Administration of Combined Solutions of Glucose-Insulin-Potassium (Gik) Versus Glucose and Insulin in Separate Solutions (Giss) in Diabetic Patients Submitted to Cardiac Surgery [Administracao de Glicose-Insulina-Potassio (Gik) Em Solucoes Combinadas Versus Glicose e Insulina Em Sistemas Separados (Giss), Em Doentes Diabeticos Submetidos a Cirurgia Cardiaca]