50 years back, there was a major incident involving the manufacture of a pharmaceutical product [ 5% Dextrose, Intra Venous infusion] in Devonport near Plymouth, England. The event is remembered as “Devonport disaster”. Given the time, many working in the pharmaceutical industry have never heard about the disaster. Many died after the administration of 5% Dextrose Intra Venous infusion [Lot D1192C] sterilized in the autoclave of a transfusion unit. The graves of those are digged now as there are many lessons to learn from the graves. The investigation report is known as “Clothier report” as it was investigated by the lawyer C.M. Clothier.
The 50-year-old incident is revisited since it has brought a revolution of changes that happened later in the pharmaceutical industry to recognize the needs of the safety of the drug / injection / infusion. It also had opened the Pandora box; of the review systems, release of the batches to the market, role of QC, importance of adequate SOP and documentation. Though, precious lives were lost and they would be in eternal sleep, it served as an eye opener for the pharmaceutical industry. The incident is described briefly and the changes that has brought about in saving the lives of the patients especially in the usage of steam heat sterilizer/ autoclave.
Devonport Incident-1971
It was a normal day in the transfusion unit for the autoclave operator to sterilize a batch of 5% Dextrose, Intra Venous infusion. The lot number was D1192C. He had followed the SOP instructions of closing the drain valve when the condensate temperature recorded 115 degrees. The chart was marked at the point where the temperature achieved 115 degrees, which was the beginning of the autoclave sterilization cycle. The temperature recorder was playing up and the pen had not moved from the baseline. It was a common practice, when a recorder did not work normally to check that the steam drain and the steam trap were working correctly and then to continue the cycle based on the gauge readings on the dial thermometer on the outside of the autoclave. The operations were continued and the appropriate processing time was supposed to be 40 minutes, although examination of the batch records later was less than this. The manufacture of the lot was complete and QC sampling for testing were taken from the top shelf [easiest to reach]. After analysis, the batch of 3600 bottles were released into the market.
Next year-1972
Many died in the hospitals due to the administration of the 5% Dextrose Intra Venous infusion that were traced to the lot no. D1192C. All the died patients had Klebsiella aerogenes in their blood and lungs. The remaining stocks were traced and 35% were found to contain the same Klebsiella aerogenes upon testing with a concentration of 1.5 x104 to 2.7×106 per/ mL. It was a biggest failure in an autoclaving process for a batch of a sterile infusion fluid.
Investigation concluded that the lowest rack of bottles failed to achieve sterilization due to the block in the condensate drain, no use of vacuum line to partially remove air prior to the introduction of steam into the chamber, retention of air within the autoclave throughout the processing cycle, failure to record any temperature rise in the autoclave was ascribed to the faulty recorder and not the autoclave. In these conditions, the upper rack of bottles reached 115 degrees and the bottom rack of bottles did not attain 115 degrees. During the inspection later, it was also found that broken glass and debris were found in the drain and not cleaned often enough and inadequate maintenance records. Additionally, the batch test results, temperature data etc. were not part of the batch record and not examined as a part of product batch release. As rightly said, Medicinal products should not be the vehicles of infection.
Basics of Steam Heat Sterilizer [SHS] / autoclave and validations.
What is an Autoclave?
1.In Greek auto, ultimately meaning self, and Latin clavis meaning key – a self-locking device. Invented by Charles Chamberland in 1879.
2.Used to sterilize products and goods, Finished product, Medical Devices, Lab Supplies, Manufacturing Equipment, Packaging Equipment, Gowns. It comes in all shapes and sizes [i.e., walk-in, bench-top, pass through, etc.]
3.All have–Chamber, Steam supply, Vacuum Source and Control System.
4.Steam is used as a sterilization medium.
5.There is importance of Time and Temperature.
General design
Sterilization Vs Sanitization
- Sterilization
1.“A process used to render a product free of viable organisms with specified probability” -PDA TR1.
2.“Validated Process used to render a product free of all forms of viable microorganisms”-ISO.
- Sanitization:
Process of reducing viable microorganisms to an acceptable level.
Saturated Steam
1.Saturated steam is important because the steam condenses and provides the maximum amount of heat transfer to the objects being sterilized. Remember passing your finger over a candle than over a tea kettle.
2.As the steam cools [condenses], the latent heat is released to the surrounding chamber and load. The condensing of steam results in a significant volume loss which the autoclave steam supply replaces.
Steam quality testing as per EN 285.
The quality of the steam feeding an autoclave is an important factor in steam sterilization. Like temperature, pressure and time – steam is a critical variable in the success and repeatability of the sterilization process. As such, steam quality should be part of the validation of any steam sterilizer.
1.Dryness factor
-The acceptance criterion for steam dryness is at least > 0.9 for porous loads and > 0.95 for metal loads. Steam below this value is considered to be wet steam. Wet steam does not deliver as much energy to the load.
-The dryness fraction of steam is the measure of the moisture carried within steam. Therefore, steam with a dryness fraction of 0.95 will be a mixture of 95% dry saturated steam and 5% water. The dryness fraction of steam is linked with the latent heat that it possesses.
2.Non-condensable gases
-Non-condensable gases are generally air and air is a poor sterilant compared to steam. Non-condensable gases decrease sterilization efficacy. The percentage of non-condensable gases in the steam should be less than or equal to 3.5% by volume.
-Non-condensable gases are gases liberated by steam when it condenses. The source of such gases is usually from the steam generator feedwater and the impact of such gases is that they modify the steam from being pure water vapour to a mixture of steam and gas and are therefore an unwanted contaminant.
3.Superheat
-The amount of superheat present in the steam should be no more than 25 degrees. When the moisture content is lower than saturation for the temperature, the condition is called superheat. The risk to the sterilization process of superheated steam is that the steam will not condense and provide moisture until the steam temperature has reduced to the saturation temperature. Until this occurs, the steam will act as hot air and at the temperatures present will have little or no sterilizing effect. The excessive temperatures generated can result in damage to both components and packaging.
Anatomy of a Steam Sterilization cycle
Phase 1: Preconditioning [Air Removal by pre pulsing]
1.For Gravity Air Removal, the basic principle is that the density of air is greater than that of steam. Thus, air will “settle” and be evacuated from the chamber as steam is introduced. While this typically does not present a problem for studies within empty chambers, it can be very difficult to remove air from items within a loaded chamber such as filters and tubing, resulting in a lack of sterility assurance.
2.The pre-vacuum step is typically executed until a specified vacuum level is reached. For many processes, multiple vacuum cycles may be employed to remove air from within various loads.
3.The use of intermittent vacuum and steam inject “pulses” allows for the complete removal of air at lower vacuum levels. Similar to forced air removal, a vacuum is pulled until a desired vacuum level is reached. This is followed by an injection of steam until the desired chamber pressure is reached. This process is then repeated for a set number of times.
Phase 2: Come-up
Come-up is simply that point within the cycle in which steam injection is taking place in an attempt to raise the chamber temperature to the desired set point [Typically 121.1oC].
Phase 3: Exposure to sterilization phase [Time and temperature]
1.Exposure is the term used to indicate that the chamber is at the desired temperature [typically 121.1oC] and the control system has begun to record the exposure “time”.
2.Once the chamber reaches the desired conditions, a “timer” is started to “time” the exposure period.
3.The completion of the exposure period is indicated by time, accumulated F0, or some combination of both.
Phase 4: Post conditioning [Exhaust / Drying]
The objective of post conditioning is to cool and dry the objects within the chamber and to return the chamber to ambient conditions.
Process performance qualification of autoclave
1.Calibration of associated Instruments and all the built-in instruments which measure the critical parameters such as temperature or pressure.
2.Calibration of the external data-logger probes used for the temperature measurements, prior to the steam sterilizer PQ. The acceptance criteria shall be a deviation of not more than 0.5oC, from the set temperature. Perform Pre calibration and post calibration of the external temperature thermo couples.
3.Gasket integrity check-The door gaskets of steam sterilizer shall be checked visually, for any physical damages and gasket fitment. No damage should be there in both the gaskets and should fit properly.
4.Testing the Internal Vent Filter for integrity.
5.Pre-Vacuum leak test -To ensure the integrity of steam sterilizer chamber, separate vacuum leak test prior to the validation exercise.
6.Post vacuum leak test-To ensure the integrity of steam sterilizer chamber, separate vacuum leak test after the validation exercise.
During chamber vacuum leak test, subject the steam sterilizer chamber to following phases:
- Depressurization of the chamber to a vacuum of – 0.7 bar.
- Chamber vacuum stabilization for 3 minutes.
- Vacuum hold for 10 minutes.
- Process End pressure – 0.1 bar.
The acceptance criterion for vacuum leak test [during the vacuum hold phase] shall be – a pressure increase of not more than 0.013 bar.
7.Spore Counts of Biological Indicator Units, in order to ensure an accurate determination of the sterility assurance levels, during the heat penetration studies, spore population determination of the biological indicator [BI] units in strips & ampoules shall be performed and the assay results must be within -50 to + 300% of the labeled spore population claim in the COA. Testing should employ the use of Biological Indicators Geobacillus stearothermophilus.
8.Bowie Dick test-3 validation cycles for air removal test shall be run.
9.Empty chamber testing [Heat Distribution Study]
-Heat distribution inside the sterilization chamber shall be studied by performing the empty chamber testing to determine if there are any cold spots inside the chamber.
-Flexible temperature probes / sensors, of an external multi-channel data-logger, shall be used during the heat distribution and placed at randomly identified positions inside the chamber.
-One flexible temperature probe / sensor, of the external multi-channel data-logger, shall be placed at the drain point to record the temperature of the condensate, if any, during all the three heat distribution cycles.
-It shall be ensured that none of the temperature probes / sensors shall touch any metal surface or walls of the chamber.
-For the next two heat distribution study cycles, the position of the temperature sensors shall be changed at random, so as to cover maximum number of points inside the chamber.
-The temperature recording, for the different positions in the chamber, shall be performed by the temperature sensors / probes, at a time interval of every 1 minute, during these sterilization cycles.
-Three consecutive sterilization cycles shall be run to study and validate the heat distribution inside the chamber.
-Empty chamber studies shall be carried out for both the standard and HPHV cycles.
Acceptance Criteria
-During empty chamber during the sterilization cycle no chamber thermocouple should differ more than 10C from the mean of all chamber thermocouple readings.
-The temperature readings recorded by both the external data logger and in-built probes shall be within the sterilization time and temperature after the commencement of sterilization phase for HPHV and standard cycle.
10.Loaded Chamber Testing [Heat Penetration Study]
-Heat penetration for the different loads shall be studied, by performing the loaded chamber testing, to ensure that there is adequate assurance on the sterility levels for the sterilized loads used in routine.
-One Validation cycle each to determine the lagging probes inside the loaded chamber for each load pattern / configuration with probes shall be run. This cycle shall be termed as pre mapping cycle and no biological indicators shall be challenged.
-Further three sterilization cycles shall be taken for each load type.
-Few external data-logger probes shall be placed outside the loaded articles to record the temperature readings & heat distribution in the chamber and few flexible temperature sensors / probes of the external data-logger shall be placed inside the loaded articles, for recording the temperature and heat penetration at these places.
-One flexible temperature sensor / RTD shall be placed at the drain point to record the temperature of the condensate.
–Challenge by Biological Indicators in solid loads-HPHV cycle: Biological indicators [Geobacillus stearothermophilus ATCC 7953] in strips shall be placed / challenged in each HPHV sterilization cycle.
–Challenge by Biological Indicators in liquid loads-Standard cycle: Biological indicators [Geobacillus stearothermophilus ATCC 7953] in ampoules shall be placed / challenged in each standard sterilization cycle.
-Biological Indicators should be placed at the hardest to heat locations within the load based on the pre mapping cycle.
Demonstrate reproducibility for:
- Loading.
- Orientation.
- Wrapping.
Acceptance Criteria:
-The temperature readings recorded by both the external data logger and in-built probes shall be within the range of sterilization time and temperature after the commencement of sterilization phase for HPHV and standard cycle.
-All the biological indicators [BI] units shall show more than 6-log reduction in the microbial population.
-Average temperature of each probed location [during exposure phase] does not fluctuate by more than 1°C.
-Average temperature throughout the chamber does not fluctuate by more than 2°C.
Revalidation should be conducted when:
- Major changes are made to the autoclave.
- Load Configuration.
- Cycle Parameters.
- Changes are made to the steam supply source that may have an impact on the performance of the autoclave.
Europe regulatory agencies approach to Steam heat sterilization
- Widespread acceptance of standard 121oC, 15 min cycle.
- Greater emphasis on measurement of entrained air in product and load, super-heated or dry steam, and non-condensable gases.
- BI use considered an added verification.
- When BI’s are used, Geobacillus stearothermophilus the microorganism of choice.
US regulatory agencies approach to Steam heat sterilization.
- Inactivation of heat resistant microorganisms to assure at least a 106 SAL is the focus.
- Variable cycle time/temperatures can be used to attain a 106 SAL. Variable cycles acceptable.
- BI’s required in cycle development and validation programs.
- Use of different types of heat resistant BI’s are acceptable.
- Recognized importance of cycle thermal profile data, but emphasis is on the use of microorganisms for validation purposes.
Conclusion
By the current standards, the adequate preventive maintenance, additional tests like Bowie Dick test, Vacuum leak test, usage of chemical indicators, biological indicators, sound validation approach, steam quality tests, routine requalification have strengthened the assurance of sterility of the products that are sterilized in the steam heat sterilizer / autoclave. Development over the years have given assurance of sterility to the products/aids/devices that are sterilized in the autoclave/ steam heat sterilizer.
Note-The images given for representation in this blog are taken from Google Images. Many thanks for Google.