Sterilization of media, glassware and instruments

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Objective: Sterilization of media, glassware and instruments
Methods: Autoclaving, filter sterilization, oven sterilization, filter sterilization


I. AUTOCLAVING/STEAM UNDER PRERSSURE
Most common sterilization by moist heat requires steam under pressure at temperature range of 121-1340C

Principles
Moist sterilization requires that the steam used for sterilization must be both Dry and Saturated.

Saturated in the sense that the steam in this context is at a phase where it is holding all the water that it can, in the form of transparent vapour.
It does not contain water droplets and therefore it describe as being dry; if it meets an object cooler than itself it condenses.
Approximately 80% of the latent energy in dry saturated steam is in the form of latent heat that is released when this forms touches a cooler object and condenses. Condensation is accompanied by an instantaneous contraction of the steam (1600ml ml of steam at 100oC condense to 1ml), creating low pressure region in which more steam flows. The result is penetration of steam into articles being sterilized.
If temperature of dry saturated steam is raised at constant pressure or if temperature is reduced at constant pressure the degree of saturation is reduced and the steam become superheated. Superheated steam condenses less readily than dry saturated steam- less effective sterilant.
Wet steam must also be avoided since this will result in reduced penetration of steam in materials and wet the loads.
It is important to keep dry is to prevent the steam water droplets soaking towels sheets i.e. porous material. A lengthy drying up period may damage articles.
Moist heat sterilization i.e. Autoclaving is performed in an autoclave.
The most common conditions for sterilization under pressure include

In any heat sterilization process the articles for sterilization must be first raised to sterilization temperature and this involves heating up stage. Then the objects have to be held at the sterilizing temperature for a sufficient period of time to ensure sterilization and SAL (Sterlity Assurance Level) is achieved. This is known as the holding stage. After this the objects must be cooled to temperatures that are safe for handling or the cooling stage.
Moist heat sterilization i.e. Autoclaving is performed in an autoclave.

Parts of a autoclave: Moist heat sterilization is carried out in an autoclave.
There are various types of autoclaves but generally they can be equated
to large pressure cookers.
Basically they are stainless containers that may be jacketed or non jacketed
with the following features:
1. Pressure gauge
2. Steam outlet and inlet valves
3. Thermometer/ temperature gauge
4. Water heating system/ steam generating system
5. Vacuum pump
6. Safety valve
7. Inlet Door

There are various types of autoclaves
1. Simple non-jacketed - small electrically heated sterilizers with simple air expulsion system – steam sterilization of unwrapped instruments and utensils – used in medical (district hospital) and dental community

Procedure:
i. Ensure there is sufficient water in the autoclave to produce required steam – usually automatic
ii. Load sterilization chamber - Ensure that all products required to be sterilized are accessible
iii. Close chamber door
iv. Air removal –all air must be removed before sterilization can commence
v. Start sterilization cycle (include heating, holding and cooling stages)
vi. Remove objects
vii. All through the process monitor sterilization temp and pressure
Disadvantages:
• Requires personal attention to monitor process
• Method of air discharge inefficient cannot really monitor that all air has been removed
• There is no internal thermometer to check coolest part of load
• There is no mechanism for drying the load
1. Downward displacement autoclaves - These are usually jacketed horizontal or cylindrical in shape. The air is removed by displacement by steam through an automatic air and condensate discharge valve at the base of the autoclave.
There are 3 main types:
• Laboratory autoclaves
• Hospital - for sterilizing unwrapped surgical instruments used in hospital theaters
• Fluid sterilizers - autoclaves for sterilizing fluid in sealed containers e.g. infusions injections etc.
2. Porous load autoclaves – these autoclaves are used for porous materials such as towels surgical gowns, dressings, swabs, gauzes, sheets etc. The sterilizer is equipped with a vacuum system to ensure a high degree of air removal. To ensure no moisture remains on the
sterilized objects.
Precautions:
For efficient sterilization
a. Keep a daily temp record chart
b. Check thermometer daily
c. Check air removal system weekly
d. Include sterilization control measure each cycle
B. DRY HEAT STERILIZATION
The value of heat in the form of fire has been known for centuries
Examples of Dry heat sterilization are:
• Incineration
• Read heat
• Flaming
• Hot air oven


Dry heat sterilization
The equilibrium of heat must be accelerated by forced air circulation using a fan. The slow rate of heat absorption and thus microbial killing by hot air combine to make this process time consuming; That is the total process time including the time taken for the free chamber space to achieve the required temp, the sterilizing time and the cooling. Thus in general dry heat sterilization requires higher temperatures and extended periods of sterilization

Due to the high temperatures required for dry heat sterilization can only
be used for thermostable, moisture sensitive or moisture impermeable
pharmaceutical and medicinal. These include products like;
• Dry powdered drugs
• Suspensions of drug in non aqueos solvents
• Oils, fats waxes, soft hard paraffin silicone
• Oily injections, implants, ophthalmic ointments, ointment base
HOT AIR OVEN
It comprises of an electrically heated, insulated chamber fitted with insulated door. The chamber is usually of stainless steel. The inner surfaces are polished to minimize heat loss. Heating arrangements are made around the chamber walls. Heat is delivered to the load primarily by convection and radiation. A fan is fitted for efficient air circulation and heat distribution within the oven. It is also fitted with thermostat to control the temperature.
Used for sterilizing glassware that needs to be used dry, for powders, fats, oils and greases that are not penetrable by moist heat. Not recommended for articles such as plastic that would be damaged by the necessary high temperature.
The glassware must be dried first before being loaded into a hot oven to avoid cracking.
The temperature varies between 160oC- 170oC and duration of 1-2 hours. Ample spacing must be allowed in the oven to permit free circulation of hot air. Containers must be placed on their sides for the same reason to avoid impeding of hot air. Powders, oils, fats and grease must be packed in small quantities or in thin layers to enable penetration of heat.


LAMINAR FLOW
• Laminar flow hood is essential for aseptic operations in the lab and usually have several requirements:
 Large enough: 120 cm (W)× 60 cm (Depth)
 Quiet: noisy hoods are more fatiguing
 Easily cleaned
 Comfortable to sit
• Two types of laminar flow
 Horizontal: give the most stable airflow and best sterile protection
 Vertical flow gives more protection to the operator (particularly for handling biohazardous materials)