1 Sodium Disorders Flashcards
What makes up the electrolyte panel?
Sodium (Na) Potassium (K) Chloride (Cl) Bicarbonate (CO2) Calcium Magnesium* Phosphate*
*Not usually part of BMP, will usually have to order them separately
Total body water = _____% of total body weight
60%
Of the total body water, how much is in the ICF and how much in the ECF?
2/3 ICF
1/3 ECF (interstitial fluid and plasma)
Percentage total body water in Newborns vs Adult Males vs Adult Females vs Elderly
Newborns = 80%
Adult Males = 60%
Adult Females = 50%
Elderly = 45%
Total body water of an obese person is …
Much lower than total body water in a lean person
What does “TIE 60,40,20” mean?
Total body water = 60%
Intracellular water = 40% (2/3 of 60)
Extracellular water = 20% (1/3 of 60)
In the ECF, how much is interstitial fluid and how much is plasma?
3/4 Interstitial fluid
1/4 plasma
Most important ECF cation?
Sodium
Most important ICF cation?
Potassium
Most important ECF anion?
Chloride
And some HCO3- (but mostly Cl-)
Most important ICF anion?
PO4 and organic anions
Oh and some protein
Total solute concentration in a fluid compartment
Osmolality
What are the main solutes that determine the calculated osmolality of the ECF?
Sodium
Glucose
Urea
Normal range of osmolality
280-295 mOsm/kg
How do we calculate Osmolality?
(2 x Na) + (Glucose/18) + (BUN/2.8)
SODIUM is the biggest factor
Symptoms occur if osmolality is > _____ or < ______.
> 320 mOsm/kg or <265 mOsm/kg
Other “osmotically active” substances that aren’t included in the calculated osmolality (because they aren’t supposed to be there)
Mannitol (given as a med for cerebral edema) and various proteins
Ethanol, methanol, and ethylene glycol
High amounts of osmotically active substances in the blood can lead to an elevated…
Osmolal Gap (Measured Osmolality - Calculated Osmolality)
What is the normal Osmolal Gap?
<10
If it’s greater than 10, it’s usually because of ethanol, methanol, or ethylene glycol
The ability of the combined effect of all the solutes to generate an osmotic driving force that causes water movement from one compartment to another
Tonicity
To increase ECF tonicity, a solute must be …
Confined to the ECF compartment (unable to cross from ECF to ICF
Examples: SODIUM, glucose, mannitol
______ easily crosses cell membranes and therefore distributes evenly throughout total body water (contributing to OSMOLALITY , but NOT TONICITY)
Urea
Why do we care about tonicity?
Because it affects the size of cells
Decreased Na+ —> decreased tonicity of the ECF —>
Shift of water from ECF to ICF —> cells (including brain cells) swell with extra water
What is the major determinant of the size of ECFV (extracellular fluid volume)
Total amount of Na+
Increased Na+ —>
Increased ECFV or HYPERVOLEMIA
Think edema
Decreased Na+ —>
Decreased ECFV or HYPOVOLEMIA
think dry patient
90-95% of the total body sodium is located in…
The ECF
Serum [Na+] (lab value) primarily refers to …
The amount of water relative to Na+ in the ECF (NOT the total body Na+ amount)
Abnormal serum Na+ is a sign of …
A disorder of water regulation
High Na+ = too little water relative to sodium
Low Na+ = too much water relative to sodium
The ECFV is determined by …
Overall volume status of the patient
An abnormality with the size of the ECFV is a marker of…
Abnormal sodium control (too much/too little total body sodium)
High ECFV = “too much sodium”
Low ECFV = “too little sodium”
How do we describe a patient’s volume status?
Hypovolemic
Euvolemic
Hypervolemic
Common causes of hypovolemia
Anything that causes dehydration
GI losses (bleeding, NG suction, diarrhea, vomiting)
Renal losses
• Salt and water loss: diuretics
• Water loss: diabetes insipidus
Skin losses: sweat, burns
Sequestration without loss
• Intestinal obstruction
• Pancreatitis
• Rhabdomyolysis
Clinical features of hypovolemia
Increased thirst, decreased sweating
Decreased skin turgor & dry mucus membranes
Oliguria with increased urine concentration
CNS depression
Weakness and muscle cramps
Decreased BP, postural hypotension/dizziness
Increased pulse, postural pulse increase