As one of the most common and serious complications after craniocerebral surgery, CNSIs seriously affects the follow-up treatment, prognosis and quality of life of patients. Under normal physiological conditions, the central nervous system is in an absolutely closed environment due to the protection of the scalp, skull, meninges, blood-brain barrier, blood-cerebrospinal fluid barrier, and cerebrospinal fluid-brain barrier. Therefore, the incidence of CNSIs is much lower than that of other systems that are connected with the external environment, such as respiratory and urinary system infections. However, neurosurgery often requires craniotomy, which destroys the protective effect of the above barrier to a certain extent, making the central nervous system communicate with the external environment, and pathogenic microorganisms from the outside can enter the brain, which increases the chance of CNSIs to a certain extent. Due to the existence of the blood-brain barrier, once CNSIs occurs, it is difficult for conventional antibiotics to penetrate the blood-brain barrier to achieve an effective blood drug concentration so as to kill pathogenic bacteria, which brings great difficulties to the clinical treatment of CNSIs. Some experts and scholars have proposed to treat CNSIs by intrathecal injection, but this method of drug administration requires frequent lumbar puncture or lumbar cisterna drainage. Frequent lumbar puncture and indwelling lumbar cisterna drainage may cause retrograde bacterial infection, which increases the incidence of CNSIs. According to previous relevant studies, the incidence of CNSIs after craniotomy is about 4.6%-10%[11], and the mortality rate can be as high as 15–30% once CNSIs occurs[12]. After the analysis of this study, it was concluded that the infection rate of secondary CNSIs after craniotomy in this group of cases was 9.38%, which was consistent with the results reported in previous literature.
CNSIs has a high disability and mortality rate. Once CNSIs occurs, it will seriously affect the prognosis and quality of life of patients. If the treatment is not timely or the emergence of multi-drug resistant bacteria will seriously endanger the life of patients. At present, the clinical diagnosis of CNSIs is mainly based on the clinical manifestations of patients combined with laboratory examination and imaging data to reach a conclusion. However, the clinical manifestations and laboratory infection indicators of early CNSIs are lack of specificity, and the early diagnosis of CNSIs is difficult. By studying the risk factors affecting the occurrence of CNSIs, the high-risk population can be intervened as soon as possible to prevent and control the occurrence of infection. Reviewing the literature at home and abroad in the past five years, it is found that there are dozens of influencing factors that may lead to CNSIs[13–17]. It mainly includes the patient's age, combined underlying diseases, operation time, indwelling drainage tube, drainage tube indwelling time, cerebrospinal fluid leakage, surgical approach and other factors. After analysis and discussion, the research group members determined 30 kinds of influencing factors of secondary CNSIs after neurosurgical craniocerebral surgery. Gender, alcohol consumption, GCS score, emergency operation, number of operation after admission, operation time, intraoperative blood loss, intraoperative use of microscope, intraoperative indwelling lumbar cisternal drainage tube, indwelling time of lumbar cisternal drainage tube, intraoperative indwelling epidural drainage tube, incision effusion, number of indwelling drainage tube, indwelling ventricular drainage tube, cerebrospinal fluid leakage, tracheal intubation, tracheotomy were obtained by univariate analysis There were statistically significant differences in albumin content between open surgery and postoperative surgery, and admission to ICU. Further multivariate Logistic regression analysis showed that gender, GCS score, operation time, intraoperative indwelling lumbar cisternal drainage tube, indwelling time of lumbar cisternal drainage tube, intraoperative indwelling epidural drainage tube, indwelling ventricular drainage tube, number of operations after admission and emergency operation were independent risk factors for CNSIs after neurosurgical craniocerebral surgery.
The effects of operation time, indwelling time of lumbar cisternal drainage tube, intraoperative indwelling lumbar cisternal drainage tube, epidural drainage tube ,ventricular drainage tube and the number of operations after admission on secondary CNSIs after craniotomy were consistent with the results of previous studies.
Some studies have shown that secondary CNSIs after craniotomy is closely related to the duration of surgery [18].Anudeng et al. [19] found that the CNSIs infection rate was 6.9% when the operation time was less than 4 hours, and the CNSIs infection rate could be as high as 21.3% when the operation time was more than 4 hours, and the operation time was positively correlated with the infection rate.In this study, operation time ranked first in the importance of Adaboost model variable, indicating that operation time had the greatest impact on postoperative secondary CNSIs. Therefore, neurosurgery craniotomy should be arranged in the sterile laminar flow operating room as far as possible, and the surgeon should strictly and carefully sterilize the skin of the patient's head operation area before the operation. The number of personnel in the operating room and The Times of entry and exit of personnel were strictly controlled, and the principle of sterility was strictly observed during the operation to ensure the success of the operation and shorten the operation time as much as possible.
Arts et al. [20] believed that the occurrence of CNSIs was closely related to the duration of drainage tube indwelling, which was consistent with the results of this study.Long-term lumbar drainage is not only prone to the risk of drainage tube blockage and reflux, but also prone to colonization of external pathogens on the drainage tube, thereby increasing the possibility of retrograde infection.Drainage tubes are usually placed during neurosurgery, which mainly include lumbar cidal drainage tubes, ventricular drainage tubes, epidural drainage tubes, subdural drainage tubes and subcutaneous drainage tubes according to different purposes. Lin et al. [21] considered that indwelling lumbar drainage tube was an independent risk factor for CNSIs. In addition, some studies have suggested that the probability of CNSIs is greatly increased when the external ventricular drainage tube is placed for more than one week, and infection usually occurs on the 3rd to 7th day after surgery. The probability of secondary CNSIs in patients undergoing external ventricular drainage is 10 times that in patients without external ventricular drainage [22–23]. The research results of Omar et al. [24] showed that the distance between the head drainage tube orifice and the surgical incision was closely related to whether the postoperative cerebrospinal fluid leakage occurred. When the subcutaneous tunnel length of the head drainage tube was more than 5cm, the infection rate of the patients was significantly reduced compared with that of the drainage tube placed in the incision. The results of this study showed that intraoperative lumbar drainage tube, epidural drainage tube and ventricular drainage tube were independent risk factors for secondary CNSIs after craniotomy, which was consistent with the results of previous studies.
Some patients undergoing craniotomy may suffer from postoperative complications such as re-bleeding in the surgical area, intracranial hypertension that is difficult to control by drugs, and severe hydrocephalus. Under the conditions of meeting the surgical indications, secondary surgery is often needed to improve the symptoms of patients and save their lives. Korinek et al. [25] believed that the original anatomical structure was destroyed in the initial operation, and the operation time may be prolonged due to the difficulty in structure resolution during the second operation. Moreover, the re-operation through the original incision in a short time may bring the oozing blood and exudate into the brain of the original operation area and induce CNSIs.
GCS score, gender, and emergency surgery were new findings of this study, which were rare in previous reports.
The lower GCS score represents the degree of disturbance of consciousness and the more serious the condition, and also reflects the severity of craniocerebral injury. Previous studies have suggested that patients with GCS scores ≤ 8 are 2.53 times more likely to develop CNSIs than those with GCS scores > 8 [26], which may be related to the pathophysiological characteristics of patients with disorders of consciousness: Patients with disturbance of consciousness have elevated brain tissue metabolism and increased oxygen consumption. Patients with disturbance of consciousness are often complicated with intracranial hypertension, which leads to cerebral blood perfusion insufficiency, which directly affects the uptake and utilization of glucose and oxygen in brain tissue, thus further aggravating brain injury and forming a vicious circle. Severe brain injury may prolong the operation time or perform multiple operations. Thus, it indirectly increases the possibility of CNSIs [27].
At present, no consensus has been reached on the effect of gender factors on CNSIs. Some research results show that gender [28] is an independent risk factor for secondary CNSIs after craniotomy, which is consistent with the results of this study, while Guo et al. [29] hold the opposite view. Summary of previous studies, the influence of gender on the occurrence of CNSIs may be related to the following aspects: ① It may be related to the bad life habits of men. For example, compared with women, men account for a large proportion of bad habits such as smoking and drinking. Some studies have shown that patients with long-term smoking history before surgery and who have not quit smoking will increase the risk of infection after deep brain surgery [30]. ② The differences caused by sex hormones and their effects on gene expression and immune system. The differences in the expression of inflammatory cytokines in different genders have been reported, among which leukotriene plays an important role in the regulation of immune and inflammatory response. The synthesis of testosterone in men will reduce the synthesis of phospholipase-D, resulting in the synthesis of leukotriene in men is weaker than that in women [31]. The influence of gender factors on secondary CNSIs after craniotomy still needs multi-center, prospective large-sample experimental research to draw a conclusion in the future.