Acid-Base Balance PDF

ACID-BASE BALANCE Tamethia Perkins MS, RRT-NPS, RRT- ACCS RT 3005/6005 CARBON DIOXIDE TRANSPORT  CO2 Transport At rest: * Tissue cells consume 250 mL of O2 and Produce 200 mL of CO2 each minute. – RQ = 200 ml CO2/250 ml O2 = 0.8 The CO2 is...

ACID-BASE BALANCE Tamethia Perkins MS, RRT-NPS, RRT- ACCS RT 3005/6005 CARBON DIOXIDE TRANSPORT  CO2 Transport At rest: * Tissue cells consume 250 mL of O2 and Produce 200 mL of CO2 each minute. – RQ = 200 ml CO2/250 ml O2 = 0.8 The CO2 is transported from the tissues in six different ways - in the RBC and in the plasma. – In Plasma » Carbamino compound » Bicarbonate » Dissolved CO2 – In RBCs » Dissolved CO2 » Carbamino Hb » Bicarbonate  PLASMA 1% of the CO2 combines with free amino groups = carbamino compound. 5% ionizes as bicarbonate. It initially combines with water (hydrolysis) to form carbonic acid (H2CO3) which rapidly converts into HCO3- and H+ ions. CO2 + H2O = H2CO3= HCO3- + H+. 5% of total dissolved CO2 is released to the lungs. This is the portion assessed in the venous blood. CO2  IN RBCs 5% of CO2 is dissolved in the intracellular fluid of the RBC. 21% combines with the Hb to form carbaminoHb. The O2 released from this reaction is available for tissue metabolism. 63% of CO2 is transported to the lungs in the form of HCO3-. Same reaction in plasma is enhanced by carbonic anhydrase. Rapid hydrolysis causes RBC to be saturated with with HCO3-, so excess HCO3- diffuses out to the plasma, combines with Na (NaCl) and it is transported as NaHCO3 in the venous blood.  In RBCs (cont.) As HCO3- moves out of the cell, the Cl- moves into the RBC to keep neutrality. – Chloride shift or Hamburger phenomenon. In the plasma the ratio of HCO3- and H2CO3 is 20:1. This ratio keeps the pH between 7.35-7.45. CO2 CO2 Elimination at the Lungs  CARBON DIOXIDE DISSOCIATION CURVE  CO2 Dissociation Curve Almost linear. There is more relationship between PCO2 and the amount of CO2 content. – PCO2 from 40 to 46 = CCO2 increases by 5vol%. – Same PO2 change results in a 2vol% change. Haldane effect: deoxygenated blood enhances CO2 loading by Hb and vice versa. CO2 dissociation curve ACID-BASE BALANCE  DEFINITION OF TERMS Electrolytes: charged ions. Buffer: neutralizes acids and bases without causing changes in the pH. Acid: substance that donates H+. Base: substance that accepts H +.  pH SCALE Quantitative measurement of the [H+]. pH=-log10[H+]. Normal: 7.35-7.45 pH narrow range is maintained by Buffer system Respiratory system Renal system.  BUFFER SYSTEMS Ability to resist large changes in pH is called a buffer action. Buffers of interest to the RT: – Plasma: » Carbonic acid/Sodium bicarbonate H2CO3/NaHCO3 » Sodium acid phosphate/Sodium alkaline phosphate NaH2PO4/NaHPO4 » Acid proteinate/Sodium proteinate Hprot/Naprot – RBCs: » Acid Hb/Potassium Hb HHb/KHb » Potassium acid phosphate/potassium alkaline phosphate KHPO4/K2HPO4 HENDERSON-HASSELBACH EQUATION pH=pK(6.1)+ log [HCO3-]/[H2CO3]. When HCO3- is 24mEq/L and the H2CO3 is 1.2 mEq/L= – pH= 6.1 + log 24mEq/L/1.2 mEq/L – pH= 6.1 + 1.3 = 7.4