Acute Stanford type A aortic dissection (ATAAD) is a fatal disease, and rapid and effective identification of its postoperative prognostic indicators is of great significance for stratifying patient prognosis. Serum chloride (Cl^-) is an important anion in the body associating with the occurrence and development of many diseases, but the relationship between serum Cl^- and ATAAD is not completely clear.

To investigate the relationship of admission serum Cl^- level with postoperative 30-day all-cause mortality and admission serum sodium (Na⁺) in patients with ATAAD.

A retrospective cohort design was adopted. Two hundred and six consecutive ATAAD patients who underwent Sun's procedure from February 2016 to December 2019 in the Fourth Hospital of Hebei Medical University were selected. All-cause death and adverse events within postoperative 30 days of patients were followed up. The clinical baseline, laboratory and intraoperative data and postoperative 30-day prognosis were compared between tertile groups of admission serum Cl^-〔T1≤102 mmol/L (n=69), 102<T2≤106 mmol/L (n=70), T3>106 mmol/L (n=67) 〕. ROC curve analysis was used to measure the performance of admission serum Cl^- and Na⁺ in predicting all-cause mortality in ATAAD, in which the area under the ROC curve (AUC), the Youden index, sensitivity, specificity, and optimal cut-off value were calculated. Multivariate Logistic regression model was used to evaluate the association between admission serum Cl^- and postoperative 30-day all-cause mortality. For assessing the relationship between admission serum Cl^- and Na⁺, postoperative 30-day all-cause mortality and cumulative survival rate were compared between ATAAD patients in four groups divided by the optimal cut-off value of admission serum Cl^- (107 mmol/L) and Na⁺ (139 mmol/L): high Cl^- and high Na⁺ (Cl^->107 mmol/L+Na⁺>139 mmol/L, n=35), high Cl^- and low Na⁺ (Cl^->107 mmol/L+Na⁺≤139 mmol/L, n=21), low Cl^- and high Na⁺ (Cl^-≤107 mmol/L+Na⁺>139 mmol/L, n=41), low Cl^- and low Na⁺ (Cl^-≤ 107 mmol/L+Na⁺≤ 139 mmol/L, n=109). The cumulative survival curves in different Cl^- groups or Cl^- and Na⁺ groups were presented as Kaplan-Meier curves and compared by Log-rank test. Pearson correlation analysis was used to explore the correlation between serum Cl^- and Na⁺. Then their relationship was further analyzed by age (≥ 50 and <50 years), sex (male and female), prevalence of hypertension, smoking and drinking, and Na⁺>139 mmol/L (Na⁺>139 mmol/L and ≤139 mmol/L), and the interaction between serum Cl^- and age, sex, hypertension, smoking and drinking was examined using multiplicative interaction model.

The AUC of admission serum Cl^- for predicting postoperative 30-day all-cause mortality was 0.695 〔95%CI (0.595, 0.795), P<0.01〕, and the Youden index, sensitivity, specificity and optimal cut-off value were 0.331, 54.5%, 78.6% and 107 mmol/L, respectively. The AUC of admission serum Na⁺ for predicting postoperative 30-day all-cause mortality was 0.648〔95%CI (0.544, 0.752), P<0.01〕, and the Youden index, sensitivity, specificity and optimal cut-off value were 0.282, 60.6%, 67.6% and 139 mmol/L, respectively. Logistic regression analysis indicated that elevated admission serum Cl^-〔OR=1.168, 95%CI (1.058, 1.289), P=0.002〕, elevated admission serum Na⁺〔OR=1.098, 95%CI (1.012, 1.191), P=0.024〕and preoperative hypoperfusion〔OR=5.837, 95%CI (2.395, 14.226), P<0.001〕 were independent risk factors for postoperative 30-day all-cause mortality. The risk of postoperative 30-day all-cause mortality in T3 group was 3.785 times higher than that in T1 group 〔95%CI (1.121, 12.782), P=0.032〕. And the risk of postoperative 30-day all-cause mortality in Cl^->107 mmol/L group was 3.367 times higher than that in Cl^- ≤ 107 mmol/L group 〔95%CI (1.469, 9.186), P=0.005〕. Kaplan-Meier survival analysis showed that the cumulative survival rate within 30 days after surgery was lower in T3 group than that of T1 group (χ²=8.711, P=0.003) or T2 group (χ²=9.079, P=0.011). Cl^->107 mmol/L group had a lower cumulative survival rate within 30 days after surgery than Cl^-≤107 mmol/L group (χ²=13.326, P<0.001). Pearson correlation analysis showed admission serum Cl^- and Na⁺ were weakly positively correlated (r=0.401, P<0.001). The postoperative 30-day all-cause mortality varied across groups with different admission serum Cl^- and Na⁺ levels (χ²=20.89, P<0.001), and it was lower in the high Cl^-and high Na⁺ group than that of the other three groups (χ²=16.398, P<0.001; χ²=13.719, P<0.001; χ²=9.225, P=0.002). Subgroup analysis found that there was no significant interaction between admission serum Cl^- and age, sex, hypertension, smoking or drinking (P_interaction> 0.05). But there was a certain interaction effect between admission serum Cl^- and Na⁺ (Na⁺>139 mmol/L, P_interaction =0.012) .

Admission serum Cl^- associates with admission serum Na⁺ level in ATAAD patients. And elevated admission serum Cl^- may be an independent risk factor for postoperative 30-day all-cause mortality.