ACID - BASE PHYSIOLOGY

2. ACID - BASE PHYSIOLOGY DEFINITIONS • ACID - can donate a hydrogen ion • BASE – can accept a hydrogen ion • STRONG ACID – completely or almost completely dissociates into a hydrogen ion and its conjugate base in aqueous solution • WEAK ACID – only slightly dissociated in aqueous solution • Strong acids usually have weak conjugate bases; weak acids usually have strong conjugate bases • BUFFER – mixture of substances in aqueous solution. Usually a weak acid and its conjugate base, that can resist changes in hydrogen ion concentration when strong acids or bases are added.

3. ACID - BASE PHYSIOLOGY DEFINITIONS pH - negative log of hydrogen ion concentration ACIDOSIS - pH < 7.35 ALKALOSIS - pH > 7.45

6. ACID - BASE PHYSIOLOGY BUFFERS OF THE BODY • ISOHYDRIC PRINCIPLE – All buffer pairs in a homogeneous solution are in equilibrium with the same hydrogen ion concentration • BICARBONATE • PHOSPHATE • BLOOD PROTEINS – especially hemoglobin • INTERSTITIAL FLUID – mainly bicarbonate, some phosphate • BONES – mainly phosphate in hydroxyapatite • INTRACELLULAR BUFFERS – intracellular proteins and organic phosphates

7. Transport of CO2 by the Blood CO2 (Gas phase) Carbonic Anhydrase _ CO2 + H2O H2CO3 H+ + HCO3 (Dissolved in the aqueous phase)

8. Taking Logarithms Since pH is negative logarithm

9. Henderson – Hasselbalch Equation [HCO-3] p pH = pK´ + log 0.03 x Pco2

12. 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 Respiratory acidosis Metabolic alkalosis and respiratory acidosis F 40 D 35 Compensated E 30 HCO3- Pco2 [HCO3- ]p , mmol/ liter C Uncompensated respiratory acidosis 25 A I B 20 G 15 H pH

13. Common Causes of Respiratory Acidosis • Depression of Respiratory Control Centers • Anesthetics • Sedatives • Opiates • Brain injury or disease • Severe hypercapnia, hypoxia • Neuromuscular disorders • Spinal cord injury • Phrenic nerve injury • Poliomyelitis • Botulism, tetanus • Myasthenia gravis • Administration of curare-like drugs • Diseases affecting the respiratory muscles • Pulmonary diseases • Acute asthma • Pulmonary vascular disease

14. Common Causes of Respiratory Acidosis • Chest wall restriction • Kyphoscoliosis • Extreme obesity • Lung restriction • Pulmonary fibrosis • Sarcoidosis • Pneumothorax • Pulmonary parenchymal diseases • Pneumonia • Pulmonary edema • Airway obstruction • Chronic obstructive pulmonary disease • Upper airway obstruction

15. 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 Respiratory alkalosis F 40 D HCO3- Pco2 35 E 30 [HCO3- ]p , mmol/ liter C 25 A Uncompensated respiratory alkalosis I B 20 G Compensated 15 H Metabolic acidosis and respiratory alkalosis pH

16. Common Causes of Respiratory Alkalosis • Central Nervous System • Anxiety • Hyperventilation • Inflammation (encephalitis, meningitis) • Cerebrovascular disease • Tumors • Drugs or hormones • Salicylates • Progesterone • Pulmonary diseases • Acute asthma • Pulmonary vascular disease (pulmonary embolism)

17. Common Causes of Respiratory Alkalosis • Bacteremias, fever • Overventilation with mechanical ventilators • Hypoxia,high altitude

18. 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 Metabolic acidosis F 40 D 35 E 30 HCO3- Pco2 C [HCO3- ]p , mmol/ liter 25 A Metabolic acidosis I B 20 G Compensated Uncompensated metabolic acidosis 15 H Metabolic acidosis and respiratory alkalosis pH

19. Common Causes of Metabolic Acidosis • Ingested drugs or toxic substances • Methanol • Alcohol • Salicylates • Ammonium Chloride • Ethylene glycol • Loss of bicarbonate ions • Diarrhea • Pancreatic Fistulas • Renal dysfunction • Inability to excrete hydrogen ions • Renal dysfunction

20. Common Causes of Metabolic Acidosis • Lactic acidosis • Hypoxemia • Anemia, carbon monoxide • Shock (hypovolemic,cardiogenic, septic, etc.) • Severe exercise • Acute respiratory distress syndrome (ARDS) • Ketoacidosis • Diabetes mellitus • Alcoholism • Starvation

21. 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 Metabolic alkalosis Metabolic alkalosis and respiratory acidosis F Compensated 40 D 35 E Metabolic alkalosis 30 HCO3- Pco2 [HCO3- ]p , mmol/ liter C 25 A 20 I B G 15 H pH

22. Common Causes of Metabolic Alkalosis • Loss of hydrogen ions • Vomiting • Gastric fistulas • Diuretic therapy • Treatment with or overproduction of mineralocorticoids • Ingestion or administration of excess bicarbonate • Intravenous bicarbonate • Ingestion of bicarbonate or other bases (e.g. antacids)

26. ACID - BASE PHYSIOLOGY DEFINITIONS BASE EXCESS OR DEFICIT = mEq of acid or base needed to titrate 1 liter of blood to a pH of 7.4 at 37ºC if the Pco2 were 40 torr ANION GAP = [Na+] - ([Cl-] + [HCO3-]) Normally 12 ± 4 mEq / L If the anion gap is greater than 16 mEq / L : Lactic acidosis, ketoacidosis or organic anions Renal retention of sulfate, phosphate, or urate Decreased [K+], [Ca++], and/ or [Mg++]

27. Acid- Base Disturbances _ HCO3 pH Pco2 Uncompensated respiratory acidosis Uncompensated respiratory alkalosis Uncompensated metabolic acidosis Uncompensated metabolic alkalosis Partially compensated respiratory acidosis Partially compensated respiratory alkalosis Partially compensated metabolic acidosis Partially compensated metabolic alkalosis Respiratory and metabolic acidosis Respiratory and metabolic alkalosis

28. Pvo2 Cvo2 A Classification of the Causes of Hypoxia Increased FIo2 helpful? PAo2 Pao2 Cao2 Classification Hypoxic hypoxia Low alveolar Po2 Diffusion impairment Right to left shunts V/Q mismatch Anemic hypoxia CO poisoning Hypoperfusion hypoxia Histotoxic hypoxia Low Norm Norm Norm Norm Norm Norm Norm Low Low Low Low Norm Norm Norm Norm Low Low Low Low Low Low Norm Norm Low Low Low Low Low Low Low High Low Low Low Low Low Low Low High Yes Yes No Yes No Possibly No No