Can humidifier reservoir bacteria colonize the circuit during mechanical ventilation: An in vitro study.

BACKGROUND: Although the circuit condensate, an ideal bacterial reservoir during mechanical ventilation, may flow into the humidifier reservoir, no studies have investigated if humidifier reservoir colonized bacteria colonize other circuit locations with airflow. AIMS: We aimed to prove whether the humidifier reservoir colonized bacteria colonize other circuit locations with airflow and provide some advice on the disposal of condensate in the clinical setting. STUDY DESIGN: An in vitro experiment was conducted. Mechanical ventilation simulators (n = 90) were divided into sterile water group (n = 30) and broth group (n = 60). In the sterile water group, sterile water was used for humidification, either Acinetobacter baumannii or Pseudomonas aeruginosa were inoculated to humidifier water in the humidifier reservoir, each accounted for 50% of the simulators. The broth group was performed the same as the sterile water group except for the addition of broth into the humidified water. After 24, 72, and 168 h of continuous ventilation, the humidifier water and different locations of the circuits were sampled for bacterial culture. RESULTS: All bacterial culture results of the sterile water group were negative. Bacteria in the humidifier water continued to proliferate in the broth group. With prolonged ventilation, the bacteria at the humidifier reservoir outlet increased. The bacteria at the humidifier reservoir outlet were much more in the Pseudomonas aeruginosa subgroup than in the Acinetobacter baumannii subgroup and the difference was statistically significant (p < .05). During continuous ventilation, no bacterial growth occurred at 10 cm from the humidifier reservoir outlet and the Y-piece of the ventilator circuits. CONCLUSIONS: Sterile water in the humidifier reservoir was not conducive to bacterial growth. Even if bacteria grew in the humidifier reservoir and could reach the humidifier reservoir outlet, colonization of further circuit locations with the airflow was unlikely. During a certain mechanical ventilation time, the amount of bacteria reaching the outlet of the humidifier reservoir varied due to different mobility of bacteria. RELEVANCE TO CLINICAL PRACTICE: In a clinical setting, nurses should not worry about a small amount of condensate backflow into the humidifier reservoir. Draining condensate into the humidifier reservoir can be used as a low risk and convenient method in clinical practice.

[Study on pollution evaluation of heavy metal in surface soil of the original site of Qingdao North Station].

The determination of pollution extent and health risk assessment are the premise of heavy metal contaminated site remediation. The content of Cu, Cr, Pb, Cd, Zn, Ni in Qingdao North Station was detected, and the correlation of the 6 kinds of heavy metal content was analyzed. The pollution extent in excess of background values was characterized by anthropogenic influence multiple, and the pollution of heavy metal in soil was evaluated using geoaccumulation index and a new method which connects geoaccumulation index with Nemero index. Finally, human health risk assessment was carried out with health risk assessment model for heavy metal content. The results showed that Qingdao North Station soil were polluted by heavy metals. Six heavy metal pollution levels were: Cd > Cu > Ni > Pb > Cr > Zn, and Cd had reached the severity pollution level, Cu and Ni followed by, Cr, Pb and Zn were in minor pollution level. The order of coefficient variation in all heavy metals was: Cd > Ni > Cr > Zn > Pb > Cu. Within the study area soil heavy metal distribution was different, but overall discrepancy was small. The order of non-cancer hazards of heavy metals in soil was Cr > Pb > Cu > Ni > Cd > Zn, and the order of carcinogen risks of heavy metals was Ni > Cd. The non-cancer hazard and carcinogen risks values of metals were both lower than that their threshold values. They were not the direct threats to human health.

[Experimental research on in-situ auto-monitoring for underground sewage pipeline leakage].

The leakage of underground sewage pipes may seriously affect the soil and the environment of groundwater. In this paper, an in-situ automatic monitoring device on basis of multi-electrode resistivity method was developed for the leakage of underground sewage pipelines, and it was validated by a simulated experiment in laboratory that the feasibility of the new device is feasible for real-time monitoring the leakage of underground sewage pipelines at many different groundwater levels. The experimental results indicated that small leakage of sewage pipelines could be rapidly detected by the developed monitoring device when the pipeline was located in the vadose zone. The leakage could also be monitored in a prompt manner when the pipeline was located near the groundwater level, and the extent of pollutant leakage could be speculated with the gradient change in resistivity of the soil layer above the pipeline. When the pipeline was located below the groundwater level, the device could only monitor the leakage if it reached a certain concentration to produce notable changes in resistivity, because of the rapid mixing and diffusion of the pollutant in groundwater. The device set up in this paper was found capable of real-time automatic monitoring the leakage of underground sewage pipelines buried in different depths and groundwater levels.

[Monitoring of water and salt transport in silt and sandy soil during the leaching process].

Water and salt transport in soil and its mechanism is the key point of the saline soil research. The dynamic rule of water and transport in soil during the leaching process is the theoretical basis of formation, flush, drainage and improvement of saline soil. In this study, a vertical infiltration experiment was conducted to monitor the variation in the resistivity of silt and sandy soil during the leaching process by the self-designed automatic monitoring device. The experimental results showed that the peaks in the resistivity of the two soils went down and faded away in the course of leaching. It took about 30 minutes for sandy soil to reach the water-salt balance, whereas the silt took about 70 minutes. With the increasing leaching times, the desalination depth remained basically the same, being 35 cm for sandy soil and 10 cm for the silt from the top to bottom of soil column. Therefore, 3 and 7 leaching processes were required respectively for the complete desalination of the soil column. The temporal and spatial resolution of this monitoring device can be adjusted according to the practical demand. This device can not only achieve the remote, in situ and dynamic monitoring data of water and salt transport, but also provide an effective method in monitoring, assessment and early warning of salinization.

[Effect of total solids concentration on heavy metals bioleaching from contaminated sediment].

The effect of total solids concentration on heavy metals bioleaching from contaminated sediment was investigated in shake flasks. The results demonstrated that an increase in total solids concentration reduced the rates of sediment pH reduction, ORP increase and metal removal. During this bioleaching process, the removal of Zn, Cu, and Cr rapidly enhanced and then gradually approached the maximum removal efficiency when sediment pH decreased from 5.0 to 2.0 and the ORP increased from 200 mV to 520 mV. After 12 days of bioleaching, about 60%-85% of Zn, 65%-100% of Cu, and 17%-35% of Cr could be removed from various sediments of 3%-13% solids content, respectively. It was found that the variation of sediment pH in this bioleaching process could be estimated by a modified Boltzmann model. The analysis of speciation distribution of metals indicated that the unremoved Cu, Zn, and Cr in the bioleached sediment mainly existed in residual fraction, and that the percentpages of Cu, Zn, and Cr bound to this fraction were 76.2%, 81.2%, and 82.7%, respectively. From economical consideration, the recommended total solids concentration for the bioleaching of metals from the sediment is 10%.