By: Mitch Valdmanis, Senior System Designer
If you recall, back in my first post in this series, I implied that the robot arm in RIVA doesn’t qualify as one of “the big little things.” While it’s true that the robot as a whole certainly doesn’t fit the theme of these posts, there is one critical aspect of its maneuvers that does qualify. Specifically, how the robot handles inventory to avoid cross contamination and to avoid disturbing the airflow over critical sites.
Another excuse to use this fantastic image, which highlights how robot maneuvers both avoid cross contamination and disturbing airflow over critical sites. Notice that the nearest cap to the robot (holding the syringe) has been applied to the syringe.
Conceptually, not disturbing airflow over critical sites is simple: don’t position the robot in the airflow over critical sites. In large part, the layout of the RIVA compounding chamber is responsible for this, since critical sites have been laid out so as to avoid the need to move the robot directly above them. It goes a little deeper than that, though. First, it is important to not only prevent the business end of the robot from moving over critical sites, but the entirety of the robot arm. In a confined space such as the RIVA compounding chamber this can be challenging, and care must be taken to define permissible paths along which the robot may travel.
Where things get especially tricky, though, is when the robot is required to be near a critical site. Consider the scenario depicted above: applying a syringe cap to a syringe dose to be output. Notice that the entire cap tray is exposed. The robot must always apply the cap nearest to itself so as to not move over top of the other caps.
Cross contamination concerns also affect how the robot handles inventory. In particular, syringes that have been involved in a fluid transfer must be carefully handled from the time of the fluid transfer until either a syringe cap is successfully applied, or the syringe is disposed. Any drops of drug remaining on the tip of the needle, or on the syringe luer after the needle is removed, have the potential to fall and contaminate other surfaces. While efforts are taken to avoid drops on syringe needles—potentially the subject for a future post—the possibility of drips remains. By carefully handling the syringes, we can mitigate the cross contamination risk.
In this case, careful handling means not carrying the exposed syringe or needle tip over other exposed critical sites, and ensuring that the syringe tip is oriented upwards as much as possible, so that any drips that may be present flow towards the luer, rather than towards the tip where they may fall.
As with the airflow considerations above, however, there are times when the exposed syringe tip is required to be near other critical sites. And just as with the airflow, the perfect example of this is when applying caps to dosed syringes. The same pattern of not moving the robot directly over exposed caps applies just as well to the cross contamination concern. Thus, even if a drip were to fall from the syringe as it was applying the cap, the drip would fall either onto the cap itself, or onto an empty space in the cap tray left by a previously used cap.
Once again we see where, in designing a system such as RIVA, care must be taken to ensure safety even in the most subtle of interactions. In this case, syringe capping in particular is a great example of a scenario where special consideration must be given to avoid cross contamination and disrupting the airflow. If you ever have the opportunity to observe how RIVA prepares multiple syringe doses, take note of the pattern in which caps are applied from the cap tray. I hope you now have a new appreciation for why that particular pattern is used.