ABG Presentation by DJ as House Officer

1. ABG
Arterial Blood Gas Analysis
(A Basic Approach)
Dr. Dharmendra Joshi (DJ)
Dr. Basanta Sapkota

2. “Life is a struggle, not against sin, not
against the Money Power, not against
malicious animal magnetism, but
against hydrogen ions."
- H.L. MENCKEN

3. Table of Contents
1. Definition
2. Purpose
3. Information provided by ABG
4. Normal results
5. Why ABG is ordered?
6. Extraction and Analysis
7. Step wise approach to ABG
8. Acid Base Disorders

4. Pulse Oximetry ‘The 5th Vital Sign’
• Non-invasive
• Instantaneous
• Ubiquitous
• SaO2 < 95% the usual
cutoff for normal versus
‘abnormal’
• Limitations:
– Patient must have pulse
– Detects only significant
decreases in PO2
– Does not comment on
content

5. ABG: Definition:
• Blood gas analysis, also
called Arterial Blood
Gas (ABG) analysis, is an
invasive test which
measures the amount
of oxygen (O2) and
carbon dioxide (CO2) in
the blood, as well as the
acidity (pH) of the
blood.

6. Most Dyspneic Patients Don’t Require ABG Analysis
• When cause of dyspnea is established
– Asthma, CHF, restrictive lung disease, etc.
• When dyspnea is so severe as to warrant
immediate mechanical ventilation
– The decision to intubate and mechanically
ventilate is almost always one based on clinical,
not laboratory, grounds.

7. Purpose:
• Evaluates how effectively the lungs are delivering
O2 to the blood and how efficiently they are
eliminating CO2 from it.
• Indicates how well the lungs and kidneys are
interacting to maintain normal blood pH (acid-
base balance).
• Assess respiratory disease and other conditions
that may affect the lungs, and to manage patients
receiving oxygen therapy (respiratory therapy).

8. Purpose: Contd…
• Provides information on kidney function too.
• Determine the pH of the blood and the partial
pressures of carbon dioxide (PaCO2) and
oxygen (PaO2) within it.
• Assess the effectiveness of gaseous exchange
and ventilation, be it spontaneous or
mechanical.

9. Purpose: Contd…
• Assess metabolic status of the patient, giving
an indication of how they are coping with
their illness.
• It would therefore seem logical to request an
ABG on any patient who is or has the potential
to become critically ill.
• This includes patients in critical care areas and
those on wards who 'trigger' early-warning
scoring systems.

10. Limitations of ABGs
• ABGs measure gas partial
pressures (tensions)
– Remember: PO2 is not the
same as content! A severely
anemic patient may have an
oxygen content reduced by
half while maintaining
perfectly acceptable gas
exchange and therefore
maintaining pO2

11. Limitations of ABGs: Contd…
• Technical issues
– They hurt,
– Sampling from a vein by mistake,
– Finding an arterial pulse can be difficult in very
hypotensive patients,
– Complications such as arterial thrombosis are
possible, but rare.

12. Information provided by ABG
• PaCO2
• This is the partial pressure of carbon dioxide dissolved
within the arterial blood.
• It is used to assess the effectiveness of ventilation. A
high PaCO2 (respiratory acidosis) indicates
underventilation, a low PaCO2 (respiratory alkalosis)
indicates hyper- or over ventilation.
• The normal range for a healthy person is 4.7-6.0 kPa or
35-45 mmHg although in chronic pulmonary diseases
it may be considerably higher and still normal for that
patient.

13. Information provided by ABG Contd...
• PaO2
• This is the partial pressure of oxygen dissolved
within the arterial blood and will determine
oxygen binding to haemoglobin (SaO2).
• It is of vital importance but is not used in
determining patients' acid base status and
normally low readings indicate hypoxaemia.
• The normal range: 9.3-13.3 kPa or 80-100
mmHg.

14. Information provided by ABG Contd...
• SaO2
• Oxygen saturation measures how much of the
haemoglobin (Hb) in the red blood cells is
carrying oxygen (O2).
• Although similar to SpO2 (measured by a
pulse oximeter), it is more accurate.
• The normal levels are 97% and above,
although levels above 90% are often
acceptable in critically ill patients.

15. Information provided by ABG Contd...
• pH
• The pH measures hydrogen ions (H+) in blood.
• The pH of blood usually between 7.35 to
7.45. A pH of less than 7.0 is called acid and a
pH greater than 7.0 is called basic (alkaline).
So blood is slightly basic.

16. Information provided by ABG Contd...
• HCO3 (Bicarbonate)
• HCO3 is a chemical (buffer) that keeps the pH of
blood from becoming too acidic or too basic &
indicates whether a metabolic problem is present
(such as ketoacidosis).
• A low HCO3
- indicates metabolic acidosis, a high
HCO3
- indicates metabolic alkalosis.
• HCO3
- levels can also become abnormal when the
kidneys are working to compensate for a
respiratory issue so as to normalize the blood pH
• Normal range: 22–26 mmol/l

17. Information provided by ABG Contd...
• Base Excess (BE)
• The base excess is used for the assessment of the
metabolic component of acid-base disorders, and
indicates whether the patient has metabolic acidosis or
metabolic alkalosis.
• A negative base excess indicates that the patient has
metabolic acidosis (primary or secondary to respiratory
alkalosis).
• A positive base excess indicates that the patient has
metabolic alkalosis (primary or secondary to
respiratory acidosis).
• Normal range: -3 to +3 mmol/l

18. Information provided by ABG Contd...
• Other informations:
• Some electrolytes (e.g., Na+, K+, Ca++)
• Lactate
• Other assorted calculated results.

19. SpO2 SaO2
• SpO2 and SaO2 are often used interchangeably,
but they are not same.
• When O2 saturation is measured by pulse
oximeter..... SpO2
• When O2 saturation is measured by CO-
oximeter..... SaO2
• SpO2 is also called functional arterial O2
saturation and SaO2 as fractional arterial O2
saturation.
• Only true CO-oximeter can determine an
accurate value for SaO2

20. SpO2 Vs SaO2 Contd...
• SpO2 == HbO2
HbO2 + Hb
• SaO2 == HbO2
HbO2+ Hb+COHb+MetHb+SfHb+COSfHb
SaO2 == SpO2[1-SaCO]… (Nellcor equation)
Non functional Hb is 2-3%
In heavy smoker it may be up to 15%

21. Normal Results
• pH: Measurement of acidity or alkalinity,
based on the hydrogen (H+)
7.35-7.45
• partial pressure of oxygen (PaO2): The partial
pressure oxygen that is dissolved in arterial
blood.
80-100 mm Hg

22. Normal Results Contd…
• partial pressure of carbon dioxide (PaCO2):
The amount of carbon dioxide dissolved in
arterial blood.
35-45 mm Hg
• oxygen content (O2CT): 15-23%
• oxygen saturation (SaO2): The arterial oxygen
saturation.
94-100%

23. Normal Results Contd…
• Bicarbonate (HCO3
-): The calculated value of
the amount of bicarbonate in the blood.
22-26 mEq/L
• The base excess indicates the amount of
excess or insufficient level of bicarbonate.
-2 to +2mEq/L
(A negative base excess indicates a base deficit
in blood)

24. Why ABG is ordered?
• Blood gas tests are ordered for
patients with symptoms of an O2/CO2
or pH imbalance, such as difficulty
breathing or shortness of breath &
also if known to have a respiratory,
metabolic, or kidney disease or
experiencing respiratory distress to
evaluate oxygenation and acid/base
balance.
• Patients who are “on oxygen” (have
supplemental oxygen) may have their
blood gases measured at intervals to
monitor the effectiveness of
treatment.

25. Why ABG is ordered? Contd...
• Head or neck trauma, injuries that may affect
breathing.
• Prolonged anesthesia – particularly for cardiac
bypass surgery or brain surgery – during and
for a period after the procedure.

26. Buffers
• There are two buffers that work in pairs:
H2CO3 NaHCO3
Carbonic acid base bicarbonate
• These buffers are linked to the respiratory
and renal compensatory system.

27. Respiratory Buffer Response
• H2CO3 level
• Blood pH
• Rate & depth of ventilation (Lungs)
• Activation of the lungs to compensate for an
imbalance starts to occur within 1-3 minutes

28. Renal Buffer Response
• The kidneys excrete or
retain bicarbonate(HCO3
-).
• If blood pH decreases, the
kidneys will compensate
by retaining HCO3
-
• Renal system may take
from hours to days to
correct the imbalance.

29. Extraction
• Usually extracted by a
phlebotomist, nurse,
respiratory therapist or
Doctor.
• Commonly from the
radial artery because:
- it is easily accessible,
- can be compressed to
control bleeding,
- has less risk for occlusion.

30. Extraction Contd...
• The femoral artery (or
less often, the brachial
artery) is also used,
especially during
emergency situations or
with children.
• Blood can also be taken
from an arterial
catheter already placed
in one of these arteries.

31. Extraction and analysis:
• IF ULNER/RADIAL ARTERY IS USED
---MODIFIED ALLEN’S TEST
• MODIFIED ALLEN’S TEST
1. INSTRUCT PATIENT TO CLENCH HIS
FIST,
2. USING YOUR FINGER APPLY
OCCLUSIVE PRESSURE ON BOTH
RADIAL & ULNER ARTERY,
3. WHILE APPLYING OCCLUSIVE
PRESSURE TO BOTH ARTERY,
HAVE THE PATIENT RELAX HIS
HAND.BLANCHING OF PALM
&FINGER SHOULD OCCUR,

32. MODIFIED ALLEN’S TEST Contd…
4. RELEASE THE OCCLUSIVE
PRESSURE ON ULNER
ARTERY & NOTICE
FLUSHING OF HAND WITHIN
7-10 SEC.THIS DENOTE THAT
ULNER ARTERY SUPPLY IS
ADEQUATE &IT’S SAFE TO
PRICK RADIAL ARTERY. IF IT
DOES NOT OCCUR IT
MEANS ULNAR ARTERY
SUPPLY IS NOT SUFFICIENT
& RADIAL ARTERY IS NOT
SAFE TO PRICK.

33. Extraction and analysis: Contd...
1. The syringe is pre-packaged and contains a
small amount of heparin, to prevent
coagulation or needs to be heparinised, by
drawing up a small amount of heparin and
squirting it out again.
2. Once the sample is obtained, care is taken to
eliminate visible gas bubbles, as these
bubbles can dissolve into the sample and
cause inaccurate results.

34. Extraction and analysis: Contd...
3. The sealed syringe is taken to a blood gas analyzer. If
the sample cannot be immediately analyzed, it is
chilled in an ice bath in a glass syringe to slow
metabolic processes which can cause inaccuracy.
4. Samples drawn in plastic syringes should not be iced
and should always be analyzed within 30 minutes.
5. The machine used for analysis aspirates this blood from
the syringe and measures the pH and the partial
pressures of oxygen and carbon dioxide. The
bicarbonate concentration is also calculated.

35. Extraction and analysis: Contd...
6. Results usually available for interpretation
within five minutes.
7. After the blood has been taken, apply
pressure to the puncture site for 10-15
minutes to stop the bleeding, and then
places a dressing over the puncture.
8. Observe the patient for signs of bleeding or
circulation problems.

36. Contraindication for arterial puncture
I. INFECTION AT SITE.
II. ALLEN’S TEST NEGATIVE.
III. ON ANTICOAGULANT THERAPY.
IV. SEVERE PERIPHERAL VASCULAR DISEASE.
V. DISTAL TO SURGICAL SHUNT.

37. Step wise approach to ABG
• Step 1: Acidemic or Alkalemic?
• Step 2: Is the primary disturbance respiratory or
metabolic?
• Step 3. Asses to PaO2. A value below 80mm Hg
indicates Hypoxemia. For a respiratory
disturbance, determine whether it is acute or
chronic.
• Step 4. For a metabolic acidosis, determine
whether an anion gap is present.
• Step 5. Determine if there is compensatory
mechanism working to correct pH

38. Step 1: Acidemic or Alkalemic?
• Assess the pH –acidotic/alkalotic
• If above 7.5 – alkalotic
• If below 7.35 – acidotic

39. Step 2: Is the primary disturbance
respiratory or metabolic?
• Assess the paCO2 level.
• pH decreases below 7.35, the paCO2 should rise.
• If pH rises above 7.45 paCO2 should fall.
• If pH and paCO2 moves in opposite direction –
primary respiratory problem.
• Assess HCO3 value.
• If pH increases the HCO3 should also increase.
• If pH decreases HCO3 should also decrease.
• They are moving in the same direction, primary
problem is metabolic.

40. Step 3. For a respiratory disturbance,
determine whether it is acute or chronic.
• Acute respiratory disturbances change pH
0.08 units for every 10 mmHg deviation from
normal.
• Therefore, in acute respiratory acidosis, the
pH will fall by 0.08 x [(PCO2 - 40)/10]
• In acute respiratory alkalosis, the pH will rise
by 0.08 x [(40-PCO2)/10]

41. Step 3. Contd…
• Chronic respiratory disturbances only change
pH 0.03 units for every 10 mmHg deviation
from normal
• Therefore, in chronic respiratory acidosis, pH
will fall by 0.03 x [(PCO2 - 40)/10]
• In chronic respiratory alkalosis, the pH will rise
by 0.03 x [(40-PCO2)/10]

42. Appropriateness of Respiratory
Response to Metabolic Acidosis
• Predicted Change in PCO2 = (1.5 x HCO3) + 8 (+-2)
• If patient’s PCO2 is roughly this value, his or
her response is appropriate.
• If patient’s PCO2 is higher than this value, they
are failing to compensate adequately.

43. Respiratory
acidosis
pH PaCo2 HCO3
-
normal
Respiratory
Alkalosis
normal
Metabolic
Acidosis
normal
Metabolic
Alkalosis
normal

44. Base Excess
• Is a calculated value estimates the metabolic
component of an acid based abnormality.
• It is an estimate of the amount of strong acid
or base needed to correct the metabolic
component of an acid base disorder (restore
plasma pH to 7.40 at a PaCO2 40 mmHg)

45. Formula
• With the base excess is 10 in a 50kg
person with metabolic acidosis mM of
HCO3 needed for correction is:
= 0.3 X body weight X BE
= 0.3 X 50 X10 = 150 mM

46. Step 4. For a metabolic acidosis:
Anion Gap Determination
• Calculation of AG is useful approach to analyze
metabolic acidosis
• AG = (Na+ + K+) – (Cl- + HCO3
-)
• It represents the unmeasured anion in plasma.
• Normal value: 10-12mmol/l

47. REMEMBER
High Anion Gap – causes:
• K etoacidosis
• U remia
• S epsis
• S alicylate & other drugs
• M ethanol
• A lcohol (Ethanol)
• L actic acidosis
• E thylene glycol

48. In other way!!!

49. Reduced anion gap
• Increased ‘unmeasured’ cations
• Rare
• Hypermagnesaemia
• Lithium toxicity
• Xs protein
– Myeloma
– Waldenstrom’s macroglobulinaemia
– (Ig’s are strong cations)

50. Normal anion gap
• Disorders of bicarbonate homeostasis
• Hyperchloraemia causes the acidosis
• GI losses
– Vomitting
– Diarrhoea
• Renal losses
– Renal tubular acidosis
– Acetazolamide
• Iatrogenic NaCl

51. Step 5. Determine if there is compensatory
mechanism working to correct pH
• Primary respiratory disturbances i.e primary
changes in PaCO2 invoke compensatory
metabolic responses i.e Secondary changes in
HCO3 and vice versa.
• A patient can be uncompensated or partially
compensated or fully compensated,
• pH has returned within normal range- fully
compensated though other values may be still
abnormal,

52. Step 5 Contd...
• Be aware that neither the system has the
ability to overcompensate,
• If patient have primary respiratory acidosis
will have increased PaCO2 and decreased pH,
Compensation occurs when the kidneys retain
HCO3.
• The body’s attempt to return the acid/base
status to normal (i.e. pH closer to 7.4).

53. Compensation:
• Primary Problem Compensation
• respiratory acidosis metabolic alkalosis
• respiratory alkalosis metabolic acidosis
• metabolic acidosis respiratory alkalosis
• metabolic alkalosis respiratory acidosis

54. Is there appropriate compensation?
Is it chronic or acute?

55. Respiratory Acidosis
– Acute: for every 10 increase in pCO2 -> HCO3
increases by 1 and there is a decrease of 0.08 in
pH MEMORIZE
– Chronic: for every 10 increase in pCO2 -> HCO3
increases by 4 and there is a decrease of 0.03 in
pH

56. Respiratory Alkalosis
– Acute: for every 10 decrease in pCO2 -> HCO3
decreases by 2 and there is a increase of 0.08 in
pH MEMORIZE
– Chronic: for every 10 decrease in pCO2 -> HCO3
decreases by 5 and there is a increase of 0.03 in
pH

57. Assess the PaCO2
• In an uncompensated state – when the pH and
PaCO2 moves in the same direction: the primary
problem is metabolic.
• The decreasing PaCO2 indicates that the lungs
acting as a buffer response (blowing of the excess
CO2)
• If evidence of compensation is present but the pH
has not been corrected to within the normal
range, this would be described as metabolic
disorder with the partial respiratory
compensation.

58. Assess the HCO3
• The pH and the HCO3 moving in the opposite
directions, primary disorder is respiratory and
the kidneys acting as a buffer response: are
compensating by retaining HCO3 to return the
pH to normal range.

59. pH PaCO2 HCO3
-
Resp.Acidosis Normal
but<7.40
Resp.Alkalosis Normal
but>7.40
Met. Acidosis Normal
but<7.40
Met. Alkalosis Normal
but>7.40
Fully Compensated

60. Partially Compensated
pH PaCO2 HCO3
-
Res.Acidosis
Res.Alkalosis
Met. Acidosis
Met.Alkalosis

61. HOW TO KNOW THE DISORDER
pH PaCO2 HCO3ˉ
Respiratory Acidosis
Acute < 7.35 > 45 Normal
Partly Compensated < 7.35 > 45 > 26
Compensated ~ Normal > 45 > 26
Respiratory Alkalosis
Acute > 7.45 < 35 Normal
Partly Compensated > 7.45 < 35 < 22
Compensated ~ Normal < 35 < 22
Metabolic Acidosis
Acute < 7.35 Normal < 22
Partly Compensated < 7.35 < 35 < 22
Compensated ~ Normal < 35 < 22
Metabolic Alkalosis
Acute > 7.45 Normal > 26
Partly Compensated > 7.45 > 45 > 26
Compensated ~ Normal > 45 > 26

62. Evaluating Oxygenation
• What is a ‘normal’ PO2?
– Oxygenation gradually deteriorates during life,
– Several calculations available for determining ‘normal’
based on patient age.
• PaO2 = 104.2 - (0.27 x age)
• i.e., 30 year old ~ 95 mmHg
60 year old ~ 88 mmHg
• Note: Some patients with previous (and now resolved) severe pulmonary
diseases may never recover their full lung function, so any sense of
‘normal’ needs to be tempered with historical information

63. Evaluating Oxygenation in ABGs
• Determine the A-a gradient
• A-a Gradient =
• [(Patm - PH2O) x FiO2] - (PCO2/RQ) - PaO2
• Patm = 760 mmHg
• PH2O = 47 mmHg
• FiO2 = 0.21 on room air at sea level
• PCO2 is taken from the blood gas measurement
• RQ can be assumed to be 1 (possible range
from 0.7 to 1.0)

64. Evaluating Oxygenation with ABGs
Check A-a
Gradient
No Yes
Is the patient hypoxic?
Hypoventilation
Normal Elevated
Check A-a
Gradient
No defect Compensated
Defect.
i.e., patient is hyper-
ventilating or on
supplemental O2
Other Defect
Normal
Elevated

65. ~ PaCO2 – pH Relationship
80 7.20
60 7.30
40 7.40
30 7.50
20 7.60

66. pH < 7.35
Acidosis
pH > 7.45
Alkalosis
pCO2 > 45
Respiratory
HCO3 < 22
Metabolic
pCO2 < 35
Respiratory
HCO3 > 26
Metabolic
PaCO2 ↑10
→HCO3 ↑3.5
PaCO2 ↑10
→HCO3 ↑1
PaCO2 ↓10
→HCO3 ↓4
PaCO2 ↓10
→HCO3 ↓2
PaCO2 ↑7
→HCO3 ↑10
Urine Cl < 10
Cl ResponsiveAnion Gap < 12
Non-Anion Gap
Anion Gap > 12
Anion Gap
Urine Cl > 10
Cl Unresponsive
Interpreting ABGs
Osm Gap > 10
Methanol
Ethylene Glycol
Osmolar Gap < 10
Ketoacidosis
Lactic acidosis
Uremia
Aspirin/salicylate tox
Diarrhea
Renal tubular acidosis
Acetazolamide
Total parenteral nutrition
Ureteral diversion
Pancreas transplant
CNS depressants
Neuromuscular disorder
Thoracic cage abnormalities
Obstructive lung disease
Obesity/hypoventilation syndrome
Myxedema coma
Anxiety/pain
Sepsis
CNS (stroke)
Aspirin OD
Chronic liver disease
Pulmonary embolism
Pregnancy
Hyperthyroidism
Loss of body fluids:
Vomiting
Nasogastric suctioning
Diuretic use
Excess body fluids:
Exogenous steroids
Cushing’s syndrome
Hyperaldosteronism
Bartter’s syndrome
=Na - (Cl+HCO3)
Acute
Chronic
PaCO2 ↓15
→HCO3 ↓10
Compensation:
If:
ΔPCO2/ΔHCO3
=
CO2/HCO3ratio
Then it IS comp.
Acute
Chronic
(2xNa) + (Glu/18) +
(BUN/2.8) = calculated
serum osmoles
HCO3 loss Extra H+

67. ABG Vs VBG
Arterial Blood Gas
• PAINFUL
• Arterial injury
• Thrombosis with distal
ischemia
• Hemorrhage/hematoma
• Aneurysm formation
• Median nerve damage
• Infection
• Needle stick injury
• Reflex sympathetic dystrophy
Venous Blood Gas
• Samples can be drawn
simultaneously at time of
veni puncture
• Should be done without
tourniquette
• More difficult to obtain in
pulseless patients
• Controversy regarding level
of agreement with arterial
values

68. ABG Vs VBG
1. To measure pH, bicarb, or base excess, especially in
hemodynamically stable patients, a VBG is equivalent
and there is no need for an ABG.
On average for pH the difference is about 0.02 -
0.03. So for average DKA patient, no ABG is needed.
2. A VBG is a good screening tool for hypercarbia, with a
venous PCO2 < 45 mmHg having about 100%
sensitivity.
However, VBG cannot tell about the degree of
hypercarbia reliably. If an absolute number needed,
ABG is the way to go.

69. ABG Vs VBG Contd...
3. For hypoxia, or workup requiring calculations of
oxygen tension, ABG is done (hypoxic arrest,
calculating A-a gradients)
4. Studies are raising the concern for increased
mortality in patients who have hyperoxia after
return of circulation after cardiac arrest. These
patients need ABG’s to guide the vent
settings. The increased mortality in these
patients has even been seen within the first hour.

71. Acid Base Disorders
1. Respiratory Acidosis
2. Respiratory Alkalosis
3. Metabolic Acidosis
4. Metabolic Alkalosis

72. Respiratory Acidosis
• Lower pH and an
increased PCO2 and is due
to respiratory depression
(not enough oxygen in and
CO2 out).
• pH decrease (<7.35)
• PCO2 increase (>45mmHg)
• Any condition that results
in hypoventilation can
cause respiratory acidosis.

73. Causes of respiratory acidosis
CNS depression – sedatives, narcotics, CVA
Neuromuscular disorders – acute or chronic
Acute airway obstruction – foreign body, tumor, reactive airway
Severe pneumonia, pulmonary edema, pleural effusion
Chest cavity problems – hemothorax, pneumothorax, flail chest
Chronic lung disease – obstructive or restrictive
Central hypoventilation, OSA

74. Respiratory Acidosis: Signs&Symptom
• Respiratory : Dyspnoea, respiratory distress
and/or shallow respiration.
• Nervous: Headache, restlessness and confusion.
If co2 level extremely high drowsiness and
unresponsiveness may be noted.
• CVS: Tacycardia and dysrhythmias

75. Management of Respiratory Acidosis
• Increase the ventilation.
• Causes can be treated rapidly include
pneumothorax, pain and CNS depression r/t
medication.
• If the cause cannot be readily resolved,
mechanical ventilation.

76. Respiratory Alkalosis
• Respiratory alkalosis,
characterized by a raised pH
and a decreased PCO2, is
due to over ventilation
caused by hyperventilating,
pain, emotional distress, or
certain lung diseases that
interfere with oxygen
exchange.
• pH increases
• PCO2 decreases

77. Causes of Respiratory Alkalosis
Anxiety, pain, fever
Hypoxia, CHF
Lung disease with or without hypoxia – pulmonary embolus, reactive airway,
pneumonia
CNS diseases
Drug use – salicylates, catecholamines, progesterone
Pregnancy
Sepsis, hypotension
Hepatic encephalopathy, liver failure
Mechanical ventilation
Hypothyroidism
High altitude

78. Respiratory Alkalosis:
Signs/Symptoms
• CNS: Light Headedness, numbness, tingling,
confusion, inability to concentrate and blurred
vision.
• Dysrhythmias and palpitations
• Dry mouth, diaphoresis and tetanic spasms of
the arms and legs.

79. Management of Respiratory Alkalosis
• Resolve the underlying problem
• Monitor for respiratory muscle fatigue
• When the respiratory muscle become
exhausted, acute respiratory failure may
ensue

80. Metabolic Acidosis
• Metabolic acidosis is characterized by a lower
pH and decreased HCO3
-; the blood is too
acidic on a metabolic/kidney level.
• Causes include diabetes, shock, and renal
failure.
• pH decreases (<7.35)
• HCO3 decreases (<22mEq/l)

81. Causes of Metabolic Acidosis
• Renal failure
• Diabetic ketoacidosis
• Anaerobic metabolism
• Starvation
• Salicylate intoxication

82. Metabolic Acidosis: Signs/Symptoms
• CNS: Headache,
confusion and
restlessness progressing
to lethargy, then stupor
or coma.
• CVS: Dysrhythmias
• Kussmaul’s respirations
• Warm, flushed skin as
well as nausea and
vomiting

83. Management of Metabolic Acidosis
• Treat the cause
• Hypoxia of any tissue bed will produce
metabolic acids as a result of anaerobic
metabolism even if the pao2 is normal
• Restore tissue perfusion to the hypoxic tissues
• The use of bicarbonate is indicated for known
bicarbonate - responsive acidosis such as seen
with renal failure

84. Metabolic Alkalosis
• Metabolic alkalosis is characterized by an
elevated pH and increased HCO3
- and is seen
in hypokalemia, chronic vomiting (losing acid
from the stomach), and sodium bicarbonate
overdose.
• pH increases (>7.45)
• HCO3
- increases (>26mEq/l)

85. Causes of Metabolic Alkalosis
• Excess of base /loss of acid.
• Ingestion of excess antacids, excess use of
bicarbonate, or use of lactate in dialysis.
• Protracted vomiting, gastric suction,
hypchoremia, excess use of diuretics, or high
levels of aldesterone.

86. Metabolic Alkalosis: Signs/Symptoms
• CNS: Dizziness, lethargy
disorientation, siezures
& coma.
• M/S: weakness, muscle
twitching, muscle
cramps and tetany.
• Nausea, vomiting and
respiratory depression.
• It is difficult to treat.

87. Management of Metabolic Alkalosis
• Remove factors that sustain HCO3
- reabsorption:
Restore plasma volume
Restore chloride lost
Replace potassium in hypokalaemia
Stop diuretics
• Treat underlying cause.

88. • Valuable information can be gained
from an ABG as to the patients
physiologic condition
• Remember that ABG analysis is only
part of the patient assessment.
• Be systematic with your analysis, start
with ABC’s as always and look for
hypoxia (which you can usually treat
quickly), then follow the five steps.
• A quick assessment of patient
oxygenation can be achieved with a
pulse oximeter which measures SaO2.

89. It’s not magic understanding
ABG’s, it just takes a little
practice!

90. Thank You!!!