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Other centers have reported using a bridge next to the cannulas to keep circuit flow high and patient flow low [ 19, 20 ]. Another center reported a transition from VA to VAV as a weaning method [ 21 ]. Our clamp flash trial can serve as an alternative to these approaches.
Once a clamp flash trial has been completed, and if decannulation is not imminent, the previously administered exogenous unfractionated heparin will wear off between 1 and 2 h, with minimal concern for bleeding. Inherently, there are some contraindications for using heparin, such as exacerbation of existing intracranial hemorrhage or in patients with known or suspected type 2 heparin-induced thrombocytopenia thrombosis( HITT). Fortunately, these patients are a minority in our overall ECMO patient population. Therefore, this trial has been used on the great majority of our adult and pediatric VA ECMO patients with noteworthy success. In the occurrences where there would be a contraindication to heparin, the broadly described and more conventional low-flow techniques continue to be utilized. Despite the recent interest in the retrograde flow techniques as reported in the literature, our center has not yet trialed this approach or compared it to the clamp-flash trial technique. Further, our extensive use of the Cardiohelp System on adult patients and some large pediatric patients precludes this approach due to embedded safety features integrated into that device that prevent retrograde flow [ 22 ]. While certainly a unique technique, we feel that many of our adult patients would fail weaning with a reversed flow, a left-to-right shunt of between 0.5 and 1 LPM, as reported in other papers.
While these trials give great data on how a patient will wean, there is a need for an increased level of staffing during the clamp and flash period. Either a perfusionist or an ECMO specialist needs to be available to perform the clamping / unclamping and timing of these events, along with the manipulation of the sweep and FDO 2. The ability to perform these tests in the setting of an intensive care unit( ICU) is a valuable and effective way to prevent a risky and unnecessary OR trip, especially if a patient is not separable from ECMO. This also avoids costs from being accrued for the OR time, personnel, and related resources if the patient were unable to pass a clamp flash trial test.
The ACT machine that we used at our center is the i-STAT( Abott POC, Princeton, NJ) with kaolin cartridges. As reported in previous papers, there are some differences in ACT machines. Our values for a goal ACT may differ from other institutions, depending on their ACT machine or activator [ 23 ]. Given this, ECMO centers wishing to use our technique will need to digest this information and evaluate what their target ACTs should be before implementing a clamp flash trial.
The physiologic rationale and positive single-center experience over the past 13 years has yielded a highly favorable impression of the clamp flash trial at our center in assessing for ECMO removal readiness in a way that balances the risk of bleeding and thrombosis in a relatively short period. The potential benefits of this method are striking about the resilience of artificial support through ECMO flow cessation, with the patient being unsupported for 85--90 % of the duration of the trial, which itself may be safely extended to facilitate the holistic ascertainment of physiologic reserve in the absence of circuit flow. Additionally, during the trial, support flow is reduced by 90 % from the ECMO circuit as compared to a low continuous flow state. This approach compares favorably to a low continuous flow trial with no unsupported periods or a single timelimited trial achieved through the isolated application of a clamp to terminate flow. Our center’ s experience with the clamp flash trial is defined as a reliable, effective, and efficient method to assess the readiness of our patients to be weaned from VA ECMO.
Limitations
Future studies into this technique, as compared to other weaning techniques, would be the next logical step. The clamp flash technique, at this time, is being reported at a single site and lacks a scientific comparator, and has limited data on certain subgroups. While using the technique for over 13 years, the data from the trials were not always recorded or documented fully in the patient record. While reporting of data points from patients would give credibility to this technique, we do not have complete results to be able to pull from. Given this, we present this paper as a technical article with patient estimates. Our center will look to future data publication with improved recording of these trials in the future. We stress that utilizing the technique is safe when following our paper’ s outlined instructions.
Acknowledgements
We wish to thank the multidisciplinary team that cares for the pediatric and adult ECMO patients at our center. Additionally, we thank Daniel Erpelding, CCP, and Phillip Scott, CCP, FPP, for their assistance in the implementation of the clamp flash trial in its beginnings at our center.
Funding
We have no funding to declare for the effort put into this publication.
Conflicts of interest
We have no conflicts of interest to report for the authoring of this publication.
Data availability statement
No data were analyzed in this paper. Given this, we do not have a repository of data for supplementary material to acknowledge.
Author contribution statement
James Neal was the primary author of this paper and helped with the creation of the clamp flash methodology. Pavel Mishin is involved with performing clamp flash trials and assisted with editing the paper. Caitlin Blau was involved with the early use and implementation of this trial in pediatric and adult patients and assisted with editing the paper. Troy Seelhammer is the ECMO Medical Director at our center and assisted with editing the paper. Devon Aganga is the Assistant ECMO Director, pediatric ECMO director, and assisted with editing this paper.