150 J. R. Neal et al.: J Extra Corpor Technol 2025, 57, 147--152 Figure 1. A. Representation of the pediatric circuit with recirculation manifold and patient. The tubing area between the two * represents the area where intermittent clamping would occur in varied locations. B. Representation of the adult ECMO circuit and patient. The tubing area between the two * represents the area where intermittent clamping would occur in varied locations.
Table 2. Comparison of activated clotting times( ACT) targets during a clamp and flash trial with heparin only versus a heparin bolus and bivalirudin drip. I-stat ACT machine with kaolin cartridges was used for these target ACTs.
|
ACT target with heparin( s) |
ACT target with heparin + bivalirudin( s) |
Adult |
210--220 |
230--250 |
Pediatric |
200--215 |
210--225 |
Due to this concern, during clamp flash trials, heparin boluses are used concurrently with bivalirudin drips to ensure the appropriate presence of the desired intensity of systemic anticoagulation within the areas of stagnant blood flow. Another important note when performing these trials is the timing of ABGs. Our center finds the easiest time to draw an ABG from a patient is just before flashing for the 30-second period. The lab technician will inform the perfusionist / ECMO specialist once completed with the draw from the arterial line, so that flashing can commence. If there are concerns with the patient’ s respiratory status, these values will mostly reflect how the patient can tolerate being off ECMO ventilatory support.
Discussion
Numerous approaches to the weaning of VA ECMO have been described, including in the terminal phases. However, our clamp flash trial can serve as an alternative to these approaches that hybridizes the ready availability of restoration of flow with the ability to assess physiologic reserve in the absence of ongoing ECMO support. This is an essential component to the holistic comprehensive assessment because it facilitates determining physiologic reserve in the context of zero mechanical circuit flow while concurrently enabling the rapid re-application of support as necessary. Further, it facilitates a variable duration of assessment not confined to conventional trial-offs. This latter piece is a potent advantage of this approach because it enables an individualized method that recognizes the variation inherent in patient presentations. In our opinion, the clamp flash trial offers superior flexibility in duration of the terminal weaning trial in a manner that mitigates thrombotic risks and protects against undue, and potentially deleterious, physiologic strain. In assessing a patient’ s readiness for ECMO decannulation, looking at the patient’ s ejection fraction, CI, inotropic support, lactate levels, systolic blood pressure, and blood gases are all assessed during the clamp flash trial.
The clamp intervals must be thoroughly timed without guessing or lapses of flashes following stagnation periods. Improper timing could lead to thrombosis of the circuit, given the ACTs during this trial. Our center allows personal use of either a watch timer or a phone timer and does not use a wall clock as a timer. In our institution, the thought of increasing the anticoagulation further to increase the length of clamping to over 4 min was deemed not to be worth the increased risk of bleeding. When utilizing a 4-minute clamping interval for an hour trial, the patient is unsupported for 90 % of the trial time. This has provided adequate information to assess whether the heart is ready to be weaned and discontinued from ECMO support. In some isolated patients( fewer than 8) that were weaned, ECMO had to be reinstituted after 24 h due to issues that were unforeseen during the initial weaning phase. The majority of these isolated patients who required reinstitution were due to a secondary insult unrelated to the initial indication, such as new onset septicemia or respiratory failure.
In the pediatric setting, previous studies have reported leaving cannulas connected to the patient with heparin flushes to keep them patent. This would prevent the need for re-cannulation if ECMO reinstitution was necessary [ 17, 18 ].