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Subject: Best Dx/Best Rx: Disorders of Water and Sodium Balance
Date: Wed, 3 Jun 2009 21:16:08 -0700
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Best Dx/Best Rx: Disorders of Water and Sodium =
Balance
Disorders of Water and=20
Sodium Balance
Richard H. Sterns, MD, FACP Medical =
University of=20
Rochester School of Medicine and Dentistry
Irrigant absorption (prostatectomy or =
intrauterine=20
surgery)=20
Pseudohyponatremia
Severe hyperlipidemia=20
Multiple myeloma=20
Macroglobulinemia =
Acute Hyponatremia (Water Intoxication)=20
Neurologic syndrome that develops when large =
volumes of=20
water are retained within a short period (< 48 hr)=20
Headaches=20
Weakness=20
Nervousness=20
Vomiting=20
Progresses to disorientation, delirium, =
tremulousness,=20
convulsions, and coma=20
Dilated pupils=20
Bilateral Babinski signs may appear=20
Hemiparesis may appear
Causes=20
Postoperative stress; can be fatal in women =
and young=20
children=20
Oxytocin infusion=20
Cyclophosphamide=20
Psychotic self-induced water =
intoxication=20
Marathon running=20
Ecstasy (MDMA) use
Best Tests=20
Serum electrolytes=20
Serum sodium concentration < 130 =
mEq/L=20
Arterial sodium concentration may be lower =
than the=20
venous
CT scan: shows cerebral edema in severe =
cases, rules=20
out other causes of neurologic findings
Best Therapy=20
Severe symptoms: do not delay therapy while =
awaiting=20
imaging=20
Increase plasma sodium concentration by =
4=966 mEq/L to=20
decrease cerebral edema and stop seizures
Stop free-water intake=20
Hypertonic 3% saline=20
Dose: 1=962 ml/kg of body weight to raise =
plasma=20
sodium by 1=962 mEq/L/hr for 2=963 hrs; for severe neurological =
symptoms give=20
100 100 ml by bolus infusion repeated in 10 minutes x 2 if no =
clinical=20
improvement=20
Best infused in 100 ml containers to avoid =
excessive=20
dose=20
Avoid increasing plasma sodium =
concentration by >=20
12 mEq/L in first day of therapy or by > 6 mEq/L/day =
thereafter=20
Concurrent loop diuretic 40 mg I.V.=20
Furosemide=20
Bumetanide=20
Torsemide =
Chronic Hyponatremia=20
Hyponatremia that evolves over the course of =
≥ 48=20
hr=20
Abnormality in vasopressin secretion, except =
in renal=20
failure=20
Rarely fatal=20
May become life-threatening if patient rapidly =
ingests=20
large volume of water=20
Patients may have gait disturbances and an =
increased=20
risk of falls at plasma sodium concentrations less than 128 =
mEq/L=20
Plasma sodium concentrations < 115=96120 =
mEq/L produce=20
the following symptoms:=20
Anorexia=20
Nausea=20
Vomiting=20
Muscle weakness=20
Muscle cramps=20
Irritability=20
Personality changes=20
Slow response
Plasma sodium concentrations < 110 mEq/L =
produce the=20
following symptoms:=20
Stupor=20
Tremulousness=20
More rarely, seizures
Causes=20
Advanced renal failure
Thiazide diuretics=20
Hypovolemia, including Addison =
disease=20
Obsessive consumption of beer=20
Edematous conditions, including the =
following:=20
Congestive heart failure=20
Cirrhosis=20
Nephrotic syndrome
AIDS=20
Syndrome of inappropriate antidiuretic =
hormone=20
secretion (SIADH) (water is retained without abnormal sodium =
balance, volume=20
depletion, or edema); may indicate the following:=20
Malignancy=20
Chest infection=20
Tuberculosis=20
Pneumonia=20
Hypopituitarism with glucocorticoid =
deficiency=20
Hypothyroidism
NSAIDs may exacerbate other causes of=20
hyponatremia
Exclude disorders that can lower plasma sodium =
concentration without causing hypotonicity
Diet, fluid intake, GI fluid losses, and use =
of=20
diuretics, antidepressants, or other antidiuretic drugs
Signs of volume depletion or edema=20
Check for signs of disorders known to cause =
SIADH=20
Evaluate severity of neurologic symptoms to =
determine=20
the need for urgent therapy
Laboratory Tests=20
Plasma sodium concentration=20
Urinary sodium and/or chloride =
concentration=20
Urinary sodium < 20 mEq/L without edema =
indicates=20
hypovolemia=20
Urinary chloride < 20 mEq/L without edema =
indicates=20
hypovolemia in patients with metabolic alkalosis due to gastric =
fluid losses=20
(urinary sodium may be > 20 mEq/L)=20
Urinary sodium > 40 mEq/L with normal =
renal=20
function and in the absence of diuretics indicates SIADH =
BUN and serum uric acid=20
Elevated in hemodynamic abnormalities, low =
in=20
SIADH
Uric acid=20
More reliable indicator of volume status =
than=20
BUN
Serum potassium and bicarbonate=20
Levels are normal in SIADH
Hypokalemia and metabolic alkalosis=20
Suggest diuretic therapy or vomiting =
Hypokalemia and acidosis=20
Suggest diarrhea or laxative abuse =
Hyperkalemia and acidosis=20
Suggest adrenal insufficiency=20
Withdrawal of Hyponatremic=20
Drugs=20
Exclude another cause for hyponatremia before=20
attributing electrolyte disturbance to a drug=20
To diagnose drug-induced hyponatremia, =
eliminate the=20
drug and see if water excretion returns to normal (may take 1=962 wk =
in=20
thiazide-induced hyponatremia)
Response to=20
Isotonic Saline=20
Patients with subclinical edematous conditions =
retain=20
the sodium and develop edema=20
Volume-depleted patients=20
Water diuresis (dilute urine) emerges and =
hyponatremia=20
improves; avoid overly rapid correction
Patients with SIADH=20
Hyponatremia persists and may worsen; seek a =
specific=20
etiology and follow up carefully if no cause for SIADH is =
found=20
Monitor plasma sodium concentration every =
6=968 hr=20
during first 2=963 days of therapy=20
If water diuresis threatens to increase =
plasma sodium=20
too much, give oral water or 5% dextrose in water to slow the rate =
of=20
correction or administer desmopressin to stop the water =
diuresis=20
Persistent Defects in Water =
Excretion=20
SIADH=20
Water restriction alone is slow to resolve=20
hyponatremia=20
Furosemide is a useful adjunct: 20 mg p.o., =
b.i.d. (or=20
equivalent dose of bumetanide or torsemide)=20
Oral salt or slow infusion of 3% saline =
(approximately=20
15 ml/hr)=20
Demeclocycline: high cost and long duration =
of action=20
limit its effectiveness=20
Dose: 600 to 1,200 mg/day =
Conivaptan: intravenous vasopressin receptor =
antagonist to induce an "aquaresis" (increased urinary water losses =
without=20
change in urinary sodium and potassium losses) in hospitalized=20
patients
Edematous conditions=20
Do not give saline=20
Will not improve hyponatremia and worsens=20
edema
Loop diuretics plus ACE inhibitor=20
Particularly effective in patients with =
congestive=20
heart failure
Edematous patient: diuretics plus =
electrolyte-free=20
water=20
Electrolyte-free water I.V. in a 5% dextrose =
solution=20
(D5W) at < 500 ml/hr for patients who cannot drink=20
Monitor serum sodium concentration and urine =
output=20
frequently and adjust fluids appropriately
Correcting hypernatremia too rapidly can cause =
cerebral=20
edema=20
Reduce serum sodium concentration by ≤ =
10=9612=20
mEq/L/day=20
Electrolyte-free water intake should exceed =
free-water=20
losses by ≤ 2 L daily=20
Acute salt poisoning: rapid infusions of=20
electrolyte-free water plus a loop diuretic (without waiting for serum =
electrolyte test) may prevent irreversible brain injury=20
Diabetic dehydration=20
Prevent hypovolemia following correction of=20
hyperglycemia=20
1=962 L 0.45% isotonic saline at a rate =
that exceeds=20
urine output
Carefully monitor serum sodium =
concentration, blood=20
glucose level, and urine output to tailor fluid replacement to =
needs=20
Avoid rapid correction of hypertonicity in =
severe=20
hyperglycemia to prevent cerebral edema
Induce fluid loss gradually, increasing the =
dose until=20
desired weight is reached=20
Inpatients can be managed more precisely =
with=20
continuous infusion=20
Diuretic resistance=20
Loop diuretics plus thiazide or metolazone =
and/or=20
acetazolamide=20
Monitor carefully to avoid large potassium =
and=20
sodium losses=20
Loop diuretics can predispose to hearing =
loss,=20
particularly at high doses via bolus injection in patients =
receiving other=20
ototoxic drugs
Complications=20
Azotemia=20
Volume depletion=20
Thiazides and loop diuretics can cause the =
following:=20
Hypokalemic alkalosis=20
Hyperglycemia=20
Hyperuricemia (sometimes with clinical=20
gout)
Thiazides can cause hypercalcemia in =
patients with=20
underlying conditions that increase calcium absorption (e.g., =
sarcoidosis)=20
or bone reabsorption (e.g., hyperparathyroidism)=20
Avoid thiazides in patients with high =
fluid=20
intake=20
Potassium-sparing agents (e.g., =
triamterene,=20
amiloride, spironolactone) may cause hyperkalemia=20
Do not give with potassium =
supplements=20
Use with caution in patients with renal=20
insufficiency and those taking ACE inhibitors or angiotensin II =
blocking=20
agents
Cirrhotic patients with ascites but no =
peripheral=20
edema=20
Limit weight loss to 0.5 kg/day =
Repeated large-volume paracenteses plus I.V.=20
albumin=20
Alternative to diuretics=20
Avoids intravascular volume depletion =
Afterward, diuretics can prevent =
reaccumulation of=20
ascitic fluid
Fluid sequestrated in the abdominal cavity =
(pancreatitis=20
or peritonitis) or in the soft tissues (crush injuries with =
rhabdomyolysis or=20
burns)=20
Renal salt wasting from diuretics=20
Osmotic diuresis caused by glycosuria=20
Recovery phases of acute tubular necrosis or =
obstructive=20
uropathy=20
Hematocrit: increases in proportion to the =
contraction=20
of plasma volume=20
Serum albumin: may be increased
Urinary sodium: usually < 20 mEq/L except =
in=20
metabolic alkalosis (in which the urine chloride is low) or when renal =
sodium=20
wasting is the cause of the condition=20
Serum creatinine: changes very little=20
BUN: increased disproportionately to the =
increase in=20
creatinine=20
Azotemia may be blunted in patients with a =
poor dietary=20
protein intake and may be exacerbated in patients who are catabolic, =
bleeding,=20
or receiving steroid therapy