Chapter 6: IV Fluids

I.V. FLUIDS AT______________________

TITRATE___________________________

I.   Pathophysiology

A.  Four major processes are thought to contribute to the major loss of intravascular fluid[i]:

1.       change in microvascular membrane integrity

2.       change in Starling tissue forces

3.       cellular shock

4.       evaporative losses

B.  Changes in microvascular integrity

   1.   Following a burn there is a massive release of inflammatory

          mediators.

   2.   Histamine is released early,[ii] followed by complement, arachidonic acid, coagulation cascades, and cytokines, particularly IL-1 and TNF, which increase capillary permeability.

3.      Polymorphonuclear leukocytes adhere to the endothelium, releasing oxygen free radicals.  This leads to lipid peroxidation with lysis of the endothelial cell membrane and further arachidonic acid metabolism, which potentiates the above.

C.   Changes in tissue Starling forces

   1.  The capillary leak causes fluid and plasma proteins to shift from

     the intravascular to the interstitial space. 

2.  This causes hypoproteinemia, decreased intravascular oncotic pressure and increased interstitial oncotic pressure.  Edema results when the volume of interstitial fluid exceeds the capacity of  the lymphatics to remove it.  In burns greater than 35% TBSA, this edema is seen even in nonburned tissue.  Controversy exists as to when capillary integrity is restored.  Currently, this is thought to be between 8 and 12 hours.

D. Cellular shock

In burns of >30% TBSA, there is a decrease in the sodium ATPase which causes a decrease in cell transmembrane potential.[iii]  This results in an increase in intracellular sodium, cellular edema, and cell death.

       E. Evaporative losses

Additional evaporative losses through the burn wound can be between 4 and 20 times greater than normal and persist until complete wound closure is obtained.

II.  Fluid Resuscitation

A.  The principles of fluid resuscitation

            1.  Give the least amount of fluid necessary to maintain adequate organ perfusion.  This volume should be continuously titrated to urine output to avoid over- or under- resuscitation.[iv]^,[v]  

2.      Intravenous fluid resuscitation is required for all patients with 2^nd and 3^rd degree burns greater than 10% TBSA in patients under 10 or over 50 years of age.  Fluid resuscitation is also required for burns greater than 20% TBSA in all other age groups.

B.   Fluids

             1.  Lactated Ringer’s (LR) solution is the most popular resuscitation fluid used.  Table I compares the composition of LR with normal saline and plasma.

Table I:  Crystalloid Solutions[vi]

2.    There are numerous formulae that can be used for fluid

      resuscitation.  No  fluid resuscitation formula has proven to be superior.  All formulae are only a starting point.

3.    Fluid prescription for adults in the United States commonly uses the Parkland Formula which is:

    One half of this total is administered over the first 8 hours,

     and the second half over the next 16 hours. 

4.  Fluid resuscitation requirements differ in children due to their increased surface area-to-weight ratio.  The formula we use for resuscitation  in pediatric patients is the modified Carvajal formula[vii]^,[viii]:

One half of this total is administered over the first 8 hours, and second half over the next 16 hours.

[Note:  The eWheel which can be downloaded from the Journal of Burns website (www.journalofburns.com) provides an easy and quick method of calculating fluid requirements using the above formulae]

5.    The fluid rate should be titrated to keep the hourly urine output

      >0.5cc/kg/hr in an adult thermal burn; 1.0 cc/kg/hr in children.

6.  Uncertainty and inaccuracy of mathematical calculations related to resuscitation formula have been eliminated by use of the BurnWheel.[ix]^,[x] 

C.  Colloid               

1.  Proteins in plasma generate oncotic pressure and serve to maintain the intravascular volume.  The administration of colloid compensates for this protein lost.

2.      Much debate exists as to when capillary integrity is established and when or if colloid should be given.[xi]^,[xii] 

3.   Early infusion of colloid solutions may decrease overall fluid requirements and reduce edema.  However, excessive use of colloid risks iatrogenic pulmonary complications. 

4.  Guidelines for adding colloid to crystalloid regimen:

                  a.  patients with burns less than 30% TBSA do not usually require colloid

                  b.  patients with burns greater than 30% TBSA should receive colloid eight hours after injury

                  c.  patients with inadequate urine output

                  d.  colloid is administered by adding 50g of albumin to each liter of  crystalloid

D.  Hypertonic Saline

1.  Hypertonic salt solutions have been used for many years in burn resuscitation.[xiii]

2.  The use of salt solutions of 240-300 mEq/L have

      been shown to result in lower administered fluid volumes than with isotonic crystalloid.16^,[xiv] This has thought to be advantageous in the elderly and patients with premorbid cardiopulmonary disease.[xv]

3.  However, evidence has shown that when compared to crystalloid solutions, hypertonic saline does not result in a reduction in total fluid requirements or edema.[xvi]^,12

4.  Disadvantages include an osmotic diuresis which may cause difficulty in the interpretation of urine outputs and need frequent monitoring of serum sodium.  Deaths from renal failure have been reported, although the trials

     themselves use rather unusual regimens. [xvii]