Understanding Acid/Base Balance Marilyn F. Brown Broad Concepts: Body pH tolerated in very narrow range 7.35 – 7.45 pH is defined as H+ ion concentration The more hydrogen ions, the more ACIDIC pH range roughly compatible with life is 6.8 – 7.8, but that represents a 10-fold difference in H+ ion concentration The primary buffer is bicarbonate (HCO3-

CO 2 + H 2 0 = H 2 CO 3 = H + + HCO 3 - LUNGS Kidneys Carbonic Acid Hypoventilation = increased CO 2 Hypervention = decreased CO 2 Requires adequate kidney function

So……… pH = 7.35 – 7.45 Kidneys regulate the metabolic side of acid base disturbances –Kidneys are slow –Indicator is bicarbonate (HCO 3 - ) Lungs regulate the respiratory side of acid base disturbances –Lungs are fast –Indicator is carbon dioxide (CO 2 ) Carbon dioxide is POTENTIAL ACID

Above the pyloric sphincter is ACID Below the pyloric sphincter is BASE

pH < 7.35 PaCO 2 = 35 – 45 (normal) HCO 3 < 22 METABOLIC ACIDOSIS (base bicarbonate deficit) Causes: lose base (diarrhea) gain acids

Metabolic Alkalosis (base bicarbonate excess) pH > 7.45 PaCO 2 = 35 – 45 (normal) HCO 3 > 26 Causes: Lose acid (vomiting or N/G) Add base

Respiratory Acidosis (carbonic acid excess) pH < 7.35 PaCO 2 > 45 HCO 3 = 22 – 26 (normal) Cause: Hypoventilation Poor O 2 CO 2 exchange

Respiratory Alkalosis ( carbonic acid deficit ) pH > 7.45 PaCO 2 < 35 HCO 3 = 22 – 26 (normal) Cause: Hyperventilation Blow off too much CO 2

Practice Acid/Base Situations

pH HCO3 PaCO2 Imbalance Common Causes

Don’t Peek! Try the problems first Objective: given a set of abg results including pH, PaCO 2 and HCO 3, student can correctly calculate the imbalance Will always be uncompensated in Med- Surg I

pH HCO3 PaCO Metabolic Acidosis Respiratory Acidosis Metabolic Alkalosis Respiratory Alkalosis