Sterilisation Flashcards
Define Sterility according to the OED
(When something is) Free from living microorganisms
Define Sterility according to Winfield and Richards
The total absence of viable microorganisms and an absolute state
Define Sterility according to Hugo and Russell
A product that doesn’t contain viable bacteria, yeasts or fungi nor other microorganisms such as protozoa, viruses etc
Define Achievable Sterility
The probability of microorganisms surviving should be low enough to ensure patient safety
What is the Sterility Assurance Level (SAL)
10 to the power -6. (One in a million chance)
Define D value (Decimal reduction time) in terms of heat sterilisation
Time taken at a fixed temperature to reduce the number of viable organisms by 90%
Define D value in terms of radiation
The radiation dose required to reduce the number of viable organisms by 90%
Z value applies to both heat sterilisation ad radiation. TRUE or FALSE
FALSE. Z value only applies to heat sterilisation
Z value assesses the influence of heat changes on ….?
Thermal resistance
What is Bioburden
The concentration of microorganisms in a material
To assure sterility, the bioburden must be as small as possible at the start of the process. TRUE or FALSE
TRUE
What is meant by Inactivation factor (IF) ?
The number of D values needed to achieve sterility assurance level
State the IF equation
10 to the power t/D
t = contact time or dose
D = D value
Heat sterilisation is the most reliable and most widely used method. TRUE or FALSE
TRUE
State one advantage of heat sterilisation
Destroys all enzymes and other essential cell components
State one ‘disadvantage’ of heat sterilisation
Can only be used with products that can handle the heat i.e: thermostable products
State the 2 types of heat used in heat sterilisation
1) Dry heat (for moisture sensitive products i.e: dressings)
2) Moist heat such as STEAM (for moisture resistant products)
Name the 3 stages involved in heat sterilisation
1) Heating stage
2) Holding stage
3) Cooling stage
What is the most commonly used method of terminal sterilisation
Moist heat sterilisation
State 6 products sterilised using moist heat sterilisation
1) Some dressings
2) Clothing
3) Equipment
4) Aqueous injections
5) Irrigation fluids
6) Opthalmic preparations
What equipment is commonly used for moist heat sterilisation ?
Autoclave
What is temperature range of an autoclave and how long for ?
121 - 134 degrees celcius
121 - 15 minutes
or
134 - 3 minutes
Shorter time in the autoclave causes less product damage and higher IF value. TRUE or FALSE
TRUE
Moist heat sterilisation causes ….. and …. of essential proteins?
Denaturation and Coagulation
therefore stop cells from replicating etc
Describe the F value
The mathematical method of converting time in the heating and cooling stage to time spent at 121 degree Celsius.
What is the F value useful for ?
Products where holding time at 15 mins isn’t possible
Dry heat sterilisation isn’t as commonly used as moist heat. Why ?
Higher temperature and longer exposure time; is needed for this process
Dry heat sterilisation is mostly used in hospitals o surgical equipment. TRUE or FALSE
TRUE
DHS is useful for sterilisation of glassware. How ?
DHS ensures depyrogenation as pyrogens stick to glassware
Name a product sterilised using dry heat
Thermostable powders
Non-aqueous thermostable liquids such as Alcohol is used in DHS. TRUE or FALSE
TRUE
What equipment and temp range is used for DHS ?
Hot air oven. 160 - 180 degrees for up to 2 hrs
What temperature and how long for is required for depyrogenation of glassware ?
250 degree Celsius, 45 minutes
DHS has lethal effects due to oxidative processes. TRUE or FALSE
TRUE
Name 2 types of gas used in Gaseous sterilisation
1) Ethylene oxide
2) Formaldehyde (not commonly used due to smell and risk)
Gaseous sterilisation is generally used for temp sensitive items. TRUE or FALSE. Give examples of these items
TRUE;
- Medical, diagnostic and electrical equipment used in operating theatres (microscopes, tubing etc)
-
Formaldehyde and Ethylene oxide can be mutagenic and carcenogenic. TRUE or FALSE
TRUE
Ethylene oxide can be detected by smell whilst Formaldehyde cannot. TRUE or FALSE
FALSE, it’s the other way round
Gaseous sterilisation gases cause alkylation on what groups on proteins ?
- Carboxyl, Hydroxyl, Amino and Sylphydryl
basically denaturation of protein
Gaseous sterilisation gases cause alkylation on what groups on nucleic acids ?
Imino group
What does Ethylene oxide have to be mixed with in order to be used?
Carbon dioxide (10%) OR HFC 124 (8.6%)
Ethylene oxide mixed with more than 3.6% v/v of air will explode. TRUE or FALSE
TRUE
Gases are good at penetrating materials. TRUE or FALSE
TRUE. e.g: raw powders
800-1200mg/L at 45-6oC is the essential range for gases used for gaseous sterilisation. TRUE or FALSE
TRUE. Gas is left under this temp for around 4hrs
Gas is let back out into the environment at the end of the sterilisation process. TRUE or FALSE
TRUE
After gaseous sterilisation (using both ethylene oxide and Formaldehyde), products must be left for at least 24hrs to desorb toxins/toxic gas. TRUE or FALSE
TRUE
Formaldehyde is a liquid. What is it mixed with to turn it into a gas ?
Water and heat with steam to 70-75oC; for around 4hrs
Formalin contains what %w/v of formaldehyde
37% w/v
State 3 methods of Radiation sterilisation and highlight the most effective
1) Accelerated electrons (Particulate radiation)
2) Gamma-ray (Electromagnetic radiation) - Most effective/least dangerous
3) UV light (Electromagnetic radiation) - least effective
Gamma ray is usually performed on Industrial scale manufacture. TRUE or FALSE
TRUE
State one ‘disadvantage’ of Gamma ray radiation sterilisation
Can damage aqueous solutions and certain types of packaging
Gamma ray radiation sterilisation can be used on dry products such as ?
1) Surgical equipments
2) Plastic syringes
3) Dry powders
4) Dressings
The D value of GRRS is connected to …… of radiation not the time ?
Dose
What source is used for GRRS ?
Cobalt 60
What is the half life of cobalt 60 ?
What is the standard dose of cobalt 60, i kGy ?
5.25 years
25kGy
Define Disinfection
The process of removing microorganisms from the surface of inanimate objects
State 6 types of Chemical agents used for disinfection
1) Alcohol (Most safe/least toxic)
- Aldehydes
- Halogens
- Peroxygens
- Phenolics
- Quaternary ammonium compounds
State 2 types of biological indicators
1) Standardised bacterial spore preparations
2) Suspensions or Spores dried onto paper, plastic or Aluminium
- Placed in with each load for sterilisation
- Cultured after cycle has ended
State the BI organism used in Moist heat sterilisation. State its D value and Log IF also
B. Stearothermophilus
D value - 1.5 mins
Log IF - 10
State the BI organism used in Dry heat sterilisation. State its D value and Log IF also
B. subtilis var. niger
D value - 10 mins max
Log IF - Min. 12
State the BI organism used in Irradiation sterilisation. State its D value and Log IF also
B. pumilus
D value - 3kGy
Log IF - 8.3
