The present study carried out on twenty mechanically ventilated critically ill patients admitted to the department of critical care medicine, Cairo University. The patients were classified into two groups, group 1 included 10 patients (6 males and 4 females) with mean age of (68.4+6.57) with respiratory failure type II and group 2 included 10 patients (7 males and 3 females) with mean age of (62.7+7.96) with sepsis. All patients were subjected to clinical examination, plain chest X-ray, twelve leads electrocardiogram, central venous line, arterial cannulation, routine lab investigations (CBC, Na, K, Urea, Creatinine, RBS, Bilirubin and Albumin) and APACHE III scoring system was also done for all patients of both groups on daily basis during the period of mechanical ventilation.