Cooking with CQL Q&A: Functions in CQL

Each Q&A has the Cooking with CQL session number and date. For the most current and accurate information, please check the CQL Qs&As for a more recent answer to your question.

Beginning of Encounter: Encounters do not end in the Electronic Health Record (EHR) until closed. Completion of documentation could occur 3 days after the patient has left even though they were only there for 20 minutes. Most implementers figure out how to say the encounter has ended. They either say Departure Time and apply that to the ended encounter or they automatically end all encounters for the measure calculation at the end of the day. While Fast Healthcare Interoperability Resource (FHIR) or Quality Data Model (QDM) allows you say the end, that is not really where the EHR sees it as an end. The implementer has to figure that out and it can get a little complicated. Would it be reasonable to say the beginning of the encounter starts on that day, if you are talking ambulatory, because you’re looking for the number that started that day? Is that significantly different? I am asking that question to decrease implementer variability. (Session 43 - 4/23/20)

• Thank you for bringing up this concern. The QDM User Group addressed this issue on June 19, 2019 (link to minutes) based on the QDM-235 Jira tracker item. The QI-Core Implementation Guide STU 4 (v4.0.0 for FHIR 4.0.1) also includes encounter timing guidance. The resulting guidance for QDM “Encounter, Performed” relevantPeriod endTime is that implementation sites determine local mechanisms to overcome the issue. Feedback on the QDM User Group identified two approaches. Some use the check-in and check-out time for the actual encounter timing noting that the encounter may actually be opened ahead of the visit to prepare before the patient’s arrival and remain open long after the patient departs, perhaps days later. Another implementer automatically assigns an encounter end time as 23:59 of the day the encounter occurred. Your approach to limit measure expressions to compare actions only to ambulatory encounter start times may work. However, the intent of the measure may require an action after the patient departs. As you note, this is a complicated workflow issue. Hopefully the discussion in the QDM User Group minutes and the QI-Core documentation will be helpful. There are different implementation variations happening and that is the challenge.

Dosages and Number of Doses Per Day: There is significant logic involved with looking at dosages and number of doses per day. Is that part of the global library yet? (Session 32 - 2/28/19)

• Not yet. The global library is based on what measure developers identify as being used in enough measures to warrant including in the library.

Hospital Arrival Time: How is hospital arrival time defined? (Session 32 - 2/28/19)

• The definition is included in the MAT Global Common Functions, it’s the start of the first location period for the locations in the encounter, or the immediately prior emergency department encounter if one exists.

Random: Does Clinical Quality Language (CQL) support a mechanism for randomly picking an item from a list? (Session 37 - 7/25/19)

• The short answer is no. Clinical Quality Language (CQL) is purposely a deterministic language, so we don't have functions like Random(). This was a design decision in the very earliest phases of language development to ensure that systems could reliably cache intermediate results. Even functions like Today() and Now() are defined deterministically so that they return the same value within any given evaluation session. However, CQL 1.3 introduced the ability to define external libraries. From the perspective of the translator, external definitions are just function signatures; it's up to the engine to resolve external definitions and provide the run-time implementation for them. For engines, this would be fairly straightforward to support, but

  • It would tie the CQL that uses the external definitions to engines that understood those externals (reducing portability)
  • The Java-based open source engine does support external libraries, but it's not a feature that has been well-tested.