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separated from CPB and was immediately transitioned to venoarterial ECMO as native pulmonary function was deemed insufficient .
Discussion
Our perfusion team has written policies and procedures that are regularly reviewed and updated . Emergency drills are practiced and discussed in groups of 2 – 6 perfusionists at least every four months , with participation documented in departmental files . Additionally , annual multidisciplinary team training drills incorporate CPB emergencies , including oxygenator failure . This culture of actively training in different settings helps ensure optimal outcomes when this low-frequency , high-risk emergency presents during clinical practice .
A debrief was held after the recent oxygenator failure incident . The arterial piggyback technique worked during the most recent case of failure but would have limitations for other cases , given patient flow requirements relative to the device ’ s maximal flow . The arterial piggyback method creates a dependent and inverse relationship between patient flow and PaO 2 . Increasing the systemic flow decreases secondary oxygenator flow , and thus the achievable PaO 2 , if working at the limit of the manufacturer ’ s rated flow . This may not be of clinical relevance if the patient ’ sbloodflow is on the low end of an oxygenator device ’ s overall flow rating . This dependency is of clinical concern if the patient ’ s blood flow requirement during support is near a device ’ s overall maximal blood flow rating sincetheremaybeinsufficient capacity for secondary oxygenator flow to increase the PaO 2 . Again , this concern would be important if working at the limit of an oxygenator ’ s manufacturer-defined maximum flow rating , which may be linked to the integrated ALF flow efficiency .
The dependent relationship between the primary and secondary oxygenator during an arterial piggyback had the perfusion team consider a venous piggyback method ( venousassisted oxygenation ) as a better alternative to the arterial piggyback method for future cases . We believe that the venous piggyback technique of sourcing blood from the venous limb of the circuit is preferable to the other piggyback techniques . Here , blood is sourced from the venous limb , run through a secondary oxygenator , and then back to the primary CVR . Preoxygenating the venous blood in this way occurs without dependency on the overall systemic blood flow , as with the arterial piggyback technique and , to some degree , the venous piggyback technique which sources blood from the pre-oxygenator boot line . Oxygenation support and pump flow to the patient are independent considerations . Of course , the heart-lung machine needs a secondary roller head pump dedicated to this task , and bloodsourcing capacity from the venous line would need to be sufficient to support the desired flow rate to the secondary oxygenator . A stopcock on the venous limb of the circuit is nearly universal . A pump head pulling off the venous line may not be common in perfusion practices , but ours allows for it in all cases . We can utilize active ultrafiltration with a dedicated mini-pump head on all circuit sizes , sourcing blood from the venous line through a high-flow stopcock , running it through a hemoconcentrator , and then returning it to the CVR , as shown in Figure 2 .
Our practice also utilizes pre-bypass , conventional , and modified venoarterial ultrafiltration on most neonates , infants , and children under 25 kg using the same mini pump head [ 17 – 19 ]. A schematic of the circuit setup is shown in Figure 2 , with a bird ’ s-eye view picture of our standard circuit arrangement depicted in Figure 3 . Venous-assisted oxygenation using a secondary oxygenator sourcing blood through the venous limb stopcock is thus easily implemented in our practice . While the venous piggyback technique had not been part of our policy and procedure manual prior to the most recent incident , it has since been added to our intervention algorithm , per Figure 4 .
Upon reviewing the literature , we found that Boettcher et al ., reported in 2017 that they used a similar technique as a temporizing measure during oxygenator failure in pediatric patients [ 20 ]. That team experienced five oxygenator failure incidents over a four-year span . A venous piggyback technique sourcing blood from the venous limb allowed them to avoid an oxygenator change-out and interruption of surgical progress in all cases . Subsequently , they included an addendum stating that two oxygenator failures in adult patients were successfully treated with the inclusion of a pediatric oxygenator cut into their standard 1 = 4 00 arteriovenous bridge line .
Secondary oxygenator flow capacity for a venous piggyback technique was an important qualification our team had been considering . Specifically , how do we ensure sufficient flow to the secondary device since flow through a stopcock can be limiting ? We do not have an arteriovenous bridge in our selection of circuits like the Boettcher group . In our practice , one solution would be to replace the active ultrafiltration-sourcing stopcock ( pre-bypass , conventional , and modified ultrafiltration techniques ) with a Y-connection as a circuit standard as shown in Figure 5 . We believe this simple circuit modification would allow for ample venous assisted oxygenation and afford time and safety to the clinical team to decide on interventions . This method for venous piggyback oxygenation may even obviate the need for an oxygenator change-out if PaO 2 support was the original concern .
Figure 5 also depicts the replacement of the hemoconcentrator with a secondary oxygenator for illustrative purposes . Certainly , if a team builds their circuits with sufficient auxiliary venous flow access ( i . e ., a venous Y-connector for active ultrafiltration techniques instead of a stopcock ), removing the hemoconcentrator would not be necessary . In fact , our standard circuit with active ultrafiltration includes an option for traditional passive ultrafiltration during CPB , which would not interfere with the flow path for a venous piggyback technique if the need arose . Passive ultrafiltration could continue as needed , with the active ultrafiltration head providing secondary oxygenator flow without the need to separate from bypass .
Considering our recent experience and discussion at our multidisciplinary clinical practice meeting , we have updated our oxygenator failure intervention algorithm , as shown in Figure 4 . An oxygenator change-out procedure may be a rare occurrence , but when it does occur during CPB , teams must be exceptionally prepared . A cautionary tale by Moore et al ., in 2002 made this point well in their report , highlighting the need to perform two oxygenator change-out procedures during the same bypass case [ 21 ]! We believe perfusion teams should revisit their oxygenator failure intervention options since