Volum
Body Fluid Compartments
 Total Body Water (TBW): 50-70% of total body
wt.
 Avg. is greater for males.
 Decreases with age. Highest in newborn, 75-80%.
By first year of life TBW ~ 65%.
 Most in muscle, less in fat.
 TBW= ECF + ICF
 ICF ~ 2/3 & ECF ~ 1/3
 ECF = Intravascular (1/3) + Interstitial (2/3)
Electrolyte Physiology
 Primary intravascular/ECF cation is Na+. Very
small contribution of K+, Ca2+, and Mg2+.
 Primary intravascular/ECF anion is Cl-. Smaller
contribution from HCO3-, SO42- & PO43-,
organic acids, and protein.
 Primary ICF cation is K+. Smaller contribution
from Mg2+ & Na+.
 Number of intravasc anions not routinely detected.
ICF (mEq/L) ECF (mEq/L)
Cations
K+ (150-154) Na+(142)
Na+ (6-10) Ca+2 (5)
Mg+2 (40) K+ (4-5)
Mg+2 (3)
Anions
Organic PO4-3 (100-106) Cl-(103-105)
protein (40-60) HCO3- (24-27)
SO4-2 (17) protein (15)
HCO3- (10-13) PO4-3 (3-5), SO4-2 (4)
organic acids (4) Organic acids (2-5)
IV Fluid/Electrolyte Therapy
 Three key concepts in consideration of fluid and
electrolyte management:
 cell membrane permeability
 osmolarity
 electroneutrality
Cell membrane permeability refers to the ability of a
cell membrane to allow certain substances such as
water and urea to pass freely, while charged ions
such as sodium cannot cross the membrane and are
trapped on one side of it.
Osmolarity
 Osmolarity is a property of particles in solution. If
a substance can dissociate in solution, it may
contribute more than one equivalent to the
osmolarity of the solution. For instance, NaCl will
dissociate into two osmotically active ions: Na and
Cl. One millimolar NaCl yields a 2 milliosmolar
solution.
Electroneutrality
 Electroneutrality means that the overall number of
positive and negative charges balances. For
instance, in conditions like renal tubular acidosis
where HCO3- is lost, chloride is retained leading
to a hyperchloremic state.
"Expected osmolarity of plasma
can..."
 Expected osmolarity of plasma can be calculated
according to the following formula:
Osmolarity (mOsm/kg) = 2×[mEq/L Na+] + glucose
+ BUN
 Concentration of sodium is the major determinant.
Normal serum osmolarity ranges from about 280 to
295 mOsm/kg.
Maintenance fluids must be determined for basic
requirements, then existing volume or electrolyte
deficits must be evaluated to determine the
appropriate IV fluid to use and the volume to
administer.
Types of IV Fluid
 Crystalloid
 Colloid
 Balanced salt/electrolyte solution; forms a true
solution and is capable of passing through
semipermeable membranes. May be isotonic,
hypertonic, or hypotonic.
 Normal Saline (0.9% NaCl), Lactated Ringer's,
Hypertonic saline (3, 5, & 7.5%), Ringer's
solution.
 However, hypertonic solutions are considered
plasma expanders as they act to increase the
circulatory volume via movement of intracellular
and interstitial water into the intravascular space.
Crystalloid:
Colloid:
 Colloid: High-molecular-weight solutions, draw
fluid into intravascular compartment via oncotic
pressure (pressure exerted by plasma proteins not
capable of passing through membranes on
capillary walls). Plasma expanders, as they are
composed of macromolecules, and are retained in
the intravascular space.
 HAES, Gelatina (Dextran);
 Albumin, Plasma
"Free H2O solutions:"
 Free H2O solutions: provide water that is not
bound by macromolecules or organelles, free to
pass through.
 D5W (5% dextrose in water), D10W, D20W,
D50W, and Dextrose/crystalloid mixes.
"IVF can supply 3 things"
 fluid,
 electrolytes,
 calories (150 ml/h D5W)
The most common uses for IVF:
 Acutely expand intravascular volume in
hypovolemic states
 Correct electrolyte imbalances
 Maintain basal hydration
infusion:
 Ringer's lactate solution
 NaCl 0,9
Normal Saline (0.9% NaCl):
 Isotonic salt water.
154 mEq/L Na+; 154 mEq/L Cl-; 308mOsm/L.
Cheapest and most commonly used resuscitative
crystalloid.
 High [Cl-] above the normal serum 103 mEq/L
imposes on the kidneys an appreciable load of
excess Cl- that cannot be rapidly excreted. A
dilutional acidosis may develop by reducing base
bicarb relative to carbonic acid. Thus exist the risk
of hyperchloremic acidosis. Only solution that
may be administered with blood products. Does
not provide free water or calories. Restores NaCl
Lactated Ringer's solution
 isotonic, beginning of volume resuscitation
Ingredients:
* 130 mEq of sodium ion.
* 109 mEq of chloride ion.
* 28 mEq of lactate.
* 4 mEq of potassium ion.
* 3 mEq of calcium ion.
Lactate is converted readily to bicarb by the liver.
Has minimal effects on normal body fluid
composition and pH. More closely resembles the
electrolyte composition of normal blood serum.
Does not provide calories.
"Volume deficits are best
estimated..."
Volume deficits are best estimated by acute changes
in weight. Less than 5% loss is very difficult to
detect clinically and loss of 15+% will be
associated with severe circulatory compromise.
 Mild deficit represents a loss of ~ 4% body wt.
 Moderate deficit --- a loss of ~ 6-8% body wt.
 Severe deficit --- a loss of ~ >10% body wt.
Volume deficit may be a pure water deficit or
combined water and electrolyte deficit.
Resuscitative IV Fluids
Principle of trauma & surgery: Crystalloids; isotonic
balanced salt solutions. NS or RL.
Amount given based upon body wt, clinical picture,
and vital signs. ?shock.
Generally a bolus of 500-2000cc is given depending
on the above, then rates are run at 1.5-2x
maintenance or 10-20cc/kg/d on top of
maintenance. Continuous clinical r/a of vitals and
response to fluids already given is required for
ongoing IVF therapy.
Resuscitative IVF therapy is for initial stabilization
and overlaps with further replacement therapy.
Monitoring endpoints for IVF
therapy
Endpoint should be maintenance or reestablishment
of homeostasis.
 In order to reestablish homeostasis in a pt, IVF
therapy must not only provide a balance of water
and
electrolytes, but must ensure adequate oxygen
delivery to all organs and renal perfusion as
evidenced by urine output.
 Endpoints: normalization of VS, UO>0.5ml/kg/hr
(1ml/kg/hr for a child) and restoration of normal
mental status and lack of clinical signs of deficit.
 Other endpoints include normalization of labs,