1 / 21

Acid-Base Analysis

Acid-Base Analysis. Sources of blood acids. Volatile acids. Non-volatile acids. H 2 O + dissolved CO 2. Inorganic acid. Organic acid. H+ + HCO 3 -. H 2 CO 3. Keto acid. Lactic acid. Henderson-Hasselbalch. pH = pK + log _ [HCO 3 ]_ s x PCO 2

madison
Download Presentation

Acid-Base Analysis

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 Analysis

  2. Sources of blood acids Volatile acids Non-volatile acids H2O + dissolved CO2 Inorganic acid Organic acid H+ + HCO3- H2CO3 Keto acid Lactic acid

  3. Henderson-Hasselbalch pH = pK + log _[HCO3]_ s x PCO2 pK = 6.1 s = 0.0301

  4. Excrete H+ into urine Active exchange of Na+ for H+ in tubules Carbonic anhydrase, in renal epithelial cells, assures high rate of carbonic acid formation <1% urine acid is free H+ Resorb filtered HCO3-, along with Na+ Excrete H2PO4, using phosphate buffer When phosphate buffer consumed, see H+ + NH3 = NH4+ Renal mechanisms

  5. Renal Compensation • Metabolic acidosis: • Phosphate and ammonia buffers used as plasma bicarb is deficient • Respiratory acidosis: • Increased H+ excretion, HCO3- retention • Metabolic alkalosis: • Increased urine HCO3- excretion • Respiratory alkalosis: • Decreased resorption of HCO3-

  6. Other compensation • Hypokalemia • Most K+ is intracellular • When K+ deficient, see redistribution to extracellular space (there Ki low) • H+ moves intracellularly to balance • K+ (keep) exchanged for H+ in distal tubules • Excrete H+, resorb HCO3-

  7. Other compensation • Hyponatremia • Renals Na+ resorption requires H+ excretion • HCO3 resorbed • Chloride • Freely exchanged across membranes (In=Ex) • When chloride deficient, other anions must “substitute”…increase HCO3-

  8. Nomenclature

  9. Partial Pressure

  10. pCO2 pO2 0 160 40 100 45 97 Capillary ~47 ~47 <39 <54 ~5 >55 <1 Atmosphere alv systemic circulation extravascular fluid cells

  11. Endothelium RBC ECF Cells 5% CO2 Dissolved CO2 = pCO2 30% CO2 + Hb = HbCO2 CarboxyHgb CO2 65% CO2 CO2 + H2O = HCO3 + H+ Utilizes carbonic anhydrase CO2 CO2 Transport

  12. Excretion of CO2 • Metabolic rate determines how much CO2 enters blood • Lung function determines how much CO2 excreted • minute ventilation • alveolar perfusion • blood CO2 content

  13. Hgb dissociation curve 20 % Sat 40 100 75 50 pO2 25 60 80 100

  14. Dissociation curve % Sat Shifts pO2

  15. Alveolar oxygen equation • Inspired oxygen = 760 x .21 = 160 torr • Ideal alveolar oxygen = PAO2 = [PB - PH2O] x FiO2 - [PaCO2/RQ] = [760 - 47] x 0.21 - [40/0.8] = [713] x 0.21 -[50] = 100 torr or 100 mmHg • If perfect equilibrium, then alveolar oxygen equals arterial oxygen. • ~5% shunt in normal lungs

  16. Normal Oxygen Levels

  17. Predicting ‘respiratory part’ of pH • Determine difference between PaCO2 and 40 torr, then move decimal place left 2, ie: IF PCO2 76: 76 - 40 = 36 x 1/2 = 18 7.40 - 0.18 = 7.22 IF PCO2 = 18: 40 -18 = 22 7.40 + 0.22 = 7.62

  18. Predicting metabolic component • Determine ‘predicted’ pH • Determine difference between predicted and actual pH • 2/3 of that value is the base excess/deficit

  19. Deficit examples • IF pH = 7.04, PCO2 = 76 Predicted pH = 7.22 7.22 - 7.40 = 0.18 18 x 2/3 = 12 deficit • IF pH = 7.47, PCO2 = 18 Predicted pH =7.62 7.62 - 7.47 = 0.15 15 x 2/3 = 10 excess

  20. Hypoxemia - etiology • Decreased PAO2 (alveolar oxygen) • Hypoventilation • Breathing FiO2 <0.21 • Underventilated alveoli (low V/Q) • Zero V/Q (true shunt) • Decreased mixed venous oxygen content • Increased metabolic rate • Decreased cardiac output • Decreased arterial oxygen content

  21. Blood gases • PaCO2 : pH relationship • For every 20 torr increase in PaCO2, pH decreases by 0.10 • For every 10 torr decrease in PaCO2, pH increases by 0.10 • PaCO2 : plasma bicarbonate relationship • PaCO2 increase of 10 torr results in bicarbonate increasing by 1 mmol/L • Acute PaCO2 decrease of 10 torr will decrease bicarb by 2 mmol/L

More Related