Acid-Base Balance

• Acid is the substance that donates a hydrogen ion when dissolved in water.
• Base are substances that can accept hydrogen ions
• pH is the negative log of the hydrogen ion concentration
• A decrease in one pH unit represents a 10x increase in the concentration of hydrogen ions.
• Henderson-Hasselbalch Eqution
• Henderson-Hasselbalch Eqution

  
• The body produces 150 g of Hydrogen ions everyday
• The normal concentration of H+ in the extracellular body fluids in maintained at 36 to 44 nmol/L
• Normal body pH range is 7.35 to 7.45
• Buffer systems prevent radical changes in the pH of the body fluids.
• Weak Acids takes up -OH ions
• Weak bases takes up H+ ions
• The Respiratory tract can adjust blood pH upward in minutes by exhaling CO2
• The renal system adjust blood pH through excretion of hydrogen ions and conservation of bicarbonate ions, this process can take several hours.
• There are 4 Buffer systems active in the body:

  1. Plasma Protein Buffer Systems: Amino and Hemoglobin
  2. Bicarbonate-carbonic acid Buffer system
  3. Phosphate buffer system
• Nearly all proteins can function as buffers. Mainly those made up of amino acids with positively charged amino groups and negatively charged carboxyl groups.
• The primary protein buffer in the plasma is albumin, due to its high concentration.
• Protein Buffer systems can both buffer H+ and CO2
• A left shift in the oxygen disassociation curve means

  • Increase pH
  • Low PCO2
  • Low 2,3-DPG
  • Low temperature
• Hemoglobin buffer system participates in the chloride shift
• A right shift in the oxygen disassociation curve means

  • Low pH
  • Increase PCO2
  • Increase 2,3-DPG
  • Increase temperature
• The phosphate buffer system plays a major role in the elimination of H+ via the kidney
• There are 2 forms of Phosphate in blood

  1. Sodium dihydrogen phosphate or NaH2PO4 - weak acid
  2. Sodium monohydrogen phosphate or Na2HPO4 - weak base
• Bicarbonate is regulated by sodium in the blood\
• The bicarbonate-carbonic acid ratio in blood is 20:1
• The lungs regulate the blood pH by regulating the carbonic acid levels
• CO2 is transported in the blood as a dissolved form which is 5-8% and some combine with hemoglobin to form carbaminohemoglobin, which are 92-95%.
• Once bicarbonate is formed exchange for chloride will happen.
• The conversion factor for the Henderson-Hasselbach equation is 0.0307 to convert mmHg to mmol/L
• The kidney is the most effective regulator of pH. So if kidney fails, pH balance fails
• If the levels of PCO2 is affected the organ affected is the lungs. And the kidney will compensate.
• If the HCO3- levels are affected then the organ affected is the kidney. And then the lungs will compensate
• The medulla oblongata is responsible for modulating the breathing rate in order to respond in CO2 levels in the blood.
• The enzyme responsible in the catalyzation of Carbonic acid disassociation is Carbonic anhydrase.
• The higher the concentration of K+ in blood, the less the H+ absorbed in the kidney, resulting in less bicarbonate conserved.
• Sample type preffered for Blood Gas Analysis is whole blood, arteial sample
• Sites of collection for arterial blood:

  1. Radial artery
  2. Femoral artery
  3. Brachial artery
• Venous blood and capillary blood can be used for Blood gas analysis but is not usually preferred.
• The anticoagulant preferred for Arterial blood collection is dry sodium or lithium heparin.
• Siggard-Anderson nomogram is used in the calculation of Base Excess and total CO2 and HCO3- concentration