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Arterial Blood Gases
By
Dr Riham Hazem Raafat
Lecturer of Pulmonary Medicine
Ain Shams University
What is an ABG
Arterial Blood Gas
Drawn from artery- radial, brachial, femoral
It is an invasive procedure.
Caution must be taken with patient on
anticoagulants.
Why Order an ABG?
 Aids in establishing a diagnosis
 Helps guide treatment plan
 Aids in ventilator management
 Improvement in acid/base management allows
for optimal function of medications
 Acid/base status may alter electrolyte levels
critical to patient status/care
What Is An ABG?
pH [H+
]
PCO2 Partial pressure
CO2
PO2 Partial pressure O2
HCO3 Bicarbonate
SaO2 Oxygen Saturation
Basic principles
• Human bodies were designed to maintain:
pHpH 7.35-7.457.35-7.45
PaO2PaO2 80-10080-100
mmHgmmHg
PaCO2PaCO2 35-4535-45
mmHgmmHg
HCO3HCO3 22-2622-26
mmHgmmHg
Arterial Blood Gas Interpretation
 pH: negative log of H+
concentration
In blood:
•Normal range: 7.35 - 7.45
•Acidosis = pH less than 7.35
•Alkalosis = pH greater than 7.45
•A pH < 7.0 or > 7.8 can cause death
• PaCO2: partial pressure of CO2 dissolved in the
arterial plasma
– Normal: 35 - 45 mm Hg
– Is regulated in the lungs
– A primary respiratory problem is when PaCO2 is:
– > 45 mm Hg = respiratory acidosis
– < 35 mm Hg = respiratory alkalosis
• HCO3 will be normal (22 - 26 mEq/L)
Compensation
• Body attempts to recover from primary problem
and return to homeostasis
• Primary metabolic acidosis  breathe faster to
compensate (blow off CO2) by creating a
respiratory alkalosis state
• This would be labeled as: Metabolic acidosis
with a compensatory respiratory alkalosis
e.g: pH 7.30, PaCO2 = 28 & HCO3 = 15
PaCo2 & HCO3 below normal? Yes! Compensation!
Acid/Base Balance
 pH is a measurement of the acidity or alkalinity of the
blood.
 It is inversely proportional to the no. of (H+) in the blood.
 The normal pH range is 7.35-7.45.
Changes in body system functions that occur in an acidic
state decreases the force of cardiac contractions,
decreases the vascular response to catecholamines, and a
diminished response to the effects and actions of certain
medications.
An alkalotic state interferes with tissue oxygenation and
normal neurological and muscular functioning.
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
Buffers
• Limit pH changes when strong acids/bases are
introduced
• Addition of a strong acid is partly neutralized by
the weak base
HB (weak acid) H+ (strong acid) B- (conjugate weak base)
Extracellular vs. Intracellular
buffering
 H+ buffering upon entering the extracellular and intracellular
fluid
• Immediate buffering by HCO3- extracellularly
• H+ takes 2-3 hrs to enter the cell
• Then buffered by intracellular shifts in electolytes
•Cl- follows H+ into the cell to maintain
electroneutrality
•Na+ and K+ move out of the cell therefore
increasing K+ and Na+ in the extracellular fluid
• This all occurs to help maintain the PH near 7.4
Intracellular Acid/Base Buffering
Respiratory Buffer Response
 The blood pH will change acc. to the level of
H2CO3present.
 This triggers the lungs to either increase or
decrease the rate and depth of ventilation
 Activation of the lungs to compensate for an
imbalance starts to occur within 1-3
minutes
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
Acid/Base Disorders
1- Respiratory Acidosis
 is defined as a pH less than 7.35 with
a paco2 greater than 45 mmHg.
 Acidosis –accumulation of Co2, combines
with water in the body to produce carbonic
acid, thus lowering the pH of the blood.
 Any condition that results in hypoventilation
can cause respiratory acidosis.
Causes
1. CNS depression: medications such as
narcotics, sedatives, or anesthesia.
2. Impaired muscle function: spinal cord
injury, NM diseases, or NM blocking drugs.
3. Pulmonary disorders such as atelectasis,
pneumonia, pneumothorax, pulmonary edema
or bronchial obstruction
4. Massive pulmonary embolus
5. Hypoventilation due to pain chest wall
injury, or abdominal pain.
Signs & symptoms of Respiratory
Acidosis
 Respiratory: Dyspnea, respiratory distress
and/or shallow respiration.
 Nervous: Headache, restlessness and
confusion. If Co2 level extremely high
drowsiness and unresponsiveness may be
noted.
 CVS: Tachycardia and dysrhythmias
Management
 Increase the ventilation.
 Causes can be treated rapidly include
pneumothorax, pain and CNS depression r/t
medication.
 If the cause can not be readily resolved  MV
2- Respiratory alkalosis
 Is defined as a pH more than 7.35 with a
paco2 less than 45 mmHg, due to:
 Psychological responses, anxiety or fear.
 Pain
 Increased metabolic demands such as
fever, sepsis, pregnancy or thyrotoxicosis.
 Medications such as respiratory stimulants.
 CNS lesions
Signs & symptoms
 CNS: Light Headedness, numbness, tingling,
confusion, inability to concentrate and blurred
vision.
 CVS: Dysrhythmias and palpitations
 Dry mouth, diaphoresis and tetanic
spasms of the arms and legs.
Management
 Resolve the underlying problem
 Monitor for respiratory muscle fatigue
 When the respiratory muscle become
exhausted, acute respiratory failure may
ensue
3- Metabolic Acidosis
 Is Bicarbonate less than 22mEq/L with
a pH of less than 7.35.
 Caused by:
oRenal failure
oDiabetic ketoacidosis
oAnaerobic metabolism (lactic acidosis)
oStarvation
oSalicylate intoxication
Sign & 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
Management
 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
4- Metabolic alkalosis
 Is Bicarbonate more than 26m Eq /L
with a pH more than 7.45
 Causes:
o Excess of base /loss of acid
o Ingestion of excess antacids, excess use of
bicarbonate, or use of lactate in dialysis.
o Protracted vomiting, gastric suction,
hypochloremia, excess use of diuretics, or high
levels of aldosterone.
Signs/symptoms
 CNS: Dizziness, lethargy disorientation,
seizures & coma.
 M/S: weakness, muscle twitching, muscle
cramps and tetany.
 Nausea, vomiting and respiratory
depression.
It is difficult to treat.
Components of ABGpH
Measurement of acidity or alkalinity, based on the hydrogen (H+)  7.35 –
7.45
Pao2
The partial pressure oxygen that is dissolved in arterial blood  80-100
mm Hg.
PCO2
The amount of carbon dioxide dissolved in arterial blood  35– 45 mmHg
HCO3
The calculated value of the amount of HCO3 in the blood  22 – 26 mmol/L
B.E
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)
Stepwise approach to ABG
 Step 1: Acidemic or Alkalemic?
 Step 2: Is the primary disturbance respiratory
or metabolic?
 Step 3: Assess Pa O2. 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: Assess the normal compensation by the
respiratory system for a metabolic disturbance
• Step 1: Acidemic or Alkalemic?
• Step 2: Is the primary disturbance respiratory
or metabolic?
• Step 3: Assess Pa O2. 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: Assess the normal compensation by the
respiratory system for a metabolic disturbance
Step:1
 Assess the pH –acidotic/alkalotic
 If above 7.5 – alkalotic
 If below 7.35 – acidotic
• Step 1: Acidemic or Alkalemic?
• Step 2: Is the primary disturbance
respiratory or metabolic?
• Step 3: Assess Pa O2. 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: Assess the normal compensation by the
respiratory system for a metabolic disturbance
 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.
Step 2:
 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
• Step 1: Acidemic or Alkalemic?
• Step 2: Is the primary disturbance respiratory
or metabolic?
• Step 3: Assess Pa O2. 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: Assess the normal compensation by the
Step 3:
Assess pao2 < 80 mm Hg - Hypoxemia
For a respiratory disturbance : acute, chronic
 If the change in paCo2 is associated with the
change in pH, the disorder is acute.
 In chronic process the compensatory process
brings the pH to within the clinically acceptable
range ( 7.30 – 7.50)
Example 1:
A 45 years old female admitted with the severe attack of
asthma. She has been experiencing increasing
shortness of breath since admission three hours ago.
Her arterial blood gas result is as follows:
pH : 7.22
paCO2 : 55
HCO3 : 25
SO Follow the steps
• pH is low – acidosis
• paCO2 is high – in the opposite direction of the pH.
• Hco3 is Normal.
Respiratory Acidosis
Example 2:
Fifty five years old male patient admitted with recurring
bowel obstruction has been experiencing intractable
vomiting for the last several hours. His ABG is:
pH : 7.50
paCO2: 42
HCO3 : 33
Metabolic alkalosis
(IV fluids, measures to reduce the excess
base)
Scheme
Respiratory
acidosis
pH PaCo2 HC03
normal
Respiratory
Alkalosis
normal
Metabolic
Acidosis
normal
Metabolic
Alkalosis
normal
• Step 1: Acidemic or Alkalemic?
• Step 2: Is the primary disturbance respiratory
or metabolic?
• Step 3: Assess Pa O2. 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: Assess the normal compensation by the
respiratory system for a metabolic disturbance
Anion GAP
Step 4:
Calculation of AG is useful approach to
analyze metabolic acidosis: N = 12 +/- 2
AG = (Na+ + K+) – (Cl- + Hco3-)
 * A change in the pH of 0.08 for each 10 mm
Hg indicates an ACUTE condition.
* A change in the pH of 0.03 for each 10 mm
Hg indicates a CHRONIC condition.
- High anion gap occurs in:
lactic acidosis, diabetic ketoacidosis, renal failure (sulfates, phosphates &
urates accumulate), alcohol abuse & some drugs (aspirin, Fe, INH, phenformin)
-Low anion gap occurs in:
hypoalbuminemia  Albumin is a negatively charged protein and its loss from
the serum results in the retention of other negatively charged ions
-Normal anion gap occurs in:
hyperchloremic acidosis (Cl- increase in response to lowered HCO3-)  in:
oGIT loss of HCO3− (diarrhea) (N.B. vomiting causes hypochloraemic alkalosis)
oRena loss of HCO3− (i.e. proximal renal tubular acidosis (type 2 RTA)
oRenal dysfunction (i.e. distal renal tubular acidosis (type 1 RTA)
oIngestions: Ammonium chloride and Acetazolamide, ifosfamide,
Hyperalimentation fluids (i.e. total parenteral nutrition)
oSome cases of ketoacidosis, particularly during rehydration with Na+
containing IV solutions.
oAlcohol (such as ethanol) can cause a high anion gap acidosis in some
patients, but a mixed picture in others due to concurrent metabolic alkalosis.
oMineralocorticoid deficiency (Addison's disease)
• Step 1: Acidemic or Alkalemic?
• Step 2: Is the primary disturbance respiratory
or metabolic?
• Step 3: Assess Pa O2. 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: Assess the normal compensation
by the respiratory system for a
metabolic disturbance
COMPENSATION
Step 5:
 A patient can be uncompensated or
partially compensated  pH remains
outside the normal range
 pH has returned within normal range  fully
compensated though other values may be
still abnormal
Determine if there is a compensatory
mechanism working to try to correct the pH.
i.e: primary respiratory acidosis  increased
PaCO2 and decreased pH. Compensation
occurs when the kidneys retain HCO3.
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.
Arterial Blood Gas and Acid Base Balance
Assess the HCO3
The pH and the HCO3 moving in the same
directions, we would conclude that the primary
disorder is respiratory and the kidneys acting
as a buffer response: are compensating by
retaining HCO3 to return the pH to normal
range.
Fully Compensated
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
Partially compensated
pH paco2 Hco3
Res.Acidosis
Res.Alkalosis
Met. Acidosis
Met.Alkalosis
Example 3:
• Male patient was admitted, he was a kidney dialysis
patient who has missed his last 2 appointments at
the dialysis centre his ABG results:
• pH : 7.32
• paCo2 : 32
• HCO3 : 18
• Pao2 : 88
Partially compensated metabolic
Example 4:
• Male patient with COPD. His ABG is:
• pH : 7.35
• PaCO2 : 55
• HCO3 : 30
• PaO2 : 90
Fully compensated Respiratory
Acidosis
Quiz 1
 24 years old male patient with a history of
drug abuse, brought to ER cyanotic
• pH 7.08
• PaCO2 80
• PaO2 37
• HCO3 24
 24 years old male patient with of drug abuse,
brought to ER cyanotic
• pH 7.08
• PaCO2 80
• PaO2 37
• HCO3 24
 Acidemic or Alkalemic?
 Acidemic
 24 years old male patient with a history of drug
abuse, brought to ER cyanotic
• pH 7.08
• PaCO2 80
• PaO2 37
• HCO3 24
 pH in relation to PaCO2 and HCO3?
 24 years old male patient with a history of drug
abuse, brought to ER cyanotic
• pH 7.08
• PaCO2 80
• PaO2 37
• HCO3 24
 primarily respiratory
 24 years old male patient with a history of drug
abuse, brought to ER cyanotic
• pH 7.08
• PaCO2 80
• PaO2 37
• HCO3 24
 Is the compensation adequate?
 PaCO2 increased by 40
 For every 10 increase you would expect 1
increase in HCO3
 Expected HCO3 would be ~28
• 24 years old male patient with a history of drug
abuse, brought to ER cyanotic
– pH 7.08
– PaCO2 80
– PaO2 37
– HCO3 24
• Acidemic, primarily respiratory, but mild
component of metabolic
• Also hypoxemic
• Narcotic OD
Quiz 2
 42 years old female patient with DM, presents
with 4 days of unwell
• pH 7.23
• PaCO2 27
• PaO2 118
• HCO3 12
Quiz 2
 42 years old female patient with DM, presents
with 4days of unwell
• pH 7.23
• PaCO2 27
• PaO2 118
• HCO3 12
 Acidemia, metabolic
 DKA, Na 135, Cl 99
 AG = Na – Cl – HCO3 = 135 – 111 = 24
Quiz 3
 71 male patient with COPD, c/o SOB
• pH 7.21
• PaCO2 75
• PaO2 41
• HCO3 30
 Acidemia, resp (acute on chronic), hypoxic
Quiz 4
 23 years old female patient c/o SOB, lightheaded
and perioral tingling
• pH 7.54
• PaCO2 22
• PaO2 115
• HCO3 21
 Alkalemia, resp (acute)
Quiz 5
 32 years old male patient c/o of vomiting of 5
days duration, HR 110 BP 90/50, dry mouth &
mucosa
• pH 7.50
• PaCO2 47
• PaO2 80
• HCO3 38
 Alkalemia, metabolic
Precautions
 Excessive Heparin: Decreases bicarbonate and
PaCO2
 Large Air bubbles not expelled from sample PaO2
rises, PaCO2 may fall slightly.
 Fever or Hypothermia, Hyperventilation or
breath holding (Due to anxiety) may lead to
erroneous lab results
 Care must be taken to prevent bleeding
It’s not magic understanding
ABG, it just takes a little
practice!
Arterial Blood Gas and Acid Base Balance

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Arterial Blood Gas and Acid Base Balance

  • 1. Arterial Blood Gases By Dr Riham Hazem Raafat Lecturer of Pulmonary Medicine Ain Shams University
  • 2. What is an ABG Arterial Blood Gas Drawn from artery- radial, brachial, femoral It is an invasive procedure. Caution must be taken with patient on anticoagulants.
  • 3. Why Order an ABG?  Aids in establishing a diagnosis  Helps guide treatment plan  Aids in ventilator management  Improvement in acid/base management allows for optimal function of medications  Acid/base status may alter electrolyte levels critical to patient status/care
  • 4. What Is An ABG? pH [H+ ] PCO2 Partial pressure CO2 PO2 Partial pressure O2 HCO3 Bicarbonate SaO2 Oxygen Saturation
  • 5. Basic principles • Human bodies were designed to maintain: pHpH 7.35-7.457.35-7.45 PaO2PaO2 80-10080-100 mmHgmmHg PaCO2PaCO2 35-4535-45 mmHgmmHg HCO3HCO3 22-2622-26 mmHgmmHg
  • 6. Arterial Blood Gas Interpretation  pH: negative log of H+ concentration In blood: •Normal range: 7.35 - 7.45 •Acidosis = pH less than 7.35 •Alkalosis = pH greater than 7.45 •A pH < 7.0 or > 7.8 can cause death
  • 7. • PaCO2: partial pressure of CO2 dissolved in the arterial plasma – Normal: 35 - 45 mm Hg – Is regulated in the lungs – A primary respiratory problem is when PaCO2 is: – > 45 mm Hg = respiratory acidosis – < 35 mm Hg = respiratory alkalosis • HCO3 will be normal (22 - 26 mEq/L)
  • 8. Compensation • Body attempts to recover from primary problem and return to homeostasis • Primary metabolic acidosis  breathe faster to compensate (blow off CO2) by creating a respiratory alkalosis state • This would be labeled as: Metabolic acidosis with a compensatory respiratory alkalosis e.g: pH 7.30, PaCO2 = 28 & HCO3 = 15 PaCo2 & HCO3 below normal? Yes! Compensation!
  • 9. Acid/Base Balance  pH is a measurement of the acidity or alkalinity of the blood.  It is inversely proportional to the no. of (H+) in the blood.  The normal pH range is 7.35-7.45. Changes in body system functions that occur in an acidic state decreases the force of cardiac contractions, decreases the vascular response to catecholamines, and a diminished response to the effects and actions of certain medications. An alkalotic state interferes with tissue oxygenation and normal neurological and muscular functioning.
  • 10. 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 Buffers
  • 11. • Limit pH changes when strong acids/bases are introduced • Addition of a strong acid is partly neutralized by the weak base HB (weak acid) H+ (strong acid) B- (conjugate weak base)
  • 12. Extracellular vs. Intracellular buffering  H+ buffering upon entering the extracellular and intracellular fluid • Immediate buffering by HCO3- extracellularly • H+ takes 2-3 hrs to enter the cell • Then buffered by intracellular shifts in electolytes •Cl- follows H+ into the cell to maintain electroneutrality •Na+ and K+ move out of the cell therefore increasing K+ and Na+ in the extracellular fluid • This all occurs to help maintain the PH near 7.4
  • 14. Respiratory Buffer Response  The blood pH will change acc. to the level of H2CO3present.  This triggers the lungs to either increase or decrease the rate and depth of ventilation  Activation of the lungs to compensate for an imbalance starts to occur within 1-3 minutes
  • 15. 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
  • 16. Acid/Base Disorders 1- Respiratory Acidosis  is defined as a pH less than 7.35 with a paco2 greater than 45 mmHg.  Acidosis –accumulation of Co2, combines with water in the body to produce carbonic acid, thus lowering the pH of the blood.  Any condition that results in hypoventilation can cause respiratory acidosis.
  • 17. Causes 1. CNS depression: medications such as narcotics, sedatives, or anesthesia. 2. Impaired muscle function: spinal cord injury, NM diseases, or NM blocking drugs. 3. Pulmonary disorders such as atelectasis, pneumonia, pneumothorax, pulmonary edema or bronchial obstruction 4. Massive pulmonary embolus 5. Hypoventilation due to pain chest wall injury, or abdominal pain.
  • 18. Signs & symptoms of Respiratory Acidosis  Respiratory: Dyspnea, respiratory distress and/or shallow respiration.  Nervous: Headache, restlessness and confusion. If Co2 level extremely high drowsiness and unresponsiveness may be noted.  CVS: Tachycardia and dysrhythmias
  • 19. Management  Increase the ventilation.  Causes can be treated rapidly include pneumothorax, pain and CNS depression r/t medication.  If the cause can not be readily resolved  MV
  • 20. 2- Respiratory alkalosis  Is defined as a pH more than 7.35 with a paco2 less than 45 mmHg, due to:  Psychological responses, anxiety or fear.  Pain  Increased metabolic demands such as fever, sepsis, pregnancy or thyrotoxicosis.  Medications such as respiratory stimulants.  CNS lesions
  • 21. Signs & symptoms  CNS: Light Headedness, numbness, tingling, confusion, inability to concentrate and blurred vision.  CVS: Dysrhythmias and palpitations  Dry mouth, diaphoresis and tetanic spasms of the arms and legs.
  • 22. Management  Resolve the underlying problem  Monitor for respiratory muscle fatigue  When the respiratory muscle become exhausted, acute respiratory failure may ensue
  • 23. 3- Metabolic Acidosis  Is Bicarbonate less than 22mEq/L with a pH of less than 7.35.  Caused by: oRenal failure oDiabetic ketoacidosis oAnaerobic metabolism (lactic acidosis) oStarvation oSalicylate intoxication
  • 24. Sign & 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
  • 25. Management  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
  • 26. 4- Metabolic alkalosis  Is Bicarbonate more than 26m Eq /L with a pH more than 7.45  Causes: o Excess of base /loss of acid o Ingestion of excess antacids, excess use of bicarbonate, or use of lactate in dialysis. o Protracted vomiting, gastric suction, hypochloremia, excess use of diuretics, or high levels of aldosterone.
  • 27. Signs/symptoms  CNS: Dizziness, lethargy disorientation, seizures & coma.  M/S: weakness, muscle twitching, muscle cramps and tetany.  Nausea, vomiting and respiratory depression. It is difficult to treat.
  • 28. Components of ABGpH Measurement of acidity or alkalinity, based on the hydrogen (H+)  7.35 – 7.45 Pao2 The partial pressure oxygen that is dissolved in arterial blood  80-100 mm Hg. PCO2 The amount of carbon dioxide dissolved in arterial blood  35– 45 mmHg HCO3 The calculated value of the amount of HCO3 in the blood  22 – 26 mmol/L B.E 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)
  • 29. Stepwise approach to ABG  Step 1: Acidemic or Alkalemic?  Step 2: Is the primary disturbance respiratory or metabolic?  Step 3: Assess Pa O2. 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: Assess the normal compensation by the respiratory system for a metabolic disturbance
  • 30. • Step 1: Acidemic or Alkalemic? • Step 2: Is the primary disturbance respiratory or metabolic? • Step 3: Assess Pa O2. 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: Assess the normal compensation by the respiratory system for a metabolic disturbance
  • 31. Step:1  Assess the pH –acidotic/alkalotic  If above 7.5 – alkalotic  If below 7.35 – acidotic
  • 32. • Step 1: Acidemic or Alkalemic? • Step 2: Is the primary disturbance respiratory or metabolic? • Step 3: Assess Pa O2. 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: Assess the normal compensation by the respiratory system for a metabolic disturbance
  • 33.  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. Step 2:
  • 34.  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
  • 35. • Step 1: Acidemic or Alkalemic? • Step 2: Is the primary disturbance respiratory or metabolic? • Step 3: Assess Pa O2. 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: Assess the normal compensation by the
  • 36. Step 3: Assess pao2 < 80 mm Hg - Hypoxemia For a respiratory disturbance : acute, chronic  If the change in paCo2 is associated with the change in pH, the disorder is acute.  In chronic process the compensatory process brings the pH to within the clinically acceptable range ( 7.30 – 7.50)
  • 37. Example 1: A 45 years old female admitted with the severe attack of asthma. She has been experiencing increasing shortness of breath since admission three hours ago. Her arterial blood gas result is as follows: pH : 7.22 paCO2 : 55 HCO3 : 25 SO Follow the steps • pH is low – acidosis • paCO2 is high – in the opposite direction of the pH. • Hco3 is Normal. Respiratory Acidosis
  • 38. Example 2: Fifty five years old male patient admitted with recurring bowel obstruction has been experiencing intractable vomiting for the last several hours. His ABG is: pH : 7.50 paCO2: 42 HCO3 : 33 Metabolic alkalosis (IV fluids, measures to reduce the excess base)
  • 40. • Step 1: Acidemic or Alkalemic? • Step 2: Is the primary disturbance respiratory or metabolic? • Step 3: Assess Pa O2. 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: Assess the normal compensation by the respiratory system for a metabolic disturbance
  • 41. Anion GAP Step 4: Calculation of AG is useful approach to analyze metabolic acidosis: N = 12 +/- 2 AG = (Na+ + K+) – (Cl- + Hco3-)  * A change in the pH of 0.08 for each 10 mm Hg indicates an ACUTE condition. * A change in the pH of 0.03 for each 10 mm Hg indicates a CHRONIC condition.
  • 42. - High anion gap occurs in: lactic acidosis, diabetic ketoacidosis, renal failure (sulfates, phosphates & urates accumulate), alcohol abuse & some drugs (aspirin, Fe, INH, phenformin) -Low anion gap occurs in: hypoalbuminemia  Albumin is a negatively charged protein and its loss from the serum results in the retention of other negatively charged ions -Normal anion gap occurs in: hyperchloremic acidosis (Cl- increase in response to lowered HCO3-)  in: oGIT loss of HCO3− (diarrhea) (N.B. vomiting causes hypochloraemic alkalosis) oRena loss of HCO3− (i.e. proximal renal tubular acidosis (type 2 RTA) oRenal dysfunction (i.e. distal renal tubular acidosis (type 1 RTA) oIngestions: Ammonium chloride and Acetazolamide, ifosfamide, Hyperalimentation fluids (i.e. total parenteral nutrition) oSome cases of ketoacidosis, particularly during rehydration with Na+ containing IV solutions. oAlcohol (such as ethanol) can cause a high anion gap acidosis in some patients, but a mixed picture in others due to concurrent metabolic alkalosis. oMineralocorticoid deficiency (Addison's disease)
  • 43. • Step 1: Acidemic or Alkalemic? • Step 2: Is the primary disturbance respiratory or metabolic? • Step 3: Assess Pa O2. 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: Assess the normal compensation by the respiratory system for a metabolic disturbance
  • 44. COMPENSATION Step 5:  A patient can be uncompensated or partially compensated  pH remains outside the normal range  pH has returned within normal range  fully compensated though other values may be still abnormal
  • 45. Determine if there is a compensatory mechanism working to try to correct the pH. i.e: primary respiratory acidosis  increased PaCO2 and decreased pH. Compensation occurs when the kidneys retain HCO3.
  • 46. 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.
  • 48. Assess the HCO3 The pH and the HCO3 moving in the same directions, we would conclude that the primary disorder is respiratory and the kidneys acting as a buffer response: are compensating by retaining HCO3 to return the pH to normal range.
  • 49. Fully Compensated 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
  • 50. Partially compensated pH paco2 Hco3 Res.Acidosis Res.Alkalosis Met. Acidosis Met.Alkalosis
  • 51. Example 3: • Male patient was admitted, he was a kidney dialysis patient who has missed his last 2 appointments at the dialysis centre his ABG results: • pH : 7.32 • paCo2 : 32 • HCO3 : 18 • Pao2 : 88 Partially compensated metabolic
  • 52. Example 4: • Male patient with COPD. His ABG is: • pH : 7.35 • PaCO2 : 55 • HCO3 : 30 • PaO2 : 90 Fully compensated Respiratory Acidosis
  • 53. Quiz 1  24 years old male patient with a history of drug abuse, brought to ER cyanotic • pH 7.08 • PaCO2 80 • PaO2 37 • HCO3 24
  • 54.  24 years old male patient with of drug abuse, brought to ER cyanotic • pH 7.08 • PaCO2 80 • PaO2 37 • HCO3 24  Acidemic or Alkalemic?  Acidemic
  • 55.  24 years old male patient with a history of drug abuse, brought to ER cyanotic • pH 7.08 • PaCO2 80 • PaO2 37 • HCO3 24  pH in relation to PaCO2 and HCO3?
  • 56.  24 years old male patient with a history of drug abuse, brought to ER cyanotic • pH 7.08 • PaCO2 80 • PaO2 37 • HCO3 24  primarily respiratory
  • 57.  24 years old male patient with a history of drug abuse, brought to ER cyanotic • pH 7.08 • PaCO2 80 • PaO2 37 • HCO3 24  Is the compensation adequate?
  • 58.  PaCO2 increased by 40  For every 10 increase you would expect 1 increase in HCO3  Expected HCO3 would be ~28
  • 59. • 24 years old male patient with a history of drug abuse, brought to ER cyanotic – pH 7.08 – PaCO2 80 – PaO2 37 – HCO3 24 • Acidemic, primarily respiratory, but mild component of metabolic • Also hypoxemic • Narcotic OD
  • 60. Quiz 2  42 years old female patient with DM, presents with 4 days of unwell • pH 7.23 • PaCO2 27 • PaO2 118 • HCO3 12
  • 61. Quiz 2  42 years old female patient with DM, presents with 4days of unwell • pH 7.23 • PaCO2 27 • PaO2 118 • HCO3 12  Acidemia, metabolic  DKA, Na 135, Cl 99  AG = Na – Cl – HCO3 = 135 – 111 = 24
  • 62. Quiz 3  71 male patient with COPD, c/o SOB • pH 7.21 • PaCO2 75 • PaO2 41 • HCO3 30
  • 63.  Acidemia, resp (acute on chronic), hypoxic
  • 64. Quiz 4  23 years old female patient c/o SOB, lightheaded and perioral tingling • pH 7.54 • PaCO2 22 • PaO2 115 • HCO3 21
  • 66. Quiz 5  32 years old male patient c/o of vomiting of 5 days duration, HR 110 BP 90/50, dry mouth & mucosa • pH 7.50 • PaCO2 47 • PaO2 80 • HCO3 38
  • 68. Precautions  Excessive Heparin: Decreases bicarbonate and PaCO2  Large Air bubbles not expelled from sample PaO2 rises, PaCO2 may fall slightly.  Fever or Hypothermia, Hyperventilation or breath holding (Due to anxiety) may lead to erroneous lab results  Care must be taken to prevent bleeding
  • 69. It’s not magic understanding ABG, it just takes a little practice!