horowitz.py

def calculate_horowitz(df):
    """calculates the Horowitz index, defined as PaO2/FIO2.
    300-450: all fine (depending on age)
    200-300: moderately severe lung damage
    <200: severe lung damage"""
    paO2 = df["paO2"]
    if len(paO2) == 0:
        return [np.nan] * len(df)
    fiO2 = df["FiO2"]
    if len(fiO2) == 0:
        return [np.nan] * len(df)
    # Fi02s have to be between 21-100%. Everything else is unphysiological (maybe 02 flow in litres)
    horowitz = []
    last_fiO2 = None
    last_paO2 = None
    for i in paO2.index:
        if not np.isnan(fiO2.loc[i]):
            last_fiO2 = i
        if not np.isnan(paO2.loc[i]):
            last_paO2 = i
        if last_paO2 is not None and last_fiO2 is not None:
            horowitz.append(paO2.loc[last_paO2]*100/fiO2.loc[last_fiO2])
        else:
            horowitz.append(np.NaN)
    if len(horowitz) <= 0:
        raise Exception()
    horowitz = horowitz if len(horowitz)>0 else [pd.NaN]*df.shape[0]
    return horowitz