ABGs make easy, Acid Base disorders, Pulmonology

1. AN APPROACH TO ACID
BASE DISSORDERS
DR RAHEEM UDDIN

2. A Little Pathophysiology….!

3.  Blood ph 7.35-7.45….controlled by H+
ion balance.
 CO2 + H2O  H2CO3  HCO3- +
H+ [ H+] ά (PCO2/ HCO3-)
 H+ conc is determined by PCO2:HCO3-
 The loss of HCO3 has the same effect
as the gain of H+

4. PCO2
(Resp Acidosis) H+
HCO3-
(Metab Acidosis)
PCO2
Resp Alkalosis) H+
HCO3-
(Metab Alkalosis)

5.  The gain of HCO3 is the same as the loss
of H+
 About 20000mmol of CO2 per day is
produced by metab. of carbohydrate and fat
 This large amount of CO2 is eliminated by
lungs
 CO2 is not an acid, but it forms H2CO3
 About 1mEq/kg (50-100 mEq) of nonvolatile
acid is produced/day by metabolism of protein
(fixed acid)
 This H+ ion is buffered by HCO3- in the ECF
 Then why don’t we get metab acidosis???

6.  Because we have kidneys that generate new
HCO3 by eleminating H+ from the body
 When one H+ leaves the body it leaves
behind one HCO3-
 Kidneys reabsorb all the filtered HCO3- in
the proximal tubule
 Renal Excretion of of the H+ control the
plasma HCO3- level.

7. “THE BIG FOUR”

8. Respiratory Acidosis
pH < 7.35 (Normal = 7.35-7.45)
CO2 > 45 (Normal = 35-45)
HCO3= Normal

9. Qutab Din is a 45-year-old male admitted to
the nursing unit with a severe asthma attack.
He has been experiencing increasing
shortness of breath since admission three
hours ago. His arterial blood gas result is as
follows:
PATIENT: Qutab Din
DATE: 6/4/06 18:43
pH 7.22
PaCO2 55
HCO3 - 25
Dx : Respiratory Acidosis

10. Causes:
Hypoventilation
a. Depression of the Respiratory Center
(sedatives, narcotics, drug overdose, CVA,
cardiac arrest, MI)
b. Respiratory muscle paralysis (spinal
cord injury, GBS, paralytics)
c. Chest wall disorders (flail chest,
pneumothorax)
d. Disorders of the lung parenchyma
(CHF, COPD, pneumonia, aspiration,
ARDS)
e. Alteration in the function of the
abdominal system (distention)

11. Respiratory Alkalosis
pH > 7.45
CO2 < 35
HCO3= Normal

12. Ms. Parveen., a 28 year old female, is admitted
with an acute onset of fever, chills, and RUQ
pain. Her vital signs are:
T = 99.6, P = 125, RR = 32, B/P = 140/84.
Her ABG results are:
pH 7.53
PaCO2 30 mm Hg
HCO3 22 mEq/L
Dx = Respiratory Alkalosis

13. Causes:
Alveolar Hyperventilation
a. Psychogenic (fear, pain, anxiety)
b. CNS stimulation (brain injury, ETOH,
early salicylate poisoning, brain tumor)
c. Hypermetabolic states (fever,
thyrotoxicosis)
d. Hypoxia (high altitude, pneumonia,
heart failure, pulmonary embolism)
e. Mechanical overventilation
(ventilator rate too fast)

14. Metabolic Alkalosis
pH > 7.45
HCO3 > 24

15. Dolat Ram is a 55-year-old male admitted to
your nursing unit with a recurring bowel
obstruction. He has been experiencing
intractable vomiting for the last several hours
despite the use of antiemetics. Here is his
arterial blood gas result:
Clinical Laboratory
PATIENT: Dolat ram
DATE: 3/4/06 08:30
pH 7.50
PaCO2 42
HCO3 - 33
DX= Metabolic Alkalosis

16. . Causes:
--Loss of H+ or increased HCO3
a. Large losses of gastric contents
(vomiting, NG suction)
b. Loss of K+ (diarreah, vomiting)
c. Ingestion of large amounts of
bicarbonate (antacids, resuscitation)
d. Prolonged use of diuretics (distal
tubule lose ability to reabsorb Na+ and
Cl- therefore Na+, Cl-, K+,

17. Metabolic Acidosis
pH < 7.35
HCO3 < 22 (normal = 22 – 26)

18. Rahamat is admitted to the hospital. He is a
kidney dialysis patient who has missed his last
two appointments at the dialysis center. His
arterial blood gas values are reported as
follows:
PATIENT: Rahamat
DATE: 7/11/05 04:20
pH 7.32
PaCO2 32
HCO3 - 18
Dx= Metabolic Acidosis

19. Causes:
--Increased H+, excess loss of HCO3
a. Overproduction of organic acids (starvation,
ketoacidosis, increased catabolism)
b. Impaired renal excretion of acid (Renal Failure)
c. Abnormal loss of HCO3 (diarrhea, biliary fistula,
Diamox)
d. Ingestion of acid (salicylate overdose, oral anti-
freeze)

20. The Land Of ABGs
Based on a concept by Laura Gasparis
Vonfrolio, RN,PHD

21.  Once upon a time there was a land known as
“ABG”. Everyone there was related with only
a limited number of names for the population.
 Now I would like to introduce you to your
patient. Let’s figure out what her name is:
 All of the people in the land of ABG have
a first name, a middle name, and a last
name. You just have to look at them and give
one name at a time.

22. The Last Name
1. First, look at her pH. (Normal = 7.35-7.45)
2. If her pH is < (less than) 7.35; her last name
is ACIDOSIS.
3. If her pH is > (greater than) 7.45; her last
name is ALKALOSIS.
(Note: To be an absolutely perfect last name--
her pH needs to be 7.40. So, keep in mind,
that if her pH is 7.35-7.39--she’s thinking
about marrying into the ACIDOSIS family. If
her pH is 7.41-7.45--she’s thinking about
marrying into the ALKALOSIS family.)

23. The First Name
Now that you know your patient’s last name,
you would like to also learn her first name.
1. Look at her pH again.
2. If it is 7.35-7.45 (normal) then her first name
is COMPENSATED.
3. If the pH is <7.35 or >7.45--then her first
name is UNCOMPENSATED.

24. The Middle Name
Now that you know your patient’s first
and last name, you would like to know
her middle name.
(Name Alert: These people are all
related and you have many patients
with the same first and last name. A
middle name will give you more
information to go on.)

25. 1.First you need to look at the CO2 and
HCO3.
(Remember: Normal CO2 = 35-45. Normal
HCO3 = 22-26)
2. The middle name will either be
Respiratory or Metabolic.
3. If the CO2 is <35 or >45--her middle
name is RESPIRATORY.
4. If the HCO3 is <22 or >26--her middle
name is METABOLIC.

26. The Family Feud
1. pH and HCO3 are "kissin cousins"--
they like to go in the same direction.
2. But CO2 is the "black sheep"--pH runs
the opposite direction when it sees him
coming.

27. Therefore:
 Decreased pH with Decreased HCO3 =
ACIDOSIS.
 Increased pH with Increased HCO3 =
ALKALOSIS.
 Decreased pH with Increased CO2 =
ACIDOSIS.
 Increased pH with Decreased CO2 =
ALKALOSIS.

28. Consultant gives you an ABG with the following
numbers:
pH = 7.60 CO2 = 30 HCO3 = 22
 1. What is her last name?
(Her pH is >7.45 so her last name is ALKALOSIS.)
 2. What is her first name?
(Her pH is not in the normal range of 7.35-7.45 so her
first name is UNCOMPENSATED.)
 3. What is her middle name?
(Her CO2 is <35 and her HCO3 is normal so her
middle name is RESPIRATORY.)
 4. You have now been introduced to
UNCOMPENSATED RESPIRATORY ALKALOSIS.

29. pH = 7.31 CO2 = 50 HCO3 = 25
 1. What is her last name?
(Her pH is <7.35 so her last name is ACIDOSIS.)
 2. What is her first name?
(Her pH is not in the normal range so her first name is
UNCOMPENSATED.)
 3. What is her middle name?
(Her CO2 is >45 and her HCO3 is normal so her middle
name is RESPIRATORY.)
 5. You have now been introduced to
UNCOMPENSATED RESPIRATORY ACIDOSIS.

30. pH = 7.55 CO2 = 40 HCO3 = 30
 1. What is her last name?
ALKALOSIS
 2. What is her first name?
UNCOMPENSATED
 3. What is her middle name?
METABOLIC.
 4. You have now been introduced to
UNCOMPENSATED METABOLIC
ALKALOSIS.

31. pH = 7.35 CO2 = 35 HCO3 = 19
 1. What is her last name?
(Her pH is normal--but it is <7.40. So her last name
might be ACIDOSIS. She hasn’t decided if she wants
to get married yet.)
 2. What is her first name?
(Her pH is normal so her first name is
COMPENSATED.)
 3. What is her middle name?
(Her CO2 is normal but her HCO3 is <22. So her
middle name is METABOLIC. Note: Because she
has a middle name--she has decided to get married.
Talk about a good reason to marry!)
 4. You have been introduced to COMPENSATED
METABOLIC ACIDOSIS

32. 3 STEP APPROACH

33. STEP-1
 IDENTIFY ONE DISORDER

34.  Look at the pH, PCO2 and HCO3-
 Identify the most apparent acid base
disorder
Disorder pH PCO2 HCO3-
Met Acidosis Secondary Primary
Met Alkalosis Secondary Primary
Res Acidosis Primary Secondary
Res Alkalosis Primary Secondary

35.  If the pH is normal, but either the HCO3
or PCO2 (or both) is abnormal then pick
the most abnormal one. E.g.;
pH 7.40, PCO2 = 60, HCO3= 36
 Because the pH is normal in this case,
you can start by diagnosing either a
metabolic alkalosis or resp acidosis.

36. STEP-2
 APPLY THE FORMULA TO SEE IF
THE COMPENSATION IS CORRECT?

37. Step-2. FORMULAE
 Metabolic acidosis:
PCO2 = 1.5 X [ HCO3] + 8
 Metabolic alkalosis:
40 + 0.7 X HCO3

38. Step-2. FORMULAE
 Respiratory Acidosis:
1. Acute: [HCO3] increases by 1 mEq/L for
every 10 mmHg increase in PCO2.
2. Chronic: [HCO3] increases by 3.5 mEq/L for
every 10 mmHg increase in PCO2.
 Respiratory Alkalosis
1. Acute: [HCO3] dereases by 2mEq/L for
every 10 mmHg decrease in PCO2.
2. Chronic: [HCO3] dereases by 5mEq/L for
every 10 mmHg decrease in PCO2.

39. Example -1
 A pt with:
pH= 7.12, PCO2 = 38, HCO3 =12.
Step-1:Identify the single disorder?
Metabolic Acidosis
Step-2: See the compensation.
PCO2 = 1.5 X [ HCO3] + 8 = 26
Respiratory Acidosis
The risisng PCO2 is a dangerous sign in metabolic
acidosis.

40. Example - 2
A pt with:
pH= 7.52, PCO2 = 51, HCO3 = 40.
Step-1:Identify the single disorder?
Metabolic Alkalosis
Step-2: See the compensation.
40 + 0.7 X HCO3 = 51.2
Respiratory compensation

41. Example - 3
A patient’s PCO2 increases from 40 to 60
mmhg during a ch resp acidosis. For a
chronic resp acidosis serum [HCO3]
increases by 3.5 mEq/L for every 10
mmHg increase in PCO2. So what
would be the compensatory change in
the HCO3?
2 X 3.5 = 7

42. Example 4
A patient with PCO2 = 40 and HCO3=24,
an acute resp alkalosis develops. PCO2
falls to 20 mmHg. What would be the
HCO3 after compensation??
2 x 2 = 4
And the HCO3 should be 24-4= 20 mEq/L
after compensation.

43. STEP- 3
CALCULATE THE ANION GAP
AG = [Na] – [Cl + HCO3]

44. Step-3
 If AG > 30 then there is a high AG
acidosis regardless of the HCO3 and
the pH.
 If AG > 20 … probably a high AG
acidosis regardless of the HCO3 and
the pH.
 AG = 16 to 20, is abnormal. But may be
due to other things as well.
 If AG is normal, then you are finished
with the Step-3.

45. THE MAGIC STEP

46.  For Lactic acidosis and Keto acidosis only.
 To detect additional hidden metabolic
 In High AG acidosis,
The increase in AG = Decrease in HCO3.
 But a 1:1 relation b/w AG and HCO3 is often
not the case.
 For Lactic acidosis, the ratio of increase in
AG to decrease in HCO3 is not usually 1.0,
but closer to 1.5

47. HCO3 = AG / 1.5
 Is a lactic acidosis increases the AG by
15mEq then the HCO3 would fall by about
15/1.5 = 10.
 For keto acidosis, the ratio of increase in AG
to decrease in HCO3 is closer to 1.0.
HCO3 = AG

48.  Measured HCO3 much higher than
predicted by the increase in AG is a
clue that a HIDDEN metabolic alkalosis
may also be present.
 Measured HCO3 much lower than
predicted by the increase in AG is a
clue that a HIDDEN normal AG
metabolic acidosis may also be present.

49. Example - 1
 A pt begins with a serum HCO3 of 24
and AG =12, develops Lactic acidosis.
The AG increases from 12 to 22. Aprox
what would you expect the HCO3 to
be?
HCO3 = AG / 1.5
10/1.5 = 6.7
24-6.7= 17.3

50. Example - 2
 A pt begins with a serum HCO3 of 24
and AG =12, develops Keto acidosis.
The AG increases from 12 to 22. Aprox
what would you expect the HCO3 to
be?
HCO3 = AG
so HCO3 = 24 - 10 = 14

51. Example - 3
 A pt begins with HCO3 of 24, AG =12,
pH 7.40 and PCO2 40. A lactic acidosis
develops. The AG rises from 12 to 32.
The HCO3 does not fall. The pH remains
7.40 and PCO2 40.
What has happened?
3 step approach
Magic step

52. pH 7.40, HCO3 24, PCO2 40 AG= 12 to 32
 Step-1
 Step-2:
 Step-3:
 Magic Step:
No acid base disorder so far
No Resp disorder
High AG Metab Acidosis
HCO3 = AG / 1.5  20/1.5= 13
Exp HCO3 = 24-13 = 10
Dx Metabolic acidosis masked by severe
Metabolic alkalosis

53. Example-4
 A pt begins with HCO3 of 24, AG =12,
pH 7.40 and PCO2 40. A Keto acidosis
develops. The AG rises from 12 to 22.
The HCO3 falls to 4, pH 7.08 and PCO2
14.
What is going on?

54. pH 7.08, HCO3 4, PCO2 14, AG= 12 to 22
 Step-1
 Step-2:
 Step-3:
 Magic Step:
Severe metabolic acidosis
(1.5 x 4)+ 8 = 14. No Resp disorder
High AG Metab Acidosis
HCO3 = AG / 1.0  10/1.0 = 10
Exp HCO3 = 24-10 = 14
Dx A high AG and a normal AG Metabolic
acidosis

55. CHOCOLATE TIME

56. Case-1.
 pH= 7.1
 HCO3= 6
 PCO2= 18
 AG=15
Metabolic acidosis
(1.5 x 6) + 8= 17.
Normal AG Metabolic acidosis

57. Case-2.
 pH= 7.49
 HCO3= 35
 PCO2= 48
 AG=16
Metabolic Alkalosis
40+0.7 x 35-24= 47
Normal AG
Simple Metabolic Alkalosis

58. Case-3.
 pH= 7.68
 HCO3= 40
 PCO2= 35
 AG=14
Metabolic Alkalosis
40+0.7 x 40-24= 51
Normal AG
Metabolic Alkalosis+ Resp Alkalosis

59. Case-4.
 A previously well presents with a 30 min of
resp distress and
 pH= 7.26
 HCO3= 26
 PCO2= 60
 AG=14
Acute Resp Acidosis
2 x 1 = 2  24+ 2 = 26
Normal AG

60. Case-5.
 SOB- 2 wks,
 pH= 7.38
 HCO3= 40
 PCO2= 70
 AG=16
Ch. Resp Acidosis
3.5 X 3= 10.5 24+ 10.5= 35.
Normal AG
Ch Resp Acidosis + Metabolic Alkalosis

61. Case-5.
 pH= 7.68
 HCO3= 40
 PCO2= 35
 AG= 18
Metabolic Alkalosis
40+0.7 x 40-24= 51
Normal AG
Metabolic Alkalosis + Resp Alkalosis

62. Case-6.
SOB- 3 days
 pH= 7.45
 HCO3= 44
 PCO2= 65
 AG= 14
Metabolic Alkalosis
40+0.7 x 44-24= 54
Normal AG
Metabolic Alkalosis + Resp Acidosis

63. Case-7.
Pt with fever=102F, BP=80/50, diaphoretic, Urine=
numerous WBC+ Bacteria, ketone -ve
 pH= 7.65
 HCO3= 32
 PCO2= 30
 AG= 30 (delta AG= 18)
Metabolic Alkalosis
40+0.7 x 40-30= 45
High AG Metabolic Acidosis
High AG Metabolic Acidosis+ Metabolic Alkalosis +
Resp Alkalosis
Exp HCO3=18/1.5=12. But HCO3 is up by 8

64. Case-8.
Pt. With DKA.
 pH= 6.95
 HCO3= 6
 PCO2= 28
 AG= 32
Severe Metabolic Acidosis
(1.5X6)+8= 17
High AG Metabolic Acidosis
High AG Metabolic Acidosis+ Resp Acidosis
Delta HCO3=delta AG = 20. Fall inHCO3 =18

65. CASE OF THE DAY

66. 21 yrs old Diabetic with vomiting. Ketones+++
 pH= 7.75
 HCO3= 32
 PCO2= 24
 AG= 30
Metabolic Alkalosis
40+0.7 x 32-24= 45
High AG Metabolic Acidosis
High AG Metabolic Acidosis+SevereMetabolic
Alkalosis+ Severe Resp Alkalosis
Delta HCO3=delta AG = 18. Rise in HCO3 = 8

67. SHUKRYA