Burn surgery is associated with significant changes (reductions) in hematocrit. However, it is unclear whether these reductions are the result of hemodilution from non-red cell containing intraoperative transfusions or from loss of red blood cells. The investigators will be using the Daxor Blood Volume Analyzer (BVA-100), an FDA approved instrument that can measure total blood volume, plasma volume, and RBC volume using the indicator dilution technique. With this technique, a tracer substance (I-131 albumin) is mixed with an unknown volume. An identical amount of the tracer is mixed into a solution with a known volume. By comparing the concentration of the indicator between the known and unknown volumes, the investigators can determine the volume of the unknown volume (or in this case, the blood volume).

The investigators will be measuring the change in blood volume, plasma volume, and RBC volume from the pre-operative to the post-operative state after completion of burn surgery. We hypothesize that these reductions in hematocrit are primarily the result of hemodilution rather than blood loss and that there will be a statistically significant change in measured plasma volume from the pre-operative to the post-operative measurements.

Average plasma volume for male and female patients is 2950ml SD=590 ml. To detect a 10% increase in plasma volume from hemodilution with a power 0.80 and alpha error 0.05, a one tailed normal distribution t-test determines a sample size fifty. To account for a 10% data loss (technical difficulty, patient withdraw) a sample size of fifty-five would be required.

Fifty-five consecutive adult patients (18 years or older) having burn surgery will be enrolled. Patients with recognized coagulopathy will be excluded. The outcome variables included blood volume (BV, ml), plasma volume (PV, ml) and red blood cell volume (RBCV, ml). All three outcome variables will be measured at two time points; pre-surgery and post-surgery. The pre-surgery measurement will be collected precisely after induction of general anesthesia but prior to surgery start. The post-surgery measurement will be taken immediately after the operation and after all intraoperative red blood cell transfusions are complete. For those patients receiving blood transfusions in the operating room prior to all data collection points, the transfused RBC volume will be recorded and subtracted from the RBCV measured after the transfusion. Transfused RBCV will take into account Hct of 60% for pRBCs. Additional baseline information, including age (year), sex (male, female), weight (kg), and surgery type, will be collected. For the tracer dilution method, the following blood samples will be collected: a baseline (no radiation sample), a first sample 12 minutes after injection (after complete mixing in the blood volume) and additional samples every 6 minutes for at least three successive timed sample points. These multiple timed sample points produce a logarithmic curve of radiation over time, as only a small fraction of albumin leaves the blood volume into the interstitial space. The investigators will compare the pre-operative and post-operative blood volume, RBC volume, and plasma volume measurements to determine if the decrease in hematocrit associated with burn surgery is truly due to hemodilution or loss of RBC volume.