ABG

1. By M.elkhatib CIN

2.  Oxygenation.
 Ventilation.
 Acid base balance.
 Electrolytes.
 Haemoglobin.
 LACT

3.  More accurate.
 SaO2 has limitations as does pO2 but both
together provide useful information.
 Normal range (for what it is worth!) =
80-95 mm Hg.
 Different in children with cardiac lesions (usually
lower)

4.  Ventilation is assessed by looking at pCO2.
 Normal range 35-45 mm Hg.
 Hyperventilation will reduce pCO2.
 Hypoventilation will increase pCO2.
 How do we manipulate these parameters?

5.  Acidaemia – pH < 7,35
 Alkalaemia – pH > 7,45
 Acidosis – Process causing acid to accumulate
(abnormal pH not necessary)
 Alkalosis – Process causing alkali accumulation
(abnormal pH not necessary)
 pH - negative log of [H+]

6.  Normal pH is 7.35 – 7.45.
 Normal pH range is essential for cellular function
 Normal pH is maintained by the respiratory and
renal systems working together.
 Cells produce CO2 as a result of cellular
respiration.
 CO2 causes increased acidity.

7.  Renal system produces sodium bicarbonate.
Normal range = 22 -26.
 Base excess (or deficit)
The amount of acid that must be added to a litre
of blood to return the pH to 7.4 at a pCO2 of 39
mm Hg
Normal value +/- 1

8.  The body’s attempt to return the acid/base
status to normal (i.e. pH closer to 7.4) by
over or under producing bicarbonate or
CO2.
 How long does it take to compensate?
 Buffers
◦ immediate
 Lungs
◦ 10-15 min
 Kidneys
◦ 12-24 h

10.  Is the PH normal?
 Is it acidotic or alkalotic?
 Look at the oxygenation separately.
 Is it primarily respiratory or metabolic?
 Is it high LACT ?

11.  pH < 7.35
Acidosis (metabolic and/or
respiratory)
 pH > 7.45
Alkalosis (metabolic and/or
respiratory)
 paCO2 > 6.0 kPa
Respiratory acidosis
(alveolar
hypoventilation)
 paCO2 < 4.0 kPa
Respiratory alkalosis
(alveolar
hyperventilation)
 HCO3 < 22 mEq/L
Metabolic acidosis
 HCO3 > 26 mEq/L
Metabolic alkalosis

13.  paCO2 > 45, pH < 7.35 - respiratory acidosis
 paCO2 < 35, pH > 7.45 - respiratory alkalosis
Primary respiratory problem - pH & paCO2
move in opposite direction

14.  HCO3 < 22, pH < 7.35 - metabolic acidosis
 HCO3 > 26, pH > 7.45 - metabolic alkalosis
Primary metabolic problem - pH & HCO3
are in same direction, and paCO2 is also in
same direction

15.  paCO2 elevated & pH acidotic
 ↓pH accounted for entirely by ↑paCO2
 HCO3 & BE - in Normal range
◦ No adequate time for kidneys to establish effective compensatory
mechanisms
 Causes
◦ Respiratory pathophysiology
 airway obstruction
 severe pneumonia
 chest trauma
 pneumothorax
◦ Acute drug intoxication (narcotics, sedatives)
◦ Residual neuromuscular blockade
◦ CNS disease – decreased level of consciousness

16.  paCO2 low & pH alkalotic
 ↑pH accounted for entirely by ↓paCO2
 HCO3 & BE - Normal range
◦ No adequate time for kidneys to establish effective
compensatory mechanisms

17.  Causes
◦ Pain
◦ Anxiety
◦ Restrictive lung disease
◦ Severe congestive heart
failure
◦ Pulmonary emboli
◦ Sepsis
◦ Fever
◦ Overaggressive
mechanical ventilation

18.  Causes
◦ Ketoacidosis - diabetic, alcoholic, starvation
◦ Lactic acidosis - hypoxia, shock, sepsis, seizures
◦ Toxic ingestion – salicylates, methanol, ethylene glycol,
ethanol, isopropyl alcohol, paraldehyde, toluene
◦ Renal failure - uremia
ABG Interpretation 12/06/14 18

19. ◦ Renal tubular acidosis
◦ Post respiratory
alkalosis
◦ Hypoaldosteronism
◦ Potassium sparing
diuretics
◦ Pancreatic loss of
bicarbonate
◦ Diarrhea
◦ Carbonic anhydrase
inhibitors
◦ Acid administration (HCl,
NH4Cl, arginine HCl)
◦ Cholestyramine
◦ Ureteral diversions
◦ NaCl excess

20.  Causes
◦ Gastric acid loss due to vomiting or nasogastric suction
◦ Gitelman syndrome
◦ Diuretics
◦ Hypokalemia
◦ Renal failure

21.  Further evaluation of blood gas - assessment
of effectiveness of blood oxygenation
 Hypoxemia – ↓O2 content of blood
◦ paO2 < 8 kPa & SO2 < 90%
 Hypoxia – inadequate amount of O2 available
to or used by tissues for metabolic needs

22. 1. Does the patient have acidosis or alkalosis ?
◦ Look at the pH
1. What is the primary problem – metabolic or
respiratory ?
◦ Look at the pCO2
 pCO2 change in opposite direction of pH change - primary
problem is respiratory