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Liz's Clinical Chemistry Module 3 > Acid-Base Balance > Flashcards

Acid-Base Balance Flashcards

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1
Q

What is the Henderson-Hasselbach equation?

A

pH = pK + log ([HCO3-]/[H2CO3})

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2
Q

What is the ratio of bicarbonate (salt) to carbonic acid (acid) which results in a normal pH of 7.4?

A

20:1

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3
Q

What is the equilibrium equation which describes the bicarbonate-carbonic acid system?

A

CO2 + H2O ↔ H2CO3 ↔ H + HCO3

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4
Q

What enzyme catalyzes the reversible reaction in the equilibrium equation?

A

Carbonic anhydrase

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5
Q

What two cell types contain carbonic anhydrase?

A

RBCs and renal epithelium cells only

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6
Q

What is the modified Henderson-Hasselbach equation as used in the bicarbonate:carbonic acid buffer system?

A

pH = pK + log([HCO3]/(alpha){pCO2])

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7
Q

Modified Henderson-Hasselbach

- What are the values for pK n the blood and alpha, the solubility coefficient?

A
  • pK = 6.1

- alpha = 0.031

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8
Q

Two reasons why hemoglobin is an important whole blood buffer, regulating acid-base balance both in the lungs and the tissues

A
  • RBCs contain carbonic anhydrase (enzyme that converts the three forms of CO2)
  • Has 9 histidine residues on each of its four chains that can accept CO2 molecules forming stable amide bonds
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9
Q

Physiologic importanceof the isohydric shift in RBCs

A

It’s important b/c it’s a set of chemical rxns by which O2 is released into the tissues and CO2 is taken up WHILE the blood remains at a constant pH

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10
Q

Process of the isohydric shift in RBCs

A
  • CO2 is generated from metabolism
  • it joins with H2O to become H2CO3 (by carbonic anhydrase)
  • It then splits to become an H+ ion and HCO3-
  • H+ ion attaches to hemoglobin to become reduced hemoglobin (HHb)
  • when that happens, oxygen is given to the tissues
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11
Q

Chloride shift

- Movement of HCO3- and Cl-

A

HCO3 goes out of the cell and Cl- goes into the cell

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12
Q

Chloride shift
- How is this shift responsible for the hyper/hypochloremia noted in acid-base disturbances for which the body is compensating?

A

This regulates how much Co- is getting into the cell so if its too low, then its hypochloremia

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13
Q

Protein buffer system

- Specific sites of action (blood, tissue, and/or organs)

A

2/3 buffering power in blood and most of the buffering power intracellularly

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14
Q

Phosphate buffer system

- Specific sites of action (blood, tissue, and/or organs)

A

Minor component of blood but great importance in the kidneys and RBCs

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15
Q

Protein buffer system

- Processes involved

A

It accepts H+ ions b/c of its histidine residues

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16
Q

Phosphat buffer system

- Processes involved

A

H+ ions are added to filtrate in the forming urine. Dibasic phosphate picks up a H+ ion to become monobasic

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17
Q

Rank the body’s buffer systems in order of their importance

A
  1. Hemoglobin (most important in the whole blood)
  2. Bicarbonate (most important in the plasma)
  3. Proteins
  4. Phosphate
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18
Q

Organ which regulates the respiratory component of acid-base balance

A

Lungs

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19
Q

Organ which regulates the metabolic component of acid-base balance

A

Kidneys

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20
Q

Pulmonary hyperventilation
- How does it regulate acid-base balance according to how it alters the bicarbonate:carbonic acid ratio, thus compensating for acidosis or alkalosis?

A

Hyperventilation ↑ CO2 release, ↓ denominator ( in of the Henderson-Hasselbach equation

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21
Q

Pulmonary hypoventilation
- How does it regulate acid-base balance according to how it alters the bicarbonate:carbonic acid ratio, thus compensating for acidosis or alkalosis

A

Hypoventilation ↓ CO2 release, ↑ the denominator of the Henderson-Hasselbach equation

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22
Q

Four specific mehcanisms by which the kidney regulates acid-base balance

A
  • Reabsorption of bicarbonate
  • Excreting excess H+ by exchanging Na+ for H+
  • Forming titratable acids w/ phosphate
  • Excreting excess H+ as NH4+
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23
Q

Reabsorption of HCO3

- How does it correct for acidosis or alkalosis?

A

In filtrate:
- HCO3 in filtrate + H ions from renal cells form carbonic acid (H2CO3), this breaks down into H2O and CO2 which enter the renal tubular cells
In renal cells:
- H2O and CO2 come together to form H2CO3. This breaks down into H+ ion and HCO3-. Bicarb goes into the interstitial fluid

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24
Q

Excreting excess H+ by exchanging Na+ for H+

- How does it correct for acidosis or alkalosis?

A

In renal cells:

- H2CO3 (carbonic acid) breaks down into H+ ion and bicarbonate. H+ ions are exchanged (out) for a sodium (in)

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25
Q

Forming titratable acids w/ phosphate

- How does it correct for acidosis or alkalosis?

A

In filtrate:

-NaHPO4 joins with the secreted H+ ion to form NaH2PO4 which is a titratable acid that is excreted in the urine

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26
Q

Excreting excess H+ as NH4+

- How does it correct for acidosis or alkalosis?

A

H+ ion plus NH3 are secreted by the renal cells. They come together to form NH4+ which is excreted in the urine

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27
Q

How do kidneys excrete acid via Na+/H+ ion exchange?

A

?

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28
Q

Kidney excretion of acid via Na+/H+ ion exchange

- How does this mechanism maintain the Gibbs-Donnan equilibrium?

A

Electoneutrality

- Total anions = total cations

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29
Q

Kidney excretion of acid via Na+/H+ ion exchange

- Interrelationship of hydrogen, sodium, and potassium ions’ reabsorption and secretion

A
  • K+ and H+ “pair up”

- Na+ is the opposite direction

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30
Q

Kidney excretion of acid via Na+/H+ ion exchange

- The reabsorption of HCO3- when Na+ is reabsorbed

A

HCO3- is reabsorbed w/ Na+ into the blood

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31
Q

Reabsorption of HCO3 by the kidney

- Role of carbonic anhydrase in renal epithelial cells

A

CO2 is reabsorbed into the renal cell and is joined with H2O to become H2CO3 (by carbonic anhydrase)

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32
Q

Reabsorption of HCO3 by the kidney

- How does the rxn of H+ and HCO3 form CO2 and H2O aid in the reabsorption of HCO3?

A

TUBULAR LUMEN
- H + HCO3 → H2CO3 –(CA)→ H2O + CO2 (reabsorbed into renal cell)
RENAL CELL
- CO2 + H2O –(CA)→ H2CO3 → HCO3 (reabsorbed into blood) + H (exchanged for Na+)

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33
Q

Reabsorption of HCO3 by the kidney

- Importance of Na+ reabsorption in HCO3 reclamation

A

If the Na/H exchange doesn’t work properly, HCO3- doesn’t get reabsorbed into the blood b/c we’re missing the secreted H+

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34
Q

Process of renal formation of NH3 and the excretion of NH4+ in maintaining acid-base balance, including how NH4+ formation assists in the reabsorption of Na+?

A

Secreted H+ binds to NH3 from the liver which also allows for the exchange of Na+

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35
Q

Importance of renal formation of NH3 and the excretion of NH4+ in maintaining acid-base balance, including how NH4+ formation assists in the reabsorption of Na+?

A

Ammonium is more excretable than ammonia???????????

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36
Q

How does the kidney excrete acid via the formation of titratable acids (principally phosphoric acid)?

A

Acts as a buffer

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37
Q

Mechanism of compensation in maintaining a normal bicarbonate:carbonic acid ratio

A

If either the [HCO3-] or the [H2CO3] becomes out of balance, the body will alter the concentration of the other component in order to return the ratio to 20:1

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38
Q

How do lab values for pH, pCO2, and HCO3 concentration change upon partial and complete compensation?

A

Partial compensation
- When the organ NOT responsible for the initial imbalance BEGINS to correct the ratio
Complete compensation
- When the pH has returned to normal

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39
Q

Metabolic imbalance

- Which compound, HCO3 or carbonic acid, is abnormal?

A

Change in [HCO3-] or [H+]

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40
Q

Respiratory imbalance

- Which compound, HCO3 or carbonic acid, is abnormal?

A

Change in [H2CO3]

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41
Q 
Metabolic acidosis (primary HCO3 deficit)
- 3 general causes
A
  • Increased addition of H+ ions, either via excess production of organic acids that exceeds the rate of elimination or addition of metabolic acids
  • Reduced excretion of acids
  • Excessive loss of bicarbonate
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42
Q

How does an increased addition of H+ ions cause metabolic acidosis?

A

H+ causes pH to decrease making it more acidic

43
Q

How does the reduced excretion of acids cause metabolic acidosis?

A

↑ in H+ making the urine more acidic

44
Q

How does excessive loss of bicarbonate cause metabolic acidosis?

A

↓ in HCO3- → ↑ H+ making the urine more acidic

45
Q

How is the bicarbonate: carbonic acid ratio affected in metabolic acidosis?

A

In all causes of metabolic acidosis, the normal 20:1 ratio is decreased b/c of the addition of acid and ↓ in HCO3

46
Q

Two conditions associated w/ increased addition of H+ ions, either via excess production of organic acids that exceeds the rate of elimination or addition of metabolic acids

A
  • Ketacidosis
  • Lactic acidosis
  • Additon of acids in poisonings (e.g., volatile metabolites)
47
Q

Two conditions associated w/ reduced excretion of acids

A
  • Renal failure
  • Renal tubular acidosis
  • Kidney is malfunctioning and can no longer secrete sufficient H+ ions
48
Q

Two conditions associated w/ excessive loss of bicarbonate

A
  • ↑ renal excretion of HCO3-
  • ↓ renal absorption of HCO3- due to ↓ renal absorption of Na+ (e.g., Addison’s disease w/ ↓ aldosterone)
  • Excessive loss of duodenal fluid that contains HCO3- (e.g., diarrhea)
49
Q

Metabolic acidosis

- One specific respiratory compensatory mechanisms

A

Respiratory component begins partial compensation via HYPERVENTILATION (“blow off” CO2) to quickly fix the problem → ↓ [HCO3-] → ↑ pH

50
Q

Metabolic acidosis

- Four specific renal compensatory mechanisms

A
  • ↑ HCO3- reabsorption
  • ↑ NH4+ formation
  • ↑ titratable acid formation
  • ↑ Na+/H+ exchange
51
Q

Metabolic alkalosis

- 3 general causes

A
  • Administration of excess alkali
  • Hydrogen ion loss
  • Potassium depletion
52
Q

How does the administration of excess alkali cause metabolic alkalosis?

A

Alkali increases the pH making it more basic

53
Q

How does hydrogen ion loss cause metabolic alkalosis?

A

Kidneys respond to H+ loss by reabsorbing more Na+ in the PCT causing more renal reabsorption of HCO3

54
Q

How does potassium depletion cause metabolic alkalosis?

A

Diuretic therapy and/or hyperaldosteronism force the kidneys to secrete more H+ ions in exchange for Na+ and K+; HCO3 is reabsorbed w/ Na+

55
Q

How is the bicarbonate: carbonic acid ratio affected in metabolic alkalosis?

A

In all causes of metabolic alkalosis, the 20:1 ratio is INCREASED b/c the primary increase is in HCO3

56
Q

Two conditions associated conditions w/ administration of excess alkali

A
  • Excessive HCO3- intake
  • Multiple blood txns (citrate anticoagulant in blood products)
  • Milk-alkali syndrome (excess intake of calcium carbonate antacids)
57
Q

Two conditions associated w/ hydrogen loss

A
  • Prolonged vomiting w/ HCl loss

- Nasogastric suctioning

58
Q

Two conditions associated w/ potassium depletion

A
  • Diuretic therapy

- Hyperaldosteronism (e.g., Cushing’s syndrome or licorice abuse)

59
Q

Metabolic alkalosis

- One specific respiratory compensatory mechanism

A

Respiratoyr component begins partial compensation via HYPOVENTILATION (retain more CO2) to quickly try to fix the problem → ↑ [HCO3-] → ↓ pH

60
Q

Metabolic alkalosis

- Four specific renal compensatory mechanisms

A
  • ↓ HCO3- reabsorption
  • ↓ NH4+ formation
  • ↓ titratable acid formation
  • ↓ Na+/H+ exchange
61
Q

Respiratory acidosis

- General cause

A

Inadequate ventilation or exchange in the lungs

62
Q

Three general causes of acute respiratory acidosis

A
  • Respiratory chemoreceptor depression (CNS trauma, narcotics such as morphine, general anesthesia)
  • Neuromuscular system disorders (Guillain-Barre, myasthenia gravis)
  • Acute pulmonary edema (pneumothorax, multiple rib fractures)
63
Q

Four general causes of chronic respiratory acidosis

A
  • COPD (most common), asthma, pneumonia, emphysema, pulmonary fibrosis
  • Cardiac disease (less blood provided to lungs for gas exchange)
  • RDS in infants
64
Q

How is the bicarbonate: carbonic acid ratio affected in respiratory acidosis?

A

In all causes of respiratory acidosis, the normal 20:1 ratio is DECREASED b/c of primary increase of carbonic acid (measured as CO2 in lab)

65
Q

Respiratory acidosis

- One specific respiratory compensatory mechanism

A

HYPERVENTILATION

66
Q

Respiratory acidosis

- Four specific renal compensatory mechanisms

A
  • ↑ HCO3- reabsorption
  • ↑ NH4+ formation
  • ↑ titratable acid formation
  • ↑ Na+/H+ exchange
67
Q

Respiratory alkalosis

- Two general causes

A
  • Psychogenic stimulation

- Hypoxia/impaired CNS control of respiration

68
Q

Causes associated w/ psychogenic stimulation

A
  • Anxiety, nervousness
  • Excessive crying
  • Pregnancy
69
Q

At least three causes of hypoxia/impaired CNS control of respiration

A
  • Pulmonary embolism
  • Excessive use of mechanical respirators
  • Thyrotoxicosis
  • GN septicemia
  • CNS lesions (menigitis)
  • Alcoholism and DT’s
  • Strenuous exercises
  • Epinephrine
  • High altitude
  • Chronic liver disease
  • Anemia
  • CHF
70
Q

Respiratory alkalosis
- How do the causes of psychogenic stimulation and hypoxia/impaired CNS control of respiration affect the bicarbonate: carbonic acid ratio?

A

In all causes of respiratory alkalosis, the normal 20:1 ratio of HCO3- to H2CO3 is INCREASED b/c the primary decrease is in H2CO3 (measured in the lab as CO2)

71
Q

Respiratory alkalosis

- One specific respiratory compensatory mechanism

A

Respiratory component compensates via HYPOVENTILATION (sometimes patient needs help and sedatives or breathing into a paper bag are used) → ↑ [HCO3-] → ↓ pH

72
Q

Respiratory alkalosis

- Four specific renal compensatory mechanisms

A
  • ↓ HCO3 reabsorption
  • ↓ NH4+ formation
  • ↓ titratable acid formation
  • ↓ Na+/H+ exchange
73
Q

Mechanism for mixed acid-base disturbance that occurs in salicylate poisoning

A

Respiratory alkalosis followed by metabolic acidosis

74
Q

Oxygen dissociation curve

  • X-axis
  • Y-axis
  • P50
A
  • X-axis → pO2 (mmHg)
  • Y-axis → % O2 saturation
  • P50 → pO2 at which Hb is 50% saturation w/ O2
75
Q

Where do right shifts of the O2 dissociation curve normally occur?

A

Tissues (↓ affinity)

76
Q

Where do left shifts of the O2 dissociation curve normally occur?

A

Lungs (↑ affinity)

77
Q

Four normal physiological factors which causes a shift to the right of the O2 dissociation curve

A

↓ pH

↑ pCO2, 2,3-DPG, temperature

78
Q

Four normal physiological factors which causes a shift to the left of the O2 dissociation curve

A

↑ → pH

↓ → pCO2, 2,3-DPG, temperature

79
Q

What is the clinical use of the p50 value?

A
  • To assess the affinity of O2 for hemoglobin

- To assess whether a right or left shift is occurring in a patient

80
Q

What are the effects on blood gas results causes by delays in testing?

A

↓ pH
↑ pCO2
↓ pO2

81
Q

What are the effects on blood gas results caused by exposure to room air?

A

↑ pH
↓ pCO2
↑ pO2

82
Q

Reference range of pH

  • Arterial blood
  • Venous blood
  • Measured or calcualted parameter in blood gas analyzer?
A
  • Arterial blood: 7.37-7.44
  • Venous blood: 7.35-7.45
  • Measured parameter in blood gas analyzers
83
Q

Reference range for pCO2

  • Arterial blood
  • Venous blood
  • Measured or calcualted parameter in blood gas analyzer?
A
  • Arterial: 35-45 mmHg
  • Venous: 40-55 mmHg
  • Measured parameter in blood gas analyzers
84
Q

Reference range for pO2

  • Arterial blood
  • Venous blood
  • Measured or calcualted parameter in blood gas analyzer?
A
  • Arterial: 80-90 mmHg
  • Venous: 30-50 mmHg
  • Measured parameter in blood gas analyzers
85
Q

Reference range for bicarbonate

  • Venous blood
  • Measured or calcualted parameter in blood gas analyzer?
A
  • Venous: 22-27 mEq

- Calculated parameter in blood gas analyzers

86
Q

Reference range for base excess

  • Arterial blood
  • Venous blood
  • Measured or calcualted parameter in blood gas analyzer?
A
  • Arterial: 0 +/- 2
  • Venous: 0 +/- 2
  • Calculated parameter in blood gas analyzers
87
Q

Reference range for %O2 saturation

  • Arterial blood
  • Venous blood
  • Measured or calculated parameter in blood gas analyzer?
A
  • Arterial: 95-99%
  • Venous: 50-70%
  • Calculated parameter in blood gas analyzers
88
Q

Reference range for CO2

  • Venous blood
  • Measured ro calculated parameter in blood gas analyzer?
A
  • Venous: 40-55%

- Measured parameter in blood gas analyzers

89
Q

Three forms of CO2 in plasma

A
  • dCO2
  • HCO3
  • H2CO3
90
Q

Total CO2 formula

A

TCO2 = (alpha)(pCO2) + HCO3

91
Q

Number of hydrogen ions needed to raise or lower 1 L of whole blood to a pH of 7.4

A

Base excess

92
Q

What is the usefulness of base excess in determining IV therapies?

A

Used to assess the metabolic component of acid-base status and helps determine whether patient should be given sodium bicarb or ammonium chloride intravenously to help correct the problem

93
Q

Three parameters which can be obtained using the Siggaard-Anderson nomogram

A
  • [HCO3]
  • Total CO2
  • Base excess
94
Q

Three abnormal (pathological) causes of a right shift

A
  • Heart and lung
  • Severe anemia
  • High altitude (↓ 2,3-DPG production)
95
Q

Three abnormal (pathological) causes of a left shift

A
  • Abnormal Hbs present
  • CO/methemoglobinemia
  • Massive txn of 2,3-DPG-depleted blood
96
Q

↑ pH, N pCO2, ↑ HCO3
↑ pH, ↑ pCO2, ↑ HCO3
N pH, ↑ pCO2, ↑ HCO3

A

Uncompensated metabolic alkalosis
Partially compensated metabolic alkalosis
Compensated metabolic alkalosis

97
Q

↑ pH, ↓ pCO2, N HCO3
↑ pH, ↓ pCO2, ↓ HCO3
N pH, ↓ pCO2, ↓ HCO3

A

Uncompensated respiratory alkalosis
Partially compensated resp. alkalosis
Compensated resp. alkalosis

98
Q

↓ pH, N pCO2, ↓ HCO3
↓ pH, ↓ pCO2, ↓HCO3
N pH, ↓ pCO2, ↓HCO3

A

Uncompensated metabolic acidosis
Partially compensated met. acidosis
Compensated metabolic acidosis

99
Q

↓ pH, ↑ pCO2, N HCO3
↓ pH, ↑ pCO2, ↑ HCO3
↓ pH, ↑pCO2, ↑ HCO3

A

Uncompensated respiratory acidosis
Partially compensated resp. acidosis
Compensated respiratory acidosis

100
Q

↑ pCO2 indicates what?

A

Respiratory acidosis

101
Q

↑ HCO3 indicates what?

A

Metabolic alkalosis

102
Q

↓ HCO3 indicates what?

A

Metabolic acidosis

103
Q

↓ pCO2 indicates what?

A

Respiratory alkalosis

Liz's Clinical Chemistry Module 3 (7 decks)

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