Comments
Searching for observations for CDS and for display often requires only the last of a certain type of observation, e.g., last set of vital signs, last hemoglobin A1c. We could not determine a method to do so with the current search parameters. It would be very helpful to incorporate this functionality into the specification (for observation and perhaps certain other resources).

Grahame's Comments
Could do it by specifying search criteria, setting sort by date descending, and _count = 1. Not sure that a more concise syntax is wothwhile