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Clinical Pathology > Lecture 22 - Acid Base Disturbances > Flashcards

Lecture 22 - Acid Base Disturbances Flashcards

1
Q

she said to follow the learning objectives

A
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2
Q

How do we determine acid-base status of a
patient?

A
  1. Measures total carbon dioxide, which is an estimate of the plasma bicarb concentration. 95% of carbonate dioxide is in the form of bicarbonate.
    - does not give info on respiratory acid disturbances or compensation.
  2. Blood gas measures ph, pco2 and p02.
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3
Q

H+ is _________ generated but maintained at very ________ quantities

A

H+ is constantly generated but maintained at very minute quantities

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4
Q

List the Contributors to blood pH

A
  1. pCO2 (changes in ventilation)
  2. Addition or removal of acids (H+): lactated metabolites of ethylene glycol,
    loss of H+
  3. Strong ion movements: Na+, K+, Cl-
  4. Serum proteins, phosphates and other weak acids
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5
Q

Why is the maintenance of pH important?

A
  • Protein structure
  • Metabolism and enzymes
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6
Q

What keeps H+ in check?

A

Buffers & regulatory systems!
* Bicarbonate system: HCO3-, pCO2
* Non-bicarbonate: PO4, NH3-, Hgb, Albumin & other plasma proteins
* Systems: renal excretion (H+), alveolar ventilation (CO2)

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7
Q

Interpretation of ACID-BASE from biochemistry data is based on?

A

pH

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8
Q

Classification of acid-base disturbances as?

A

A. Metabolic acidosis
1. Titrational metabolic acidosis
2. Secretional metabolic acidosis
B. Metabolic alkalosis
C. Mixed acid-base disturbance
1. Both a metabolic acidosis and metabolic alkalosis
Neutral pH is 7. Anything below 7 is considered acidic, anything above is is considered alkaline.

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9
Q

Alkalemia vs. acidemia?

A

pH above 7 = alkalemia
pH below 7 = acidemia

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10
Q

Metabolic acidosis vs. metabolic alkalosis?

A

Bicarbonate measure in metabolic system

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11
Q

What is the base excess?

A
  • Characterizes the overall metabolic acid-base status independent of
    the respiratory acid-base status
  • Complex calculation
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12
Q

BICARBONATE = to?

A

TCO2/HCO3-

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13
Q

HCO3- on the biochemistry profile represents?

A

The amount of CO2 gas that is released from
plasma/serum when mixed with a strong acid

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14
Q
  • Increased TCO2 =
A

metabolic alkalosis

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15
Q
  • Decreased TCO2 =
A

metabolic acidosis

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16
Q

What is the anion gap?

A
  • Used to further characterize a metabolic acidosis (decreased TCO2)
  • Approximates unmeasured anions and/or cations in circulation
  • Calculated value on biochemistry analyzers
  • Based on the difference between measured anions and measured cations:
    • Anion Gap (AG) = [Na+ + K+] – [Cl- + HCO3-]
  • Much more common to have unmeasured anions than cations
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17
Q

When we have an increased anion gap it can be caused by?

A

Certain metabolites.
Unmeasured anions that cause an elevated anion gap
◦ Ketones
◦ Lactate
◦ Uremic acids
◦ Ethylene glycol metabolites
◦ Salicylates
◦ Hyperalbuminemia

“KLUE”

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18
Q

A metabolic acidosis with an elevated anion gap is called a?

A

titrational metabolic acidosis

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19
Q

When we have a decreased anion gap?

A
  • Uncommon and not clinically significant
    Causes:
    ◦ Decrease in unmeasured anions which happens in cases of Hypoalbuminemia
    ◦ Increase in unmeasured cations which happens in cases of Hypercalcemia and hypermagnesemia
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20
Q

What are the laws of electroneutrality?
FYI

A
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21
Q

How is blood gas data generated?

A

It is generated on electrochemical analyzers
* Many point-of-care (in clinic) analyzers available

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22
Q

What are the sample requirements for blood gas data?

A

A- Venous or arterial blood
* Venous is much more common and is adequate for acid-base evaluation
IMPORTANT –> * Arterial blood is required for complete evaluation of blood oxygenation
B- Whole blood is collected into a syringe (usually heparinized) and capped
* Avoid exposure to room air and gas bubbles in the collection syringe can affect accuracy
of pH
* Process quickly and put on ice if not immediate

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23
Q

What would happened if delayed sample
processing?

A
  • Decreased pH
  • Decreased P02

This is why:
Samples must be analyzed within 10 min if at room temp.
Samples must be analyzed within 1 h if on ice

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24
Q

What would happened if sample is exposed to air?

A
  • Increased pH
  • Increased P02
  • Decreased PCO2
  • Decreased HCO3-
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25
Q

What is measured in blood gas?

A
  1. pH (measured by H + ions)
  2. pCO2 (partial pressure of carbon dioxide)
    * Allows us to evaluate RESPIRATORY acid-base
    imbalances
  3. Electrolytes (calcium, magnesium, etc)
  4. pO2 (partial pressure of oxygen)
26
Q

What is calculated on blood gas?

A
  1. *HCO3-
  2. Base excess (BE)

total CO2 is another way to measure plasma bicarb. This is the total CO2 released when a serum or plasma sample is mixed with a strong acid.

27
Q

pH
* If below RI =
* If above RI =

A

acidemia (acidosis)
alkalemia (alkalosis)

28
Q

HCO3-
* If below RI =
* If above RI =

A

metabolic acidosis
metabolic alkalosis

29
Q

Base excess
* Not heavily used (doesn’t add any additional info) –can guide ______ and ___________ therapy
* If <0 = metabolic _______
* If >0 = metabolic ________

A

Base excess
* Not heavily used (doesn’t add any additional info) –can guide fluid and bicarbonate therapy
* If <0 = metabolic acidosis
* If >0 = metabolic alkalosis

30
Q

CO2
* If above RI = _________ or __________
- Usually from ___________
- Indicates respiratory _________
* If below RI = ________ or __________
- Usually from _________ (panting)
- Indicates respiratory ________

A

CO2
* If above RI = hypercapnia or hypercarbia
* Usually from hypoventilation
* Indicates respiratory acidosis
* If below RI = hypocapnia or hypocarbia
* Usually from hyperventilation (panting)
* Indicates respiratory alkalosis

31
Q

Interpretation of pCO2 is ________ of HCO3- interpretation
◦ When it increases, it is an _______ (not an ________)

A

Interpretation of pCO2 is opposite of HCO3- interpretation
◦ When it increases, it is an acidosis (not an alkalosis)

32
Q

Normal blood pH = _____-_____ (7.40 is average pH)
* Even ______ variations outside this range can have severe consequences
* Lungs regulate pCO2, which is an ____ via changes in ________ status
* Kidneys (renal tubules) regulate _____, which is a base via excretion of ____ or conservation of _____
* When changes in HCO3- occur, the lungs compensate by changing _____
* Respiratory compensation is _____
* When changes in pCO2 occur, the kidneys compensate by changing _____
* Metabolic compensation is ____
CO2 + H 2O ⟺ H 2CO3 ⟺ H + + HCO3-

A

Normal blood pH = 7.35-7.45 (7.40 is average pH)
* Even minor variations outside this range can have severe consequences
* Lungs regulate pCO2, which is an acid
* via changes in ventilation status
* Kidneys (renal tubules) regulate HCO3-, which is a base
* via excretion of H+ or conservation of HCO3-
* When changes in HCO3- occur, the lungs compensate by changing pCO2
* Respiratory compensation is FAST
* When changes in pCO2 occur, the kidneys compensate by changing HCO3
* Metabolic compensation is SLOW
CO2 + H 2O ⟺ H 2CO3 ⟺ H + + HCO3-

33
Q

walked through this graphic

A
34
Q

What is the stepwise approach to blood gas data?

A
  1. Evaluate the pH
  2. Evaluate HCO3-
  3. Evaluate pCO2
  4. Determine which mechanism (respiratory or metabolic) is primary and which is compensatory
    * Primary mechanism is driving the pH away from 7.4
    * The compensatory mechanism often moves in the opposite direction of the primary
    pH disturbance
    * If you can’t tell which is primary or secondary, there is probably a mixed disturbance
  5. Determine if compensation is adequate or inadequate
    * Adequate compensation should produce a pH between 7.4-7.6
35
Q

What is the stepwise approach to interpretation of acid base disturbances?

Evaluation of acid base status begins with analysis of blood _____, _________ concentration and partial pressure of ______ ______ (?)

Step 1. Evaluate ____ (______ or _______ from Reference interval limits to classify if it as alkalemia or acidemia.
Step 2: Evaluate _______ (?) conc. and identify it is Metabolic ________ or ______

Step 3: evaluate the ____ to classify the acid-base disturbance as “________ concentration abnormality” or as respiratory ______ or respiratory _______
Step 4: if needed, evaluate any combined abnormalities between ______ and ______. If both, the values are abnormal, the primary acid-base base disturbance is almost always due to the most ______ value in the pair. The change in the least abnormal value is almost always due to a ________ response in an attempt to _________ the pH. In addition, the compensating value is either abnormal or moving toward abnormal in a direction opposite what would be required to cause
the pH abnormality. This step may also aid in identification of acid-base disturbances
due to more than one process, known as a _______ acid-base disturbance.

A

Evaluation of acid base status begins with analysis of blood pH, bicarbonate
concentration and partial pressure of carbon dioxide (pCO2)
Step 1. Evaluate pH (decreased or increased from Reference interval limits to classify
it as alkalemia or acidemia.
Step 2: Evaluate bicarconate (HCO3-) concentration and identify it is Metabolic
acidosis or alkalosis
Step 3: evaluate the pCO2 to classify the acid-base disturbance as “bicarbonate
concentration abnormality” or as respiratory acidosis or respiratory alkalosis
Step 4: if needed, evaluate any combined abnormalities between HCO3- and pCO2. If
both, the HCO3- and pCO2 values are abnormal, the primary acid-base base
disturbance is almost always due to the most abnormal value in the pair. The change
in the least abnormal value is almost always due to a compensation response in an
attempt to normalize the pH. In addition, the compensating value is either abnormal
or moving toward abnormal in a direction opposite what would be required to cause
the pH abnormality. This step may also aid in identification of acid-base disturbances
due to more than one process, known as a mixed acid-base disturbance.

36
Q
A
37
Q

Respiratory acidosis =

A

retention of CO2, Hypoventilation

38
Q

What are the causes of respiratory acidosis?

A
  • Anesthesia
  • Diffuse pulmonary disease
  • Intra-thoracic lesions
  • CNS disease
39
Q

Patients with respiratory acidosis have

A

pH ↓ acidemia
pCO2 ↑ acidosis
HCO3- ↑ Alkalosis

40
Q

How does the body compensate for respiratory acidosis?

A

Compensation
* Secondary metabolic alkalosis (retention of HCO3-)

41
Q

Respiratory alkalosis =

A

release of CO 2 Hyperventilation

42
Q

What are the causes of respiratory alkalosis?

A
  • Hypoxemia
  • Pain, anxiety, etc
  • Hyperthermia
  • Drugs that stimulate the medullary respiratory center
43
Q

Patients with respiratory alkalosis have

A

pH ↑ Alkalemia
pCO2 ↓ Alkalosis
HCO3- ↓ Acidosis

44
Q

How does the body compensate for respiratory alkalosis?

A

Secondary metabolic acidosis (renal retention of H+)

45
Q

What are the two mechanisms of metabolic acidosis?

A
46
Q

What are the compensatory mechanisms for metabolic acidosis in the short term and long term?

A
  • Short-term: respiratory alkalosis, increased ventilation
  • Long-term: increased renal excretion of H+
47
Q

Metabolic acidosis patients will have

A

pH ↓ Acidemia
pCO2 ↓ Alkalosis
HCO3- ↓ Acidosis

48
Q

Biochemical findings for metabolic acidosis
1-Titrational Metabolic Acidosis
(increase in acid)

  • __________ TCO2
  • _________ anion gap
  • Cl- _______ RI
A
  • Decreased TCO2
  • Elevated anion gap
  • Cl- within RI
49
Q

Biochemical findings for metabolic acidosis
1-Secretional Metabolic Acidosis
(loss of Base)

  • __________ TCO2
  • _________ anion gap
  • Cl- _______ RI or _________
  • If Cl- is increased in excess of Na+ –> ________ metabolic __________
A
  • Decreased TCO2
  • Normal anion gap
  • Cl- within RI or increased
  • If Cl- is increased in excess of Na+ –> hyperchloremic metabolic acidosis
50
Q

What are the two mechanisms of metabolic alkalosis?

A

1) increase in Base
2)Loss of Acid

51
Q

Excessive Renal loss of H+ –> Differentials:
1. ___________
2. _____________
- Stimulates H+, K+, ATPase pump
* K+ ________
* H+ _______
* HCO3- _________
3. Chronic respiratory _______ (>3-5 days)

A

Excessive Renal loss of H+ –> Differentials:
1. Diuretics
2. Hypokalemia
- Stimulates H+, K+, ATPase pump
* K+ retention
* H+ secretion
* HCO3- generation
3. Chronic respiratory acidosis (>3-5 days)

52
Q

Hypochloremic metabolic alkalosis –> Differentials:
A. Monogastrics:
- Severe gastric ________
- Pyloric outflow _________
B. Ruminants:
- Sequestration of fluid in the _________
* ______
* __________ displacement

A

Hypochloremic metabolic alkalosis –> Differentials:
A. Monogastrics:
- Severe gastric vomiting
- Pyloric outflow obstruction
B. Ruminants:
- Sequestration of fluid in the abomasum
* Ileus
* Abomasal displacement

53
Q

Biochemical findings in METABOLIC ALKALOSIS
* _________ TCO2
* ________ anion gap
* __________ Cl- in excess of Na+
* ____________ metabolic alkalosis

A

Biochemical findings in METABOLIC ALKALOSIS
* Increased TCO2
* Normal anion gap
* Decreased Cl- in excess of Na+
* Hypochloremic metabolic alkalosis

54
Q

What are the compensatory mechanisms of metabolic alkalosis both in the short term and long term?

A
  • Short-term: respiratory acidosis, decreased ventilation
  • Long-term: increased renal retention of H+
    These patients will have
    pH ↑ Alkalemia
    pCO2 ↑ Acidosis
    HCO3- ↑ Alkalosis
55
Q

PARADOXICAL ACIDURIA
* Defined as an _______ (__________) urinary pH when there is a metabolic alkalosis (________ pH)
* Because of hypochloremia, HCO3- instead of Cl- is _________ along with ______ (__________ concept)
* Na+ resorption is coupled with __________ of H+ –> ____ of H+ into the urine –> ________ urinary pH
* Treatment involves correcting the ______ deficit with appropriate fluids

A

PARADOXICAL ACIDURIA
* Defined as an acidic (decreased) urinary pH when there is a metabolic alkalosis (increased pH)
* Because of hypochloremia, HCO3- instead of Cl- is resorbed along with Na+ (electroneutrality concept)
* Na+ resorption is coupled with secretion of H+ –> loss of H+ into the urine –> acidic urinary pH
* Treatment involves correcting the NaCl deficit with appropriate fluids

56
Q

When to be suspicious of a mixed acid-base
disturbance?

  • When the AG is ____ but the TCO2 is normal
  • When Cl- is ____ in excess of Na+ but the TCO2 is _____
  • When Cl- is ____ in excess of Na+ but the TCO2 is ______
A
  • When the AG is high but the TCO2 is normal
  • When Cl- is lost in excess of Na+ but the TCO2 is normal
  • When Cl- is high in excess of Na+ but the TCO2 is normal
57
Q

You should suspect a mixed acid-base disturbance when?

A

When the data just don’t quite fit together and TCO2 often falls within the RI but not always

58
Q

List some examples of mixed acid-base disturbances

  • _____ anion gap with a _____ TCO2- and ____ Cl- (what??)
  • *Possible patient signalment: ?
  • Interpretation: ?
  • Acidosis from _________; alkalosis from _________
A
  • High anion gap with a normal TCO2- and low Cl- (what??)
  • *Possible patient signalment: diabetic ketoacidotic dog with vomiting
  • Interpretation: Titrational metabolic acidosis AND hypochloremic metabolic alkalosis (mixed disturbance)
  • Acidosis from ketones; alkalosis from vomiting
59
Q

When do mixed acid-base disturbances occur?

A
  • Occur when 2 primary acid-base disturbances occur simultaneously
  • Look for them when you have an animal with:
    1. Electrolyte disturbances and/or
    2. A disease associated with an acid-base disturbance, yet has a
    normal bicarbonate (chemistry panel) or pH (blood-gas)
    3. A compensatory response is moving in the wrong direction
60
Q

Case 1. Chemistry and blood Gas Data from a 2 day old F Calf who was septic. The patient had profuse diarrhea (scours) and pneumonia.

A

The pH is low indicating an acidemia.
The pCO2 is high, indicating a respiratory acidosis (primary)
The HCO3 is low, indicating a metabolic acidosis (primary)
There are two primary changes driving the acidemia, not a
primary change with a compensatory change.
The bicarbonate (base) is decreased indicating a metabolic acidosis.
There is a high anion gap present supporting a titrational metabolic
acidosis, in this case it was due to lactate.
The sodium and chloride are decreased proportionally, no acid-base
change here

Clinical Pathology (31 decks)

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