Bleeding is a known complication of this therapy. The most common complications of negative pressure wound therapy (NPWT) are pain, bleeding, infection, and inadvertent retention of foam dressing, which can lead to infection.
Here’s why it isn’t treated as a minor fault with the machine. Additional damage to the wound may occur, including erosion or necrosis, as well as damage to underlying structures such as blood vessels or bowel, including recent surgical connections (anastomoses). Negative pressure acts on whatever is in the wound bed, and what is in the wound bed is not always skin and foam.
That is why the assessment before a device goes on is so specific. Any exposed blood vessels, bowel, or other vulnerable structures should be identified, and where they are exposed, dressing materials and pressure settings should be modified accordingly. Before the foam is placed at all, active bleeding is controlled with electrocautery or direct pressure until it stops. Bleeding is meant to have stopped before the system starts.
What that means for you is simple enough. All active systems should be routinely monitored for proper function and for the volume and characteristics of wound drainage. Blood in the tubing is a change in the character of that drainage — which is exactly what the monitoring exists for. Report it to the team that set up the device rather than deciding at home whether the amount is enough to matter.
Two honest limits. There’s no set amount of blood that counts as too much, and no simple rule that separates a streak in the tubing from a steady flow. And stopping the machine or opening the dressing isn’t a step to take on your own. The instructions that came with your device, and the people who set it up, are the authority on both.