Arterial Blood Gases Mark Carpenter January 2013

Can I use anonymised data from this presentation for future teaching/Research? 1.Yes 2.No

Objectives Develop an organised system for looking at blood gasesDevelop an organised system for looking at blood gases Be able to comment on the arterial pO2 in relation to the FiO2Be able to comment on the arterial pO2 in relation to the FiO2 Detect metabolic acidosis and it’s significance in the acutely unwellDetect metabolic acidosis and it’s significance in the acutely unwell

6-step approach 1.Assess Oxygenation –Is the patient hypoxic –Is there a problem with oxygenation? 2.Determine Acid-Base Deficit –pH>7.45 (H (H + < 35) alkalaemia –pH 45) acidaemia 3.Determine the respiratory component, and does this explain the acid-base deficit –PaCO 2 :>6.0 kPa - respiratory acidosis <4.7kPa - respiratory alkalosis <4.7kPa - respiratory alkalosis

6-step approach 4.Determine the metabolic component, and does this explain the acid-base deficit –HCO 3 -: <22 mmol/l - metabolic acidosis >26 mmol/l - metabolic alkalosis 5.Which is the primary problem : remember compensation never (rarely) completely restores pH to the normal range, and a mixed picture may be present 6.Is there any compensation and if so what is it?

Different metabolic processes, of different magnitudeDifferent metabolic processes, of different magnitude Net effect is what determines pHNet effect is what determines pH “Like a bath”“Like a bath” Alkalaemia normal Acidaemia

Respiratory Acidosis Any cause of hypoventilation –CNS depression –Neuromuscular disease –Acute or chronic lung disease –Cardiac arrest –Ventilator malfunction

Respiratory Alkalosis Any cause of hyperventilation –Hypoxia –Acute lung conditions –Anxiety –Fever –Pregnancy –Hepatic failure –Some central CNS lesions

Metabolic Acidosis Increased anion gap (added acid)Increased anion gap (added acid) –Renal failure –Ketoacidosis –Lactic acidosis –Salicylate/Tricyclic overdose

Metabolic Acidosis Decreased anion gap (loss of bicarbonate)Decreased anion gap (loss of bicarbonate) –Renal tubular acidosis –Diarrhoea –Carbonic anhydrase inhibitors –Ureteral diversion –Chloride administration

Metabolic Alkalosis Loss of acid or gaining alkali –Vomiting –Diarrhoea –Diuretics (and hypokalaemia generally) –Ingestion of alkali

Reminder of normal values pH = 7.35 – 7.45pH = 7.35 – 7.45 pO 2 = kPa on airpO 2 = kPa on air pCO 2 = 4.6 – 6.0 kPapCO 2 = 4.6 – 6.0 kPa HCO 3 = 25 – 35 mmols/lHCO 3 = 25 – 35 mmols/l Base excess ± 2.0Base excess ± 2.0 Anion gap Anion gap

Case 1 Young female admitted with overdose of unknown tablets pO 2 15 kPa on air pH7.24 PaCO HCO 3 8

1: Assess Oxygenation: Is the patient Hypoxaemic? 1.Yes 2.No

1: Is there a problem with Oxygenation? 1.Yes 2.No

2: Assess Acid-Base Status 1.Acidaemic 2.Neutral 3.Alkalaemic

3: Assess Metabolic Component… 1.Metabolic Acidosis 2.Metabolic Alkalosis 3.Neither

3b: Does this explain the pH? 1.Yes 2.No

4: Assess the Respiratory Component 1.Resp Acidosis 2.Resp Alkalosis 3.Neither

4b: Does this explain the pH? 1.Yes 2.No

5: Which is Primary? 1.Metabolic Acidosis 2.Metabolic Alkalosis 3.Respiratory Acidosis 4.Respiratory Alkalosis 5.Mixed Acidosis 6.Mixed Alkalosis 7.No Acid/Base problem

6: Is there any compensation? 1.No it’s mixed 2.No 3.Resp Acidosis 4.Resp Alkalosis 5.Met Acidosis 6.Met Alkalosis

Case 1 Alkalaemia normal Acidaemia

Case 2 Elderly male admitted from nursing home with one week history of fever and vomiting pO 2 12 kPa on 4l by mask pH7.49 PaCO HCO 3 35

1: Assess Oxygenation: Is the patient Hypoxaemic? 1.Yes 2.No

1: Is there a problem with Oxygenation? 1.Yes 2.No

2: Assess Acid-Base Status 1.Acidaemic 2.Neutral 3.Alkalaemic

3: Assess Metabolic Component… 1.Metabolic Acidosis 2.Metabolic Alkalosis 3.Neither

3b: Does this explain the pH? 1.Yes 2.No

4: Assess the Respiratory Component 1.Resp Acidosis 2.Resp Alkalosis 3.Neither

4b: Does this explain the pH? 1.Yes 2.No

5: Which is Primary? 1.Metabolic Acidosis 2.Metabolic Alkalosis 3.Respiratory Acidosis 4.Respiratory Alkalosis 5.Mixed Acidosis 6.Mixed Alkalosis 7.No Acid/Base problem

6: Is there any compensation? 1.No it’s mixed 2.No 3.Resp Acidosis 4.Resp Alkalosis 5.Met Acidosis 6.Met Alkalosis

Case 2 Alkalaemia normal Acidaemia

Case 3a Middle aged man admitted with cough sputum and haemoptysis. Life-long smoker pO 2 4 on air pH7.19 PaCO HCO 3 28

1: Assess Oxygenation: Is the patient Hypoxaemic? 1.Yes 2.No

1: Is there a problem with Oxygenation? 1.Yes 2.No

2: Assess Acid-Base Status 1.Acidaemic 2.Neutral 3.Alkalaemic

3: Assess Metabolic Component… 1.Metabolic Acidosis 2.Metabolic Alkalosis 3.Neither

3b: Does this explain the pH? 1.Yes 2.No

4: Assess the Respiratory Component 1.Resp Acidosis 2.Resp Alkalosis 3.Neither

4b: Does this explain the pH? 1.Yes 2.No

5: Which is Primary? 1.Metabolic Acidosis 2.Metabolic Alkalosis 3.Respiratory Acidosis 4.Respiratory Alkalosis 5.Mixed Acidosis 6.Mixed Alkalosis 7.No Acid/Base problem

6: Is there any compensation? 1.No it’s mixed 2.No 3.Resp Acidosis 4.Resp Alkalosis 5.Met Acidosis 6.Met Alkalosis

Case 3a Alkalaemia normal Acidaemia

Case 3b Middle aged man admitted with cough sputum and haemoptysis. Life-long smoker pO 2 6 on airSpO2 92% pH7.32 PaCO HCO 3 39

1: Assess Oxygenation: Is the patient Hypoxaemic? 1.Yes 2.No

1: Is there a problem with Oxygenation? 1.Yes 2.No

2: Assess Acid-Base Status 1.Acidaemic 2.Neutral 3.Alkalaemic

3: Assess Metabolic Component… 1.Metabolic Acidosis 2.Metabolic Alkalosis 3.Neither

3b: Does this explain the pH? 1.Yes 2.No

4: Assess the Respiratory Component 1.Resp Acidosis 2.Resp Alkalosis 3.Neither

4b: Does this explain the pH? 1.Yes 2.No

5: Which is Primary? 1.Metabolic Acidosis 2.Metabolic Alkalosis 3.Respiratory Acidosis 4.Respiratory Alkalosis 5.Mixed Acidosis 6.Mixed Alkalosis 7.No Acid/Base problem

6: Is there any compensation? 1.No it’s mixed 2.No 3.Resp Acidosis 4.Resp Alkalosis 5.Met Acidosis 6.Met Alkalosis

Case 3b Alkalaemia normal Acidaemia

Case 4 Middle aged man awake and breathing spontaneously on ET tube following cardiac arrest pO 2 35 FiO2 0.8 pH6.9 PaCO HCO 3 13

1: Assess Oxygenation: Is the patient Hypoxaemic? 1.Yes 2.No

1: Is there a problem with Oxygenation? 1.Yes 2.No

2: Assess Acid-Base Status 1.Acidaemic 2.Neutral 3.Alkalaemic

3: Assess Metabolic Component… 1.Metabolic Acidosis 2.Metabolic Alkalosis 3.Neither

3b: Does this explain the pH? 1.Yes 2.No

4: Assess the Respiratory Component 1.Resp Acidosis 2.Resp Alkalosis 3.Neither

4b: Does this explain the pH? 1.Yes 2.No

5: Which is Primary? 1.Metabolic Acidosis 2.Metabolic Alkalosis 3.Respiratory Acidosis 4.Respiratory Alkalosis 5.Mixed Acidosis 6.Mixed Alkalosis 7.No Acid/Base problem

6: Is there any compensation? 1.No it’s mixed 2.No 3.Resp Acidosis 4.Resp Alkalosis 5.Met Acidosis 6.Met Alkalosis

Case 4 Alkalaemia normal Acidaemia

Case 5 Elderly lady with congestive cardiac failure pO 2 9 on 40% oxygen pH7.64 PaCO HCO 3 29

So what is it?? 1.Resp Acidosis with compensation 2.Met Alkalosis with compensation 3.Resp Alkalosis with compensation 4.Met Alkalosis with compensation 5.Mixed Acidosis 6.Mixed Alkalosis

1: Assess Oxygenation: Is the patient Hypoxaemic? 1.Yes 2.No

1: Is there a problem with Oxygenation? 1.Yes 2.No

2: Assess Acid-Base Status 1.Acidaemic 2.Neutral 3.Alkalaemic

3: Assess Metabolic Component… 1.Metabolic Acidosis 2.Metabolic Alkalosis 3.Neither

3b: Does this explain the pH? 1.Yes 2.No

4: Assess the Respiratory Component 1.Resp Acidosis 2.Resp Alkalosis 3.Neither

4b: Does this explain the pH? 1.Yes 2.No

5: Which is Primary? 1.Metabolic Acidosis 2.Metabolic Alkalosis 3.Respiratory Acidosis 4.Respiratory Alkalosis 5.Mixed Acidosis 6.Mixed Alkalosis 7.No Acid/Base problem

6: Is there any compensation? 1.No it’s mixed 2.No 3.Resp Acidosis 4.Resp Alkalosis 5.Met Acidosis 6.Met Alkalosis

So what is it?? 1.Resp Acidosis with compensation 2.Met Alkalosis with compensation 3.Resp Alkalosis with compensation 4.Met Alkalosis with compensation 5.Mixed Acidosis 6.Mixed Alkalosis

Did you change your answer?? 1.Yes 2.No Be Honest!!

Case 5 Alkalaemia normal Acidaemia

Case 6 Young diabetic male admitted with chest infection, vomiting and drowsiness pO 2 12 on air pH7.31 PaCO HCO 3 6.0

So what is it?? 1.Resp Acidosis with compensation 2.Met Alkalosis with compensation 3.Resp Alkalosis with compensation 4.Met Alkalosis with compensation 5.Mixed Acidosis 6.Mixed Alkalosis

1: Assess Oxygenation: Is the patient Hypoxaemic? 1.Yes 2.No

1: Is there a problem with Oxygenation? 1.Yes 2.No

2: Assess Acid-Base Status 1.Acidaemic 2.Neutral 3.Alkalaemic

3: Assess Metabolic Component… 1.Metabolic Acidosis 2.Metabolic Alkalosis 3.Neither

3b: Does this explain the pH? 1.Yes 2.No

4: Assess the Respiratory Component 1.Resp Acidosis 2.Resp Alkalosis 3.Neither

4b: Does this explain the pH? 1.Yes 2.No

5: Which is Primary? 1.Metabolic Acidosis 2.Metabolic Alkalosis 3.Respiratory Acidosis 4.Respiratory Alkalosis 5.Mixed Acidosis 6.Mixed Alkalosis 7.No Acid/Base problem

6: Is there any compensation? 1.No it’s mixed 2.No 3.Resp Acidosis 4.Resp Alkalosis 5.Met Acidosis 6.Met Alkalosis

So what is it?? 1.Resp Acidosis with compensation 2.Met Alkalosis with compensation 3.Resp Alkalosis with compensation 4.Met Alkalosis with compensation 5.Mixed Acidosis 6.Mixed Alkalosis

Did you change your answer?? 1.Yes 2.No Be Honest!!

Case 6 Alkalaemia normal Acidaemia

Case 7 54 yr-old lady post MI. Acutely unwell, cold, clammy, hypotensive and oliguric pO 2 10 on 60% oxygen pH6.99 PaCO HCO 3 14

So what is it?? 1.Resp Acidosis with compensation 2.Met Alkalosis with compensation 3.Resp Alkalosis with compensation 4.Met Alkalosis with compensation 5.Mixed Acidosis 6.Mixed Alkalosis

1: Assess Oxygenation: Is the patient Hypoxaemic? 1.Yes 2.No

1: Is there a problem with Oxygenation? 1.Yes 2.No

2: Assess Acid-Base Status 1.Acidaemic 2.Neutral 3.Alkalaemic

3: Assess Metabolic Component… 1.Metabolic Acidosis 2.Metabolic Alkalosis 3.Neither

3b: Does this explain the pH? 1.Yes 2.No

4: Assess the Respiratory Component 1.Resp Acidosis 2.Resp Alkalosis 3.Neither

4b: Does this explain the pH? 1.Yes 2.No

5: Which is Primary? 1.Metabolic Acidosis 2.Metabolic Alkalosis 3.Respiratory Acidosis 4.Respiratory Alkalosis 5.Mixed Acidosis 6.Mixed Alkalosis 7.No Acid/Base problem

6: Is there any compensation? 1.No it’s mixed 2.No 3.Resp Acidosis 4.Resp Alkalosis 5.Met Acidosis 6.Met Alkalosis

So what is it?? 1.Resp Acidosis with compensation 2.Met Alkalosis with compensation 3.Resp Alkalosis with compensation 4.Met Alkalosis with compensation 5.Mixed Acidosis 6.Mixed Alkalosis

Did you change your answer?? 1.Yes 2.No Be Honest!!

Case 7 Alkalaemia normal Acidaemia

Case 8 50 yr-old man admitted with exacerbation of long-standing bronchial asthma. Respiratory rate of 30 pO on 60% oxygen pH7.39 PaCO HCO 3 26

So what is it?? 1.Resp Acidosis with compensation 2.Met Alkalosis with compensation 3.Resp Alkalosis with compensation 4.Met Alkalosis with compensation 5.Mixed Acidosis 6.Mixed Alkalosis 7.No Acid–Base issue

1: Assess Oxygenation: Is the patient Hypoxaemic? 1.Yes 2.No

1: Is there a problem with Oxygenation? 1.Yes 2.No

2: Assess Acid-Base Status 1.Acidaemic 2.Neutral 3.Alkalaemic

3: Assess Metabolic Component… 1.Metabolic Acidosis 2.Metabolic Alkalosis 3.Neither

3b: Does this explain the pH? 1.Yes 2.No

4: Assess the Respiratory Component 1.Resp Acidosis 2.Resp Alkalosis 3.Neither

4b: Does this explain the pH? 1.Yes 2.No

5: Which is Primary? 1.Metabolic Acidosis 2.Metabolic Alkalosis 3.Respiratory Acidosis 4.Respiratory Alkalosis 5.Mixed Acidosis 6.Mixed Alkalosis 7.No Acid/Base problem

6: Is there any compensation? 1.No it’s mixed 2.No 3.Resp Acidosis 4.Resp Alkalosis 5.Met Acidosis 6.Met Alkalosis

So what is it?? 1.Resp Acidosis with compensation 2.Met Alkalosis with compensation 3.Resp Alkalosis with compensation 4.Met Alkalosis with compensation 5.Mixed Acidosis 6.Mixed Alkalosis 7.No Acid–Base issue

Did you change your answer?? 1.Yes 2.No Be Honest!!

Case 8 Alkalaemia normal Acidaemia

Questions ?

Summary Develop an organised system for looking at blood gases Develop an organised system for looking at blood gases Be able to comment on the arterial pO2 in relation to the FiO 2 Be able to comment on the arterial pO2 in relation to the FiO 2 Detect metabolic acidosis and it’s significance in the acutely unwell Detect metabolic acidosis and it’s significance in the acutely unwell