Basics in Adult Fluids & Electrolytes
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(I) Body fluids:
     45-60% weight is fluid*
	60-70% is intracellular (IC)
	30-40% is extracellular (EC)
	     25-30% of EC is intravascular

     * varies with age and gender
         (see TBW calculation below)

(II) Maintenance fluid:

	60 + [WT(kg)-20]= IVF(cc/hr)

	WT= adjusted body weight
	    corrected for excess weight:
		[weight-IBW]*[0.3 to 0.4]

	Alternatively:
	  4 cc/kg/hr for first 10 kg
	  2 cc/kg/hr for second 10 kg
	  1 cc/kg/hr for every kg >20 kg

(III) Fluid deficits:
   (a)  dehydration: water deficit
   (b)  volume depletion: saline deficit
   (c)  combined deficit

  (a) free water deficit (FWD):
	characterized by elevated Na+

     FWD=
       [TBW]*[(measured Na+/140) - 1]
	(corrected Na+ if glucose high)

	TBW	= total body water 
		= K*WT(kg)
		    K		 Patient:
		  0.60		M <65 yr.
		  0.50		  F <65 yr.
		  0.50		M >65 yr.
		  0.45		  F >65 yr.

	TBW is replaced with D5W.
	Limit Na+ correction to
		<12 mEq/L/day
	Contraindications to D5W:
		hyponatremia
		impaired H2O excretion
			CHF
			cirrhosis
			CNS or lung disease

  (b) volume deficit (VD):
         estimated by H & P.
	    weight loss is useful
		(one L for each kg lost)
	    orthostatic hypotension 
		suggests volume loss>10%
	    other relevant clinical signs:
		JVP
		skin turgor
		blood pressure and pulse
		urine output
		moistness of mucosal 
			membranes

	VD is corrected with NS or LR.
	      in severe volume loss, add K+
	      (particularly with DKA)
	Correct rapdily.
	Contraindications to NS or LR:
		hypertension
		CHF, edema, ascites

  (b) combined deficits (FWD + VD):
        calculate FWD
	estimate VD (often VD ~ FWD)
	rapidly replace VD, then slowly correct  FWD
	
(IV) Electrolyte requirements:

	K+ 20-60 mmol/day
	Na+ 50-150 mmol/day
	Ca++ 1-3 g/day
	Mg++ 20 mEq/day
	Dextrose 100-150 g/day
	Fluid 2-3 l/day

(V) Electrolyte deficits:

	Na+ is primarily extracellular
	K+ is primarily intracellular

	for Na+, HCO3- and Cl-
	  deficit= [WT][normal-actual]DF

	  DF= distribution factor
	  for	Na+		0.6-0.7 l/kg
		HCO3-	0.4-0.5
		Cl-		0.2-0.3

	Most Na+ is extracellular. Hyponatremia usually reflects free water excess. Asymptomatic hyponatremia is corrected with free water restriction. Hypertonic saline is used if symptomatic or at risk (Na<111).

    When replacinq Na+, change in [Na]
     = { Infused (Na+K) + TB(Na+K) } /
					   (TBW + V)
 		- TB(Na+K) /TBW
    = { Infused (Na + K)- V[ Na] } /
 					(TBW + V)
	units: mEq, [mM], L
	V= infused volume
	TB=total body
	see TBW calculation  above
	TBW may be less than calculated if volume depleted

	K+ body content varies with muscle mass. For a "normal" adult:
       • K+ deficit~ (normal-actual)(10)
       • each 10 mEq of K+ raises
	serum [K+] by ~0.1 mmol/l

	For Na+ and/or K+ deficits, correct half of the deficit over the first 24 hours. Rapidly correct deficits in symptomatic patients (i.e. mental status changes, seizure, coma in hyponatremia; or N/V, abdominal tenderness, weakness in hypokalemia). 
	With symptoms, raise Na+ 1.5-2.0 mEq/h for first few hours and then taper rate to <8-12 mEq/d; without symptons, correct 0.8-1.2 mEq/h for first few hours and then  <8-12 mEq/d.

	The above formula do NOT account for isotonic volume losses, and hence do not correct for these.  If a concomitant volume deficit exists, it should be corrected with isotonic solutions (as outlined above).  HCO3- and or K+ may be administered in NS or LR if needed.
	
	The above equations are only estimates, hence serial measurements are needed to confirm electrolyte replenshment.

(VI) Fluid compositions (mEq/l)

		Na+	K+	Cl-	HCO3-  Ca
NS		154		154
1/2NS	  77		  77
3% NaCl	513		513
5% NaCl	855		855
LR		130	4.0	109	  28	    3

LR:	         9 kcal/l
D5W:    170 kcal/l;    50 g/l glucose
D10W: 340 kcal/l;  100 g/l glucose

		Na+	K+	Cl-	HCO3- 
Plasma	142	4.0	103	  27
ICF		  10	150		  10
diarrhea	  50	 35	  40	  45
______________________________________
by Michael T. Milano, MD PhD
MTMilano@yahoo.com
www.geocities.com/MTMilano/palm/