Fluids Overview

Body fluid compartments as a percentage of total body weight and their approximate total volumes

a.    Total body water (TBW)

  • 60% of body weight for adults
    • 40% intracellular
    • 15% interstitial
    • 5 % intravascular
  • 1 L of fluid = 2.2 lbs  (1 kg)
    • Ex. A 154lb male:  (154/2.2) * 0.60 = 42.0 L

b.    Extracellular fluid (ECF)

  • Interstitial (15%) + Plasma aka intravascular (5%) = 20%
    • Ex. 150 lb male: (150/2.2) * 0.2 = 13.6364 L

c.    Intracellular fluid (ICF)

  • 40% of body weight
    • Ex. 154lb male: (154/2.2) * 0.4 = 28 L

d.    Interstitial fluid

  • 15% of body weight
    • Ex. 154lb male: (154/2.2) * 0.15 = 10.5 L

e.    Plasma

  • 5% of body weight
    • Ex. 150lb male:  (150/2.2) * .05 = 3.4091 L

Total daily fluid input/output

  • (1400/2600) * 100% = 53.85 % (input)                      (1500/2600) * 100% = 57.69 % (output)

Daily maintenance fluid requirements

  • Neonate (1-10 kg)     100 mL/kg
  • Child (10-20 kg)        1000 mL + 50 mL for each kg > 10
  • Adult (> 20 kg)       1500 mL + 20 mL for each kg > 20

Total fluid deficit.

  • Total fluid deficit = normal total body weight (TBW) – present total body weight (TBW)
  • Water deficit = 0.6 (LBW) [(present Na concentration / 140 mEq/L) – 1]
  • Water deficit can also be measure by acute weight change where 1 kg change in weight = 1 L water
    • If a patient loses 4.4 lbs then they have a 2 L water deficit

Colloids vs. crystalloids therapeutic fluids.

  • Crystalloid solutions:  plasma volume-expanding capability of a crystalloid is directly related to its sodium concentration
    • Crystalloids require more volume than colloids to achieve the same effect
    • Normal saline  (0.9% NaCl)
      • Isotonic solution: provides 154 mEq/L of both Na & Cl   (308 mEq NaCl / L total)
      • Used to treat metabolic alkalosis, hemorrhage, pre/post operative fluid mgmt, shock, burns, fluid challenge (BP is a little bit too low, use NS to normalize it)
    • Half-normal saline (0.45% NaCl)
      • Hypotonic to plasma
        • Can cause hyponatremia (closely watch Na levels)
      • Used for the treatment of hypertonic ECFV depleted states
    • Hypertonic Saline (3.0% NaCl)
      • Used for treatment of hyponatremia, lowers intracranial pressure (used after traumatic brain injury/stroke)
        • Be careful b/c it can cause hypernatremia, hyperosmolality, CHF, hypokalemia, hyperchloremic acidosis, renal failure, seizures, decreased consciousness
      • Raises Na osmolality in the blood  (infuse slowly)
    • Ringer’s Solution
      • Provides Na, Cl, Ca, K
      • Doesn’t provide free water or lactate
    • Lactated Ringer’s Solution
      • Perioperative fluid that replaces Na, Cl, K, Ca, lactate & provides ECFV replacement (burns, dehydration, lower GI fluid loss, mild metabolic acidosis)
        • It’s K can cause fluid overload in CHF or renal failure
        • Lactate acts as a buffer to increase pH
    • D5W (5% dextrose in water)
      • Provides free water, useful in treatment in fluid loss, severe hypernatremia, diving meds to non-diabetics
    • D5W in NS
      • Used to treat fluid volume deficit, hypotonic dehydration
      • Caution in patients w/ cardiac or renal issues b/c it can cause heart failure and pulmonary edema
    • D5W in 0.45% NaCl
      • Used for daily maintenance of fluids when Cl & Na are required, treatment of hypernatremia, replace hypotonic losses
  • Colloidal Solutions–increase plasma oncotic pressure: moves fluid from the interstitial to the plasma compartment
    • Probably no therapeutic advantage vs. crystalloids  (more likely to induce fluid overload in comparison to crystalloids)
    • Albumin 5% or 25%
      • Both are indicated for the treatment of hypovolemia with/without shock, hypotension in hemodialysis
        • Restore intravascular volume, maintain cardiac output
    • Dextrans   (Dextran 40–Low MW     Dextran 70–High MW)
      • Glucose solution with collodial activity similar to albumin that expands plasma volume by pulling fluid from interstitial to intravascular space
      • These products may cause anaphylactic reactions and prolonged bleeding times have limited the use of dextrans
    • Hetastarch    (6% starch & NS)
      • Large carb used for treatment of hypovolemia
      • Risk of hypersensitivity reactions, bleeding and impairment of clotting mechanisms
      • Need to reduce dose in ppl with kidney dysfunction
    • Fresh Frozen Plasma (FFP)
      • Increases collodial oncotic pressure and moves fluid into the vascular space
      • Risks: anaphylaxis, viral transmission through the plasma, hepatitis, increased nosocomial infection rate

Intravascular depletion vs. TBW depletion.

  • Intravascular depletion
    • Symptoms tend to occur acutely, generally due to the loss of isotonic fluid (loss of both Na & water)
    • Causes decreased tissue perfusion (resulting in decreased urine output, faintness/dizziness) hypovolemic shock
    • Requires rapid and aggressive fluid replacement
    • Causes: external fluid losses or internal redistribution of ECF from vascular space to body cavities (shock, ascites)
  • TBW depletion
    • Dehydration  (signs, symptoms, causes can all be described as such)
    • More of a gradual, chronic problem
    • Loss of hypotonic fluid from all body compartments–disturbance of osmolality

Need to define the fluid problem (TBW depletion vs ECF–intravascular depletion)

  • In the case of the latter, standard therapy is NS (150-500 mL/hr) until tissue perfusion has been minimized at which time the patient may be switched to a more hypotonic solution (0.45% NS) at a rate to deliver daily needs
    • Lactacted ringer’s is an alternative but the lactate may cause problems for large or prolonged infusions
    • Colloid solutions may be indicated in order to increase oncotic pressure within the vasculature space
  • In the case of patients with TBW depletion (high plasma osmolality and Na)
    • Use hypotonic solutions b/c they reduce plasma osmolality quicker and are more efficient at replenishing ICF than isotonic solutions.
      • D5W-0.45% NS is commonly used

Monitoring the adequacy and safety of a fluid replacement therapy regimen

  • Want to monitor:
    • Physical signs/symptoms
    • Orthostatic BP
    • Pulse rate
    • Weight changes
    • Blood chemistries (Na, hemoglocin, hematocrit, serum albumin, BUN/Scr)
    • Fluid in’s and out’s
    • Cardiac output
  • Need to be extra careful in patients w/ renal, cardiac, or liver failure and in the elderly
  • When considering IV fluids, keep in mind 4 types of patients:
    • Hypovolemic patients (most common):  these patients usually have sepsis, pneumonia, intractable N/V
      • Treatment:  Normal Saline
    • Hypervolemic patients:  these patients usually have CHF, cirrhosis, renal failure
      • Treatment:  Avoid Fluids
    • Euvolemic patients unable to take oral fluids (perioperative period): normal people who are going for an elective surgery for example
      • Treatment for patients prior to a procedure or who are NPO:  D5W-0.45% NaCl
    • patients with electrolyte abnormalities
  • Patients who are healthy or getting elective surgery and can still drink fluids do not need to receive IV fluids

Correction Fluids:  Normal Saline, Hypertonic Saline, Lactated Ringers

Maintenance Fluids:  D5W,  D5W-0.45% NaCl, D5W-1/4NS

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