Massive acute pulmonary embolism (MAPE) is a rare and life-threatening condition that the cardiothoracic surgeon could face during its clinical practice. It’s usually caused by a sudden and extensive occlusion of the main pulmonary artery or of the more than 60% of its branches by a dislodged thrombus frequently embolized from legs or arms during a deep vein thrombosis or after a major trauma. MAPE usually occurs in the 4.2% of the pulmonary embolism cases (1) with a mortality rate that depends on the percentage of pulmonary vascular bed involved and hemodynamic and clinical state: it usually ranges between 1% and 36% (2,3) but it seems to reach the 70% in presence of hemodynamic instability, when more than the half of pulmonary branches are occluded (4) or if emergency cardiopulmonary bypass (CPB) is required (3,5,6). As result of the wide pulmonary occlusion, respiratory and cardiac function quickly deteriorate due to increased right ventricle (RV) pressure and reduced left ventricle preload while marked hypoxia usually occurs in the first hours after the thromboembolic event and requires endotracheal intubation. This is related to the increased alveolar death space caused by blood flow redistribution together with RV depression and ischemia. Vasopressors and phosphodiesterase inhibitors are often enough to sustain the cardiac output, but sometimes peripheral CPB is necessary to stabilize the patients. In these situations, surgical treatment still remains the gold standard technique and its timing is dictated by hemodynamic status of the patient (4,7).
First example of MAPE successful surgical treatment has been described by Cooley and colleagues in 1961 (8). Since then, the surgical technique is evolved thank to improvement in materials and to a deeper knowledge of the extracorporeal circulation physiology which made possible to avoid deep hypothermia and circulatory arrest. In order to describe our surgical technique and perioperative management of patients with MAPE, it will be presented the case of a 43-year-old Italian man who was transferred to cardiac surgery intensive care unit (CICU) due to sudden heart and respiratory failure.
Patient’s clinical history
The patient was previously hospitalized in the cardiologic intensive care unit (ICU) to treat a diffuse pulmonary embolism, clinically and radiologically confirmed. A few days before, due to fever and mild dyspnea, he went to the emergency department where, according to the chest X-ray pattern, he was treated for infective pneumonia. Clinical conditions quickly deteriorated therefore an angio-CT scan was performed. This revealed a wide and bilateral pulmonary embolism so the patient was transferred to the cardiologic ICU to start the most appropriate treatment. He was hemodynamically stable, but he presented dyspnea and cyanosis for mild efforts and no previous history of actual or recent trauma/deep vein thrombosis. No lab or clinical evidence of thrombophilic conditions was found. Therefore, continuous unfractionated heparin infusion was started at 1,250 units/h with a targeted activate partial thromboplastin time (aPTT) of at least 80 s (9,10). The patients seemed to be resistant to medical treatments, probably for unacknowledged congenital thrombophilia, and 2 days after he developed marked hypotension, dyspnea and distension of the neck veins. Echocardiogram revealed a great increase in RV pressure, a prominent “a” wave and a depressed RV function. An urgent chest angio-CT scan was performed and showed in the two lungs the subtotal occlusion of the principal pulmonary artery extended to the all lobar arteries and their segmental and subsegmental branches (Figure 1), in contrast with literature where the most reported involvement is of the lower lobes, more often in the right than the left lung (5). According to recent guidelines (9), thrombolytic treatment was started but it resulted ineffective.
Indications and preoperative management
Patient was moved to CICU because of progressive heart and respiratory failure. Endotracheal intubation was performed, and continuous vasopressors infusion was started in order to stabilize hemodynamic and to maintain arterial oxygen pressure (aPO2) at least over 60 mmHg. Once the patient was stabilized, according to the literature (10) and our institution protocol, urgent surgery was planned for the next day. Meanwhile, continuous unfractionated Heparin infusion was started in order to obtain an activated clotting time (ACT) over than 200 s and blood gases analysis was hourly performed paying particular attention to serum lactate levels and aPO2. Increase in serum lactate or decrease in aPO2 was indication to anticipate surgery. For these reasons, truly massive “acute” pulmonary embolism that undergo surgical treatment are today very rare because surgery is considered only after the failing of medical therapy. This approach, indeed, usually brings to the surgeon a “subacute” pattern that, due to the progressive thrombus stratification, requires a surgical technique much more similar to that used in chronic pulmonary embolism than the acute one.
One of the key points of the MAPE surgery is the management of the CPB, especially respect to hypothermia and circulatory arrest. Some cardiothoracic surgeons usually treat this condition using the same technique for the chronic pulmonary embolism recurring to deep hypothermia and circulatory arrest (11) but this approach usually leads to neurologic or splanchnic hypoperfusion problems. When this technique is not strictly necessary, in order to avoid these possible complications and to accelerate postoperative recovery of the patient, at our institution we established a particular surgical protocol that proved to be very effective to treat MAPE without recurring to deep hypothermia or circulatory arrest. To show the standard protocol, the above presented patient’s surgery was described.
Anaesthesiologic preparation was made using the standardized protocols for cardiac surgeries. Continuous cerebral oximetry monitoring was used in order to assess brain perfusion during the CPB but, because of deep hypothermia and circulatory arrest were not used, any cerebrospinal fluid pressure monitoring was placed. This, in addition, avoids the risks of spinal cord injuries.
Median sternotomy was performed, and pericardium was widely opened using inverted-T technique. To establish CPB, perfusion cannulas were placed into the upper ascending aorta in order to easily mobilize it and both caval veins. A left atrium vent was placed in order to decompress left ventricle and to realize a “back aspiration” during the main procedure. After total CPB was achieved, lungs were ventilated with low tidal volumes in order to reduce postoperative lung atelectasis until the cooling at 24 °C (rectal temperature) was completed. CPB was decreased until reaching perfusion flow ranging 1–1.2 L/min. This approach, together with mild hypothermia, allows to reduce pulmonary backflow at the opening of the pulmonary arteries and, simultaneously, to maintain an effective organ perfusion and a good surgical vision. Meanwhile, superior vena cava was mobilized circumferentially avoiding to divide azygos or to damage right phrenic nerve; in this way, right pulmonary artery is well visible and, through the opening of right pleural space, it can be isolated until the lobar and segmental branches. After doing this, modified Bretschneider cardioplegia was antegrade administered according to the manufacture’s protocol. The right pulmonary artery was reached by moving the upper caval vein laterally and the aorta medially using a rubber covered retractor paying attention to not damage the posterior wall of the aorta. Pulmonary artery was incised until the trifurcation distally and until 1 cm before the pulmonary trunk proximally (Figure 2). At this moment, if the thrombus is not fresh, an important key point is to find the correct endarterectomy plane because a deeper plane risks to damage the vessel wall and to cause difficulties in bleedings control. Usually, after reaching pulmonary branches, thrombus starts to be covered by platelets and fibrin that make difficult to dissect it from the vessel wall (Figure 3). As protocol, thrombus core was isolated circumferentially using a particular long-shaped dissector and removing was extended first to the upper lobe and then to the others. If blood disturbs the operative field view, a good trick can be to incline laterally the surgical table towards one or other side. After the removing is complete, arteriotomy was closed with a 6-0 polypropylene running suture or using an autologous pericardial patch. Left pulmonary artery was reached by retracting the heart up and medially, as well as in coronary bypass surgery to achieve lateral wall vessels (Figure 4). Technique was the same of the right pulmonary artery beginning from the upper and lingular branches. When thrombus removing was complete (Figure 5), deairing procedure was performed and rewarming was started. As recommended by protocol, patient was slowly weaned from CPB in order to well washout all the effects of prolonged hypothermia and ischemia. Serum lactate was always good during the CPB (CPB parameters are shown in Table 1) as well as continuous cerebral saturation. Perfusion arterial pressure was always maintained around 45 mmHg during the aortic cross clamping in order to balance organ perfusion and risk of cerebral edema; in order to increase cerebral perfusion arterial carbon dioxide pressure (PCO2) was maintained between 40–45 mmHg. CPB length was of 235 minutes, of which 143 minutes were of total CPB and 120 minutes of aortic cross clamping. Mild hypothermia allows, in addition, to not achieve extreme haemodilution: in this case patient’s haemoglobin was above 11 g/dL during all the CPB. After CPB weaning, course was uneventful.
Postoperative management of MAPE patients is usually difficult, especially due to long surgery and CPB times. In this regard, avoiding the hypothermic arrest allows to speed up postoperative recovery reducing the negative effect of hypothermia on renal and cerebral function. In the postoperative period, our protocol recommends, indeed, to slowly awake the patient and to gradually wean him from mechanical ventilation in order to allow the decreasing of the post-reperfusion related pulmonary edema and to increase the patient’s response. Infusion of prostaglandin E1 or inhaled nitric oxide (12) may be useful after the surgery especially when occurs reactive postoperative pulmonary arterial hypertension. In these cases, after recovery or at follow-up, a right heart angiographic study could be performed to assess pulmonary pressures and vascular resistances (Patient’s results are shown in Table 1).
Conclusions and comment
Surgical treatment of MAPEs without using deep hypothermia and circulatory arrest, unless this is strictly necessary, proved to be a very effective technique (13). Circulatory arrest, indeed, needs very low body temperatures (18–20 °C) and long cooling-rewarming times that significantly increase the surgical length and the risks of renal and neurological injuries; in addition, circulatory arrest cannot be maintained for more than 30 minutes without damaging tissues so the surgeon is forced to rewarm the patient, to re-perfuse the patients for a while and, then, to re-cool. This approach, therefore, leads to a significantly waste of time that can be avoided with the above described technique. Our protocol, indeed, not only can reduce surgical length but it can also speed up postoperative recovery in the ICU: shorter CPB times means lower haemodilution and decreased inflammatory response therefore it leads to a decreased risk of cerebral, lung and renal edema and a faster ICU discharge.
Provenance and Peer Review: This article was commissioned by the Guest Editors (Andrea Dell’Amore and Nizar Asadi) for the series “Mechanical Extracorporeal Cardio-Respiratory Supports in General Thoracic Surgery” published in Current Challenges in Thoracic Surgery. The article was sent for external peer review organized by the Guest Editors and the editorial office.
Conflicts of Interest: The authors have completed the ICMJE uniform disclosure form (available at http://dx.doi.org/10.21037/ccts-20-84). The series “Mechanical Extracorporeal Cardio-Respiratory Supports in General Thoracic Surgery” was commissioned by the editorial office without any funding or sponsorship. The authors have no other conflicts of interest to declare.
Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Helsinki Declaration (as revised in 2013). Written informed consent was obtained from the patient.
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Cite this article as: Pilato E, Comentale G. Surgical treatment of acute pulmonary embolism: a modified surgical technique to avoid deep hypothermia and circulatory arrest. Curr Chall Thorac Surg 2020;2:37.