MYSQL Audit Trail

Question

Hello I use the following way to use an audit trail:

First a user log into a database with the following procedure:

CREATE DEFINER=`root`@`%` PROCEDURE `oms_Insert_AuditTrailLogin`(
    IN `EmployeeRefID` BIGINT,
    IN `IPAdress` VARCHAR(50),
    IN `LoginTime` DATETIME
)
LANGUAGE SQL
NOT DETERMINISTIC
CONTAINS SQL
SQL SECURITY DEFINER
COMMENT ''
BEGIN
   SET @EmployeeID = EmployeeRefID;

    INSERT INTO omsdb.tbl_data_AuditTrailLogin
   (EmployeeRefID, IPAdress, LoginTime)
   VALUES
   (EmployeeRefID, IPAdress, LoginTime);

   SELECT Last_Insert_ID() AS ID;
END

I need the variable @EmployeeID to identify the user.

After update trigger:

...

INSERT INTO omsdb.tbl_data_AuditTrail 
(evType, Tablename, DatabaseName, PrimaryKey, UpdateDate, @EmployeeID) 
VALUES 
('UPDATE', 'tbl_data_bcrabl', 'molbiolabdb', @Pk, NOW(), @EmployeeID); 

SET @AuditTrailRefID = LAST_INSERT_ID(); 

IF NEW.bcrabl != OLD.bcrabl OR OLD.bcrabl IS NULL THEN INSERT INTO omsdb.tbl_data_AuditTrailData 
(AuditTrailRefID, FieldName, OldValue, NewValue) 
VALUES 
(@AuditTrailRefID, 'bcrabl', OLD.bcrabl, NEW.bcrabl); 
END IF; 
...

the after update trigger works fine but the @EmployeeID has no value - it's always "NULL" How could I create variables outside a trigger and use this information in the trigger to identify the user? I could not use the function USER() etc.

Thank you very much

Elmar