ARTERIAL BLOOD GAS ANALYSIS

S.MEENATCHI SUNDARI,II YEAR PG.

A.Y.T 1

DEFINITION

It is a diagnostic procedure in which a blood is obtained from an artery directly by an arterial puncture or accessed by a

way of indwelling arterial catheter

A.Y.T 2

EQUIPMENT

Blood gas kit OR• 1ml /2ml syringe • 23-26 gauge needle• Stopper or cap• Alcohol swab• Disposable gloves• Plastic bag & crushed ice• Lidocaine (optional)• Vial of heparin (1:1000)• Par code or label

A.Y.T 3

Preparatory phase:

• Record patient inspired oxygen concentration

• Check patient temperature• Explain the procedure to the patient• Provide privacy for client• If not using hepranized syringe ,

hepranize the needle• Perform Allen's test• Wait at least 20 minutes before

drawing blood for ABG after initiating, changing, or discontinuing oxygen therapy, or settings of mechanical ventilation, after suctioning the patient or after extubation.

A.Y.T 4

EXCESSIVE HEPARIN Dilutional effect on results HCO3

- & PaCO2 Only .05 ml heperin required for 1 ml blood.

So syringe be emptied of heparin after flushing or only dead space volume is sufficient or dry heperin should be used

ALLEN’S TESTIt is a test done to determine that

collateral circulation is present from the ulnar artery in case thrombosis occur in the radial

A.Y.T 6

Sites for obtaining abg

• Radial artery ( most common )

• Brachial artery• Femoral artery

Radial is the most preferable site used because:

• It is easy to access• It is not a deep artery

which facilitate palpation, stabilization and puncturing

• The artery has a collateral blood circulation

A.Y.T 7

Performance phase:• Wash hands• Put on gloves• Palpate the artery for maximum pulsation• If radial, perform Allen's test• Place a small towel roll under the patient

wrist• Instruct the patient to breath normally

during the test and warn him that he may feel brief cramping or throbbing pain at the puncture site

• Clean with alcohol swab in circular motion• Skin and subcutaneous tissue may be

infiltrated with local anesthetic agent if needed

A.Y.T 8

• Insert needle at 45 radial ,60 brachial and 90 femoral

• Withdraw the needle and apply digital pressure

• Check bubbles in syringe

• Place the capped syringe in the container of ice immediately

• Maintain firm pressure on the puncture site for 5 minutes, if patient has coagulation abnormalities apply pressure for 10 – 15 minutes

A.Y.T 9

AIR BUBBLES: 1. PO2 150 mmHg & PCO2 0 mm Hg in air bubble(R.A.)

2. Mixing with sample, lead to PaO2 & PaCO2

To avoid air bubble, sample drawn very slowly and preferabily in glass syringe

Steady State:

Sampling should done during steady state after change in oxygen therepy or ventilator parameterSteady state is achieved usually within 3-10 minutes

Follow up phase:• Send labeled, iced specimen to the lab

immediately• Palpate the pulse distal to the puncture

site• Assess for cold hands, numbness, tingling

or discoloration• Documentation include: results of Allen's

test, time the sample was drawn, temperature, puncture site, time pressure was applied and if O2 therapy is there

• Make sure it’s noted on the slip whether the patient is breathing room air or oxygen. If oxygen, document the number of liters . If the patient is receiving mechanical ventilation, FIO2 should be documented

A.Y.T 11

complication

• Arteriospasm • Hematoma• Hemorrhage• Distal ischemia• Infection• Numbness

A.Y.T 12

ABG component• PH: measures hydrogen ion concentration in the

blood, it shows blood’ acidity or alkalinity• PCO2 : It is the partial pressure of CO2 that is carried

by the blood for excretion by the lungs, known as respiratory parameter

• PO2: It is the partial pressure of O2 that is dissolved

in the blood , it reflects the body ability to pick up oxygen from the lungs

• HCO3 : known as the metabolic parameter, it reflects

the kidney’s ability to retain and excrete bicarbonate A .Y .T 13

Parameter 37 C (Change every 10 min)

4 C (Change every 10 min)

pH 0.01 0.001

PCO2 1 mm Hg 0.1 mm Hg

PO2 0.1 vol % 0.01 vol %

Temp Effect On Change of ABG Values

A.Y.T15

Steps for ABG analysis1. What is the pH? Acidemia or Alkalemia?2. What is the primary disorder present?3. Is there appropriate compensation?4. Is the compensation acute or chronic?5. Is there an anion gap?6. If there is a AG check the delta gap?

Normal values:

PH = 7.35 – 7.45

PCO2 = 35 – 45 mmhg

PO2 = 80 – 100 mmhg HCO3 = 22 – 28 meq/L

A.Y.T17

Calculation of pH

203.0log10.6 3

PaCOHCOpH

3

224HCOPaCO

HHenderson-Hesselbachequation

Step 1 Look at the pH: is the blood acidemic or

alkalemic?

pH normal value 7.35-7.45

ACIDIC:below 7.35

ALKALOSIS:above 7.45

Step 2: What is the primary disorder?

What disorder is present?

pH pCO2 HCO3

Respiratory Acidosis

pH low high high

Metabolic Acidosis

pH low low low

Respiratory Alkalosis

pH high low low

Metabolic Alkalosis

pH high high high

ROME

Step 4:

Calculation of compensationMean "whole body" response equations for simple acid-base disturbances.

Note: The formula calculates the change in the compensatory parameter.

Disorder pH Primary change

Compensatory Response

Equation

Metabolic Acidosis

[HCO3-] PCO2 ΔPCO2 1.2 ΔHCO3

Metabolic Alkalosis

[HCO3-] PCO2 ΔPCO2 0.7 ΔHCO3

Respiratory Acidosis

PCO2 [HCO3-] Acute:

ΔHCO3- 0.1 ΔPCO2

Chronic:ΔHCO3

- 0.3 ΔPCO2

Respiratory Alkalosis

PCO2 [HCO3-] Acute:

ΔHCO3- 0.2 ΔPCO2

Chronic:ΔHCO3

- 0.5 ΔPCO2

1.2

0.7

0.1 0.3

0.2 0.5

Compensation Formula Simplified

Acute Chronic

Metabolic

Respiratory

Acidosis

Alkalosis

Acidosis

Alkalosis

Step 3-4: Is there appropriate compensation? Is it chronic or acute? Respiratory Acidosis

Acute (Uncompensated): for every 10 increase in pCO2 -> HCO3 increases by 1 and there is a decrease of 0.08 in pH

Chronic (Compensated): for every 10 increase in pCO2 -> HCO3 increases by 4 and there is a decrease of 0.03 in pH

Respiratory Alkalosis Acute (Uncompensated): for every 10 decrease in pCO2 ->

HCO3 decreases by 2 and there is a increase of 0.08 in PH Chronic (Compensated): for every 10 decrease in pCO2 -> HCO3

decreases by 5 and there is a increase of 0.03 in PH

Partial Compensated: Change in pH will be between 0.03 to 0.08 for every 10 mmHg change in PCO2

Step 3-4: Is there appropriate compensation? Metabolic Acidosis

Winter’s formula: Expected pCO2 = 1.5[HCO3] + 8 ± 2 OR pCO2 = 1.2 ( HCO3) If serum pCO2 > expected pCO2 -> additional

respiratory acidosis and vice versa Metabolic Alkalosis

Expected PCO2 = 0.7 × HCO3 + (21 ± 2) OR pCO2 = 0.7 ( HCO3) If serum pCO2 < expected pCO2 - additional

respiratory alkalosis and vice versa

Step 5: Calculate the anion gap AG used to assess acid-base status esp in D/D of

metabolic acidosis AG & HCO3

- used to assess mixed acid-base disorders

AG based on principle of electroneutrality: Total Serum Cations = Total Serum Anions Na + (K + Ca + Mg) = HCO3 + Cl + (PO4 + SO4

+ Protein + Organic Acids) Na + UC = HCO3 + Cl + UA Na – (HCO3 + Cl) = UA – UC Na – (HCO3 + Cl) = AG Normal =12 ± 2

Contd… AG corrected = AG + 2.5[4 – albumin] If there is an anion Gap then calculate the

Delta/delta gap (step 6) to determine additional hidden nongap metabolic acidosis or metabolic alkalosis

If there is no anion gap then start analyzing for non-anion gap acidosis

Step 6: Calculate Delta Gap Delta gap = (actual AG – 12) + HCO3 Adjusted HCO3 should be 24 (+_ 6) {18-30} If delta gap > 30 -> additional metabolic alkalosis If delta gap < 18 -> additional non-gap metabolic

acidosis If delta gap 18 – 30 -> no additional metabolic

disorders

Step 5: Calculate the “gaps”

Anion gap = Na+ − [Cl− + HCO3−]

Δ AG = Anion gap − 12

Δ HCO3 = 24 − HCO3

Δ AG = Δ HCO3 −, then Pure high AG Met. Acidosis

Δ AG > Δ HCO3 −, then High AG Met Acidosis + Met. Alkalosis

Δ AG < Δ HCO3 −, then High AG Met Acidosis + HCMA

Nongap metabolic acidosis For non-gap metabolic acidosis, calculate the urine anion

gap URINARY AG

Total Urine Cations = Total Urine AnionsNa + K + (NH4 and other UC) = Cl + UA(Na + K) + UC = Cl + UA(Na + K) – Cl = UA – UC (Na + K) – Cl = AG

Distinguish GI from renal causes of loss of HCO3 by estimating Urinary NH4+ .

Hence a -ve UAG (av -20 meq/L) seen in GI, while +ve value (av +23 meq/L) seen in renal problem.

UAG = UNA + UK – UCL

Metobolic acidosis: Anion gap acidosis

Causes of nongap metabolic acidosis - DURHAM

Diarrhea, ileostomy, colostomy, enteric fistulas

Ureteral diversions or pancreatic fistulas

RTA type I or IV, early renal failure

Hyperailmentation, hydrochloric acid administration

Acetazolamide, Addison’s

Miscellaneous – post-hypocapnia, toulene, sevelamer, cholestyramine ingestion

Dictums in ABG AnalysisDictums in ABG Analysis1. Primary change & Compensatory change always

occur in the same direction.

2. pH and Primary parameter change in the same direction suggests a metabolic problem.

pH and Primary parameter change in the opposite direction suggests a respiratory problem.

3. Renal and pulmonary compensatory mechanisms return pH toward but rarely to normal. Corollary:A normal pH in the presence of changes in PCO2 or HCO3 suggets a mixed acid-base disorder.

Steps for ABG analysis1. What is the pH? Acidemia or Alkalemia?2. What is the primary disorder present?3. Is there appropriate compensation?4. Is the compensation acute or chronic?5. Is there an anion gap?6. If there is a AG check the delta gap?