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PHTY 800 > Week 10 - Arterial Blood Gas Analysis > Flashcards

Week 10 - Arterial Blood Gas Analysis Flashcards

1
Q

2 main tools use to measure blood gas levels’ (O2 + CO2)

A

Pulse oximetry + Arterial blood gas analysis

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2
Q

What is pulse oximetry?

A

Non-invasive method for measuring oxygen saturation (SpO2) + pulse/HR

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3
Q

What does Arterial Blood Gas measure?

A

Invasive method, measures:

  • O2 + CO2 levels in the blood
  • Oxygen saturation (SaO2)
  • Blood pH
  • Bicarbonate values
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4
Q

Oxygen is transported to + from lungs in blood via:

A

Oxyhaemoglobin + oxygen molecules dissolved in the blood

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5
Q

Oxyhaemoglobin:

normal range/ how is it measured Sa02 and Sp02 measured?

A
  1. 5% O2 in blood transported this way
    - Normal range: 95-100%
    - Measured as oxygen saturation
    - SaO2 measured by ABG sample
    - SpO2 measure by pulse oximetry
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6
Q

The remaining 1.5% of oxygen dissolves directly into the:

+ Pa02 - normal range?

A
  • plasma in the blood and is measured as the partial pressure of oxygen (PaO2)
  • Normal PaO2 range is 80-100 mmHg (measured by ABG sample)
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7
Q

Oxygen saturation (SaO2/SpO2): what is it, + what does hemoglobin carry and to where?

What does it mean when Sa02 is low?

A
  • O2 carrying capability of blood
  • Well-saturated Hb carries sufficient O2 to the tissues, where it then releases O2 molecules as the RBC pass thru capillaries
  • when its low: insufficient oxygen is transported/delivered to tissues
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8
Q

Pulse oximetry: what is it used for? what does it measure? when is it accurate and inaccurate?

A
  • assessment, monitoring, re-evaluation
  • Measures oxyhaemoglobin saturation + pulse rate
  • Accurate in high saturation readings, inaccurate in low saturation levels/poor peripheral circulation (cardiac failure)
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9
Q

PaO2: what is it? whats the normal range? what does a higher range mean?

A
  • Partial pressure of oxygen
  • Normal: 80-100 mmHg
  • Higher PaO2: Hb quickly takes up O2 molecules until Hb is saturated = High SaO2 = good delivery of O2 to the tissues.
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10
Q

Hypoxaemia

A

Abnormally low oxygenation of arterial blood (low PaO2/SaO2)

Pa02 less than 80

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11
Q

Hypoxia

A

When O2 delivery to tissues is inadequate to maintain normal tissue oxygenation/meet metabolic needs (hypoxaemia is one cause of tissue hypoxia)

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12
Q

Consequences of acute hyopxaemia

A

Tachycardia, increase cardiac output, arrhythmias, hypotension (peripheral vasodilation)

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13
Q

PaO2 < 55mmHg effects

A

Short term memory alteration, confusion, euphoria

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14
Q

PaO2 < 30 mmHg effect

A

Loss of consciousness

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15
Q

Stats for normal PaO2 + SaO2

A

PaO2 - 80-100 mmHg

SaO2 - 95-100%

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16
Q

Stats for low PaO2 + SaO2 (hypoxaemia)

A

PaO2 - <80 mmHg

SaO2 - <95%

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17
Q

Stats for respiratory failure (PaO2 + SaO2)

A

PaO2 - <60 mmHg

SaO2 - < 90%

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18
Q

FiO2

A

The % oxygen a person breaths in
Pts on O2 therapy - FiO2 will be >.21
Normal = .21 (room air)

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19
Q

Equations for interpreting PaO2

A

(1) PaO2 = FiO2 (%) x 5
(2) P(mmHg)/F(decimal) ratio; Normal ~ 350-450

The smaller the value - the worse the patient’s gas exchange + oxygenation

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20
Q 
Carbon dioxide (CO2)
What is it and how is it carried thru the body?
A

Gaseous waste product from metabolism

- Blood carries CO2 to the lungs, where it is exhaled

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21
Q

Normal PaCO2 =

A

35-45 mmHg

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22
Q

Hypocapnia (low PaCO2) =

23
Q

Hypercapnia (high PaCO2) =

24
Q

CO2 transport in the blood, what form is it carried in and where does the rest get dissolved?

A

60-70% CO2 carried in the blood in the form of bicarbonate (HCO3-)
- The rest is either dissolved CO2 gas or carbonic acid (H2CO3)

25
CO2 effects on ventilation
- Most important influence | - Blood level of CO2 acts directly on the resp. centres in the medulla, affecting cerebrospinal fluid pH
26
Pathophysiology of CO2's effect on ventilation (5)
(1) increase CO2 in blood (Hypercapnia) (2) decrease in blood pH (3) Stimulates central chemoreceptors in medulla (4) Body trying to remove CO2 + get pH back to normal by stimulating phrenic + intercostal nerves --> increase resp. muscle activity. (5) Increased depth/rate of respiration (alveolar hypervent.) until normal PaCO2/pH restored.
27
ABG analysis
An invasive method for measuring oyxgenation, CO2 clearance, + acid-base balance (H+/pH) in the arterial blood
28
Normal pH range
7.35-7.45
29
Extreme pH range compatible w/ life
6.8-7.8
30
ACIDAEMIA levels
pH = <7.35 PaCO2 = >45 mmHg HCO3- = < 22 Base excess = < 02
31
ALKALINE levels
pH = > 7.45 PaCO2 = < 35mmHg HCO3- = >26 Base excess = >+2
32
Normal HCO3- levels
22-26 mmol/L
33
Normal base excess levels
-2 to +2 mEq/L
34
BE (base excess) | What is it and when does it increase or decrease?
The amount of acid (H+ ions) required to restore 1 litre of blood to its normal pH at a PaCO2 of 40 mmHg - increases in metaboblic alkalosis + decreases in metabolic acidosis
35
The four types of acid-base disturbance:
Respiratory acidosis Respiratory alkalosis Metabolic acidosis Metabolic alkalosis
36
What can be used to determine if an acid-base disturbance is caused by the respiratory system?
- PaCO2 b/c is regulated by lungs | - Hyper/hypo ventilation can affect this
37
Hypoventilation (PaCO2/pH/resp acidosis or alkalosis?)
High PaCO2 = acidosis (retaining CO2) Decreases pH Respiratory acidosis
38
Hyperventilation (PaCO2/pH/resp acidosis or alkalosis?)
Low PaCO2 = alkalosis (blowing off an excess of CO2) Increases pH Respiratory alkalosis
39
What can be used to determine if an acid-base disturbance is caused by the metabolic system?
- Bicarbonate ion (HCO3-) is the acid-base component regulated by the kidneys - or BE
40
What happens if there's a decrease in HCO3- or BE?
The reaction shifts right (metabolic acidosis) - Increase in H+ - Decrease in pH (acidaemia)
41
What happens if there's an increase in HCO3- or BE?
The reaction shifts left (metaoblic alkalosis) - Decrease in H+ - Increase in pH (alkalaemia)
42
Acidaemia pH =
<7.35
43
Alkalaemia pH =
>7.45
44
Acidosis pH | What is it + what can it cause ?
Physiological process that lowers the blood pH (causes acidaemia) - Depresses muscular contractility (espec in heart/diaphragm)
45
Alkalosis pH | What is it + what can it cause?
A physiological process that raises the blood pH (causes alkalaemia) - Arrhythmias, neruomuscular irritability
46
How to interpret ABG
(1) Nature of disturbance - pH (2) The cause of the primary disturbance - resp./metabolic/both (3) Determine compensation by other system
47
Combined respiratory + metabolic
Change in pH, PaCO2 + HCO3-
48
Determine whether a compensation is occurring:
- Body tries to return the pH back to normal range - if compensating, the system that isn't causing the primary disturbance will be: out of normal range + moving in the opp. direction
49
Partial v. complete compensation
- Partial : pH towards normal but not yet normal | - Complete: pH now restored back to normal
50
Common causes of respiratory acidosis
- alveolar hypoventilaiton - Resp muscle weakness/fatigue - Post-op drowsy - Effects of analgesia depressant drugs
51
Common causes of respiratory alkalosis
- Hyperventilation - Anxiety/ fear/ pain/ - Acute asthma mechanical over-ventilation
52
Common causes of metabolic acidosis:
- Renal failure - Diarrhoea - Diabetes mellitus
53
Common causes of metabolic alkalosis:
- Excessive alkaline ingestion for ulcers | - Persistent vomitting

PHTY 800 (8 decks)

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