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What cation is responsible for the generation of the action potential?
What Cation of important for regulating normal osmolarity and what is the normal osmolarity?
Na+, 275-290 mOsm/L
Will small percentage changes in osmolalaity precipitate the release of ADH?
yes, even a small change like 1%
Where are the osmoreceptors that measure the osmolality of the plasma?
in the hypothalamus
What determines the balance of the Na+ in the extracellular fluid?
intake of Na+ relative to excretion
What happens to the excess sodium that we normally take in?
it is filtered out of system by the kidneys
How much Na+ is required per day?
it is a range, premature infants 3mEq-adults 1.5 mEq/kg/day
How much sodium in mEq does the average 70 kg healthy adult require in one day?
what units are Na+ usually reported in the body?
mEq, normal is 135-145 (130-150 Barash)
What is the most common cause of hyponatremia?
excess free water
What is Hypernatremia?
What can cause hypernatremia?
- excess salt intake
- Excess water excretion, or lack of ADH action
- inadequate water intake
Are disorders in total body sodium more closely related to plasma sodium level or of total body water?
total body water, because sodium follows water
Does the plasma level of sodium give a good measure of total body sodium?
What two systems partner to regulate the total body sodium and sodium concentration?
What hormone helps to regulate the concentration of sodium?
What hormones regulate the total body sodium?
ANP and aldosterone
Normally the amount of sodium _______ by the kidney equal the amount of sodium _______.
What situations can sodium losses be greater than normal?
- Extreme sweating
How what is the ratio of urine to mOsm of solute normally excreted?
10ml urine/mOsm solute
What normally happens when we give a free water challenge to a pt?
kidney will diuresis
What is the bodies normal response to a sodium load?
naturesis, or excretion of sodium
What occurs when there is a reduction in free water, and a reduction of sodium?
antiduriesis, and antinaturesis respectively
What is hyponatremia?
Decrease in plasma concentration of sodium
What causes hyponatremia?
- loss of Na+ from the ECF
- Addition of excess water to ECF
Why would a primary loss of Na+ result in hypovolemia?
- because water follows Na+
- There would be hyponatremia and hypovolemia
What are some causes of hyponatremia?
- overuse of diuretics
- diarrhear (he he) and vomiting
- pt's with addisons disease
Why would a pt with addisons be at risk for hyponatremia?
decrease in aldosterone impairs the ability to absorb Na+
What is usually responsible for hyponatremia?
Excess water, dilution of bodies sodium
What could cause an inability to excrete free water?
an increase in ADH
What common factors decrease ADH secretion?
- Sympathetic stimulation
Would we see an increase or decrease in ADH with the average surgery pt?
usually an increase that would lead to a decrease in water excretion
Why would we assess the osmolarity of pt who is hyponatremic?
a loss in sodium can result in a decrease of of overall osmolarity of the plasma
What is TURP syndrome and what types of procedures is it associated with?
- Intravascular absorption of fluid used for irrigation.
- TURPs and operative hysteroscopy
Can hyponatremia occur in a pt that is hypovolemic?
- Yes in cases of
- -cerebral salt wasting
Does hyponatremia occur in hypervolemic patients?
- yes in cases of:
- -Nephrotic syndrome
- -TURP syndrome
Does hyponatremia occur in euvolemic patients?
- yes in cases of:
- -psuedohyponatremia syndrome
What is the most common electrolyte disturbance in hospitalized pt's?
In most pt's with hyponatremia is the total body sodium decreased?
no, it is usually normal or increased
What are the most commonly seen situations that hyponatremia is common?
- Post operative state
- acute intracrainial disease
- malignant disease
- acute pulmonary disease
Why does hyponatremia represent an increased mortality
combo of the lyte disturbance and the underlying cause
What do the s/s of hyponatremia depend on?
The rate of the loss of sodium and also the severity of sodium loss.
What is severe Hyponatremia?
Na+ <120 mEq/L
Why would we choose to do a TURP with spinal anesthesia vs. General?
So the patient is awake and we can assess for s/s of hyponatremia by gauging LOC
Why do we see such dramatic disturbances in the CNS because of hyponatremia?
over-hydration of the brain
Will acute changes in Na+balance create more serious symptoms than chronic changes?
How many (%) post op pt's will develop a sodium of <130?
4% and it is usually dilutional
Is it anemier or anemia? I'm confused.
Sue would say anemier so I better stick with that.
When there is a rapid decrease in sodium concentration what happens to the rest of the cells?
they will grow in volume, specifically the brain will grow
Following the growth from excess water what happens in the brain cells regarding the solutes?
because of the excess growth the solutes will leave the cell
Following the loss of solutes from dilution of cell contents in the brain what occurs next?
Water follows the solutes as they leave the cell.
When we rapidly correct sodium by replacing IV what can occur if done too quickly?
Additional water will leave the cell causing a dehydration of brain tissue and demyelination of neurons
What is a hazard of giving hypertonic saline solutions?
central pontine myelinolysis: aka loss of central myelin in response to acute hypernatremia.
How do we avoid replacing saline too fast?
limit correction of Na+ to 10-12 mEq/L in 24 hrs, 18 mEq/L in 18 hrs
What are the symptoms of central pontine myelinolysis?
- mild behavioral disturbances
What is the main component of determining the magnitude of symptoms associated with CPM?
- the chonicity (is that a word?)
- and the rate of correction
How would we treat normo or hyperosmolar (>280 mOsm/kg) hyponatremia?
- water restriction
How would we treat a hypervolemic hyponatremic pt?
- Restrict both Na+ and water
- give meds to improve cardiac output and renal perfusion if indicated
How would we treat hypovolemic hyponatremic pt's?
- Restore volume with NS
- Removal of stimulus of ADH
What is the treatment of SIADH?
- Free water restriction
- removal of ADH stimulus
What is usually the reason for hypernatremia?
Absolute or relative water deficit
How is hypernatremia opposed by a healthy body?
normal thirst mechanism and action of ADH, only seen in people who are having a break down in these mechanisms
What patients are at risk for developing hypernatremia secondary to inadequate physiology?
very young and the very old, under anesthesia
Older patients have issues with ______ mechanism and also have a harder time _______ urine leading to hypovolemia and hypernatremia.
thirst; concentrating urine.
What is the mortality of hypernatremia?
Is a chronic state of hyperNa+ better than an acute one?
Can you ever have a hyposomolar and hyperNa+?
no, always associated with hyperosmolar state
What types of abnormalaties can cause a loss of hypotonic fluid leading to hyperNa+?
A pt that is polyuric and hypernatremic may have what issue?
Diabetes Insipidus, (Urine osmolarity<150 oSm + hypertonic state + plyuria)= DI
How do we treat hyperNa+?
slowly, water deficit should be treated over 24 hrs
How fast is too fast to decrease the serum Na+?
More than 1-2mEq/L/hr
Will we treat the hypernatremia with a hypotonic fluid?
No, replace with NS because it acts both on the fluid and the solute, but will have a greater effect on the fluid balance
How is neurogenic (central) DI treated?
How is nephrogenic DI treated?
- Salt and water restriction
- poss thyazide diuretics