CDS Hooks & decision support

The answer in one paragraph

SMART on FHIR waits for a human to open an app; CDS Hooks inverts the arrow. At defined workflow moments — opening a chart (patient-view), signing an order (order-sign), selecting one (order-select) — the EHR POSTs context to your CDS service, and you respond with cards: informational notes, warnings, concrete suggestions (with FHIR resources the EHR can apply in one click), or a link that launches a full SMART app. It is how external intelligence — drug-interaction checks, guideline nudges, AI risk scores — appears inside the clinician's flow instead of in yet another portal.

The exchange, concretely

The EHR calls your service with the hook name, context (patient, draft orders as FHIR), and often prefetch data you asked for in your discovery document — so you don't have to query back. You reply:

{ "cards": [{
    "summary": "Renal dosing: reduce dose 50%",
    "indicator": "warning",
    "source": { "label": "Nephrology guideline v4" },
    "suggestions": [{ "label": "Apply renal dose", "actions": [
      { "type": "update", "resource": { "resourceType": "MedicationRequest", "...": "…" } }
    ]}]
}]}

indicator (info / warning / critical) drives display; suggestions carry ready-to-apply FHIR; links can hand off to a SMART app for anything richer than a card. Latency is product-critical: the clinician is mid-click — slow services get disabled.

Designing decision support people don't hate

Alert fatigue is the graveyard of CDS. The discipline: fire on the narrowest hook that works, say one thing per card, make the right action one click, measure override rates, and retire noisy rules. An AI-generated risk score follows the same rules — and in this platform's framing, a card must cite its grounding the same way Vaidya does.

Why this completes the path

You can now read the whole modern interop stack in one breath: v2 feeds the plumbing, FHIR resources + national profiles structure the data, SMART authorises apps, CDS Hooks injects intelligence into the moment of care. That stack is exactly what the Interoperability labs will let you build against — synthetic patients, real standards.