Patients
Patients who were admitted to the NICU of Guangzhou Women and Children's Medical Center between March 2014 and December 2016 were retrospectively reviewed. Inclusion criteria of preterm infants were: 1) patients’ birth weight ≤1.8 kg, and required total or partial parenteral nutrition (TPN or PPN), 2) patients received routine retention of PICC line for more than 2 weeks, and 3) patients were not systemically administrated antibiotics during the catheter lock. Patients who: 1) had birth weight >1.8 kg,2) died during the first week after birth or died of non-CRBSI reasons, 32) received routine retention of PICC line for less than 2 weeks, 43) were administrated with antibiotics before the catheter lock,54) required umbilical venous catheters (UVCs), 65) were transferred to other hospitals or departments or failed to complete a clinical observation for at least two weeks, or 76) with congenital immunodeficiency, multiple malformations or congenital hypoglycemia, were excluded. The study was approved by the Ethics Committee of Guangzhou Women and Children's Medical Center (No. 2013-32). Written informed consent was obtained from each infant’s guardians.
Treatment
Patients received treatment of heparin plus vancomycin (vancomycin-lock group) or heparin only (control group).
Before the lock of PICC catheter, clinicians’ hands and catheter interface were strictly disinfected, and the lock solution was prepared by a qualified staff. Lock was carried out since the first day after the placement of PICC catheter, 3 times daily (q8h). PICC catheter position, redness and swelling, secretion, phlebitis, and obstruction were regularly recorded in a unified and strict way by an independent PICC management team at the NICU according to the centralized management and standard process. 6
In the vancomycin-lock group, 0.5 mL lock solution of 10 IU/mL heparin and 25 μg/mL vancomycin was given. If the disease status required systemic antibiotic treatment, vancomycin-lock was stopped, and only heparin solution would be used instead (q12h).
For each lock, the lock solution was retained for 30 min and was then discarded and flushed away from the catheter with 2 ml of normal saline, followed by addition of the former solution used in the catheter. The lock procedure was carried out 3 times daily (q8h). Blood glucose was measured before and after the lock. Blood samples from the inner PICC catheters and peripheral veins were cultured in a BACT/ALERT 3D automatic blood bacteria culture system (BioMerieux, France). Positive blood samples showing bacteria growth were transferred to blood plates and chocolate plates, and were then cultured in a carbon dioxide incubator at 37℃ for 24 h. The bacteria species were then further identified using a VITEK 2 COMPACT automatic microbial identification and susceptibility system (BioMerieux) and a VITEK MS automatic rapid microbial mass spectrometry detection system (BioMerieux). Cultures that had not been detected bacteria growth for 5 days were considered negative blood culture.
The blood concentrations of vancomycin were measured every 2 weeks. Infection indicators were regularly monitored; once clinical symptoms were observed or infection indicators were elevated, blood from the peripheral vein and inner PICC catheter was cultured immediately. If PICC catheter needed to be removed, the catheter tip was cultured to identify the causative bacteria. At the end of the study, the catheter tip was cultured and the blood vancomycin concentrations were measured.
In the control group, only 0.5 mL 10 IU/mL heparin was used, and most of the other procedures weresimilar to those in the vancomycin-lock group.
Patients were not administrated with antibiotics before the catheter lock. However, during the treatment if the patients’symptoms became worse and they were suspected with sepsis, the physicians empirically used antibiotics (such as sulperazone, tienam/mepem, and vancomycin) until a line of indicators excluded the occurrence of sepsis.
During the study period there was no consensus on the selection of heparin- or vancomycin-lock strategy in our center, and physicians themselves decided to choose heparin-or vancomycin-lock. In addition, there was no obvious turning point about the strategy of PICC lock (such as switching from heparin- to vancomycin-lock), although since the late-stage of this study the number of patients received vancomycin-lock increased.
Measurement
The incidence and onset time of CRBSI were recorded. The pathogenic microorganisms from blood were cultured and identified, and the usage of antibiotics was recorded. The side effects of ALT, such as allergy to vancomycin, influence on body function, incidence of hypoglycemia, PICC fracture, embolism and slippage, and local port abscess during the lock, were observed.
Definition
CRBSI was determined according to the definition of CRBSI by the United States Center for Disease Control in 2012[6].
Confirmed CRBSI was determined if:1) infants exhibited symptoms of sepsis, 2) blood cultures from both the peripheral veins and catheters were identified same types of bacteria, and the catheter blood culture had a positive result 2 h earlier; or the culture of the catheter tip was positive and had the same types of bacteria as the peripheral blood culture, 3) other sources of infection were excluded.
Suspected CRBSI was determined if: 1) there was clinical symptoms of sepsis, 2) peripheral blood culture was positive but without consistent types of the identified bacteria with those from the inner catheter blood or catheter tip, or the culture of the peripheral blood was identified common skin symbionts, such as Staphylococcus epidermidis, coagulase-negative Staphylococcus, Bacillus and Candida, 3) bloodstream infection at other lesions were excluded, and antibiotic treatment was needed and clinical symptoms disappeared thereafter.
Suspected infection was defined if there was manifestation of clinical infection or the indicators of inflammation and infection, such as white blood cells (WBC), C-reactive protein(CRP) and procalcitonin, were abnormal, while the culture of blood or catheter tip was negative.
Colonization was defined if the catheter tip culture was positive after the observation, but there were no clinical symptoms in patients and the blood culture was negative.Non-catheter-related infection (i.e.non-CRBSI neonatal sepsis) was mainly determined based on at least 3 of the following criteria[21,22]: 1) having clinical symptoms of sepsis, such as respiratory distress, apnea, hyperglycemia, hypoglycemia, vomiting and feeding intolerance, 2) blood cultures from within and outside catheters and thosefrom the catheter tips werenegative, 3) abnormal laboratory parameters, such as CRP concentration >10 mg/L and WBC<5*109/L, 4) incidence of high risk factors for infection, such as group B Streptococcus positive in mothers, chorioamnionitis and premature rupture of membranes (PROM) for over 18 h, and 5) antibiotic treatment was needed, and symptoms disappeared after that.
Infection rate per 1000 catheter-days was defined as the number of the infected cases/ total catheter-days X 1000‰. During the treatmentif patients needed to be systematically administratedwith antibiotics, the systematic administration time of antibiotics was determined as the time (day) of intravenous injection of antibiotics, such as sulperazone, tienam/mepem, and vancomycin, during the whole hospital stay.
Data collection and statistical analysis
Infants’ basic physiological characteristics (such as gestational age, weight, APGAR score, mechanical ventilation [MV] time), suspectedinfection, major comorbidity (such as neonatal respiratory distress syndrome [NRDS], patent ductus arteriosus [PDA], and non-catheter-related infection), major complications (such as intracranial infection, intracranial hemorrhage, NEC), death, and all adverse events (including local redness and swelling, PICC embolism, rupture and slipping, allergy, adverse drug reactions, and hypoglycemia) during the usage of PICC were collected. The incidence of CRBSI, identified types of pathogenic microorganisms, usage of antibiotics, parenteral nutrition time, PICC time, hospital stay, and hospitalization expenses were also collected.
Data were expressed as mean ± standard derivation or median ± interquartile range. All the above data were analyzed by a qualified statistician who did not participate in this work and was blinded to the grouping situation using SPSS 23 statistical software (SPSS Inc., Chicago, Illinois, USA). Measurement data were compared between the vancomycin-lock and control groups using t-test. Enumeration data were compared between groups using Pearson Chi-square test or Fisher's exact test. CRBSI risk ratios (RR) and 95% confidence intervals (CIs) were assessed by COX statistical analysis. Probability of non-CRBSI was evaluated by Kaplan-Meier curve analysis. Comparisons with p<0.05 (two-tailed) were thought to be statistically significant.