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Chapter 14 Acid Base Concepts

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Chapter 14 Acid Base Concepts

  1. 1. Acid Base Imbalance Peggy D. Johndrow 2009
  2. 2. Must it be so complicated! <ul><li>Key concepts </li></ul><ul><ul><li>pH </li></ul></ul><ul><ul><li>PC02 </li></ul></ul><ul><ul><li>Base Excess </li></ul></ul>
  3. 3. What I need to know Components <ul><li>Two Components </li></ul><ul><ul><li>Respiratory </li></ul></ul><ul><ul><li>Metabolic </li></ul></ul>
  4. 4. What I need to know Respiratory <ul><li>Respiratory </li></ul><ul><li>When breathing is inadequate carbon dioxide (respiratory acid) accumulates. Extra C02 combines with water to form carbonic acid which leads to an acid PH </li></ul><ul><li>Evaluate PC02 </li></ul>
  5. 5. What I need to know Metabolic <ul><li>Metabolic </li></ul><ul><li>When metabolism is impaired acid forms , poor blood supply stop oxidative metabolism and lactic acid forms. “Metabolic Acid” </li></ul>
  6. 6. Why do we care? <ul><li>Variations in pH or PC02 are not causes of pathology (lab values) </li></ul><ul><li>Both may be well tolerated when circulation and oxygenation maintained </li></ul><ul><li>Abnormal levels of pH and PC02 are best indicators of trouble </li></ul>
  7. 7. Let’s Review <ul><li>pH represents degree of acidity of fluid </li></ul><ul><li>Major concern pH of blood </li></ul><ul><li>Normal range 7.35-7.45 </li></ul><ul><li>Incompatible with life value 6.8-7.8 </li></ul>
  8. 8. Normal Blood pH <ul><li>Keeping pH within normal range involves balancing acids and bases in body fluids </li></ul><ul><li>Normal pH for arterial blood: 7.35 to 7.45 </li></ul><ul><li>Normal pH for venous blood: 7.31 to 7.41 </li></ul><ul><li>Changes from normal blood pH interfere with many normal functions by: </li></ul><ul><ul><li>Changing shape of hormones & enzymes </li></ul></ul><ul><ul><li>Changing distribution of other electrolytes, causing fluid & electrolyte imbalances. </li></ul></ul><ul><ul><li>Changing of excitable membranes </li></ul></ul><ul><ul><li>Decreasing effectiveness of many hormones & medications </li></ul></ul>
  9. 9. Acid-Base Chemistry <ul><li>Acids </li></ul><ul><li>Bases </li></ul><ul><li>Buffers </li></ul><ul><li>Body fluid chemistry: </li></ul><ul><ul><li>Bicarbonate ions </li></ul></ul><ul><ul><li>Relationship between carbon dioxide and hydrogen ions </li></ul></ul><ul><ul><li>Calculation of free hydrogen ion level </li></ul></ul>
  10. 10. pH Control <ul><li>Controlled precisely because even minor deviation from normal can affect body organs </li></ul><ul><li>Hydrogen ion concentration directly relates to pH </li></ul>
  11. 11. Acid pH <ul><li>Higher hydrogen ion concentration more acid the fluid </li></ul><ul><li>More acid solution lower the pH </li></ul>
  12. 12. Sources of Acids <ul><li>Incomplete breakdown of glucose </li></ul><ul><li>Destruction of cells </li></ul><ul><li>Bicarbonate </li></ul>
  13. 13. Alkaline pH <ul><li>Lower hydrogen ion concentration more alkaline the pH </li></ul><ul><li>More alkaline fluid higher the pH </li></ul>
  14. 14. Acid Base Balance Table
  15. 15. Mechanisms Regulate Acid Base Balance <ul><li>pH Buffers: Bicarbonate-Carbonic Acid Buffer System </li></ul><ul><li>Lungs </li></ul><ul><li>Kidneys </li></ul>
  16. 16. Bicarbonate-Carbonic Acid Buffer System <ul><li>Normal ratio 20 to 1 </li></ul><ul><li>20 parts HC03- to 1 part H2C03 </li></ul><ul><li>If alter 20:1 ratio pH will change (not value but ratio that determines pH) </li></ul>
  17. 17. What is carbonic acid? <ul><li>Carbon dioxide(C02) potential acid when dissolved in H20 becomes carbonic acid (C02 + H20 = H2C03) </li></ul><ul><li>Key : </li></ul><ul><ul><li>When C02 the H2C03 </li></ul></ul><ul><ul><li>When C02 the H2C03 </li></ul></ul><ul><li>If either changes so the 20:1 ratio is no longer maintained results in acid base imbalance </li></ul>
  18. 18. Respiratory Acid-Base Control Mechanisms <ul><li>Chemical buffers alone cannot prevent changes in blood pH, respiratory system second line of defense against changes: </li></ul><ul><ul><li>Hyperventilation </li></ul></ul><ul><ul><li>Hypoventilation </li></ul></ul>
  19. 19. Respiratory Mechanism Diagram
  20. 20. Lungs Alkaline <ul><li>Excretion of carbon dioxide(C02) </li></ul><ul><li>Respiratory center regulates amount of C02 exhaled by controlling speed and depth of respirations </li></ul><ul><li>Increased respiration (tachypnea) C02 level decreases and blood pH becomes more base </li></ul>
  21. 21. Lungs Acid <ul><li>Decreased respirations (bradypnea) C02 increases and the blood becomes more acidic. </li></ul><ul><li>By adjusting the speed and depth of respirations; the respiratory center and lungs are able to regulate blood pH minute to minute </li></ul>
  22. 22. Renal Acid-Base Control Mechanisms <ul><li>Kidneys third line of defense against wide changes in body fluid pH </li></ul><ul><li>Stronger for regulating acid-base balance but take longer to completely respond than chemical & respiratory mechanisms </li></ul><ul><li>Kidney movement of bicarbonate </li></ul><ul><li>Formation of acids </li></ul><ul><li>Formation of ammonium </li></ul>
  23. 23. Kidneys <ul><li>Excess acid excreted by kidneys </li></ul><ul><li>Have ability to alter amount of acid or base excreted but generally process takes hours to days </li></ul><ul><li>Can retain or excrete hydrogen(H+) and Bicarbonate(HC03-) to restore balance </li></ul><ul><li>Kidneys can’t compensate with renal failure or severe impairment </li></ul>
  24. 24. Compensation <ul><li>Body attempts correct changes in blood pH </li></ul><ul><li>pH below 6.9 or higher than 7.8 usually fatal </li></ul><ul><li>Respiratory system more sensitive to acid-base changes; can begin compensation efforts within seconds to minutes </li></ul><ul><li>Renal compensatory mechanisms much more powerful & result in rapid changes in ECF composition not fully triggered unless imbalance continues for several hours to days </li></ul>
  25. 25. Respiratory Compensation <ul><li>Lungs compensate for acid-base imbalances of metabolic origin </li></ul><ul><li>Example: Prolonged running causes buildup of lactic acid, hydrogen ion levels in ECF increase, pH drops; breathing triggered in response to increased carbon dioxide levels to bring pH level back to normal </li></ul>
  26. 26. Renal Compensation <ul><li>Healthy kidney can correct or compensate for changes in blood pH when respiratory system either overwhelmed or unhealthy </li></ul><ul><li>Example: Person has chronic obstructive pulmonary disease, retains carbon dioxide in blood, blood pH level falls (becomes more acidic); kidney excretes more hydrogen ions & increases re-absorption of bicarbonate back into blood </li></ul>
  27. 27. Acidosis and Alkalosis <ul><li>Metabolic caused by an imbalance in production and excretion of acids or bases by kidney </li></ul><ul><li>Respiratory caused primarily by lung or breathing disorders which affect CO2 </li></ul>
  28. 28. Normal Arterial Values Parameter Arterial Sample pH 7.35-7.45 PaC02 35-45 mmHg Pa02 80-100 mmHG Oxygen Saturation 95-100% Base Excess + or - 2 HC03- 22-26 mEq/L
  29. 29. Acid Base Guide Disorder Initial Event Compensation Respiratory Acidosis PaC02 or normal HC03 pH Kidneys eliminate H+ and retain HCO3- Respiratory Alkalosis PaC02 or normal HC03 pH Kidneys conserve H+ and excrete HC03- Metabolic Acidosis or normal PaC02 HC03- pH Lungs eliminate C02 conserve HC03- Metabolic Alkalosis or normal Pac02 HCO3- pH Lungs ventilation to PC02 kidneys conserve H+ to excrete HC03-
  30. 30. Acid Base Key Concept <ul><li>With Respiratory reverse relationship </li></ul><ul><li>Increase PaC02/HC02 Decrease pH </li></ul><ul><li>Decrease PaC02/HC02 Increase pH </li></ul><ul><li> </li></ul><ul><li>Metabolic </li></ul><ul><li>acidosis all values decreased (equal) </li></ul><ul><li>alkalosis all values increased (equal) </li></ul>
  31. 31. Metabolic Acidosis <ul><li>Excessive blood acidity characterized by inappropriate low level of bicarbonate </li></ul><ul><li>Increase in acid and blood becomes acidic </li></ul>
  32. 32. Metabolic Acidosis Causes <ul><li>Kidney Failure </li></ul><ul><li>Diabetic Ketoacidosis </li></ul><ul><li>Lactic Acidosis </li></ul><ul><li>Poison: Salicylate(overdose), Methanol(wood alcohol), paraldehyde, ethylene glycol (antifreeze),acetazolamide, ammonia chloride </li></ul><ul><li>Loss of base through GI tract (diarrhea, ileostomy or colostomy) </li></ul>
  33. 33. Metabolic Acidosis Symptoms <ul><li>Mild </li></ul><ul><ul><li>Nausea, vomiting , fatigue, tachypnea </li></ul></ul><ul><li>Moderate </li></ul><ul><ul><li>Extreme weakness, sleepy, confusion, increased nausea </li></ul></ul><ul><li>Severe </li></ul><ul><ul><li>Severe drop in BP, shock, coma, death </li></ul></ul>
  34. 34. Metabolic Acidosis Treatment <ul><li>Depends on cause </li></ul><ul><li>Treat underlying cause such as control diabetes or remove toxin from blood </li></ul><ul><li>Occasionally dialysis </li></ul><ul><li>Direct treatment </li></ul><ul><ul><li>Mild: IV fluids and underlying disorder </li></ul></ul><ul><ul><li>Severe: bicarbonate IV (used with caution) </li></ul></ul>
  35. 35. Metabolic Alkalosis <ul><li>Condition in which the blood is alkaline because of an inappropriately high level of bicarbonate </li></ul>
  36. 36. Metabolic Alkalosis Causes <ul><li>Body loses too much acid or ingest too much alkali from substance like bicarbonate of soda(baking soda for indigestion) </li></ul><ul><li>Excessive loss of Na or K affects kidneys ability to control blood acid-base balance </li></ul><ul><li>Diuretics (thiazides, furosemide, loop diuretics) </li></ul><ul><li>Loss of acid from vomiting or GI suction </li></ul><ul><li>Overactivity of adrenal gland (Cushing's or use of steroids) </li></ul>
  37. 37. Metabolic Alkalosis Symptoms <ul><li>Mild </li></ul><ul><ul><li>Can have no symptoms at all </li></ul></ul><ul><ul><li>Irritably, muscle twitching and muscle cramps </li></ul></ul><ul><li>Severe </li></ul><ul><ul><li>Prolonged contraction of and spasms of muscle tetany </li></ul></ul>
  38. 38. Metabolic Alkalosis Treatment <ul><li>Replace water and electrolytes (NA and K) </li></ul><ul><li>Treat underlying cause </li></ul><ul><li>Severe occasionally dilute acid in the form of ammonium chloride is given IV </li></ul>
  39. 39. Respiratory Acidosis <ul><li>Excessive blood acidity caused by build up of carbon dioxide </li></ul>
  40. 40. Respiratory Acidosis Causes <ul><li>Anything that interferes with lungs ability to expel carbon dioxide adequately </li></ul><ul><ul><li>Emphysema, Chronic bronchitis, Asthma </li></ul></ul><ul><ul><li>Severe pneumonia </li></ul></ul><ul><ul><li>Pulmonary edema </li></ul></ul><ul><ul><li>Over-sedation with narcotics sleeping medication or overdose </li></ul></ul><ul><li>Also with impairment of nerves or muscles that impair mechanics of breathing </li></ul>
  41. 41. Respiratory Acidosis Treatment <ul><li>Improve lung function </li></ul><ul><li>Medications to improve lung function </li></ul><ul><li>Artificial respirations with a mechanical ventilator </li></ul>
  42. 42. Respiratory Alkalosis <ul><li>Condition in which blood is alkaline because of rapid or deep breathing results in a low blood carbon dioxide </li></ul>
  43. 43. Respiratory Alkalosis Causes <ul><li>Hyperventilation </li></ul><ul><li>Anxiety </li></ul><ul><li>Pain </li></ul><ul><li>Cirrhosis of the liver </li></ul><ul><li>Low oxygen levels in the blood </li></ul><ul><li>Fever </li></ul><ul><li>Aspirin(salicylate) overdose </li></ul>
  44. 44. Respiratory Alkalosis Treatment <ul><li>Slow rate of breathing </li></ul><ul><li>Administer pain medication </li></ul><ul><li>Breathe into paper bag helps raise C02 level, person rebreathes C02 back in after breathing out. </li></ul><ul><li>Hold the breath as long as possible and repeat the sequence 6 to 10 times </li></ul>
  45. 45. Let’s Practice <ul><li>http://www.mhhe.com/biosci/ap/ap_casestudies/cases/ap_case14.html </li></ul><ul><li>http://www.rnceus.com/abgs/abgframe.html </li></ul>
  46. 46. Acid Base References <ul><li>http://www.tmc.tulane.edu/departments/anesthesiology/acid/default.html </li></ul><ul><li>http://qldanaesthesia.com/AcidBaseBook/Abindex.htm </li></ul><ul><li>Or type in acid base and see what helps you </li></ul>

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