Final answer:
The destruction of red blood cells after an injection meant to be isotonic suggests the solution was not isotonic, possibly being hypertonic or hypotonic, causing the cells to crenate or lyse.
Step-by-step explanation:
When a patient receives an injection of what is presumed to be an isotonic saline solution and subsequently dies, with an autopsy revealing destruction of many red blood cells, it suggests that the solution may not have been truly isotonic after all. True isotonic solutions, like normal saline (0.9% m/v NaCl) or lactated Ringer's solution, have the same osmotic pressure as body fluids, which prevents the net movement of water into or out of the body's cells. If the solution had been hypertonic, water would have flowed out of the cells, causing them to shrivel and die, a process known as crenation. Conversely, if the solution had been hypotonic, water would have rushed into the cells, causing them to swell and possibly burst in a condition known as lysis. The fact that red blood cells were destroyed in this scenario indicates the solution injected could have been hypertonic or hypotonic, rather than isotonic as intended.