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Define Acid
Capable of giving up H+ ions
Define Base
Accepts H+ ions
Acid-base balance
H+ ion concentration maintained at normal values by body's physiologic process
Define pH
Measure of H+ ion concentration in solution, is a logarithmic value (pH of 5.0 is 10 times as acid as pH of 6.0)
Define Acidemia
Blood more acid than normal pH < 7.35
Define Alkalemia
Blood more alkaline than normal pH > 7.45
Normal values for PaO2
80-100 torr
Normal values for PaCO2
35-45 torr
Normal values for O2 sat %
Normal values for pH
Normal values for HCO3
22-26 mEq/L
Define Base Excess
Number of mEq/L above normal HCO3 level of 24. Normal base excess is -2/+2
What is H2CO3 ?
Carbonic acid, the primary acid in blood
Define Buffer
Agent that can neutralize both acids and bases or partially control pH flucuations
Define Chronic
Long duration
Define Electrolytes
Electrically charged particles (ions) in blood. Ion has either a (-) or (+) electrical charge
Define HCO3
  • Bicarb (anion)
  • Normal value 22-26 mEq/L
Define Cl
  • Chloride (anion)
  • Normal value 98-106 mEq/L
Define K+
  • Potassium (cation)
  • Normal value 3.5-5.0 mEq/L
Define Na+
  • Sodium (cation)
  • Normal value 136-145 mEq/L
Key Points of Electrolytes
  • They maintain internal chemical balance
  • Metabolic process responsable for this process necessitates a delicate balance
  • Electrolytes must be maintained within narrow limits to preserve normal metabolic function
Define Cations
Positivley charge ions
Define Anions
Negatively charged ions
Primary electrolytes manipulated by kidneys
  • Na+
  • K+
  • Cl-
  • HCO3
Electrolyte mechanism of K+
  • Distribution of K+ within intracellular and extracellular spaces influence acid-base balance
  • Most K+ is intracellular
  • Abnormal levels of K+ very dangerous
Electrolyte mechanism of K+ Part 2
  • If K+ is forced to leave cell, H+ must move into intracellular fluid from plasma to maintain electrical balance.
  • This causes increased level of K+ in extracellular fluid called hyperkalemia


Electrolyte mechanism of Cl-
  • 66% of all Cl- is stored in plasma (extracellular space)
  • Cl- is most abundant anion
  • Cl- concentration is regulated
Define acid-base balance
The physiological mechanism that maintains body pH in a range that is compatible with life.
Two catagories of acids
  • Volatile- primarily carbonic acid (H2CO3)
  • Non volatile- (fixed) sulfuric acid, phosphoric acid and lactic acid
Function of buffer solutions
Resist changes in pH when an acid or base is added
Two mechanisms buffer solutions utilize to maintain pH values

  • Closed system- primarily hemoglobin and plasma proteins

  • Open system- plasma and erythrocytes

Fundamental acid-base equation
H + HCO3 <-> H2CO3 <-> H2O + CO2
Acid-base equation specifics
  • H2O comes from our body
  • CO2 produced during aerobic metabolism
  • If CO2 increases pH goes down
  • If CO2 decreases pH goes up
Two primary acid excreting organs
Lungs and kidneys
Acid excreting specifics of lungs
  • Lungs only excrete CO2
  • Lungs control CO2 through hyper or hypo ventilation (respiratory)
  • When lungs "blow off" CO2 that causes chemical reaction, drives equation to right
Acid excreting specifics of kidneys

  • Kidneys primarily control acid base balance by utilizing H and HCO3 (metabolic)

  • Kidneys balance acid base by means of excretion, secretion and reabsorbtion

Define excretion
Removing substance from body
Define secretion
Circulating substance within the kidney
Define reabsorbtion
Transporting substance back into capillary system
Function of glomerulus
Responsable for filtering the blood and assisting in acid base balance
Glomerulus consists of :
  • Blood filled peritublular capillary that is permeable to CO2, Na, and HCO3 and not permeable to H
  • Tubule cell which collects filtrate and excretes fluid as urine
  • it is here that kidneys titrate H and HCO3
When CO2 is high this :
  • Drives equation to left
  • More HCO3 is reabsorbed into the peritubular capillary to maintain acid-base balance
  • More H is secreted to combine with HCO3 to create H2CO3
  • Excess H is excreted in urine
When CO2 is low this :
  • Drives equation to the right
  • Less H is secreted
  • Less HCO3 is reabsorbed into the blood maintaining acid-base balance
  • More HCO3 is excreted in urine
Rules for interpeting ABG's
  • Combined = All same
  • Compensated = Normal pH
  • Partially compensated = no normal values
  • Uncompensated = Normal CO2 or HCO3
Acid Excretion
  • Lungs and kidneys are primary acid excreting organs.
  • Only lungs excrete CO2
  • Lungs can rapidly remove large quantities of CO2 from blood.
  • Kidneys remove acid but at a slower pace.
Normal Venous Blood Gas Values
  • O2 Sat- 70%-75%
  • PaO2 - 35-40 torr
  • PaCO2 - 41-51 torr
  • pH- 7.36-7.41 mEq/L
  • Bicarb- 22-26 mEq/L
Define Compensation
When any primary acid-base defect occurs the body intiates a compensatory response
Define Respiratory Acidosis
  • Cause- any process in which alveolar ventilation fails to eliminate CO2 as rapidly as the body produces it.
  • PaCO2 > 45 torr and pH < 7.35
  • Correction- improve alveolar ventilation, increase Vt, RR, amd Ve.
Define Respiratory Alkalosis
  • Cause-any process that decreases PaC
    O2 < 35 torr and pH > 7.45
  • Clinical signs- numbness, tingling, and lightheadedness
  • Correction- removal of stimulus causing the hyperventilation (use medications)
If PAO2 is high ________
Decrease FIO2 given
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