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.