Inclusion Criteria:  (1) Age ≥18 years old; (2) Patients with mechanical ventilation; (3) First admission to ICU； (4) The time of receiving enteral nutrition support in ICU was ≥ 3 days.  Exclusion Criteria:  (1)Ppregnant women or lactating patients;(2) Patients with incomplete information;(3) There are other risk factors leading to hypophosphatemia, such as continuous hemodialysis , hyperphosphatemia treatment,Parathyroid gland resection was performed within 3 months.