Electrolytes                    Sodium
                                ======
þ Sodium Correction for ^ glucose
 - Corrected Sodium
 = Measured sodium + (((Serum glucose - 100)/100) x 1.6)
 Alternatively (equivalent equation):
 = Measured sodium + 0.016 x (Serum glucose - 100)
 
 In marked hyperglycemia, ECF osmolality rises and exceeds that of ICF, since 
 glucose penetrates cell membranes slowly in the absence of insulin, resulting 
 in movement of water out of cells into the ECF. Serum Na concentration falls in 
 proportion to the dilution of the ECF, declining 1.6 mEq/ L for every 100 mg/dL 
 (5.55 mmol/L) increment in the plasma glucose level above normal. This 
 condition has been called translational hyponatremia because no net change in 
 total body water (TBW) has occurred. No specific therapy is indicated, because 
 Na concentration will return to normal once the plasma glucose concentration is 
 lowered." Source: http://www.merck.com/mrkshared/mmanual/section2/chapter12
 
þ HYPERNATREMIA
---------------
þ Quick and dirty
 - Look for causes of DI; if central DI, give DDAVP 1-2 mcg IV/SC/intranasal BID 
 - IV NS until volume repleted
 - D5-1/4NS @ 150 mL/hr 

þ Algorithmic approach:
 - First, determine volume status:  dehydrated, euvolemic, or total body Na+
   excess

Hypernatremia and Dehydration
 - give IV NS until blood vascular volume repleted, then replace water deficit
   with with D5 or D5-1/2 NS
 - to approximate present body water:
     140 * (Ideal TBW)/Na+
   where (Ideal TBW) = 60% of normal body weight

Hypernatremia and Euvolemia
 - probably from a hypothalamic lesion, e.g., from a CVA
 - can treat with Diabenese

Hypernatremia and Fluid Excess
 - means an excess in total body Na+
 - can come from primary hyperaldosteronism, Cushing's disease, IV saline, or
   salt tablets
 - correct ^Na+ SLOWLY:  remember that, in hypernatremia, the brain protects
   itself from dehydration generates "idogenic osmoles" by breaking down large
   molecules
   
þ HYPONATREMIA
---------------
 - Who gets exercise-induced hyponatremia? (NEJM 2005)
  + weight gain
  + drank more than 3 L during marathon
  + drank fluids every mile
  + racing time > 4 hours
  + female
  + low body-mass index (BMI)
 - adults with chronic hyponatremia: correct _no_more_than_ 0.5 mEq/hr (12
   mEq/day) (Tintinalli, 4E). Or 1-2 mmol/L/hr, no more than 8 mmol/day per
   others.
 - Indications for hypertonic saline:
  + Postop due to hypotonic fluids, especially in young women
  + Exercise-induced
  + use of ecstasy
  + known intracerebral pathology
  + self-induced water intoxication (psychogenic polydipsia)
 - Hypertonic Saline:
  + Simple:
   - only if neuro sx
   - Start at 1-2 ml/kg/hr (~100 mL/hr; can give 1st 100 mL over 10-15') for 4
     hours
   - Check Na+ hourly
   - Stop when neuro sx resolve

  + (Pediatric): "Aggressive treatment with 3% hypertonic saline (514 mL/kg) 
    should only be initiated if significant symptoms are present, such as 
    seizures or coma. A dose of 5 mL/kg over 10 to 15 minutes should raise the 
    sodium level by approximately 5 mEq/L; smaller additional doses of 2 to 3 
    mL/kg can be considered if there is no clinical improvement."
    [Kwon KT, Tsai VW. Metabolic emergencies. Emergency medicine clinics of 
    North America 2007;25:1041-60, vi.]
  
 - see also pseudohyponatremia <osmo.txt>