This study intends to strengthen the discussion on the risk factors of RFS in critically ill patients, and construct an RFS risk prediction model which is easy for clinical medical staff to use and has a high sensitivity and specificity; In order to help medical staff to identify the high-risk groups of RFS in critically ill patients efficiently and accurately, and take targeted care and treatment for patients, so as to reduce the adverse consequences of RFS on critically ill patients.

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.

Modeling queue: Relevant information of 433 patients who received enteral nutrition from January 2018 to July 2020 in ICU of a tertiary hospital in Zhejiang .

Authentication queue: Relevant information of 120 patients who received enteral nutrition from August 2020 to October 2020 in ICU of four tertiary hospitals in Zhejiang .