On white blood cells, chrome-plated instruments, density ceilings and UV light - CS Questions & Answers

Healthcare Purchasing News, Dec, 2002

Ray Taurasi

Editor's Note: CS Questions, CS Answers is a feature of Healthcare Purchasing News in which we offer practical solutions to questions and problems that are common to many central service and sterile processing departments. HPN welcomes your participation in this interactive feature. To ask a question, e-mail it to cwerner@nelsonpub.com, phone it in to Curt Werner, HPN editor, at (941) 966-9521, or mail it to HPN CS Questions, 2500 Tamiami Trail North, Nokomis, FL 34275. Names and hospital identification will be withheld upon request.

CS Question: I always thought that the body's immune system produced white blood cells to defend and rid the system of infections. I recently was reading an article that referred to T cells as the body's major defense against infectious agents. Would you clarify this?

CS Answer: You are correct. In a healthy person, the hod/s immune system will produce more white blood cells to combat pathogenic organisms that have invaded the body. There are many types of white blood cells. Lymphocytes are one type of white blood cells, and two major classes of lymphocytes are T cells and B cells. T cells are critical immune system cells that help to destroy infected cells and coordinate the overall immune response. The T cell has a molecule on its surface called the T cell receptor. This receptor interacts with molecules called MHC (major histocompatibility complex). MHC molecules are on the surfaces of most other cells of the body and help T cells recognize antigen fragments. B cells are best known for making antibodies. An antibody binds to an antigen and marks the antigen for destruction by other immune system cells.

Other types of white blood cells are macrophages and neutrophils. Macrophages and neutrophils circulate in the blood and survey the body for foreign substances. When they find foreign antigens such as bacteria, they engulf and destroy them. Macrophages and neutrophils destroy foreign antigens by making toxic molecules such as reactive oxygen intermediate molecules. If production of these toxic molecules continues unchecked, not only are the foreign antigens destroyed, but tissues surrounding the macrophages and neutrophils are also destroyed. This results in conditions known as autoimmune diseases.

CS Question: Why does some literature state that chrome-plated instruments should not be cleaned in an ultrasonic washer? We frequently run such instruments through our ultrasonic and have wonderful results.

CS Answer: All cleaning processes require some form of mechanical action or friction to dislodge and remove soil. In manual washing, the mechanical action is scrubbing; in automated instrument washers or decontaminators, mechanical action is accomplished by agitation, forced water circulation through spray arms or water jets. The mechanical action in ultrasonic washers is known as cavitation. Sound waves are emitted through the water, which causes cavitation, which is the formation and collapse of low-pressure bubbles in the water. The bubbles implode (burst inward) and dislodge or virtually tear soil from instruments.

Chrome-plated instrumentation that may have minor scratches on the surface may easily have plating ripped off by the cavitation. Undetected chips in plating on surgical instruments can cause trauma and damage to tissue and internal organs during surgery. Sharp edges on lifted chrome may be hazardous to the surgical team and may cause contamination through tearing or puncturing sterile gloves. Once the chrome plating is removed from an instrument, it is likely to cause rusting and staining not only to that instrument but also to any others processed along with it. For these reasons chrome-plated instruments should never be processed through an ultrasonic washer.

CS Question: How can one be certain that an instrument pack doesn't exceed the maximum density of 72 pounds?

CS Answer: The 7.2-pound density ceiling applies to linen packs only. It is not used as a parameter for instrument sets. The density of a linen pack may be determined by calculating the cubic inches of the pack. This number is then divided by 1,728 and equals the cubic feet of the pack. The weight of the pack divided by the cubic feet of the pack equals the density in pounds per cubic foot. The formula for calculating linen pack density is as follows:

Calculating linen pack density

1. Dimensions of pack (in inches)

/ 1.728 (number of cubic inches in a cubic foot)

= volume of pack in cubic feet

2. Weight of pack

/ cubic feet of pack

= density (pounds per cubic foot)

Example of calculation using a standard linen pack of 12" x 12" x 20" @ 12 pounds

1. 12 x 12 x 20 = volume of 2,880

2,880 + 1,728 = 1.666 cubic feet

2. 12 pounds + 1.666 cubic feet = density of 7.2 pounds per cubic foot

CS Question: What is UV lighting, and what does it have to do with sterilization?

CS Answer: UV (ultraviolet radiation) is the invisible component of the sun's radiation. Its wavelengths can range from 400 to 4,000 angstrom units. The radiation waves are effective in the destruction of microorganisms found in the air or on inanimate objects. UV light strips may be placed across entrances to isolation rooms to degerm the air. UV is not frequently used as a sterilant for inanimate objects because more effective means for sterilization are available. HPN