Do Your Cleaning Processes Have a Sweet Spot?

Some of you have experienced my sterile processing department (SPD) song parodies at conferences. Here’s the latest, with homage and apologies to the late, great Sam Cooke:

It was cold in the wash phase,

The enzymes could not get a start.

It was too hot in the wash phase,

Their biochemistry fell apart.

Well my friends, just like me and you,

Too cold, too hot, you’re gonna be blue.

Yes indeed, enzymes are people, too.

I’ll be recording this one of these days. But for now, the lesson is there in the lyrics: enzymes work best in a certain, limited temperature range. But why?

Biological systems

Enzymes are biological systems. This means that their activity, in our case, the rate of breakdown of biological soil on instruments, doubles every time the temperature is increased by 10°C.

So, let’s crank up the temperature! The enzymes will clean that much faster. After all, the enzymes need to be warm, warmer, hot to be effective cleaners. Not so fast.

Enzymes have a specific range of temperature in which they work well. Too cold means less or no activity. Too hot and the enzymes start to denature (fall apart). This is shown in the graph here.

Enzymes work by fitting a target molecule into a matching shape in the enzyme where the molecule is held so it can be broken down. Let’s call this area the “chop shop” to be biologically inaccurate, but as clear as

graph showing optimum temperature for enzyme reaction

possible as to what happens in it. If the enzyme denatures, the shape of the holding area in the enzyme changes and the target molecule no longer fits. If it doesn’t fit, it can’t be broken down by the enzyme.

Picky eaters

Enzymes break down certain items well, and others not at all. Typical enzymes found in enzyme detergents for medical device applications are:

  • Proteases, which break down proteins like blood fibrin, as well as muscle and other tissue residues
  • Lipases, which break down fats and oils
  • α-amylases, which break down carbohydrates, starches, and sugars

Proteases have little-to-no effect on fats, oils, carbohydrates, starches, and sugars. Lipases have little-to-no effect on proteins, carbohydrates, starches, and sugars. And α-amylases have little-to-no effect on proteins, fats, and oils. Enzymes are very picky eaters. So, what happens if you change the nature of the soil that you want the enzymes to break down? They don’t know how to attack it and they won’t effectively break it down. How do you change the nature of the soil that the enzymes are supposed to break down? Heat it up too high.

What happens to the soil in a washer load as you raise the temperature?

  • Get above about 95°F/35°C and blood clots
  • Get much above about 120°F/50°C and biological molecules like proteins (patient soil) begin to denature

Suddenly, the picky eaters that are enzymes don’t like what they are presented with to break down and don’t know how to eat them. If you heat up a target molecule, it changes. Clotted blood is not the same as blood. Proteins, fats, or carbohydrates are not the same when they are denatured as they were when they were in their original form. As the enzymes change in shape with higher temperature, the target molecules that make up the soil also change in shape. Even if the enzymes don’t change because of the increased temperature (they do, but let’s look at one effect at a time), the soil molecules do, and they don’t fit in the enzymes’ chop shops anymore. So, the enzymes can’t do their job.

Temperature compromise

Because of this, cleaning processes must run at a temperature that is a compromise between the need for speed (higher temperature) and the need to avoid denaturation (shape change) of the soil molecules and the enzymes (not too hot).

The manufacturers of enzyme detergents (most of them) know about the need for this compromise and have tested their detergents at different temperatures. This is how they come up with the range of temperatures over which the detergent will be effective. These temperatures are in the detergent IFU. If they are not in the detergent IFU, ask. If you don’t get a clear answer, use a different manufacturer’s detergent.

But this isn’t the whole story. In many cases, especially in manual soaking, but also on many washer-disinfectors and ultrasonics, you can set the temperature of the enzyme cleaning phase. If you can set the temperature, and if you want to find the temperature for the best cleaning, you can do a study using cleaning indicators to see what the effect is on cleaning by using enzyme detergents at different temperatures.

Comparison testing

To make sure that you can see the effect of temperature, you’ll want to run a shortened cycle so you don’t get the indicator completely clean. What? Why? Because if it’s completely clean, you can’t see if the process did a better or worse job at cleaning it. When you are done with the comparison testing, change the cycle phase length back to where it was. You should have clean indicators with a safety margin beyond just making it over the cleaning finish line.

What about the load and the soil (okay, bioburden)? Different procedures leave different soil behind. Some procedures are bloody. Some result in a lot of fats (liposuction, procedures on fatty areas). You want to make sure that both the detergent and the cleaning procedure you are using respect that aspect of the load. If it’s bloody, a nice, cold water soak is a great way to start by getting rid of the hemoglobin. If it’s fatty, the lipase has to be given enough time to do its job (at the right temperature).

Unlike steam sterilization, cleaning is a multidimensional problem with a lot of factors that must be taken into account. If you take them into account, you can build a robust cleaning procedure that removes the soils from the instruments in ways that are best for the soils at hand. This will give you the best cleaning performance and the greatest margin of safety for avoiding recleaning and potential infection of staff from soiled instruments on the clean side, and most importantly, improve patient safety.

As Goldilocks taught us, we want the bowl of porridge that isn’t too cold or too hot. We want the one that is just right.