Inhaled nitric oxide reduces the intrapulmonary shunt to ameliorate severe hypoxemia after acute type A aortic dissection surgery

Abstract

Background: To assess the relationship between the intrapulmonary shunt and PaO₂/FiO₂ in severe hypoxemic patients after acute type A aortic dissection (ATAAD) surgery and to evaluate the effect of inhaled nitric oxide (iNO) on intrapulmonary shunt.

Methods: Postoperative ATAAD patients with PaO₂/FiO₂ ≤ 150 mmHg were enrolled. Intrapulmonary shunt was calculated from oxygen content of different sites (artery [CaO₂], mixed venous [CvO₂], and alveolar capillary [CcO₂]) using the Fick equation, where intrapulmonary shunt = (CcO₂-CaO₂)/(CcO₂-CvO₂). Related variables were measured at baseline (positive end expiratory pressure [PEEP] 5 cm H₂O), 30 min after increasing PEEP (PEEP 10 cm H₂O), 30 min after 5 ppm iNO therapy (PEEP 10 cm H₂O + iNO), and 30 min after decreasing PEEP (PEEP 5 cm H₂O + iNO).

Results: A total of 20 patients were enrolled between April 2019 and December 2019. Intrapulmonary shunt and PaO₂/FiO₂ were correlated in severe hypoxemic, postoperative ATAAD patients (adjusted R² = 0.467, p < 0.001). A mixed model for repeated measures revealed that iNO, rather than increasing PEEP, significantly decreased the intrapulmonary shunt (by 15% at a PEEP of 5 cm H₂O and 16% at a PEEP of 10 cm H₂O, p < 0.001 each) and increased PaO₂/FiO₂ (by 63% at a PEEP of 5 cm H₂O and 65% at a PEEP of 10 cm H₂O, p < 0.001 each). After iNO therapy, the decrement of intrapulmonary shunt and the increment of PaO₂/FiO₂ were also correlated (adjusted R² = 0.375, p < 0.001).

Conclusions: This study showed that intrapulmonary shunt and PaO₂/FiO₂ were correlated in severe hypoxemic, postoperative ATAAD patients. Furthermore, iNO, rather than increasing PEEP, significantly decreased the intrapulmonary shunt to improve severe hypoxemic conditions.

Keywords: Aortic dissection; Hypoxemia; Inhaled nitric oxide; Intrapulmonary shunt.