Pre-operative renal impairment increases the risk of clinically important deterioration of renal function after surgery. Studies of changes in creatinine after sevoflurane have included only a small number of patients with pre-existing renal impairment 10. None of these small studies has shown that sevoflurane aggravates pre-existing renal impairment more than other anaesthetic drugs. This includes a subgroup analysis in our Cardiac Anaesthesia study. No study, however, has examined creatinine changes in those with pre-existing renal impairment and with low fresh gas flow. This would expose those with increased risk of further renal impairment to greater doses of Compound-A. From other research and our own, we believe that sevoflurane would not affect renal function more than isoflurane in patients with preexisting renal impairment receiving low flow anesthesia.