Blood pH and Blood Gases

• ACID


  Substance that can yield H+ (hydronium ions) when dissolved in water
• BASE


  Substance that can yield OH- (hydroxyl ions)
• pKa


  pH in which protonated and unprotonated forms are equal in concentration
• BUFFER


  • Bicarbonate-carbonic acid system 6.1
  • Combination of weak acid or weak base and its salt
• H2CO3


  Weak acid, carbonic acid
• HCO3


  Weak base, bicarbonate
• pH


  Power of hydrogen, negative log of H concentration, inversely proportional to H concentration
• Venous blood pH 7.35, Arterial blood pH 7.45
• Phosphate Buffer System


  Uses HPO4 and H2PO4 to minimize changes in the plasma and erythrocytes
• REGULATION OF ACID-BASE BALANCE: LUNGS AND KIDNEYS

  1. Lungs (Respiratory Mechanism)

  2. Kidney (Renal Mechanism)
• Henderson Hasselbalch Equation


  • pH = pK + log HCO3/H2CO3
  • pH = pK + log 0.0307 x PCO2
• Reference ranges at 37°C: pH 7.35-7.45, PCO2 35-45 mmHg, HCO3 22-26 mmol/L
• Lungs (Respiratory Mechanism)


  • Hyperventilation: ↓ CO2 release, ↓ H2CO3
  • Hypoventilation: ↑ CO2 release, ↑ H2CO3
• Kidney (Renal Mechanism)


  • Excretion of H+
  • NH4+ HPO4 - H2PO4- H+
• Acid Base Balance: Maintenance of H+

  H+ concentration: 36-44 nanomole/L, pH 7.35-7.45 (normal range), H+ excess can lead to alteration in consciousness, tetany, coma and death, Acidosis pH <7.35, Alkalosis pH >7.45
• Bicarbonate - Carbonic Acid System


  Weak acid: Carbonic acid (H2CO3) - lungs, Conjugate base: Bicarbonate (HCO3) - kidneys, H2CO3 dissociates into CO2 and H2O, CO2 modifies ventilation rate, HCO3 can be affected by the kidneys, Major extracellular buffer
• Hemoglobin Buffer System


  Used hemoglobin in RBC to minimize pH changes in the blood, Most important intracellular buffer
• Plasma Protein Buffer System

  Reabsorption of filtered H2O, Directly proportional to pH (acidic)
• Acid-Base Disorders: Acidosis and Alkalosis


  • Respiratory Origin
  • Metabolic Origin
• Respiratory Alkalosis


  • Excessive Reduction of H2CO3 or CO2, Caused by: High fever, Hysteria (hyperventilation), Pulmonary emboli and fibrosis, Compensation: ↓ Na/H exchange, ↓ NH3 production, ↓ Reabsorption of HCO3, ↓ Excretion of Acid H+
• Metabolic Acidosis


  • Primary Bicarbonate Deficit <24 mmol/L, Addition acidosis (diabetic ketoacidosis), Subtraction acidosis (diarrhea), Caused by: Renal Tubular Acidosis, Toxins, Starvation, Lactic Acidosis, Excessive loss of electrolytes and intestinal fluids, Compensation: Hyperventilation-control the rate of breathing
• Metabolic Alkalosis


  • Bicarbonate Excess (↑ pH), Caused by: Addition alkalosis (ingestion of Alkali), Subtraction alkalosis (vomiting), Diuretics, Excessive gastric suctioning, Intestinal obstructions, Compensation: Hypoventilation
• Compensation


  Goal: To maintain normal pH, Organs: Lungs and Kidneys
• Oxygen Transport


  Oxygen is transported to the tissue by hemoglobin
• Variations in Hemoglobin


  • Oxyhemoglobin
  • Deoxyhemoglobin
  • Carboxyhemoglobin
  • Methemoglobin
• Oxygen Saturation (SO2)


  Represents the ratio of oxygen that is bound to its carrier protein, hemoglobin
• Fractional (Percent) Oxyhemoglobin (FO2Hb)

  Ratio of the concentration of oxyhemoglobin to the concentration of total hemoglobin
• Partial Pressure of Oxygen Dissolved in Plasma (PO2)


  Counts for the little of the body's O2 stores
• Pulse Oximetry (SPO2)


  Uses a device to pass light to two or more wavelength through the tissue in the capillary bed of toe, finger, or ear
• Hemoglobin Oxygen Binding Capacity


  Maximum amount of oxygen that can be carried by hemoglobin in a given quantity of blood
• Oxygen Content


  Total oxygen in blood and is the sum of the oxygen bound to hemoglobin (O2Hb) and the amount dissolved in plasma (PO2)
• Blood Gas Analysis


  Measures pH, pCO2, PO2 using electrodes and gas analyzers
• Cathode


  Negative electrode, site to which cations tend to travel, site at which reduction occurs
• Anode


  Positive electrode, site to which anions tend to travel, site at which oxidation occurs
• PO2 Electrodes (Clark Electrode)

  Measure amounts of current flow in a circuit that is released to the amount of O2 being reduced at the cathode
• Continuous Measurement of PO2

  Made possible by using transcutaneous electrode (TC) placed directly in the skin
• pH


  Glass membrane coated placed around an internal Ag-AgCl electrode (measuring electrode)
• PCO2


  Severinghaus electrode - an outer semipermeable membrane that allows CO2 to diffuse into a layer of electrode
• Respiratory Acidosis

  • Excess H2CO3 or CO2, Caused by: Asthma, Emphysema, Bronchoneumia, Depression of Respiratory Center, Hypoventilation due to drugs, Congestive Heart Failure, Compensation: ↑ Na/H exchange, ↑ NH3 production, Reabsorption of HCO3, Excretion of Acid H