first-icu-stay

First ICU Stay Selection

Identifies first ICU stays and hospital admissions for cohort construction. Critical for avoiding correlated observations and inflated sample sizes from readmissions.

When to Use This Skill

• Creating research cohorts with independent observations
• Excluding readmissions that may have different characteristics
• Selecting incident (first-time) ICU patients
• Matching cohorts by admission characteristics

Pre-computed Table

SELECT
    subject_id,
    hadm_id,
    stay_id,
    -- Demographics
    gender,
    dod,  -- Date of death (if applicable)
    -- Hospital admission
    admittime,
    dischtime,
    los_hospital,  -- Hospital length of stay (days)
    admission_age,
    race,
    hospital_expire_flag,
    hospstay_seq,       -- Hospital admission sequence number
    first_hosp_stay,    -- TRUE if first hospitalization
    -- ICU stay
    icu_intime,
    icu_outtime,
    los_icu,            -- ICU length of stay (days)
    icustay_seq,        -- ICU stay sequence within hospitalization
    first_icu_stay      -- TRUE if first ICU stay of this hospitalization
FROM mimiciv_derived.icustay_detail;

Key Columns Explained

Hospital-Level

• hospstay_seq: Order of hospital admission for this patient (1 = first ever)
• first_hosp_stay: TRUE if this is the patient's first hospital admission

ICU-Level (Within Hospitalization)

• icustay_seq: Order of ICU stays within this hospitalization (1 = first ICU stay)
• first_icu_stay: TRUE if this is the first ICU stay of the current hospitalization

Age Calculation

Age is calculated as:

anchor_age + (YEAR(admittime) - anchor_year)

Important: MIMIC-IV shifts ages for patients > 89 years old at any admission. These patients have anchor_age = 91 and ages are not exact.

Common Cohort Selection Patterns

First ICU Stay Only (Most Common)

SELECT *
FROM mimiciv_derived.icustay_detail
WHERE first_icu_stay = TRUE;

First-Ever ICU Stay (Strictest)

SELECT *
FROM mimiciv_derived.icustay_detail
WHERE first_hosp_stay = TRUE
    AND first_icu_stay = TRUE;