1. Arterial blood gas analysis Workshop Version: Jun 2016

2. At the end of this workshop you should be able to: understand the terms used to describe the results of arterial blood gas analysis use the 5-step approach to arterial blood gas interpretation identify some of the common causes of arterial blood gas abnormalities and how they should be managed Learning outcomes

3. PaO 2 ; the partial pressure of oxygen in arterial blood – normal range breathing air > 75 mmHg on air (increases with FiO 2 ) pH; the acidity or alkalinity of the blood, determined by the concentration of hydrogen ions [H + ] – normal range 7.35 – 7.45 PaCO 2; the partial pressure of carbon dioxide in arterial blood – normal range 35 – 45 mmHg Bicarbonate; a buffer, neutralises the effects of excess acid – normal range 22 – 26 mmol L -1 Base excess; a measure of the degree of excess acid or alkali (base) in the blood – normal range +2 to -2 mmol L -1 Terms used in arterial blood gas analysis

4. 5-step approach to arterial blood gas interpretation

5. 1.How is the patient? – this will provide useful clues to help with interpretation of the results.

6. 5-step approach to arterial blood gas interpretation 1.How is the patient? 2.Assess oxygenation: – is the patient hypoxaemic? – the PaO 2 should be > 75 mmHg breathing air – Bedside calculation - the % inspired concentration multiplied by 5 (result should be within 75 mmHg of calculation).

7. 5-step approach to arterial blood gas interpretation 1.How is the patient? 2.Assess oxygenation 3.Determine the pH (or H + concentration): – Is the patient acidaemic; pH < 7.35 – Is the patient alkalaemic; pH > 7.45

8. 5-step approach to arterial blood gas interpretation 1.How is the patient? 2.Assess oxygenation: 3.Determine the pH (or H + concentration) 4.Determine the respiratory component: – If the pH 45 mmHg – respiratory acidosis – if the pH > 7.45, is the PaCO 2 < 35 mmHg – respiratory alkalosis

9. 5-step approach to arterial blood gas interpretation 1.How is the patient? 2.Assess oxygenation: 3.Determine the pH (or H + concentration) 4.Determine the respiratory component 5.Determine the metabolic component: – If the pH < 7.35, is the HCO 3 - < 22 mmol L -1 (base excess < -2 mmol L -1 )? – metabolic acidosis – If the pH > 7.45, is the HCO 3 - > 26 mmol L -1 (base excess > +2 mmol L -1 )? – metabolic alkalosis

10. 5-step approach to arterial blood gas interpretation In summary: 1.How is the patient? 2.Assess oxygenation 3.Determine the pH (or H + concentration) 4.Determine the respiratory component 5.Determine the metabolic component

11. IED staff member has asked you to assist. S21-year-old woman who on the way to hospital has become increasingly drowsy. BShe was thrown from her horse at a local event AA: Clear, tolerating an oropharyngeal airway, on 40% oxygen via face mask B: Respiratory rate 8 min -1, SpO 2 99%, reduced equal air entry both lungs, percussion note resonant both sides, trachea central. C: Pulse 54 min -1 regular, BP 166/105 mmHg. An arterial blood sample to check her blood gases and acid base status has been taken D: AVP U, Glucose 5.3 mmoll -1, no medications given E: IV in right forearm, Eyes swollen/bruising. No external bleeding RYou take an arterial blood sample to check her blood gases and acid base status. Case study 1

12. Case study 1 (continued) The first of the five steps in analysing an arterial blood sample is to ask ‘how is the patient?’ From your ABCDE assessment what might you expect?

13. Case study 1 (continued) The first of the five steps in analysing an arterial blood sample is to ask ‘how is the patient?’ From your ABCDE assessment what might you expect? her reduced level of consciousness may impair oxygenation and ventilation. as a result she may be hypoxic and have an increased PaCO 2 causing a respiratory acidosis and a low pH. compensation (change in bicarbonate) is unlikely because of the acuteness of the situation.

14. Inspired oxygen 40% (FiO 2 0.4) normal values PaO 2 110 mmHg> 75 mmHg on air pH7.197.35 – 7.45 PaCO 2 78 mmHg35 – 45 mmHg Bicarbonate23.6 mmol l -1 22 – 26 mmol l -1 Base excess-2.4 mmol l -1 +/- 2 mmol l -1 Case study 1 (continued) What are you going to do now?

15. Inspired oxygen 40% (FiO 2 0.4) normal values PaO 2 110 mmHg> 75 mmHg on air pH7.197.35 – 7.45 PaCO 2 78 mmHg35 – 45 mmHg Bicarbonate23.6 mmol l -1 22 – 26 mmol l -1 Base excess-2.4 mmol l -1 +/- 2 mmol l -1 Case study 1 (continued) What are you going to do now? Step 2: assess oxygenation: – is the patient hypoxaemic? – the PaO 2 should be about 5 times the % inspired concentration (and within 75 mmHg).

16. Inspired oxygen 40% (FiO 2 0.4) normal values PaO 2 110 mmHg> 75 mmHg on air pH7.197.35 – 7.45 PaCO 2 78 mmHg35 – 45 mmHg Bicarbonate23.6 mmol l -1 22 – 26 mmol l -1 Base excess-2.4 mmol l -1 +/- 2 mmol l -1 Case study 1 (continued) What are you going to do now?

17. Inspired oxygen 40% (FiO 2 0.4) normal values PaO 2 110 mmHg> 75 mmHg on air pH7.197.35 – 7.45 PaCO 2 78 mmHg35 – 45 mmHg Bicarbonate23.6 mmol l -1 22 – 26 mmol l -1 Base excess-2.4 mmol l -1 +/- 2 mmol l -1 Case study 1 (continued) What are you going to do now? Step 3: Determine the pH (or H + concentration): – Is the patient acidaemic; pH < 7.35? – Is the patient alkalaemic; pH > 7.45?

18. Inspired oxygen 40% (FiO 2 0.4) normal values PaO 2 110 mmHg> 75 mmHg on air pH7.197.35 – 7.45 PaCO 2 78 mmHg35 – 45 mmHg Bicarbonate23.6 mmol l -1 22 – 26 mmol l -1 Base excess-2.4 mmol l -1 +/- 2 mmol l -1 Case study 1 (continued) What are you going to do now?

19. Inspired oxygen 40% (FiO 2 0.4) normal values PaO 2 110 mmHg> 75 mmHg on air pH7.197.35 – 7.45 PaCO 2 78 mmHg35 – 45 mmHg Bicarbonate23.6 mmol l -1 22 – 26 mmol l -1 Base excess-2.4 mmol l -1 +/- 2 mmol l -1 Case study 1 (continued) What are you going to do now? Step 4: Determine the respiratory component: – If the pH 45 mmHg ? – respiratory acidosis. – If the pH > 7.45, is the PaCO 2 < 35 mmHg ? – respiratory alkalosis.

20. Inspired oxygen 40% (FiO 2 0.4) normal values PaO 2 110 mmHg> 75 mmHg on air pH7.197.35 – 7.45 PaCO 2 78 mmHg35 – 45 mmHg Bicarbonate23.6 mmol l -1 22 – 26 mmol l -1 Base excess-2.4 mmol l -1 +/- 2 mmol l -1 Case study 1 (continued) What are you going to do now?

21. Inspired oxygen 40% (FiO 2 0.4) normal values PaO 2 110 mmHg> 75 mmHg on air pH7.197.35 – 7.45 PaCO 2 78 mmHg35 – 45 mmHg Bicarbonate23.6 mmol l -1 22 – 26 mmol l -1 Base excess-2.4 mmol l -1 +/- 2 mmol l -1 Case study 1 (continued) What are you going to do now? Step 5: Determine the metabolic component: – If the pH < 7.35, is the HCO 3 - < 22 mmol L -1 (base excess < -2 mmol L -1 )? – metabolic acidosis. – If the pH > 7.45, is the HCO 3 - > 26 mmol L -1 (base excess > +2 mmol L -1 )? – metabolic alkalosis.

22. Inspired oxygen 40% (FiO 2 0.4) normal values PaO 2 110 mmHg> 75 mmHg on air pH7.197.35 – 7.45 PaCO 2 78 mmHg35 – 45 mmHg Bicarbonate23.6 mmol l -1 22 – 26 mmol l -1 Base excess-2.4 mmol l -1 +/- 2 mmol l -1 Case study 1 (continued) In summary: The patient has an acute respiratory acidosis with impaired ventilation. Because of the acuteness of the situation, there is no compensation.

23. Use the 5-step approach to analyse the results of the arterial blood sample IYou have been called to a medical emergency S“A patient is currently in respiratory arrest”. BPatient admitted with COPD - initial assessment by the ward nurse he was found to be apnoeic AA: Apnoeic - head tilt chin lift opening manoeuvre B: Nurse is attempting to ventilate with bag-mask, oxygen at 15 l min -1, Oropharyngeal airway, SaO 2 90%. Widespread wheeze in both lungs and coarse crackles at the left base C: Easily palpable carotid pulse – 56 bpm – regular (not monitored) Capillary refill < 3 seconds, IV inserted, BP not recorded (150/94 earlier) D: AVP U, Glucose 6.2 mmoll -1, no medications given recently E: Nil. IV in right forearm RPlease review urgently and an arterial blood gas sample has been taken Respiratory arrest

24. The first of the five steps in analysing an arterial blood sample is to ask ‘how is the patient?’ From your ABCDE assessment what might you expect? Respiratory arrest

25. The first of the five steps in analysing an arterial blood sample is to ask ‘how is the patient?’ From your ABCDE assessment what might you expect? impaired oxygenation due to his underlying lung disease an increased PaCO 2 as a result of the period of apnoea and his COPD. a reduced pH signs of compensation for his chronic respiratory acidosis due to his COPD with an increased bicarbonate Respiratory arrest

26. Inspired oxygen 85% (FiO 2 0.85) normal values PaO 2 147 mmHg> 75 mmHg on air pH7.107.35 – 7.45 PaCO 2 135 mmHg35 – 45 mmHg Bicarbonate36 mmol l -1 22 – 26 mmol l -1 Base excess+12 mmol l -1 +/- 2 mmol l -1 Respiratory arrest Go through the remaining 4 steps to complete your analysis

27. Inspired oxygen 85% (FiO 2 0.85) normal values PaO 2 147 mmHg> 75 mmHg on air pH7.107.35 – 7.45 PaCO 2 135 mmHg35 – 45 mmHg Bicarbonate36 mmol l -1 22 – 26 mmol l -1 Base excess+12 mmol l -1 +/- 2 mmol l -1 Respiratory arrest In summary: He is hypoxic. He has a significant acidaemia There is an acute respiratory acidosis as a result of the respiratory arrest. There is a metabolic alkalosis - from his pre-existing, compensated, chronic respiratory acidosis.

28. Use the 5-step approach to analyse the results of the arterial blood sample IED staff call for assistance SMrs Harris, 86, who has been successfully resuscitated after an out-of-hospital cardiac arrest. ROSC was achieved after a three shocks, but she didn’t regain consciousness so she was intubated before transfer. BThe arrest witnessed by paramedics had been preceded by 30 min of severe central chest pain AA: intubated, 7.5 mm diameter tube, 22 cm at lips B: manual ventilation, about 18 to 20 breaths min -1 /emptying about 750 ml of bag each time, end-tidal CO 2 23 mmHg, good air entry both lungs, SpO 2 97% C: pulse 126 min -1, sinus tachycardia, blood pressure 94/68 mmHg, IV present D: : AV P U, no eye opening (1), intubated (-), extending to pain (2) – GCS 4+ E: nothing gross. IV in left antecubital fossa. Adrenaline and amiodaone given as per algorithm RPlease review urgently and an arterial blood gas sample has been taken Ventilated post VF arrest

29. The first of the five steps in analysing an arterial blood sample is to ask ‘how is the patient?’ From your ABCDE assessment what might you expect? Ventilated post VF arrest

30. The first of the five steps in analysing an arterial blood sample is to ask ‘how is the patient?’ From your ABCDE assessment what might you expect? impaired oxygenation due to complications of the arrest (e.g. aspiration) a low PaCO 2 due to the excessive ventilation an alkalaemia and raised pH from the excessive ventilation a metabolic acidosis from anaerobic respiration during the cardiac arrest a low bicarbonate as it will have been consumed to try and buffer the acidosis Ventilated post VF arrest

31. Inspired oxygen 100% (FiO 2 1.0) normal values PaO 2 192 mmHg> 75 mmHg on air pH7.627.35 – 7.45 PaCO 2 20 mmHg35 – 45 mmHg Bicarbonate19 mmol l -1 22 – 26 mmol l -1 Base excess-4 mmol l -1 +/- 2 mmol l -1 Ventilated post VF arrest Go through the remaining 4 steps to complete your analysis

32. Inspired oxygen 100% (FiO 2 1.0) normal values PaO 2 192 mmHg> 75 mmHg on air pH7.627.35 – 7.45 PaCO 2 20 mmHg35 – 45 mmHg Bicarbonate19 mmol l -1 22 – 26 mmol l -1 Base excess-4 mmol l -1 +/- 2 mmol l -1 Ventilated post VF arrest In summary the patient has: A respiratory alkalosis from the excessive ventilation. A mild metabolic acidosis.

33. Use the 5-step approach to analyse the results of the arterial blood sample IYou have been called as carers for a patient are concerned SA 21-year old insulin dependent diabetic is unwell BMr George is an insulin dependant who has been vomiting for 48 hours. Because he was unable to eat, he has taken no insulin. AA: airway clear/patent B: breathing spontaneously RR 32 min -1, oxygen 6 l min -1 via Hudson mask, SpO 2 98%. Obvious smell of ketones on his breath C: cold and clammy, pulse 120 min -1, BP 90/66 mmHg, IV in left hand - saline running at rate of 50 ml per hour D: A V PU (Alert earlier), Eye opening to speech (3), confused (4), obeys commands (6), GCS 13. “No insulin given” recorded, bedside Blood sugar “Hi” E: slightly distended abdomen, tender on examination, no bowel sounds RPlease review urgently and an arterial blood gas sample has been taken Diabetic patient

34. The first of the five steps in analysing an arterial blood sample is to ask ‘how is the patient?’ From your ABCDE assessment what might you expect? Diabetic patient

35. The first of the five steps in analysing an arterial blood sample is to ask ‘how is the patient?’ From your ABCDE assessment what might you expect? Knowing that the patient has type 1 diabetes the following might be present: He is likely to be acidaemic with a low pH. He will be trying to compensate by hyperventilating and have a low PaCO 2 He will have a reduced bicarbonate as a result of buffering the ketoacids. No significant impairment of oxygenation. Diabetic patient

36. Inspired oxygen 30% (FiO 2 0.3) normal values PaO 2 129 mmHg> 75 mmHg on air pH6.897.35 – 7.45 PaCO 2 19 mmHg35 – 45 mmHg Bicarbonate4.7 mmol l -1 22 – 26 mmol l -1 Base excess-29.2 mmol l -1 +/- 2 mmol l -1 Diabetic patient The blood glucose is 30 mmol L -1 and there are ketones +++ in the urine Go through the remaining 4 steps to complete your analysis

37. Inspired oxygen 30% (FiO 2 0.3) normal values PaO 2 129 mmHg> 75 mmHg on air pH6.897.35 – 7.45 PaCO 2 19 mmHg35 – 45 mmHg Bicarbonate4.7 mmol l -1 22 – 26 mmol l -1 Base excess-29.2 mmol l -1 +/- 2 mmol l -1 Diabetic patient In summary: There is no impairment in oxygenation. He has a primary metabolic acidosis (with an element of compensation provided by the respiratory alkalosis) as his pH remains low. These blood gas results are consistent with severe diabetic ketoacidosis. Further evidence is the presence of ketones in his urine and the very high blood glucose.

38. IYou are met by one of the nurses in ED who gives you the following handover SThis is Mr Brown, 63, who has been successfully resuscitated after an out-of- hospital cardiac arrest. BHe arrested about 20 min ago, had bystander CPR for about 5 min. When the paramedics arrived he was in VF and got ROSC some time after the second shock. AA: he is intubated, on 50% oxygen RR 8-10 B: saturation 98% C: systolic blood pressure 130 mmHg, HR 120 min -1. He’s had about 750 ml saline IV. D: AVP U, Glucose 6.8, Adrenaline 1mg post 2 nd shock E: cyanosed. Temp 35.7 o C RPlease review urgently and an arterial blood gas sample has been taken Out of Hospital witnessed arrest

39. The first of the five steps in analysing an arterial blood sample is to ask ‘how is the patient?’ From the ISBAR handover what might you expect? Out of Hospital witnessed arrest

40. The first of the five steps in analysing an arterial blood sample is to ask ‘how is the patient?’ From the ISBAR handover what might you expect? hypoxaemia as a result of aspiration, pulmonary oedema, pneumothorax, alone or in combination. an increased PaCO 2 due to a period of hypoventilation. a low pH as a result the anaerobic metabolism during the arrest. consumption of bicarbonate in an attempt to buffer the acidaemia. Out of Hospital witnessed arrest

41. Inspired oxygen 50% (FiO 2 0.5) normal values PaO 2 56 mmHg> 75 mmHg on air pH7.107.35 – 7.45 PaCO 2 47 mmHg35 – 45 mmHg Bicarbonate14 mmol l -1 22 – 26 mmol l -1 Base excess-10 mmol l -1 +/- 2 mmol l -1 Out of Hospital witnessed arrest Go through the remaining 4 steps to complete your analysis

42. Inspired oxygen 50% (FiO 2 0.5) normal values PaO 2 56 mmHg> 75 mmHg on air pH7.107.35 – 7.45 PaCO 2 47 mmHg35 – 45 mmHg Bicarbonate14 mmol l -1 22 – 26 mmol l -1 Base excess-10 mmol l -1 +/- 2 mmol l -1 Out of Hospital witnessed arrest In summary: This is a typical ABG result after prolonged cardiac arrest There is significant impairment of oxygenation There is a mixed metabolic and respiratory acidosis – the predominant component is metabolic

43. Any questions?

44. Summary The terms used to describe the results of arterial blood gas analysis. The normal ranges for arterial blood gas values. How to use the 5-step approach to arterial blood gas interpretation. Some common causes of arterial blood gas abnormalities and what to do to correct them.

45. Advanced Life Support Level 2 Course Slide set All rights reserved © Australian Resuscitation Council (June 2016)

46. Optional Extra Slides

47. IWard staff activated medical emergency SA 75-year-old man is on the surgical ward has become increasingly hypotensive over the last 6 h despite 1000 ml 0.9% saline. B2 days post operative - laparotomy for a perforated sigmoid colon secondary to diverticular disease. AA: Patient speaking – Airway clear B: RR 35 min -1, (SpO 2 90%) started on 6 l min -1 oxygen via facemask SpO 2 now poor signal, Symmetrical chest movement. C: HR 120 min -1, sinus tachycardia, warm peripheries/sweaty cold centrally, BP 70/40 mmHg, Capillary Refill 3 seconds. D: A VPU, Glucose 5.8 mmoll -1, Urine output 90 ml in the last 6 h GCS 13 (E3, M6, V4) E: Temperature not recorded, Patient lethargic. RPlease review urgently and an arterial blood gas sample has been taken Hypotension Emergency

48. The first of the five steps in analysing an arterial blood sample is to ask ‘how is the patient?’ From the ISBAR handover what might you expect? Hypotension Emergency

49. The first of the five steps in analysing an arterial blood sample is to ask ‘how is the patient?’ From the ISBAR handover what might you expect? Poorly perfused for some time – sepsis likely. He is likely to be acidaemic with a low pH. A low pH as a result of the increased lactate level. He will be trying to compensate by hyperventilating and have a low PaCO 2. Consumption of bicarbonate in an attempt to buffer the acidaemia. Hypotension Emergency

50. Inspired oxygen 50% (FiO 2 0.5) normal values PaO 2 62 mmHg> 75 mmHg on air pH7.177.35 – 7.45 PaCO 2 24 mmHg35 – 45 mmHg Bicarbonate12 mmol l -1 22 – 26 mmol l -1 Base excess-15 mmol l -1 +/- 2 mmol l -1 Go through the remaining 4 steps to complete your analysis Hypotension Emergency

51. Inspired oxygen 50% (FiO 2 0.5) normal values PaO 2 62 mmHg> 75 mmHg on air pH7.177.35 – 7.45 PaCO 2 24 mmHg35 – 45 mmHg Bicarbonate12 mmol l -1 22 – 26 mmol l -1 Base excess-15 mmol l -1 +/- 2 mmol l -1 In summary: There is a primary metabolic acidosis with an element of attempted compensation. The degree of this is probably limited by the presence of an acute abdomen. The most likely diagnosis is sepsis syndrome secondary to intra- abdominal infection. Hypotension Emergency