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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) =

A

< 35 mmHg

23
Q

Hypercapnia (high PaCO2) =

A

> 45 mmHg

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
Q

CO2 effects on ventilation

A
  • Most important influence

- Blood level of CO2 acts directly on the resp. centres in the medulla, affecting cerebrospinal fluid pH

26
Q

Pathophysiology of CO2’s effect on ventilation (5)

A

(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
Q

ABG analysis

A

An invasive method for measuring oyxgenation, CO2 clearance, + acid-base balance (H+/pH) in the arterial blood

28
Q

Normal pH range

A

7.35-7.45

29
Q

Extreme pH range compatible w/ life

A

6.8-7.8

30
Q

ACIDAEMIA levels

A

pH = <7.35
PaCO2 = >45 mmHg
HCO3- = < 22
Base excess = < 02

31
Q

ALKALINE levels

A

pH = > 7.45
PaCO2 = < 35mmHg
HCO3- = >26
Base excess = >+2

32
Q

Normal HCO3- levels

A

22-26 mmol/L

33
Q

Normal base excess levels

A

-2 to +2 mEq/L

34
Q

BE (base excess)

What is it and when does it increase or decrease?

A

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
Q

The four types of acid-base disturbance:

A

Respiratory acidosis
Respiratory alkalosis
Metabolic acidosis
Metabolic alkalosis

36
Q

What can be used to determine if an acid-base disturbance is caused by the respiratory system?

A
  • PaCO2 b/c is regulated by lungs

- Hyper/hypo ventilation can affect this

37
Q

Hypoventilation (PaCO2/pH/resp acidosis or alkalosis?)

A

High PaCO2 = acidosis (retaining CO2)
Decreases pH
Respiratory acidosis

38
Q

Hyperventilation (PaCO2/pH/resp acidosis or alkalosis?)

A

Low PaCO2 = alkalosis (blowing off an excess of CO2)
Increases pH
Respiratory alkalosis

39
Q

What can be used to determine if an acid-base disturbance is caused by the metabolic system?

A
  • Bicarbonate ion (HCO3-) is the acid-base component regulated by the kidneys
  • or BE
40
Q

What happens if there’s a decrease in HCO3- or BE?

A

The reaction shifts right (metabolic acidosis)

  • Increase in H+
  • Decrease in pH (acidaemia)
41
Q

What happens if there’s an increase in HCO3- or BE?

A

The reaction shifts left (metaoblic alkalosis)

  • Decrease in H+
  • Increase in pH (alkalaemia)
42
Q

Acidaemia pH =

A

<7.35

43
Q

Alkalaemia pH =

A

> 7.45

44
Q

Acidosis pH

What is it + what can it cause ?

A

Physiological process that lowers the blood pH (causes acidaemia)
- Depresses muscular contractility (espec in heart/diaphragm)

45
Q

Alkalosis pH

What is it + what can it cause?

A

A physiological process that raises the blood pH (causes alkalaemia)
- Arrhythmias, neruomuscular irritability

46
Q

How to interpret ABG

A

(1) Nature of disturbance - pH
(2) The cause of the primary disturbance - resp./metabolic/both
(3) Determine compensation by other system

47
Q

Combined respiratory + metabolic

A

Change in pH, PaCO2 + HCO3-

48
Q

Determine whether a compensation is occurring:

A
  • 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
Q

Partial v. complete compensation

A
  • Partial : pH towards normal but not yet normal

- Complete: pH now restored back to normal

50
Q

Common causes of respiratory acidosis

A
  • alveolar hypoventilaiton
  • Resp muscle weakness/fatigue
  • Post-op drowsy
  • Effects of analgesia depressant drugs
51
Q

Common causes of respiratory alkalosis

A
  • Hyperventilation
  • Anxiety/ fear/ pain/
  • Acute asthma mechanical over-ventilation
52
Q

Common causes of metabolic acidosis:

A
  • Renal failure
  • Diarrhoea
  • Diabetes mellitus
53
Q

Common causes of metabolic alkalosis:

A
  • Excessive alkaline ingestion for ulcers

- Persistent vomitting

PHTY 800 (8 decks)

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