Incidence of Methemoglobinemia in Cardiothoracic Surgery ICU Patients on Inhaled Nitric Oxide

Inhaled nitric oxide (iNO) is a selective pulmonary vasodilator utilized for the treatment of right ventricular dysfunction in the cardiac surgery patient population, which carries a risk of developing methemoglobinemia. The actual frequency of methemoglobinemia is not well defined.

The purpose of this study was to evaluate the incidence of methemoglobinemia in a cardiothoracic surgery intensive care unit (ICU) patient population.

This was a single-center, retrospective cohort study of 208 cardiothoracic surgery ICU patients who received at least 24 hours of iNO between July 1, 2020 and July 1, 2022. Patients were excluded if they did not have methemoglobin levels collected, received less than 24 hours of iNO therapy, or had documented use of other inhaled vasodilatory therapy during the same admission.

A total of 208 patients were included. Zero patients in this study developed methemoglobinemia. The median duration of iNO therapy was 4 (interquartile range [IQR] = 2.4 to 6.5) days, and the median dose of iNO was 20 (IQR = 20-40) ppm. The median number of methemoglobin levels collected was 3 (IQR = 2-5), with a median methemoglobin level of 1.3% (IQR = 0.9%-1.7 %).

Our findings suggest that treatment with iNO in adult cardiothoracic surgery ICU patients has a low risk of developing methemoglobinemia. In addition, the outcomes collected provide information regarding iNO use, adverse events, and health care resource use in clinical practice. Routine monitoring of methemoglobin levels may not be necessary for this patient population. Further research is needed to assess the true risk of methemoglobinemia and to establish the appropriate frequency of monitoring in this group.