(1) Could I use the words "serious", "critical" and "severe" as synonyms in English?
(2) I put some terms in parenthesis. Will I make myself clear if I ommit them?
O paciente estava em estado grave, mas estável, respirando com ajuda de aparelhos:
(1) The patient was in critical condition but (it was) stable on life-support.
(2) The patient's conditions were serious / critical / severe but (he / she was) stable on artificial respiration.