Pengaruh Pemberian Lactobacillus Acidophilus Terhadap Gastric Residual Volume pada Pasien Pasca Operatif Pembedahan Laparotomi Digestif Bawah di Unit Perawatan Intensif = Effect of Lactobacillus Acidophilus Administration on Gastric Residual Volume in Postoperative Lower Digestive Laparotomy Surgery Patients in the Intensive Care Unit