this is a lecture I used for ABG analysis for nurses...sources not included...typographycal.

1. ACID-BASE
IMBALANCES
Nick Alfaro

2. OBJECTIVES
after the completion of this concept you should be
able to:
• Characterize an acid and a base
• Describe the intracellular and extracellular
mechanisms for buffering changes in body pH
• Compare the role of the kidneys and
respiratory system in regulation of acid-base
balance
• Identify the causes of acid-base imbalances
• Analyze an ABG result

3. ACID-BASE CHEMISTRY
• ACID : a molecule that can release an H+
ion
• BASE : molecule that can accept or
combine with H+ ion
• Acid + water = dissociation H+ (+) anion
• CARBONIC ACID :the most important acid
• BICARBONATE : the most important base

4. Hydrogen ion
• Expressed in terms of pH
– The negative logarithm (p) of H+ ion concentration
in equivalents per liter
– Example : pH 7.0
• hydrogen ion concentration of 10 (negative power of 7)
equivalents per liter (mEq/L)
• pH is inversely related to H+ ion concentration:
– Low pH = high H+ ion concentration
– High pH = low H+ ion concentration

5. Metabolic acid and bicarbonate
production
• Acids are byproducts of metabolic processes
• 2 GROUPS OF ACIDS
– Volatile acids : carbonic acid (H2CO3)
• Leaves the body through the lungs
– Nonvolatile/fixed acids : sulfuric acids,
hydrochloric, phosphoric
• Source ; metabolism of dietary proteins
• Buffered by body proteins or bicarbonate
• Excreted by the kidney

6. • Lactic acid : incomplete oxidation of
glucose
• Ketoacids : incomplete oxidation of fats

7. • MAJOR SOURCE OF BASE:
– Metabolism of amino acids ( aspartate and
glutamate)
– Metabolism of anions ( citrate, lactate,
acetate)

8. Carbon dioxide and
bicarbonate
PRODUCTION

9. CARBON DIOXIDE
• TRANSPORTED IN 3 FORMS
– Attached to hemoglobin
– Dissolved CO2
• Combines with water in the blood streamcarbonic acid
(H2CO3)
– Catalyzed by CARBONIC ANHYDRASE
– As bicarbonate
• CARBONIC ANHYDRASE
– Present in RBC, renal tubular`cells, other tissues in the body
• to calculate H2CO3:
– CO2 X .03 = _____ H2CO3
– EXAMPLE : PCO2 45 mmHg X 0.03 = 1.35 mEq/L

10. Sequence of events
1. CO2 produced by tissue
diffuses to interstitial fluid
2. CO2 diffuses into plasma
3. CO2 diffuses into RBC
4. Some CO2 picked up by Hb
5. Most CO2 reacts with water to
form carbonic acid-carbonic
anhydrase
6. Carbonic acid dissociates into
H+ and bicarbonate
7. Proton picked up by Hb
preventing acidifying blood
8. Bicarbonate diffuses into
plasma
9. Bicarbonate carried to lungs

11. 10.Bicarbonate diffuses
into RBC
11. H+ released from Hb
combines with
bicarbonate to form
carbonic acid
12. CO2 formed from
carbonic acid and
unloaded from Hb.
Diffuses out of blood
into interstitial fluid
13.CO2 diffuses into
alveolar space of lung

12. Regulation of pH
• Intracelular/extracellular
• Lungs kidneys
• Carbon dioxide conserve HCO3
excrete excess H+

13. Chemical buffer systems
• Buffer is a substance that act as a chemical sponge. It
soaks up or release H ions to maintain stable Ph
• ACTION TIME OF CHEMICAL BUFFER SYSTEM :
INSTANTANEOUS
• CARBONIC ACID-BICARBONATE BUFFER
SYSTEM
– Present in ECF
– Carbonic acid is formed by the combination of carbon dioxide
and water (CO2+H2O=H2CO3)
– 20 parts bicarbonate : 1 part carbonic acid
– Maintained by lungs and kidney

14. • PHOSPHATE BUFFER SYSTEM
– Present in cells and ECF
– Activate in the kidneys
• PROTEIN BUFFER SYSTEM
– Present in plasma and in cells
– Albumin and plasma globulins are the major
protein buffers in the vascular compartment
– Hgb is one of the proteins involved
– Most plentiful buffer system

15. Respiratory control of pH
action time : minutes to hours
• Dec. in pH (more acid)
• Inc. RR and depth
• Inc. excretion of CO2
• alkalinity

16. • Inc. pH (more alkaline)
• Dec. RR and depth
• Retention of CO2
• acidity

17. Renal regulation of pH
• Controls bicarbonate concentration in
ECF
• H ions can be exchanged for Na and K
ions in the renal tubules
• Excretion or conservation of hydrogen
ions can result in imbalances of Na and K
• Action time : hours to days

18. ABG ANALYSIS
• NORMAL VALUES
• Blood pH 7.35-7.45
• pO2 80-100 mmHg
• pCO2 35-45 mmHg
• HCO3 22-26 mEq/L
• BE / BD ± 2

19. DRAWING OF ARTERIAL BLOOD SAMPLE FOR ABG
USING RADIAL ARTERY

20. Basic knowledge in interpretation
• If pH and pCO2 are primarily affected,
respiratory acid-base imbalances will occur
• If pH and HCO3 are primarily affected,
metabolic acid-base will be experienced
• The kidneys and lungs attempt to compensate
one another in maintaining acid-base balance
• In acid-base imbalances, the normal
bicarbonate-carbonic acid ratio of 20:1 is lost.
The body attempts to compensate in an effort
to maintain the normal 20:1 ratio

21. • In compensation, the kidneys attempt to
compensate for changes in blood CO2 by
making a corresponding adjustment in blood
bicarbonate. Normally, almost all the
bicarbonate formed by the kidneys are retained
• The lungs attempt to compensate for abnormal
changes in blood bicarbonate by making
corresponding adjustment in blood CO2
• Another compensatory mechanism for acid-
base imbalances is shifting of hydrogen ions
from the ECF to the ICF or vice versa

22. Shifting of hydrogen ions
• Inc. H ions (metabolic acidosis)
• H ions shift into ICF
• K moves out from ICF
• Inc. K (hyperkalemia)

23. • Dec. H ions ( metabolic alkalosis)
• H ions shift out from ICF
• K moves into ICF
• Dec. K (hypokalemia)

24. METABOLIC ACIDOSIS
• IMPAIRED ELIMINATION OF
METABOLIC ACID
– Kidney failure
• EXCESS PRODUCTION OF METABOLIC
ACIDS
– Diabetic ketoacidosis
– Fasting and starvation
– Poisoning (salicylate, methanol, ethylene glycol)

25. Metabolic acidosis
• EXCESS BICARBONATE LOSS
– Diarrhea
– Intestinal suction
– Hyperaldosteronism (CUSHING SYNDROME)
• INCREASED CHLORIDE LEVEL
– Excess reabsorption of chloride by the kidney
– Parenteral hyperalimentation

26. METABOLIC ALKALOSIS
• EXCESS GAIN OF BICARNONATE
– Administration of sodium bicarbonate
– Blood transfusion (citrate-containing)
• EXCESS LOSS OF HYDROGEN ION
– Vomiting
– Gastric suction
– Diuretic therapy (potassium deficit)
– Hyperaldosteronism
– Loss of body fluid

27. RESPIRATORY ACIDOSIS
• DEPRESSION OF RESPIRATORY CENTER
– Drug overdose
– Head injury
• LUNG DISEASE
– COPD
– Pneumonia
– Pulmonary edema
– Respiratory distress syndrome
• AIRWAY OBSTRUCTION/DISORDER OF CHEST WALL
AND RESPIRATORY MUSCLE
– Chest injuries
– Extreme obesity
– Respiratory muscle paralysis
• BREATHING AIR WITH HIGH CO2 CONTENT

28. RESPIRATORY ALKALOSIS
• EXCESSIVE VENTILATION
– Anxiety and psychogenic hyperventilation
– Hypoxia and reflex stimulation of ventilation
– Stimulation to respiratory center
• Elevated blood ammonia level
• Salicylate toxicity
• Encephalitis
• fever
• MECHANICAL VENTILATION

29. interpretations
• pH
• < 7.35
• acidosis
• > 7.45
• alkalosis
• pCO2 (RESPIRATORY SIDE)
• < 35
• alkalosis
• >45
• acidosis
• HCO3 (METABOLIC SIDE)
• < 22
• acidosis
• >26
• alkalosis

30. 4. Determine the extent of
compensation
• ABSENT: the value that does not match the
acid-base status of the pH is normal
• PARTIAL: both the value that doesn’t match
the acid-base status of the pH and the pH itself
are abnormal
• COMPLETE: the value that doesn’t match the
acid-base status is abnormal but the pH is
normal

31. Interpret the following
• 1. pH 7.60, PaCO2 25, HCO3 24
• Respiratory alkalosis, uncompensated
• 2. pH 7.49, PaCO2 48, HCO3 38
• Metabolic alkalosis partially compensated
• 3. pH 7.36, PaCO2 66, HCO3 35
• Respiratory acidosis completely compensated

32. • 4. pH 7.45, PaCO2 47, HCO3 34
• Metabolic alkalosis completely compensated
• 5. pH 7.25 PaCO2 60, HCO3 26
• Respiratory acidosis uncompensated

33. • 6. pH 7.45 PaCO2 47 HCO3 34
• 7. pH 7.30 PaCO2 30 HCO3 19
• 8. pH 7.32 PaCO2 34 HCO3 17
• 9. pH 7.52 PaCO2 49 HCO3 40
• 10. pH 7.33 PaCO2 55 HCO3 29

34. • 6. pH 7.45 PaCO2 47 HCO3 34
• Alkalosis metabolic completely compensated
• 7. pH 7.30 PaCO2 30 HCO3 19
• Acidosis metabolic partially compensated
• 8. pH 7.32 PaCO2 34 HCO3 17
• Acidosis metabolic partially compensated
• 9. pH 7.52 PaCO2 49 HCO3 40
• Alkalosis metabolic partially compensated
• 10. pH 7.33 PaCO2 55 HCO3 29
• Acidosis respiratory partially compensated