Could a Non-Rebreathing Mask or Simple Mask Be Used to Deliver Inhaled Nitric Oxide During Cardiac Catheterization Vasodilator Challenges

Background:

Inhaled nitric oxide (INO) is commonly used during cardiac catheterization to help diagnose whether pulmonary hypertension is fixed or reactive to vasodilators. We have typically delivered nitric oxide in this setting via a non-rebreathing mask connected to the bagger blender with a sample line monitoring the dose delivers. The manufacturer does not recommend this. However the manufacturers recommendation is to use a fairly complex circuit with multiple parts and connectors. This somewhat takes away the time benefit of using INO in this setting. The risk of using the non-rebreather in this setting is the potential for the build up of nitrogen dioxide in the reservoir bag. We decided to test whether NO₂ buildup occurs at the dose and flow that we use in our cardiac cath lab, via non-rebreathing mask and simple mask.

Methods:

The Inomax DSIR plus was used to deliver the nitric oxide. The non-rebreather was connected to the bagger via a barbed sample line adapter. The simple mask was connected in the same manner. For each mask the flow was set to 14 L/min. For the non-rebreather mask, gas was sampled at the blender, inside the mask and at the bottom of the reservoir bag. For the simple mask, the gas was sampled at the adapter and inside the mask. Nitric oxide, NO₂, and oxygen were sampled at doses of 20, 40 and 60 ppm, the typical doses used during cardiac catheterization.

Results:

The measured nitrogen dioxide was less than or equal to 0.5 ppm in the simple mask. The measured nitrogen dioxide in the non-rebreather was < 0.5 ppm in the mask and in the reservoir bag at all doses except in the reservoir at 40 and 60 ppm, it measured 0.7 and 1.5 ppm respectively. It also measured 0.8 ppm at the mask of the non-rebreather.

Conclusions:

Based on the results of this bench test, there is a small risk using the non-rebreather at higher doses given that the NO₂ was much higher in the reservoir bag. This could become more problematic is the clinician accidentally used too low of a flow. We recommend changing our practice to using a simple mask to reduce the risk of NO₂ build up in the reservoir bag. More tests should be performed at different flows.

Measured Nitrogen Dioxide