Section
3b
Practical
Approach To Treatment
The
key decisions to be made are:
- What
type of fluid to use
- What
type of vascular access
- How
much to give
- What
parameters to monitor
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CHOICE
OF RESUSCITATION FLUID
In general,
fluids that contain salt at least in quantities
isotonic with plasma are appropriate for use in
resuscitation if given in sufficient amounts.
Restoration of the sodium loss, is essential.
Fluids should be free of glucose (exception
being small children), since glucose intolerance
is characteristically present due to high
circulating levels of stress hormones. The oral
route can be used for small burns. The
most appropriate fluid is lactated Ringers
because it’s composition is the closest to
that of extra cellular fluid. Also the lactate
is a source of base vs. conversion to
bicarbonate in the liver.
PRELOAD
EXPANDING PROPERTIES OF STANDARD FLUIDS
| Fluid |
Osmolarity
(mOms/L) |
Colloid
Osmotic Pressure |
pH |
Distribution
Space |
Ratio
of fluid infused to intravascular
expansion |
| 5%
dextrose |
250 |
0 |
4 |
Total
body water |
8:1 |
| Normal
saline |
308 |
0 |
5 |
Extracellular |
3:1 |
| Ringer's
lactate solution |
270 |
0 |
6.5 |
Extracellular |
3:1 |
| Hypertonic
lactated saline (250 mEq Na+/L) |
450 |
0 |
6-7 |
Extracellular
expansion by fluid shifts from cells |
<3:1* |
| 6%
albumin |
250 |
20-24 |
6-7 |
Intravascular |
1:1 |
| 6%
dextran 70 |
300-303 |
20-40+ |
6-7 |
Intravascular
expansion fluid shift |
<1:1 |
*
Depends on tonicity of fluid and plasma
osmolarity
What
to Monitor
No
one monitor of perfusion in the burn patient can
be considered to be a completely reliable
indicator of tissue oxygenation (perfusion) and
therefore several standard hemodynamic monitors
and laboratory tests should be utilized. The
correct and incorrect parameters to follow will
be presented.
Physiologic
Measurements
Oxygeation.
Use
of pulse oximeter is standard for a major burn.
Baseline Body
Weight. The
baseline weight is used to help estimate the
initial fluid infusion rate (via formula) which
can be obtained by history or estimated.
Arterial
Pressure.
The increased sympathetic tone characteristic of
this early period makes arterial pressure an
insensitive measure of volume status; however, a
minimal level of perfusion pressure (more than
80 mean) must be maintained and therefore blood
pressure monitoring is necessary.
An arterial
line may be required if:
- Patient is
hemodynamically unstable
- Extremities
are burned so that sphingomanometric
pressure cannot be obtained manually.
- If
frequent blood gases are required
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The arterial
catheter should be placed through non burned
skin and should be removed as soon as possible.
Pulse Rate.
Tachycardia is inevitable early post burn due to
hypovolemia and catechol release from tissue
trauma and pain. The degree of tachycardia can
be very useful for determining adequacy of
volume replacement. The exception would be the
elderly or the patient with pre-existing heart
disease in which the heart rate cannot increase
in proportion to the stimulus. In most patients:
Response
to Pulse Rate:
- Pulse less
than 120 usually indicates adequate volume
- Pulse more
than 130 usually indicates more fluid is needed
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Urine Output.
The
status of renal blood flow is usually an
accurate reflection of the adequacy of systemic
perfusion during this early phase of injury. A
urine output of 0.5 to 1 mg/kg/hr normally
reflects adequate renal blood flow, assuming
there are no factors such as alcohol,
hyperglycemia, or mannitol, that alter the
relationship between renal blood flow and urine
output.
Intake-Output.
What
goes in and what comes out should be carefully
tabulated. Intake will far exceed output during
this phase as edema develops.
Blood Gases.
The
method and importance of monitoring arterial
oxygen and carbon dioxide tension has been
described. The measurement of pH and acid-base
balance are extremely useful for the assessment
of tissue oxygenation. A base deficit during
this phase usually reflects impaired tissue
oxygenation due to hypovolemia or carbon
monoxide toxicity (also cyanide).
Electrocardiographic
Monitoring. Arrhythmias
are not common in the young patient as long as
oxygenation is adequate, but they become a major
concern in the patient older than 45 years as a
result of the burn stress response.
Body
Temperature.
The burn patient is very prone to hypothermia
during this early period, especially with
infusion of cool fluids. A decrease in
temperature will lead to further hemodynamic
instability and impaired perfusion.
Central
Venous Pressure (CVP). The
central venous pressure in the large burn at
this stage is usually low, 0 to 5 cm H2O,
even with adequate fluid resuscitation. Therefore
it can be very dangerous to use an arbitrary
value of central venous pressure as an endpoint
of resuscitation. Too much or too little fluid
can be infused based on an arbitrary value.
Pulmonary
Artery Wedge Pressure. The
majority of young patients, even with massive
burns, do not require the use of these
measurements for initial resuscitation. A
selected group of patients can benefit from this
measurement. These include:
Indications
for use:
- Elderly
or patients with pre-existent heart
disease with large burn or smoke
inhalation.
- Young
patient with massive burn who is not
maintaining perfusion despite fluid intake
well in excess of predicted.
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Cardiac
Output, Mixed Venous Oxygen Tension. The
primary objective of fluid management is to
maintain adequate tissue oxygen delivery. The
direct measurement of cardiac output (cardiac
index) can assist in the determination of
oxygen delivery. A cardiac index in excess of
2.5 L/min/m2 would be considered
normal for a non-injured person. The value for
mixed venous oxygen tension (PvO2) however,
can greatly assist in this determination.
Association
of mixed venous gas
- PvO
> 35 mmHg: oxygen delivery adequate
- PvO
> 30-35 mmHg: oxygen delivery marginal
- PvO
> 30 mmHg: oxygen delivery inadequate
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Laboratory
Measurements
Hemoglobin
and Hematocrit.
Baseline
hematocrit and hemoglobin is useful to
monitor, although changes in the values may
not accurately reflect changes in blood volume
due to the selective loss of the plasma
component of blood.
Hematocrit
Changes After Large Burn
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Finding
|
Cause
|
| Hematocrit
increased |
Plasma
volume decreases while circulating
red blood cell volume remains
relatively constant |
| Hematocrit
normal |
Normalization
of blood volume has occurred. Decrease
in both plasma and red blood cell
volume, the latter from, e.g.
hemolysis |
| Hematocrit
decreased |
Hemolysis
from prolonged heat exposure, with
only plasma volume replacement.
Major loss of blood from non-burn
injury with only plasma volume
replacement.
Pre-existing anemia
Hypervolemia (unlikely)
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White
Blood Cell. Initial
white blood cell count may be high, normal, or
low, depending on the magnitude of the stress
response and white cell sequestration into the
burn.
Electrolytes.
Since
the initial losses are primarily plasma, the
Na+, Cl` , K+ values remain relatively constant
despite hypovolemia and vary mainly as a result
of the type of resuscitation fluid used. K+ will
increase if severe hemolysis has occurred or
renal impairment is present. The HCO ` 3
content will vary, depending on the status of
perfusion and acid-base balance.
Creatinine
and Blood Urea Nitrogen. Baseline
values are helpful to rdefine normal status.
Plasma Proteins. A marked decrease in
plasma proteins occurs early postburn.
Plasma
Myoglobin. The
plasma value of myoglobin is obtained with very
deep burns, especially electrical burns.
Myoglobin released from deeply injured muscle
will affect renal function. A higher urine
output should be maintained.
Prothrombin
Time, Partial Thromboplastin Time, and
Platelets. An
initial value during this period is useful for
determining whether clotting factors will be
needed. It is not common to have to replace
clotting factors and platelets during the first
36 hour period unless a prolonged shock state
has initiated disseminated intravascular
coagulation of pre-existing liver or hematologic
disease was present.
  
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