SM 214a - Hypernatremia Flashcards
Describe the changes in fluid compartments upon acute exposure to hypertonic Na solutions (Sea water).
What are the consequences?
Shift in total body water from ICF to ECF
- -> Brain shrinkage
- -> Cerebral blood vessel tears
- -> Limbic demyelination
- -> Elevation of EBV
- -> Acute pulmonary edema
Hypertonic hypernatremia is recognized as a SNa above…
145 mEq/L
What two things can cause hypertonic hypernatremia (dehydration?)
- Salt intake
- Persistent H2O losses not replaced by H2O intake
If a patient has hypernatremia (Na+ >145) and ther urine osmolality is high, what is the cause?
Insensible losses or GI loses
+
Decreased H2O intake
What is the treatment for hypernatremia resulting from sweating, GI loss, or solute diuresis?
Need to replace Na+, K+, and H2O
Use 0.9% or 0.45% saline with potassium
Caution: Do not cause serum Na to fall too quickly!
What factors could impair H2O diuresis?
- ADH release
- -> Reabsorption of water
- Decreased renal solute load
- -> Decreased osmotic pressure in the tubule
- -> Increased H2O reabsorption
- Volume depletion
- -> Decreased filtration
If a patient has hypernatremia and their urine osmolality is low, what is the most likely cause?
Diabetes Insipidus:
Renal H2O losses due to absent or ineffective ADH
- Central diabetes insipidus
- Low serum ADH
- Nephrogenic diabetes insipidus
- High serum ADH - the kidneys are resistant
Describe the general process of an H2O deprivation test in the setting of polyuria.
What do the results mean?
Evaluation of polydipsia vs. central DI vs. nephrogenic DI
- Water deprivation to increased serum osm >298 mOsm/L
- If urine osmolality increases, polydipsia is the cause of polyuria
- ADH is working properly
- Give desmopressin (ADH analog)
- If urine osmolality increases significantly = central DI
- Kidneys can resopnd to ADH
- If urine osmolality does not increase = nephrogenic DI
- Kidneys are resistant to AHD
- If urine osmolality increases significantly = central DI
What is the correction of SNa in the setting of high serum glucose?
Corrected SNa = SNa + [(Glucose – 100) ÷ 100 x 2 mEq/L]
Important to correct for glucose so hypernatremia in diabetes is not missed!
What is the treatment for nephrogenic DI?
Low sodium, low protein diet \+ Thiazide diuretics \+ NSAIDS
What is the treatment for central DI?
- Acute: 2 mcg desmopressin IV every 12 hours
- When polyuria resolves and patient is able, can switch to intranasal desmopressin
Gastrointestinal losses from vomiting or osmotic diarrhea are…
A. Hypertonic
B. Hypotonic
C. Isotonic
B. Hypotonic
Which patients are most likely to develop hypertonicity?
Elderly
Infirm
Infants
Intubuated
People with absent or decreased thirst drive, or who cannot freely respond to thirst
How do you estimate the water deficit in a patient with hypernatremia?
Current TBW x ( [SNa ÷ 140] – 1)
- TBW in men is 0.6 * lean body weight (kg)
- TBW in women is 0.5 * lean body weight (kg)
- TBW in the elderly is 0.45 * lean body weight (kg)
What are the causes of polyuric hypertonic hypernatremia
(increased CefH2O)
- Solute diuresis
- Gluose (diabetics)
- Mannitol
- Urea
- Diuretics
- Pure H2O diuresis
- Central Diabetes Insipidus
- Nephrogenic Diabetes Insipidus
