arterial blood.

Back 1

False, PO2 is the only parameter that has to be interpreted on arterial blood

Front 2

What tube should you use for blood gas analysis?

Back 2

Green top or heparinized syringe
-Some instruments can use non-anticoagulated blood

Front 3

Why is it very important to have NO ROOM AIR IN SAMPLE for blood gas analysis (i.e. no bubbles)?

Back 3

Increases PO2 and decreases PCO2

Front 4

What are 3 ways to improve accuracy of blood gas analysis?

Back 4

1) Cap syringe with rubber stopper
2) Bring to lab and run immediately or put into ice bath for up to 3 hours
3) Record patient body temp if instrument corrects for it

Front 5

How are pH, PO2, PCO2 and HCO3 values determined?

Back 5

Measured directly: pH, PO2, PCO2
Calculated: HCO3 (Henderson Hasselbach equation)

Front 6

What 5 parameters are included in a blood gas analysis?

Back 6

1) pH: measure of [H+]
2) PO2: partial pressure of oxygen in blood (in mmHg)
3) PCO2: partial pressure of CO2 in blood (in mm Hg)
4) HCO3-: bicarbonate concentration of blood (mEq/L)
5) TCO2: total carbon dioxide (mEq/L)

Front 7

What does the total CO2 represent?

Back 7

An estimate of bicarbonate-which comprises about 96% of TCO2
-Only an estimate!

Front 8

What is O2 sat?

Back 8

The % of hemoglobin that is oxygenated-dependent on the PO2 and to a lesser extent, the pH

Front 9

How is oxygen saturation measured?

Back 9

By pulse oximeters (then its called SpO2)

Front 10

What is the base excess?

Back 10

"actual" bicarbonate concentration minus "normal" bicarbonate concentration
-based on calculations for humans so not widely used in vet med, can use for calculations for fluid therapy

Front 11

When would you expect a negative base excess?

Back 11

When a patient is acidotic-means the "actual" bicarbonate was lower than the "normal"

Front 12

True or false. There is a range of normals for each parameter of a blood gas analysis for each species.

Back 12

True

Front 13

What is the most important buffer system that minimizes change in pH?

Back 13

Bicarbonate/carbonic acid system
CO2 + H2O <-----> H2CO3 <----> H+ + HCO3-

Front 14

What is the respiratory control of pH?

Back 14

CO2 + H2O
-Can breathe off CO2 to shift H+ ---> CO2 ---> decreased pH
-Hyper or hypoventilation

Front 15

What is metabolic control of pH?

Back 15

H+ + HCO3-
-Excretion or reabsorption of HCO3- in urine

Front 16

What do you call it if there's a decreased pH with a decreased [HCO3-]?

Back 16

Metabolic acidosis
-More renal excretion of bicarb

Front 17

What does it mean if the pH is increased and the concentration of bicarbonate is increased?

Back 17

Metabolic alkalosis
-Increased retention of bicarbonate in kidneys and increased H+ secretion into filtrate

Front 18

What does it mean if the pH is increased and the concentration of bicarbonate is increased?

Back 18

Metabolic alkalosis
-Increased retention of bicarbonate in kidneys and increased H+ secretion into filtrate

Front 19

What does it mean if the pH is decreased and the PCO2 is increased?

Back 19

Respiratory acidosis
-More CO2---> H+

Front 20

What does it mean if the pH is decreased and the PCO2 is increased?

Back 20

Respiratory acidosis
-More CO2---> H+

Front 21

What does it mean if the pH is increased and PCO2 is decreased?

Back 21

Respiratory alkalsosis
-Breathing off CO2 so H+---> CO2

Front 22

What does it mean if the pH is increased and PCO2 is decreased?

Back 22

Respiratory alkalsosis
-Breathing off CO2 so H+---> CO2

Front 23

How long does respiratory changes in pH take? Metabolic?

Back 23

Respiratory: occur within minutes
Metabolic (kidneys): days to weeks

Front 24

How long does respiratory changes in pH take? Metabolic?

Back 24

Respiratory: occur within minutes
Metabolic (kidneys): days to weeks

Front 25

What does it mean if a compensatory response doesn't seem appropriate for the change in pH?

Back 25

The body won't over compensate!!!!! so it means there's a problem in another system

Front 26

What does it mean if a compensatory response doesn't seem appropriate for the change in pH?

Back 26

The body won't over compensate!!!!! so it means there's a problem in another system

Front 27

How does the body compensate for metabolic acidosis?

Back 27

Hyperventilate, blow off CO2 ----> pH returns to normal

Front 28

How does the body compensate for metabolic alkalosis?

Back 28

Hypoventilation---> blow off less CO2---> increase in H+--> pH returns to normal

Front 29

When does compensation happen? Correction?

Back 29

Compensation: When changes in respiratory system (or metabolic system) occurs
Correction: occurs when primary cause is corrected

Front 30

How does the body compensate for respiratory acidosis?

Back 30

Renal excretion of H+ and reabsorption of HCO3 ---> pH eventually returns to normal
-renal response=compensatory
-Correction= when respiratory abnormality is corrected

Front 31

What are the 3 easy steps to evaluation of acid-base problems?

Back 31

1) Determine the direction of pH change
-If pH> 7.4 alkalosis
2) Determine which system, respiratory or metabolic has shifted in the direction of the pH change
-determines what system the primary abnormality is in
-If both shift in same direction as pH=mixed metabolic and respiratory problem
3) Evaluate compensatory response of the other system

Front 32

What does it mean if both the metabolic and respiratory control has shifted in the same direction as the pH?

Back 32

There is a mixed metabolic and respiratory problem

Front 33

What are the 2 basic mechanisms for decreased bicarbonate?

Back 33

1) Loss of bicarbonate from the body
2) Retention, generation or ingestion of acid

Front 34

What is it called when metabolic acidosis occurs because of loss of bicarbonate from the body?

Back 34

Secretional or hyperchloremic metabolic acidosis

Front 35

Why are animals with secretional acidosis often hyperchloremic?

Back 35

Because kidneys will resorb Cl- to make up for loss of HCO3-
-Balance charge

Front 36

What are 3 ways bicarbonate be lost from the body?

Back 36

1) Intestinal fluid-diarrhea or trapped by GI obstruction
2) Saliva-especially in ruminants
3) Urine-rare, happens with renal tubular acidosis where kidneys are unable to resorb bicarb

Front 37

What is it called when an animal has metabolic acidosis from retention, generation, or ingestion of acid?

Back 37

Titrational metabolic acidosis

Front 38

What buffers the excess H+ ions when there's retention, generation or ingestion of acid?

Back 38

Excess acid and bicarb
-More acid, the more anions because acid dissociates into H+ and A-, bicarb binds with H+ and gets rid of it so there's increased anions

Front 39

What are 4 causes of retention, generation or ingestion of acid?

Back 39

1) Lactic acid-from shock, grain overload
2) Keto acids-diabetes & starvation
3) Uremic acids (normally cleared by kidney, BUN & creatinine will be increased)
4) Exogenous acids e.g. ethylene glycol, salicylates

Front 40

How do you determine if metabolic acidosis is secretional or titrational?

Back 40

If the anion gap is higher than normal than it's titrational (based on large amounts of unmeasured negative charges produced w/ titrational)
-Hyperchloremia occurs with secretional not titrational

Front 41

How do you calculate the anion gap?

Back 41

([Na+] + [K+]) - ([HCO3-] + [Cl-]) = difference b/w measured cations and measured anions= unmeasured anions and unmeasured cations, but unmeasured cations are very tightly regulated so it's an increased in unmeasured anions= organic acids

Front 42

What is the normal anion gap in dogs & cats? other species?

Back 42

Dogs and cats: 15-25
Other species: 10-20

Front 43

What accounts for an increase in the anion gap?

Back 43

Unmeasured anions, that is organic acids (lactic acid, uremic acid, ketoacid)

Front 44

What can decrease the anion gap?

Back 44

Hypoalbuminemia

Front 45

What is the treatment of metabolic acidosis?

Back 45

Usually fluid replacement +/- bicarbonate

Front 46

What is USUALLY the cause of metabolic alkalosis?

Back 46

Loss of HCl from stomach or abomasum:
-Vomiting
-Abomasal displacement/impaction
-Vagal indigestion

Front 47

What is paradoxic aciduria?

Back 47

When an animal has metabolic alkalosis but acidic urine is produced

Front 48

Why is Na+ resorbed by the kidneys in an animal in metabolic alkalosis?

Back 48

Animals are usually hypovolemic (fluid is sequestered or lost with H+ and Cl- ions) so Na+ is resorbed by kidneys to maintain blood pressure

Front 49

What is the pathogenesis of paradoxic aciduria?

Back 49

Animals in metabolic alkalosis are usually hypovolemic so resorb Na+, then to maintain electroneutrality the body would normally resorb Cl-, but Cl- is low so H+ is excreted in urine to balance Na+ resorption

Front 50

What are 2 less common causes of metabolic alkalosis?

Back 50

1) Over-administration of bicarb
2) Other electrolyte imbalances

Front 51

What is the treatment of metabolic alkalosis?

Back 51

Correct what is causing it!
Generally replace fluid volume and Cl-

Front 52

What are 3 extrathoracic causes of hyperventilation?

Back 52

1) Fever
2) Pain
3) Anxiety

Front 53

What are 5 intrathoracic causes of respiratory alkalosis?

Back 53

1) Pneumonia
2) Pulmonary edema
3) Pleural effusion
4) Thoracic masses
5) Congestive heart failure
-All result in decreased PO2

Front 54

What is ALWAYS the cause of respiratory alkalosis?

Back 54

Hyperventilation

Front 55

What is the treatment of respiratory alkalosis?

Back 55

Treat the underlying cause

Front 56

In general, what causes respiratory acidosis?

Back 56

Anything that decreases gas exchange across alveoli

Front 57

What are 6 specific causes of respiratory acidosis?

Back 57

1) Decrease gas exchange across alveoli
2) Severe pulmonary disease
3) CNS depression
4) Severe bloat/abdominal masses that decrease tidal volume
5) Pleural effusion
6) Neuromuscular disease

Front 58

Basically anything that causes _________ causes respiratory acidosis if its bad enough.

Back 58

Intrathoracic respiratory alkalosis, because gets so bad CO2 can't be exchanged at alveoli -->> increased H+

Front 59

What usually happens to PO2 in animals in respiratory acidosis?

Back 59

Usually decreased PO2 unless on supplemental O2

Front 60

What is the most common non-traditional approach to acid-base abnormalities?

Back 60

Stewart's quantitative approach
-Includes consideration of proteins (and Ca++, Mg++, lactates, sulfates and urates)

Front 61

What are the serum electrolytes?

Back 61

Na+, K+, Cl-, HCO3-

Front 62

What type of sample is collected for evaluation of electrolyte balance?

Back 62

Serum is most common
Heparinized plasma can be used

Front 63

What 2 factors may interfere with electrolyte assays?

Back 63

Hemolysis & lipemia

Front 64

What is the major cation in the plasma?

Back 64

Sodium

Front 65

What 3 things regulate sodium levels?

Back 65

1) Aldosterone
2) Atrial natriuretic factor
3) ADH

Front 66

How does aldosterone affect Na+ levels? Atrial natriuretic factor?

Back 66

Aldosterone: increase Na+ reabsorption
Atrial natriuretic factor: increased renal Na+ excretion by inhibiting aldosterole

Front 67

What is the overall general cause of hypernatremia?

Back 67

Pure water loss or solute gain

Front 68

What are the 5 specific causes of hypernatremia?

Back 68

1) Dehydration-by far most common
2) Salt poisoning i.e. lots of salt, limited access to water
3) Abnormal sweating or panting
4) Primary adipsia (neurologic disorder that makes you not drink) RARE
5) Hyperadrenocorticism-very slight hypernatremia

Front 69

What is almost always the general cause of hyponatremia?

Back 69

Loss of Na+ rich fluids

Front 70

What are 8 specific causes of hyponatremia?

Back 70

1) Hypoadrenocorticism-Na+ is lost in urine
2) Diarrhea-especially horses, dogs w/ whipworms
3) Renal disease-if Na+ wasting in proximal tubules
4) Dietary salt deficiency
5) Low Na+ fluid therapy
6) Diabetes mellitus-hyperosmolality (very uncommon)
7) Third space loss e.g. displaced abomasum
8) Artifact-lipemia/hyperproteinemia

Front 71

What is the major intracellular cation?

Back 71

Potassium

Front 72

What electrolyte has a very narrow range for normal function?

Back 72

K+

Front 73

Where is most K+ located?

Back 73

In cells-can be quickly shifted in and out to maintain serum levels

Front 74

True or false. Serum K+ reflects the body K+.

Back 74

False, not always

Front 75

What 3 things affect the K+ serum concentration?

Back 75

1) Diet
2) Renal excretion
3) Shifting in & out of cells

Front 76

What are 5 more common causes of hyperkalemia?

Back 76

1) Decreased glomerular filtration/urinary obstruction
2) Hypoadrenocorticism- aldosterone deficiency leads to retention of K+
3) Acidosis-H+ shift into cells and K+ shift out (into plasma)
4) Tissue necrosis-because K+ is high in cells
5) Insulin deficiency-because it shifts K+ into cells

Front 77

What are the 5 less common causes of hyperkalemia?

Back 77

1) Hemolysis-breeds/species that have high K+ in erythrocytes
2) Marked thrombocytosis
3) Parenteral K+ administration
4) Hyperkalemic periodic paralysis- in horses
5) Artifact-use of potassium EDTA in sample

Front 78

What are 7 causes of hypokalemia?

Back 78

1) GI loss-vomiting & diarrhea
2) Urinary loss
3) Hyperadrenocorticism-w/ excessive urinary loss
4) Alkalosis-H+ shifts out of cells, K+ moves in
5) Insulin therapy-moves K+ into cells
6) Dietary deficiency
7) Artifact-lipemia or hyperproteinemia

Front 79

What are 3 situations where urinary loss can result in hypokalemia?

Back 79

1) Osmotic diuresis
2) Diuretics
3) Cats w/ chronic metabolic acidosis

Front 80

What is the major anion of the extracellular fluid?

Back 80

Chloride

Front 81

What usually results in a change of chloride levels?

Back 81

Changes in water balance in body- tends to go along w/ Na+ to maintain electroneutrality

Front 82

*What is the normal difference b/w Na and chloride concentrations?

Back 82

around 29-42 mEq/L

Front 83

What are 3 causes of a change in chloride balance that's not due to a change in water balance in the body?

Back 83

1) Hypochloridemia in metabolic alkalosis, where Cl- is lost w/ gastric or abomasal fluids
2) Hyperchloridemia in secretional metabolic acidosis
3) Artifact in K+ bromide therapy- the instrument reads Br- as Cl-

Front 84

What determines osmolality?

Back 84

Determined by number of particles in solution (NOT size of particles)
-Small but numerous molecules, like Na+ more important in osmolality than proteins

Front 85

What electrolyte basically controls osmolality?

Back 85

Na+
-Control of water in body related to control of Na+

Front 86

How is serum/plasma osmolality measured?

Back 86

By Osmometer
-Usually 280-310 mOsm/kg
-Or can be calculated using equation

Front 87

What is the equation for the osmolal gap?

Back 87

=actual Osm-calculated Osm

Front 88

What does an increase in the osmolality gap mean?

Back 88

Indicates osmotically active molecule such as ethylene glycol, lactate, ketones, uremic acids etc.
-Not used commonly in clinics