Which is NOT a circuit emergency that can occur on ECMO?

Pneumothorax is not considered a circuit emergency in the context of ECMO management. While it is a serious condition that requires immediate intervention, it is typically related to complications of central venous access or mechanical ventilation rather than a direct failure or issue with the ECMO circuit itself.

In contrast, circuit air embolism poses a direct threat to patient safety during ECMO as it can lead to significant complications, including stroke or organ dysfunction. Cardiac arrest during veno-venous (VV) ECMO is also a potential circuit emergency, as it may require urgent interventions to stabilize the patient and maintain the ECMO circuit's functionality. Additionally, pump failure can lead to inadequate blood flow and oxygenation, necessitating immediate troubleshooting to restore proper circuit function. Thus, pneumothorax, while critical, does not directly stem from issues with the ECMO circuit, distinguishing it from the other options presented.