Discussion
ATAAD progresses rapidly, and the surgical procedure used to treat the condition is complex and difficult to perform. Therefore, postoperative lung injury after ATAAD repair is not rare. Studies have shown that the incidence of severe ALI after surgery is 15.9–36.6%3, 5 , which is in line with our results. In this study, a prediction model for severe ALI after ATAAD was successfully established, and its effectiveness was evaluated. Finally, a nomogram was constructed. Since all preoperative data used in this study were findings that were determined upon admission to the emergency room, our prediction model may potentially better facilitate the identification of patients at high risk of postoperative severe ALI than those that have been described previously.6 This will facilitate the early diagnosis of postoperative severe ALI, and allow clinicians to provide timely treatment.
In previous studies, different methods were used to designate postoperative ALI and postoperative non-ALI groups. Most studies distinguished patients based on OI values > or ≤ 200 mmHg at 24 h or 48 h post-surgery.2, 7 Some patients did not develop lung injury immediately after surgery. Further, the incidence of mild and moderate ALI after surgery was close to 50%, and there was no significant difference between mild, moderate, and non-ALI patients regarding prognosis. Contrastingly, mortality and postoperative complication rates of patients with and without severe ALI differed.8, 9 Therefore, in this study, groups were designated based on at least one occurrence of OI ≤ 100 mmHg in arterial blood gas analysis within a 72-h period post-surgery, and we were able to show that the model obtained using this grouping method showed good calibration and discrimination.
The mechanism by which ALI forms after ATAAD has not been completely elucidated; however, it is generally believed that inflammation plays an important role in the process. Some inflammatory factors such as C-reactive protein (CRP), interleukin-6 (IL-6), and white blood cell count have been confirmed to be related to ALI after ATAAD.10, 11 However, the role of neutrophils, which are key contributors to acute inflammatory responses that are associated with adverse outcomes in various cardiovascular diseases,12, 13 remain unclear. In this study, CRP and IL-6 levels were not statistically analyzed due to their high missing rates. However, we found that a NEUT level of ≥ 0.824 was a risk factor for severe ALI after ATTAD and incorporated the parameter into the model after multivariate analysis. There have been many studies on the influence of CPB duration on the occurrence of adverse events after aortic dissection surgery.14 In our study, patients with a CPB duration of ≥ 257.5 min were more likely to suffer severe ALI after surgery than those with a CBP duration of < 257.5. Decreased hemoglobin levels have been associated with poor prognosis in a variety of cardiovascular diseases.15-17 However, interestingly, hemoglobin levels of ≤ 139.5 g/L were determined to be associated with a reduction in postoperative severe ALI risk in this study.
TTE is widely used to evaluate patients with ATAAD as it is non-invasive, is a convenient bedside operation, and has high sensitivity and specificity in the diagnosis of ATTAD18 . Compared with previous studies,6, 19 this study innovatively assessed and evaluated the influence of preoperative echocardiographic data of patients. After analysis, it was concluded that an LA diameter ≥ 35.5 mm and LVPWT ≥ 10.5 mm were independent risk factors for severe ALI after surgery (OR: 2.384, 95% CI: 1.167–5.763, P = 0.019). However, elucidation of the mechanism by which LA diameter and LVPWT contribute to ALI require further studies.
In our study, the length of ICU stay and duration of mechanical ventilation were significantly higher than those reported previously. We believe that as an authoritative cardiovascular center in the southern region, the preoperative condition of ATAAD patients admitted to our hospital tends to be severe, and in addition to ALI, a relatively high proportion of patients experience complications that contribute to difficulties associated with removal of tracheal intubation postoperatively, such as low cardiac output, stroke, and delirium. For such patients, we time tracheal intubation removal conservatively. Therefore, the average length of ICU stay and the duration of mechanical ventilation were longer in this study compared to those of previous studies.
This study has several limitations. First, it was a single-center, retrospective study, which may have led to a selection bias. Second, the end point assessed was the occurrence of severe ALI within the 72-h period that followed surgery, but the status of patients with severe ALI after discharge was not followed-up. Additional studies are needed to explore the impact of severe ALI after ATAAD on the long-term patient survival.