The Journal of ExtraCorporeal Technology No 56-2 | Page 42

S . Robertson and K . White : J Extra Corpor Technol 2024 , 56 , 65 – 70 69

Table 1 . Pressure transducer passive infusion volume ( mL ) over 24 h period .

Table 2 . Pressure transducer active infusion volume ( mL ) over 10 s .

to patients per hour or per day through pressure transducers connected to the ECMO circuit based on different circuit pressures ( Table 1 ). The final three experiments quantify how much volume can be infused while actively flushing pressure transducers against common circuit pressures by taking note of how many seconds the clinician pulls on the Snap-Tab ( Table 2 ).

Discussion

Experiment 4 ( 300 mmHg to 0 mmHg )

The experiments outlined above provide evidence that the fluid transfused to ECMO patients through circuit pressure transducers can be significant when using an Edwards TruWave transducer and pressurized IV bag . Passive volume transfused daily to a patient using the data from Table 1 would equal 154.6 mL , assuming three transducers reading pressures on the venous line as well as pre and post-oxygenator respectively . This is using the conservative values from the 0 mmHg experiment for the venous line and 150 mmHg for both of the oxygenator transducers . Anticipating a 1-second pull per hour on all transducer snap tabs , an additional 165.1 mL would be actively transfused in the same 24-hour period . Combining both passive and active values shows that 319.6 mL would be transfused . While these findings may not be clinically significant in the adult population , in a neonate , this can equate to nearly their entire circulating blood volume in crystalloid flush alone [ 9 ]. Excessive crystalloid infusion of this nature is known to exacerbate acute inflammatory response and lead to the third spacing of fluid [ 10 ].

The tests performed also reveal the total volume given is difficult to calculate with 100 % accuracy . Different variables such as constantly changing circuit pressures , as well as clinician practice , yield a variety of outcomes . For example , a patient requiring higher flows might have a higher negative pressure on the venous line , resulting in more passive volume transfused . Compare that to an aging oxygenator having a higher positive pressure on the pre oxygenator line , resulting in less volume given . Also , a clinician on the morning shift might only pull the snap tab for half a second each hour , leading to less volume transfused compared to their night shift counterpart who pulls for over 2 s out of an abundance of caution , resulting in more volume transfused . For these reasons , IV bags pressurized to 300 mmHg should not be considered best practice . As an alternative , syringe pumps can be used to deliver a constant infusion through the pressure transducers . With this proposed method , active flushing is eliminated and the crystalloid volume can be accurately captured lending to a more precise daily fluid balance . The infusion can also be titrated to the location of each pressure port .

As a result of the findings from these experiments , pressurized IV bags were removed from practice and syringe pumps were adopted as part of the institutional protocol to use for flushing pediatric ECMO circuit pressure transducers . The pumps were set at 0.5 mL / h on the pre-membrane , 0.3 mL / h on the post membrane , and 0.2 mL / h on the venous return port . This equates to a total volume of 1 mL per hour or 24 mL within a 24-hour period . The most noted advantage of the syringe pump is that the total volume transfused can be drastically reduced , thus reducing fluidoverloadonECMO , andyieldingimprovedpatientoutcomes [ 11 ]. Additionally , syringe pumps hold an advantage over IV pumps as the syringes provide a visual of volume transfused when device precision is in question [ 12 ].

Due to the immense variation in practice , it is proposed that a survey be completed to discover all the methods being used to monitor ECMO pressures as well as maintaining patency . Additionally further studies need to be done and guidelines should be developed by ELSO in order to standardize the practice of monitoring and flushing pressure ports on ECMO .

Funding The authors did not receive any funding for this work .

Conflicts of Interest The authors declare no conflict of interest .

Data availability statement All available data are incorporated into the article .

Author contribution statement

S . R . conception of the study , experiment design , data collection , and result analysis . S . R . and K . W . wrote the manuscript . Both authors reviewed and approved the data and final manuscript .