Resuscitation  Rehydration  Rectification  Regular (Maintenance) 

Situation  
Shock
 Hypovolemia +/ electrolyte abnormalities
 Electrolyte abnormalities +/ hypovolemia
 NPO 
Choice of fluids  
 Typically composition is directed by published guidelines (as in DKA) or fluids can be formulated by the considerations for maintenance fluids given in the column furthest to the right. Remember that 40 mEq of potassium in a peripheral line has a maximal infusion rate of 125 mL/hr  Hypovolemic hyponatremia
 Based on electrolytes, specifically: sodium, potassium, chloride, bicarbonate, and glucose (and occasionally phosphate) as well as blood pressure. If they are hypertensive consider hypotonic (1/2 NS) rather than isotonic (NS, LR) solutions even if they are mildly hyponatremic.

Rate  
20 mL/kg of crystalloid (NS or LR) over 1520 minutes (thus a pressure bag is needed)  1001000 mL/hr titrated to whatever volume deficit you are correcting  Hypovolemic hyponatremia
 402010 "rule" (for patients with normal electrolyte hemostatic mechanisms)

How do you know it's working  

 Hypovolemic hyponatremia
 The patient remains hemodynamically stable without electrolyte abnormalities or worsening renal function 
 Assuming NaHCO3 comes in a stock solution of 1 mEq/mL, then [C] = solute osmolarity / solution volume
= solute osmolarity / (solute volume + solvent volume)
= 150 mEq / (0.150 L + 1 L) = 130 mEq NaHCO3/L
In 850 mL of solvent, then [C] = 150 / 1000 = 150 mEq Na HCO3/L
 Assuming total body water [L] = 0.5 x wgt [kg] (acutally TBW fraction varies between 0.45 and 0.6 depending on gender and age). We want to change the current plasma sodium by 10 mEq/L/24 hours (i.e. the maximum safe change in serum sodium that will not precipitate central pontine myelinolysis) and recall that the concentration of sodium in 0.9% saline or NS is 154 mEq/L, then:
infusion rate = 0.5 x wgt [kg] x 10 / 154 (L x mEq/L/24 hr) / (mEq/L)
= 5 x 1000 x wgt [kg] / (154 x 24) mL/hr
= 1.35 x wgt [kg] mL/hr for NS
If we are using 3% saline, multiply by 0.9/3 (0.9% / 3%) or 0.3
In the case of hypernatremia, we know that 1/2 NS is half the concentration of NS, such that if we did a similar infusion rate calculation the denominator would be half what is above, or simply multiplying by 2.
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