Total body water=
60% of total body weight
Female total body water=
50%
Infant total body water=
80%
Elderly total body water=
45%
Male total body water=
60%
ofc bc everything is set to men
Overweight total body water=
smaller %
ICF total body water=
40%
ECF total body water=
20%
ECF=
plasma + interstitial fluid
Extracellular ions:
primarily Na+, Cl-
Intracellular ions:
primarily K+, Po4-
ECF osmolarity=
sodium + glucose + urea
ICF osmolarity=
potassium + magnesium + phosphate + proteins
normal osmolarity
280-295 mOsm/kg
calculated osmolarity
2Na+ + Glucose/18 + BUN/2.8
symptoms occur when osmolarity is out of range:
<265
>320
Osmolal gap due to osmotically active substances not accounted for in calculated osmolarity _________. Normal is ____
mannitol, ethanol, methanol, ethylene glycol
Normal <10
Tonicity
The ability of the combined effect of all the solutes to generate an osmotic driving force
To generate tonicity
the solutes must be confined in one comparment
Urea is an example of a substance which contributes to ______
osmolarity
does not contribute to tonicity because it crosses cell membranes
decreasing ECF tonicity by decreasing sodium would cause
water to move into cells, swelling
major determinant of the size of the extracellular fluid volume
Na+
increased ECF Na+ would cause
hypervolemia
decreased ECF Na+ would cause
hypovolemia
serum sodium refers to
Refers to the amount of water relative to the Na+ in the ECF
NOT the total body Na+ amount
abnormal serum Na+ is a sign of
disorder of water regulation
ECFV is determined by
overall volume status of the patient
sodium control
abnormal ECFV is a sign of
abnormal sodium control
Sequestration without loss:
intestinal obstruction, pancreatitis, rhabdomyolysis
renal cause of H20 and Na+ loss
Diuretic
renal cause of water loss
Diabetes Insipidus
Oliguria means
producing little urine
CNS depression, weakness, muscle cramps occur with
hypovolemia
reasson why an otherwise healthy patient might be hypervolemic
Pregnancy
bolded causes of hypervolemia
Liver disease
Heart failure
Orthopnea, paroxysmal nocturnal dyspnea (PND), SOB, and crackles are pulmonary symptoms of
hypervolemia
influence water retention
Thirst
ADH
influence salt retention
Renin angiotensin system**
ANP
catecholamines,
renal: GFR, RBF
ADH definition
produced in hypothalamus, transported to posterior pituitary then released into blood stream
Causes retention of water but normal excretion of Na+
Aldosterone causes
- increases sodium reabsorption
2. Increases K+ excretion
Most common electrolyte abnormality in hospitalized patients
hyponatremia
Hyponatremia is defined as serum sodium
Hypotonic, Na+ <135, dangerous if <125
hyponatremia presentation
Very young/very old
HA, dizziness, N/V, lethargy, weakness, confusion, hypoventilation→ respiratory arrest, seizures, coma, death
seizures are common in
hyponatremia
hyponatremia causes fluid to move
into cells, symptoms result from movement into brain cells–> cerebral edema
after realizing sodium levels are out of range, next determine
patient’s volume status: hypovolemic, euvolemic, hypervolemic
hyponatremia is associated with which disorders?
Pulmonary disease
CNS disorders
pseudohyponatremia is seen with
Hyperlipidemia
Hyperproteinemia
Obstructive jaundice
Multiple myeloma
pseudohyponatremia definition
Na+ <135 but isoosmolar
Falsely low serum sodium: laboratory artifact
→ relative percent of water is reduced and flame photometry reports artificially low sodium→ do specialized tests
Redestributive hyponatremia aka
Hyperosmolar hyponatremia
Hyperosmolar hyponatremia cause
Hyperglycemia:
Add 1.5 mEq/L to sodium value for every 100 mg/dl of serum glucose greater than baseline (100 mg/dl)
Redestributive hyponatremia definition
Hyperosmolar state, “relative hyponatremia”
Caused by osmotically active solutes in extracellular space that draw H2O out of the cell into the extracellular space
True hyponatremia is
hypo-osmolar hyponatremia
causes of hypovolemic hyponatremia
Renal losses:
Diuretics, esp thiazide
Osmotic diuresis: glucose/mannitol
Addison’s disease: decreased cortisol → increased ADH
Non-renal losses:
GI: V/D, NG suction, fistula, pancreatitis, peritonitis
Burns
causes of hypervolemic hyponatremia
Hepatic cirrhosis Congestive Heart Failure Renal failure Nephrotic syndrome Pregnancy
treatment of hypervolemic hyponatremia
Diuretics
Dialysis
Fluid restriction
treatment of hypovolemic hyponatremia
Replace fluid losses with isotonic fluid
treat underlying cause
Causes of euvolemic hyponatremia
SIADH
Psychogenic polydipsia→ urine is maximally dilute
Hypothyroidism
Adrenal insufficiency
Euvolemic Hyponatremia treatment
Fluid restriction
Treat underlying cause
SIADH cause
Impairs free water excretion, but sodium continues to be excreted normally
Causes of SIADH
hospitalization
medications
CNS disorder (do CT/MRI of head)
lung tumor/infection (check CXR)
SIADH labs
Concentrated urine >100mOsm/kg with low serum osmolality and euvolemia
SIADH treatment
Fluid restriction Treat underlying pathology Refractory cases: Hypertonic saline Demeclocycline Urea Lithium Vaptan
when to hospitalize hyponatremic patient
if <125
slowly correct chronic hyponatremia or else
risk of Cerebral pontine myelinolysis/osmotic demyelination syndrome
meds for chronic hyponatremia
Demeclocycline
Vaptans
Vaptans
vasopressin receptor antagonists
Demeclocycline
induces nephrogenic diabetes insipidus
when to treat chronic hyponatremia with Hypertonic solutions 3% NaCl
severe, symptomatic cases
rate of correction for severe symptomatic hyponatremia
6-12 mEqL, <18 mEq/L in 48 hours
Chronic: <8 mEq/L 1st 24 hours
Check serum sodium every 2 hours
osmotic demyelination syndrome aka
central pontine myelinolysis
central pontine myelinolysis
irreversible focal demyelination in the pons and extra-pontine areas
central pontine myelinolysis symptoms
Dysarthria, dysphagia, seizures, AMS, quadriparesis, hypotension 1-3 days after sodium overcorrection
hypernatremia is defined as
Hypertonic, Na+ >145 mEq/L
hypernatremia pathophysiology
→ increased ECF osmolality → water leaves cells → brain shrinkage → clinical features
general causes of hypernatremia
too little water intake
very high dietary salt
excessive water loss
specific general causes of hypernatremia
elderly/infant diarrhea
Sweating/fever
Renal losses
Drugs: diuretics, lithium (induces nephrogenic diabetes insipidus)
Osmotic diuresis: hyperglycemia, mannitol
lithium MOA
induces nephrogenic diabetes insipidus
hypernatremia symptoms
Asymptomatic Thirst, volume depletion AMS, weakness Neuromuscular irritability Focal neurologic deficit Seizures, coma
most hypernatremia is due to
water loss
normal mechanisms to respond to hypernatremia
- thirst
2. concentrate urine to prevent further water loss
central diabetes insipidus causes
head injury
nephrogenic diabetes insipidus causes
Genetic
Acquired: chronic renal insufficiency tubulointerstitial renal disease Amyloidosis Lithium
Diabetes insipidus definition
Nonosmotic urinary water loss with elevated serum sodium: urine is dilute when it should be concentrated, water is not reabsorbed in collecting duct
Central/Neurogenic: impaired secretion of ADH
Nephrogenic: lack of kidney response to ADH
Treatment of central diabetes insipidus
desmopressin: IV/inhaled ADH analog
Treatment of nephrogenic diabetes insipidus
Thiazide diuretic
Amiloride
Chlorpropamide
indomethacin
Amiloride
potassium sparing diuretic
indomethacin
NSAIDS
Chlorpropamide
antidiabetic oral agent
hypernatremia tx
Hospitalize if severe
Stop water loss
Replace water deficit SLOWLY (esp if chronic):
Orally, NG tube, IV hypotonic fluid
If water is replaced too rapidly in hypernatremia
water into brain cells → seizures, brain damage, cerebral pontine myelinolysis
water deficit=
normal TBW-current TBW
Normal TBW=
.6 x body weight in kg
Current TBW=
Normal serum Na+ x normal TBW / measured serum Na+