1. Acid-Base Imbalance

2. What is pH? pH is the concentration of hydrogen (H+) ions
The pH of blood indicates the net result of normal acid-base regulation, any acid-base imbalance, and the body’s compensatory mechanisms
The human body must maintain a very narrow pH range

3. What is pH? In terms of the human body:
acidosis< >alkalosis
Carbon dioxide is the “acid” (CO2)
Normal: mmHg
Bicarbonate is the “base” (HCO3)
Normal: mEq/L

4. How does the body maintain pH?
Buffer systems
Prevent major changes in pH by removing or releasing a hydrogen (H+) ion
Act chemically to change strong acids into weaker acids or to bind acids to neutralize their effects
Carbonic acid (H2C03) buffer system neutralized hydrochloric acid
2. Phosphate buffer system neutralizes strong acids

5. How does the body maintain pH?
Buffer systems
Intracellular and extracellular proteins act as buffer systems
The cell can act as a buffer by shifting hydrogen in and out of the cell

6. How does the body maintain pH?
Kidneys
Regulate bicarbonate in the ECF
The kidneys will retain or excrete H+ ions or HCO3 ions as needed
Normally acidic urine
Lungs
Control CO2
Adjust rate and depth of ventilation in response to amount of CO2 in the blood
A rise in arterial blood CO2 stimulates respiration
Oxygen content of arterial blood will also stimulate respiration

7. Acidosis and Alkalosis
Metabolic acidosis
Decreased HCO3 or increase in other acids
Metabolic alkalosis
Increased HCO3 and excess loss of acids
Respiratory acidosis
Increased PaCO2 due to hypoventilation
Respiratory alkalosis
Decreased PaC02 due to hyperventilation

8. Imbalances Imbalances in PaCO2 are influenced by respiratory causes
Imbalances in HCO3 are influenced by metabolic processes

12. Metabolic Acidosis Low pH (<7.35) Low HCO3 (<22 mEq/L)
Body may attempt to compensate by increasing respirations to decrease CO2
High anion gap acidosis
Results from excessive accumulation of fixed acid
Normal anion gap acidosis
Results from direct loss of bicarbonate

14. Metabolic acidosis Primary feature is decrease in serum HCO3
Hyperkalemia may also occur due to shift of potassium out of the cells
Hypokalemia may occur once the acidosis is corrected
Treatment is aimed at correcting the metabolic defect
IV bicarbonate
Potassium management
Dialysis

15. Metabolic Alkalosis High pH (>7.45) High serum HCO3 (>26)
Body may attempt to compensate by decreasing respirations to increase CO2
Treatment is aimed at treating the underlying disorder
Chloride supplementation
Restore normal fluid volume
Maintain potassium
Carbonic anhydrase inhibitor if unable to tolerate volume resuscitation

17. Respiratory Acidosis Low pH (<7.35) High serum CO2 (>42)
Body may attempt to compensate through renal retention of HCO3 (does not happen quickly - hours to days)
Chronic respiratory acidosis occurs with chronic pulmonary disease (eg, emphysema, OSA)
Pt. will often be asymptomatic, as the body has time to compensate
Acute respiratory acidosis may be severe and will produce symptoms

18. Respiratory Acidosis
Treatment is directed at improving ventilation --> treat the underlying cause
Pulmonary hygiene to clear respiratory tract
Adequate hydration to help clear secretions
Supplemental oxygen
Adjustment of mechanical ventilation as appropriate

20. Respiratory Alkalosis
High pH (>7.45)
Low PaCO2 (<35)
Always due to hyperventilation
Body may compensate through increased kidney excretion of bicarbonate (does not happen quickly - hours to days)
Treatment is aimed at correcting the cause of hyperventilation
If anxiety-related, may breathe into a closed system (rebreathe CO2)

22. Interpreting Arterial Blood Gases
pH ( )
PaO2 ( mmHg on room air)
O2 saturation (95-100%)
PaCO2 (35-45 mmHg)
HCO3 (22-26 mEq/L)
Base excess (or deficit) (+2 to -2 mEq/L)
Sum of bases (alkalis)

23. Interpreting Arterial Blood Gases
1. Determine if acidosis or alkalosis
*use 7.40 as normal in this step
2. Determine the component that caused the abnormality in step 1
3. Determine if the gas is compensated
If the pH is , it is compensated
If the pH is <7.35 or >7.45, it is uncompensated

24. Practice pH 7.46 ↑ Alkalosis CO2 30 ↓ Respiratory HCO3 22 Low normal
Uncompensated Respiratory Alkalosis

25. Practice pH 7.28 ↓ Acidosis CO2 35 Low normal HCO3 18 ↓ Metabolic
Uncompensated Metabolic acidosis

26. Practice pH 7.51 ↑ Alkalosis CO2 42 Normal HCO3 27 ↑ Metabolic
Uncompensated Metabolic Alkalosis

27. Practice pH 7.32 ↓ Acidosis CO2 54 ↑Respiratory HCO3 25 normal
Uncompensated Respiratory acidosis

28. Practice pH 7.38 Normal CO2 51 ↑Respiratory HCO3 29 ↑
Compensated Respiratory acidosis