Sentence: To compare cardiopulmonary and sedative effects following administration of dexmedetomidine alone or with butorphanol , methadone , morphine or tramadol in healthy sheep .
Drug combination annotation:
[{'class': 'COMB', 'spans': ['dexmedetomidine', 'methadone'], 'is_context_needed': True}, {'class': 'COMB', 'spans': [0, 1], 'is_context_needed': True}, {'class': 'COMB', 'spans': [0, 3], 'is_context_needed': True}]