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Spallation and particles infusion into the extracorporeal circuit during CRRT: a preventable phenomenon – Scientific Reports

The experiments were carried out with an effective treatment time of 303 min [295–309 min], in accordance with the set time frame (5 h). There were no alarms during the treatments and the transmembrane pressure (TMP) was maintained with an average of 115 mmHg in “control phase” and 118 mmHg during the “filtering phase” (Fig. 2). Comparison of the equations parameterising the two trend lines, shown in Fig. 2, highlight the slopes of the two TMP signals.

Figure 2
figure 2

Transmembrane pressures (TMP) in “control phase” and “filtering phase”.

Specifically, the slopes of the two curves, as shown in the equations in Fig. 2 are approximately zero (− 0.0037 for control and − 0.0171 for filtering) for both configurations. Therefore, for both the control and filtering phases, the slopes of the curves are similar.

Wide-field optical microscope images highlight the particles, mainly micrometer-sized, detected in the “patient solution” at the beginning and interruption of the treatment either with or without the use of in-line filtration. The Fig. 3 shows the different qualitative behaviour between “control phase” and “filtering phase” in the “patient solution”. The average particle diameter in both “control” and “filtering” phases at the beginning of the treatment is about 2 μm, while at the end of the treatment it is of 4 μm in the “control phase” and 0.6 μm in the “filtering phase”.

Figure 3
figure 3

Wide-field optical microscope images of the “patient line” solutions (P circuit sampling point) in “control phase” (a) and in “filtering phase” (b) at the CRRT initiation and interruption. The scale bars are of 10 μm.

Additional images acquired by wide-field optical microscopy are in the Supplementary Information (Figs. S1S5).

In the “filtering” phase, the wide field optical microscope also analyzed the presence of the particles in the replacement lines. Figure 4 shows the representative images of a single replacement line, while the behavior of the two lines is similar. Particles found at the beginning and interruption of CRRT, straddling the ({{text{Fb}}}_{{text{pre}}}), ({{text{Fb}}}_{{text{post}}}), ({{text{Fs}}}_{{text{pre}}}) and ({{text{Fs}}}_{{text{post}}}) in-line filters, were highlighted.

Figure 4
figure 4

Wide-field optical microscope images of solutions sampled from the post-filter replacement line. Representation of treatment at the beginning and interruption of CRRT downstream of the replacement bag (a) (E, F circuit sampling points) and downstream of the peristaltic pump (b) (G, H circuit sampling points). The scale bars are of 10 μm.

Additional images acquired by wide-field optical microscopy are in the Supplementary Information (Figs. S6S13).

Quantitatively, particle loading was evaluated in the two replacement lines, pre-dilution, and post-dilution. Assuming that the amount of salts contained within each replacement bag, and therefore of each sample, is the same, the weight of microplastic particles present in each sample, and thus their concentration, can be assessed. Figure 5 shows the trend of the dry residue, in terms of concentration, i.e., residue weight normalized by the dried solution volume, taken straddling the ({{text{Fb}}}_{{text{pre}}}), ({{text{Fb}}}_{{text{post}}}), ({{text{Fs}}}_{{text{pre}}}) and ({{text{Fs}}}_{{text{post}}}) in-line filters in two replacement lines at the beginning and end of CRRT treatment.

Figure 5
figure 5

Medians and interquartile range of the dry residue concentrations (N = 5) obtained from the replacement lines (pre-haemodifilter, top panel- and post-haemodiafilter, bottom panel) evaluated straddling the in-line filters (({{text{Fb}}}_{{text{pre}}}), ({{text{Fb}}}_{{text{post}}}), ({{text{Fs}}}_{{text{pre}}}) and ({{text{Fs}}}_{{text{post}}})) at the beginning (yellow lines) and end (green lines) of the treatment.

Additional images is given in the Supplementary Information. One showing a quantitative analysis of particle concentration (n.particles/μL) (Fig. S16) and other one the amount of residue in the patient solution, P points (Fig. S17).

Finally, a chemical and morphological analysis of the microparticles contained in the different samples was performed using the FESEM-EDX method. Straddling the ({{text{Fb}}}_{{text{pre}}}), ({{text{Fb}}}_{{text{post}}}) in-line filters are predominantly salt particles contained in the replacement bags, while straddling the ({{text{Fs}}}_{{text{pre}}}) and ({{text{Fs}}}_{{text{post}}}) in-line filters are predominantly micro-sized plastic particles resulting from the wear of the circuit tubes that are continuously compressed by peristaltic pumps (Fig. 6). The salts consist mainly of elements such as sodium and chlorine. The microplastic particles, on the other hand, are composed of carbon and oxygen and morphologically are an aggregate of nanosized particles. Additional images acquired by FESEM-EDX methods are in the supplementary information (Figs. S14, S15).

Figure 6
figure 6

Examples of salt (a) and microplastic particle (c) detected within samples acquired by FESEM at 20.00 KX and 100.00 KX, respectively. The spectra detected by EDX analysis show the chemical composition of the salt particles (b) (NaCl) and of the microplastic particles (d) (C–O). The Si detected derives from the wafer substrate.