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REVIEW ARTICLE
Basic Principles of Disinfection and Sterilization in Intensive
Care and Anesthesia and Their Applications during COVID-19
Pandemic
1 2
Amol T Kothekar , Atul P Kulkarni
AbstrAct
Understanding the concepts of disinfection, sterilization, cleaning and asepsis is of prime importance to prevent transmission of infection to
patients and to protect healthcare workers (HCWs). Proper disinfection of surfaces after cleaning, an important consideration at all times, has
assumed special significance during the current pandemic. The global shortage of disposable equipment such as personal protective equipment
(PPE), specifically N95 masks and surgical 3 ply masks, and other items makes the HCWs vulnerable to transmission of infection while caring
for these patients. Therefore, resterilization of such items has assumed equal importance. Cleaning, the first step in the process of sterilization,
is of vital importance to reduce bioburden. The type of disinfection required depends on the nature of the equipment and its intended use.
For example, critical items need high-level decontamination. In this narrative review, we elaborate on the methods of decontamination and
sterilization. Many chemicals can be used for both sterilization and disinfection, and the difference lies in the concentration of the chemical and
exposure time. We have also summarized strategies which can be used for resterilization of single-use items, in view of the shortages caused
by the current pandemic.
Keywords: Chemical methods of sterilization, COVID-19 pandemic, Disinfection, Physical methods of sterilization, Personal protective equipment,
Resterilization, Reuse, Sterilization.
Indian Journal of Critical Care Medicine (2020): 10.5005/jp-journals-10071-23562
IntroductIon 1,2
Department of Anesthesia, Critical Care and Pain, Division of Critical
Disinfection, sterilization, cleaning and maintenance of asepsis are Care Medicine, Tata Memorial Center, Homi Bhabha National Institute,
extremely important for health care workers (HCWs), particularly Mumbai, Maharashtra, India
in the intensive care units (ICUs) and operating rooms. This helps Corresponding Author: Atul P Kulkarni, Department of Anesthesia,
in preventing transmission of infections to patients and protecting Critical Care and Pain, Division of Critical Care Medicine, Tata Memorial
HCWs, not only every day, but also during outbreaks and pandemics. Center, Homi Bhabha National Institute, Mumbai, Maharashtra, India,
Nonadherence to established guidelines can cause outbreaks of Phone: +91 9869077526, e-mail: kaivalyaak@yahoo.co.in
1
infection and has adverse impact on outcomes. How to cite this article: Kothekar AT, Kulkarni AP. Basic Principles of
In pre-coronavirus disease 2019 (COVID-19) era, single use Disinfection and Sterilization in Intensive Care and Anesthesia and
(disposable) items were resterilized and used due to cost constraints Their Applications during COVID-19 Pandemic. Indian J Crit Care Med
in the low-income countries. During the current pandemic, due 2020;24(11):1114–1124.
to the upsurge in the number of patients, the developed world is Source of support: Nil
forced to resterilize single-use items (Fig. 1). Conflict of interest: None
In this narrative review, we discuss sterilization of equipment
and disinfection of environmental surfaces, and strategies for the
reuse of disposable items. For further in-depth understanding, the
reader is referred to a review by McDonnell et al.2
understAndIng the concepts of cleAnIng,
bIoburden, dIsInfectIon, sterIlIzAtIon,
And AsepsIs
Bioburden is the number of microorganisms present on the
surface before disinfection or sterilization. Biological byproducts
of patients, e.g., upper and lower respiratory tract secretions, saliva,
feces, and urine, can potentially transmit infections.
Cleaning is a process of reducing the bioburden by the physical
Fig. 1: A giant sterilizer machine that can sterilize up to 80,000 respirator removal of organic matter, involving washing (with soap and cold
masks per day water) and scrubbing (mechanical action).
© The Author(s). 2020 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (https://creativecommons.
org/licenses/by-nc/4.0/), which permits unrestricted use, distribution, and non-commercial reproduction in any medium, provided you give appropriate credit to
the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain
Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Disinfection and Sterilization in COVID-19 Pandemic
Disinfection eliminates many or all microorganisms, except cleAnIng
some bacterial spores. It is further classified into high-, intermediate-, This is the first and key step during the decontamination process.
and low-level disinfection. Disinfection or sterilization is not effective unless the equipment
Sterilization destroys or eliminates all forms of microorganisms is completely cleaned. If possible, the equipment should be
including bacterial spores. (Details below). dismantled. A temperature above 45°C causes coagulation of the
Asepsis ensures maintenance of the sterility of the already proteinaceous material (which forms a protective layer), making
sterilized products or equipment. By itself, it does not ensure removal of microorganisms difficult and should be avoided.
sterility, if sterilization is flawed. Cleaning should be done in a separate room to prevent potential
McDonnell described a triad of human safety, machine exposure to patients and HCWs.
compatibility and agent efficacy for disinfection or sterilization Automated methods for cleaning, such as washer disinfectors,
process, which can be adapted for HCWs. low-temperature steam, and ultrasonic baths, can be used to avoid
exposure of the HCWs to the chemicals and microorganisms.
cAtegorIes of hospItAl equIpment Manufacturer’s recommendations should be followed while using
Spaulding classified all hospital equipment into three categories automated methods.
based upon their intended use.4
These categories depended on the sterIlIzAtIon
risk of infection, nature of exposure to tissues and meticulousness
of the sterilization, and disinfection. Sterilization can be done by physical or chemical methods. Steam
5,6 under pressure, dry heat, ethylene oxide (EtO) gas, gas plasma, and
Critical Items liquid chemicals like glutaraldehyde are the principal sterilizing
These are used in the sterile tissues or the vascular system. These agents used in healthcare. The key features of different methods
are surgical instruments, cardiac, vascular and urinary catheters, of sterilization are summarized in Table 2.
pressure transducers, implants, and various needles. They need
complete sterility before use, and hence, they are either sterilized Other Chemicals Used for Sterilization and
(e.g., steam sterilization for surgical instruments) or procured as 2
Disinfection
sterile single-use devices (needles or catheters). Equally important The key features of other chemicals used in healthcare are
is the maintenance of asepsis during their use. enumerated in Table 3.
Semicritical Items Quaternary Ammonium Compounds
These are exposed to intact mucous membranes or nonintact Quaternary ammonium compounds are cationic surfactants, with
skin, but do not ordinarily break the tissue barrier, hence pose wide antimicrobial spectrum including bacteria, enveloped viruses
an intermediate risk. The tissues are susceptible to infections like human immunodeficiency virus (HIV) and Hepatitis B virus
produced by bacteria and viruses but are resistant to infection (HBV). Quaternary ammonium compounds kill microorganisms by
caused by bacterial spores, so sporicidal sterilization is not required. adsorption, penetration, and destruction of cytoplasmic membrane
These include breathing systems, laryngoscope blades, fiberoptic and cell wall and by degradation of proteins and nucleic acids.
endoscopes, etc. A high-level disinfection (HLD) is mandatory for They are sporostatic at low concentrations (0.5–5 mg/L) and do
these items. not act against nonenveloped viruses but are microbiocidal at
higher concentrations (10–50 mg/L).28,29
Noncritical Items Quaternary ammonium
These include blood pressure cuffs, pulse oximeters, compounds of different generations have been used; the first
electrocardiography (ECG) cables and electrodes, and patient generation being benzalkonium and alkyl chains, and the latest
surroundings such as furniture and floors that are in touch with 7th generation is Bis-QACs with polymeric QACs.
intact skin. The risk of transmission of the infections to patients Peracetic Acid30
with these items is very low, but they should not be exposed to Peracetic acid is a high-potency biocidal oxidizer with a similar
nonintact skin (pressure sore, skin abrasions, etc.). These need mechanism of action to other oxidizing agents. It releases free
either intermediate-level or low-level disinfection based on the oxygen and hydroxyl radicals leading to microbiocidal effects
bioburden. It is important to remember that incorrect method against bacteria (including mycobacterium) and bacterial spores,
or inadequate sterilization/disinfection can expose both the fungi, and viruses (poliovirus, rotavirus, HBV, and HIV) rapidly (<10
patient and the HCWs to the risks of infection. On the other hand, minutes). It acts by denaturation of proteins, disruption of cell
unnecessary high level of sterilization/disinfection wastes resources wall permeability, oxidization of sulfhydral and sulfur bonds in
and reduces the life of the equipment. proteins, enzymes, etc. Its constituents are acetic acid and H O . In
It is vital to always follow the manufacturer’s recommendation 2 2
the concentrated form, peracetic acid is corrosive and irritating. It
for disinfection, sterilization, and cleaning. The use of incompatible is available as 0.2% and 0.35% solutions. It is safer but costlier than
methods voids the warranty and can permanently damage the glutaraldehyde, and in the future, after further trials, it may be an
equipment beyond repair and, thus, worsen the supply shortage. alternative to glutaraldehyde.
For example, the use of alcohol-based disinfectants for disinfection
of ultrasound probes can cause permanent damage to the probes Ultraviolet (UV) Radiation or Ultraviolet Germicidal Irradiation
7 31,32
due to its reaction with the rubber head of the transducer. The (UVGI)
methods for sterilization and disinfection for the routinely used Ultraviolet germicidal irradiation (UVGI), which damages the
equipment in ICU and operation theater (OT) are given in Table 1. microbial nucleic acid, has been used for the disinfection of titanium
Indian Journal of Critical Care Medicine, Volume 24 Issue 11 (November 2020) 1115
Disinfection and Sterilization in COVID-19 Pandemic
Table 1: Sterilization/disinfection of routinely used equipment in ICU and ORs
Categories of hospital
equipment Item Preferred method Alternative method
Semicritical Steel laryngoscope Cleaned with cool running tap water. Immersed in disinfectant solution Autoclave
blades8 as per manufacturer’s recommendations (glutaraldehyde, hydrogen
peroxide, ortho-phthalaldehyde, and peracetic acid with hydrogen
peroxide 1% sodium hypochlorite or alcohol-based disinfectants) for a
minimum of two minutes and rinsed with lukewarm running tap water.
Brushed in enzymatic detergent and rinsed again in reverse osmosis
(RO) water to remove detergent residuals. Dried with a lint-free cloth
or filtered pressurized air. The bulb may be cleaned with a cotton ball
dampened in alcohol (IPA), 1% sodium hypochlorite or alcohol-based
disinfectants
Video laryngoscope Plasma sterilization
9
blades 70% IPA Wipe
10
Ethylene oxide (EtO) gas
Silicone face mask and Disassemble and rinse parts under cold running water. Autoclave
manual resuscitator Submerge all parts in water containing dish washing detergent at
bag11 60–70°C and clean with brush
Cidex OPA (ortho-phthalaldehyde) 0.55% solution for 60 minutes
Silicone breathing Or sodium hypochlorite 0.5% solution for 20 min ETO (banned in
systems (circuits) of Autoclave or chemical disinfection as per manufacturer’s some countries)
12 recommendation
ventilators
Oral thermometers 1% sodium hypochlorite or alcohol-based disinfectants
Temperature probes
Noncritical ECG cable 1% sodium hypochlorite or alcohol-based disinfectants
9 Cleaning with alcohol solution 1 : 10 bleach
Pulse oximeter
Disinfection with glutaraldehyde solution: 2.0% CIDEX OPA if HLD
is required
Axillary thermometers Wash with cool water
1% sodium hypochlorite or alcohol-based disinfectants
Stethoscopes 70% isopropyl alcohol solution
Plastic blood pressure 0.5% hydrogen peroxide
cuffs
Cloth blood pressure Remove the tubing and inflation bag. Wash cuff with soap water
cuffs
13 Alcohol-free quaternary ammonium wipes Sodium hypochlo-
Ultrasound probe
rite wipes
Environmental Ventilator screen9 Isopropyl alcohol (70% solution)
surfaces
Bleach (10% solution)
Anesthesia Disinfection as per manufacturer’s recommendation Can be covered
workstation with sterile plastic
sheet which
can be changed
between two
cases
14
Monitor screen Cleaning with a lint-free cloth, moistened with warm water (40°C) Do not use bleach
and soap, a diluted noncaustic detergent, ammonia- or alcohol-based
cleaning agent
Disinfection with ethanol 70%, isopropanol 70%, or Cidex-activated
dialdehyde solution
Ultrasound machine13 Covering with plastic sheet to change between the patients Alcohol-free
quaternary
ammonium wipes
1116 Indian Journal of Critical Care Medicine, Volume 24 Issue 11 (November 2020)
Disinfection and Sterilization in COVID-19 Pandemic
Table 2: Commonly used sterilization techniques in health care
Technique Process Mechanism of action Uses Advantages Disadvantages
Steam 121°C for 15 minutes Denaturation and Surgical instruments Safe to patient, HCWs Damage to heat-
sterilization or 134°C for 3 minutes coagulation of en- can be used for stain- and environment sensitive equipment
zymes and structural less steel laryngoscope Low cost Loss of sharpness
proteins (battery removed) Can work in the pres- (needles, etc.)
ence of moisture
Ethylene Concentration of Alkylation (replace- Heat-sensitive Can sterilize heat- or Moderate cost, pro-
oxide (EtO) gas 450–1200 mg/L, at ment of a hydrogen equipment and moisture-sensitive longed cycle time
15 temperatures of 37 to atom with an alkyl instruments medical equipment Potential toxicity to
sterilization
63°C and RH of 40 to group) of microbial Disposable catheters patients, HCWs, and
80% for 1 to 6 hours proteins, DNA and and guidewires environment
RNA Banned for use in
respiratory equipment
in some countries
Hydrogen perox- Concentration of 6 Hydroxyl [·OH, the Heat-sensitive equip- Low-temperature High cost
ide vapor (HPV) mg/L, temperature neutral form of the ment and instruments sterilization Does not work in the
and hydrogen range of 37–44°C hydroxide ion (OH−)] Safe to patient, HCW, presence of moisture,
peroxide gas Cycle time of 75 and hydroperoxyl and environment cellulose, or cotton.
plasma (HPGP) (HO ·)-free radical and Poor penetration due
16 minutes 2
sterilization gas plasma formation to condensation at
17
surface
HCWs, healthcare workers
implants, contact lenses, etc. Its maximum bactericidal effect occurs can also be achieved with alcohol or QACs, etc., at lower exposures.
at 240–280 nm (UV-C). Mercury vapor lamps are commonly used as Low-level disinfection is used for noncritical items.
they emit radiation at 253.7 nm.
Upper-room UVGI provides disinfection of the upper part of surfAce contAmInAtIon And trAnsmIssIon
air in the room and can be used in the occupied rooms without of coVId-19 InfectIon
using protective clothing. Effective air disinfection in the lower part
of the room depends on vertical air movement. There is a lack of Transmission of the SARS-CoV-2 virus can occur directly between
data supporting its use in isolation rooms. It can cause occasional humans and indirectly through contact with surfaces or objects.33
skin erythema and keratoconjunctivitis in patients and visitors. The It remains viable in the surroundings of the infected person. The
use of UVGI for the decontamination of masks [filtering face piece viability of the virus depends on bioburden, ambient temperature,
respirators (FFRs)] is described below in detail. relative humidity (RH), and pH. In the areas surrounding even stable
COVID-19 patients, there is high likelihood of contamination of
dIsInfectIon1 environmental surfaces and ICU furniture, including common
Disinfection can be classified into high-, intermediate-, and electronic equipment, e.g., telephones, computers, etc. It is
low-level disinfection. While sterilization mandates prolonged therefore vital that all surfaces are frequently cleaned and
exposure, disinfection needs shorter exposure. These terms are disinfected.
not interchangeable. VIAbIlIty of sArs-coV-2 In VArIous
High-level Disinfection enVIronmentAl condItIons34,35
It destroys all microorganisms but not bacterial spores. Many SARS-CoV-2 virus can survive up to seven days at room temperature
chemicals can be used for disinfection (glutaraldehyde, hydrogen (22°C) with a RH of 65% on stainless steel and plastic surfaces,
peroxide, etc.) with exposure times varying from 8 to 45 minute, indicating possible fomite transmission. It is extremely stable over
at 20 to 25°C. They can be used for sterilization when used for a pH of 3–10. Viable virus can still be present on the outer layer
prolonged period. High-level disinfection is mainly used for of a surgical mask on the seventh day. It becomes nonviable on
semicritical items. cardboard in 24 hours.36
On copper surfaces, it becomes nonviable
Intermediate-level Disinfection within 4 hours. Soap solution (1:49) did not achieve effective
It destroys all microorganisms but spares spores and some small virucidal effect.
nonenveloped viruses. Intermediate-level disinfection is used for
noncritical items, which are visibly soiled with patient’s fluids and current recommendAtIons for
blood. This is done with alcohol or QACs, etc. sterIlIzAtIon And dIsInfectIon of medIcAl
Low-level Disinfection (LLD) equIpment And enVIronment
It destroys most microorganisms and some viruses but has no action The selection of disinfectants should be based on various factors
on Mycobacterium tuberculosis and spores. Low-level disinfection such as targeted microorganisms, availability of disinfectants, etc.
Indian Journal of Critical Care Medicine, Volume 24 Issue 11 (November 2020) 1117
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