HTHSCI 1LL3 Lecture Notes - Lecture 2: Bowel Obstruction, Perfusion, Shortness Of Breath
21 Apr 2018
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Lungs: normal paco2 value is between 35-45 mm hg, regulation directly related to rate and depth of air movement in lungs, chemoreceptors in arteries and medulla increase/decrease ventilation in response to ph, pao2, Paco2 changes: elevated paco2 = hypoventilation, decreased paco2 = hyperventilation. Kidneys: maintains bicarbonate concentration, normal hco3- value approx. 24 meq/l: 3 mechanisms to maintain acid-base balance, reabsorption of filtered bicarbonate in proximal tubule (catalyzed by carbonic anhydrase, titratable acid formation, excretion of nh4 (ammonium) in urine. Inhibited carbonic anhydrase can lead to metabolic acidosis: bicarbonate will be excreted, not enough bicarbonate to "mop up" excess hydrogen ions. If a patient presents with metabolic acidosis, an anion gap should be calculated. Acid-base principles: respiratory alkalosis: primary issue is elevated ph and decreased paco2. Kidneys compensate by excreting hco3- to lower the ph: complete respiratory compensation requires adequate lung capacity.
