Currently, the most commonly utilized scoring systems are the APACHE (acute physiology and chronic health evaluation) system and the SAPS (simplified acute physiology score) system. These systems were designed to predict outcomes in critical illness and use common variables that include age; vital signs; assessments of respiratory, renal, and neurologic function; and an evaluation of chronic medical illnesses. The APACHE II system is the most commonly used SOI scoring system in Noh America. Age, type of ICU admission (after elective surgery vs. nonsurgical or after emergency surgery), a chronic health problem score, and 12 physiologic variables (the most severely abnormal of each in the first 24 h of ICU admission) are used to derive a score. The predicted hospital moality is derived from a formula that takes into account the APACHE II score, the need for emergency surgery, and a weighted, disease-specific diagnostic category. ref:harrison&;s principles of internal medicine,ed 18,pg no 2196