**2. Perioperative role and indications of ECLS in PEA**

The mechanism of PH in CTEPH is multifactorial: the first step is due to the fibrotic organization of acute emboli that chronically occlude proximal pulmonary arteries (main, lobar, and segmental), the second step is the redistribution of blood flow and increase of shear stress in nonoccluded segments. Then micro-vasculopathy (affecting muscular pulmonary arteries, capillaries, and veins) progressively induces the increase in PVR, onset of symptoms, and, at last, RV dysfunction and failure [4, 5].

Timely diagnosis and treatment prevent from worsening of PH and reduce perioperative morbidity and mortality because a more compromised hemodynamic status is at higher risk of perioperative need for ECLS [9].

Basically, there are three main indications for ECLS:


Patients could require ECLS with three different therapeutical approaches or strategies:

• Bridge to surgery: the target is hemodynamic stabilization in patients with preoperative acute severe cardiorespiratory decompensation;

*The Role of Extracorporeal Membrane Oxygenation Support after Pulmonary… DOI: http://dx.doi.org/10.5772/intechopen.108472*


The vast majority of patients are referred in stable conditions with long-standing symptoms but, in a few cases, such as in acute-on-chronic PE or massive main trunk involvement, patients could rapidly deteriorate with respiratory failure and/or cardiogenic shock due to RV failure: in these cases, PEA should not be further deferred, but ECLS could be the only chance of preoperative stabilization, especially in non-expert centers, allowing urgent PEA as next step [9, 12].

In stable patients, an appropriate preoperative evaluation allows the risk stratification of postoperative heart and lung failure: many clinical features may represent a red flag, and surgeons should forecast and plan the appropriate strategy, including ECLS and, even, organ transplantation [9, 11].

The anatomical location of thromboembolic lesions, assessed with multimodal imaging, is extremely important: distal lesions are not a contraindication, but they make surgery technically demanding, also in expert hands. High PVR increases the risk of an unsuccessful procedure and persistent residual PH, especially in case of unfavorable anatomy [9, 13].

However, distal lesions and high PVR alone must not be considered formal contraindications for surgery. In many series, patients with a need for ECLS often demonstrated preoperative high PVR and previous signs and symptoms of RV failure [9, 11, 13–15].

Regardless of the preoperative clinical profile, PEA patients are prone to specific severe complications tightly linked to surgical trauma, such as reperfusion edema/ injury, bronchial or parenchymal bleeding, residual pulmonary hypertension, and RV failure.

As originally described by Jamieson, PEA consists of a "true endarterectomy": the surgeon must identify a subintimal cleavage plane in order to be radical, removing entirely the fibrotic tissue from main trunk to subsegmental arteries. It is important to inspect and free all the pulmonary vascular segments: it has been demonstrated that hemodynamic improvement and prognosis are proportional to number of reopened segments [16, 17].

On the other side, good surgical results could be burdened by extensive parenchymal edema due to a large re-perfused territory. Reperfusion edema occurs in up to 20% of cases and, probably, it is the most common complication after PEA. The pathogenesis is not completely explained but it is due to a dysfunction of capillaryalveolar membrane at the level of previously occluded territories. Different degrees of reperfusion edema can be managed with a stepwise approach: in uncomplicated initial stages, optimization of mechanical ventilatory support and maximization of diuretic therapy should be adequate. However, in complicated cases, with massive lung involvement and refractory respiratory failure, bridge-to-recovery ECLS is often necessary [10, 14].

Another technical challenge of PEA is to carry out the endarterectomy not too deep, avoiding transmural lesions that can cause parenchymal bleeding: it is a rare, but life-threatening complication, with a prevalence between 0.5 and 2% of cases. Technical problems, the fragility of the endarterectomies wall and the presence of parenchymal infarcted areas may contribute to hemorrhagic complications after

reperfusion [18, 19]. Precautionary measures include a careful endarterectomy and proper pulmonary venting during reperfusion/rewarming period. Moreover, an intraoperative double check is routinely performed, first with the "bubble technique" during gentle ventilation and then with bronchoscopy during re-warming, once a normal core temperature is reached. Typically, bleeding starts just after weaning from CPB, because of the increase in pulmonary pressure. If bleeding is mild, complete re-coagulation could be sufficient. In case of severe parenchymal or endobronchial hemorrhage, ECLS with bridge-to-recovery strategy represents a life-saving tool, associated with mechanical and/or pharmacological local hemostasis and optimal reversal of post-CPB coagulopathy [19, 20].

Residual PH after PEA ranges from 8.2% to 44.5% [21]. It is due to microvasculopathy, incomplete revascularization of pulmonary vascular tree or both; predictors of residual PH have been reported: high preoperative PVR, distal surgical material, and associated medical conditions (splenectomy, ventriculoatrial shunt, permanent central intravenous lines, inflammatory bowel disease, and osteomyelitis). Unsuccessful procedures with persistent PH in addition to surgical trauma (long CPB time, DHCA, reperfusion lung injury) can lead to an RV overload and failure requiring ECLS [10, 22, 23].

In summary, clinical indications for ECLS can be divided into different groups:

