1.3 Acid-base Imbalance - simplified.pptx

HEALTH

1. XIANG ZHUXING Acid and Base Imbalance [email protected]

2. The Body and pH Homeostasis of pH is tightly controlled Blood = 7.35 – 7.45 < 6.8 or > 8.0 death occurs Acidosis ( acidemia ) below 7.35 Alkalosis ( alkalemia ) above 7.45

3. The body produces more acids than bases Acids take in with foods Acids produced by metabolism of lipids and proteins Cellular metabolism produces CO 2 . CO 2 + H 2 ↔ H 2 CO 3 ↔ H + + HCO 3 -

4. Control of Acids: Buffer systems 1. Bicarbonate buffer (ECF) Take up H+ or release H+ as conditions change Buffer pairs – weak acid and a base Exchange a strong acid or base for a weak one Results in a much smaller pH change

5. Phosphate buffer Major intracellular buffer H + + HPO 4 2- ↔ H 2 PO4 - OH - + H 2 PO 4 - ↔ H 2 O + HPO 4 2-

6. Protein Buffers Includes hemoglobin, work in blood and ICF Carboxyl group gives up H + Amino Group accepts H + Side chains that can buffer H + are present on 27 amino acids.

7. 2. Respiratory mechanisms Exhalation of carbon dioxide Powerful, but only works with volatile acids (CO2) Doesn’t affect fixed acids like lactic acid CO 2 + H 2 ↔ H 2 CO 3 ↔ H + + HCO 3 - Body pH can be adjusted by changing rate and depth of breathing

8. 3. Kidney excretion Can eliminate large amounts of acid Can also excrete base Can conserve and produce bicarb ions Most effective regulator of pH If kidneys fail, pH balance fails

9. Rates of Correction Chemical buffers function almost instantaneously Respiratory mechanisms take several minutes to hours Renal mechanisms may take several hours to days

10. Acid-Base Imbalances pH< 7.35 acidosis pH > 7.45 alkalosis The body response to acid-base imbalance is called compensation May be complete if brought back within normal limits Partial compensation if range is still outside norms.

11. Compensation If underlying problem is metabolic, hyperventilation or hypoventilation can help : respiratory compensation . If problem is respiratory, renal mechanisms can bring about metabolic compensation. NORMAL RANGE: HCO3- = 22 - 26 mEq / L pCO2 = 35 – 45 mm Hg

12. Respiratory Acidosis Carbonic acid excess P CO2 > 45mm Hg ( hypercapnia ) pH < 7.35 Primary cause : hypoventilation

13. Respiratory Acidosis Chronic conditions: Depression of respiratory center in brain that controls breathing rate – drugs or head trauma Paralysis of respiratory or chest muscles Emphysema Acute conditons : Adult Respiratory Distress Syndrome Pulmonary edema Pneumothorax

14. Compensation for Respiratory Acidosis Kidneys eliminate hydrogen ion and retain HCO3-

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16. Respiratory Alkalosis Carbonic acid deficit P CO 2 < 35 mm Hg ( hypocapnia ) pH > 7.45 Most common acid-base imbalance Primary cause is hyperventilation

17. Respiratory Alkalosis Conditions that stimulate respiratory center: Oxygen deficiency at high altitudes Pulmonary disease and Congestive heart failure – caused by hypoxia Acute anxiety Fever, anemia Early salicylate intoxication Cirrhosis Gram-negative sepsis

18. Compensation of Respiratory Alkalosis Kidneys conserve hydrogen ion and eliminate HCO3-

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20. Metabolic Acidosis Bicarbonate deficit HCO3- < 22mEq/L pH < 7.35 Causes: Gain of strong acid; Loss of base Accumulation of acids (lactic acid or ketones ) Failure of kidneys to excrete H+ Loss of bicarbonate through diarrhea or renal dysfunction

21. Compensation for Metabolic Acidosis Increased ventilation Renal excretion of hydrogen ions if possible

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23. Metabolic Alkalosis Bicarbonate excess HCO3- > 26 mEq /L pH > 7.45 Causes: (more base; less acid) Excess vomiting = loss of stomach acid Excessive use of alkaline drugs Certain diuretics Endocrine disorders Heavy ingestion of antacids Severe dehydration

24. Compensation for Metabolic Alkalosis Alkalosis most commonly occurs with renal dysfunction, so can’t count on kidneys Respiratory compensation difficult – hypoventilation limited by hypoxemia PO2: 80-100 mmHg O2 sat: 95%-100%

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26. Diagnosis of Acid-Base Imbalances Note whether the pH is low (acidosis) or high (alkalosis) Decide which value, pCO 2 or HCO 3 - , is outside the normal range and could be the cause of the problem. If the cause is a change in pCO 2, the problem is respiratory. If the cause is HCO 3 - the problem is metabolic .

27. 3. Look at the value that doesn’t correspond to the observed pH change. If it is inside the normal range, there is no compensation occurring. If it is outside the normal range, the body is partially compensating for the problem. Diagnosis of Acid-Base Imbalances

28. Example A patient is in intensive care because he suffered a severe myocardial infarction 3 days ago. The lab reports the following values from an arterial blood sample: pH = 7.3 HCO3- = 20 mEq / L ( 22 - 26) pCO2 = 32 mm Hg (35 - 45)

29. Diagnosis Metabolic acidosis With compensation

30. 7. 7.35 35 7.45

31. Cheat Sheet Increase pH – alkalosis Decrease pH – acidosis Respiratory – CO2 Metabolic(kidneys )– HCO3 - CO2 has an inverse relationship with pH When pH goes down, CO2 goes up HCO3 follows pH , If pH goes up so does HCO3 - CO2 increases, pH decreases – resp. acidosis CO2 decreases, pH increases – resp. alkalosis HCO3 increases, pH increases – metabolic alkalosis HCO3 decreases, pH decreases – metabolic acidosis

32. Practice : Analyzing ABG 6 7.5 51 35 7 7.29 49 32

33. THANK YOU

34. References John T. Hansen; Bruce M. Koeppen (2002).  Netter's Atlas of Human Physiology . Teterboro , N.J: Icon Learning Systems. ISBN 1-929007-01-9. Yeomans , ER; Hauth , JC; Gilstrap , LC III; Strickland DM (1985). "Umbilical cord pH, PCO2, and bicarbonate following uncomplicated term vaginal deliveries (146 infants)". Am J Obstet Gynecol.  151  (6): 798 800.  doi:10.1016/0002-9378(85)90523-x https://www.msdmanuals.com/home/hormonal-and-metabolic-disorders/acid-base-balance/overview-of-acid-base-balance#v26463921 Stewart P (1978). "Independent and dependent variables of acid-base control".  Respir Physiol. 33 (1): 9–26. doi:10.1016/0034-5687(78)90079-8. Kaufman CE and Papper S (eds.) Review of Pathophysiology . Boston: Little,Brown,1983. https://www.sciencedirect.com/topics/medicine-and-dentistry/acid-base-imbalance Rose BD. Clinical Physiology of Acid-Base and Electrolyte Disorders(4 th ed ). New York and St. Louis: McGraw Hill,1994. https://www.slideshare.net/nikhilnanjappa1/acid-base-balance-and-imbalance