Table 1.
Algorithm 1 used systemic total calcium and Algorithm 2 used an initial blood gas as input.
Fig 1.
Flow diagram for inclusion and exclusion criteria for patient enrollment and measurement points analyzed.
Table 2.
Mean and standard deviation for the modelled data compared to the measured value on BGA.
Complete data set and quality checked data set included 1290 and 1034 individual measurements respectively in 57 patients. The number measurements for each patient could range from 3 unique post-filter iCa measurements to over 20.
Fig 2.
Average differences between measured post-filter iCa and calculated post-filter iCa for quality checked data for Algorithm 1 (2a) and Algorithm 2 (2b).
There are instances when the algorithms are returning values both higher and lower to the BGA. Algorithm 2 has a tendency to underestimate postfilter iCa, while Algorithm 1 does not seem to have the same tendency.
Fig 3.
Regression plots for Algorithm 1 (3a) and Algorithm 2 (3b). r2 is the Pearson R-value squared, SSE is the sum of squared error. The equation for the regression line is also calculated and shown as a straight black line. The ideal equation would be y = x and shown as a dotted black line. The differences between the calculated value and the measured value are shown for algorithm 1 (3c) and algorithm 2 (3d), it can be discovered that the calculated value overestimate more the higher the measured postfilter value is. This could suggest a systemic confounding factor, most likely in the mathematics predicting the citrate concentration in the patient.
Fig 4.
Measured versus calculated postfilter iCa values in a patient, with no obvious explanation on changes in measured BGA post-filter iCa values.
There were no machine setting changes or changes in systemic iCa or other parameters that could explain the decrease in the BGA post-filter iCa over time (starting at 37th hour into the treatment and continuing to the 68th hour). Of note, the treatment was stopped at the 37th hour and restarted at the 39th hour, at a high postfilter iCa value. Most probably the pause in the treatment has an impact. What can also be noted is that the calculated values follow the decline.