ARTERIAL BLOOD GASARTERIAL BLOOD GAS

ABGABG

MonitorsMonitors::

Arterial oxygenation – PaO2Arterial oxygenation – PaO2 Alveolar ventilation – PACO2Alveolar ventilation – PACO2 Acid-base status – pHAcid-base status – pH Oxygen delivery to tissues – PvO2Oxygen delivery to tissues – PvO2

Common sites in obtaining sampleCommon sites in obtaining sample

Radial – most common siteRadial – most common site BrachialBrachial Femoral Femoral Dorsal artery of the footDorsal artery of the foot

Allens test – to determine collateral Allens test – to determine collateral circulationcirculation

Arterial oxygenationArterial oxygenation

PaO2 ( partial pressure of arterial oxygen) – PaO2 ( partial pressure of arterial oxygen) – portion of O2 dissolved in plasmaportion of O2 dissolved in plasma

PAO2 (partial pressure of alveolar oxygen) PAO2 (partial pressure of alveolar oxygen) – is compared with PaO2 to determine P(A-– is compared with PaO2 to determine P(A-a) gradienta) gradient

FormulaFormulaPAO2 =((PB–47torr)(FIO2))-PAO2 =((PB–47torr)(FIO2))-

(PaCO2 X 1.25)(PaCO2 X 1.25)PAO2 = (760 – 47torr)(0.21) – PAO2 = (760 – 47torr)(0.21) –

(40torr X 1.25(40torr X 1.25PAO2 = (713 X 0.21) – 50PAO2 = (713 X 0.21) – 50PAO2 = 150 – 50 = 100torrPAO2 = 150 – 50 = 100torr

Oxyhemoglobin Dissociation CurveOxyhemoglobin Dissociation Curve

Factors affecting the affinity of O2Factors affecting the affinity of O2

Shift to the right: indicates that hgb affinity Shift to the right: indicates that hgb affinity for O2 has decreasedfor O2 has decreased

a. hypercapniaa. hypercapnia b. acidosisb. acidosis c. hyperthermiac. hyperthermia d. increased 2,3- DPGd. increased 2,3- DPG

Factors affecting the affinity of O2Factors affecting the affinity of O2

Shift to the left: hgb affinity for O2 has Shift to the left: hgb affinity for O2 has increasedincreased

a. hypocapniaa. hypocapnia

b. alkalosisb. alkalosis

c. hypothermiac. hypothermia

d. decreased of 2,3 DPGd. decreased of 2,3 DPG

e. carboxyhemoglobine. carboxyhemoglobin

Haldane effectHaldane effect

As oxygen combines with the As oxygen combines with the hemoglobin this enhances the hemoglobin this enhances the release of carbon dioxiderelease of carbon dioxide

Bohr effectBohr effect

As the RBC travels to the tissue, it releases As the RBC travels to the tissue, it releases the oxygen. This release of oxygen is due to the oxygen. This release of oxygen is due to the fact that elevated carbon dioxide levels, the fact that elevated carbon dioxide levels, which are present around tissues, which are present around tissues, decreases hemoglobin’s affinity for oxygendecreases hemoglobin’s affinity for oxygen

Normal PaO2 levelsNormal PaO2 levels

AgeAge <60-------------------------<60------------------------- 60---------------------------60--------------------------- 65---------------------------65--------------------------- 70---------------------------70--------------------------- 75---------------------------75--------------------------- 80---------------------------80---------------------------

PaO2 (torr)PaO2 (torr) 80-10080-100 8080 7575 7070 6565 6060

SaO2SaO2

Arterial oxygen saturation refers to the Arterial oxygen saturation refers to the quantity of oxygen being carried by the quantity of oxygen being carried by the hemoglobin compared with the maximum hemoglobin compared with the maximum that may be carried.that may be carried.

Normal = 95% and aboveNormal = 95% and above

PaCO2PaCO2

CO2 CO2 -dissolves in plasma-dissolves in plasma -enters the RBC-enters the RBC -bound to hemoglobin-bound to hemoglobin -as bicarbonate-as bicarbonateThe adequacy of ventilation is determined by The adequacy of ventilation is determined by

PaCO2 levelPaCO2 levelNormal = 35 – 45 torrNormal = 35 – 45 torr

pHpH

Determined by the amount of acid in the Determined by the amount of acid in the blood in relation to the amount of base.blood in relation to the amount of base.

Acid – carbonic acid ( H2CO3)Acid – carbonic acid ( H2CO3)

Base – bicarbonate (HCO3)Base – bicarbonate (HCO3)

Bicarbonate to carbonic acid ratio is 20:1Bicarbonate to carbonic acid ratio is 20:1

Normal = 7.35 – 7.45Normal = 7.35 – 7.45

pH CompensationpH Compensation

The challenge? The challenge?

correct the pH levelcorrect the pH level

How?How?

The levels of HCO3 and CO2 will always The levels of HCO3 and CO2 will always change in order to keep the pH normal.change in order to keep the pH normal.

Important notesImportant notes

If the compensated pH is 7.35 to 7.40, the If the compensated pH is 7.35 to 7.40, the pH must be assumed to have been acidotic pH must be assumed to have been acidotic initially. Decide if the PCO2 or HCO3 cause initially. Decide if the PCO2 or HCO3 cause the initial acidemiathe initial acidemia

If the compensated pH is 7.40 to 7.45, the If the compensated pH is 7.40 to 7.45, the pH must be assumed to have been alkalotic pH must be assumed to have been alkalotic initially. Decide if the PCO2 or HCO3 cause initially. Decide if the PCO2 or HCO3 cause the initial alkalemiathe initial alkalemia

ABG interpretationABG interpretation

pH--------------------------pH-------------------------- PaCO2--------------------PaCO2-------------------- PaO2----------------------PaO2---------------------- HCO3---------------------HCO3--------------------- B.E.------------------------B.E.------------------------

7.35 – 7.457.35 – 7.45 35 -45 torr35 -45 torr 80 -100 torr80 -100 torr 22 – 26 mEq/L22 – 26 mEq/L -2 to +2 ( refers to the -2 to +2 ( refers to the

total base deficit or total base deficit or excessexcess

Basic stepsBasic steps

1.1. Determine the acid base status by Determine the acid base status by observing the pHobserving the pH

2.2. Determine if the pH change is the result of Determine if the pH change is the result of a PCO2 change or a HCO3 changea PCO2 change or a HCO3 change

3.3. When this is determined, observe for signs When this is determined, observe for signs of compensation.of compensation.

4.4. Determine oxygenation status by Determine oxygenation status by observing PO2.observing PO2.

ABG interpretation chartABG interpretation chart

NormalNormal

pH PCO2 HCO3pH PCO2 HCO3

N N NN N N

ABG interpretation chartABG interpretation chart

UncompensatedUncompensated

Respiratory acidosisRespiratory acidosis Respiratory alkalosisRespiratory alkalosis Metabolic acidosisMetabolic acidosis Metabolic alkalosisMetabolic alkalosis

pH PCO2 HCO3pH PCO2 HCO3

D I ND I N

I D NI D N

D N DD N D

I N II N I

ABG interpretation chartABG interpretation chart

Partially compensatedPartially compensated

Respiratory acidosisRespiratory acidosis Respiratory alkalosisRespiratory alkalosis Metabolic acidosisMetabolic acidosis Metabolic alkalosisMetabolic alkalosis

pH PCO2 HCO3pH PCO2 HCO3

D I ID I I

I D DI D D

D D DD D D

I I II I I

ABG interpretation chartABG interpretation chart

Fully compensatedFully compensated

Respiratory acidosisRespiratory acidosis Respiratory alkalosisRespiratory alkalosis Metabolic acidosisMetabolic acidosis Metabolic alkalosisMetabolic alkalosis

pH PCO2 HCO3pH PCO2 HCO3

N I IN I I

N D DN D D

N D DN D D

N I IN I I

ABG interpretation chartABG interpretation chart

MixedMixed

AcidosisAcidosis alkalosisalkalosis

pH PCO2 HCO3pH PCO2 HCO3

D I DD I D

I D II D I

Blood Gas ElectrodesBlood Gas Electrodes

Sanz – pHSanz – pH

Severinghaus –PCO2Severinghaus –PCO2

Clark – PO2Clark – PO2

Thank you. GodblessThank you. Godbless

Jay Mark B. Burgos, RMTJay Mark B. Burgos, RMT