cases with ABG for interpretation as quizz

1. Arterial Blood Gas Analysis
Anwar Yusr
Critical Care Consultant
Egyptian Fellowship in ICU 2015
USTH
28/4/2024

2. Six step method
1) Identify any abnormality (is there acidemia or
alkalemia?)
2) Is the primary process metabolic or respiratory?
3) If the primary process is respiratory, is it acute or
chronic?
4) Is the compensation adequate?
5) Is there an AG?
6) Is there a mixed disorder?

3. Case: A Man with CCF and Vomiting
 A 70 year old man was admitted with severe congestive
cardiac failure. He has been unwell for about a week and
has been vomiting for the previous 5 days. He was on no
medication. He was hyperventilating and was very
distressed. Admission biochemistry is listed below. He
was on high concentration oxygen by mask.
 Biochemistry results: Na+ 127, K+ 5.2, Cl- 79, HCO3- 20, urea 50.5,
creatinine 0.38 & glucose 171mg/dl.
Arterial Blood Gases
pH 7.58
pCO2 21 mmHg
pO2 154 mmHg
HCO3 19 mmol/l

4. Initial Assessment
The history suggests the following possibilities:
 Respiratory alkalosis in response to the
dyspnea associate with the congestive heart
failure.
 A lactic acidosis is possible if cardiac output is
low and tissue perfusion is poor.
 Vomiting suggests metabolic alkalosis.

5. Six Steps for Acid-Base Analysis
Step 1.
Is there an acidemia or alkalemia?
PH 7.58
Alkalaemia

6. Six Steps for Acid-Base Analysis
Step 2.
Is the primary process metabolic or
respiratory?
PCO2 = 21 should drive pH ↑
HCO3
- = 19 should drive pH ↓
The primary disorder is a
respiratory alkalosis.

7. Six Steps for Acid-Base Analysis
Step 3:
If the primary process is respiratory, is
it acute or chronic?
From history its chronic.

8. Six Steps for Acid-Base Analysis
Step 4:
Is there an anion gap?
AG= Na+ - (Cl- + HCO3
- )> 12?
127 – (79 + 19) = 29!!
Anion Gap Metabolic Acidosis

9. Six Steps for Acid-Base Analysis
Step 5:
Is the metabolic compensation adequate?
Expected Hco3 range:
chronic respiratory alkalosis
(using rule - "the 5 for 10" rule)
The expected HCO3 is (24 - 10) = 14.
The actual HCO3 is higher (19) which indicates
the presence of a metabolic alkalosis.

10. Final Assessment
This patient has a triple acid-base disorder:
1. Acute metabolic acidosis probably due to
renal failure (?prerenal failure) and possibly to
lactic acidosis (hypoperfusion due heart failure
and hypovolaemia).
2. Metabolic alkalosis due to severe vomiting.
3. Respiratory alkalosis due to dyspnoea from
congestive heart failure.

11. Triple acid-base disorder:
1. Respiratory alkalosis,
2. High anion gap metabolic acidosis
3. Metabolic alkalosis.
Lactate
VOMITING
Dyspnea
CHF

12. CASE 2
 A 57-year-old man with a history of type 1 diabetes
mellitus is evaluated in the emergency department for
severe abdominal pain, nausea, and vomiting. he is
admitted to the ICU, pulse 120/min, BP 80/60.
 ABG was done and revealed:
 PH 7.12
 PaCO2 40 mmHg
 PaO2 60 mmHg on room air
 HCO3 15 mmHg
 Na 145
 K 3.1
 Cl 95
 RBS 220 mmHg
 What is the acid base status of this patient?
 What is most probable cause?

13. Six Steps for Acid-Base Analysis
Step 1.
Is there an acidemia or alkalemia?
Acidemia

14. Six Steps for Acid-Base Analysis
Step 2.
Is the primary process metabolic or
respiratory?
PCO2 = 40
HCO3
- = 15 should drive pH ↓

15. Six Steps for Acid-Base Analysis
Step 3:
If the primary process is respiratory, is
it acute or chronic?
Skip this step as primary process is
metabolic!

16. Six Steps for Acid-Base Analysis
Step 4:
Is there an anion gap?
AG= Na+ - (Cl- + HCO3
- )> 12?
145 - 95 - 15 = 35!!
Anion Gap Metabolic Acidosis

17. Six Steps for Acid-Base Analysis
Step 5:
Is the respiratory compensation adequate?
Expected pCO2 range = Winter formula:
[1.5 x Hco3 + 8 +/- 2
[1.5 (15) +8] +/- 2 = [30.5 – 32.5]
PCO2 = 40, therefore there is concomitant
respiratory Acidosis.

18. Six Steps for Acid-Base Analysis
Step 6:
Are there any other metabolic disturbances?
decrease in plasma bicarbonate = increase in AG
Anion Gap = 35 – 12 = 23
HCO3 = 24 – 15 = 9
SO
Change in AG >> Change in Bicarb
Since this over corrects bicarbonate there is
a metabolic ALKALOSIS!!
> 2

19. Final Assessment
In this case, the anion gap is 35 so an anion gap
metabolic acidosis must be present. DKA
The body attempts to compensate by
hyperventilating in order to remove carbon
dioxide. but the Paco2 does not decrease at all
from 40 mm Hg. Respiratory Acidosis.
In this case, the patient was admitted for nausea
and vomiting, which could lead to a mixed
picture, including a metabolic alkalosis.

20. 1. Anion Gap Metabolic Acidosis.
2. Concurrent Respiratory Acidosis.
3. Metabolic Alkalosis.
DKA
VOMITING
Resp failure

21. Metabolic Acidosis— Bad??
Impaired cardiac contractility.
Decreased threshold for VF.
Decreased Hepatic and Renal perfusion.
Increased Pulmonary Vasc resistance.
Inability to respond to catecholamines.
Vascular collapse.

22. “Understanding ABG is not
Magic but an art learned by
continued practice”