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Prepared by NLERT Feb,2015
Make it EasyMake it EasyMake it EasyMake it Easy
The 6 steps to ABG Interpretation
Prepared by NLERT Feb,2015
HomeostatsisHomeostatsisHomeostatsisHomeostatsis
體內平衡又稱恆定狀態或恆定性"The maintenance of a constant internal
environment".
“ All living creature keeping their inside as
constant and stable operating condition as
possible, whatever may be happening on the
outside”
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Example homeostatis in human bodyExample homeostatis in human bodyExample homeostatis in human bodyExample homeostatis in human body
�Acid-base (pH) balance, body temperature,
Calcium and Phosphate level, blood glucose, fluid
volume, blood pressure etc.
Prepared by NLERT Feb,2015
Prepared by NLERT Feb,2015
Importance of acid base (pH) balanceImportance of acid base (pH) balanceImportance of acid base (pH) balanceImportance of acid base (pH) balance
� If the pH changes whether up or
down:
1. protein and enzymes becomes stop
functioning.
2. muscles and nerves becomes
weakening.
3. metabolic activities becomes
impaired.
4. blood pH below 6.9 or above 7.9 would
be life threatening.
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Carbonic acid Carbonic acid Carbonic acid Carbonic acid ----Bicarbonate Bicarbonate Bicarbonate Bicarbonate
Buffering SystemBuffering SystemBuffering SystemBuffering System�A major buffer system in the acid-base balance.
�To alter any acid base imbalance thus maintain a
constant plasma pH.
�Base on carbonic acid equilibrium equation and involve
2 systems: lung and kidney
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Carbonic acid Carbonic acid Carbonic acid Carbonic acid ----Bicarbonate Bicarbonate Bicarbonate Bicarbonate
Buffering SystemBuffering SystemBuffering SystemBuffering System� The way of 2 systems interact is through the formation of
carbonic acid (H2CO3).
� Movement through the carbonic acid system is tend
maintain a equilibrium status.
� If necessary, H2CO3 can break up to form either H+ and
HCO3 or CO2 and H2O
� The system works in both directions.
� By balancing back and forward, a normal pH is achieved.
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Renal mechanisms
�Can eliminate large amounts of acid (H+)
�Excretion or retention of base (HCO3-)
�Can reserve and produce bicarb ions
HCO3 ion + Na ion NaHCO3
�Most effective regulator of pH but slow
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Respiratory mechanisms
�Exhalation of carbon dioxide
�Excretion and retention of CO2
�Adjust body pH by changing rate and
depth of breathing
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Response to acidosis
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Response to alkalosis
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Acidosis and alkalosis: Acidosis and alkalosis: Acidosis and alkalosis: Acidosis and alkalosis:
There are two abnormalities of acid-base
balance:
� Acidosis: Too much acid or too little base,
resulting in a decrease in blood pH<7.35
� Alkalosis: Too much base or too little acid,
resulting in an increase in blood pH>7.45
Metabolic or Respiratory Metabolic or Respiratory Metabolic or Respiratory Metabolic or Respiratory
acid base imbalanceacid base imbalanceacid base imbalanceacid base imbalance
�Acidosis and alkalosis are categorized as metabolic
or respiratory
�Depends on their primary cause. 1. Metabolic acidosis and metabolic alkalosis are caused by
an imbalance acids or bases production or excretion by the
kidneys.
2. Respiratory acidosis and respiratory alkalosis are caused
by amount of carbon dioxide exhalation due to lung or
breathing disorders.
Cause of Respiratory AcidosisCause of Respiratory AcidosisCause of Respiratory AcidosisCause of Respiratory Acidosis
�Lung diseases e.g. COPD, asthma or pneumonia.
�Airway obstruction e.g. swelling, sputum retention.
�Drugs (anesthetics, sedatives, and narcotics)
induce respiratory depression.
�Neuromuscular diseases impair breathing effort.
�Chest wall desfunction or deformities.
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Cause of Metabolic AcidosisCause of Metabolic AcidosisCause of Metabolic AcidosisCause of Metabolic Acidosis
�DKA (metabolism of amino acid ����ketoacidosis)
�Lactic acidosis (anaerobic metabolism during heavy exercise, hypoxia or CPR)
�Chronic renal failure
�Diarrhea (excreted large amounts of bicarbonate).
�DO: methanol or excessive salicylate drug (aspirin)
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Cause of Respiratory AlkalosisCause of Respiratory AlkalosisCause of Respiratory AlkalosisCause of Respiratory Alkalosis
�Hyperventilation (rapid, deep breathing)
�Mechanical overventilation
�Anxiety
�Fever
�Sepsis
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Cause of Metabolic AlkalosisCause of Metabolic AlkalosisCause of Metabolic AlkalosisCause of Metabolic Alkalosis
�Loss of H ions from the GI tract (free drain of R/T,
R/D, vomiting, nasal gastric suctioning).
�Diuretics use such as Frusemide.
�Excessive NaHCO3 use.
�Massive blood transfusion (metabolism of
citrate��������HCO3)
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CompensationCompensationCompensationCompensation�Our body regulates pH by using the opposing
system to balance pH.
�It involves 2 opposing system :
�Respiratory system
�Renal system
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CompensationCompensationCompensationCompensation
� If pH is out of balance because of primary respiratory
disorder.
� Renal system will make the corrections of pH.
�If the renal system is the primary cause of pH disorder.
�Respiratory system will make the corrections of pH.
This is called compensation.
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Indications of ABGIndications of ABGIndications of ABGIndications of ABG
1. Assess respiratory function: PaO2, PaCO2
2. Assess metabolic status (Acid-Base)
3. Assess any electrolyte imbalance
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Factors affecting ABG resultsFactors affecting ABG resultsFactors affecting ABG resultsFactors affecting ABG results
1. Temperature
2. The presence of air bubbles in ABG sample
3. Excessive heparin sodium in the sample
4. Clotted sample
5. Time between taken and analysis
6. Site of sampling (venous, arterial)
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pH 7.35-7.45
pCO2 35-45mmHg or
4.7 -6 kPa
pO2 80-100mmHg or
10.3-13.3 kPa
O2 saturation 95-100%
HCO3- 22-26mEq/L
Base Excess + 2
Normal rangeNormal rangeNormal rangeNormal range
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TestTestTestTest NormalNormalNormalNormal ↓ ↓ ↓ ↓ ValueValueValueValue ↑ ↑ ↑ ↑ ValueValueValueValue
pHpHpHpH 7.357.357.357.35----7.457.457.457.45 AcidosisAcidosisAcidosisAcidosis AlkalosisAlkalosisAlkalosisAlkalosis
pCO2pCO2pCO2pCO2 35353535----45mmHg45mmHg45mmHg45mmHgOrOrOrOr
4.74.74.74.7----6Kpa6Kpa6Kpa6Kpa
AlkalosisAlkalosisAlkalosisAlkalosis AcidosisAcidosisAcidosisAcidosis
HCO3HCO3HCO3HCO3 22222222----26 26 26 26 mEqmEqmEqmEq/L/L/L/L AcidosisAcidosisAcidosisAcidosis AlkalosisAlkalosisAlkalosisAlkalosis
pO2pO2pO2pO2 80808080----100 mmHg100 mmHg100 mmHg100 mmHg HypoxemiaHypoxemiaHypoxemiaHypoxemia ________________________________
SaO2 SaO2 SaO2 SaO2 95959595----100%100%100%100% HypoxemiaHypoxemiaHypoxemiaHypoxemia ________________________________
↓
↓
↓ ↑
↑
↑
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6 Easy Steps to ABG 6 Easy Steps to ABG 6 Easy Steps to ABG 6 Easy Steps to ABG
InterpretationInterpretationInterpretationInterpretation
(1)Is the pH normal?
(2)Is the CO2 normal?
(3)Is the HCO3 normal?
(4)Match the CO2 or HCO3 with the pH?
(Identifying primary cause)
(5)Does the CO2 or HCO3 in the opposite direction
of the pH?
(Compensation)
(6)Are the PaO2 and SaO2 normal?
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Step 1: pH analysisStep 1: pH analysisStep 1: pH analysisStep 1: pH analysis
�Normal range of blood pH: 7.35 to Normal range of blood pH: 7.35 to Normal range of blood pH: 7.35 to Normal range of blood pH: 7.35 to
7.457.457.457.45
�pH < 7.35 is acidicpH < 7.35 is acidicpH < 7.35 is acidicpH < 7.35 is acidic
�pH. > 7.45 is alkaloticpH. > 7.45 is alkaloticpH. > 7.45 is alkaloticpH. > 7.45 is alkalotic
Prepared by NLERT Feb,2015
Step 2: CO2 analysisStep 2: CO2 analysisStep 2: CO2 analysisStep 2: CO2 analysis
�Normal pCO2 level: 35-45mmHg
�Below 35mmHg or 4.7Kpa is alkalosis
�Above 45mmHg or 6Kpa is acidosis
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Step 3: HCO3 analysisStep 3: HCO3 analysisStep 3: HCO3 analysisStep 3: HCO3 analysis
�Normal HCO3 level is 22Normal HCO3 level is 22Normal HCO3 level is 22Normal HCO3 level is 22----26 mEq/L26 mEq/L26 mEq/L26 mEq/L
�Below 22 mEq/L is acidosisBelow 22 mEq/L is acidosisBelow 22 mEq/L is acidosisBelow 22 mEq/L is acidosis
�Above 26 mEq/L is alkalosisAbove 26 mEq/L is alkalosisAbove 26 mEq/L is alkalosisAbove 26 mEq/L is alkalosis
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Step 4: Match CO2 and HCO3 Step 4: Match CO2 and HCO3 Step 4: Match CO2 and HCO3 Step 4: Match CO2 and HCO3
with the pH levelwith the pH levelwith the pH levelwith the pH level
�Match either PCO2 and HCO3 with pH level to
determine the primary cause of acid-base
disorder
� If primary acid base disorder caused by
respiratory, CO2 level is opposite to pH level
� If Primary acid base disorder caused by
metabolic, HCO3 level is equal to pH level
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MatchingMatchingMatchingMatchingRespiratory (Primary cause)
pH↓PCO2↑ Respiratory acidosis
pH↑PCO2↓ Respiratory Alkalosis
Metabolic (Primary cause)
pH↓HCO3↓Metabolic acidosis
pH↑HCO3↑Metabolic alkalosis
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Opposite
Equal
Mixed acid base disorder
� That means more than one primary acid base
disturbance at the same time. (particularly in
critically illness).
For example
COPD patient who develops shock and lactic acidosis
pH↓ CO2 ↑HCO3↓and matched with primary cause
=> Mixed acidosis
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Step 5: Does CO2 or HCO3 go to the
opposite direction of pH
(determinate the compensation)
�Either CO2 or HCO3 go to the opposite direction of pH, that means compensation in progress.
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Primary system causing imbalance Compensating system
Respiratory (pCO2↑) acidosis Metabolic (HCO3 ↑)
Respiratory (pCO2↓) alkalosis Metabolic (HCO3↓)
Metabolic (HCO3 ↓) acidosis Respiratory (pCO2↓)
Metabolic (HCO3 ↑) Alkalosis Respiratory (pCO2↑)
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Respiratory system Respiratory system Respiratory system Respiratory system
compensationcompensationcompensationcompensation
� Respiratory system balances pH by ↑ or ↓ RR to
manipulating the CO2 level.
� Fast and deep breathing “blows off” CO2 in
primary metabolic acidosis.
� Slow and shallow breathing “retains” CO2 in
primary metabolic alkalosis.
The process is fast.
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Renal System Renal System Renal System Renal System
CompensationCompensationCompensationCompensation
�Primary respiratory alkalosis:Primary respiratory alkalosis:Primary respiratory alkalosis:Primary respiratory alkalosis:
KidneyKidneyKidneyKidney▶▶▶▶▶▶▶▶▶▶▶▶Excreting more HCO3Excreting more HCO3Excreting more HCO3Excreting more HCO3---- in in in in
urine and retaining more H+ urine and retaining more H+ urine and retaining more H+ urine and retaining more H+
�Primary respiratory acidosis:Primary respiratory acidosis:Primary respiratory acidosis:Primary respiratory acidosis:
KidneyKidneyKidneyKidney▶▶▶▶▶▶▶▶▶▶▶▶Excreting more H+ in urine Excreting more H+ in urine Excreting more H+ in urine Excreting more H+ in urine
and retaining more HCO3and retaining more HCO3and retaining more HCO3and retaining more HCO3----
The process is slow The process is slow The process is slow The process is slow
but more powerful.but more powerful.but more powerful.but more powerful.
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Partial/Complete Partial/Complete Partial/Complete Partial/Complete
compensationcompensationcompensationcompensation�Compensation may not always be Compensation may not always be Compensation may not always be Compensation may not always be
complete and time consuming. complete and time consuming. complete and time consuming. complete and time consuming.
� If pH remains abnormal, it is partial If pH remains abnormal, it is partial If pH remains abnormal, it is partial If pH remains abnormal, it is partial
compensation.compensation.compensation.compensation.
� If pH returns to normal range, the If pH returns to normal range, the If pH returns to normal range, the If pH returns to normal range, the
compensation is complete. compensation is complete. compensation is complete. compensation is complete.
NoteNoteNoteNote
Nothing to do = no compensationNothing to do = no compensationNothing to do = no compensationNothing to do = no compensation
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Step 6: Analysis pO2 and O2 Step 6: Analysis pO2 and O2 Step 6: Analysis pO2 and O2 Step 6: Analysis pO2 and O2
saturation saturation saturation saturation
�Evaluate the PaO2 and O2 saturation. If
they are below normal there is evidence of
hypoxemia.
�PaO2 (80-100mmHg or 10.3-13.3 kPa).
�SaO2 (95~100%).
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ABG quiz
1. Metabolic Acidosis has a low level of
what?
A: PO2
B: CO2
C: Compensated Respiratory Acidosis
D: Bicarbonate (HCO3)
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2. pH=7.18 PaCO2=68 HCO3=29
A: Uncompensated Metabolic Acidosis
B: Partly compensated respiratory acidosis
C: Combined Acidosis
D: Uncompensated respiratory Acidosis
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3.Decrease HCO3 and decrease pH may
causes what?
A: Uncompensated
B: Increase arterial PO2
C: It will lower the pH
D: Metabolic Acidosis
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4.The primary drive to breath comes from
the patient?
A: Acidosis
B: Bicarbonate (HCO3)
C: Uncompensated Metabolic Acidosis
D: CO2 level
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5. A high CO2 will impact the pH?
A: Lower the pH value (acidosis)
B: Bicarbonate (HCO3)
C: Increase arterial PO2
D: Metabolic Acidosis
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6. pH = 7.56 CO2 = 50 HCO3 = 38
A: Normal
B: Respiratory alkalosis without
compensation
C: Partly compensated metabolic alkalosis
D: Metabolic alkalosis
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7. pH = 6.96 CO2 = 71 HCO3 = 16
A: Metabolic alkalosis
B: Normal
C: Mixed acidosis
D: Compensated acidosis
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8. Interpret this blood gas
pH=7.50 PaCO2=60 HCO3=38
A: Combined acidosis
B: Partly compensated metabolic Alkalosis
C: Bicarbonate (HCO3)
D: Increase ventilation
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9. pH = 7.16 CO2 = 82 HCO3 = 29
A: Metabolic acidosis
B: Partly compensated metabolic alkalosis
C: Respiratory alkalosis
D: Partly compensated respiratory acidosis
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10. pH = 7.50 CO2 = 9 HCO3 = 7
A: Partly compensated respiratory
alkalosis
B: Respiratory alkalosis
C: Metabolic alkalosis
D: Partly compensated metabolic alkalosis
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11. pH = 7.75 CO2 = 29 HCO3 = 40
A: Combined acidosis
B: Mixed alkalosis
C: Compensated respiratory acidosis
D: Compensated metabolic alkalosis
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12. pH = 7.33 CO2 = 66 HCO3 = 35
A: Compensated respiratory acidosis
B: Metabolic alkalosis
C: Metabolic acidosis
D: Partly compensated respiratory acidosis
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13. pH = 6.68 CO2 = 85 HCO3 = 10
A: Combined alkalosis
B: Compensated respiratory alkalosis
C: Mixed acidosis
D: Metabolic respiratory acidosis
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14. pH = 7.35 CO2 = 42 HCO3 = 23
A: Combined alkalosis
B: Normal
C: Combined acidosis
D: Partly compensated metabolic acidosis
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15. pH = 7.21 CO2 = 60 HCO3 = 24
A: Respiratory acidosis without
compensation
B: Compensated metabolic alkalosis
C: Compensated respiratory acidosis
D: Compensated respiratory alkalosis
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16. pH = 7.48 CO2 = 19 HCO3 = 14
A: Normal
B: Respiratory acidosis
C: Compensated metabolic acidosis
D: Partly compensated respiratory
alkalosis
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ReferenceReferenceReferenceReference
� Irwin RS & Rippe JM 2011 Irwin and Rippe’s Intensive Care Medicine (7th edition) Lippincott Williams & Wilkins: Philadelphia
� Domino FJ 2013 The 5-Minute Clinical Consult 21st Edition Lippincott Williams & Wilkins: Philadelphia
� Nettina SM 2010 Lippincott Manual of Nursing Practice (9th edition). Lippincott Williams & Wilkins: Philadelphia
� Carpenito-Moyet LJ 2009 Nursing Care Plans and Documentation: Nursing Diagnosis and Collaborative Problems (5th Edition). Lippincott Williams & Wilkins: Philadelphia
Prepared by NLERT Feb,2015
Prepared by NLERT Feb,2015