feature: Sepsis Early Warning Engine
This commit is contained in:
voltsrage
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using System.Text.Json;
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using Microsoft.EntityFrameworkCore;
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using StackExchange.Redis;
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public class SirsDetector
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{
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// 30 minutes in seconds. This is a clinical parameter: SIRS criteria evaluated
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// outside a 30-minute window are clinically stale. The TTL enforces the window
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// automatically — no cleanup job required.
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private const int SirsTtlSeconds = 1800;
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private readonly IConnectionMultiplexer _redis;
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private readonly IServiceProvider _services;
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private readonly ILogger<SirsDetector> _logger;
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public SirsDetector(
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IConnectionMultiplexer redis,
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IServiceProvider services,
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ILogger<SirsDetector> logger)
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{
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_redis = redis;
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_services = services;
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_logger = logger;
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}
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public async Task<SirsResult> ProcessObservationAsync(
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Guid encounterId,
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Guid patientId,
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string observationCode,
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decimal value,
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CancellationToken ct = default)
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{
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// Fast exit for non-SIRS codes. The sepsis engine subscribes to the full
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// observation.recorded stream — the majority of messages (SpO2, potassium, glucose)
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// are not SIRS-relevant and are discarded here without touching Redis or PostgreSQL.
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if (!SirsEvaluator.SirsCodes.Contains(observationCode))
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return SirsResult.NotSirsCode;
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var cache = _redis.GetDatabase();
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var key = SirsEvaluator.CriterionKey(encounterId, observationCode);
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if (SirsEvaluator.MeetsCriterion(observationCode, value))
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{
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// SET with EX refreshes the TTL on every qualifying observation.
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// A patient with tachycardia posting a reading every 60 seconds will keep
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// sirs:{id}:HEART_RATE alive for 30 minutes after the LAST qualifying reading,
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// not the first — the window slides forward with each new abnormal value.
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await cache.StringSetAsync(key, "1", TimeSpan.FromSeconds(SirsTtlSeconds));
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_logger.LogDebug("SIRS criterion set: {Key} (TTL={Ttl}s)", key, SirsTtlSeconds);
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}
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else
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{
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// Criterion no longer met — remove the key immediately rather than waiting
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// for TTL expiry. If a patient's temperature normalises at 37.0 °C, the
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// fever criterion must stop contributing to the count right away.
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// Without this DEL, a recovered criterion could persist for up to 30 minutes
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// and falsely sustain a SEPSIS_WARNING count.
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await cache.KeyDeleteAsync(key);
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_logger.LogDebug("SIRS criterion cleared: {Key}", key);
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}
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// Count active criteria in one MGET round-trip.
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// MGET is O(N) where N = number of keys requested (4 here, always).
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// Never use KEYS pattern for this check: KEYS scans the entire keyspace
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// and blocks all other Redis operations until the scan completes.
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var allKeys = SirsEvaluator.AllCriterionKeys(encounterId);
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var values = await cache.StringGetAsync(allKeys);
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var activeCount = values.Count(v => v.HasValue);
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_logger.LogDebug(
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"SIRS state for encounter {Id}: {Active}/4 criteria active after {Code}={Value}",
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encounterId, activeCount, observationCode, value);
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if (activeCount < 2)
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return SirsResult.InsufficientCriteria(activeCount);
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// Two or more criteria are active — attempt to create the alert.
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var created = await TryCreateAlertAsync(encounterId, patientId, activeCount, ct);
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return created ? SirsResult.AlertCreated : SirsResult.AlertAlreadyOpen;
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}
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// Creates the SEPSIS_WARNING alert and its outbox event in one atomic transaction.
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// The INSERT WHERE NOT EXISTS pattern makes this safe under at-least-once delivery:
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// if the consumer crashes after the INSERT but before committing the Kafka offset,
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// the observation is reprocessed on restart. The second run hits the WHERE NOT EXISTS
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// subquery, finds the existing open alert, inserts 0 rows, and returns false — no
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// duplicate alert, no duplicate outbox event.
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private async Task<bool> TryCreateAlertAsync(
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Guid encounterId,
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Guid patientId,
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int activeCount,
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CancellationToken ct)
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{
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using var scope = _services.CreateScope();
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var db = scope.ServiceProvider.GetRequiredService<AppDbContext>();
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await using var tx = await db.Database.BeginTransactionAsync(ct);
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var alertId = Guid.NewGuid();
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var triggeredAt = DateTimeOffset.UtcNow;
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var details =
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$"SIRS criteria met: {activeCount} of 4 criteria active within the 30-minute window.";
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// One SQL round-trip: check + insert atomically.
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// status IN ('OPEN', 'ESCALATED') prevents re-creating an alert that has been
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// escalated but not yet resolved — the patient is still in danger.
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var affected = await db.Database.ExecuteSqlInterpolatedAsync($"""
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INSERT INTO clinical_alerts
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(id, encounter_id, patient_id, alert_type, severity, details, status, triggered_at)
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SELECT {alertId}, {encounterId}, {patientId},
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'SEPSIS_WARNING', 'CRITICAL', {details}, 'OPEN', {triggeredAt}
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WHERE NOT EXISTS (
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SELECT 1 FROM clinical_alerts
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WHERE encounter_id = {encounterId}
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AND alert_type = 'SEPSIS_WARNING'
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AND status IN ('OPEN', 'ESCALATED')
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)
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""", ct);
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if (affected == 0)
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{
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await tx.RollbackAsync(ct);
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_logger.LogDebug(
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"SEPSIS_WARNING already open for encounter {Id} — no new alert", encounterId);
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return false;
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}
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// Alert was created — write the outbox event in the same transaction.
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// The relay (Phase 3) will publish to alert.generated, which Phase 6's
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// notification worker reads to page the attending physician via RabbitMQ.
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db.OutboxEvents.Add(new OutboxEvent
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{
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Id = Guid.NewGuid(),
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Topic = "alert.generated",
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Payload = JsonSerializer.Serialize(new
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{
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alertId,
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encounterId,
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patientId,
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alertType = AlertType.SepsisWarning.ToDbString(),
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severity = "Critical",
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triggeredAt,
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partitionKey = encounterId.ToString()
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}),
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PartitionKey = encounterId.ToString(),
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CreatedAt = DateTimeOffset.UtcNow
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});
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await db.SaveChangesAsync(ct);
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await tx.CommitAsync(ct);
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_logger.LogWarning(
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"SEPSIS_WARNING alert {AlertId} created for encounter {EncounterId} " +
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"— {Active}/4 SIRS criteria active",
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alertId, encounterId, activeCount);
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return true;
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}
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}
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