Arterial Blood Gas Analysis

By the end of this session you should understand: The normal ranges for arterial blood gas values How to use the 5-step approach to arterial blood gas interpretation Some of the common causes of arterial blood gas abnormalities and what to do to correct them Learning outcomes

Venous Blood Gasses Significant correlation in pH, PaCO 2, PaO 2, Bicarbonate, and Base Excess among ABG and VBG values in healthy individuals Caution: in the presence of shock, hypothermia, and hyperthermia, including during cardiac arrest, there is a poor correlation (in PaO 2 in particular) Venous blood gas analysis reveals results rapidly for Electrolytes and Haemoglobin VBG normal values (with good perfusion) Many slight variations to normal reference ranges are given in published literature PvO 2 35 – 40 mmHg on air pH7.33 – 7.44 PvCO 2 40 – 55 mmHg HCO 3 24 – 28 mmol l -1 BE+/- 2 mmol l -1

5-step approach to arterial blood gas interpretation

1. How is the patient? Will provide useful clues to help with interpretation of the results

5-step approach to arterial blood gas interpretation 1. How is the patient? Will provide useful clues to help with interpretation of the results 2. Assess oxygenation Is the patient hypoxaemic? PaO 2 > 75 mmHg on air (and increased with higher FiO 2 ) Aim for normal PaO 2

5-step approach to arterial blood gas interpretation 1. How is the patient? Will provide useful clues to help with interpretation of the results 2. Assess oxygenation 3. Determine the pH (or H + concentration) Normal pH  7.35 to 7.45

5-step approach to arterial blood gas interpretation 1. How is the patient? Will provide useful clues to help with interpretation of the results 2. Assess oxygenation 3. Determine the pH (or H + concentration) 4. Determine the respiratory component Normal PaCO 2  35mmHg to 45mmHg

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 Normal HCO 3  22 mmol l -1 to 26 mmol l -1 Normal base excess  -2 mmol l -1 to +2 mmol l -1

Initial Information I:Paramedics have called S:21-year-old woman on the way to hospital has become increasingly drowsy B:She has been thrown from her horse at a local event A:A Was snoring/threatened - inserted an oropharyngeal airway - improved B RR 8-10 given oxygen via a face-mask (FiO 2 approximately 40%) C Pulse 51 - regular, BP 130/60, Capillary refill < 2 seconds, IV inserted and functioning (bloods taken) D AVP U, Glucose 5.3, no medications given. Dilated left pupil E Eyes swollen/bruising R:Please review urgently and an arterial blood gas sample has been taken 21 year old woman thrown from horse

Step 1: How is the patient? 21 year old woman thrown from horse (continued) Initial Information I:Paramedics have called S:21-year-old woman on the way to hospital has become increasingly drowsy B:She has been thrown from her horse at a local event A:A Was snoring/threatened - inserted an oropharyngeal airway - improved B RR 8-10 given oxygen via a face-mask (FiO 2 approximately 40%) C Pulse 51 - regular, BP 130/60, Capillary refill < 2 seconds, IV inserted and functioning (bloods taken) D AVP U, Glucose 5.3, no medications given. Dilated left pupil E Eyes swollen/bruising R:Please review urgently and an arterial blood gas sample has been taken

Step 1: How is the patient? - The reduced level of consciousness will impair oxygenation and ventilation, causing an increased PaCO 2, a respiratory acidosis 21 year old woman thrown from horse (continued) Initial Information I:Paramedics have called S:21-year-old woman on the way to hospital has become increasingly drowsy B:She has been thrown from her horse at a local event A:A Was snoring/threatened - inserted an oropharyngeal airway - improved B RR 8-10 given oxygen via a face-mask (FiO 2 approximately 40%) C Pulse 51 - regular, BP 130/60, Capillary refill < 2 seconds, IV inserted and functioning (bloods taken) D AVP U, Glucose 5.3, no medications given. Dilated left pupil E Eyes swollen/bruising R:Please review urgently and an arterial blood gas sample has been taken

Step 1: How is the patient? There is unlikely to be much compensation (change in bicarbonate) because of the acuteness of the situation 21 year old woman thrown from horse (continued) Initial Information I:Paramedics have called S:21-year-old woman on the way to hospital has become increasingly drowsy B:She has been thrown from her horse at a local event A:A Was snoring/threatened - inserted an oropharyngeal airway - improved B RR 8-10 given oxygen via a face-mask (FiO 2 approximately 40%) C Pulse 51 - regular, BP 130/60, Capillary refill < 2 seconds, IV inserted and functioning (bloods taken) D AVP U, Glucose 5.3, no medications given. Dilated left pupil E Eyes swollen/bruising R:Please review urgently and an arterial blood gas sample has been taken

Arterial blood gas analysis reveals: Inspired oxygen40% (FiO 2 0.4) normal values PaO mmHg> 75 mmHg on air pH – 7.45 PaCO 2 78 mmHg35 – 45 mmHg Bicarbonate23.6 mmol l – 26 mmol l -1 Base excess-2.4 mmol l -1 +/- 2 mmol l -1 What is the next step? 21 year old woman thrown from horse (continued)

Arterial blood gas analysis reveals: Inspired oxygen40% (FiO 2 0.4) normal values PaO mmHg> 75 mmHg on air pH – 7.45 PaCO 2 78 mmHg35 – 45 mmHg Bicarbonate23.6 mmol l – 26 mmol l -1 Base excess-2.4 mmol l -1 +/- 2 mmol l -1 What is the next step? Step 2: Assess oxygenation Is the patient hypoxaemic? 21 year old woman thrown from horse (continued)

Arterial blood gas analysis reveals: Inspired oxygen40% (FiO 2 0.4) normal values PaO mmHg> 75 mmHg on air pH – 7.45 PaCO 2 78 mmHg35 – 45 mmHg Bicarbonate23.6 mmol l – 26 mmol l -1 Base excess-2.4 mmol l -1 +/- 2 mmol l -1 What is the next step?

Arterial blood gas analysis reveals: Inspired oxygen40% (FiO 2 0.4) normal values PaO mmHg> 75 mmHg on air pH – 7.45 PaCO 2 78 mmHg35 – 45 mmHg Bicarbonate23.6 mmol l – 26 mmol l -1 Base excess-2.4 mmol l -1 +/- 2 mmol l -1 What is the next step? Step 3: Determine the pH (or H + concentration) Is the patient acidaemic; pH < 7.35? Is the patient alkalaemic; pH > 7.45? 21 year old woman thrown from horse (continued)

Arterial blood gas analysis reveals: Inspired oxygen40% (FiO 2 0.4) normal values PaO mmHg> 75 mmHg on air pH – 7.45 PaCO 2 78 mmHg35 – 45 mmHg Bicarbonate23.6 mmol l – 26 mmol l -1 Base excess-2.4 mmol l -1 +/- 2 mmol l -1 What is the next step? 21 year old woman thrown from horse (continued)

Arterial blood gas analysis reveals: Inspired oxygen40% (FiO 2 0.4) normal values PaO mmHg> 75 mmHg on air pH – 7.45 PaCO 2 78 mmHg35 – 45 mmHg Bicarbonate23.6 mmol l – 26 mmol l -1 Base excess-2.4 mmol l -1 +/- 2 mmol l -1 What is the next step? 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 21 year old woman thrown from horse (continued)

Arterial blood gas analysis reveals: Inspired oxygen40% (FiO 2 0.4) normal values PaO mmHg> 75 mmHg on air pH – 7.45 PaCO 2 78 mmHg35 – 45 mmHg Bicarbonate23.6 mmol l – 26 mmol l -1 Base excess-2.4 mmol l -1 +/- 2 mmol l -1 What is the next step? 21 year old woman thrown from horse (continued)

Arterial blood gas analysis reveals: Inspired oxygen40% (FiO 2 0.4) normal values PaO mmHg> 75 mmHg on air pH – 7.45 PaCO 2 78 mmHg35 – 45 mmHg Bicarbonate23.6 mmol l – 26 mmol l -1 Base excess-2.4 mmol l -1 +/- 2 mmol l -1 What is the next step? 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 21 year old woman thrown from horse (continued)

Arterial blood gas analysis reveals: Inspired oxygen40% (FiO 2 0.4) normal values PaO mmHg> 75 mmHg on air pH – 7.45 PaCO 2 78 mmHg35 – 45 mmHg Bicarbonate23.6 mmol l – 26 mmol l -1 Base excess-2.4 mmol l -1 +/- 2 mmol l -1 In summary: An acute respiratory acidosis with impaired ventilation.

Initial Information - Use the 5-step approach to analyse the results of an arterial blood sample I:Nurses have called a medical emergency S: A 65-year-old man has been found collapsed in the respiratory unit B: Patient admitted with with severe COPD - initial assessment by the ward nurse he was found to be apnoeic A:A 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 99% C Easily palpable carotid pulse – 90 bpm – regular (not monitored) Capillary refill < 3 seconds, IV inserted, BP not recorded D AVP U, Glucose 6.2mmoll -1, no medications given recently E Nil R:Please review urgently and an arterial blood gas sample has been taken Respiratory arrest

Respiratory arrest (continued) Arterial blood gas analysis reveals: Inspired oxygen 85% (FiO ) estimated normal values PaO mmHg> 75 mmHg on air pH – 7.45 PaCO mmHg35 – 45 mmHg HCO mmol l – 26 mmol l -1 BE+ 12 mmol l -1 +/- 2 mmol l -1

Respiratory arrest (continued) Arterial blood gas analysis reveals: Inspired oxygen 85% (FiO ) estimated normal values PaO mmHg> 75 mmHg on air pH – 7.45 PaCO mmHg35 – 45 mmHg HCO mmol l – 26 mmol l -1 BE+ 12 mmol l -1 +/- 2 mmol l -1 In summary: The significant acidaemia (pH 7.10) indicates an acute respiratory acidosis as a result of the respiratory arrest. There is pre-existing compensated chronic respiratory acidosis, the pH would have been close to normal.

Initial Information - Use the 5-step approach to analyse the results of an arterial blood sample I:Emergency Department staff require assistance S:75-year-old woman is admitted to the ED following a VF cardiac arrest. Spontaneous circulation restored after 2 shocks, but the patient remained apnoeic and unresponsive. B: The arrest witnessed by paramedics had been preceded by 30 min of severe central chest pain A:A Intubated – ETT confirmed in trachea B Ventilated her with an automatic ventilator tidal volume of 900 ml rate of 18 breaths min -1, 100% oxygen, Symmetrical chest movement C Pulse 100 min -1, BP 90/54 mmHg, IV inserted, Cap refill >3seconds D AVP U, Glucose 4.8 mmol l -1, 1mg Adrenaline given during arrest E Nil, Temp 36.7 o C R:Please review urgently and an arterial blood gas sample has been taken Ventilated Post VF Arrest

Ventilated Post VF Arrest (continued) Arterial blood gas analysis reveals: Inspired oxygen100% (FiO 2 1.0) normal values PaO mmHg> 75 mmHg on air pH – 7.45 PaCO 2 20 mmHg35 – 45 mmHg HCO mmol l – 26 mmol l -1 BE- 4 mmol l -1 +/- 2 mmol l -1

Ventilated Post VF Arrest (continued) Arterial blood gas analysis reveals: Inspired oxygen100% (FiO 2 1.0) normal values PaO mmHg> 75 mmHg on air pH – 7.45 PaCO 2 20 mmHg35 – 45 mmHg HCO mmol l – 26 mmol l -1 BE- 4 mmol l -1 +/- 2 mmol l -1 In summary: A respiratory alkalosis, mild metabolic acidosis.

Initial Information - Use the 5-step approach to analyse the results of an arterial blood sample I:Staff require assistance S:An 18-year-old insulin dependent diabetic is unwell and staff concerned B:He has been vomiting for 48 h and because he was unable to eat, he has taken no insulin A:A Airway clear/patent B Breathing spontaneously RR 35 min -1, oxygen 4 l min -1 via Hudson mask, SpO 2 98% C Pulse 100 min -1, BP 90/54 mmHg, IV inserted, Cap refill >3seconds D A V PU (Alert earlier), GCS 12 (E3, M5, V4), No insulin given, bedside Blood sugar “Hi” E Nil, Temp 36.2 o C, Decreased skin turgor, dry tongue/mouth R:Please review urgently and an arterial blood gas sample has been taken Diabetic Patient Unwell

Diabetic Patient Unwell (continued) Arterial blood gas analysis reveals: Inspired oxygen 30% (FiO 2 0.3) estimated normal values PaO mmHg> 75 mmHg on air pH – 7.45 PaCO 2 19 mmHg35 – 45 mmHg HCO mmol l – 26 mmol l -1 BE mmol l -1 +/- 2 mmol l -1 The blood glucose is 30 mmol l -1 and there are ketones +++ in the urine

Diabetic Patient Unwell (continued) Arterial blood gas analysis reveals: Inspired oxygen 30% (FiO 2 0.3) estimated normal values PaO mmHg> 75 mmHg on air pH – 7.45 PaCO 2 19 mmHg35 – 45 mmHg HCO mmol l – 26 mmol l -1 BE mmol l -1 +/- 2 mmol l -1 The blood glucose is 30 mmol l -1 and there are ketones +++ in the urine In summary: 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. There is a primary metabolic acidosis with an element of compensation provided by the respiratory alkalosis.

Initial Information - Use the 5-step approach to analyse the results of an arterial blood sample I:Ward staff activated medical emergency S:A 75-year-old man is on the surgical ward has become increasingly hypotensive over the last 6 h despite 1000 ml 0.9% saline B: 2 days post operative - laparotomy for a perforated sigmoid colon secondary to diverticular disease A:A Patient speaking – Airway clear B RR 35 min -1, (SpO 2 90%) started on 4 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 R:Please review urgently and an arterial blood gas sample has been taken Hypotension Emergency

Hypotension Emergency (continued) Arterial blood gas analysis reveals: Inspired oxygen 40% (FiO 2 0.4) estimated normal values PaO 2 62 mmHg> 75 mmHg on air pH – 7.45 PaCO 2 24 mmHg35 – 45 mmHg HCO mmol l – 26 mmol l -1 BE- 15 mmol l -1 +/- 2 mmol l -1

Hypotension Emergency (continued) Arterial blood gas analysis reveals: Inspired oxygen 40% (FiO 2 0.4) estimated PaO 2 62 mmHg> 75 mmHg on air pH – 7.45 PaCO 2 24 mmHg35 – 45 mmHg HCO mmol l – 26 mmol l -1 BE- 15 mmol l -1 +/- 2 mmol l -1 In summary: There is a primary metabolic acidosis with an element of 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.

Initial Information - Use the 5-step approach to analyse the results of an arterial blood sample I: Nurse has called as paramedics bring in patient S: Intubated, ventilated patient arrived post arrest B: A 60-year-old man, witnessed out-of-hospital cardiac arrest. The paramedics arrived after 7 min, during which CPR had not been attempted. His initial rhythm was VF and the paramedics subsequently restored a spontaneous circulation after the 3 rd shock. A: A Intubated B RR 8-10, FiO 2 50% C Pulse 120 min -1 – SinusTachycardia, BP 150/95, Capillary refill < 2 seconds, IV inserted D AVP U, Glucose 6.8, Adrenaline 1mg post 2 nd shock & Amiodarone 300mg after 3 rd shock E Cyanosed. Temp 35.7 o C R:Please review urgently and an arterial blood gas sample has been taken Out of hospital witnessed arrest

Arterial blood gas analysis reveals: Inspired oxygen 50% (FiO 2 0.5) normal values PaO 2 56 mmHg> 75 mmHg on air pH – 7.45 PaCO 2 47 mmHg35 – 45 mmHg HCO mmol l – 26 mmol l -1 BE- 10 mmol l -1 +/- 2 mmol l -1 Out of hospital witnessed arrest (continued)

Arterial blood gas analysis reveals: Inspired oxygen 50% (FiO 2 0.5) normal values PaO 2 56 mmHg> 75 mmHg on air pH – 7.45 PaCO 2 47 mmHg35 – 45 mmHg HCO mmol l – 26 mmol l -1 BE- 10 mmol l -1 +/- 2 mmol l -1 In summary: This is a typical ABG result after prolonged cardiac arrest. There is a mixed metabolic and respiratory acidosis – the predominant component is metabolic, with significant impairment of oxygenation. Out of hospital witnessed arrest (continued)

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Summary This workshop has covered: The terms used to describe the results of arterial blood gas analysis The normal ranges for arterial blood gas values How respiration and metabolism are linked How to use the 5-step approach to arterial blood gas interpretation Some of the common causes of arterial blood gas abnormalities and what to do to correct them

Advanced Life Support Course Slide set All rights reserved ©Australian Resuscitation Council and Resuscitation Council (UK) 2010; updated 2013