Fluids And Electrolytes Flashcards
effective osmolality or tonicity is
2 × [Na+ ] + glucose/18 (normal range, 275 to 290 mOsm/L)
The concentration of Na + does not give information regarding volume status. Therefore, the first step in the evaluation should include
clinical evaluation of ECF volume status plus comparing measured and calculated plasma osmolalities
HYPEROSMOLAR HYPONATREMIA common cause
(PLASMA OSMOLALITY [POSM ] >295 mOsm/kg H2 O)
This happens commonly with severe h glycemia.
Each 100 milligram/dL increase in plasma glucose above the normal level of 100 milligrams/dL decreases the serum [Na+ ] by 1.6 mEq/L.
Administration of osmotic agents such as mannitol, glycerol, and maltose, causing an osmolar gap and hyponatremia
Syndrome of Inappropriate Secretion of Antidiuretic Hormone Diagnostic Criteria
- Hypotonic hyponatremia with (P OSM <275 mOsm/kg H2 O)
- Inappropriately elevated urinary osmolality (usually >200 mOsm/kg)
- Elevated urinary [Na+ ] (typically >20 mEq/L)
- Clinical euvolemia
- Normal adrenal, renal, cardiac, hepatic, and thyroid functions
severe neurologic symptoms initial treatment?
vomiting, seizures, reduced consciousness, cardiorespiratory arrest
includes infusion of 3% hypertonic saline
Raising serum sodium by 5 mEq/L is typically all that is required to see an improvement in severe neurologic symptoms.
mild or moderate or in chronic hyponatremia
the [Na+] correction should be slower than for acute hyponatremia
For chronic hyponatremia [Na+ ], the correction rate should not exceed 6 mEq/24 h in high-risk patients and 12 mEq/24 h in low-risk patients
Rapid correction increases risk for the most dangerous complication
the osmotic demyelination syndrome
Hypertonic (3%) saline can be given at a low infusion rate
0.5 to 1 mL/kg/h, with frequent [Na+] checks
Treatment of Hyponatremia Symptomatic With Seizures or Coma
Step 1 Assess for indication for 3% hypertonic saline: severe symptoms of hyponatremia such as seizures or coma with suspected impending brainstem herniation in setting of acute *or chronic †hyponatremia
Step 2
Infuse 100–150 mL of 3% hypertonic saline IV over 15–20 min
Step 3
Measure serum sodium level after each 3% hypertonic saline infusion
Step 4
Stop infusion when symptoms improve or a target of a 5 mEq/L (range, 4–6 mEq/L) increase in serum sodium concentration is achieved
Step 5
May repeat 150 mL of 3% hypertonic saline up to 3 total doses, or a total of 450 mL IV of 3% hypertonic saline
Step 6
Keep the IV line open with minimal volume of 0.9% normal saline until cause-specific treatment is started. Limit increase in sodium level to no more than 8–12 mEq/L during the first 24 h or 18 mEq/L over 48 h
Risk factors for osmotic demyelination syndrome
[Na+] <120 mEq/L, chronic heart failure, alcoholism, cirrhosis, hypokalemia, malnutrition, and treatment with vasopressin antagonists such as tolvaptan.
Symptoms
dysarthria, dysphagia, lethargy, paraparesis or quadriparesis, seizures, and coma
Treatment forovercorrection
5% dextrose in water at 3 mL/kg/h, loop diuretics, and desmopressin
Treatment of Hypernatremia
Isotonic (0.9%) saline
Use for correction of volume deficits
Etiology-specific therapy
Treat fever with antipyretics, vomiting with antiemetics, and diabetes insipidus with desmopressin (see “Diabetes Insipidus” section)
D5 W or oral free water to replace free water deficit over 2–3 d
In cases of chronic hypernatremia, it is suggested that correcting (lowering) the sodium level should occur at a rate of no more than 0.5 mEq/L/h or 10–12 mEq/24 h
D5 W to replace free water deficit over 1–2 h
Reserved only for those cases where acuity is known to be <6 h and the salt load is known to be lethal (0.75–3.0 grams/kg of body weight).
Hemodialysis
An alternative or as a supplement to D5 W to replace free water deficit in life-threatening acute cases of salt ingestion.
estimated K +deficit in mEq/L
estimated K +deficit in mEq/L = (expected serum [K+ ] in mEq/L – measured serum [K+ ] in mEq/L) × ICF (calculated as 40% of total body weight)
Acid-base imbalance plays an important role in critically ill patients: there
inverse proportionality between serum pH and [K+], with [K+ ] rising about 0.6 mEq/L for every 0.1 decrease in pH and vice versa, through an exchange between H +and K+
Symptoms of hypokalemia
serum concentrations reach 2.5 mEq/L