THIS PRESENTATION WILL COVER THE FOLLOWING AREAS Definitions Buffer systems Regulatory systems Anion Gap and Osmolar gap Metabolic acidosis Metabolic alkalosis Respiratory acidosis Respiratory alkalosis

1. ACID BASE IMBALANCE
PRESENTER: DR. ORIBA DAN LANGOYA
TUTOR: DR. PEACE BAGASHA,
NEPHROLOGIST
27TH NOV, 2021

2. OBJECTIVES
• Definitions
• Buffer systems
• Regulatory systems
• Anion Gap and Osmolar gap
• Metabolic acidosis
• Metabolic alkalosis
• Respiratory acidosis
• Respiratory alkalosis

3. Definitions
• Hydrogen ion: proton released from a hydrogen atom
• Acid: molecule containing hydrogen atoms that release
hydrogen ions
• Base: An ion or a molecule that can accept an H+.
• Acidosis: Excess addition of H+ ions into body fluids.
• Alkalosis: Excess removal of H+ ions from body fluids.
• Buffer: any substance that reversibly binds H+.

4. • pH and hydrogen ions are related by the equation:
• Normal pH of arterial blood and interstitial fluid is 7.4
• Venous blood 7.35 (extra CO2 released from tissues forms
carbonic acid)
• Intracellular pH: ranges from 6-7.4 (metabolism leads to acid
production)
• Urine pH ranges from 4.5-8

5. Regulation of hydrogen ions
Done by three major systems
o Chemical acid base buffer systems of body fluids
o The respiratory system
o The kidneys

6. Chemical acid buffer system
• Buffer is a substance that binds hydrogen ions
reversibly
• Buffer systems include: bicarbonate, phosphate
and proteins
Bicarbonate buffer system
• Involves; weak H2CO3 and NaHCO3

7. Chemical acid buffer system
Phosphate buffer
• Plays a role in buffering renal tubular fluid and intracellular fluid
Consists of H2PO4 and HPO4
• If strong acid is added; ↑H+ are buffered by HPO4 to form
H2PO4–(weak acid) decreasing pH
If strong base is added; OH- is buffered by H2PO4 to form
HPO4 (weak base) +H2O

8. Chemical acid buffer system
Proteins
• present in cells
• 60-70% of chemical buffer occurs intracellularly due to
proteins.
• Commonly is Hb combine with H+ to form HHb
• All the buffer systems work together, hydrogen ion is common
to reactions of all systems
• Whenever there is a change in H ion concentration in ECF, the
balance of all buffer systems changes at the same
time(isohydric principle)

9. Acid base disorders
• Based on Henderson-Hasselbalch equation

10. Anion Gap
o Gauge of the unmeasured anions in the blood stream,
majority of unmeasured anions in blood is albumin
o Na+ and cations = HCO-3 and Cl- and anions
AG= (Na+) - (HCO-3 + Cl- )
o Normal range 8-12 mmol/l

11. Albumin-corrected Anion Gap
Anion Gap + 2.5 × (Normal albumin – Measured
albumin g/dl)

12. Metabolic acidosis
• Decreased serum HCO3
• Decreased pH and ↓ PCO2 [resp compensation]
Acute: Pco2 =(1.5)(HCO3)+8
Chronic: Pco2=(HCO3)+15
• Compensation; increased ventilation facilitate decrease in PCO2,
reduce hydrogen ions
• Addition of new bicarbonate from the kidneys.

13. Types of metabolic acidosis
Normal Anion gap acidosis- diarrhoea, RTA
ureterosigmoidostomy
Decreased Anion gap acidosis-Myeloma, hypoalbuminemia
Increased Anion gap acidosis- LA MUD PIE

14. Increased anion gap acidosis
o Calculation of the corrected bicarbonate is helpful in assessing
the possible presence of coexisting normal anion gap metabolic
acidosis/metabolic alkalosis
o Corrected bicarbonate = 24mEq/l – Δ Anion gap mEq/l
o Δ Anion gap = increase in albumin-corrected anion gap above normal
o Measured bicarbonate < Corrected bicarbonate = concomitant
normal AG metabolic acidosis
o Measured bicarbonate > Corrected bicarbonate = concomitant
metabolic alkalosis

15. Osmolar Gap
In patients with increased anion gap acidosis calculation of
Osmolar gap is useful in accessing the presence of unmeasured
solutes e.g. methanol, Ethelene glycol
 Osmolar gap = Measured OG – calculated OG
 Calculated OG = 2 × serum Na + plasma Glucose/18 + BUN/2.8
Osmolar gap > 10 = Elevated OG (presence of unmeasured
solutes)

17. Metabolic alkalosis
• Increase in serum HCO3 , loss of H ions
• Compensation; decreased ventilation to increase
PCO2 therefore H ions
o For every ↑ 1.0mmol/l in HCO3 there is a ↑
0.7mmHg of Pco2
• In kidneys increase filtered HCO3 from serum,
increase bicarbonate excretion.

19. Acid base disorders
Respiratory acidosis
• Caused by decreased ventilation and increased PCO2
• Decreased ventilation results in increased PCO2
reacts with H ions to form H2CO3
• Compensation; increase plasma bicarbonate, adding
new HCO3 from kidneys

20. Causes of respiratory acidosis
Inadequate ventilation e.g. ↓ respiratory drive,
neuromuscular dysfunction and musculoskeletal
dysfunction
Impaired arterial-alveolar gas exchange e.g.
pneumonia, haemothorax, pleural effusion, ARDS
Airway obstruction e.g. Asthma , COPD

21. Respiratory alkalosis
• Low PCO2,
• Compensation; decreased H Ion secretion In urine.
• Reduced H ion to combine with HCO3 so its
excreted in urine

22. Causes of Respiratory Alkalosis
o Enhanced respiratory drive e.g. sepsis, psychosis,
anxiety
o Hypoxemia e.g. high altitude, severe anaemia
o Pulmonary disease with thoracic stretch receptor
stimulation e.g. pneumonia, ARDS, haemothorax

23. APPROACH TO ABGS
• PH
• PACO2
• HCO3
• ANION GAP
• DELTA RATIO

24. Summary
1. PH 7.44, PCO2=56, HCO3=37
2. PH 7.29, PCO2=58 , HCO3=22
3. PH 7.32, PCO2=34, HCO3=14, Na, 135, cl-109
4. PH 7.25, PCO2=25, HC03=10, Na=140,CL 77,
5. PH 7.26, PCO2= 58 HCO3=29
6. PH 7.28, PCO2=26,HCO3= 11, NA=129, CL-100

25. Treatment
• Correct underlying cause
• Neutralize excess acid or base in serum
Excess acid – use NaHCO3, Na lactate or gluconate
Excess base – use ammonium chloride, lysine
monohydrochloride

26. References
• Guyton and Hall; Textbook of Medical Physiology;
11th Edition, 2006
• MKSAP 17.