Description of The Surgery
A PTE has significant risk; mortality for the operation is typically 5%, but less in centers with high volume and experience. PTEs are risky because of what is done and how it is done. PTEs involve a full cardiopulmonary bypass (CPB), deep hypothermia and full cardiac arrest, with the critical procedure carried out in a standstill operation. The reason for the complexity of procedure comes from the anatomy. The obvious part is that a pulmonary bypass is required. Surgeons cannot operate on something they cannot see; the blood going to the lungs has to be diverted from the pulmonary vasculature and lung function taken care of by a machine. Less obvious is that hypothermia is required. This goes back to the pathophysiology of emboli; they are organized, somewhat delicate, essentially part of the vessel wall, and hard to remove completely, unlike in an acute pulmonary embolectomy (for acute pulmonary embolism, which is done without hypothermia). Making this task more difficult is the anatomy of the lung and pathophysiology of chronic thromboembolic pulmonary hypertension (CTEPH); lungs also get blood from the bronchial arteries are often enlarged. The practical implication is that a conventional cardiopulmonary bypass (CPB) is not sufficient to do the surgery because
- too much blood would be in the surgical field and
- the delicate thrombi would be difficult to remove completely.
The solution is a full cardiac arrest, which can be done with hypothermia. So, after going on to CPB and they induce a deep hypothermia (18-20 degrees Celsius), to preserve the patient's brain. Once the patient is cooled off sufficiently the CPB machine is turned off and the surgeon has time to do the delicate work, which takes about 40 minutes, and consists of carefully removing the organized thrombus. The most challenging part of the surgery is finding the optimal plane to dissect the pulmonary artery. If the surgeon dissects too deeply into the vessel wall the pulmonary vessels may rupture. If the surgeon does not dissect deep enough the clot breaks proximally during extraction and the distal part of the pulmonary vasculture will not have its pulmonary blood flow restored. The right lung is typically done first. At the end an almost beautiful negative of the pulmonary arteries exists—as the emboli over time fill the larger vessels that feed the smaller occluded vessel.. It is not uncommon that collectively this negative almost represents the whole pulmonary tree—the only part missing being what the person was living off before the surgery. Bypass time is typically 345 minutes.
Read more about this topic: Pulmonary Thromboendarterectomy
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