Condensation in a Membrane Oxygenator Analyzed by Bronchoscopy and Ultrasonography

To elucidate the mechanism of condensation-related oxygenator dysfunction (CROD) and explore preventive strategies, we directly visualized the interior of a membrane oxygenator using bronchoscopy and ultrasonography and evaluated the effect of external warming.

The CROD model consisted of a circuit incorporating a membrane oxygenator perfused with water at 3 L/min and supplied with gas (50% O₂ in air) at 2 L/min. The hollow fiber bundle was observed bronchoscopically at the outlet surface and ultrasonographically from the lateral aspect. The percentage droplet area was quantified. In a heating model, the oxygenator was externally warmed with circulating 39°C water. Changes in droplet area, gas-supply pressure, and outlet-surface temperature were analyzed. A single experiment was conducted for each model.

In the CROD model, condensation appeared at approximately 2 h, predominantly in the cooler outer zone. The droplet area increased over time and showed a strong positive association with gas-supply pressure (r = 0.9041). Gas flushing partially reduced both parameters but did not restore baseline values. Ultrasonographic findings remained similar to those of a dry oxygenator. In the heating model, the outer zone was approximately 1°C warmer than the inner zone, and no visible condensation developed over 24 h, with stable gas pressure.

Two-directional visualization demonstrated that outlet-surface condensation, mainly in the outer zone, was associated with elevated gas-supply pressure in this mechanistic model of CROD. Uniform external heating suppressed condensation, suggesting that temperature control and early detection may represent practical strategies to mitigate CROD.