cognition state evaluation by n-back in mustard gas casualties: dexmedetomine versus remifentanil in cataract surgery

background: sulfur mustard (sm) is an alkylating agent that has been used as a chemical warfare gas during world war ii and by iraqi army in the iran-iraq conflict between 1983 and 1988. sm can cause serious organ damages especially ocular, neurologic, coetaneous, bone marrow and pulmonary complications. on the other hand dexmedetomidine is a α2 agonist with sedative and analgesic effect with a short duration half-life. considering these benefits, usage of dexmedetomidine would be a good choice in ophthalmic outpatient’s surgeries to keep the cognition state in an acceptable condition comparing with other available drugs especially in patients with concurrent chemical burn injury. methods: after informed consent, patients with inclusion criteria were randomly divided in to two groups: dexmedetomidine (group d, n=50) and remifentanil (group r, n=50). cardiovascular signs, mini mental state examination (mmse) score were recorded as baseline. patients received respectively dexmedetomidine by infusion with a loading dose of 0.5µg/kg (during 10 minutes) in group d. the maintenance dose of 0.2µg/kg/hr was then started. loading dose of remifentanil was given by 0.1µg/kg (during 10 minutes); 5 minutes before local anesthesia in group r and maintenance dose of 0.05µg/kg/min was then started. in post anesthesia care unit (pacu) after 120 minutes of stopping drug infusions n-back and mmse tests were performed. results: the mmse score had no statistically difference between two groups before surgery (in subgroup age>=65 p= 0.5, and in subgroup age<65 p= 0.6) but in the pacu the score diverged statistically between two subgroups in age>=65 and age<65 years old respectively (in subgroup age>=65 p<0.0001, and in subgroup age<65 p= 0.03). the results of n-back test showed a more precision and rapidity in working memory in group d. (p<0.001 and p=0.002 respectively). conclusion: the result of n-back and mmse revealed that the cognition state improves better in patients receiving dexmedetomidine comparing with those of remifentanil. dexmedetomidine is safe for protecting the cognition state especially in patients with borderline respiratory reserve due to chemical burn injury.