A high index fluid is preferable in cases of?

A high index fluid is preferable in cases of dehydration because it has a higher concentration of formaldehyde and other chemicals that can help to effectively preserve tissues that may be compromised due to a lack of moisture. When a body is dehydrated, the tissues can become firm and dry, making it necessary to use a more potent embalming fluid to ensure thorough preservation and a natural appearance of the body.

In addition, high index fluids provide better penetration and fixation of the tissues, which is crucial in cases where moisture deficiency is present. Using a high index fluid aids in effectively restoring a level of balance in the tissues, ensuring that the embalmers can achieve optimal results.

The other options, including overhydration and normal hydration, do not specifically call for a high index fluid because they may require different formulations that are less concentrated, allowing for proper moisture balance without the risk of excessive firmness or edema.