1) How to Draw and Handle?1) How to Draw and Handle?

2) Normal values and Definitions2) Normal values and Definitions

3) Interpretation3) Interpretation

1) How to Draw and Handle?1) How to Draw and Handle?

• Usually drawn from radial a.

(superficial, easily located and compressed).

• Palpate radial a. at lateral aspect of wrist against lower end radius.

• Alternative arteries: femoral, brachial.

• Infiltration with local anaesthetic is seldom required.

• Glass syringes are gas-Impermeable, contrary to plastic syringes which may allow some gas leak. However, glass syringes are expensive and not readily available.

•The syringe is heparinized with little heparin which is then expressed.

• Syringes pre-loaded with heparin powder eliminate the dilutional effect, but mixing becomes more important. Na or K level may change.

• Insert the needle nearly parallel to the artery, to minimize arterial wall trauma and help later sealing.

•The sample should preferably be > 2 mL to minimize dilution effect.

• To avoid haemolysis, allow the syringe to fill spontaneously or use the least suction force.

• Withdraw the needle and apply local pressure.

• Gently mix the sample by rolling the syringe between the palms and expel any air bubbles ( PO2, PCO2).

• Because the WBCs are metabolically active, they will consume oxygen.

• Placing the sample in ice may help minimize changes. It is probably not as important if the specimen is delivered immediately.

• Record the conditions under which the sample was taken: (time, FiO2, ventilator settings, patient position and temperature).

Contraindications:• Local:

o Infection.o Peripheral arterial insufficiency.o AV Fistula.

• Systemic (Relative): bleeding diathesis.

Parameter(Abbreviat

ed)

Parameter(Full)

Normal Range

UnitDefinition

pH7.35 – 7.45

Negative log of hydrogen ion activityIf [H+] = 10-7.4 then pH = 7.4

PaO2Partial pressure of O2

80 – 100mm Hg

Partial pressure of oxygen in arterial blood

PaCO2Partial pressure of CO2

35 - 45mm Hg

Partial pressure of CO2 in arterial blood

HCO3-Bicarbonate

Level21 – 27mEq/LBicarbonate plasma concentration

(calculated and not measured)

SaO2Oxygen saturation

95 - 100%Percent of oxygen content to maximum oxygen carrying capacity of blood

FiO2Fraction of inspired oxygen

21%Fraction of oxygen in relation to inspired air

PaO2 with age (= 100 – age in years above 40)

FiO2 at time of ABG sampling should be included in the report, though it is not a measured ABG parameter.

2) Normal values and Definitions2) Normal values and Definitions

3) ABG Interpretation3) ABG Interpretation

StepLook atThink: Is there…

1PaO2, PaCO2Respiratory Failure

2PaO2/FiO2ARDS

3 - 5pH, PaCO2, Bicarb

Acid/Base Disturbance

Respiratory failure is a syndrome of inadequate gas exchange due to dysfunction of one or more essential components of the respiratory system.

(Airways, Lungs, Respiratory Muscles, Nerve and Blood Supply)

Step 1)Step 1) Look at PaO Look at PaO22 & PaCO & PaCO22

Is there Respiratory Failure?Is there Respiratory Failure?

TypeNameDefinitionMechanisms,

Examples

1Hypoxic RFPaO2 < 60 mm HgShunt, DD, V/Q Mismatch: COPD, IPF, Pneumonia, ARDS

2Hypercapnoeic RFPaCO2 > 46 mm Hg

Hypoventilation:Neuromuscular disorders affecting respiratory

muscles

3Hypoxic/

Hypercapnoeic RF

PaO2 < 60 mm Hg,

PaCO2 > 46 mm Hg

Advanced or combined disorders

Oxygen Haemoglobin Dissociation Curve

ARDS Severity  PaO2/FiO2 Mortality

Mild< 30027%

Moderate< 20032%

Severe< 10045%

Step 2)Step 2) Calculate PaO Calculate PaO22/FiO/FiO22

Is there ARDS?Is there ARDS?

Acute Respiratory Distress Syndrome is an acute condition characterized by bilateral pulmonary infiltrates and severe hypoxaemia in absence of evidence for cardiogenic pulmonary oedema (Non-Cardiogenic Pulmonary Oedema).

PiO2/FiO2 (Carrico Index) is a quick and simple measure for integrity of lung tissue and its capacity to oxygenate the blood.

Normal > 300 – 500 mmHg (at sea level)

PiO2/FiO2 can also indicate the degree of lung tissue injury in other pulmonary disorders, eg Pneumonia

Two cases of ARDS with bilateral patchy opacities in middle and lower lung zones.

Common Causes: severe infection, aspiration, irritant gases, extensive trauma, multi-organ failure.

7.337.347.357.367.377.387.397.407.417.427.437.447.457.467.477.487.497.57.517.527.537.547.55

7.287.297.307.317.32

7.247.257.267.27

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pH pCO2Bicarb

Steps 3-5)Steps 3-5) Look at Look at pH, PaOpH, PaO22, PaCO, PaCO22

Is there Acid/Base Is there Acid/Base Disturbance?Disturbance?

7.337.347.357.367.377.387.397.407.417.427.437.447.457.467.477.487.497.57.517.527.537.547.55

7.287.297.307.317.32

7.247.257.267.27

33343536373839404142434445464748495

5152535455

2829303132

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pH PCO2BicarbSevere Diarrhoea

1ry Defect Compensation

Bicarb(M Ac)

PCO2

(R Alk)

M Ac & Comp R Alk

M Ac & R Ac

M Ac & R Alk

7.337.347.357.367.377.387.397.407.417.427.437.447.457.467.477.487.497.57.517.527.537.547.55

7.287.297.307.317.32

7.247.257.267.27

33343536373839404142434445464748495

5152535455

2829303132

24252627

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pH PCO2Bicarb

Persistent Vomiting

1ry Defect Compensation

Bicarb(M Alk)

PCO2

(R Ac)

M Alk & Comp R Ac

M Alk & R Ac

M Alk & R Alk

7.337.347.357.367.377.387.397.407.417.427.437.447.457.467.477.487.497.57.517.527.537.547.55

7.287.297.307.317.32

7.247.257.267.27

33343536373839404142434445464748495

5152535455

2829303132

24252627

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pH PCO2Bicarb

Hypoventilation

1ry Defect Compensation

PCO2

(R Ac) Bicarb(M Alk)

R Ac & Comp M Alk

R Ac & M Alk

R Ac & M Ac

7.337.347.357.367.377.387.397.407.417.427.437.447.457.467.477.487.497.57.517.527.537.547.55

7.287.297.307.317.32

7.247.257.267.27

33343536373839404142434445464748495

5152535455

2829303132

24252627

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pH PCO2Bicarb

Hyperventilation

1ry Defect Compensation

PCO2

(R Alk) Bicarb(M Ac)

R Alk & Comp M Ac

R Alk & M Alk

R Alk & M Ac

Prediction of Compensatory Response

DisorderPredicted Compensation

Metabolic AcidosispCO2 = (1.5 X Bicarb) + 8 + 2

Metabolic AlkalosispCO2 = (0.7 X Bicarb) + 20 + 5

Acute Respiratory Acidosis Bicarb = 0.1 pCO2

Chronic Respiratory Acidosis Bicarb = 0.4 pCO2

Acute Respiratory Alkalosis Bicarb = 0.2 pCO2

Chronic Respiratory Alkalosis Bicarb = 0.5 pCO2

or Bicarb in relation to 24 mEq/L or PCO2 in relation to 40 mm Hg