###HUMAN: give the number of patients whose drug code is phen10i and lab test category is blood gas., ###ASSISTANT: SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic INNER JOIN prescriptions ON demographic.hadm_id = prescriptions.hadm_id INNER JOIN lab ON demographic.hadm_id = lab.hadm_id WHERE prescriptions.formulary_drug_cd = "PHEN10I" AND lab."CATEGORY" = "Blood Gas"