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