How would you calculate the total blood volume of the body, without exsanguination?

Inject a solution of known volume into the blood. Allow this to circulate for an appropriate length of time, e.g. 5-10 mins, then take a blood sample. The dilution of the initial solution can then be calculated by measuring the concentration in the sample.Say 1M of solution is injected, and a 10ml blood sample taken after the wait period with concentration of 2 x 10^-3 . Volume = concentration/moles therefore volume = 1/(2 x 10^-3) = 5000ml.