1 / 22

Acid-Base Balance Disturbances

Acid-Base Balance Disturbances. Hydrogen ion h omeostasis. Acids are produced continuously during normal metabolism. (provide H+ to blood) H + ion concentration of blood varies between narrow limits pH of the extracellular fluid = 7.35 – 7.45

keefe
Download Presentation

Acid-Base Balance Disturbances

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Acid-Base Balance Disturbances

  2. Hydrogen ion homeostasis • Acids are produced continuously during normal metabolism. • (provide H+ to blood) • H+ ion concentration of blood varies between narrow limits pH of the extracellular fluid = 7.35 – 7.45 • Constant H+ concentration within physiological limits is physiologically • important to preserve the enzyme activity and metabolism

  3. Sources of acids of blood • 1- Volatile acids: - Carbon Dioxide CO2 (H2CO3) 2- Nonvolatile acids: 1- Organic acids: - Lactic Acid - Ketone bodies 2-Inorganic acids - Sulphuric Acid - Phosphoric Acid

  4. Buffering of acids (H+) in blood • H+ is generated during intracellular metabolism from several sources(~ 150 000 mmol H+ is produced every day) • They are continuously neutralized by buffers resulting in no gain of H+ ions = No pH change

  5. Carbonic Acid -Bicarbonate Buffer System • ( H2CO3 – HCO3-) The equilibrium reactions of the buffer system H+ + HCO3-H2CO3(Reaction 1) H2CO3CO2+ H2O(Reaction 2) excreted by the lungs Accordingly,the addition of H+ causes the equilibrium to be shifted to the right (towards CO2production and excretion by the lungs)

  6. Carbonic Acid -Bicarbonate Buffer System • ( H2CO3 – HCO3-) cont. In case of increased H+ production, H2CO3- HCO3-bufferwill reduce H+ as follows: • H+ + HCO3-H2CO3(Reaction 1) • H2CO3CO2+ H2O (Reaction 2) First Stage: In this case, pH of blood may be within normal range i.e. not much affected However, amount of buffer (HCO3-) is reduced (COMPENSATED ACIDOSIS) End Stage: Continuous reduction of H+ will lead to continuous reduction of buffer (HCO3-) will finally end in lowering pH of blood to below normal limits i.e. acidemia (UNCOMPENDSATED ACIDOSIS)

  7. Disorders of Acid-Base Balance • Increase in H+ concentrations results in a decrease in pH of blood (acidosis) • Decrease in H+concentrations results in an increase in pH of blood (alkalosis) Alkalosis or Acidosisdescribes any abnormality in H+ balance whether: 1- Compensated Alkalosis or Acidosis • Noblood pH changes (pH of blood is within normal range). • Buffer concentrations are abnormal • Compensatory mechanisms try to restore pH to normal if pH is changed. 2-Uncompensated alkalosis or acidosis (alkalaemiaoracidaemia) • AbnormalpHof blood (above or below normal range) • Buffer concentrations are abnormal

  8. Relation between pH & buffer Assessment of Acid-Base Balance Henderson-Hasselbach Equation Normal pH of blood is not an indication of acid-base balance. Accordingly, in order to assess acid-base balance (status) of blood , we should assess pH& buffer concentration of blood [HCO3-] pH= 6.1 + log --------------------------------- pCO2+ 0.225

  9. Assessment of Acid-Base Balance cont. Blood pH & bicarbonate buffer are to be measured Bicarbonate buffer measurement: 1- INDIRECTLY From arterial blood sample Using blood gas analyzer to measure pH& PCO2in arterial blood Accordingly, bicarbonatein blood can be measured indirectly by applying Henderson-Hasselbach Equation 2- DIRECTLY From venous blood Samples: used to measure HCO3-directly [HCO3-] pH= 6.1 + log --------------------------------- PCO2+ 0.225

  10. Acid-Base Balance Disturbances Acid-base 1- Acidosis: - Metabolic - Respiratory 2- Alkalosis: - Metabolic - Respiratory DIAGNOSIS IS CONFIRMED BY LABORATORY INVESTIGATIONS OF pH, pCO2 & pO2 & HCO3- Sample: Arterial Blood using Procedure: Blood gas analysis

  11. 1-Metabolic Acidosis Causes: I-Increased production of H+ Common Causes of increased H+ (acids) in the blood: 1- Increased endogenous acid production. - Diabeticketoacidosis (increased ketone bodies in blood) - Lactic acidosis (increased lactic acid in blood). 2-Ingestion of acids (or substance that produces an acid) - Poisons: as salicylate (aspirin) overdose - Methanolingestion - High protein diet. 3-decreased acid (H+) excretion by the kidney: in renal failure. II- Loss of bicarbonate: e.g. in diarrhea

  12. Metabolic Acidosis cont. Mechanism: The more decrease in HCO3- in blood leads to finally end in an decrease in pH as follows: [HCO3-] pH = 6.1 + Log ---------------------- PCO2 X 0.225 H+ is increased. It reacts with HCO3-. HCO3- is reduced.CO2 is produced then exhaled by lungs (increase respiration)H++ HCO3-H2CO3(Reaction 1) H2CO3CO2+ H2O (Reaction 2) CO2 is produced (increased) & then exhaled by lungs (increase respiration)

  13. Metabolic Acidosis cont Compensatory mechanisms of metabolic acidosis 1- Exhaustion of bicarbonate buffer with shift of reactions to CO2 production. Stimulation of the respiratorycentre to eliminate excess CO2 formed 2- Increase in renal acid excretion of H+

  14. LABORTORY INVESTIGATION: Sample: Arterial Blood Equipment: Blood Gas Analyzer pH: Low HCO3: Low PCO2: Low: asCO2 is produced then exhaled by lungs by increasing respiration PO2: Normal

  15. 2-Respiratory Acidosis Causes Impaired carbon dioxide excretion and thus blood pCO2increases. caused by any pulmonary (lung) cause resulting in hypoventilation. 1-Chronic respiratory acidosis: occurs due to chronic obstructive airway diseases. Chronic bronchitis Emphysema Bronchial asthma 2-Acute respiratory acidosis: occurs due to acute respiratory failure Cardiac arrest Neuromuscular disorders of chest wall Depression of the respiratory centre in the brain by: cerebral disease or drugs

  16. Respiratory Acidosis Mechanism: The increase in pCO2 in blood leads to an decrease in pH as follows: [HCO3-] pH = 6.1 + Log ---------------------- PCO2 X 0.225 CO2 is increased in blood (due to respiratory disease). So, the reaction is directed as followsCO2+ H2OH2CO3(Reaction 1)H2CO3H+ + HCO3-(Reaction 2)H+ is produced & pH is decreased (acidosis)

  17. Compensation:by kidney via ↑ HCO3- reabsorption ↑ H+ excretion LABORTORY INVESTIGATION: Sample: Arterial Blood Equipment: Blood Gas Analyzer pH: Low HCO3: High PCO2: High (due to the respiratory problem) PO2 : Low (due to the respiratory problem)

  18. 3-Metabolic ALkalosis The primary abnormality in metabolic alkalosis is the increased plasma bicarbonate level. (HCO3-). Causes: Less common 1- Intake of a large amounts of alkali as sodium bicarbonate: (if intake is more than 1000 mmol/day) More common 2- Loss of H+ (acids) from the body: 1- From the kidneys(increased excretion of acids, H+ ions): a- Mineralcorticoid(aldosterone) excess b- Severe potassium deficiency 2- From the GIT(increased loss acids, H+ ions): vomiting and gastric wash

  19. Metabolic ALkalosis Mechanism: The increase in HCO3- in blood leads to an increase in pH as follows: [HCO3-] pH = 6.1 + Log ---------------------- PCO2 X 0.225 H+ is reduced. So, the reaction is directed as followsCO2 production is increased by respiratory depression (compensatory)CO2+ H2O H2CO3(Reaction 1)H2CO3H+ + HCO3-(Reaction 2)HCO3-is produced & pH is increased (alkalosis)

  20. Compensation: by lungs via inhibition of respiration which leads to ↑ PCO2 LABORTORY INVESTIGATION: Sample: Arterial Blood Equipment: Blood Gas Analyzer pH: High HCO3: High PCO2 : High (due to compensatory respiratory depression)

  21. 4- Respiratory Alkalosis Causes: The PCO2 is reduced due to: Hyperventilationwhich may be due to: 1- Respiratory centre stimulation as in cases of: Anxiety Salicylateoverdose Cerebral disease (infection, tumour) 2- pulmonary embolism. 3- Fevers 4- Hepatic failure Mechanism The decrease in PCO2 leads to an increase in pHas follows: [HCO3-] pH = 6.1 + Log ---------------------- PCO2 X 0.225

  22. Respiratory Alkalosis CO2 is decreased. So, the reaction is as follows to produce CO2:H++ HCO3-H2CO3(Reaction 1) H2CO3CO2+ H2O (Reaction 2) Compensation : by kidney by ↓ HCO3 reabsorption and ↓ H+ secretion LABORTORY INVESTIGATION: Sample: Arterial Blood Equipment: Blood Gas Analyzer pH: High HCO3: Low PCO2 : Low

More Related