Acid-Base Balance for Allied Health Majors

1. H2O + CO2H2CO3H+ + HCO3- HCO3- α =0.03 pH = pK + log pCO2 (α) Acid-Base Balance for Allied Health Majors Using the Henderson-Hasselbach Equation

2. Acid • An acid is a substance that will disassociate a H+ and become more negatively charged (electron acceptor). • When hydrogen ions accumulate in a solution, it becomes more acidic ([H+] increases = more acidity). HCl 2 7 H + Cl- H + Cl- pH H + Cl- H + Cl- H + Cl- Hydronium ions in solution Concentration of hydrogen ions increases, pH drops

3. Base • A base is chemical that will remove hydrogen ions from the solution • the base has a negative charge (or extra electrons) to donate to hydrogen ions and thus create a bond with hydrogen 2 7 NaOH Na+ OH- H + Cl- H + Cl- pH Na+ OH- Acids and basis neutralize eachother H + Cl- H + Cl- Na+ OH- H + Cl- Na+ OH-

4. A change of 1 pH unit corresponds to a 10-fold change in hydrogen ion concentration 2 7 Na+ Cl- Na+ Cl- pH H+ H2O OH- Na+ Cl- Na+ Cl-

5. Acids are being created constantly through metabolism • Inorganic phosphates (mostly from ATP, etc.) • Anaerobic respiration of glucose produces lactic acid • Fat metabolism yields organic acids and ketone bodies • Carbon dioxide!!!!!

6. Acids must be buffered, transported away from cells, and eliminated from the body Phosphate:important renal tubular buffer HPO4- + H+ H2PO 4 Ammonia:important renal tubular buffer NH3 + H+ NH4+ Proteins:important intracellular and plasma buffers H+ + Hb HHb Histidine in proteins is particularly good at neutralizing hydrogen ions

7. Bicarbonate: most important ECF buffer CA H2O + CO2 H2CO3 H+ + HCO3- Hydrogen is buffered by hemoglobin From metabolism

8. Buffering is good, but it is a temporary solution. Excess acids and bases must be eliminated from the body gas aqueous CA H2O + CO2 H2CO3 H+ + HCO3- Kidneys can remove excess non-volatile acids and bases Lungs eliminate carbon dioxide

9. Excessive Acids and Bases can cause pH changes---denature proteins • Normal pH of body fluids is 7.40 • Alkalosis or alkalemia – arterial blood pH rises above 7.45 • Acidosis or acidemia – arterial pH drops below 7.35 (physiological acidosis) • For our class, we will stick to 7.40 as normal! • Acidosis: • too much acid • Too little base • Alkalosis • Too much base • Too little acid

10. Compensation for deviation • Lungs (only if not a respiratory problem) • If too much acid (low pH)—respiratory system will ventilate more (remove CO2) and this will raise pH back toward set point • If too little acid (high pH)—respiratory will ventilate less (trap CO2 in body) and this will lower pH back toward set point • Kidneys • If too much acid (low pH)—intercalated cells will secrete more acid into tubular lumen and make NEW bicarbonate (more base) and raise pH back to set point. • If too little acid/excessive base (high pH)- proximal convoluted cells will NOT reabsorb filtered bicarbonate (base) and will eliminate it from the body to lower pH back toward normal.

11. Alveolar Ventilation [H+] pCO2 H2O + CO2 H2CO3 H+ + HCO3- How would your ventilation change if you had excessive acid? This is too high and this means the buffer system swings this way! CO2 vented out

12. How would your ventilation change if you had too little acid? Alveolar Ventilation [H+] pCO2 H2O + CO2 H2CO3 H+ + HCO3- This is too low and this means the buffer system swings this way! CO2 trapped

13. How can the kidneys control acids and bases? • Bicarbonate is filtered and enters nephron at Bowman’s capsule • Proximal convoluted tubule • Can reabsorb all bicarbonate (say, when you need it to neutralize excessive acids in body) OR • Can reabsorb some or NONE of the bicarbonate (maybe you have too much base in body and it needs to be eliminated)

14. How can the kidneys control acids and bases? • Acidosis • Intercalated cells • Secrete excessive hydrogen • Secreted hydrogen binds to tubular buffers (ammonia and phosphate bases) • Secretion of hydrogen leads to gain of bicarbonate (NEW!) HPO4- NH3

15. What would happen if the respiratory system had a problem with ventilation?Respiratory Acidosis and Alkalosis PCO2 levels-Normal PCO2 fluctuates between 35 and 45 mmHg • Respiratory Alkalosis (less than 35mmHg- lowered CO2) • Hyperventilation syndrome/ psychological (fear, pain) • Overventilation on mechanical respirator • Ascent to high altitudes • Fever • Respiratory Acidosis (elevated CO2 greater than 45mmHg) • Depression of respiratory centers via narcotic, drugs, anesthetics • CNS disease and depression, trauma (brain damage) • Interference with respiratory muscles by disease, drugs, toxins • Restrictive, obstructive lung disease (pneumonia, emphysema)

16. Metabolic acidosis bicarbonate ion levels below normal (22 mEq/L) Metabolic alkalosis bicarbonate ion levels higher (greater than 26mEq/L) What if your metabolism changed? • Excessive loss of fixed acids due to ingestion, infusion, or renal reabsorption of bases • Loss of gastric juice during vomiting • Intake of stomach antacids (Leisure world syndrome) • Diuretic abuse (loss of H+ ions) • Severe potassium depletion (increased aldosterone) • Steroid therapy (mineralcorticoid excess) • Ingestion, infusion or production of more acids (alcohol) • Carbonic anhydrase inhibitors (decreased H+ secretion) • Salicylate overdose (aspirin) • Diarrhea (loss of intestinal HCO3-) • Accumulation of lactic acid in severe Diabetic ketoacidosis • starvation

17. Mechanisms of Acidosis and Alkalosis H2O + CO2H2CO3H+ + HCO3- HCO3- α =0.03 pH = pK + log pCO2 (α) Acidosis: pH < 7.4 - metabolic:HCO3- - respiratory:pCO2 Alkalosis: pH > 7.4 - metabolic:HCO3- - respiratory:pCO2

18. Compensation

19. Analysis of Simple Acid-Base Disorders Step One: <22 >45 >26 <35 Step Two Resp and renal compensation Resp and renal compensation Step 3 Figure 30-10; Guyton and Hall <35 >26 >45 <22

20. H2O + CO2 H2CO3 H+ + HCO3- H+ secretion complete HCO3- reabs. PCO2 + excess tubular H+ pH Buffers (NH4+, NaHPO4-) Buffers - H+ + new HCO3- Let’s practice What is the problem?: pH pCO2 HCO3- What is the correction and which organ system does this?

21. H+ secretion reabs. HCO3- + excess tubular HCO3- pH HCO3- + excretion excretion H+ Let’s practice What is the problem?: pH pCO2 HCO3- What is the correction and which organ system does this? PCO2

22. Let’s practice What is the problem?: pH pCO2 HCO3- What is the correction and which organ system does this? HCO3- complete HCO3- reabs. HCO3- + excess tubular H+ filtration pH Buffers (NH4+, NaHPO4-) Buffers - H+ + new HCO3- What is the respiratory system doing at the same time?

23. HCO3- + excretion H+ Let’s practice What is the problem?: pH pCO2 HCO3- What is the correction and which organ system does this? excess tubular HCO3- HCO3- HCO3- filtration reabs. HCO3- pH excretion What is the respiratory system doing at the same time?

24. Anion Gap-- protein , phosphate, citrate, sulfate Na+ Cl- Anion gap Na+ Cl- Anion gap Na+ Cl- Anion gap HCO3- HCO3- HCO3- Meta. acidosis: too little base More Cl- and anion gap same Diarrhea, renal acidosis Meta. acidosis: too little base More Cl- and anion gap bigger Ketoacidosis, salicylate, lactate Chronic renal failure electroneutrality

25. Clinical Correlation: Abuse of Diuretics or Conn’s disease Overuse of Diuretics extracell. volume angiotensin II K+ depletion Conn’s disease aldosterone tubular H+ secretion HCO3 reabsorption + new HCO3 Production Metabolic Alkalosis