The diagnostic criteria for dilatation of the pulmonary artery due to an unknown etiology established by Greene et al.  and Deshmukh et al.  have been used for the diagnosis of IDPA. In the present case, the patient had pulmonary artery dilatation of 64 mm in the pulmonary artery stem, but no medical history indicative of a potential cause. Additionally, transthoracic echocardiography did not suggest evident valvular disease or intracardiac shunting in the right ventricle system. Consequently, the patient was diagnosed with IDPA. Typically, IDPA is a condition that does not cause tissue degeneration of the pulmonary arteries. Correspondingly, it does not increase the pressure of the pulmonary arteries and right ventricle. An occurrence of idiopathic pulmonary artery dilatation is very rare, and few reports on the outcomes of the treatment strategies used for this condition exist. Therefore, there is no clear consensus on indications for surgery to treat IDPA.
On the contrary, there are some reports on dilatation of the pulmonary artery in response to particular precipitating factors : complicating pulmonary regurgitation, rapid growth of the dilated artery, which can lead to dissection and rupture of the pulmonary artery , pulmonary incompetence , and myocardial ischemia . Thus, dilatation of the pulmonary artery beyond a certain extent may be a factor influencing prognosis. Similar complications are thought to occur in patients with IDPA once the pulmonary artery exceeds the capacity of the mediastinum. Thus, surgery should be performed when dilatation reaches 6 cm or more .
In the present case, the procedure for anesthesia management in pulmonary artery replacement for IDPA did not differ substantially from other typical anesthesia management strategies in cardiovascular surgery that use CPB. However, there are two presumed disease-specific critical conditions in anesthetic management: rupture of the dilated pulmonary artery and airway compression.
Surgical injury or rupture of the pulmonary artery is the greatest concern. Particularly, rupture before ensuring CPB can rapidly result in a fatal hemorrhage. Since sternotomy is thought to confer the highest risk of damage to the pulmonary artery, understanding the degree of dilatation of the pulmonary artery and the location and position of the adjacent structures on the basis of preoperative imaging is necessary. For patients whose dilated pulmonary artery is in close proximity to the sternum, CPB via femoral cannulation should be considered to avoid damage caused by sternotomy. Furthermore, intraoperative transient elevation of pulmonary arterial pressure may lead to dissection and rupture of the pulmonary artery . However, for patients with IDPA only, previous reports have indicated that the pulmonary arterial pressure is maintained at a normal or slightly elevated level . Additionally, insertion of the PAC may cause dissection or rupture of the pulmonary artery. Kearney et al. analyzed 32,000 complications of PAC insertion over a period of 17 years; the incidence of pulmonary artery injury associated with catheterization was 3 per 10,000 cases, with a resulting mortality of 70% .
Considering these facts, it may not be worthwhile to monitor the pulmonary arterial pressure in the perioperative period for a patient with IDPA. However, in the present case, the surgeon requested PAC placement prior to surgery to monitor perioperative pulmonary arterial pressure. Kearney et al. reported the following risk factors for PAC-associated rupture of the pulmonary artery: (1) age of 60 years or more, (2) pulmonary hypertension, (3) inappropriate balloon dilatation, (4) inappropriate catheter position, (5) use of CPB, and (6) poor anticoagulation . In the present case, PAC placement was performed since it was considered to be relatively low-risk, provided the catheter was inserted appropriately. Moreover, we focused on certain important aspects in order to prevent rupture of the pulmonary artery. During mechanical ventilation, low airway pressure and mild hypocapnia were maintained to avoid raising pulmonary vascular resistance. In addition, we took care to avoid excessive transfusion, and initiated continuous infusion of dobutamine and milrinone prior to weaning the patient from extracorporeal circulation. This strategy may have allowed us to maintain the patient’s pulmonary arterial pressure within the normal range throughout the perioperative period.
Another complication is compression of the airways by the dilated pulmonary artery. Additionally, 50% of patients with pulmonary artery dilatation suffer from some form of congenital heart disease . Our patient had a Kommerell’s diverticulum, which slightly displaced the trachea. Such displacement by an aneurysm or arterial ring may occur with Kommerell’s diverticulum. Regarding induction of anesthesia, administration of a muscle relaxant and intermittent positive-pressure ventilation may change the diameters of the trachea and the bronchus that are damaged by external pressure due to aneurysms . Since not only Kommerell’s diverticulum but also dilated pulmonary arteries may affect airways, it is important to identify potential risk factors that could hinder airway management.
In conclusion, we present a case of IDPA with a Kommerell’s diverticulum treated by pulmonary artery replacement. Regarding the anesthetic management for this procedure, it is particularly important to prevent rupture of the dilated pulmonary artery and anticipate potential difficulties in airway management. A strategy for the surgical procedures and CPB management should be carefully designed, and special attention should be paid to anatomic abnormalities.