ABG analysis

Analysis of arterial blood sample provides precise measurement of acid-base balance in the body and of the lungs ability to oxygenate the blood and remove excess carbon dioxide

Assessment of a patient with respiratory dysfunction is incomplete without an ABG report

1. INTERPRETATION OF ARTERIAL BLOOD GASES (ABG) Dr. Nidhi Ahya ( M.P.T Cardio-Pulmonary) Assistant Professor, Cardio-Vascular & Respiratory PT DVVPF College of Physiotherapy, Ahmednagar 414111

2. CONTENTS Introduction to ABG Background Definitions & Terminology Normal Acid-Base Status Normal Values Steps in Interpretation of ABG Acid-Base Disorders and Compensatory Mechanisms Respiratory Acidosis Respiratory Alkalosis Metabolic Acidosis Metabolic Alkalosis Examples 4/12/18 2 Dr.Nidhi Ahya

3. Introduction to ABG Analysis of arterial blood sample provides precise measurement of acid-base balance in the body and of the lungs ability to oxygenate the blood and remove excess carbon dioxide Assessment of a patient with respiratory dysfunction is incomplete without an ABG report 4/12/18 3 Dr.Nidhi Ahya

4. Arterial Vs Venous Blood Assess respiratory function Oxygen & Carbon dioxide levels determined primarily by lungs Does not reflect respiratory function Exposed to peripheral vascular beds where gas exchange with tissues alters oxygen &carbon dioxide levels 4/12/18 4 Dr.Nidhi Ahya

5. Arterial Blood Sampling 4/12/18 Dr.Nidhi Ahya 5 Arteriotomy - Invasive procedure Review patients chart for clinical laboratory tests- PT/INR and APTT Arterial blood sample obtained from- Radial, Dorsalis Pedis , Brachial or femoral arteries Radial Artery is the preferred accessible easy to stabilize post-puncture

6. Modified Allen’s Test 4/12/18 Dr.Nidhi Ahya 6 To evaluate the degree of collateral circulation to the hand before puncture of radial artery

7. Obtaining Arterial Blood Sample 4/12/18 Dr.Nidhi Ahya 7 Requirements- Anticoagulant (liquid sodium) Sterile glass or low diffusibility plastic syringe Short bivel 20-22 gauge needle Isopropyl alchohol Sterile gauze squares Ice water bath

8. 4/12/18 Dr.Nidhi Ahya 8 Sample must be obtained without being exposed to the environment Air bubbles if any, should be removed, sample stored in ice water bath to inhibit continued metabolism Samples at room temperature to be analyzed within 10-15 minutes

9. Background Definitions & Terminology 4/12/18 Dr.Nidhi Ahya 9 pH : The negative logarithm to the base 10 of the hydrogen ion concentration in mol/L ph = 1 log 10 (H + )ion concentration Neutral pH : It is the pH at which there are equal no. of H + ions and OH – ions The body preserves neutrality inside our cells maintaining the blood at pH 7.4

10. 4/12/18 Dr.Nidhi Ahya 10 Henderson- Hasselbalch equation: pH œ OH - ion concentration H + ion concentration An increase in the pH indicates a proportionate decrease in the [H+] and a decrease in the pH indicates a proportionate increase in the [H+].

11. 4/12/18 Dr.Nidhi Ahya 11 Acidosis and alkalosis : Acidosis is an abnormality which tends to produce an acidic pH i.e < 7.45 Alkalosis is the opposite. It produces an alkaline pH i.e pH > 7.45 7.00 7.25 7.45 7.67 7.85

12. Normal Acid-Base Status 4/12/18 Dr.Nidhi Ahya 12 Normal metabolism of proteins and nucleotides generates about 100 mmol H+ per day in the form of sulphuric and phosphoric acids. By comparison, hydration of CO 2 to form H 2 CO 3 generates 12,500 mmol H+ per day. The hydrogen ion environment is tightly controlled by buffer systems Minutes: CO 2 excretion by the lungs Hours to days: renal excretion of H+ , reabsorption of HCO 3

13. Normal Values 4/12/18 Dr.Nidhi Ahya 13 pH - Measure of acid/base balance & ventilation 7.35-7.45 PaCO 2 - Measure of ventilation 35-45mmHg PaO 2 - Measure of oxygenation or gas exchange 85-100mmHg HCO 3 - Measure of metabolic disturbance 22-28 mEqm /l Base Excess - Measure of metabolic disturbance -2 to +2

14. Steps in Interpretation of ABG 4/12/18 Dr.Nidhi Ahya 14 Step 1: Identify the pH. Is it within normal range? pH >7.45 Alkalosis, pH < 7.35 Acidosis Alkalosis- Respiratory or Metabolic Acidosis- Respiratory or Metabolic To confirm Step 2: Look at PaCO 2 and HCO 3 Increase in PaCO 2 and decrease in HCO 3 contributes to acidosis Decrease in PaCO 2 and increase in HCO 3 contributes to alkalosis

15. 4/12/18 Dr.Nidhi Ahya 15 Step 3: If pH is normal, but PaCO 2 and HCO 3 are not in the ideal range- Compensatory mechanisms are active. For metabolic abnormality, respiratory system compensates, and for respiratory abnormality, metabolic system acts. RULE: Compensation always happens in the same direction as the pH i.e. To increase pH, HCO 3 should increase To decrease pH, HCO 3 should decrease. Alkolotic pH should decrease to become normal Acidotic pH should increase to become normal

16. Interpretation of Acid Base Disorders 4/12/18 Dr.Nidhi Ahya 16 pH- 7.22 PaCo 2 - 56mmHg PaO 2 -78 mmHg HCO 3 - 23 mEqm /lit Respiratory Acidosis

17. 4/12/18 Dr.Nidhi Ahya 17 Respiratory Acidosis : Abnormality in which there is primary reduction in alveolar ventilation relative to rate of CO 2 production PaCO 2 levels are above normal Respiratory acidosis is seen in- Severe diffuse airway obstruction Massive pulmonary edema Drug overdose Neuromusculoar disease Identifying the expected change in HCO 3 is useful to determine the level of compensation HCO 3 increases 1mEq/L for each 10-15mmHg rise in PaCO 2

18. Interpretation of Acid Base Disorders 4/12/18 Dr.Nidhi Ahya 18 pH- 7.54 PaCo 2 - 29mmHg PaO 2 -85 mmHg HCO 3 - 23 mEqm /lit Respiratory Alkalosis

19. 4/12/18 Dr.Nidhi Ahya 19 Respiratory Alkalosis: Abnormality in which there is primary increase in alveolar ventilation relative to rate of CO 2 production PaCO 2 levels are below expected level indicating Hyperventilation Respiratory alkalosis is seen in- Pain Anxiety Fever Kidneys compensate by excreting HCO 3 Normal HCO 3 with low PaCO 2 and increased pH is a uncompensated respiratory alkalosis.

20. Interpretation of Acid Base Disorders 4/12/18 Dr.Nidhi Ahya 20 pH- 7.28 PaCo 2 - 39mmHg PaO 2 -89 mmHg HCO 3 - 19 mEqm /lit Metabolic Acidosis

21. 4/12/18 Dr.Nidhi Ahya 21 Metabolic Acidosis: It is identified when the plasma HCO 3 or base excess falls below normal Occurs when increased load of H + ions is present or body is unable to excrete acids Loss of HCO 3 - Diarrhea, renal disease Increase in metabolic acid production- Ketoacidosis , Lactic acidosis or ingestion of certain toxins like methanol A reduction in PaCO 2 via hyperventilation compensates for metabolic acidosis Kussmaul’s respiration is obvious sign of metabolic acidosis

22. Interpretation of Acid Base Disorders 4/12/18 Dr.Nidhi Ahya 22 pH- 7.50 PaCo 2 - 42mmHg PaO 2 -89 mmHg HCO 3 - 33 mEqm /lit Metabolic Alkalosis

23. 4/12/18 Dr.Nidhi Ahya 23 Metabolic alkalosis: It is identifies by an above normal elevation of plasma HCO 3 Occurs whenever HCO 3 - ions accumulate in the blood or when abnormal no. of H + ions are lost from plasma Common causes- Hypokalemia Persistant vomiting Diuretic Therapy Hypoventilation and an elevation of PaCO 2 compensate for metabolic alkalosis

24. Summary 4/12/18 Dr.Nidhi Ahya 24 Introduction to ABG Background Definitions & Terminology Normal Acid-Base Status Normal Values Steps in Interpretation of ABG Acid-Base Disorders and Compensatory Mechanisms Examples

25. QUESTION 4/12/18 Dr.Nidhi Ahya 25 WRITE THE DEFINATION AND TERMINOLOGY OF THE ABG ANALYSIS. 5MARKS

26. Thank You… Solve the examples on the board....Before a Bye Bye ….!!! 4/12/18 Dr.Nidhi Ahya 26