5. •Osmolality is a measure of the solute
concentration per kg in a solution.
•Solute is a substance dissolved in a solvent
•Solvent is a substance that is capable of
dissolving a solute (liquid or gas).
•Tonicity is the tension or effect that the
osmotic pressure of a solution with
impermeable solutes exerts on cell size due
to water movement across the cell
membrane.
55
23. SSooddiiuumm
Na+: 135-145 mEq/L
- the most abundant cation in ECF
- functions: maintain water balance, nerve
impulse transmission, regulate acid-base
balance, and participate in cellular
chemical reactions.
- regulated by dietary intake & aldosterone
secretion
2233
Most sodium losses occur in the kidneys. Small amt (<10%) lost in the GI tract.
Inability to concentrate their urine d/t large volume diuresis; excessive thirst
Excretion of 3-20 L/day
Neurogenic (or central) DI – d/t defect in synthesis or release of ADH. May follow traumatic head injury or surgery around hypothalamohypophysial tract.
Nephrogenic – kidneys do not respond to ADH
Intense thirst and craving for ice water
Hypernatremia & dehydration if limited access to water
Tx for chronic DI: desmopressin (DDAVP)
Tx
depends on severity…if mild, fluid restriction; if not sufficient, Lasix or mannitol diuretics
If severe water intoxication: 3% sodium chloride. Other meds: conivaptan, block ADH V2 receptors and results in aquaresis
Most common electrolyte imbalance in hospitalized pts ; common in elderly (decrease renal sodium conservation)
1 kg = 1L water weight
S&S develop once 120 mEq/L
Sticky mm..swallowing becomes difficult
Another cause: administration of NaHCO3- during cardiopulmonary arrest
K maintains many body functions
Also regulates acid-base balance; necessary for the kidneys to concentrate urine
ECG changes: ↓K decreases the resting membrane potential, causing prolonged PR interval, and prolonged relative refractory pd which causes ST segment depression, flattened T wave, and presence of a U wave
Abnormal breakdown and rformation of bone. But new bone is weaker and breaks easily. Cause unknown.
STARVED:
Seizures
Tetany
Anorexia & arrhythmias
Rapid heart rate
Vomiting
Emotional lability
Deep tendon reflexes increased
RENAL acronym: Remember that poor renal excretion is a major cause of hypermagnesemia.
S&S:
Reflexes decreased (plus weakness & paralysis)
ECG changes (bradycardia) & hypotension
Nausea & Vomiting
Appearance flushed
Lethargy (plus drowsiness & coma)