ECMO in patients with circulatory arrest
Deep hypothermic circulatory arrest (DHCA) is a technique utilised during procedures requiring circulatory arrest such as surgery involving the aortic arch for the purpose of organ protection, specifically for cerebral protection, as hypothermia inhibits injury-inducing ischaemic pathways driven by hypoxia24-26. DHCA utilises CPB to maintain perfusion to the rest of the body during the procedure but the need for prolonged CPB comes with its own complications such as coagulopathy and failure to wean from CPB, thereby requiring ECMO for circulatory support.
There is little to no evidence on ECMO use following DHCA in adult patients but there are a few studies that have looked at outcomes in paediatric patients who required ECMO following DHCA as part of the Norwood procedure used for surgical treatment of cardiac defects characterised by the presence of shunted single-right ventricle circulation such as hypoplastic left heart syndrome (HLHS)27-29. Analysis of 549 patients with single-right ventricle anomalies enrolled in the Pediatric Heart Network Single Ventricle Reconstruction trial found that post-operative ECMO requirement was a significant indicator for increased 30-day mortality (OR 4.38; 95% CI 1.76-10.90; P =0.002) and for hospital mortality (Hazard ratio 3.41; 95% CI 1.94-5.98;P <0.001)27. The study was carried out across paediatric cardiac surgery centres with a large volume of cases annually meaning these findings cannot be generalised to centres with smaller case volumes. However, similar results were shown in a retrospective study analysing risk factors for 1-year mortality in 158 patients that underwent the Norwood procedure which demonstrated that ECMO or VAD support was associated with increased risk of death (OR 17.8; 95% CI 4.4-71.0; P< 0.001)28.
Further separate analysis of subjects enrolled in the Single Ventricle Reconstruction trial of 461 patients discharged home after undergoing the Norwood procedure showed that 66 of them (14.3%) developed heart failure, with 15 of these dying from the heart failure whilst 39 were listed for transplant29. The study found that need for ECMO post-operatively, among other factors, was significantly associated with increased risk of developing heart failure within a year post-Norwood procedure (Hazard ratio 5.83; 95% CI 1.75-19.46;P =0.004) when compared to those not requiring extracorporeal support. Outcomes for ECMO instituted following DHCA are summarised in Table 5.
The little data that does exist on ECMO following DHCA suggests that those patients requiring post-operative ECMO had an increased mortality both in hospital and following hospital discharge; though mortality for PCCS without MCS would be far worse. However, there are very few studies that have been carried out meaning it may not be appropriate to generalise these findings to other populations. The gap in research in this area suggests the need for more to be carried out to see if there is a survival benefit associated with use of ECMO in patients who have undergone DHCA.