Perbandingan pemberian norepinefrin dini dengan terapi standar pada tatalaksana pasien yang menjalani Bedah Abdomen Mayor : Kajian Terhadap durasi hipotensi, laktat, mixed vein dan profil hemodinamik = The Comparison of early administration of norepinephrine with standard therapy in major abdominal surgery: hypotension time, Lactate Levels, Mixed Vein and hemodynamic profile study (Index contractility, thoracic fluid content, stroke volume variation