Respiratory Acid base balance by Dr. Samreena


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Respiratory Acid base balance by Dr. Samreena

  2. 2. pH Review
  3. 3. The Body and pH
  4. 4. <ul><li>Acids are H + donors. </li></ul><ul><li>Bases are H + acceptors, or give up OH - in solution. </li></ul><ul><li>Acids and bases can be: </li></ul><ul><ul><li>Strong – dissociate completely in solution </li></ul></ul><ul><ul><ul><li>HCl, NaOH </li></ul></ul></ul><ul><ul><li>Weak – dissociate only partially in solution </li></ul></ul><ul><ul><ul><li>Lactic acid, carbonic acid </li></ul></ul></ul>
  5. 5. Types of Acids in the Body <ul><li>Volatile acids: </li></ul><ul><ul><li>Can leave solution and enter the atmosphere. </li></ul></ul><ul><ul><li>H 2 C0 3 (carbonic acid). </li></ul></ul><ul><ul><li>Pco 2 is most important factor in pH of body tissues. </li></ul></ul>
  6. 6. Types of Acids in the Body <ul><li>Fixed Acids: </li></ul><ul><ul><li>Acids that do not leave solution. </li></ul></ul><ul><ul><li>Sulfuric and phosphoric acid. </li></ul></ul><ul><ul><li>Catabolism of amino acids, nucleic acids, and phospholipids. </li></ul></ul>
  7. 7. Types of Acids in the Body <ul><li>Organic Acids: </li></ul><ul><ul><li>Byproducts of aerobic metabolism, during anaerobic metabolism and during starvation, diabetes. </li></ul></ul><ul><ul><li>Lactic acid, ketones. </li></ul></ul>
  8. 8. Small changes in pH can produce major disturbances <ul><li>Most enzymes function only with narrow pH ranges </li></ul><ul><li>Acid-base balance can also affect electrolytes (Na + , K + , Cl - ) </li></ul><ul><li>Can also affect hormones </li></ul>
  9. 9. The body produces more acids than bases <ul><li>Acids take in with foods </li></ul><ul><li>Acids produced by metabolism of lipids and proteins </li></ul><ul><li>Cellular metabolism produces CO 2 . </li></ul><ul><li>CO 2 + H 2 0 ↔ H 2 CO 3 ↔ H + + HCO 3 - </li></ul>
  10. 10. Henderson-Hasselbalch Equation
  11. 11. APPLICATIONS OF HH EQUATION <ul><li>Analysis of dissociation of the alanine in the same way as described for acetic acid </li></ul><ul><li>Use to calculate how pH of a physiologic solution responds to changes in the concentration of a week acid and/or it’s corresponding salt form. </li></ul><ul><li>Example Bicarbonate buffer system (How HCO 3 and CO 2 Influence pH) </li></ul>
  12. 12. APPLICATIONS OF HH EQUATION <ul><li>Useful for calculating ionic forms of acidic and basic drugs. </li></ul><ul><li>Acidic drug </li></ul><ul><li>HA H + +A - </li></ul><ul><li>Example: Aspirin </li></ul><ul><li>Basic drug </li></ul><ul><li>BH + B+H + </li></ul><ul><li>Example: Morphine </li></ul><ul><li>Drug can readily pass through the membrane if it is uncharged </li></ul>
  13. 13. APPLICATIONS OF HH EQUATION <ul><li>How much drug is found on either side of a membrane that separates two compartments that differ in pH, for example, the stomach (pH 1.0-1.5) and blood plasma (pH 7.4) </li></ul>
  14. 14. Buffer Systems <ul><li>Provide or remove H + and stabilize the pH. </li></ul><ul><li>Include weak acids that can donate H + and weak bases that can absorb H + . </li></ul><ul><li>Change in pH, after addition of acid, is less than it would be in the absence of buffer. </li></ul>
  15. 15. Chemical Buffers <ul><li>Act within fraction of a second. </li></ul><ul><li>Protein. </li></ul><ul><li>HCO 3 - . </li></ul><ul><li>Phosphate. </li></ul>
  16. 16. Proteins <ul><li>COOH or NH 2 . </li></ul><ul><li>Largest pool of buffers in the body. </li></ul><ul><li>pKa close to plasma. </li></ul><ul><li>Albumin, globulins such as Hb. </li></ul>
  17. 17. Protein Buffers <ul><li>Includes hemoglobin, work in blood </li></ul><ul><li>Carboxyl group gives up H + </li></ul><ul><li>Amino Group accepts H + </li></ul><ul><li>Glutamate, aspartate, histidine, arginine, lysine </li></ul><ul><li>Additional potentially charged groups in side chain </li></ul>
  18. 18. Bicarbonate buffer <ul><li>Sodium Bicarbonate (NaHCO 3 ) and carbonic acid (H 2 CO 3 ) </li></ul><ul><li>Maintain a 20:1 ratio : HCO 3 - : H 2 CO 3 </li></ul><ul><li>HCl + NaHCO 3 ↔ H 2 CO 3 + NaCl </li></ul><ul><li>NaOH + H 2 CO 3 ↔ NaHCO 3 + H 2 O </li></ul>
  19. 19. HCO 3 - <ul><li>pk= 6.1 </li></ul><ul><li>Most important ECF buffer. </li></ul><ul><li>Present in large quantities. </li></ul><ul><li>Respiratory and renal systems act on this buffer system. </li></ul>
  20. 20. Phosphate buffer <ul><li>Major intracellular buffer </li></ul><ul><li>H + + HPO 4 2- ↔ H 2 PO4 - </li></ul><ul><li>OH - + H 2 PO 4 - ↔ H 2 O + HPO 4 2- </li></ul><ul><li>pk = 6.8 </li></ul><ul><li>Better buffer in ICF (kidneys and bone) </li></ul>
  21. 21. Rates of correction <ul><li>Buffers function almost instantaneously </li></ul><ul><li>Respiratory mechanisms take several minutes to hours </li></ul><ul><li>Renal mechanisms may take several hours to days </li></ul>
  22. 23. Respiratory System <ul><li>2nd line of defense. </li></ul><ul><li>Acts within min. maximal in 12-24 hrs. </li></ul><ul><li>H 2 CO 3 produced converted to CO 2 , and excreted by the lungs. </li></ul><ul><li>Powerful, but works with volatile acids </li></ul><ul><li>Exhalation of carbon dioxide. </li></ul><ul><li>CO 2 + H 2 0 ↔ H 2 CO 3 ↔ H + + HCO 3 - </li></ul><ul><li>Body pH can be adjusted by changing rate and depth of breathing </li></ul>
  23. 24. Renal system <ul><li>Can eliminate large amounts of acid </li></ul><ul><li>Can conserve and produce bicarbonate ions </li></ul><ul><li>Most effective regulator of pH </li></ul><ul><li>If kidneys fail pH balance fails </li></ul>
  24. 25. Urinary Buffers <ul><li>Urine pH = 4.5 </li></ul><ul><li>H + secreted into the urine tubule and combines with HPO 4 -2 or NH 3 . </li></ul><ul><li>HPO 4 -2 + H + H 2 PO 4 -2 </li></ul><ul><li>NH 3 + H + NH 4 + </li></ul>
  25. 27. Acid-Base Imbalances <ul><li>pH< 7.35 acidosis </li></ul><ul><li>pH > 7.45 alkalosis </li></ul><ul><li>The body response to acid-base imbalance is called compensation </li></ul><ul><li>May be complete if brought back within normal limits </li></ul><ul><li>Partial compensation if range is still outside norms. </li></ul>
  26. 28. Compensation <ul><li>If underlying problem is metabolic, hyperventilation or hypoventilation can help : respiratory compensation </li></ul><ul><li>If problem is respiratory, renal mechanisms can bring about metabolic compensation </li></ul>
  27. 29. Acidosis <ul><li>Principal effect of acidosis is depression of the CNS through ↓ in synaptic transmission </li></ul><ul><li>Generalized weakness </li></ul><ul><li>Deranged CNS function the greatest threat </li></ul><ul><li>Severe acidosis causes </li></ul><ul><ul><li>Disorientation </li></ul></ul><ul><ul><li>Coma </li></ul></ul><ul><ul><li>Death </li></ul></ul>
  28. 30. Alkalosis <ul><li>Alkalosis can cause </li></ul><ul><li>It can cause : </li></ul><ul><ul><li>Nervousness </li></ul></ul><ul><ul><li>Muscle spasms or tetany </li></ul></ul><ul><ul><li>Convulsions </li></ul></ul><ul><ul><li>Loss of consciousness </li></ul></ul><ul><ul><li>Death </li></ul></ul>
  29. 32. Respiratory Acidosis <ul><li>Carbonic acid excess caused by blood levels of CO 2 above 45 mm Hg </li></ul><ul><li>Hypercapnia – High levels of CO 2 in blood </li></ul><ul><li>Chronic conditions: </li></ul><ul><ul><li>Depression of respiratory center in brain that controls breathing rate – drugs or head trauma </li></ul></ul><ul><ul><li>Paralysis of respiratory or chest muscles </li></ul></ul><ul><ul><li>Emphysema </li></ul></ul>
  30. 33. Respiratory Acidosis <ul><li>Acute conditions: </li></ul><ul><ul><li>Adult Respiratory Distress Syndrome </li></ul></ul><ul><ul><li>Pulmonary edema </li></ul></ul><ul><ul><li>Pneumothorax </li></ul></ul>
  31. 34. Compensation for Respiratory Acidosis <ul><li>Kidneys eliminate hydrogen ion and retain bicarbonate ion </li></ul><ul><li>Acute respiratory failure: </li></ul><ul><li>pH low,[HCO - 3 ] high normal, or slightly raised </li></ul><ul><li>Chronic respiratory failure: </li></ul><ul><li>pH normal or low depending upon chronicity,[HCO - 3 ] raised </li></ul>
  32. 35. Signs and Symptoms of Respiratory Acidosis <ul><li>Breathlessness </li></ul><ul><li>Restlessness </li></ul><ul><li>Lethargy and disorientation </li></ul><ul><li>Tremors, convulsions, coma </li></ul><ul><li>Respiratory rate rapid then gradually depressed </li></ul><ul><li>Skin warm and flushed due to vasodilatation caused by excess CO 2 </li></ul>
  33. 36. Treatment of Respiratory Acidosis <ul><li>Restore ventilation </li></ul><ul><li>Treat underlying dysfunction or disease </li></ul>
  34. 38. Respiratory Alkalosis <ul><li>Carbonic acid deficit </li></ul><ul><li>pCO 2 less than 35 mm Hg (hypocapnea) </li></ul><ul><li>Primary cause is hyperventilation </li></ul>
  35. 39. Respiratory Alkalosis <ul><li>Conditions that stimulate respiratory center: </li></ul><ul><li>Hysterical over breathing (overrides normal respiratory control) </li></ul><ul><li>Raised ICP (Which stimulate respiratory centre) </li></ul><ul><li>Hypoxia </li></ul><ul><li>Pulmonary edema </li></ul><ul><li>Lobar pneumonia </li></ul><ul><li>Pulmonary collapse or fibrosis </li></ul><ul><li>Excessive artificial ventilation </li></ul>
  36. 40. Compensation of Respiratory Alkalosis <ul><li>Compensatory fall in plasma [HCO - 3 ] tends to correct the pH </li></ul><ul><li>Pco 2 always reduced </li></ul><ul><li>[HCO - 3 ] low normal or low </li></ul><ul><li>pH raised (uncompensated or partly compensated) or normal (fully compensated) </li></ul>
  37. 41. Treatment of Respiratory Alkalosis <ul><li>Treat underlying cause </li></ul><ul><li>IV Chloride containing solution – Cl - ions replace lost bicarbonate ions </li></ul>
  38. 43. THANKS