I am using LLBLGen 5.5 and the latest driver for NPGSql.

await adapter.ExecuteSQLAsync(@"
DO $$
BEGIN
    SELECT * FROM institute_view WHERE institute_id=@instituteid AND day=@day AND month=@month AND year=@year;
END
$$
", new{
        instituteid = notification.Id,
        day = notification.DateUTC.Day,
        month = notification.DateUTC.Month,
        year = notification.DateUTC.Year
        })

returns PostgresException: 42703: column "instituteid" does not exist.

If I remove the function declaration, it will work

await adapter.ExecuteSQLAsync(@"
    SELECT * FROM institute_view WHERE institute_id=@instituteid AND day=@day AND month=@month AND year=@year;
", new{
        instituteid = notification.Id,
        day = notification.DateUTC.Day,
        month = notification.DateUTC.Month,
        year = notification.DateUTC.Year
        })

It's seems like if the parameter name is not recognized as it's out of scope of the function. Any reason you would like to use an anonymous code block here (function)?