Acid-Base Gas Interpretation Understanding the Basic Philippine Nurses Association - Cebu Chapter Dr. Emiliano Ian Suson II

1. Acid-base disorders and its
implications: Therapy in a Nursing
Perspective
(July 23, 2014)
EMILIANO IAN B. SUSON II, ED.D, USRN, MAN, RN
“SIR EYE”

2. Objectives
 Describe physiology involved in acid base balance of
the body
 Review causes and treatments of acid base disorders
 Identify normal arterial blood gas values
 Interpret results of ABG samples
 Interpret oxygenation state of a patient using reported
ABG values
2

3. Interpretation of ABG
» Very important for health care providers
» Usefulness of this tool depends on being able to
interpret correctly the results
» Critically ill patients
3

4. Acid base disorders
 12000 to 15000 mEq of volatile acids are
produced daily by body and excreted as CO2
by lungs
 1 mEq / kg / day of non-volatile acids
(sulfuric and phosphoric acids) are produced
daily by body and excreted by the kidneys
 The most important buffers in the body are,
hemoglobin, plasma proteins and
bicarbonate
4

5. Acid base disorders
SIMPLE ACID BASE DISORDER:
when there is only one primary
disorder
MIXED ACID BASE DISORDER: when
there are two or more primary
disorders present at the same time
5

6. Normal values
pH 7.35-7.45 7.40
PaCO2 35-45 mmHg 40
PaO2 70-100 mmHg
HCO3- 24±2 24
Met-Hb <2%
CO-Hb <3%
BE -2 to 2 mEq/L
CaO2 16-22 ml/dL
A gap 10±2 12
6

7. 7

8. 8

9. 9

10. 10

11. Buffers
1. Protein Buffer Systems
 Amino Acid buffers
 Hemoglobin buffers
 Plasma Protein buffers
2. Phosphate Buffer Systems
3. Carbonic Acid – Bicarbonate
Buffer System
11

12. 12Bicarbonate buffer
 Sodium Bicarbonate (NaHCO3) and carbonic acid
(H2CO3)
 Maintain a 20:1 ratio : HCO3
- : H2CO3
HCl + NaHCO3 ↔ H2CO3 + NaCl
NaOH + H2CO3 ↔ NaHCO3 + H2O

13. 13Phosphate buffer
 Major intracellular buffer
H+ + HPO4
2- ↔ H2PO4-
OH- + H2PO4
- ↔ H2O + H2PO4
2-

14. 14Protein Buffers
 Includes hemoglobin, work in blood and ISF
Carboxyl group gives up H+
Amino Group accepts H+
 Side chains that can buffer H+ are present on 27 amino acids.
 The 10 essential amino acids are:(PVTMATHILL)
Phenylalanine, Valine, Tryptophan, Methionine, Arginine,
Threonine, Histidine, Isoleucine, Leucine, Lysine
 10 Amino acids the body produces:
alanine, asparagine, aspartic acid, cysteine, glutamic acid,
glutamine, glycine, proline, serine and tyrosine

15. 152. Respiratory mechanisms
 Exhalation of carbon dioxide
 Powerful, but only works with volatile acids
 Doesn’t affect fixed acids like lactic acid
 CO2 + H20 ↔ H2CO3 ↔ H+ + HCO3
-
 Body pH can be adjusted by changing rate and depth
of breathing

16. 163. Kidney excretion
 Can eliminate large amounts of acid
 Can also excrete base
 Can conserve and produce bicarb ions
 Most effective regulator of pH
 If kidneys fail, pH balance fails

17. 17Rates of correction
Buffers function almost instantaneously
Respiratory mechanisms take several
minutes to hours
Renal mechanisms may take several
hours to days

18. 18

19. 19

20. 20

21. 21Acidosis
 Principal effect of acidosis is depression of the CNS through ↓ in synaptic
transmission.
 Generalized weakness
 Deranged CNS function the greatest threat
 Severe acidosis causes
Disorientation, Coma, Death

22. 22
Alkalosis
 Alkalosis causes over excitability of the central
and peripheral nervous systems.
 Numbness
 Lightheadedness
 It can cause :
 Nervousness
 muscle spasms or tetany
 Convulsions
 Loss of consciousness
 Death

23. 23Respiratory Acidosis
Acute conditons:
Adult Respiratory Distress
Syndrome
Pulmonary edema
Pneumothorax

24. 24Compensation for Respiratory
Acidosis
Kidneys eliminate hydrogen
ion and retain bicarbonate ion

25. 25Signs and Symptoms of
Respiratory Acidosis
 Breathlessness
 Restlessness
 Lethargy and disorientation
 Tremors, convulsions, coma
 Respiratory rate rapid, then gradually depressed
 Skin warm and flushed due to vasodilation caused by
excess CO2

26. 26Treatment of Respiratory
Acidosis
Restore ventilation
IV lactate solution
 Treat underlying dysfunction or disease

27. 27Respiratory Alkalosis
 Conditions that stimulate respiratory center:
 Oxygen deficiency at high altitudes
Pulmonary disease and Congestive heart failure
– caused by hypoxia
 Acute anxiety
Fever, anemia
 Early salicylate intoxication
Cirrhosis
 Gram-negative sepsis

28. 28Compensation of Respiratory
Alkalosis
 Kidneys conserve hydrogen ion
 Excrete bicarbonate ion

29. 29Treatment of Respiratory
Alkalosis
 Treat underlying cause
Breathe into a paper bag
IV Chloride containing solution – Cl- ions
replace lost bicarbonate ions

30. 30Metabolic Acidosis
 Bicarbonate deficit - blood concentrations of bicarb drop below 22mEq/L
 Causes:
 Loss of bicarbonate through diarrhea or renal dysfunction
 Accumulation of acids (lactic acid or ketones)
 Failure of kidneys to excrete H+

31. 31Symptoms of Metabolic
Acidosis
Headache, lethargy
Nausea, vomiting, diarrhea
Coma
Death

32. 32Compensation for Metabolic
Acidosis
 Increased ventilation
 Renal excretion of hydrogen ions if
possible
 K+ exchanges with excess H+ in ECF
 ( H+ into cells, K+ out of cells)

33. 33Treatment of Metabolic
Acidosis
IV lactate solution

34. 34Metabolic Alkalosis
 Bicarbonate excess - concentration in blood is greater than
26 mEq/L
 Causes:
Excess vomiting = loss of stomach acid
 Excessive use of alkaline drugs
 Certain diuretics
 Endocrine disorders
 Heavy ingestion of antacids
Severe dehydration

35. 35Symptoms of Metabolic
Alkalosis
 Respiration slow and shallow
Hyperactive reflexes ; tetany
 Often related to depletion of electrolytes
Atrial tachycardia
Dysrhythmias

36. 36Treatment of Metabolic
Alkalosis
Electrolytes to replace those lost
IV chloride containing solution
 Treat underlying disorder

37. 37Example
 A patient is in intensive care because he suffered a
severe myocardial infarction 3 days ago. The lab
reports the following values from an arterial blood
sample:
 pH 7.3
 HCO3- = 20 mEq / L ( 22 - 26)
 pCO2 = 32 mm Hg (35 - 45)

38. 38Diagnosis
 Metabolic acidosis
 With compensation

39. Acid base disorders
 METABOLIC ACIDOSIS: HCO3 <24 OR Anion Gap
>12
 METABOLIC ALKALOSIS: HCO3 >24
 RESPIRATORY ALKALOSIS: PCO2 <40 or PCO2 less
than expected for primary metabolic abnormality
 RESPIRATORY ACIDOSIS: PCO2 >40 or PCO2 higher
than expected for primary metabolic abnormality
 HIGH ANION GAP (>12-20) always indicates primary
metabolic acidosis
39

40. Acid base disorders and
compensatory response
pH HCO3- PaCO2
Metabolic
acidosis
Metabolic
alkalosis
Respiratory
acidosis
Respiratory
alkalosis
Compensatory response never brings the pH back to normal
if the pH is in acidic direction, it tells you that the process or processes in acidic direction are the primary
disorders
40

41. Anion Gap
Na-(Cl+HCO3)= 12±2
 Estimates unmeasured anions
 Normal is 12
 Hypoalbuminemia:
 Correct anion gap: 2.5 per gram of albumin below 4
 Calculate osmolal gap if anion gap is elevated
 OSM gap = measured OSM-2(Na)-glu/18-BUN/2.8 =
<10
41

42. Urinary anion gap
 Useful in differential diagnosis of non gap
acidosis
 U anion gap= Na + K – Cl
 A negative U. Anion Gap ie Cl >> Na + K
suggests appropriate urinary NH4
excretion and G.I. loss of HCO3
 A positive U. Anion Gap ie. Cl << Na + K
suggests RTA with distal acidification
defect and inadequate NH4 excretion in
urine
42

43. Acidosis (Low pH)
 Lowering extracellular pH by rising concentration of
hydrogen ions
 Fall in bicarbonate concentration
 Elevation in PCO2
 Decreases force of cardiac contractions
 Decreases vascular response to catecholamines
 Decreases response of certain medications
43

44. Alkalosis (High pH)
 Elevation of the pH of the extra cellular fluid
 Lowering hydrogen ion concentration
 Elevation in plasma bicarbonate
 Reduction in PCO2
 Impairs oxygenation
 Impairs muscular function
 Impairs neurological function
44

45. Metabolic acidosis
Anion Gap
 Methanol
 Uremia
 DKA
 Paraldehyde
 INH
 Lactic acidosis
 Ethylene glycol
 Salicylate
Non Gap
 Hyperalimentation
 Acetazolamide
 Renal tubular acidosis
 Diarrhea
 Ureterosigmoidostomy
 Pancreatic fistula
45

46. Metabolic alkalosis
 Gain of bicarbonate by abnormal renal absorption
 Volume contraction (low urine chloride)
 Vomiting: loss of H+
 Diuretics: depletion ECF
 Severe hypokalemia
 Renal failure
 Mineralocorticoid excess (high urine chloride)
46

47. At a Glance Acid- Base Disorders
Acid-base
disorder
Causes Signs and
Symptoms
Respiratory
acidosis
Hypoventilation,
Neuromuscular
disorders, Airway
obstruction, CNS
depression
↑PR, ↑RR, ↑BP,
Mental
cloudiness,
Feeling of
fullness in the
Head, ↑ICP
Ventricular
Fibrillation, Papilledema,
Dilated
Conjunctival
Blood vessel,
Hyperkalemia,
Tachypnea,
Cyanosis

48. Acid-base
disorder
Causes Signs and
Symptoms
Respiratory
alkalosis
Hyperventilation,
Sepsis,
Pregnancy,
Mechanical
Ventilation, fever
Lightheadedness
Inability to
Concentrate,
Numbness and
Tingling, Tinnitus
Loss of
consciousness
At a Glance Acid- Base Disorders

49. Acid-base
disorder
Causes Signs and
Symptoms
Metabolic
acidosis
Diabetic
Ketoacidosis,
Renal failure
Methanol/aspirin
Overdose,
Renal tubular
Acidosis,
Diarrhea, Chronic
alcoholism
Headache, ↓ BP
Confusion
Drowsiness
↑ RR and depth
Nausea, Vomiting
↓Cardiac output
Cold and clammy
Skin, Shock,
Dysrhythmias
At a Glance Acid- Base Disorders

50. Acid-base
disorder
Causes Signs and
Symptoms
Metabolic
alkalosis
vomiting
diuretics
alkali ingestion
Tingling of fingers
and toes, Dizziness,
Hypertonic muscles,
Symptoms of
Hypocalcemia, ↓ RR,
Atrial tachycardia
Hypokalemia, Paralytic
Ileus, Dysrhythmia
At a Glance Acid- Base Disorders

51. Acid-Base Imbalances Management
TYPE OF
IMBALANCE
MANAGEMENT
Respiratory
Acidosis
- Improving ventilation
- Bronchodilators
- Antibiotics for infection
- Thrombolytics & anticoagulants
(pulmonary emboli)
- Pulmonary hygiene
- Mechanical ventilation
- Semi-Fowler’s position

52. Acid-Base Imbalances Management
TYPE OF
IMBALANCE
MANAGEMENT
Respiratory
Alkalosis
- Treatment of the underlying
cause
- Breathe into a paper bag
- Sedative

53. Acid-Base Imbalances Management
TYPE OF
IMBALANCE
MANAGEMENT
Metabolic
Acidosis
- Treatment is correcting the
underlying defect.
- Eliminating source of chloride
- Bicarbonate
- Alkalizing agents
- Hemodialysis
- Peritoneal dialysis

54. Acid-Base Imbalances Management
TYPE OF
IMBALANCE
MANAGEMENT
Metabolic
Alkalosis
- Treatment of underlying
disorder
- Chloride supply
- Sodium chloride fluids
- KCl
- H2-receptor antagonists
(Cimitidine)
- Carbonic anhydrase inhibitors

55. 55
Cases

56. 56
HEMOGLOBIN
PLT
WBC
HEMATOCRIT
SEGMENTERS
RBC
pH K
Na

57. 57
12-14
140k-440k
5k-10k
38-42
SEGMENTERS
4-8
7.35-7.45 4.0-5.1
135-145

58. 58
Hemoglobin – this is the part of your red blood cell which carries
oxygen all over the body. If your hemoglobin levels are decreased it
could pertain to anemia, bleeding, patients with chronic kidney
disease, or a possible blood dyscrasia. If your hemoglobin levels
are elevated we could consider polycythemia vera and dehydration.
Red Blood Cell (RBC) – this part of the CBC tells you the number
of cells that could carry oxygen in the body. Same with hemoglobin,
decrease levels of RBC could also be secondary to anemia or
bleeding and increase levels could also be secondary to
polycythemia or dehydration.
Hematocrit – this measures the amount of space in the blood
being occupied by your red blood cells. Causes for the increased
and decreased of hematocrit are the same with your hemoglobin
and red blood cells.

59. 59
White Blood Cell (WBC) – this are the cells in the body that fight
off invaders like infections. An increase or decrease in WBC count
could represent an ongoing infection or a malignancy like your
leukemia. Also included in the CBC is the 5 differential count for
your WBC, namely:
Neutrophils or segmenters – this type of WBC are the primary
cells that respond to a bacterial infection. High levels of your
neutrophils usually represent and ongoing infection, an
inflammation, malignancy, cause by some drugs, etc. Low levels of
your neutrophils could be seen in patients with viral infection,
autoimmune diseases, some medications and malignancy.
Lymphocytes – this type of WBC represent 20-40% of your
circulating WBC in the blood. An increased in lymphocyte count
usually represents an acute infection especially viral infections,
leukemia, smoking, etc. Low lymphocyte count is usually not
significant.

60. 60
Monocytes – this comprises 3-8% of all white blood cells in the
body. An increase in monocyte could signify a chronic infection like
your tuberculosis or a chronic inflammation condition like your
inflammatory bowel disease and malignancy. Low levels of
monocytes are usually none significant if other cells are normal.
Basophils – this comprises only 0.01-0.3% of all white blood cells
in the blood. This type could produce histamine. Increased
numbers could represent a myeloproliferative disorder.
Eosinophils – comprises 1 – 6% of all white blood cells in the
blood stream. They are usually increase in cases of allergy, asthma
and in parasitic infections. Low levels are usually not significant.
Platelet Count – the normal platelet count ranges from 150,000 –
400,000 /L and this cell is involved in the clotting cascade of the
body. Low levels of this cell could cause easy bruising and
bleeding. Causes of low platelet count include infections (ex:
dengue fever), autoimmune disease, liver disease, idiopathic
thrombocytopenic purpura, etc.

61. 61
Red Cell Indices – this are investigated when considering
diseases like your thalassemia or sickle cell anemia.
MCV (mean corpuscle volume) – telling you the average size of
the red blood cell (80-100)
MCH (mean corpuscle hemoglobin) – shows the average
amount of hemoglobin in each red blood cell (26-34)
MCHC (mean corpuscle hemoglobin concentration) – average
amount of hemoglobin in the red blood cell compared to their
average size. (31-37)
RDW – (11.5 -14.5)

62. ABG SHORTCUT
Laboratory studies
ABG: pH/PaCO2/PaO2/HCO3/O2sat
ABG: 7.38-7.44/35-45/80-100/22-26/95-100
What is the acid base disturbance and what is the cause
Na
135-145
62
K
3.5-5.1
AG
7-16
CO2
22-30
BUN
5-25
Crea
0.6-1.2
Glu
70-110
Ca
8.5-10.1
Cl
98-107

63. CHEMICAL COMPOSITIONS OF BODY FLUIDS
Extracellular Fluid Intracellular Fluid
Na+ 142 mEq/L 10mEq/L
K+ 4mEq/L 140 mEq/L
Ca2+ 2.4 mEq/L 0.0001 mEq/L
Mg2+ 1.2 mEq/L 58 mEq/L
Cl- 103 mEq/L 4 mEq/L
HCO3- 28 mEq/L 10 mEq/L
Phosphates 4 mEq/L 75 mEq/L
SO42- 1 mEq/L 2 mEq/L
Glucose 90 mg/dl 0-20 mg/dl
Amino Acids 30 mg/dl 200 mg/dl

64. CHEMICAL COMPOSITIONS OF BODY FLUIDS
Extracellular Fluid Intracellular Fluid
Cholesterol 0.5 g/dl 2-95 g/dl
Phospholipids 0.5 g/dl 2-95 g/dl
Neutral fat 0.5 g/dl 2-95 g/dl
PO2 35 mm Hg 20 mm Hg
PCO2 46 mm Hg 50 mm Hg
pH 7.4 7.0
Proteins 2 g/dl 16 g/dl
5 mEq/L 40 mEq/L

65. Arterial Blood
Sampling
NURSE PHLEBOTOMIST

66. Indications
To assess.
 Respiratory Status
Assess oxygenation and ventilation
 Acid Base Balance
 Phlebotomy. Used if venous route is unavailable or
inaccessible due to trauma or burns. Usually a
femoral puncture, uncommon variation.

67. Contraindications
 Overlying infection or burn at insertion site.
 Absent collateral circulation.
 Arteriovenous shunt. Often radial or brachial.
 Severe atherosclerosis
 Raynauds disease.
 Coagulopathy.

68. Sites
 Preferred radial or femoral arteries.
 Less common. Dorsalis pedis and posterior tibial.
 Avoid. Branches without collateral supply. Example is
the brachial artery.

69. Complications
 Bleeding causing hematoma.
 Arterial occlusion causing thrombus or
dissection.
 Infection causing arteritis or cellulitis.
 Embolization
 Last 3 uncommon.

70. Normal Values
 pH, 7.36 to 7.44. For acid base status of blood.
 pCO2, 38 to 44 mmHg. Reflects ventillation.
 pO2, 85 to 95 mmHg. Reflects oxygenation.
 HCO3, 21 to 27 meq per litre. Key blood buffer.
 Base excess, plus or minus 2 meq per litre
 ABG quiz. http://www.vectors.cx/med/apps/abg.cgi

71. Pathophysiology
 Metabolic alkalosis
 Metabolic acidosis
 Respiratory alkalosis
 Respiratory acidosis

72. Initial Preparation
 Wash hands
 Gloves
 Protective eye wear
 Iodine swab. Povidone-iodine, betadine. Followed by
alcohol swab
 Arterial blood gas sampling kit
 2 x 2 cm gauze
 Bag of ice. To store sample

73. Allens Test
 Indicates collateral circulation to hand.
 Radial artery on non dominant hand.
 Palpate radial artery.
 Simultaneouslys palpate ulnar artery, or as
close to that area as possible.
 Patient makes a fist. Palpate both arteries
for10 seconds.
 Release ulnar artery and witness blood flow
and pinking of the hand via collateral radial
artery
 Radial artery is now a candidate for testing.

74. Set Up
 Patient seated on stretcher
 Rolled up towel under wrist. That hyperextends wrist,
bringing artery closer to surface.
 Clean area in a cicular motion with iodine. Allow to dry.
 Wipe away iodine with alcohol. While drying, open
sampling kit.

75. Sampling Kit
 3 pieces
1. Orange air ball or cube. Used to expel excess air
from the syringe.
2. Black cap for syringe, used for transport.
3. 3 cc, cubic centimetres heparinised syringe. With
needle attached.

76. Sampling Kit Use
 Pull back slightly on plunger, so once needle is in
artery, natural pulsations will fill the syringe.
 Remove clear needle cap. Locate the bevel. Bevel is a
slanted opening on one side of the needle tip. We
want bevel facing upward, so you can see it.

77. Syringe Use
 45 degrees, sharper angle.
 Hold like a dart or pen.
 Feeling pulse under non syringe finger is the only
landmark for orientation.
 Before piercing skin, roll finger back slightly from
artery, so you dont stab yourself in the finger.
 Flash of blood into hub of needle. Artery has been
accessed.
 Blood will pulse into syringe. 1.5 to 2.0 cc
required.
 Cover needle with gauze. Quickly remove needle.

78. After Care
 Physician applies pressure to gauze for 5 minutes. 10
minutes if patient is on anticoaggulant therapy.
 Optional to ask patient to do this instead.

79. Blood Care
 Insert needle into orange air cube or ball. Want
bevel covered, dont want needle to go through
cube.
 Push down on plunger to expell excess air. So it
doesnt affect results. Key point because we are
measuring air component levels in blood.
 Remove cube and needle as one.
 Attach black cap to syringe.
 Roll test tube between hands, to ensure blood
heparinisation.
 Place in iced bag. Send to lab.
 Needle and cube to sharps container.

80. THANK YOU
80

81. References
 Bishop, M., Fody, E., & Schoeff, l. (2010). Clinical Chemistry:
Techniques, principles, Correlations. Baltimore: Wolters
Kluwer Lippincott Williams & Wilkins.
 Carreiro-Lewandowski, E. (2008). Blood Gas Analysis and
Interpretation. Denver, Colorado: Colorado Association for
Continuing Medical Laboratory Education, Inc.
 Sunheimer, R., & Graves, L. (2010). Clinical Laboratory
Chemistry. Upper Saddle River: Pearson .
81

82. Resources to learn more
www.acid-base.com
www.acidbasedisorders.com
Haber RJ. A practical approach to acid-base
disorders. West J Med 1991; 155: 146
www.postgradmed.com/issues/2000/03_00/fall.ht
m
http://medicine.ucsf.edu/housestaff/handbook/H
ospH2002_C5.htm