This document discusses blood gases and acid-base disorders. It provides information on indications for blood gas analysis, proper sampling techniques, normal values, precautions, and in vitro changes over time. It explains the steps to analyze acid-base disorders, including determining if there is a primary respiratory or metabolic disturbance, appropriate compensation, and whether there are mixed disorders. Examples are provided to demonstrate how to interpret blood gas results and diagnose the acid-base disorder.

1. BLOOD GASES AND
ACID–BASE DISORDERS
DR. SATYABRATA ROY CHOWDHOURY
PEDIATRIC INTENSIVE CARE UNIT
MEDICAL COLLEGE KOLKATA

2. INDICATION
 Severe respiratory or metabolic disorders
 Clinical features of hypoxia or hypercarbia
 Shock
 Sepsis
 Decreased cardiac output
 Renal failure
 monitoring of babies on ventilator care

3. Proper sample
• Arterial stab sample
• Indwelling arterial catheter
• Arterialized capillary sample
• Venous sample

5. Radial Artery
Ulnar Artery

6. Arterialized capillary sample
• Warm the heal with
steam towel ( 42-43 C
for 5 min)
• Do not squeeze
• Fill the drop from
tissue.
• Rotate the sample to
mix heparine well

7. Normal Value of ABG
PH 7.35- 7.45
HCO3 20-28 mEq/L
PCo2 35-45 mm Hg
Po2 60- 80 mm Hg
BE ±2

8. PRECAUTION
• Heparin - Strength and Volume
• The syringe – Avoid air bubble, Tighten the
cap
• Delay in measurement
• Transport

9. In vitro change in every 10 min
37°C 4°C
PH .01 .001
PCO2 .1 mm Hg .01 mm Hg
PO2 .1 Vol% .01 vol%

10. Base deficit and base excess
• A pH change of 0.15 is equivalent to a base
change of 10 mEq/L.
• A decrease in base (i.e, [HCO3-]) is termed a
base deficit, and an increase in base is termed
a base excess.

11. pCO2 and pH
• A change in pCO2 up or down 10 mm Hg is
associated with an increase or decrease in pH
of 0.08 units.
• As the pCO2 decreases, the pH increases; as
the pCO2 increases, the pH decreases.

12. Normal compensatory response
• Any primary disturbance in acid-base homeostasis
invokes a normal compensatory response.
• A primary metabolic disorder leads to respiratory
compensation, and a primary respiratory disorder
leads to an acute metabolic response due to the
buffering capacity of body fluids.
• Kidney is slow organ, so metabolic compensation
may be acute or chronic compensation (1-2 days).

13. Mixed acid-base disorder
• Acid-base disorders result from a single primary disturbance with
the normal physiologic compensatory response : simple acid-base
disorders.
• In seriously ill patients, two or more different primary disorders
may occur simultaneously: mixed acid-base disorder.
• The net effect of mixed disorders may be additive (eg, metabolic
acidosis and respiratory acidosis) and result in extreme alteration
of pH;
• Or they may be opposite (eg, metabolic acidosis and respiratory
alkalosis) and nullify each other’s effects on the pH.

14. Steps for ABG analysis
1. What is the pH? Acidemia or Alkalemia?
2. Determine a cause of the acidemia or alkalemia.
3. Determine level of compensation and whether a mixed
disorder is present.

15. Step 1:
 Look at the pH: is the blood acidemic or alkalemic?
 EXAMPLE :
 5yr M with DKA presenting with Diarrhoea, Shock and acute
respiratory distress
 ABG :ABG 7.16/17/235 on 50% O2
 Na 123/ Cl 97/ HCO3 7/BUN 75, Blood glucose
550mg/dl, Urinary ketone positive
 ACIDMEIA OR ALKALEMIA ????

16. Step 2: What is the primary disorder?
What disorder is
present?
pH pCO2 or HCO3
Respiratory Acidosis pH low Hco3 high
Metabolic Acidosis pH low HCO3 low
Respiratory Alkalosis pH high HCO3 low
Metabolic Alkalosis pH high HCO3 high

18. EXAMPLE
 ABG 7.16/17/235 on 50% O2
 Na 123/ Cl 97/ HCO3: 7/BUN 76
• PH is low , HCO3 is Low
• PH and HCO3 are going in same directions then its most likely
primary metabolic will check to see if there is a mixed disoder.

19. Step 3: Is there appropriate
compensation?
Respiratory Acidosis
 Acute: for every 10 increase in pCO2 -> HCO3 increases by 1
 Chronic: for every 10 increase in pCO2 -> HCO3 increases by 3.5
Respiratory Alkalosis
Acute: for every 10 decrease in pCO2 -> HCO3 decrease by 2 and
Chronic: for every 10 decrease in pCO2 -> HCO3 decrease by 4

20. Step 3: Is there appropriate
compensation?
Metabolic Acidosis
Winter’s formula: pCO2 = 1.5[HCO3] + 8 ± 2
If serum pCO2 > expected pCO2 -> additional
respiratory acidosis
Metabolic Alkalosis
For every 10 increase in HCO3 -> pCO2 increases by
7

21. EXAMPLE
 ABG 7.16/17/235 on 50% O2
 Na 123/ Cl 97/ HCO3 7/BUN 76.
• Winter’s formula : 17= 1.5 (7) +8 = 18.5
• So correct compensation so there is only one
disorder Primary metabolic

22. METABOLIC ACIDOSIS
 AG = Na+K – Cl – HCO3 (normal 12 ± 2)
 AG corrected = AG + 2.5[4 – albumin]

25. Delta ratio
 If there is a high anion Gap metabolic acidosis then
calculate the Delta/delta gap to determine additional
hidden metabolic nongap metabolic acidosis or
metabolic alkalosis.
 If there is no anion gap then start analyzing for non-
anion acidosis
(AG – 12)
___________
(24 - [HCO3¯])

26. • < 0.4 due to a pure NAGMA
• 0.4 - 0.8 due to a mixed NAGMA + HAGMA
• 0.8 - 2.0 due to a pure HAGMA
• >2.0 due to a mixed HAGMA + metabolic
alkalosis (or pre-existing compensated
respiratory acidosis)

27. Case 1
A child with D.K.A. has following status:
pH - 7.14
PaO2 - 112.0 mm Hg
PaCO2 - 10.3 mm Hg
HCO3
-- 2.8 mmol/L

28. Blood glucose - 442 mg%
Na - 129 meq/L
K - 5.9 meq/L
Cl - 94 meq/L
Urine sugar - 3+

29. • What is the primary disorder ?
• Is the compensation appropriate?

30. INTERPRETATION
Acid base disturbance?
Severe Metabolic Acidosis
compensated ?
Severe Metabolic Acidosis with respiratory
compensation
pCO2 = 1.5[2.8] + 8 ± 2=12.2 ±2=10.2-14.2

31. • What is the anion gap?
• Delta gap?
Anion gap:
129-94-2.8=32.2
(32.2 – 12)
___________ = 0.95 = pure HAGMA
(24 – 2.8)

32. Case 2
A 10yr old child with nephrotic syndrome on
steroids and lasix has general weakness.
pH - 7.49
PaO2 - 92 mm Hg
PaCO2 - 45 mm Hg
HCO3
-- 32.4 mmol/L
Na+ - 130
K+ - 2.8
Cl- - 96

33. INTERPRETATION
Acid Base Electrolyte disturbance?
Metabolic Alkalosis (fully compensated)
Hypokalemia
Contributing Factors?
Steroids, diuretics

34. • For every 10 increase in HCO3 -> pCO2 increases by 7
• Bicab increase: 32.4-24=8.4
• P Co2 increase=5.8
• So PCo2= 40+5.8=45.8

35. Case 3
A 3-years old comatose child with h/o accidental
ingestion of several tablets of phenobarbitone has
following ABG at admission (room air)
pH - 7.10
PaO2 - 65 mm Hg
PaCO2 - 80 mm Hg
HCO3
-- 23.7 mmol/L

36. INTERPRETATION
Acid- base disturbance?
Acute Respiratory Acidosis
Compensated or uncompensated?
No compensation

37. Child is intubated and ventilation started with 30% O2.
Repeat ABG after 6 hrs .
pH - 7.28
PaO2 - 155 mmHg
PaCO2 - 56 mmHg
HCO3
- - 26 mmol/L

38. INTERPRETATION
Acid- base disturbance?
Acute Respiratory Acidosis
Compensated or uncompensated?
yes compensation
Compensation adequate?

39. Respiratory Acidosis
 Acute: for every 10 increase in pCO2 -> HCO3 increases by 1
 Chronic: for every 10 increase in pCO2 -> HCO3 increases by
3.5
• It is acute
• Increase in CO2=56-40=16
• Increase in HCO3=24+1.6=25.6

40. Thank You !