Risk Factors for Post-Operative Multi-Drug–Resistant Organism Bacterial Infection in Patients With Stanford Acute Type A Aortic Dissection

Patients

Our inclusion criteria were as follows: patients diagnosed with ATAAD who underwent thoracotomy from January 2011 to June 2021. Our exclusion criteria were as follows: patients who did not undergo surgical treatment or only underwent endovascular exclusion; patients with Stanford type B aortic dissection; patients who died or were discharged automatically within 48 hours after surgery; and patients with incomplete data.

Data collection

The study subjects included 82 patients. They were subdivided into the MDRO group (31 cases) and the non-MDRO (51 cases) group according to whether they had acquired MDR bacterial infection based on the diagnostic criteria of MDR bacterial infection.

Six pre-operative factors were collected, including age, gender, hospital stay, clinical diagnosis, time from onset to admission, and past medical history. Three intra-operative factors were collected, including surgical duration, intra-operative bleeding volume, and intra-operative urine volume. Twenty-six post-operative indicators, including aspartate aminotransferase/alanine aminotransferase (AST/ALT), ALT, alkaline phosphatase (ALP), γ-glutamyl transferase (GGT), creatinine, total protein, albumin, methylprednisolone, imipenem and cilastatin, third-generation cephalosporin use, tigecycline, vancomycin, olanzapine, the total days of antibiotic exposure, ventilator use duration, sputum suction times, ordinary frozen plasma dosage, leukocyte-depleted platelets dosage, leukocyte-depleted red blood cell suspension dosage, cryoprecipitate coagulation factor dosage, fresh frozen plasma dosage, extracorporeal circulation duration, endotracheal intubation duration, endotracheal intubation times, blood purification, and antibiotic species of exposure were collected. The Ethics Committee of The Fourth Affiliated Hospital of Harbin Medical University approved the retrospective study.

Multi-drug–resistant organism definition

The definition of MDR bacteria refers to bacteria resistant to three or more classes of antibiotic agents commonly used in clinical practice at the same time, including cephalosporins, penicillins, quinolones, aminoglycosides, β-lactams, etc. Refer to the diagnostic criteria for nosocomial infections issued by the Ministry of Health of the People's Republic of China in 2001. The sputum, drainage fluid, urine, bronchoalveolar lavage fluid, blood, secretions, and other specimens of post-operative patients are sent to the pathogenic bacteria culture plus drug susceptibility test. When MDR bacterial strains are cultured, the patient can be diagnosed with MDR bacterial infection.

Statistical analyses

The measurement data were expressed as the mean ± standard deviation, and χ ² tests were used for comparisons between groups if the conditions met χ ² tests; otherwise, Fisher's exact probabilistic approach was used. The occurrence of post-operative MDR in the patients with ATAAD was regarded as a dependent variable (0 = MDRO; 1 = non-MDRO). Variables with a single factor <0.05 were included in the binary logistic regression analysis model. To avoid collinearity between variables, stepwise regression was used to filter variants. Statistical significance was defined as p < 0.05. All statistical analyses were performed using SAS 9.4 (SAS Institute, College Station, TX) international standard statistical programming software.

Risk factor analysis

There were no differences in age, gender, clinical outcomes, hospital stay, or past medical history between the two groups (all p > 0.05). However, there was a difference in the length of hospital stay (p < 0.05) because patients who developed MDR bacterial infections required more extended treatment and incurred higher medical costs (Table 1). No differences were found between the two groups regarding their surgical duration, surgical modality, intra-operative bleeding volume, and intra-operative urine volume (all p > 0.05). This result suggested that these intra-operative factors had a negligible effect on MDR bacterial infections (Table 2).

Among post-operative factors, there was no evidence for a statistically significant difference in hepatic insufficiency, total protein, methylprednisolone, imipenem and cilastatin, olanzapine, extracorporeal circulation duration, endotracheal intubation duration, or endotracheal intubation times (all p > 0.05). Other post-operative factors, including creatinine, albumin, utilization of third-generation cephalosporins, linezolid or vancomycin, tigecycline, antibiotic species of exposure, ventilator use duration, sputum suction times, ordinary frozen plasma dosage, leukocyte-depleted platelet dosage, leukocyte-depleted red blood cell suspension dosage, cryoprecipitate coagulation factor dosage, fresh frozen plasma dosage, application of blood purification, and the total antibiotic days of exposure had differences between the two groups (all p < 0.05; Table 3).

To identify the independent risk factors for MDRO infection further, a logistic analysis was performed. The multivariable analysis revealed that the utilization of third-generation cephalosporins (odds ratio [OR], 2.32; 95% confidence interval [CI], 1.01–5.33; p = 0.0478), antibiotic species of exposure (OR, 5.76; 95% CI, 1.45–22.83; p = 0.0128), leukocyte-depleted red blood cell suspension dosage (OR, 12.43; 95% CI, 2.71–57.07; p = 0.0012), and fresh frozen plasma dosage (OR, 5.05; 95% CI, 1.18–21.56; p = 0.0286) were independent risk factors for post-operative MDR bacterial infection (Table 4).

Multi-drug–resistant pathogen infection

In total, we detected 151 bacterial pathogens in 82 patients. The micro-organisms are summarized in Table 5. We found that gram-negative isolates (72.9%) accounted for the major proportion of bacterial pathogens in patients with ATAAD. Acinetobacter baumannii (45.7%) and Streptococcus pneumoniae species (7.9%) were mainly identified, followed by Pseudomonas aeruginosa (5.3%). A total of 134 cases of MDR pathogens were detected, of which 95 (70.9%) were gram-negative bacteria and 39 (29.1%) were gram-positive bacteria. The top two MDR pathogens were Acinetobacter baumannii (n = 69) and Streptococcus pneumoniae (n = 12). A total of 134 MDR pathogens were derived from six biologic samples, 56 from sputum, 15 from drainage, 10 from percutaneous ascites, 37 from blood specimens, 12 from catheter terminals, and four from secretions.