Electrolytes & Acid-Base Balance Flashcards
Control of Cell Excitability
K controls…
Ca controls…
RMP (-90)
Threshold (-60)
Does hypocalcemia or hypercalcemia lead to an increase in nerve and muscle excitability?
Hypocalcemia - threshold (-60) becomes more negative and shifts toward the RMP (-90)
*Parathyroid glands removed - hypocalcemia - risk of larynospasm
Does hypokalemia or hyperkalemia cause cells to become more excitable?
Hyperkalemia - RMP (-90) becomes more positive and moves toward threshold (-60)
*Makes sense why we give Ca in the setting of hyperkalemia (increase threshold)
Does alkalosis or acidosis cause a decrease in free ionized calcium levels?
Acute respiratory alkalosis
Causes a functional hypocalcemia (total calcium doesn’t change, free ionized active calcium levels decrease)
Hyperventilate - H concentration decreases - H breaks away from proteins to become active - now there is more protein to bind to ionized Ca
Therapies for Treating Hyperkalemia
- Give Ca in order to make threshold more positive (RMP is more positive)
- Give HCO3 - alkaline urine = increases K secretion, increased HCO3 - decreased H (metabolic alkalosis) - H shifts OUT cells + K shifts IN cells
- Hyperventilate - respiratory alkalosis - H shifts OUT cells + K shifts IN cells
- Insulin + glucose - stimulates the Na-K pump
- Beta-2 agonist - stimulates the Na-K pump
- Dialyze
For each 10 mmHg decrease in PaCO2, serum K decreases by ____mEq/L.
0.5 mEq/L
Why do you see PVCs with hypokalemia?
Hypokalemia - RMP hyperpolarizes - excitability is decreased
Exception: purkinje cells more readily depolarize to cause the PVCs
Hyperventilation causes what 2 electrolyte abnormalities?
- Hypokalemia
2. Hypocalcemia (functional)
Can complete compensation be achieved if there is metabolic acidosis or metabolic alkalosis?
NO
If it is completely compensated, then it is a respiratory disturbance
What is the fundamental event in the kidney’s regulation of acid-base balance?
Na-H exchange
Permits Bicarb to be reabsorbed
Permits acids to be excreted (H, NH3 to NH4 diffusion trapping)
Is HCO3 normally excreted?
NO
90% is reabsorbed from the PCT
10% is reabsorbed in later segments
Describe the Na-H exchange.
Na is being reabsorbed
HCO3 is being reabsorbed
H is being secreted in urine
Carbonic anhydrase plays a role
Anion Gap Formula
What is the normal anion gap?
AG = Na - Cl + HCO3 HCO3 = Na - Cl - AG Normal = 12 (this accounts for the unmeasured anions)
Diagnosis of metabolic acidosis
High AG - uremia, lactic acidosis, ketoacidosis, ingested acids
Normal AG = hyperchloremic acidosis diarrhea, carbonic anhydrase inhibitors
What does acidosis do to neuronal activity? What does acidosis do to the seizure threshold?
Depresses neuronal activity
Raises the seizure threshold - more difficult to have a seizure
What is the acid-base status of the hypothermic patient?
Metabolic acidosis
What is the major intracellular buffer?
Proteins
The kidneys excrete H as what 2 types of acids?
- H2PO4
2. NH4
What is the most common cause of normal anion gap metabolic acidosis?
Diarrhea
What % of body weight is water?
60%
What fraction of total body water is found in the extracellular space?
1/3
Sodium salts represent what % of all electrolytes in the ECF?
90%
Sodium concentration is regulated by what 2 factors?
- Thirst
- ADH
- ADH - osmolality - CONCENTRATION of Na
- Aldosterone - volume - AMOUNT of Na
What is the most common electrolyte disturbance in the hospitalized patient?
Hyponatremia < 135
If 120, severe s/s
Which hormone works faster: ADH or aldosterone?
ADH 5-10 mins
aldosterone 30-45 min
