Dorsal Lung Ventilation Drop During Surgery Flags Postoperative Pulmonary Complications

A greater reduction in dorsal lung ventilation during surgery is independently associated with postoperative pulmonary complications in patients undergoing laparoscopic colorectal cancer surgery, according to a prospective cohort study conducted by the team of Professor Xiangming Fang from Zhejiang University School of Medicine, China, and Professor Guohao Xie from the First Affiliated Hospital, Zhejiang University School of Medicine. The findings, made available online on August 14, 2026, and published in the Chinese Medical Journal on the same date, used electrical impedance tomography to track regional ventilation in real time throughout the operative course. The researchers report that patients whose dorsal ventilation fell by 14.5 percent or more from baseline to the end of surgery experienced markedly higher complication rates and longer hospital stays than those with smaller reductions.

Postoperative pulmonary complications are prevalent adverse events following major surgery, closely associated with prolonged hospital stay and elevated perioperative morbidity and mortality. Early identification of high-risk patients and precise, effective pulmonary protection remain key challenges in perioperative medicine. The new study addresses that gap by linking a continuously measurable physiological variable to clinical outcomes measured after surgery.

The physiological backdrop is well characterized. Mechanical ventilation during general anesthesia alters the physiological distribution of pulmonary ventilation. Compared with spontaneous breathing in the awake state, ventilation during anesthesia is redistributed toward the ventral regions of the lung, accompanied by a reduction in ventilation within the dorsal dependent regions. Electrical impedance tomography monitoring has shown that, following endotracheal intubation, tidal ventilation distribution shifts markedly toward the ventral lung regions, whereas aeration within the dorsal dependent lung regions decreases substantially. What remained unclear before this study was whether this intraoperative heterogeneity in regional lung ventilation is actually associated with the development of postoperative pulmonary complications in surgical patients.

The ratio of dorsal ventilation, abbreviated RDV, was measured at four time points: spontaneous breathing in the awake state (T0), after anesthesia induction and endotracheal intubation (T1), after body position change and pneumoperitoneum (T2), and at the end of surgery (T3). The magnitude of RDV reduction relative to the awake baseline at T0 was then calculated for each patient, yielding an individualized index of how much dependent lung tissue lost its share of ventilation over the course of the operation.

The study was conducted in patients undergoing elective laparoscopic colorectal cancer surgery. Data revealed that general anesthesia caused significant ventilation redistribution, with markedly reduced dorsal aeration, which was further aggravated by body position change and pneumoperitoneum, according to Professor Xie. In other words, the ventilation shift is not a single event at intubation but a progressive process that accumulates across the phases of the operation, and EIT made each step quantifiable in real time.

The outcome association was striking. Patients with a reduction of dorsal lung ventilation at the end of surgery, RDVT0–T3, of 14.5 percent or greater had a 54.8 percent incidence of postoperative pulmonary complications within seven days after the operation, compared with only 18.3 percent among patients whose RDVT0–T3 remained below that threshold. These patients also presented a lower PaO2/FiO2 ratio at the end of surgery, an indicator of impaired oxygenation, and experienced a longer hospital stay. The pattern held across the cohort, suggesting that the degree of dorsal ventilation loss tracks with both immediate respiratory physiology and downstream recovery measures.

Crucially, the association survived statistical adjustment. Multivariable logistic regression confirmed that a high reduction of RDVT0–T3, at or above 14.5 percent, was an independent risk factor for postoperative pulmonary complications, with an adjusted odds ratio of 11.28 and a 95 percent confidence interval of 2.58 to 49.25. An odds ratio of this magnitude indicates that, after accounting for other measured risk factors in the model, patients crossing the 14.5 percent threshold faced roughly eleven-fold higher odds of developing complications within the first postoperative week. The wide confidence interval reflects the modest sample size of 91 patients, so the point estimate should be interpreted with appropriate caution even though the association itself remained robust.

From a clinical standpoint, the study establishes RDVT0–T3 of 14.5 percent or greater as a critical early warning threshold, according to Professor Xie, who notes that it demonstrates the ability of non-invasive EIT technology to achieve real-time visualization and quantitative assessment of intraoperative lung ventilation. This provides new evidence for early risk stratification and precise perioperative lung management in abdominal surgery. Because the measurement is continuous and non-invasive, it can in principle be monitored throughout an operation rather than assessed only before or after, giving the anesthesia team a dynamic signal of how regional ventilation is evolving as positioning and pneumoperitoneum are applied.

Professor Fang emphasizes the therapeutic implication: the findings will support personalized lung-protective ventilation strategies, such as optimized positive end-expiratory pressure and recruitment maneuvers, to reduce dorsal atelectasis and improve postoperative outcomes, thereby enhancing postoperative recovery and shortening hospital stays, with significant clinical translational value. It is important to note what the study does and does not show. As a prospective observational cohort, it demonstrates an association between intraoperative ventilation redistribution and complications; it does not prove that intervening on RDV would prevent them. Testing whether EIT-guided adjustments to ventilation actually reduce complication rates would require a randomized interventional trial. Nevertheless, the work supplies a concrete, quantified threshold that future trials and bedside protocols can build on.

Subject of Research: Intraoperative dorsal lung ventilation reduction measured by electrical impedance tomography and its association with postoperative pulmonary complications in laparoscopic colorectal cancer surgery.

Article Title: Intraoperative dorsal lung ventilation reduction and postoperative pulmonary complications

Article References: Intraoperative dorsal lung ventilation reduction and postoperative pulmonary complications. Original publication (Bibliographic details unavailable.)

Image Credits: AI Generated

DOI: Not provided

Keywords: electrical impedance tomography, postoperative pulmonary complications, laparoscopic colorectal cancer surgery, lung-protective ventilation, dorsal ventilation ratio, general anesthesia, pneumoperitoneum, prospective cohort study, perioperative medicine, mechanical ventilation, oxygenation, risk stratification