This document discusses acid-base balance and interpreting blood gas results. It defines terms like acidosis, alkalosis, respiratory acidosis, and metabolic alkalosis. It provides normal ranges for pH, pCO2, HCO3, and base excess. Causes of different acid-base imbalances are outlined, such as respiratory acidosis resulting from alveolar hypoventilation or metabolic acidosis from ketoacidosis. The document concludes with instructions to first examine the pH to determine if acidosis or alkalosis is present, then examine pCO2 to determine if the primary problem is respiratory or metabolic based on the relationship between pH and pCO2 changes.

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