The primary change in aging lung tissue among older people is atrophy, leading to a significant decline in ventilatory function. Intraoperative mechanical ventilation further decreases lung compliance and ventilatory function in elderly patients, making them more susceptible to respiratory dysfunction and postoperative pulmonary complications, which severely affects patient safety and postoperative recovery. Dexmedetomidine is a highly selective α2-adrenergic receptor agonist, and several studies have found that intravenous infusion of dexmedetomidine exerted lung protective effects during single-lung ventilation thoracic surgery. However, one study found that continuous intravenous dexmedetomidine infusion during low-temperature cardiac arrest aortic surgery did not improve perioperative respiratory mechanics and oxygenation. Therefore, this project aims to investigate the lung protective effects of continuous intravenous infusion of dexmedetomidine during laparoscopic surgery for elderly patients with rectal or sigmoid colon cancer.