Infection Prevention

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The True Value of Chemical Indicators


Dan Mayworm

Question: My OR manager insists that we place an internal chemical indicator in every pack, regardless of the type of package or the contents. I contend this is a waste of time and money, as an internal indicator is not a guarantee of sterility, nor does it guarantee that we did our job properly. Who is right?

Answer: You are right on both counts. Indiscriminate use of internal indicators is a waste of time and money and will often give a false sense of security to those who do not understand how monitors should be used (see "How to Monitor Your Steam Sterilizer," November 2000). Nevertheless, the proper use of chemical indicators is an important part of a complete sterilization monitoring system.

Internal chemical indicators will change color in the presence of steam. When internal indicators don't change color, you can deduce these three things:

  • There was no steam where the indicator was.
  • There was air where the indicator was.
  • Therefore, no sterilization could take place.

Dan Mayworm

When asked why they use internal indicators, most OR nurses will say they are looking for the presence of steam, but you should be looking for the absence of steam (air). This brings us to our first lesson: Only place indicators in a package where air can be trapped.

Where air can be trapped
Figure 1 is a schematic of typical surgical packs. The upper left is a basin set placed flat on the cart. Note that in a gravity system this would let air compress at the bottom of the basin, preventing contact with steam. If you were to simply toss an internal indicator on the top of the set (Fig.2), it would change color even though the pack was not sterile. Similarly, in the next illustration in Figure 1, if the basin set had been placed upside down, it would still trap air in the bottom of the pans. The correct placement of an internal indicator in a basin set to be gravity steam sterilized would be in the towels placed in the bottom of the pans to keep them separated.

You were probably taught that the correct way to place a basin set on a sterilizer cart was on edge, so that any air and liquid condensate would be drained out of the set. This holds true for gravity sterilization only. In vacuum sterilization, the air would be vacuumed out and not trapped by the downward displacement steam. Only the moisture would be trapped in the first illustration in Figure 1, but not in the second. Therefore, where is the value in placing an internal indicator in a basin set that is going to be vacuum steam sterilized?

The upper right illustration is a linen pack. You were probably taught that the proper placement of an internal indicator was the center of the pack. That is true only if the density of the pack is uniform throughout the pack. A typical OR major pack will have linens of a variety of densities. You should check your packs to see if the geometric center of the pack is the correct place for an internal indicator.

When Using Internal Indicators

Start with the end in mind when using internal indicators. Ask yourself, "What am I looking for?" If you're looking for packs that are too tightly placed together, place packs together too tightly intentionally and run a test. If you're looking for where air can be trapped in an instrument set, place a lot of indicators throughout your sets, run an aborted cycle, then see if the indiccators inside the sets tell you anything different that the indicators outside the pack tell you.

Placement is critical
Simply tossing an indicator anywhere into a pack has little or no value. Remember that an indicator can determine if steam is present only in the one-quarter inch square where you place the indicator. It can't tell you anything about steam or trapped air anywhere else in the pack. Once you determine where in your packs is the most likely place to trap air, you have to make up your packs the same way every time or the tests will be of no value.

The lower left illustration in Figure 1 is a gusseted paper/plastic peel pouch placed flat on the cart, paper side down. Note that as in the basin set, air can be trapped only up against the plastic side of the pouch, and only in a gravity sterilizer. An indicator placed inside the pouch would fall to the paper side and change even though air was trapped in the pouch. If you place pouches on edge in a basket, loose enough that air can circulate between the pouches, internal indicators would still fall against the paper side where air cannot be trapped.

The lower right illustration in Figure 1 is a mesh bottom instrument tray that must be placed flat on the cart (not on its end). Over the years I have tried every way possible to trap air in a mesh bottom tray, to no avail. If it is a perforated bottom tray, it is conceivable that the corners of the tray could trap air but that is highly unlikely. So, where should you place an internal indicator in your instrument trays?

Some years ago, I ran a test of all the chemical indicators that were then on the market. Color changes occurred in as little as 30 seconds in a 270oF sterilizer. This test showed that to get ink to change a specific color as a function of time and temperature is very difficult. Variables such as age, moisture content and pigment concentration all affect the density of the color. The important thing to note is that they all changed in the presence of steam, so they did indicate that there was no air. And that is what they are supposed to do. Do not rely on any chemical indicator to tell you time at temperature unless the supplier can back up their claims with independent documentation.

A sacred cow
An Infection Control Nurse recently posted a question on the APIC-list concerning various internal chemical indicator (ICI) practices. She received 44 responses, including the following results:

  • Six respondents did not use any internal chemical indicators.
  • One hospital used only a daily chemical integrator pack, but no ICIs.
  • Two hospital/clinic systems used ICIs in packs only.
  • Four hospitals used integrators in each pack or an integrator pack in each load and an ICI in every pack.

The reasons given for their policies were varied, but no facility had validated its policy with documented tests. So, as you can see, this practice of putting an internal indicator in every pack is another one of those "sacred cows" that needs critical examination.

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