Only use secondary sources if you are unable to access the original source i.e. it is out of print, or unavailable through the library. It is better to refer back to the original source yourself so you can check the accuracy of the quoted material.
The original authors are named in your in-text, but only the source you actually read goes into the reference list. For example, if a study by Bendz et al. was referred to in a work that you read by Olson et al., you would only list Olson et al. in your reference list.
In the reference list
Olson, D. M., Meek, L. G., & Lynch, J. R. (2004). Accurate patient history contributes to differentiating diabetes insipidus: A case study. Journal of Neuroscience Nursing, 36(4), 228-230.
If the original source is unavailable, use as cited in within your text.
Bendz, Sjodin, and Aurell (1990, as cited in Olson, Meek, & Lynch, 2004) discussed the importance of accurate patient history taking with diabetes …
OR
… showed in the study (Bendz, Sjodin, & Aurell, 1990, as cited in Olson, Meek, & Lynch, 2004).