Theoretically, OLV has several detrimental effects in patients with Fontan circulation. The physiological changes associated with OLV, such as hypercarbia, hypoxia, and hypoxic pulmonary vasoconstriction (HPV), disturb the blood flow to the pulmonary circulation through elevation of the PVR [7, 8, 11, 12]. Moreover, the rise in the intrathoracic pressure due to the high positive pressure ventilation during OLV also potentially interferes with the systemic venous return in patients with Fontan circulation . In previous case reports, OLV indeed resulted in the disruption of Fontan circulation, manifesting as severe hypotension, elevated CVP, and elevated PVR, necessitating the use of vasopressors and inotropes [9, 10].
Contrary to these precedents, however, we did not encounter any major difficulties in the management of OLV in this patient. Given the limited number of available reports [9, 10, 13], it remains difficult to predict in which patients with Fontan circulation OLV would carry a higher risk of hemodynamic instability.
In the previous cases of OLV-induced hemodynamic derangements, the patients had severely failing Fontan circulation, manifesting as circulatory shock complicated by the presence of refractory atrial fibrillation and severe protein-losing enteropathy , or pre-existing oxygen desaturation . Although the presently reported patient showed early signs of failing Fontan circulation preoperatively, she had not yet developed severe circulatory collapse or other Fontan-associated late comorbidities. In addition, as failing Fontan circulation can be characterized by an increased PVR , the relatively low preoperative PVR value, as well as the low BNP and the CVP that was equivalent to that immediately after TCPC conversion, may have indicated the existence of some reserve capacity in her Fontan circulation. Although further studies are mandatory, the presence of a reserve capacity in the Fontan circulation may partly determine the ability to tolerate OLV-induced hemodynamic derangements.
Second, the presence of the hemidiaphragmatic paralysis could have conferred a unique condition with respect to the impact of OLV on hemodynamics in Fontan circulation. In the presence of hemidiaphragmatic paralysis, HPV may have already been established to some extent preoperatively, owing to the reduced ipsilateral lung volume. This possibility is supported by the preoperative PA angiogram, which clearly showed a marked reduction of the blood flow to the left PA and compensatory increase of the right PA flow. Thus, the impact of further HPV induced by OLV on the re-distribution of the pulmonary blood flow may have been limited to be minimal.
The positioning of the patient during surgery also requires special considerations for the maintenance of Fontan circulation. Although the gravitational blood shift to the dependent lung during the lateral decubitus position would be favorable in terms of V/Q matching during OLV, this would also cause a further volume overload to the vasculature in the dependent lung. In addition, the lateral decubitus position is often associated with the development of atelectasis in the dependent lung, which can deleteriously increase the shunt fraction and PVR. Therefore, as we applied PEEP in the current case, strategies to prevent atelectasis during OLV are also important.
If the risk of hemodynamic derangement is estimated to be high, transabdominal approach for diaphragm plication can be a preferred option to circumvent OLV . Care must be taken that a high degree of intra-thoracic adhesion due to repeated operations may complicate the procedure.
Taken together, our experience suggests that OLV can be safely implemented in patients with hemidiaphragmatic paralysis with preserved Fontan circulation. Thorough preoperative evaluation of the pulmonary blood flow pattern may provide useful information for estimating the impact of OLV on the hemodynamics in patients with Fontan circulation. Nevertheless, OLV in patients with Fontan circulation remains challenging and requires meticulous preoperative evaluation, preparation, and perioperative monitoring. Further accumulation of experience and integration of information are needed to establish the safe management of OLV in patients with Fontan circulation.