SHA24/005001

Arterial Blood Gas Made Easy

Saudi Heart Association 2013 Prince Sultan Cardiac centre 1

Objectives  Indications for the Arterial Blood Gas  Understand oxygenation and the difference between hypoxemia and hypoxia

 Discuss the normal ranges  Identify the difference between respiratory 



and metabolic acidosis and alkalosis Understand the causes of acid base disturbances Be able to interpret blood gas results

2

Indications      

To determine respiratory and metabolic status.

To assess arterial oxygenation.

To assess acid – base balance.

To assess electrolyte balances.

To assess Haemoglobin.

To use all mentioned data in order to determine appropriate ventilator settings and treatment.

Oxygenation ď‚Ą

1.

2.

3.

Tissue oxygenation depends on PaO2 Hb saturation Perfusion status

1. PaO2 





10.7 – 13 kPa

The partial pressure of oxygen dissolved in plasma An indicator of oxygenation But one component of assessing oxygenation

5

2. Haemoglobin ď‚Ą ď‚Ą

3% 97 %

O2 dissolved in plasma O2 carried bound to Haemoglobin in the red blood cell

Haemoglobin + Oxygen = Oxyhaemoglobin

Hb

+

O2

= O2Hb

Heme and other gases 

Heme (Iron) molecule of Hb can  Transport oxygen  be altered by other gases or other agents e.g. nitric oxide / lidocaine / sulfa drugs

7

Heme and other gases 





Heme carrying oxygen creates oxyhaemoglobin (O2Hb) Heme carrying carbon monoxide creates carboxyhaemoglobin (COHb) Heme that changes its shape creates methemoglobin (MetHb) 8

Heme and other gases Carboxyhemoglobin (COHb) and

Methemoglobin (MetHb) CANNOT CARRY OXYGEN

SaO2 ď‚Ą

Measured in 2 ways 1. By

ABG analysis

2. Pulse

oximeter - SpO2

SaO2 (Fractional) ď‚Ą

ď‚Ą

Measured with a co-oximeter Fractional SaO2 compares the percentages of oxyhemoglobin, carboxyhemoglobin and methemoglobin and gives overall percentage

11

SaO2 (Fractional)

12

SaO2 (Functional) 





Measured with a saturation probe The saturation probe cannot identify Hb carrying other gases The saturation probe assesses only Hb that is free to carry oxygen

13

SaO2 (Functional) Of the hemoglobin left to carry oxygen, what percentage is saturated

14

Hypoxemia 

-

-

Hypoxemia – deficient oxygenation of the blood (PO2) PO2 < 10.7kPa = Mild hypoxemia PO2 < 8.0kPa = Moderate hypoxemia PO2 < 5.3kPa = Severe hypoxemia

Hypoxemia ď&#x201A;Ą -

Causes of Hypoxemia: V/Q mismatches (common cause) hypoventilation diffusion problems e.g. sedation, anaesthetics, secretions, pneumonia, asthma

Hypoxia 



Hypoxia – insufficient O2 delivered to the cells to meet oxygen demand Anaemic hypoxia: ↓ haemoglobin or inability of haemoglobin to carry O2 e.g. carbon monoxide poisoning, sickle cell, haemorrhage ** transport problem

Hypoxia 



Circulatory hypoxia: a ↓ in Cardiac Output, ↑ in Systemic Vascular Resistance, that impedes the perfusion of tissues ** delivery problem Histotoxic hypoxia: Tissues cannot use oxygen effectively e.g. shock, alcohol poisoning **utilization problem

3. Perfusion status ď&#x201A;Ą

ď&#x201A;Ą

The oxygen needs to be delivered by the heart via arteries to the tissues and cells of the body In order to do that we need a good cardiac output to maintain good tissue perfusion

Arterial Blood Gas Indices Normal Ranges kPa

mmHg

10.7 - 13

80 - 100

7.35 – 7.45

7.35 – 7.45

PaCO2:

4.7 – 6.0

35 - 45

HCO3:

22 – 26 mEq

22 – 26 mEq

-2 to +2

-2 to +2

PaO2: pH:

BE:

20

pH 

7.35 – 7.45

Measures whether a solution is acid or alkaline



pH < 7.35 - Acidosis



pH >7.45

- Alkalosis

21

PaCO2 





4.7 – 6.0 kPa

The partial pressure of carbon dioxide dissolved in plasma It a natural by-product of cellular metabolism Primarily regulated by the lungs, therefore it is known as the RESPIRATORY factor 23

PaCO2 

 PaCO2 < 4.7 is alkalosis



 PaCO2 > 6.0 is acidosis

HCO3 





22 – 26 mEq/L

Plasma bicarbonate level An indicator of metabolic acid-base status Primarily regulated via the kidneys therefore is the METABOLIC factor

25

HCO3 

 amounts of HCO3 = alkalosis



 amounts of HCO3 = acidosis

Base Excess 

-2 to +2

Also an indicator of metabolic acidbase status



< -2 = acidosis



> +2 = alkalosis

27

Respiratory Disturbances 

PaCO2 is the single best indicator of respiratory acid-base status



 PaCO2

=

acidosis



 PaCO2

=

alkalosis

28

Metabolic Disturbances 

HCO3 is the single best indicator of metabolic acid-base status



 HCO3

= alkalosis



 HCO3

= acidosis

29

ABG Analysis

30

How to Analyze an ABG? 1.

2.

3.

4.

5.

-

Assess PaO2 & SaO2 for oxygen status Assess pH for acidity or alkalinity Look at the PaCO2 Look at the HCO3 If pH is abnormal match either the PaCO2 or HCO3 reading to the pH to determine the cause

Primary Acid-Base Disorders Respiratory Acidosis Respiratory Alkalosis

Metabolic Acidosis Metabolic Alkalosis

32

Interpretation •

PaO2

……

7.4 kPa(56 mm Hg)

•

pH

…… 7.32

•

PaCO2

…… 6.65 kPa(50 mm Hg)

•

HCO3

…… 24 mEq/L

Interpretation •

PaO2

……

7.4 kPa(56 mm Hg)

•

pH

…… 7.32

•

PaCO2

…… 6.65 kPa(50 mm Hg)

•

HCO3

…… 24 mEq/L

Respiratory Acidosis with moderate hypoxemia

Interpretation •

PaO2

……

12.3 kPa(93 mm Hg)

•

pH

…… 7.48

•

PaCO2

……

•

HCO3

…… 24 mEq/L

4.2 kPa(32 mm Hg)

Interpretation •

PaO2

……

12.3 kPa(93 mm Hg)

•

pH

…… 7.48

•

PaCO2

……

•

HCO3

…… 24 mEq/L

4.2 kPa(32 mm Hg)

Respiratory Alkalosis with good oxygenation

Interpretation •

PaO2

…… 12.6 kPa(95 mm Hg)

•

pH

…… 7.31

•

PaCO2

…… 5.32 kPa(40 mm Hg)

•

HCO3

…… 15 mEq/L

Interpretation •

PaO2

…… 12.6 kPa(95 mm Hg)

•

pH

…… 7.31

•

PaCO2

…… 5.32 kPa(40 mm Hg)

•

HCO3

…… 15 mEq/L

Metabolic Acidosis with good oxygenation

Interpretation •

PaO2

……

13 kPa(98 mm Hg)

•

pH

……

7.48

•

PaCO2

……

5.32 kPa(40 mm Hg)

•

HCO3

……

32 mEq/L

Interpretation •

PaO2

……

13 kPa(98 mm Hg)

•

pH

……

7.48

•

PaCO2

……

5.32 kPa(40 mm Hg)

•

HCO3

……

32 mEq/L

Metabolic Alkalosis with good oxygenation

ANY questions????

Compensation 



The return of an abnormal pH to within normal range

To maintain the body’s acid base balance

46

Compensation 

The organ system that was not primarily affected will change (compensate) to correct the pH



For respiratory abnormalities there will be metabolic compensation (via the kidneys)



For metabolic abnormalities there will be respiratory compensation (via the lungs)



Respiratory and metabolic factors are opposite to each other 47

Compensation 

Normal pH 7.35 - 7.45



In compensation pH value of 7.4 is used < 7.4 = acidosis



> 7.4 = alkalosis



Patient Haya •

PaO2

……

12.0 kPa(90 mm Hg)

•

pH

……

7.49

•

PaCO2

…...

3.5 kPa(26 mm Hg)

•

HCO3

……

20 mEq/L

Patient Haya •

PaO2

……

12.0 kPa(90 mm Hg)

•

pH

……

7.49

•

PaCO2

…...

3.5 kPa(26 mm Hg)

•

HCO3

……

20 mEq/L

Respiratory Alkalosis - partial compensation

Patient Haya •

PaO2

…… 12.0 kPa(90 mm Hg)

•

pH

……

7.43

•

PaCO2

…...

3.0 kPa(21 mm Hg)

•

HCO3

……

17 mEq/L

Patient Haya •

PaO2

…… 12.0 kPa(90 mm Hg)

•

pH

……

7.43

•

PaCO2

…...

3.0 kPa(21 mm Hg)

•

HCO3

……

17 mEq/L

Respiratory Alkalosis - full compensation

Patient Fayez •

PaO2

……

11.3 kPa

(85 mm Hg)

•

pH

……

7.33

•

PaCO2

…...

7.0 kPa(52 mm Hg)

•

HCO3

……

30 mEq/L

Patient Fayez PaO2

……

11.3 kPa

•

pH

……

7.33

•

PaCO2

…...

7.0 kPa(52 mm Hg)

•

HCO3

……

30 mEq/L

•

(85 mm Hg)

Respiratory Acidosis - partial compensation

Patient Fayez •

PaO2

……

10.5 kPa(79 mm Hg)

•

pH

……

7.38

•

PaCO2 …... 7.0 kPa (52 mm Hg)

•

HCO3

……

35 mEq/L

Patient Fayez •

PaO2

……

10.5 kPa(79 mm Hg)

•

pH

……

7.38

•

PaCO2 …... 7.0 kPa (52 mm Hg)

•

HCO3

……

35 mEq/L

Respiratory Acidosis - complete compensation

Patient Noura •

PaO2

……

13.0 kPa(97 mm Hg)

•

pH

……

7.43

•

PaCO2

……

7.1 kPa(53 mm Hg)

•

HCO3

……

35 mEq/L

Patient Noura •

PaO2

……

13.0 kPa(97 mm Hg)

•

pH

……

7.43

•

PaCO2

……

7.1 kPa(53 mm Hg)

•

HCO3

……

35 mEq/L

Metabolic Alkalosis - complete compensation

Patient Abdullah •

PaO2

……

11.00 kPa(83 mm Hg)

•

pH

……

7.33

•

PaCO2

……

4.5 kPa (34 mm Hg)

•

HCO3

……

16 mEq/L

Patient Abdullah •

PaO2

……

11.00 kPa(83 mm Hg)

•

pH

……

7.33

•

PaCO2

……

4.5 kPa (34 mm Hg)

•

HCO3

……

16 mEq/L

Metabolic Acidosis - partial compensation

Patient Abdullah •

PaO2

……

11.00 kPa(83 mm Hg)

•

pH

……

7.37

•

PaCO2

……

3.5 kPa(26 mm Hg)

•

HCO3

……

16 mEq/L

Patient Abdullah •

PaO2

……

11.00 kPa(83 mm Hg)

•

pH

……

7.37

•

PaCO2

……

3.5 kPa(26 mm Hg)

•

HCO3

……

16 mEq/L

Metabolic Acidosis - complete compensation

ABG Analysis

63

Analyze this gas •

PaO2

……

11.3 kPa(85 mm Hg)

•

pH

……

7.32

•

PaCO2

……

6.2 kPa(47 mm Hg)

•

HCO3

…… 21 mEq/L

•

SaO2

……

87%

Analyze this gas •

PaO2

……

11.3 kPa(85 mm Hg)

•

pH

……

7.32

•

PaCO2

……

6.2 kPa(47 mm Hg)

•

HCO3

…… 21 mEq/L

•

SaO2

…… 87%

Combined respiratory and metabolic acidosis Treatment:

Analyze this ABG •

PaO2

……

7.4 kPa(56 mm Hg)

•

pH

……

7.32

•

PaCO2

…...

6.65 kP(50 mm Hg)

•

HCO3

…… 24 mEq/L

•

SaO2

…… 77%

Analyze this ABG •

PaO2

……

7.4 kPa(56 mm Hg)

•

pH

……

7.32

•

PaCO2

…...

6.65 kP(50 mm Hg)

•

HCO3

…… 24 mEq/L

•

SaO2

…… 77%

Respiratory Acidosis - acute (noncompensated) with moderate hypoxemia Treatment:

Analyze this ABG •

PaO2

……

11.97 kPa(90 mm Hg)

•

pH

…… 7.30

•

PaCO2

……

•

HCO3

…… 16 mEq/L

•

SaO2

…… 92 %

3.7 kPa(28 mm Hg)

Analyze this ABG •

PaO2

……

11.97 kPa(90 mm Hg)

•

pH

…… 7.30

•

PaCO2

……

•

HCO3

…… 16 mEq/L

•

SaO2

…… 92 %

3.7 kPa(28 mm Hg)

Metabolic Acidosis - partial compensation with good oxygenation Treatment:

Analyze this ABG •

PaO2

……

12.6 kPa(95 mm Hg)

•

pH

……

7.49

•

PaCO2

……

6.3 (48 mm Hg)

•

HCO3

……

32 mEq/L

•

SaO2

……

98 %

Analyze this ABG •

PaO2

……

12.6 kPa(95 mm Hg)

•

pH

……

7.49

•

PaCO2

……

6.3 (48 mm Hg)

•

HCO3

……

32 mEq/L

•

SaO2

……

98 %

Metabolic Alkalosis - partial compensation with good oxygenation Treatment:

Analyze this ABG •

PaO2

……

13 kPa(98 mm Hg)

•

pH

…… 7.48

•

PaCO2

……

5.32 kPa(40 mm Hg)

•

HCO3

……

32 mEq/L

•

SaO2

……

99 %

Analyze this ABG •

PaO2

……

13 kPa(98 mm Hg)

•

pH

…… 7.48

•

PaCO2

……

5.32 kPa(40 mm Hg)

•

HCO3

……

32 mEq/L

•

SaO2

……

99 %

Metabolic Alkalosis - acute (noncompensated) with good oxygenation Treatment:

Analyze this ABG •

PaO2

……

11.00 kPa(83 mm Hg)

•

pH

……

7.36

•

PaCO2

……

3.5 kPa

•

HCO3

……

16 mEq/L

•

SaO2

……

90 %

(28 mm Hg)

Analyze this ABG •

PaO2

……

11.00 kPa(83 mm Hg)

•

pH

……

7.36

•

PaCO2

……

3.5 kPa

•

HCO3

……

16 mEq/L

•

SaO2

……

(28 mm Hg)

90 %

Metabolic Acidosis - complete compensation with good oxygenation Treatment:

Analyze this ABG •

PaO2

…… 8.6 kPa(65 mm Hg)

•

pH

…… 7.28

•

PaCO2

…… 6.2 kPa(47 mm Hg)

•

HCO3

…… 16 mEq/L

•

SaO2

…… 89 %

Analyze this ABG •

PaO2

…… 8.6 kPa(65 mm Hg)

•

pH

…… 7.28

•

PaCO2

…… 6.2 kPa(47 mm Hg)

•

HCO3

…… 16 mEq/L

•

SaO2

…… 89 %

Combined Respiratory & Metabolic Acidosis with mild hypoxemia Treatment:

Analyze this ABG •

PaO2

……

7.9kPa(93 mm Hg)

•

pH

……

7.48

•

PaCO2

……

4.2 kPa(32 mm Hg)

•

HCO3

……

24 mEq/L

•

SaO2

……

85 %

Analyze this ABG •

PaO2

……

7.9kPa(93 mm Hg)

•

pH

……

7.48

•

PaCO2

……

4.2 kPa(32 mm Hg)

•

HCO3

……

24 mEq/L

•

SaO2

……

85 %

Respiratory Alkalosis - acute (noncompensated) with moderate hypoxemia Treatment:

Analyze this ABG •

PaO2

…… 13.0 kPa(95 mm Hg)

•

pH

…… 7.43

•

PaCO2

…… 6.6 kPa(50 mm Hg)

•

HCO3

…… 35 mEq/L

•

SaO2

…… 98 %

Analyze this ABG •

PaO2

…… 13.0 kPa(95 mm Hg)

•

pH

…… 7.43

•

PaCO2

…… 6.6 kPa(50 mm Hg)

•

HCO3

…… 35 mEq/L

•

SaO2

…… 98 %

Metabolic Alkalosis - complete compensation with good oxygenation Treatment:

Analyze this ABG •

PaO2

…… 10.5 kPa(79 mm Hg)

•

pH

…… 7.38

•

PaCO2

…... 6.5 kPa(49 mm Hg)

•

HCO3

…… 30 mEq/L

•

SaO2

……

95 %

Analyze this ABG •

PaO2

…… 10.5 kPa(79 mm Hg)

•

pH

…… 7.38

•

PaCO2

…... 6.5 kPa(49 mm Hg)

•

HCO3

…… 30 mEq/L

•

SaO2

……

95 %

Respiratory Acidosis - complete compensation with mild hypoxemia Treatment

Analyze this ABG •

PaO2

……

12.0 kPa(90 mm Hg)

•

pH

…… 7.49

•

PaCO2

…... 3.5 kPa(27 mm Hg)

•

HCO3

…… 20 mEq/L

•

SaO2

…… 98 %

Analyze this ABG •

PaO2

……

12.0 kPa(90 mm Hg)

•

pH

……

7.49

•

PaCO2

…... 3.5 kPa(27 mm Hg)

•

HCO3

…… 20 mEq/L

•

SaO2

…… 98 %

Respiratory Alkalosis - partial compensation with good oxygenation Treatment:

Analyze this ABG •

PaO2

…… 12.0 kPa(90 mm Hg)

•

pH

…… 7.43

•

PaCO2

….. 3.0 kPa(23 mm Hg)

•

HCO3

…… 17 mEq/L

•

SaO2

…… 98 %

Analyze this ABG •

PaO2

…… 12.0 kPa(90 mm Hg)

•

pH

…… 7.43

•

PaCO2

….. 3.0 kPa(23 mm Hg)

•

HCO3

…… 17 mEq/L

•

SaO2

…… 98 %

Respiratory Alkalosis - complete compensation with good oxygenation Treatment

Analyze this ABG •

PaO2

…… 12.6 kPa(95 mm Hg)

•

pH

…… 7.31

•

PaCO2

…… 5.32 kPa(40 mm Hg)

•

HCO3

…… 15 mEq/L

•

SaO2

…… 99 %

Analyze this ABG •

PaO2

…… 12.6 kPa(95 mm Hg)

•

pH

…… 7.31

•

PaCO2

…… 5.32 kPa(40 mm Hg)

•

HCO3

…… 15 mEq/L

•

SaO2

…… 99 %

Metabolic Acidosis - acute (noncompensated) with good oxygenation Treatment:

Analyze this ABG •

PaO2

…… 16.6 kPa(124 mm Hg)

•

pH

…… 7.55

•

PaCO2

…… 4.74 kPa(36 mm Hg)

•

HCO3

…… 31 mEq/L

•

SaO2

……

97%

Analyze this ABG •

PaO2

…… 16.6 kPa(124 mm Hg)

•

pH

…… 7.55

•

PaCO2

…… 4.74 kPa(36 mm Hg)

•

HCO3

…… 31 mEq/L

•

SaO2

……

97%

Metabolic Alkalosis - acute (noncompensated) with good oxygenation Treatment:

Analyze this ABG •

PaO2

……

6.9 kPa(52 mm Hg)

•

pH

……

7.41

•

PaCO2

……

5.88 kPa(44 mm Hg)

•

HCO3

……

26 mEq/L

•

SaO2

……

87%

Analyze this ABG •

PaO2

……

6.9 kPa(52 mm Hg)

•

pH

……

7.41

•

PaCO2

……

5.88 kPa(44 mm Hg)

•

HCO3

……

26 mEq/L

•

SaO2

……

87%

Normal ABG result with poor oxygenation Treatment:

94

References 







Woodruff, D.W., (2011) 6 Easy steps to ABG Analysis, E-booklet http://www.ed4nurses.com/resources/1/pd f/ABGebook.pdf (accessed 25.07.12) Hennessey, I.A.M., Gapp, A.J., (2007) Arterial Blood Gases Made easy, London:Churchill Livingstone Elsevier.

Coggan, J.M., (2008) Arterial blood gas analysis 1: understanding ABG reports Nursing times 104(18) 28-29 Coggan, J.M., (2008) Arterial blood gas analysis 2: compensatory mechanisms Nursing times 104(19) 24-25

References ď&#x201A;Ą

Nursing education consultants, inc (2007) Blood gases made easy http://www.nursinged.com (accessed 18.06.12