Blood Gas and pH measurements Flashcards
(105 cards)
1
Q
What will diagnostic tests identify?
A
(and evaluate) dysfunction if patient’s history and physical examination reveal evidence of respiratory dysfunction
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
3
Q
Any substance that can yield hydrogen (H+) or hydronium ion (H3O+) when dissolved in water
A
Acid
release of proton or H+
4
Q
Substance that can yield hydroxyl ions (OH-)
A
Base
ACCEPT proton or H+
5
Q
negative logarithm of the ionziation constant of an acid
A
pK or pKa
6
Q
pKa value of strong acids
A
<3
7
Q
pKa value of strong bases
A
> 9
^pKa ^pH
8
Q
It is the affinity of the acid whether or not to give out its H+
A
pKa
9
Q
negative logarithm of H+ concentration
A
pH
represents hydrogen concentration
*pH= pKa + log [base]/[acid]
10
Q
combination of a weak acid and/or weak base and its salt
A
buffer
*able to resist changes in pH
11
Q
Effectiveness of buffer depends on
A
pK of buffering system
pH of environment in which it is placed
12
Q
Normal pH range, acidosis and alkalosis
A
Normal: 7.35-7.45
Acidosis: < 7.35
Alkalosis > 7.45
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
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)
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
16
Q
Components of ABG
A
pH
pCO2
pO2
HCO3-
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
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
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
20
Q
[Components of ABG]
metabolic parameter;; reflects kidneys ability to retain and excrete bicarbonate
A
HCO3-
normal value: 22-28 mEq/L
21
Q
T or F: The body constantly works to maintain a balance (homeostasis) between acids and bases
A
True
22
Q
These are byproducts formed as cells use nutrients to produce energy
A
H+ and CO2
23
Q
Where does Acid-base balance depend on?
A
regulation of free H+
*slight imbalances affect emtabolism and essential body functions
24
Q
What conditions affect acid-base balance?
A
infection or trauma
25
Disorder trend for respiratory acidosis
Respiratory
Acidosis ↓pH ↑pCO2
uncompensated HCO3-
26
Disorder trend for respiratory ALKALOSIS
MATAAS NA PH
MABABANG PCO2
UNCOMPENSATED HCO3-
27
Disorder trend for METABOLIC ACIDOSIS
LOW PH
UNCOMPENSATED PCO2
LOW HCO3-
28
Disorder trend for METABOLIC ALKALOSIS
HIGH PH AND HCO3-
| Uncompensated pCO2
29
T or F: The circulatory and metabolic system works together to keep the body’s acid-base balance within normal limits (compensation)
respiratory and metabolic
30
Compensation mechanism for respiratory acidosis and respiratory alkalosis
Metabolic system
r. acid: high hco3- reabsorption
r. alkal: low hco3- reabsorption
31
Compensation mechanism for metabolic acidosis and alkalosis
Respiratory rate
m. acid: increase in rate and depth (low pCO2)
m. alkal: decrease in rate and depth (high pCO2)
32
Why is pH decreased and pCO2 increased in uncompensated phase of respiratory acidosis?
no response from kidneys yet to the acidosis, so the HCO3- will remain normal
33
What happens during the partially compensated phase of respiratory acidosis?
The kidneys start to respond to the acidosis by increasing the amount of circulating HCO3–
↓ pH ↑ pCO2 ↑HCO3-
34
Stage in respiratory acidosis where pH returns to normal pCO2 and HCO3- levels are still high to correct acidosis
Fully compensated
N ↑ ↑
*results are opposite in respiratory alkalosis (see trans)
35
Why are both pH and HCO3- decreased in uncompensated phase of metabolic acidosis?
there is no response from the lungs yet to acidosis the PaCO2 will remain normal
36
T or F: all are decreased in partially compensated phase of metabolic acidosis
True
*lungs start to respond to the acidosis by decreasing the amount of circulating pCO2
37
T or F: pH, pCO2 and HCO3- are the same in fully compensated phase of metabolic acidosis and respiratory alkalsosi
true (NpH ↓pCO2 ↓HCO3-)
*pH returns to normal; pCO2 and HCO3– levels are still low to correct acidosis
38
What are increased in uncompensated phase of metabolic alkalosis?
pH and HCO3-
| no response from lungs yet to alkalosis so the pcO2 remains normal
39
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?
↑ ↑ ↑
40
What are high during the fully compensated phase of metabolic alkalosis?
pCO2 and HCO3- to correct alkalosis
ph = normal
41
pCO2 and HCO3- for respiratory ACIDOSIS and metabolic ALKALOSIS
↑ ↑
*pco2 is compensated in respi, HCo3- in metabolic
42
pCO2 and HCO3- for RESPIRATORY ALKALOSIS and metabolic ACIDOSIS
↓ ↓
43
Direct relation of the production and retention of acids and bases
regulation of pH
44
Systems involved in regulation of pH
* Respiratory Center and Lungs
* Kidneys
* Buffers
45
T or F: buffers are not found in blood
false, buffers are found in all body fluids
46
T or F: weak acids are poor buffers
false, weak acids are good buffers (tilt reaction in other reaction)
47
What are poor puffers?
strong acids
| make system more acidic
48
What causes the pH of the body to drop?
Acids produced from the catabolism of food and other cellular processes that are not removed or buffered
49
T or F: Significant drops in pH interferes with cell enzyme systems
True
50
four major buffer systems
* protein buffer systems (amino acids and hemoglobin buffer system)
* Phosphate buffer system
* Bicarbonate-carbonic acid buffer system
51
Where does the protein buffer system originate from?
amino acids (primary protein: albumin; due to high concentration of albumin in plasma)
52
What ions do the protein buffer system buffer?
hydrogen ions and carbon dioxide
53
Functions of the hemoglobin buffer system
* Binds CO2
* Binds and transports hydrogen and oxygen
* Participates in the chloride shift
* Maintains blood pH as hemoglobin changes from oxyhemoglobin to deoxyhemoglobin
54
effect of the buffer system can be visualized through
Oxygen Disassociation Curve
| explained by bohr effect
55
Bohr effect
Phenomenon in which declining blood pH (acidosis) and increasing pCO2 weaken the Hb-O2 bond (all about hemoglobin's affinity for oxygen)
56
(see oxygen dissociation curves observing bohr effect)
(see oxygen dissociation curves observing bohr effect)
57
An increased affinity of Hb to O2 is indicated by
↑pH ↓pCO2 ↓2,3-DPG
| ↓temp
58
This buffer system has a major role in the elimination of H+ via the kidney
Phosphate buffer system
59
What happens when there is a decreased affinity of Hb to O2?
O2 is released into tissues (↓pH ↑pCO2 ↑2,3-DPG, ↑temp)
60
How does the phosphate buffer system help in eliminating H+ via the kidney?
* Assists in the exchange of sodium for hydrogen
| * Participates in the reaction: HPO4^2- + H+ <> H2PO4-
61
Where is phosphate buffer system essential in?
within erythrocytes
62
T or F: Phosphate buffer system is kidney compensation for metabolic acidosis
true
Reabsorption of all filtered HCO3-
Excretion of H+ as NH4+ and H2PO4-
63
interpretations of kidney compensation
urine pH < 5.5
| urine anion gap: negative
64
T or F: bicarbonate/carbonic acid buffer system functions slowly
false, instantaneously
65
why is there a need for bicarb acid buffer system?
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
What percentage of CO2 is transported in dissolved form?
5-8%
67
What happens to 92-95% of CO2?
Enters RBC under reaction: CO2 + H2O ↔ H+ + HCO3
68
What happens to bicarbonate formed in co2 transportation?
exchanged for chloride
69
normal ratio of bicarbonate to carbonic acid
20: 1
| * allows for blood pH of 7.40
70
What happens to pH as bicarbonate decreases in relation to carbonic acid?
pH falls
71
normal ratio of bicarbonate to carbonic acid can also be interpreted as
ratio of kidney function (metabolic) to lung function (respiratory) in relation to maintaining acid-base balance
72
general equation of henderson-hasselback equation
pH = pKa + log A-/HA
bicarb/carbo acid equn: A= HCO3-, HA= H2CO3
73
The henderson-hasselback equation explains the relationship between
pH and bicarbonate-carbonic acid buffer system in plasma
| for calculation of pH
74
(see steps on how to calculate HH eqn)
(see steps on how to calculate HH eqn)
75
These are derived from blood gas analyzer
pCO2 and HCO3-
76
[Physiologic buffer systems] These are the quickest way to respond for correcting pH
lungs or respiratory
77
Lungs or respiratory physiologic buffer systems eliminate these
volatile respiratory acids ie CO2
78
T or F: Lungs or respiratory physiologic buffer systems affects fixed acids
false, does not
79
How can body pH be adjusted?
changing rate and depth of breathing (blowing off)
• Metabolic acidosis: ↑ respiratory rate and depth; ↓pCO2
• Metabolic alkalosis: ¯ ↓ respiratory rate and depth; ↑pCO2
80
How long does it take for kidney or metabolic physio buffers to correct pH?
several hours to days
81
What does kidney or metab physio buffers eliminate?
large amounts of acids
*excrete base as well
82
T or F: lungs or respiratory is the most effective regulator of pH
False, kidney or metabolic
83
T or F: kidney failure does not necessarily indicate pH balance failure
False, it does
84
Acid-base disorders are classified into
Simple and Mixed
85
What is the difference between simple and mixed disorders?
- 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
What are the steps involved in diagnosing acid-base disorders?
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
(see table of organ dysfunctions in Respi Acid-base disturbances and Metabolic Acid-base disturbances)
(see table of organ dysfunctions in Respi Acid-base disturbances and Metabolic Acid-base disturbances)
88
This pH signifies acidosis (either metabolic or respi)
pH<7.35
89
This pH signifies alkalosis (either metabolic or respi)
pH> 7.45
90
pH signifying normal or mixed disturbance
7.35 < pH < 7.45
91
What does a [ Normal CO2 + High Anion Gap ] indicate?
* Metabolic Acidosis with concurrent Metabolic Alkalosis; OR
* Metabolic Acidosis with concurrent Respiratory Acidosis
92
A high CO2 content indicates
metabolic ALKALOSIS
| Respiratory ACIDOSIS
93
A low CO2 content indicates
Metabolic ACIDOSIS
| Respiratory ALKALOSIS
94
A normal CO2 content indicates
normal or mixed disturbance
95
Equation for anion gap
* normal range = 8+/- 2
* see correction for low serum albumin
AnionGap=Na+– (Cl–+HCO–3)
96
What is the kidney compensation for metabolic acidosis?
```
• Reabsorbing all filtered HCO3–
• Excreting H+ as NH4+ and H2PO4–
• Normal range
− Urine pH < 5.5
− Urine anion gap is negative
```
97
Respiratory compensation for metabolic acidosis?
pCO2 =1.5×HCO3– +(8±2)???
98
Compensation for metabolic alkalosis
pCO2 increases by 7 for every 10 mEq increase in HCO3–
99
Compensation for Respiratory ACIDOSIS
→ 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
Compensation for Respiratory ALKALOSIS
→ 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
Mixed Respiratory Alkalosis and Metabolic Acidosis would lead to
Aspirin overdose
Sepsis
Liver Failure
102
Mixed Respiratory Acidosis and metabolic ALKALOSIS would lead to
COPD with excessive use of diuretics
103
Mixed Respiratory ACIDOSIS and metabolic ACIDOSIS would lead to
Cardiopulmonary arrest
| Severe pulmonary edema
104
Mixed High-Gap METABOLIC acidosis and alkalosis would lead to
Renal failure with vomiting
| Diabetic ketoacidosis with severe vomiting
105
(see case studies)
(see case studies)
