The penetration of steam in all parts of the autoclave is essential for achieving and holding sterilization time. A Bowie dick test is done to know steam penetration within the autoclave with the help of the Bowie test pack.
Although the concentrated bubble in the load may inhibit steam penetration, the presence of air pockets and non-condensable gases in the load is ensured by the bowie dick test autoclave validation.
Principle of Bowie dick test:
Principle: Chemical indicator stuck to a piece of paper in the form of adhesive tape to form an st. Andrew’s cross.
How to Perform a Test Pack?
To perform this test, Run a test for about 240 seconds, known as the bowie dick cycle. Keep folded huckaback towels at the center of the chamber Indicator and then subject them to an operating cycle in an empty chamber.
The indicator tape starts to show a change in color in response to a combination of time, temperature, and moisture. A change in the sheet color pattern was used to determine the test result. The chamber must be empty during the test, and only the Bowie Dick test pack should lie inside it.
Procedure for Autoclave Validation:
The Bowie Dick test for autoclave validation is generally preceded by a warm cycle to check the effectiveness of air removal. Air removal is essential because it may give a false result even after satisfactory sterilization.
To perform it, place the standard test pack and indicator paper on the sheet nearest the center of the pack. Place the test pack in the chamber at the center of the chamber base supports above 100-200 mm by selecting the bowie dick test cycle to ensure that the holding time will not be longer than specified.
The indicator may change if the time exceeds, in such a way as to make it difficult to detect the variations that would indicate a failed condition.
Bowie test Operation cycle:
Note down the chamber temperature and pressure reading during hold time or after the operating cycle and until the end of the cycle. Remove the indicator paper from the test pack. The test should be considered satisfactory if the following requirements are met:
- It must consistently change throughout the indicator; otherwise, it has been considered positive or failed.
- The automatic controller indicates that the Dick test cycle has just been completed.
It is essential to compare the center and corner points of the paper to see the clear difference between them. If there is any distinct difference in the test, It should be recorded as positive or failed, and the paper marked accordingly.
The indicator paper should be marked with the result and kept for reference for a few months or at least three months. The associate batch process should be kept at least for 11 years.
Common causes of Bowie dick test failure:
The failure of the bowie dick test may be due to Insufficient air removal from the chamber, air leak during the air removal stage, the presence of non-condensable gases within the steam provided, and leaks in the piping.
Bowie dick test failure Solution:
Air leak: An air leak may result in less steam penetration, so it is recommended to run a vacuum leak test at that time.
Warm-up cycle: It recommends running a warm-up cycle to reach the desired temperature in the chamber, so for this, run the sterilization cycle for 5 minutes before a run of the Bowie dick cycle.
Wrong procedure: The test pack is designed under a specific environmental condition, so make sure the test pack is placed over the drain point inside the bottom chamber.
Guidelines for the composition of the test pack:
The bowie test for autoclave validation consists of folded 100% cotton surgical towels, which are freshly launched but not ironed. The towels must be folded into a size not smaller than 9 inches ( 23 cm) in the other direction and placed one above the others.
The height of the test pack must be 10 to 11 inches (25 to 28 cm), and the weight must be 7 kg. The total number of towels may vary from test to test depending on towel thickness and wear. A commercially available bowie Dick test sheet must be placed within the center of the pack.
A single wrap made of 100% cotton 140 threads count, two-ply fabric, and freshly laundered is then loosely applied.
The innovation in Autoclave Validation.
Sterisense: it is an electronics bowie Dick test device, that provides depth information on sterilization parameters.
It can store reports and ensure all process records are in electronic documentation.
Advantage of SteriSense for bowie dick test:
- Eliminate false results or gray zone readings.
- It is easy to store and perform according to ISO 17665.
- No need to guess data, easy to compare and retrieve data from the database.
Process challenge device(PCD) may be a unique advantage of being replaceable, permitting several test cycles during a row with minimal need for cooling. Its patent is pending now.
Frequently Asked Questions (FAQ):
A leak test is performed to check the airtightness of the vacuum autoclave chamber.
A leak test is to check the airtightness integrity of the chamber and plumbing system. The frequency of autoclave leak tests should be done at least weekly in an empty chamber to ensure the airtightness of the pre-vacuum steam sterilizer. It must be performed if the Bowie Dick test fails.
DART (Daily Air Removal Test) is widely used for the Bowie Dick test. It is a light pack for fast use. So place the dart test pack on the lowest self over the drain point to remove air during the vacuum phase of the cycle through the chamber of the dart test.
Steam will enter the chemical indicator chamber during the exposure phase and then open the door to see immediate results.
If the indicator line turns black, it is good to pass the test, showing that air is removed completely. If failure, all bars will not turn black.
The Temperature must be specified to kill microorganisms, and the standard Temperature is 121 °C and 132 °C. Temperatures must be maintained to kill all forms of microorganisms.