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sql/durations/ventilation_durations.sql

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+-- THIS SCRIPT IS AUTOMATICALLY GENERATED. DO NOT EDIT IT DIRECTLY.
+DROP TABLE IF EXISTS ventilation_durations; CREATE TABLE ventilation_durations AS 
+-- This query extracts the duration of mechanical ventilation
+-- The main goal of the query is to aggregate sequential ventilator settings
+-- into single mechanical ventilation "events". The start and end time of these
+-- events can then be used for various purposes: calculating the total duration
+-- of mechanical ventilation, cross-checking values (e.g. PaO2:FiO2 on vent), etc
+
+-- The query's logic is roughly:
+--    1) The presence of a mechanical ventilation setting starts a new ventilation event
+--    2) Any instance of a setting in the next 8 hours continues the event
+--    3) Certain elements end the current ventilation event
+--        a) documented extubation ends the current ventilation
+--        b) initiation of non-invasive vent and/or oxygen ends the current vent
+
+-- See the ventilation_classification.sql query for step 1 of the above.
+-- This query has the logic for converting events into durations.
+with vd0 as
+(
+  select
+    icustay_id
+    -- this carries over the previous charttime which had a mechanical ventilation event
+    , case
+        when MechVent=1 then
+          LAG(CHARTTIME, 1) OVER (partition by icustay_id, MechVent order by charttime)
+        else null
+      end as charttime_lag
+    , charttime
+    , MechVent
+    , OxygenTherapy
+    , Extubated
+    , SelfExtubated
+  from ventilation_classification
+)
+, vd1 as
+(
+  select
+      icustay_id
+      , charttime_lag
+      , charttime
+      , MechVent
+      , OxygenTherapy
+      , Extubated
+      , SelfExtubated
+
+      -- if this is a mechanical ventilation event, we calculate the time since the last event
+      , case
+          -- if the current observation indicates mechanical ventilation is present
+          -- calculate the time since the last vent event
+          when MechVent=1 then
+            DATETIME_DIFF(CHARTTIME, charttime_lag, 'MINUTE')/60
+          else null
+        end as ventduration
+
+      , LAG(Extubated,1)
+      OVER
+      (
+      partition by icustay_id, case when MechVent=1 or Extubated=1 then 1 else 0 end
+      order by charttime
+      ) as ExtubatedLag
+
+      -- now we determine if the current mech vent event is a "new", i.e. they've just been intubated
+      , case
+        -- if there is an extubation flag, we mark any subsequent ventilation as a new ventilation event
+          --when Extubated = 1 then 0 -- extubation is *not* a new ventilation event, the *subsequent* row is
+          when
+            LAG(Extubated,1)
+            OVER
+            (
+            partition by icustay_id, case when MechVent=1 or Extubated=1 then 1 else 0 end
+            order by charttime
+            )
+            = 1 then 1
+          -- if patient has initiated oxygen therapy, and is not currently vented, start a newvent
+          when MechVent = 0 and OxygenTherapy = 1 then 1
+            -- if there is less than 8 hours between vent settings, we do not treat this as a new ventilation event
+          when CHARTTIME > DATETIME_ADD(charttime_lag, INTERVAL '8' HOUR)
+            then 1
+        else 0
+        end as newvent
+  -- use the staging table with only vent settings from chart events
+  FROM vd0 ventsettings
+)
+, vd2 as
+(
+  select vd1.*
+  -- create a cumulative sum of the instances of new ventilation
+  -- this results in a monotonic integer assigned to each instance of ventilation
+  , case when MechVent=1 or Extubated = 1 then
+      SUM( newvent )
+      OVER ( partition by icustay_id order by charttime )
+    else null end
+    as ventnum
+  --- now we convert CHARTTIME of ventilator settings into durations
+  from vd1
+)
+-- create the durations for each mechanical ventilation instance
+select icustay_id
+  -- regenerate ventnum so it's sequential
+  , ROW_NUMBER() over (partition by icustay_id order by ventnum) as ventnum
+  , min(charttime) as starttime
+  , max(charttime) as endtime
+  , DATETIME_DIFF(max(charttime), min(charttime), 'MINUTE')/60 AS duration_hours
+from vd2
+group by icustay_id, vd2.ventnum
+having min(charttime) != max(charttime)
+-- patient had to be mechanically ventilated at least once
+-- i.e. max(mechvent) should be 1
+-- this excludes a frequent situation of NIV/oxygen before intub
+-- in these cases, ventnum=0 and max(mechvent)=0, so they are ignored
+and max(mechvent) = 1
+order by icustay_id, ventnum