Hubungan Antara Status Kalium dan Kejadian Sulit Weaning Ventilasi Mekanik pada Pasien Sakit Kritis di Intensive Care Unit Rumah Sakit Cipto Mangunkusumo dan Rumah Sakit Universitas Indonesia = Relationship between Potassium Status and the Event of Mechanical Ventilation Weaning Difficulty in Critically Ill Patients in the Intensive Care Unit Cipto Mangunkusumo Hospital and University of Indonesia Hospital