Using a roller pump for establishing extra-corporal membrane oxygenation (ECMO) – technical considerations for times of crisis

Objective: The COVID-19 pandemic requires thinking about alternatives to establish ECMO when often-limited hardware resources are exhausted. Heart-lung-machines may potentially be used for ECMO but contain roller pumps as compared to centrifugal pumps in ECMO-circuits. We here tested roller pumps as rescue pump for ECMO-establishment. Methods: We set up in vitro circuits on roller pumps from C5 heart-lung-machine with 5 l/minutes flow. In two series, we placed either PVC or silicon tubing for an ECMO circuit into the roller pump. We assessed the mechanical stress on the tubing (aiming to run the pump for at least 1 week), measured the temperature increase generated by the friction and assessed flow characteristics and its measurement in simulated situations resembling tube kinking and suction. Results: The roller pumps led to expected and unexpected adverse events. PVC tubing burst between 36 and 78 hours, while silicon tubing lasted for at least 7 days. At 7 days, the silicone tubing showed significant signs of roller pump wear visible on the outside. The inside, however, was free of surface irregularities. Using these tubings in a roller pump led to a remarkable increase in circuit temperature (PVC: +12.0°C, silicone +2.9°C). Kinking or suction on the device caused the expected dramatic flow reduction (as assessed by direct measurement) while the roller pump display continued to show the preset flow. The roller pump is therefore not able to reliably determine the true flow rate. Conclusion: Roller pumps with silicone tubing but not PVC tubing may be used for running ECMO circuits. Silicone tubing may endure the roller pump shear forces for up to 1 week. Thus, repeated tubing repositioning may be a solution. Circuit heating and substantial limitations in flow detection should increase attention if clinical use in situations of crisis is considered.

The ‘Pull’ Technique for Removal of Peritoneal Dialysis Catheters: A Call for Re-Evaluation of Practice Standards

BackgroundThe most commonly used peritoneal dialysis (PD) catheters have silicon tubing with attached Dacron cuffs. The current standard of care for PD catheter removal is by complete surgical dissection, withdrawing both the tubing and the cuffs. The intention is to avoid infection of any residual part of the catheter. We retrospectively analyzed our results with the alternative ‘pull’ technique, by which the silicon tube is pulled out, leaving the Dacron cuffs within the abdominal wall. This technique never gained popularity due to concern that the retained cuffs would get infected.MethodsWe reviewed our experience from an 18-month period, between January 2014 and June 2015. There were 46 catheter removals in 40 patients. All the catheters were of the double-cuffed coiled Tenckhoff type (Covidien, Dublin, Ireland).ResultsOf the 46 catheter removals by the ‘pull’ technique, there was only 1 case of retained cuff infection.ConclusionsThe ‘pull’ technique is a safe method for Tenckhoff catheter removal with low risk of infection. We strongly recommend it as the procedure of choice.

Assessing approaches to determine the effect of ocean acidification on bacterial processes

Bacterial extracellular enzymes play a significant role in the degradation of labile organic matter and nutrient availability in the open ocean. Although bacterial production and extracellular enzymes may be affected by ocean acidification, few studies to date have considered the methodology used to measure enzyme activity and bacterial processes. This study investigated the potential artefacts in determining the response of bacterial extracellular glucosidase and aminopeptidase to ocean acidification, and the relative effects of three different acidification techniques. Tests confirmed that the fluorescence of the artificial fluorophores was affected by pH, and that addition of MCA fluorescent substrate alters seawater pH. In experiments testing different acidification methods, bubbling with CO2 gas mixtures resulted in higher β-glucosidase activity relative to acidification by their introduction via gas-permeable silicon tubing, or by acid addition (HCl). In addition, bacterial numbers were 15–40 % higher with bubbling relative to seawater acidified with gas-permeable silicon tubing and HCl. Bubbling may lead to overestimation of carbohydrate degradation and bacterial abundance, and consequently incorrect interpretation of the impacts of ocean acidification on organic matter cycling.

Optimising methodology for determining the effect of ocean acidification on bacterial extracellular enzymes

To fully understand the impact of ocean acidification on biogeochemical cycles, the response of bacterial extracellular enzymes needs to be considered as they play a central role in the degradation and distribution of labile organic matter. This study investigates the methodology, and potential artefacts involved in determining the response of bacterial extracellular glucosidase and protease to ocean acidification. The effect of pH on artificial fluorophores and substrates was examined, as well as the impact of three different acidification methods. The results indicate that pH has a significant effect on the fluorescence of the artificial fluorophore 4-methylumbeliferone for glucosidase activity, and 7-amino-4-methylcoumarin for protease activity, while artificial aminopeptidase substrate alters the pH of seawater, confirming previous observations. Before use in ocean acidification research these enzyme assay components must be buffered in order to stabilise sample pH. Reduction of coastal seawater pH to 7.8 was shown to increase β-glucosidase activity rapidly (0.5 h), while no significant response was detected for leucine aminopeptidase, highlighting the need for short-term direct effects of pH on enzyme activities. Bubbling with CO2 gas resulted in higher β-glucosidase activity when compared to acidification using gas-permeable silicon tubing and acidification with HCl. Although bubbling showed variable effects between two experiments conducted at different times of the year. In addition, bacterial cell numbers were 15–40% higher with bubbling relative to seawater acidified with gas-permeable silicon tubing and HCl. Artefacts associated with bubbling may lead to the overestimation of extracellular enzyme activities, and interpretation of the impacts of ocean acidification on organic matter cycling.