Which observation is MOST useful for determining if an 86-year-old patient has deficient fluid volume?

The observation regarding skin turgor, particularly on the sternum, is most useful for assessing whether an 86-year-old patient has a deficient fluid volume. Skin turgor refers to the skin's elasticity and its ability to return to its normal position after being pinched. In older adults, the skin tends to lose elasticity due to natural aging processes and decreased hydration. When fluid volume is deficient, a decrease in skin turgor can indicate dehydration, as the skin becomes less supple and does not return to its normal shape quickly.

In assessing fluid volume status, other options can indeed provide relevant information. Blood pressure measurements can give insights into the cardiovascular response to volume depletion, but they may not provide a definitive indication of fluid deficit. Similarly, while urine output can reflect hydration status, it may vary significantly depending on other factors such as kidney function and medications rather than just fluid intake. Observing the condition of mucous membranes can also indicate fluid status; however, skin turgor is often considered a more direct and quicker assessment for fluid deficiency in older adults.

In summary, skin turgor is particularly valuable in this demographic as it provides immediate and visually observable feedback regarding fluid volume status.