arterial blood gases (3)

اللهم علمني ما ينفعني ( )وانفعني بما علمتني

الرحمن الله بسمالرحيم

Arterial Blood GasesArterial Blood Gases

This article will help us to

1. Interpret arterial blood gases.

2 .Translate informations into effective action.

IndicationsIndications

It is essential in evaluation of critical ill patient , giving an idea about his acid base balance and oxygenation . In a respiratory disturbance , it is a diagnostic assessment of the nature , severity and progress of the illness .

TechniqueTechnique

•Choose vessels that have best collateral circulation.

•Puncture of a site where the artery is superficial .

•Radial artery is the best choice , if not accessible : dorsalis pedis , posterior tibial , brachial and femoral arteries .

•Brachial and femoral arteries puncture are contraindicated in patients with abnormal haemostatic mechanism .

PH 7.35 – 7.45

PaCO2 35 – 45 mmHg

PaO2 80-100 mmHg

HCO3 22 – 26mq / L

O2 saturation 95 – 100 %

Normal values of ABG,s

Interpretation of ABG,sInterpretation of ABG,s

Does the patient have acidosis or alkalosis ?

If PH < 7. 35 acidosis

If PH > 7. 45 alkalosis

Is acidosis / alkalosis respiratory or metabolic?

If PH and PaCO2 move in the same direction

If PH and PaCO2 move in the opposite direction it is primary respiratory acid - base disturbance.

it is primary metabolic acid – base disturbance .

PH PaCO2

Metabolic acidosis

Metabolic alkalosis

Respiratory acidosis

Respiratory alkalosis

Is the respiratory disorder is acute Is the respiratory disorder is acute ( uncompensated ) or chronic ( uncompensated ) or chronic ( compensated ) ?( compensated ) ?

•If PH is unaccepted it is acute.

•If PH is accepted it is chronic.

N.B accepted PH is from 7.30 to 7.50.

Acid – Base Disorder Primary change Compensatory change

Respiratory acidosis PaCo2HCo3Respiratory acidosis

Respiratory alkalosis PaCo2HCo3

Metabolic acidosis HCo3 PaCo2

Metabolic alkalosis HCo3 PCo2

Is the patient hypoxemic or not ?Is the patient hypoxemic or not ?

.If PaO2 between 80 – 100 mmHg , oxygenation is normal.

.If PaO2 is < 60 mmHg , hypoxic state is existing.

* In respiratory disturbances : .If ABG,s show only that PaO2 is < 60 mmHg

Hypoxaemic ( type I ) Respiratory Failure .

.If PaO2 < 60 mmHg & PaCO2 > 45mmHg, Hypoxaemic , Hypercapnic ( type II )

Respiratory Failure.

Indication for Critical Care Indication for Critical Care Unite admissionUnite admission

1. Persistent or worsening hypoxemia ( PaO2 < 50 mmHg ) .

2 .Severe or worsening hypercapnia ( PaCO2 > 70 mmHg ) .

3 .Severe or worsening respiratory acidosis ( PH < 7.30 ) .

Measures to improve Measures to improve ventilation ventilation

1. Enhancing alveolar ventilation i.e treatment of the cause ( drug over dose / central hypoventilation / neuromuscular disease / airway obstruction ) .

2 .Decrease CO2 production -Bring fever down . -Avoid excessive nutritional calories.

Measures to improve Measures to improve oxygenationoxygenation

1. O 2 supplementation

* RF type I nasal catheter / face mask .

* RF type II venturi mask “ controlled oxygen “ .

2 .Treatment of the cause .

3 .Anaemic patients should be transfused to haemoglobin of 10 gm. %

adequate delivery of oxygenated blood to tissues .

4. Hypotensive patients should be resuscitated to an adequate cardiac output to assure

EXAMPLE 1EXAMPLE 1

PH 7.34 (academia )

Pa CO2 48 ( academia )

Pa O2 129 ( normal )

HCO3–

26 ( normal )

BE + 1 ( normal )

Sa O 2 99 % ( normal )

Interpretation

Respiratory acidosis , adequate oxygenation.

EXAMPLE 2EXAMPLE 2

PH 7.40 ( normal )

Pa CO2 58 ( academia )

Pa O2 57 ( hypoxemia )

HCO3–

35 ( alkalemia )

BE + 9 ( alkalemia )

Sa O 2 89 % ( hypoxemia )

Interpretation

Respiratory acidosis with complete metabolic compensation and hypoxemia.

EXAMPLE 3EXAMPLE 3

PH 7.29 (academia )

Pa CO2 40 ( normal )

Pa O2 192 ( normal )

HCO3–

19 (academia )

BE - 5.6 (academia )

Sa O 2 97.5 % ( normal )

Interpretation

Metabolic acidosis with no compensation , adequate oxygenation.

EXAMPLE 4EXAMPLE 4

PH 7.37 ( normal )

Pa CO2 40 ( normal )

Pa O2 126 ( academia )

HCO3–

20 ( academia )

BE - 3.1 ( academia)

Sa O 2 98 % ( normal )

Interpretation

Fully compensated metabolic acidosis , adequate oxygenation.