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Clinical Chemistry > Blood Gas and pH measurements > Flashcards

Blood Gas and pH measurements Flashcards

1
Q

What will diagnostic tests identify?

A

(and evaluate) dysfunction if patient’s history and physical examination reveal evidence of respiratory dysfunction

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2
Q

one of the first test ordered to assess respiratory status because it helps evaluate gas exchange in lungs

A

Arterial blood gas

*measures how well the person’s lung and kidneys are working and how well the body is using energy

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3
Q

Any substance that can yield hydrogen (H+) or hydronium ion (H3O+) when dissolved in water

A

Acid

release of proton or H+

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4
Q

Substance that can yield hydroxyl ions (OH-)

A

Base

ACCEPT proton or H+

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5
Q

negative logarithm of the ionziation constant of an acid

A

pK or pKa

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6
Q

pKa value of strong acids

A

<3

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7
Q

pKa value of strong bases

A

> 9

^pKa ^pH

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8
Q

It is the affinity of the acid whether or not to give out its H+

A

pKa

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9
Q

negative logarithm of H+ concentration

A

pH

represents hydrogen concentration
*pH= pKa + log [base]/[acid]

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10
Q

combination of a weak acid and/or weak base and its salt

A

buffer

*able to resist changes in pH

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11
Q

Effectiveness of buffer depends on

A

pK of buffering system

pH of environment in which it is placed

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12
Q

Normal pH range, acidosis and alkalosis

A

Normal: 7.35-7.45
Acidosis: < 7.35
Alkalosis > 7.45

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13
Q

diagnostic procedure in which blood is obtained from an artery directly by an arterial puncture or accessed by a way of indwelling arterial catheter

A

Arterial Blood Gas

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14
Q

Arterial blood gas is only taken for (indications):

A
  • To obtain information about patient ventilation (pCO2), oxygenation (pO2), and acid-base balance
  • To monitor gas exchange and acid-base abnormalities for patient on mechanical ventilator or not
  • To evaluate response to clinical intervention and diagnostic evaluation (oxygen therapy)
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15
Q

When is arterial blood gas most useful?

A

when a person’s breathing rate is increased or decreased

when person has very high blood sugar levels, sever infection or heart failure

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16
Q

Components of ABG

A

pH
pCO2
pO2
HCO3-

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17
Q

[Components of ABG]

Measures hydrogen ion concentration in the blood, it shows blood acidity or alkalinity

A

pH

normal value: 7.35-7.45

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18
Q

[Components of ABG]

carried by the blood for excretion by the lungs, known as respiratory parameter

A

pCO2

It is the partial pressure of CO2
normal value: 35-45 mmHg

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19
Q

[Components of ABG]

dissolved in the blood; reflects body’s ability to pick up oxygen from the lungs

A

pO2
(partial pressure of O2)
normal value: 80-100 mmHg

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20
Q

[Components of ABG]

metabolic parameter;; reflects kidneys ability to retain and excrete bicarbonate

A

HCO3-

normal value: 22-28 mEq/L

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21
Q

T or F: The body constantly works to maintain a balance (homeostasis) between acids and bases

A

True

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22
Q

These are byproducts formed as cells use nutrients to produce energy

A

H+ and CO2

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23
Q

Where does Acid-base balance depend on?

A

regulation of free H+

*slight imbalances affect emtabolism and essential body functions

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24
Q

What conditions affect acid-base balance?

A

infection or trauma

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25
Q

Disorder trend for respiratory acidosis

A

Respiratory
Acidosis ↓pH ↑pCO2
uncompensated HCO3-

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26
Q

Disorder trend for respiratory ALKALOSIS

A

MATAAS NA PH
MABABANG PCO2
UNCOMPENSATED HCO3-

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27
Q

Disorder trend for METABOLIC ACIDOSIS

A

LOW PH
UNCOMPENSATED PCO2
LOW HCO3-

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28
Q

Disorder trend for METABOLIC ALKALOSIS

A

HIGH PH AND HCO3-

Uncompensated pCO2

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29
Q

T or F: The circulatory and metabolic system works together to keep the body’s acid-base balance within normal limits (compensation)

A

respiratory and metabolic

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30
Q

Compensation mechanism for respiratory acidosis and respiratory alkalosis

A

Metabolic system

r. acid: high hco3- reabsorption
r. alkal: low hco3- reabsorption

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31
Q

Compensation mechanism for metabolic acidosis and alkalosis

A

Respiratory rate

m. acid: increase in rate and depth (low pCO2)
m. alkal: decrease in rate and depth (high pCO2)

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32
Q

Why is pH decreased and pCO2 increased in uncompensated phase of respiratory acidosis?

A

no response from kidneys yet to the acidosis, so the HCO3- will remain normal

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33
Q

What happens during the partially compensated phase of respiratory acidosis?

A

The kidneys start to respond to the acidosis by increasing the amount of circulating HCO3–
↓ pH ↑ pCO2 ↑HCO3-

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34
Q

Stage in respiratory acidosis where pH returns to normal pCO2 and HCO3- levels are still high to correct acidosis

A

Fully compensated

N ↑ ↑

*results are opposite in respiratory alkalosis (see trans)

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35
Q

Why are both pH and HCO3- decreased in uncompensated phase of metabolic acidosis?

A

there is no response from the lungs yet to acidosis the PaCO2 will remain normal

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36
Q

T or F: all are decreased in partially compensated phase of metabolic acidosis

A

True

*lungs start to respond to the acidosis by decreasing the amount of circulating pCO2

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37
Q

T or F: pH, pCO2 and HCO3- are the same in fully compensated phase of metabolic acidosis and respiratory alkalsosi

A

true (NpH ↓pCO2 ↓HCO3-)

*pH returns to normal; pCO2 and HCO3– levels are still low to correct acidosis

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38
Q

What are increased in uncompensated phase of metabolic alkalosis?

A

pH and HCO3-

no response from lungs yet to alkalosis so the pcO2 remains normal

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39
Q

In partially compensated phase of metabolic alkalosis, lungs start to respond to alkalosis by increasing the amount of circulating PaCO2 so what is the trend?

A

↑ ↑ ↑

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40
Q

What are high during the fully compensated phase of metabolic alkalosis?

A

pCO2 and HCO3- to correct alkalosis

ph = normal

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41
Q

pCO2 and HCO3- for respiratory ACIDOSIS and metabolic ALKALOSIS

A

↑ ↑

*pco2 is compensated in respi, HCo3- in metabolic

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42
Q

pCO2 and HCO3- for RESPIRATORY ALKALOSIS and metabolic ACIDOSIS

A

↓ ↓

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43
Q

Direct relation of the production and retention of acids and bases

A

regulation of pH

44
Q

Systems involved in regulation of pH

A
  • Respiratory Center and Lungs
  • Kidneys
  • Buffers
45
Q

T or F: buffers are not found in blood

A

false, buffers are found in all body fluids

46
Q

T or F: weak acids are poor buffers

A

false, weak acids are good buffers (tilt reaction in other reaction)

47
Q

What are poor puffers?

A

strong acids

make system more acidic

48
Q

What causes the pH of the body to drop?

A

Acids produced from the catabolism of food and other cellular processes that are not removed or buffered

49
Q

T or F: Significant drops in pH interferes with cell enzyme systems

50
Q

four major buffer systems

A
  • protein buffer systems (amino acids and hemoglobin buffer system)
  • Phosphate buffer system
  • Bicarbonate-carbonic acid buffer system
51
Q

Where does the protein buffer system originate from?

A

amino acids (primary protein: albumin; due to high concentration of albumin in plasma)

52
Q

What ions do the protein buffer system buffer?

A

hydrogen ions and carbon dioxide

53
Q

Functions of the hemoglobin buffer system

A
  • Binds CO2
  • Binds and transports hydrogen and oxygen
  • Participates in the chloride shift
  • Maintains blood pH as hemoglobin changes from oxyhemoglobin to deoxyhemoglobin
54
Q

effect of the buffer system can be visualized through

A

Oxygen Disassociation Curve

explained by bohr effect

55
Q

Bohr effect

A

Phenomenon in which declining blood pH (acidosis) and increasing pCO2 weaken the Hb-O2 bond (all about hemoglobin’s affinity for oxygen)

56
Q

(see oxygen dissociation curves observing bohr effect)

A

(see oxygen dissociation curves observing bohr effect)

57
Q

An increased affinity of Hb to O2 is indicated by

A

↑pH ↓pCO2 ↓2,3-DPG

↓temp

58
Q

This buffer system has a major role in the elimination of H+ via the kidney

A

Phosphate buffer system

59
Q

What happens when there is a decreased affinity of Hb to O2?

A

O2 is released into tissues (↓pH ↑pCO2 ↑2,3-DPG, ↑temp)

60
Q

How does the phosphate buffer system help in eliminating H+ via the kidney?

A
  • Assists in the exchange of sodium for hydrogen

* Participates in the reaction: HPO4^2- + H+ <> H2PO4-

61
Q

Where is phosphate buffer system essential in?

A

within erythrocytes

62
Q

T or F: Phosphate buffer system is kidney compensation for metabolic acidosis

A

true

Reabsorption of all filtered HCO3-
Excretion of H+ as NH4+ and H2PO4-

63
Q

interpretations of kidney compensation

A

urine pH < 5.5

urine anion gap: negative

64
Q

T or F: bicarbonate/carbonic acid buffer system functions slowly

A

false, instantaneously

65
Q

why is there a need for bicarb acid buffer system?

A

Cells which utlize o2 produce and build up co2 (more co2 is found in tissue cells than in nearby blood cells which results in pressure pCO2)

66
Q

What percentage of CO2 is transported in dissolved form?

67
Q

What happens to 92-95% of CO2?

A

Enters RBC under reaction: CO2 + H2O ↔ H+ + HCO3

68
Q

What happens to bicarbonate formed in co2 transportation?

A

exchanged for chloride

69
Q

normal ratio of bicarbonate to carbonic acid

A

20: 1

* allows for blood pH of 7.40

70
Q

What happens to pH as bicarbonate decreases in relation to carbonic acid?

71
Q

normal ratio of bicarbonate to carbonic acid can also be interpreted as

A

ratio of kidney function (metabolic) to lung function (respiratory) in relation to maintaining acid-base balance

72
Q

general equation of henderson-hasselback equation

A

pH = pKa + log A-/HA

bicarb/carbo acid equn: A= HCO3-, HA= H2CO3

73
Q

The henderson-hasselback equation explains the relationship between

A

pH and bicarbonate-carbonic acid buffer system in plasma

for calculation of pH

74
Q

(see steps on how to calculate HH eqn)

A

(see steps on how to calculate HH eqn)

75
Q

These are derived from blood gas analyzer

A

pCO2 and HCO3-

76
Q

[Physiologic buffer systems] These are the quickest way to respond for correcting pH

A

lungs or respiratory

77
Q

Lungs or respiratory physiologic buffer systems eliminate these

A

volatile respiratory acids ie CO2

78
Q

T or F: Lungs or respiratory physiologic buffer systems affects fixed acids

A

false, does not

79
Q

How can body pH be adjusted?

A

changing rate and depth of breathing (blowing off)
• Metabolic acidosis: ↑ respiratory rate and depth; ↓pCO2
• Metabolic alkalosis: ¯ ↓ respiratory rate and depth; ↑pCO2

80
Q

How long does it take for kidney or metabolic physio buffers to correct pH?

A

several hours to days

81
Q

What does kidney or metab physio buffers eliminate?

A

large amounts of acids

*excrete base as well

82
Q

T or F: lungs or respiratory is the most effective regulator of pH

A

False, kidney or metabolic

83
Q

T or F: kidney failure does not necessarily indicate pH balance failure

A

False, it does

84
Q

Acid-base disorders are classified into

A

Simple and Mixed

85
Q

What is the difference between simple and mixed disorders?

A
  • Simple: appropriate compensation (i.e.: simple respiratory alkalosis; there is enough decrease in bicarb reabsorption to compensate for the decrease in pCO2)
  • Mixed: inappropriate compensation (i.e.: mixed metabolic acidosis; decrease in pCO2 is not enough to compensate for the decreased bicarb reabsorption)
86
Q

What are the steps involved in diagnosing acid-base disorders?

A
  1. History and Physical Examination
  2. Arterial Blood Gas for pH, pCO2, and [HCO3–]
    • Use HCO3– from ABG to determine compensation
  3. Serum Na+, K+, Cl–, CO2 content
    • Use CO2 content to calculate anion gap
  4. Calculate anion gap
    • Aniongap=Na+ –(Cl– +CO2)
  5. Determine appropriate compensation
  6. Determine the primary cause
87
Q

(see table of organ dysfunctions in Respi Acid-base disturbances and Metabolic Acid-base disturbances)

A

(see table of organ dysfunctions in Respi Acid-base disturbances and Metabolic Acid-base disturbances)

88
Q

This pH signifies acidosis (either metabolic or respi)

89
Q

This pH signifies alkalosis (either metabolic or respi)

90
Q

pH signifying normal or mixed disturbance

A

7.35 < pH < 7.45

91
Q

What does a [ Normal CO2 + High Anion Gap ] indicate?

A
  • Metabolic Acidosis with concurrent Metabolic Alkalosis; OR
  • Metabolic Acidosis with concurrent Respiratory Acidosis
92
Q

A high CO2 content indicates

A

metabolic ALKALOSIS

Respiratory ACIDOSIS

93
Q

A low CO2 content indicates

A

Metabolic ACIDOSIS

Respiratory ALKALOSIS

94
Q

A normal CO2 content indicates

A

normal or mixed disturbance

95
Q

Equation for anion gap

  • normal range = 8+/- 2
  • see correction for low serum albumin
A

AnionGap=Na+– (Cl–+HCO–3)

96
Q

What is the kidney compensation for metabolic acidosis?

A 
• Reabsorbing all filtered HCO3–
• Excreting H+ as NH4+ and H2PO4–
• Normal range
− Urine pH < 5.5
− Urine anion gap is negative
97
Q

Respiratory compensation for metabolic acidosis?

A

pCO2 =1.5×HCO3– +(8±2)???

98
Q

Compensation for metabolic alkalosis

A

pCO2 increases by 7 for every 10 mEq increase in HCO3–

99
Q

Compensation for Respiratory ACIDOSIS

A

→ Acute Respiratory Acidosis
• HCO3– increases by 1 for every 10 mmHg increase in pCO2
→ Chronic Respiratory Acidosis
• HCO3– increases by 3 for every 10 mmHg increase in pCO2

100
Q

Compensation for Respiratory ALKALOSIS

A

→ Acute Respiratory Alkalosis
• HCO3– decreases by 2 for every 10 mmHg decrease in pCO2
→ Chronic Respiratory Alkalosis
• HCO3– decreases by 4 for every 10 mmHg decrease in pCO2

101
Q

Mixed Respiratory Alkalosis and Metabolic Acidosis would lead to

A

Aspirin overdose
Sepsis
Liver Failure

102
Q

Mixed Respiratory Acidosis and metabolic ALKALOSIS would lead to

A

COPD with excessive use of diuretics

103
Q

Mixed Respiratory ACIDOSIS and metabolic ACIDOSIS would lead to

A

Cardiopulmonary arrest

Severe pulmonary edema

104
Q

Mixed High-Gap METABOLIC acidosis and alkalosis would lead to

A

Renal failure with vomiting

Diabetic ketoacidosis with severe vomiting

105
Q

(see case studies)

A

(see case studies)

Clinical Chemistry (9 decks)

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