Complex sentence: Mortality rates approach 10% to 40% even with treatment; however, a study determined that with prompt treatment and good preoperative stabilization of the patient, mortality is significantly lessened to 10% overall (in a referral setting).
Split into simpler sentences: Mortality rates approach 10% to 40% even with treatment. A study determined that with prompt treatment and good preoperative stabilization of the patient, mortality is significantly lessened to 10% overall (in a referral setting).