Arterial Blood Gas Analysis Jane Roe Practice Educator
Arterial Blood Gas Analysis Jane Roe Practice Educator Wednesday 17 th January 2018
ABG An arterial blood gas (ABG) analysis provides information about the patient’s respiratory & metabolic function, including acid-base status. Can gain other useful information such as electrolyte levels, Hb, lactate.
Indications • Respiratory compromise • Post cardiopulmonary arrest • Metabolic conditions e. g. DKA • Sudden/unexplained deterioration • Evaluation of interventions • Changes/titration in invasive/non-invasive ventilation settings • Major trauma • Prior to major surgery
Parameters • p. H : - 7. 35 - 7. 45 overall acid-base balance of the blood sample. It is affected by both respiratory and metabolic function. • Pa. O 2 : - 10 – 13. 3 k. Pa measurement of partial pressure of O 2 dissolved in the blood sample. • Pa. CO 2 : - 4. 5 – 6. 0 k. Pa measurement of partial pressure of dissolved CO 2 in the blood. In order to be carried to the lungs to be exhaled CO 2 is transported in the plasma solution as carbonic acid.
Parameters Continued. . . • Bicarbonate (HCO 3 -) : - 22 – 26 mmol/l Most important buffer in the body. Buffers in the body act as chemical sponges which absorb excess alkali or acid. • Base Excess (BE) : - -2 mmol to +2 mmol It is the quantity of acid or base required to restore the blood to a p. H of 7. 4 A negative value indicates excess of acid & a positive value indicates an excess of base. • Sa. O 2 : - 92 – 99% Arterial O 2 saturation is the % of O 2 that has combined with the Hb molecule.
Acid-base definitions Acid – Substance capable of providing Hydrogen ions. Base – (Alkali) substance capable of accepting Hydrogen ions. p. H - Potential hydrogen. A Measure of how acid or alkaline (base) a substance is. Acid-base is controlled through respiratory and metabolic functions (Renal, chemical buffers).
Systematic Analysis of ABG Results 1) Assess the oxygenation (Pa. O 2). Is the patient hypoxic? What supplementary O 2 are they receiving? What is their Hb? What is their Sa. O 2? 2) Determine the p. H level Is there an acidosis (p. H <7. 35) or alkalosis (p. H >7. 45) present?
Systematic Analysis of ABG Results Continued. . 3) Determine the respiratory component (Pa. CO 2) *Pa. CO 2 > 6 k. Pa; Acid *Pa. CO 2 < 4. 5; Alkaline 4) Determine the metabolic component (HCO 3 -) *HCO 3 - > 26 mmol/l; Alkaline *HCO 3 - < 22 mmol/l; Acid 5) Determine for each of these parameters whether the values are acid, normal or alkaline.
Systematic Analysis of ABG Results Continued. . 6) Combine the findings from steps 2, 3, 4 & 5 and determine what the primary disturbance is. 7) Determine whethere is any compensation for abnormal p. H. Complete? Partial? Uncompensated?
0 Acidic Alkaline 14 Acid Normal Alkaline p. H <7. 35 - 7. 45 >7. 45 Pa. CO 2 >6 k. Pa 4. 5 - 6. 0 k. Pa <4. 5 k. Pa HCO 3 - <22 mmol/l 22 - 26 mmol/l >26 mmol/l
Classification Of Imbalance -1 Respiratory Acidosis p. H and Pa. CO 2 are in the acid column and HCO 3 - is normal. Caused by inadequate ventilation leading to retention of CO 2 ie COPD, pneumonia, pulmonary oedema, mechanical chest injury, over sedation, neurological disorder. Acid p. H 7. 24 Pa. CO 2 8. 0 k. Pa HCO 3 - Normal 24 mmol/l Alkaline
Classification Of Imbalance -2 Metabolic Acidosis p. H and HCO 3 - are in the acid column and Pa. CO 2 is normal. Caused by excess acid production ie lactate or loss of HCO 3 -. Causes include diarrhoea, cardiac arrest, DKA, renal failure etc. Acid p. H 7. 20 Pa. CO 2 HCO 3 - Normal 4. 7 k. Pa 16 mmol/l Alkaline
Classification Of Imbalance -3 Respiratory Alkalosis p. H and Pa. CO 2 are in the alkaline column and HCO 3 - is normal. Caused by excessive ventilation leading to over excretion of CO 2 ie hysteria, excessive mechanical ventilation. Acid Normal Alkaline p. H 7. 50 Pa. CO 2 2. 5 HCO 3 - 22 mmol/l
Classification Of Imbalance -4 Metabolic Alkalosis p. H and HCO 3 - are in the alkaline column and Pa. CO 2 is normal. Caused by loss of acid or ingestion of bases ie severe vomiting, overdose of antacids, diuretics etc Acid Normal p. H Pa. CO 2 HCO 3 - Alkaline 7. 67 4. 2 k. Pa 38 mmol/l
Classification of Imbalance - 5 Respiratory Acidosis with Metabolic Compensation p. H is normal, Pa. CO 2 is acid, HCO 3 - is alkaline. Compensation for acidosis is achieved by the other system. Here, the kidneys are compensating for respiratory derangement. Acid p. H Pa. CO 2 HCO 3 - Normal Alkaline 7. 37 7. 9 k. Pa 32
Classification of Imbalance - 6 Metabolic Acidosis with Respiratory Compensation p. H is normal, HCO 3 - is in the acid column and Pa. CO 2 is in the alkaline column. The patient will have a high respiratory rate to achieve this Pa. CO 2 and compensate for metabolic acidosis. Acid p. H Alkaline 7. 35 Pa. CO 2 HCO 3 - Normal 2. 7 12 mmol/l
Classification of Imbalance - 7 Metabolic Alkalosis with Partial Compensation p. H is alkaline, HCO 3 - is in the alkaline column and Pa. CO 2 is in the acid column. The parameter not associated with the p. H is abnormal and on the opposite side of the scale indicating partial compensation. Acid p. H Pa. CO 2 HCO 3 - Normal Alkaline 7. 48 6. 6 29
Arterial Blood Gas Examples -1 Acid Pa. O 2 11 k. Pa p. H 7. 30 Pa. CO 2 6. 9 k. Pa HCO 3 - 24 mmol/l Normal Alkaline
Arterial Blood Gas Examples -2 Acid Pa. O 2 11. 5 k. Pa p. H 7. 49 Pa. CO 2 4. 6 k. Pa HCO 330 mmol/l Normal Alkaline
Arterial Blood Gas Examples -3 Acid Pa. O 2 10. 5 k. Pa p. H 7. 32 Pa. CO 2 5. 2 k. Pa HCO 3 - 18 mmol/l Normal Alkaline
Arterial Blood Gas Examples -4 Acid Pa. O 2 14 k. Pa p. H 7. 5 Pa. CO 2 3. 3 k. Pa HCO 3 - 26 mmol/l Normal Alkaline
Arterial Blood Gas Examples -5 Acid Pa. O 2 8. 15 k. Pa p. H 7. 5 Pa. CO 2 3. 3 k. Pa HCO 3 - 26 mmol/l Normal Alkaline
Arterial Blood Gas Example -6 Acid Pa. O 2 11. 4 k. Pa p. H 7. 39 Pa. CO 2 5. 3 k. Pa HCO 3 - 23. 6 mmol/l Normal Alkaline
Arterial Blood Gas Example -7 Acid Pa. O 2 26. 4 k. Pa p. H 7. 38 Pa. CO 2 9. 85 k. Pa HCO 3 - 31. 2 mmol/l Normal Alkaline
Arterial Blood Gas Example - 8 Acid Pa. O 2 8. 3 p. H 7. 37 Pa. CO 2 3. 9 k. Pa HCO 3 - 19. 2 mmol/l Normal Alkaline
Arterial Blood Gas Example -9 Acid Pa. O 2 8. 3 p. H 7. 26 Pa. CO 2 8. 3 k. Pa HCO 3 - 30 mmol/l Normal Alkaline
Classification of Imbalance Double Trouble… p. H is acid, Pa. CO 2 is acid, HCO 3 - is acid… This patient is very sick…. Acid p. H 7. 13 Pa. CO 2 9. 9 HCO 3 - 10 Normal Alkaline
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