Therapeutics Exam 3 (Acid/Base) Flashcards
What is a normal physiological pH?
7.35-7.45
Acid-Base disorders fall into what 2 categories?
Metabolic
Respiratory
Kidney/Metabolic acid-base disorders refer to which 2 ions?
H+ and HCO3-
Lungs/Respiratory acid-base disorders refer to which 2 ions?
CO2 and H2O
Which type of acid-base disorder is easier to overcome? Metabolic or Respiratory?
Metabolic
-the lungs compensate much faster than the kidneys
-compensation for a disorder comes from the OPPOSITE SIDE
What is a normal PaCO2 value?
35-45 mmHg (40)
What is a normal HCO3 value?
22-26 meq/L (24)
What is a normal PaO2 value?
95-100 mm Hg
What is a normal SaO2 value?
> or = 95%
What are the consequences of acidemia?
Cardiac: Decreased output, Impaired contractility, Increased pulmonary vascular resistance
Metabolic: Insulin resistance, Inhibition of anaerobic glycolysis, *Hyperkalemia
CNS: Coma, Altered mental status
Other: Decreased respiratory muscle strength, hyperventilation, dyspnea
What are the consequences of alkalemia?
Cardiac: Decreased coronary blood flow, Arteriolar constriction, Anginal threshold, Arrhythmias
Metabolic: *Hypokalemia, Low Ca, Low Mg, Stimulation of anerobic glycolysis
CNS: Decreased cerebral blood flow, Seizures
Other: Decreased respirations
Where does acid come from?
Diet (1 mEq/day consumed)
Aerobic metabolism of glucose
Nonvolatile acid formation
-Anaerobic metabolism, Triglyceride oxidation, Metabolism of sulfur-containing amino acids and phospholipids
What are the 3 mechanisms of acid regulation?
Buffering
Renal regulation
Ventilatory regulation
What is the body’s first line of defense for acid regulation?
Extracellular/Intracellular buffering systems
What are the 3 main buffers in the body?
Bicarb/Carbonic Acid
Phosphate
Proteins
What is the principle buffer in the body?
Bicarbonate
*present in the largest concentration extracellularly over any of the other buffers
What happens when acid is added to your system?
HCO3- picks up H+ and becomes H2CO3 (carbonic acid)
H2CO3 dissociates to CO2 and H2O
How much new bicarb needs to be ingested by the body each day?
The body needs new bicarb added to the system in an amount that is equivalent to the H+ load ingested every day
What properties do phosphates have as a buffer?
Intermediate onset and capacity
-Slower
-Not as many available compared to bicarb
What properties do proteins have as buffers?
Rapid onset
Limited capacity
*very quick but limited
–more effective intracellularly than extracellularly
What are the 2 main purposes of the kidneys?
- Reabsorb filtered bicarb
- Excrete H+ ions released from nonvolatile acids (help regenerate new bicarb through hydrogen excretion)
How much bicarb gets reabsorbed by the body?
*Body is supposed to reabsorb all bicarb daily
-should have virtually none present in the urine
*Bicarb is also reabsorbed with no net loss of H+
Where does bicarb reabsorption take place?
85-90% is reabsorbed in the proximal tubule
10-15% is reabsorbed via distal tubule or collecting duct
Which enzyme is responsible for the dissociation of carbonic acid to for H2O + CO2?
Carbonic anhydrase
H+ Is excreted into the urine/tubular lumen in exchange for what?
Na+
How do bicarbonate losses in the urine occur?
When anything limits H+ secretion into the proximal tubule lumen and bicarb is not able to convert to carbonic acid, then to H2O + CO2 and get reabsorbed
-ex: carbonic anhydrase inhibitors
How do carbonic anhydrase inhibitors work?
-Inhibit activity of carbonic anhydrase
-Carbonic acid is not able to change to H2O + CO2 and cross into the proximal tubule
Note that metabolic acidosis occurs with increased bicarb excretion
*this is a way to correct alkylosis
Why must bicarbonate be generated?
Reclamation of all filtered bicarb is not sufficient to maintain normal blood pH
**Where does H+ excretion primarily take place?
Distal tubule
*this is a different area than where reabsorption is occurring
What are the 2 ways H+ excreted?
Ammonium Excretion
Secreted H+ ions combine with ammonia (NH3) in the distal tubule to make ammonium (NH4+) which cannot cross membranes
-this is excreted
Titratable Activity
Phosphoric acid (HPO4^2-) combines with secreted H+ in the distal tubule to become dihydrogen phosphate (H2PO4-)
It is too big to cross the membrane and gets excreted
Ammonium excretion is able to produce how much bicarb?
New HCO3- (40 mEq/day) can be increased to 300 mEq/day
Titratable activity (phosphate H+ excretion) is able to account for how much bicarb?
30 mEq/day of new bicarb
*capacity is smaller than ammonium excretion
*cannot be increased because it is limited by the buffer
Hydrogen ion secretion in the distal tubule comprises what % of net acid excretion?
50%
How does ventilatory regulation of acid occur?
-Rapid onset and large capacity
-Chemoreceptors detect increased PaCO2 and increase the rate and depth of ventilation
-More CO2 is expelled through ventilation