Thanks for the reply. I am not sure if this is what you mean but this is what I went with and it seems to be doing the trick..
Code:
CREATE OR REPLACE TRIGGER AXIUM."RMVBALTRG" 
BEFORE UPDATE OF
"LastPaymentAmount"
ON "PATIENT"
REFERENCING NEW AS NEW
FOR EACH ROW
DECLARE
v_bal NUMBER(10);
BEGIN
update  PTBAL_TMP set "Sum" = (Select sum("Sum" - :NEW."LastPaymentAmount" ) from ptbal_tmp where "Patient" = :NEW."Patient") where "Patient"= :NEW."Patient";
select "Sum" into v_bal from PTBAL_TMP where "Patient"=:NEW."Patient" ;
IF (v_bal <=0) and :NEW."Office1"='BAL' THEN
:New."Office1" := ' ';
elsif (v_bal <=0) and :NEW."Office2"='BAL' THEN
:New."Office2" := ' ';
elsif (v_bal <=0) and :NEW."Office3"='BAL' THEN
:New."Office3" := ' ';
elsif (v_bal <=0) and :NEW."Office4"='BAL' THEN
:New."Office4" := ' ';
elsif (v_bal <=0) and :NEW."Office5"='BAL' THEN
:New."Office5" := ' ';
END IF;
exception
  when others then
    null;
END;
/