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Why pure water is not directly injected into blood?

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Why pure water is not directly injected into blood?

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  1. Any solution that is injected into your general circulation needs to be isotonic. This means  that is needs to have an osmolarity of about 300mOsm/L. Significant deviations from this measure can cause serious harm.

    When you inject pure water (which is hypotonic because it contains no solute) water will diffuse into the intracellular space to attempt to create a chemical equilibrium with the sodium ions that are within your cell. This is a process called crenation. The cell swells to accommodate the increase in volume and may lyse.

    Conversly, injecting a solution which is hypertonic, or higher than 300mOsm/L will cause water to diffuse out of the cell and the cell will shrink.

    This is why fluid replacement via IV is generally always done with Normal Saline, Dextrose 5% in water, Lactated Ringer's solution or other isotonic solutions. There are, however, times when injecting hypertonic or hypotonic solutions may be indicated to treat a patients pathology.


  2. In addition to the issues of osmolarity with distilled water, pharmaceutical grade parenteral solutions undergo rigorous filtration to remove even the slightest pathogens/pyrogens to ensure patient saftety.  

    NB:  I strongly discourage the recreational parenteral administration of tap water.

  3. because it is not osmotically similar to blood

  4. Because it is hypotonic, and your cells might burst.

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