Links: Compartments | Free Water | Normal Losses | Maintenance | Other | Hypervolemia | Hypovolemia | Dehydration | Oral Rehydration | IV Solutions | Electrolytes | Hypodermoclysis / Proctoclycis / Other | See Vascular Access |
Tips on correcting FEN abnormalities: R/o Laboma–> lab error, re-check lab 1st. Correlate to the pt’s condition. Correct ½ the deficit, reassess the labs, then correct the remaining.
If multiple problems correct 1st Volume >pH > K/Ca/Mg > Na/Cl (osmolarity).
• Over-aggressive perioperative fluid administration could contribute to postoperative morbidity, at least in older pt’s who are undergoing elective surgery (Ann Surg 2003;238:641-8) –> Median IV fluid volumes on the day of surgery were 2740 mL in the restricted group and 5388 mL in the standard group. On the first postop day, volumes were 500 mL and 1500 mL, respectively. Complications occurred in a significantly lower proportion of restricted pt’s than standard pt’s (33% vs. 51%).
• Administration of chloride-restrictive intravenous (IV) fluid in a tertiary ICU was associated with reduced incidence of acute kidney injury and a decrease (50%) in the use of renal replacement therapy (RRT) with no difference in mortality from any cause (JAMA. 2012;308:1566-1572)……The low-chloride intervention period included complete discontinuation of a gelatin preparation, use of 20% albumin instead of 4% albumin, and discontinuation of normal saline and use of Hartmann solution or Plasma-Lyte (Cardinal Health). The authors were not able to distinguish which change or changes led to the observed outcome.
• Elemental Composition of the Human Body By Weight (%): Oxygen O 65.0%. Carbon C 18.0%. Hydrogen H 10.0%. Nitrogen N 3.0%. Calcium Ca 1.5%. Phosphorus P 1.0%. Potassium K 0.4%. Sulfur S 0.3%. Sodium Na 0.2%. Chloride Cl 0.1%. Magnesium Mg 0.1%. Total 99.6%: The remaining 0.4% by weight is contributed by the trace elements: chromium (Cr), copper (Cu), zinc (Zn), selenium (Se), molybdenum (Mo), fl uorine (F), iodine (I), manganese (Mn), and iron (Fe). Cells may also contain variable traces of some of the following: boron (B), cobalt (Co), lithium (Li), strontium (Sr), aluminum (Al), silicon (Si), lead (Pb), vanadium (V), arsenic (As), bromine (Br), and others.
Serum Uric Acid: level is a rough correlate with intravascular volume, but a need baseline to compare too.
Total Body Water (TBW): ~60% Ideal Body Weight. Increased with incr muscle mass (600ml/kg in male, 500ml in female), decr with age (highest in newborn, @ ~77%).
TBW = 0.6 in child or non-elderly male.
TBW = 0.5 in an elderly male or a non-elderly female. 0.45 in elderly females. Normally the intracellular + extracellular fluid = 40-60% of the TBW.
Desired TBW: (Measured Na X current TBW)/ normal serum Na.
Body Water Deficit: Desired TBW- current TBW.
Body Water Distribution (70 kg male):
TBW: 42 Liters (60% Total body weight).
Intracellular water: 25.2-29.4 Liters, 36-42% Total body weight, 60-70% Total body water.
Extracellular water: 12.6-16.8 Liters, 18-24% Total body weight, 30-40% Total body water.
Plasma water: 3-3.5 Liters, 4-5% Total body weight, 7-8% Total body water.
Interstitial & connective tissue, bone, etc.: 9-14 Liters, 13-20% Total body weight, 22-23% Total body water.
Intracellular Fluid (ICF): 40% of body wt or 66% of TBW, ~28 L, primarily in muscle, 160ml/kg.
Extracellular Fluid (ECF): 33% of TBW. Interstitial is 15-20% TBW (~8 L). Intravascular (Plasma) is 5% TBW, ~3-4 L (plasma volume is 38ml/kg, blood volume is 70ml/kg).
Fluid Volume:
Women: Total body fluid–> 500 mL/kg. Whole blood –> 60 mL/kg.
Plasma –> 36 mL/kg. Erythrocytes –> 24 mL/kg.
Men: 80-kg Man: Total body fluids @48 L (600 mL/kg). Whole blood @5.3 L (66 mL/kg).
Plasma @3.2 L (40 mL/kg). Erythrocytes @2.1 L (26 mL/kg).
For obese and elderly pt’s, estimate the volumes based on lean body weight and reduce the values by 10%. For pt’s with a marked weight loss within 6 mo’s, use the premorbid weight loss to estimate volumes. Values expressed for lean body weights.
Body Fluid Distribution in Healthy Adult:
Parameter | Derivation | Male | Female | |
Total body water (TBW) | 0.6 × Lean body weight (kg) | 600 ml/kg | 500 ml/kg | |
| Male | 0.5 × Lean body weight (kg) |
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Female | ||||
Intracellular body water | 0.4 × Lean body weight (kg) | 400 ml/kg | 333 ml/kg | |
Extracellular body water | 0.2 × Lean body weight (kg) | 200 ml/kg | 167 ml/kg | |
Interstitial fluid volume | 0.16 × Lean body weight (kg) | 160 ml/kg | 160 ml/kg | |
Blood volume (BV) | 0.065 × Lean body weight (kg) | 70 ml/kg | 65 ml/kg | |
Plasma volume (PV) | PV = BV- (BV × Hematocrit) | 37 ml/kg | 38 ml/kg | |
Free Water: water in the body that can be removed by ultrafiltration and in which substances can be dissolved. Minimum water requirements for daily fluid balance can be approximated from the sum of the urine output necessary to excrete the daily solute load (500 ml/day) plus the insensible water losses from the skin and respiratory tract (500 ml/day), minus the amount of water produced from endogenous metabolism (250-350 ml/day). It is common to administer 2-3 liters of water daily to produce a urine volume of > 1000-1500 ml/day, as there is no advantage to minimizing urine output. Weighing the pt daily is the best means of assessing net gain or loss of total body fluid, because GI, renal, and insensible fluid losses of pt’s are unpredictable.
Free (body) Water Deficit (FWD) in Liters:
FWD in Hypernatremia: FWD = [Serum Na (measured) – serum Na (normal) x 0.6 Wt in kg/ normal serum Na].
Also written as, FWD = [(Na-140)/140] baseline wt X F. (F = fraction of wt that is water, 0.6 for male, 0.5 for females).
Also written as, FWD = FWD = 0.6 X wt in kg X (1- 140/Na). Kg is estimated wt when fully hydrated.
FWD in Hyperglycemia: Use corrected Na if necessary, particularly if hyperglycemia is present–> FWD = ( baseline wt in kg — 0.45) — [(290/Eosm) X current wt X 0.45]. Effective Osm = 2 X (Na+K) + (glucose/18) = TBW in kg X 0.6 (1- normal Osm/observed Osm). Generally, about half of deficit can be replaced in the first 24 hours; rest over 1-2 days. Avoid correcting the serum Na concentration >1mEq/L/hr.
Free Water Clearance (FWC): Used to asses a solute Vs water diuresis when have polyuria (>3L/d).
FWC = Ur volume in 1 day – Osmolar clearance.
Osmolar Clearance = (Ur Osm X Ur volume)/ plasma Osm. No FWC if Ur Osm >300 mOsm/kg H2O. Excess FWC if Ur Osm <150 mOsm/kg H2O.
Normal Losses of Fluid: Insensible = stool + skin = ~500ml/d.
Stool–> ~300ml/d.
Renal excretion–> 1-1.5L/d.
Insensible Loss–> 400ml/m2/d (~750ml/d for adults = 10ml/kg/d, 60% as free water vapor from lungs, 40% perspiration).
Sweat: 50 mEq/L Na+, 40 mEq/L Cl-, 5 mEq/L K+, Avg. daily production varies.
Saliva: 60 mEq/L Na+, 15 mEq/L Cl-, 26 mEq/L K+, 50 mEq/L HCO3-, Avg. daily production 1,500 mL.
Gastric Juice: 60-100 mEq/L Na+, 100 mEq/L Cl-, 10 mEq/L K+, Avg. daily production 1,500-2,500 mL.
Duodenum: 130 mEq/L Na+, 90 mEq/L Cl-, 5 mEq/L K+, 0-10 mEq/L HCO3-, Avg. daily production 300-2,000 mL.
Bile: 145 mEq/L Na+, 100 mEq/L Cl-, 5 mEq/L K+, 15 mEq/L HCO3-, Avg. daily production 100-800 mL.
Pancreatic juice: 140 mEq/L Na+, 75 mEq/L Cl-, 5 mEq/L K+, 115 mEq/L HCO3-, Avg. daily production 100-800 mL.
Ileum: 140 mEq/L Na+, 100 mEq/L Cl-, 2-8 mEq/L K+, 30 mEq/L HCO3-, Avg. daily production 100-9000 mL.
Diarrhea: 120 mEq/L Na+, 90 mEq/L Cl-, 25 mEq/L K+, 45 mEq/L HCO3-.
Increased Loss of Fluid: fever–> Incr 15% =~150ml insensible loss/ 1 deg C above 37. (or 100ml/deg F >98.6), tachypnea. Incr 50% for each doubling of RR, evaporation (perspiration, ventilator, open wounds), GI (fistula, emesis, diarrhea, NGT), third space, operative loss (~800ml/hr for major abd surgery).
Maintenance Fluid: If wt>20kg, simplify 4:2:1 rule by adding 40 to pts weight in kilograms = ml/hr.
Maintenance: D5-1/4NS (= D5-.2NS) with 25 mEq K. If >20kg. Maintenance = 110 + wt in kg.
Daily Fluid Volume: 100ml/kg/d (4cc/hr) for 1st 10kg + 50ml/kg/d (2cc/hr) for 2nd 10kg + 20ml/kg/d (1cc/hr) any kg >20.
Average adult needs: 30-35ml/kg/d water (1500ml/m2/d). 35 kcal/kg/d. Need ~1g Na/ 160 kcal’s.
70kg Male–> D5 ½NS +20mEq KCL/L @125ml/hr = ~3L free water.
Goal: maintain urine output of 1-1.5L/d. Maintenance therapy can be provided enterally or IV for pt’s who are unable to take food or liquid by mouth. Minimum water requirements for daily fluid balance can be approximated from the sum of the urine output necessary to excrete the daily solute load (500 ml/day) plus the insensible water losses from the skin and respiratory tract (500 ml/day), minus the amount of water produced from endogenous metabolism (250–350 ml/day). It is not uncommon to administer 2–3 L water/day to produce a urine volume of > 1000–1500 ml/day, because there is no advantage to minimizing urine output. Weighing the pt daily is the best means of assessing net gain or loss of total body fluid, since GI, renal, and insensible fluid losses of pt’s are unpredictable.
| For 24-Hour Period | For an Hourly Rate |
For first 10 kg | 100 ml/d/kg | 4 ml/hr/kg |
For second 10 kg | 50 ml/d/kg | 2 ml/hr/kg |
For each additional kg | 20 ml/d/kg | 1 ml/hr/kg |
Body Surface Area (BSA) = square root of (Ht in cm X wt in kg)/ 3600. BSA (m2)= 0.007184 X wt- 0.425th X Ht- 0.725th. (Use wt in kg, ht in cm).
Banana Bag: MVI 1 amp + 100mg Thiamine + 1mg Folate + 2g MgSO4 @ 100-125 ml/hr X 3days.
Urine Volume: should be 0.5-1 ml/kg/hr if adequate intravascular volume, renal function, cardiac output.
Anion Gap: Na – (Cl + HCO3). Normal 8-16 mEq/L.
Osmol Gap: Measured Osm – Calculated Osm–> if 0-10= normal, if >10 abnormal, if <0 lab/ calculation error.
Serum (Plasma) Osmolality: tonicity of body fluids. A major determinant of total body water homeostasis, is measured by the number of solute particles present in 1 kg of plasma. It is calculated in mmol per L by using this formula:
Calculated Osmolality (mOsm/L): 2 (Na) + Glucose / 18 + BUN / 2.8. For “effective osmols“, need to add in mannitol (mOsm) + Sorbitol + Glycerol as these solutes do not easily cross into muscle cells.
Fractional Excretion of Sodium (FENa %): (UNa X PlCr)/ (PlNa X UCr) X 100. (<1=prerenal, >1=renal).
Usually secondary to parenteral overhydration, fluid retaining states (CHF, Acute RF), or mobilization of previously sequestered fluid.
S/s: wt gain, pedal/sacral edema, rales/wheezing, JVD, incr CVP and PCWP.
Lab: decr HCT, decr albumen, incr/ decr Na.
Tx: water restrict to 1500ml/d, diuretics, Na restrict to 0.5g/d, anasarca may respond to combined colloid (albumen) infusion with parenteral loop diuretics.
Seen in trauma (crush injury, burn), GI loss (vomit, NGT, diarrhea), third spacing (ascites, effusions, bowel obstruction), incr insensible losses. See Dehydration and Hypovolemia |
Mild–> 4% of Total Body Water (TBW), 15% blood volume.
Mod–> 6% TBW, 15-30% blood volume.
Severe–> 8% TBW, 30-40% blood volume.
Shock–> >8% TBW, >40% blood volume.
S/s: sleepy, apathy, coma, OH, tachycardia, decr pulse pressure, decr CVP and PCWP, decr skin turgor, hypothermia, pale extremities, dry tongue, decr fontanelle in infant, ileus, oliguria, weakness.
Lab: BUN:Cr is >20:1, incr HCT (3% for each Liter deficit), FENa <1%, incr Ur sg.
Tx: Bolus therapy with NS or LR. Replace free water loss with D5W or D5W ¼ NS.
