Page 52 - Journal of Special Operations Medicine - Summer 2016

Flash Sterilization There are some variations in the recommendations
An alternative to traditional steam sterilization is a pro- among the respected organizations for the optimum
cess known as flash sterilization. This is “a process de- temperature and time. The WHO recommends a mini-
signed for the steam sterilization of unwrapped patient mum temperature of 170°C (340°F), for a minimum of
care items for immediate use.” This method should not 2 hours once the load has reached an equalized tem-
8
be used for convenience or to save time but can be used perature of 170°C (340°F). The CDC, however, recom-
to sterilize critical items that are needed for immediate mends a wider range of time/temperature relationships
use or cannot be otherwise stored, provided the item is at 170°C (340°F) for 60 minutes, 160°C (320°F) for 120
cleaned before being placed in the autoclave. Addition- minutes, or 150°C (300°F) for 150 minutes. The United
ally, instruments are best placed unwrapped in the auto- Nations High Commissioner for Refugees (UNHRC)
clave and packing materials should not be used. also recommends a temperature of 170°C (340°F) for
60 minutes. The Special Operations Forces Medical
7
As described by Underwood and Perkins as a form Handbook, however, recommends 60 minutes at 160°C
17
18
of emergency sterilization, flash sterilization involves a (320°F). In any case, it should be noted that the steril-
cycle of 3 to 5 minutes at 132°C (270°F) at 27 to 28lb ization time does not start until the internal load has
of pressure in a gravity displacement autoclave. Current reached the recommended temperature.
recommendations depend on the type of autoclave used
and the type of instruments to be sterilized, but in gen- The question then arises, can a standard home appliance
eral, for a gravity displacement autoclave, 3 minutes is oven be used in the local setting as a dry heat sterilizer?
recommended for metal instruments and 10 minutes is It would be rational to assume so, as it uses heating coils
recommended for more porous instruments like rubber in a similar fashion as a static-air type dry heat sterilizer
and plastic. 8 used in hospitals. If this were the case, then this could
potentially be of use to the forward deployed Special
There are two primary drawbacks to this method. First, Operations Forces medical team if a simple appliance
the items must be used immediately once sterilized, and oven could be located in the local environment. The
care must be taken to prevent recontamination when works of Ewald and Schmid in 1953 and Darmady and
the instruments are transported from the autoclave Brock in 1954 would suggest not, since they both found
to the patient. Second, there have been a few cases of that internal temperatures in hot air ovens can vary as
patients sustaining contact thermal burns from instru- much as 30° to 40°C. They did, however, find that pre-
ments that have not properly cooled after removal from heating the oven to the specified sterilization tempera-
the autoclave. Therefore, a standard operating pro- ture and making sure that the instruments were loosely
11
cedure must be made to either allow air-cooling of in- packed in single layer before loading them reduced the
struments in a sterile fashion or place instruments in amount of variation in internal temperature. According
an immersion pool or sterile saline for a more rapid to WHO guidance, it is best to use dry heat devices that
cooling before use. were specifically designed for sterilization; if these are
not available, then an ordinary household gas or electric
Dry Heat Sterilization oven may be used. If a household oven is used, an elec-
Shortly after the Second World War, sterilization by tric oven is preferred over gas, as it has been shown to
dry heat gained some popularity, particularly in Great provide a more reliable and uniform heat. 17
Britain due to the limited supply of autoclaves in the
post-war period. Dry heat has two distinct advantages Other Types of Heat Sterilization
3
over steam autoclaves: it is comparatively inexpensive
and readily available in the local economy/environment, One novel approach to heat sterilization reported by the
and it depends on heat penetration of the object to be CDC is the use of microwave ovens. These ovens make
8
sterilized. Steam sterilization, on the other hand, relies use of microwaves to generate friction between water
on surface area contact, which can be more difficult to molecules, and they have been shown to be capable of
achieve. destroying microbes. Several studies have shown that
the common home appliance microwave oven in the
The disadvantages of dry heat sterilization are (1) the 2.45GHz range was capable of destroying bacterial cul-
time and temperature required for effective sterilization tures, mycobacteria, viruses, and certain types of bacte-
are significantly higher and longer than those required rial spores and Candida albicans when heated between
for steam sterilization; (2) there can be significant varia- 60 seconds and 5 minutes. 8,22 A variety of materials
tion in internal temperature within the appliance during could potentially be sterilized in this method, but metal
sterilization, thus decreasing its effectiveness; and (3) poses a unique challenge. Metal reflects microwaves and
some objects may not tolerate the high temperature and creates an arc. Once initiated, an arc will return to the
become subject to oxidation and rust. megatron inside the microwave and risk damaging both

38 Journal of Special Operations Medicine Volume 16, Edition 2/Summer 2016