CARBON DIOXIDE LOSS FROM BURNED SKIN
Donald E. Watson, Paul R. Schloerb, and Daniel C. Darrow
Departments of Pediatrics and Surgery
University of Kansas School of Medicine.
Surgical Forum 10: 355-356 (1960)
Investigation of a convulsion in a 3-year old child suffering from
a 25% second degree burn demonstrated a respiratory alkalosis. She had
been treated with 33 cc./kg. normal saline and 90 cc./kg. 5% glucose in
water, and had vomited several times over an 8-hour period. Serum electrolytes
at that time were: Na 150, K 4.0, Cl 98, HCO3 19.0, and serum
pH 7.59. Alveolar ventilation rate at the time the blood was drawn is not
known, and possibly was excessive.
The probability of CO2 loss from a large area of extracellular
fluid exposed to air was obvious, and it was decided to quantitate this
loss. Requirements for such loss by diffusion are threefold: the gas must
be in solution, the solution must be in contact with air, and there must
exist a diffusion gradient.
If the CO2 escaping from a surface of known area is caught
in a container, and the time allowed for the diffusion is known, the rate
of diffusion in cc. CO2/min./cm.2 can be computed.
The rate of diffusion in a closed chamber will decrease exponentially as
the partial pressure of CO2 within the chamber approaches that
of the tissue juice at the interface. Therefore, log time may be used for
The gas collection chambers are sterile rubber baby bottle nipples,
chosen because they conform to the skin and can be punctured with a needle
for aspiration. They are sealed to the skin surface with antibiotic ointment
and left in place for 2, 4, 8, and 16-minute collection intervals. The
gas samples are collected by needle aspiration in 1O cc. syringes equipped
with 3-way stopcocks. The CO2 and O2 analyses are
then accomplished with a Scholander gas analyzer, and results recorded
in per cent CO2 in air. The volume Of CO2 is derived
by knowing the volume of the collection chamber. The diffusion area is
equal to the area of the base of the chamber. The accuracy of our gas analyses
is poor in low concentrations, but in the significant ranges, the accuracy
is on the order of 3%.
Carbon dioxide diffusion studies have been made on several burned patients
having different aged burns. No animal work has been done. Volume of CO2
was plotted against time for each case and the expected exponential shape
of the diffusion curves was found. There was individual variation among
the subjects as to the partial pressure of CO2 at equilibrium. This seemed
to be related to the age of the burn. A two-hour-old burn study demonstrated
equilibrium had not been reached in 16 minutes at 21 mm. Hg p.p. CO2.
Normal skin and third degree burned skin failed to lose CO2.
The maximum diffusion rate calculated was .0083 cc. CO2/min.
/cm.2 This value will be used in the discussion, although further
studies may reveal faster rates.
The maximum measured rates of diffusion were from fresh second degree burns
in which there was obvious tissue fluid in contact with air. This allows the
gas to escape rapidly, unimpeded. The third degree burns failed to diffuse CO2
because the skin and its vessels had been effectively sealed away from the body
In order for the measured rate of diffusion to assume much meaning, an example
of a hypothetical 50% burn can be considered. A square meter of surface area
is a convenient unit of measure since it is proportional to the metabolic
rate. At the measured rate of diffusion the CO2 lost from a 50%
burn is calculated to be 41.0 cc./min./M.2 skin. Assuming a metabolic rate
of 1000 cal./24hr./M.2 an O2 consumption of 224 L./1000
cal., and a respiratory quotient of 0.8, the CO2 production by
the body is 120 cc./min./M.2 The skin loss Of CO2 from
a 50% burn is therefore about 0.3 of the total production.
If 0.3 the CO2 produced by the body is lost from burned skin,
blood pH change is significant. Further study relating the effects of respiratory
rate and metabolic acidosis on that change is needed.