This study will be conducted in the Affiliated Hospital of Nantong University. Sixty colorectal cancer(CRC) patients are randomized into traditional ventilation strategy group (control group) and lung protective ventilation strategy group (experimental group), there were 30 cases in each group. The control group adopted conventional ventilation strategy; the experimental group used lung protective ventilation strategy. 4ml of central venous blood was extracted at 3 time points within 24h, and relevant experimental indexes were determined. Observe the effect of lung protective ventilation strategy on the microenvironment of tumor inflammation and related hematological indexes in patients undergoing colorectal cancer surgery. Follow-up frailty score and quality of recovery score at 1,3,6, and 12 months after surgery (QoR-15 score scale).

This study will be conducted in the Affiliated Hospital of Nantong University. Sixty CRC patients are randomized into traditional ventilation strategy group (control group) and lung protective ventilation strategy group (experimental group), there were 30 cases in each group. The control group adopted conventional ventilation strategies: tidal volume (VT)=10-12 ml/kg, respiratory rate ( f)=12 breaths / minute, positive end expiratory pressure（PEEP）=0 cmH₂O, fraction of inspired oxygen =0.5; the experimental group used lung protective ventilation strategies: tidal volume ( VT)=6-8 ml/kg, f=12 breaths / minute, positive end expiratory pressure (PEEP)=6-8 cmH₂O, fraction of inspired oxygen =0.5, mechanical ventilation every 30 minutes (continuous positive airway pressure 30 cmH₂O about 30 seconds). 4 ml of central venous blood was extracted at 3 time points within 24h, and relevant experimental indexes were determined. Observe the effect of lung protective ventilation strategy on the microenvironment of tumor inflammation and related hematological indexes NLDA, PDM, SII and PNI in patients undergoing colorectal cancer surgery. Follow-up frailty score and quality of recovery score at 1,3,6, and 12 months after surgery (QoR-15 score scale).

Inclusion Criteria:

1. pathologic diagnosis of Colorectal Cancer
2. American society of Aneshesiologists（ASA）physical status classification system Grade Ⅱ-Ⅲ;
3. From 51-70 years old with no gender restrictions
4. Normal cardiopulmonary function before operation
5. Body Mass Index:18-30

Exclusion Criteria:

1. Preoperative anemia (hemoglobin<10g/dl)
2. Patients with preoperative mechanical ventilation;
3. A history of pulmonary infection and pulmonary tuberculosis within 1 month before surgery;
4. Preoperative blood oxygen saturation (SpO₂) was less than 90% (SpO₂<90%), or the oxygen partial pressure (PaO₂) was less than 90% (PaO₂<60 mmHg), or PaO₂/fraction of inspired oxygen（FiO₂）ratio<300 mmHg, or arterial blood carbon dioxide partial pressure (PaCO₂) was greater than 45 mmHg (PaCO₂>45 mmHg);
5. Patients who take immunosuppressants, neoadjuvant chemotherapy and radiotherapy before surgery;
6. Preoperative abnormal coagulation function.