After reading about this and the way His heart must have been pounding, I've wondered about him developing pulmonary edema.
Heart rates exceeding cardiovascular reserve lead to the water component of the blood leaking into the lungs.
Pulmonary edema further limits your ability to breathe because your alveoli are filled with fluid.
Lance could certainly draw water and blood.
I believe it was the Chief Medical Examiner of New York—a retired man with over 10,000 autopsies to his credit—who looked over several studies and said categorically that the Christ did, indeed, die of pulmonary edema due to shock, hypovolemia, and exhaustion.
In a sense, His heart could not continue to pump due to cardiogenic shock brought on by fluid depletion. The lance of the Legionnaire who Catholics have traditionally named “Longinus” (and who later is said to have become a martyr), pierced the lower level of His lung or pleural cavity and “both blood and water” poured out in a veritable stream. In other words, the Gospel account agreed with what the M.E. felt would be the case. The estimate he gave of the volume was quite high: over 800 ccs or so.
The whole thing is somewhere on the web, but it makes total sense to me.
Jesus, I adore you!