Sterilisation 5 Flashcards
what is downwards displacement
comes in at the top and forces the air out at a drain at the bottom
2 types of cooling down?
natural decay- natural cooling down
active: pumping in sterile cold air
for moist heat sterilisation there’s __ cycles
4
moist heat sterilisation is ______ under pressure
always
as the temperature increases the amount of time needed for moist heat sterilisation ______
decreases
what are the 4 moist heat sterilisation cycle conditions
115-118 degrees C
30 minutes
10 psi
121-124 degrees C
15 minutes
15psi
126-129 degrees C
10 minutes
20 psi
134-138 degrees C
3 minutes
30psi
what is the most common cycle for the autoclave
fluid cycle
what materials is the fluid cycle used for
aqueous fluids
can be sold as long as its moisture resistant
what materials is the porous load cycle used for ?
fabrics and dressings
how long does a porous load cycle take? why
30 minutes
dont take long to heat up
on a porous load cycle graph why does it go up and down at the start (think like an ECG)
they hold air- so you need to remove with steam . gradually replace air with steam- red up and down at start of the graph.
what is the air ballasted cycle used for?
plastic containers with no screw tops
how does the air ballasted cycle work
sealed and sterilised
must get pressure right as its completely sealed unit
what is the master temperature record (MTR)
a test load- to ensure it works. They are the real products but wont see a patient.
what are thermocouples
these are probes that you put on the product which monitor the temperature
what is the temperature record chart (TRC)?
put a probe in the drain
probe in the drain- should in theory be the coldest part of the autoclave. As soon as the drain reaches the correct temperature, this means that the rest of the autoclave should be at the right temperature
what is the MTR and TRC apart of?
the moist heat sterilisation cycle validation and monitoring
minimum of ___ thermocouples used in a chamber
12
is the MRT load specific?
yes need to revalidated if you add or take out any product
the F0 concept is specific to?
moist heat sterilisation
what is gross overkill
good regarding micro-organisms but can be over processed
problems with product degradation
what is compendia lethality
calculating the amount of lethality associated with the kill curve
compendial cycles are based on? why can this be an issue when estimating compendia lethality
the green period- holding period.
MOs also die in the heating and cooling down period, not just the holding period. we want the lethality for the whole process- this brings us to the F0 value
F0 is an alternative to the ______ ______
compendial cycles
what does the F0 value allow?
Allows lethality’s to be compared- previously we only used cycles and took it as fact but don’t know how much we are over processing
what is the F0 value defined as?
The lethality expressed in terms of the equivalent time in minutes at a temperature of 121oC delivered by the process to the product in its final container with reference to microorganisms possessing a z-value of 10.
121 degrees is our standard reference
So whatever value we calculate for an F0 e.g. 3, it means that for the conditions we’ve calculated the F0 at, we get the same amount of lethality as if we did it at 121 degrees for 3 minutes
if we calculated an F0 value of 3 what does that mean?
it means that for the conditions we’ve calculated the F0 at, we get the same amount of lethality as if we did it at 121 degrees for 3 minutes
the F0 should assure a minimum SAL of?
10-6
what is the minimum F0?
8 ( ie equivalent to 8 mins @ 1210C)
FOR BIOLOGICAL DATA : cell count,
calculating F0: what is the relationship between F and D values?
F= D (logN0- LogN)
Where:
D is the D-value at the given temperature
N0 is the initial number of microorganisms present (bioburden)
N is the number of MO’s surviving the process (actual or expected) expected could be 10^-6 as that’s our SAL
why is thermal data more accurate than biological data for calculating F0
not using organisms
how do you calculate F0 using thermal data
divide the kill curve into intervals e.g. every minute and calculate the lethality at each minute
F0 = F1 + F2 + F3…. + FN
thermal data for F0 calculation is a ______ process. meaning?
cumulative
if process is 120 minutes you’ll have 120 measurements
when calculating F0, what does the cumulative value for thermal data represent
measure of total process lethality for the whole cycle
what is the equation for F0 with thermal data
F0= [Log-1 (t-121)/z] x dt
121 degrees is the reference temperature
T is the temp of heating
Z is 10 degrees C
dt is the time of heating
if a cycle has a F0 of 7.5 is it acceptable?
no- must be above 8
must ensure its not just for holding time as then if you added in the heating up and cooling down time the F0 value could be above 8
if at higher temperatures such as 134-138 degrees, the value of F0 is 60-150, what does this mean
we are massively over processing
what can the F0 value allow us to do?
customise the sterilisation cycle
the F0 value allows us to compare ______
lethality’s
similarities between the FH and F0 value?
the equation:
FH= [Log-1 (T-170)/Z] x dt
170o is the reference temp. (Bacillus subtilus)
T is the temp. of heating
Z is 20oC
dt is the time of heating
differences between the FH and F0 value?
the standards are different
for FH: 170 degrees is the reference temperature
for F0: 121 if the reference temperature
equation of ethylene oxide?
(CH2)20
what is ethylene oxide used on? what materials
disposables
medical devices
how does ethylene oxide kill MOs?
alkylation of groups on proteins and blockage of MOs active sites
shotgun approach
what is EtO lethality limited by
concentration
temperature
and relative humidity
how does relative humidity effect EtO
for EtO to be effective you need a moisture content in the chamber of the sterilising unit
is EtO easy to get the SAL
no, not as good as other methods as there’s so many variables that effect It
EtO leaves _____ ______ on the product
toxic products
problems with EtO
toxic residues
toxic to humans- blown up
what must EtO be mixed with? why?
CO2 or N2- eliminates air explosive aspect
temperature needed for EtO
26-65 degrees
time needed for EtO
1-24 hours
humidity for EtO
40-85%
how does high humidity help kill the MOs with EtO
EtO is more lethal in moisture and the bacteria is more susceptible to it in moisture
what is used for both validation and moitoring of EtO
B.subtilus
