Acid-Base Disorders Flashcards
What does pH represent?
The [ ] of free hydrogen ions (protons) in circulation
What is normal human pH?
7.4
What pH level of extracellular fluid must be maintained for optimal functioning of body cells?
7.35-7.45
What is pH > 7.4?
alkalosis
What is pH < 7.4?
acidosis
What is an acid?
A molecule that releases hydrogen ions in solution
What is a base?
Any substance that can accept a hydrogen ion (removes free protons from solution)
What are 3 ways the body eliminates acids?
(1) pulmonary excretion of CO2
(2) metabolic utilization of organic acids
(3) renal excretion of nonvolatile acids (H+ + buffers)
Excess CO2 causes a(n) (inc/dec) in H+ leading to an (acidic/alkalotic) pH level in the body.
Inc in H+ → acidic
Excess HCO3- causes a(n) (inc/dec) in H+ leading to an (acidic/alkalotic) pH level in the body.
Dec in H+ → alkalotic
What are 4 sources of H+ gain?
(1) inc CO2
(2) production of phosphoric and sulfuric acids-metabolism of proteins and other organic molecules
(3) loss of bicarb from GI losses
(4) loss of bicarb from urine
What are 2 sources of H+ loss?
(1) loss of H+ in vomit
(2) loss of H+ in urine
Hypoventilation or respiratory diseases result in what?
Retention of CO2→ respiratory acidosis
Hyperventilation results in what?
Blowing off CO2→ respiratory alkalosis
What are 3 common causes of metabolic acidosis?
(1) excess production of lactic acid (>4 mEq/L): severe exercise or seizure, shock/hypoxia
(2) formation of ketone bodies: uncontrolled DM, fasting states
(3) loss of bicarbonate: diarrhea
What is the anion gap?
Difference b/w the plasma [ ] of the major cation (Na+) and the sum of the measured anions (Cl- and HCO3-) → AG = Na+ - [Cl- + HCO3-]
What does the difference of the anion gap represent?
The [ ] of unmeasured anions such as phosphates, sulfates, organic acids and proteins
What is responsible for a normal anion gap?
Excessive bicarbonate loss either intestinally or renally
What 2 things are responsible for an elevated anion gap?
Excess metabolic acid production and impaired elimination of metabolic acids; kidney dysfunction
What is the most common cause of metabolic acidosis in hospitalized pts?
Lactic acidosis
What are the 2 types of lactic acidosis? Describe each and say which is the most common.
Type A (hypoxic): most common
- Dec tissue perfusion→ inc lactic acid production
- Ex: cardiogenic, septic, hemorrhagic shock, carbon monoxide or cyanide poisoning
Type B (metabolic causes):
- Impaired cellular metabolism or tissue ischemia w/o systemic hypoperfusion
- Ex: DKA, alcoholism, infxns, malignancy, metformin, bowel necrosis
What does the AG metabolic acidosis mnemonic MUDPILES stand for?
Methanol Uremia DKA Propylene glycol Isoniazid Lactic acidosis Ethylene glycol and ethanol Salicylates (aspirin) and starvation
What are 4 causes of metabolic alkalosis?
(1) ingestion or admin of alkali
(2) stomach loss of H+
(3) renal loss of H+
(4) diuretic use
What are 4 causes of contraction alkalosis?
(1) loss of large volumes of bicarb free fluid
(2) bicarb [ ] remains constant
(3) admin of IV loop diuretics is the most common cause
(4) NaCl loss in cystic fibrosis
What causes impaired chloride reabsorption?
Diuretics block Cl reabsorption and further enhance NaHCO3 reabsorption
What affect does hypercalcemia have on bicarbonate?
Hypercalcemia reduces GFR→ inc bicarb reabsorption
A respiratory problem is suspected when there is a change in what?
pCO2
A metabolic problem is suspected when there is a change in what?
HCO3-
What are 3 renal responses to acidosis?
(1) bicarb in kidneys binds up as much H+ as possible
(2) additional H+ are excreted bound to other buffers
(3) new bicarb is formed during tubular glutamine metabolism
What are 3 renal responses to alkalosis?
(1) H+ binds as much bicarb as possible
(2) bicarb is excreted in urine
(3) tubular glutamine metabolism is decreased to lower new bicarb production
What are the initial 3 steps to interpreting ABG?
1: acidosis vs. alkalosis (look at pH)
2: does pCO2 explain the problem? (elevated in acidosis, dec in alkalosis)
3: yes pCO2 explains problem= respiratory, no= metabolic
