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Fundamentals of Nursing Care: Concepts, Connections, & Skills
Chapter 14
Medical Asepsis and Infection Control
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Key Terms/Infection Control
 Pathogens
 Microorganisms causing infection in humans
 Normal flora and fauna
 Plants and animals normally found in the human
body
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Types of Pathogens
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Bacteria
Viruses
Protozoa
Fungi
Helminths
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Bacteria
 Once celled microorganisms found virtually
everywhere
 Invade area not normally found
 Ex. E. coli normally found in intestines—
helpful
 Introduced to urinary system—trouble
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Bacteria
 Name two bacteria that can only reproduce
inside the cells of the host.
 Often spread through the bites of insects
(ticks and mites). These insects would be
referred to as ____________________.
 Treatment for bacterial infections?
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Classifications of Bacteria by Shape
• Identifying bacteria in the laboratory
• Cocci—sphere shaped bacteria
• Clusters—staphylococci
• Chain—streptococci
• Bacilli—rod shaped
• Log like, vary in length
• Spirilla—spiral or coil shaped
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Gram Stain
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Dark purple stain applied to slide
Other steps followed in lab
Bacteria take up stain
Under microscope—purple or blue—gram
negative organism; pink or red—gram positive
organism
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Viruses
 Not a cell—a parasite—live within the cells of
the host and reproduce
 Can only be seen with an electron microscope
 All viruses potentially cause illness
 Medication to treat a viral infection?
 Are most viral infections severe?
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Viruses
 Why not use an antibiotic?
 When is an antibiotic appropriate with a viral
infection?
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Protozoa
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Single celled animal
Lives in water
Ingested through water or food
Result—intestinal disease
If parasite—prescribed antiparasitic
medication
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Fungi
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Can only be seen with use of a microscope?
How can fungi enter body?
Most suseptible individuals?
What is a systemic fungal infection?
In what forms are antifungal medications
available?
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Helminths
 Parasitic worms
 Target area in humans?
 Enter most commonly through contaminated
food
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Bacterial Infections
 Staphylococcus aureus (gram + coccus)
 Boils, toxic shock syndrome, osteomyelitis
 Treatment—antibiotic (most not sensitive to
penicillin)
 MRSA—methicillin resistant staphylococcus
aureus
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Bacterial Infections
 MRSA
 Health care associated—hospital, nursing home,
dialysis center…….
 Can develop anywhere
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Bacterial Infections
 Health care associated risk factors
 Most vulnerable elderly and those with weakened
immune systems
 Invasive medical devices
 Long term care facilities—prevalent—don’t always
know who has it—colonized
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Bacterial Infections
 Community acquired MRSA
 Small red bumps—resembling pimple, boil or
spider bite
 Can spread quickly—deep, painful abscesses
 May stay confined to skin but can burrow deep to
bones, joints, bloodstream, heart, lungs and
produce potentially life-threatening infections
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Bacterial Infections
 Treatment
 Vancomycin
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Bacterial Infections
 Streptococcus group A (gram + coccus)
 Strep throat, ear infections, scarlet fever,
endocarditis
 Necrotizing fasciitis—flesh-eating strep (rare but
can be fatal)
 Treatment—antibiotics
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Bacterial Infections
 Clostridium perfringens (gram + bacillus spore
forming)
 Gas gangrene in contaminated wounds
 Usually occur after injury or surgery
 Can occur anywhere on body, most common in
extremities
 Occurs suddenly and spreads quickly
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Bacterial Infections
 Spore forming bacteria
 Spores form around the organism
 Protect organism from hostile environments
 Chemicals and heat
 Organism can be dormant for years unaffected by:
change in temperature, absence of air, water and
nutrients
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Bacterial Infections
 Gas gangrene
 Spores live in dead tissue
 Produce toxins that destroy more tissue
 The gas forms bubbles in the dead tissue
 Treatment
 Antibiotics
 Debridement
 Amputation
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Bacterial Infections
 Clostridium Difficile (C-diff) (gram + bacillus
spore forming)
 Antibiotic use
 Contamination of food, objects and surfaces with
lack of or poor handwashing
 Mild cases may get better when stop using
antibiotic
 More severe cases need to take an antibiotic
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Bacterial Infections
 C-diff
 Vancomycin or metronidazole (Flaggyl)
 Most commonly affects older adult in hospitals or
long term care facilities
 Symptoms range from diarrhea to life-threatening
inflammation of the colon
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Bacterial Infections
 Signs and symptoms of C-diff
 Mild—watery diarrhea 3 or more times/day for
several days with abdominal pain or tenderness
 Severe—watery diarrhea 15 or more times/day
 Abdominal pain
 Loss of appetite
 Fever
 Blood or pus in stool
 Weight loss
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Bacterial Infections
 C-diff
 Bacteria produces toxins that attack the lining of
the intestines
 Inflammation
 Complications
 Dehydration, kidney failure, perforation of
intestine, potential death
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Bacterial Infections
 C-diff Risk Factors
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Taking antibiotics
65 years of age or >
Health care setting
Immunocompromised
Inflammatory bowel disease, abdominal surgery
or GI procedure or previous C-diff infection
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Bacterial Infections
 C-diff
 Healthy individuals usually protected
 Normal flora present
 Unfortunately, a new aggressive strain has
appeared
 Produces more toxins, more resistant to meds and
occurring in people who have not been hospitalized or
on antibiotics
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Bacterial Infections
 E. coli (Escheria coli) (Gram – bacillus)
 Normally found in the colon
 Causes infection when enters other parts of the
body
 Common cause of health care associated
infections
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Bacterial Infections
 E. coli
 VRE (Vancomycin Resistant Enterococci)
 Generally enterococci are not very harmful or
virulent
 But when infect urinary tract, surgical wounds or
bloodstream—may be difficult to treat, can be life
threatening
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Viral Infections
 Herpes Simplex
 Type 1—cold sore
 Type 2—genital herpes
 Herpesvirus 3
 Varicella-zoster—shingles
 Must have had chicken pox or chicken pox vaccine
 Virus lies dormant in nerve endings
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Viral Infections
 Shingles
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Reactivation of chicken pox virus
Clusters of fluid filled vesicles along nerve
Painful
Immunocompromised individuals
Contagious?
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Viral Infections
 Treatment
 Antiviral medication when necessary
 Example: Acyclovir
 Must start within a particular time frame to be
most effective
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Viral Infections
 Influenza
 Flu
 Flu versus common cold
 Fever, respiratory congestion, sore throat, cough,
chills, headache, aching muscles and/or fatigue
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Viral Infections
 Treatment
 Symptomatic treatment
 If necessary—antivirals (Tamiflu or Relenza)
 Prevention
 Annual flu immunization
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Viral Infections
 West Nile Virus
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Virus found in birds
Spread by mosquitos
Causes headache and confusion in some
May be asymptomatic in others
 Treatment
 Symptomatic—no antiviral exists
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Fungal Infections
 Ringworm (microsporum epidermophyton)
 Tinea—found on skin or scalp
 Tinea capitis
 Tinea pedis
 Tinea cruris
 Itchy, red, round patches
 Treatment—antifungals
 Start topical due to side effects
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Fungal Infections
 Yeast infection (candida albicans)
 Mouth—thrush
 White lesions (cottage cheese), painful, bleed easily
 Vagina
 Itching, burning, swelling, irritation, discharge
 May be due to antibiotic use
 Can cause pneumonia and heart infections
 Treatment--antifungal
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Protozoan Infections
 Amebic dysentery
 Causes severe bloody diarrhea
 Can cause abscesses in body organs (liver, lungs
and/or brain
 Spread through food or water contaminated with
stools
 Can be spread person to person when contact
with mouth or rectal area of infected person
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Protozoan Infections
 Amebic dysentery
 Treatment
 Amebicides and antibiotics
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Protozoan Infections
 Giardiasis (giardia lamblia)
 Often found in water
 May also be spread through food prepared by
people who have a mild case of the illness
 Causes diarrhea, abdominal cramps, nausea,
bloating
 Treatment
 Antibiotics
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Helminth Infections
 Pinworms (Enterobius)
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Look like white threads
Grow in the intestine
Most common parasitic worm in the U.S.
Swallow the eggs—hatch in the intestines
Spread easily
 Treatment--antihelmintics
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Helminth Infections
 Tapeworm (Taenia)
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Undercooked meat containing the worm cysts
Head of wom attaches to wall of intestine
Grows
Bloating, constipation or diarrhea
 Treatment--Antihelmintics
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Links in the Chain of Infection
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Infectious agent or causative organism
Reservoir or place where the organism grows
Portal of exit
Mode of transmission
Portal of entry
Susceptible host or person
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Chain of Infection
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Types of Infections
 Health-care-associated infection (HAI)
 Previously referred to as nosocomial infection or
hospital acquired infection
 Monitored very closely
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Nonreimbursement for HAIs
 The Centers for Medicare and Medicaid
Services (CMS) have now ceased to pay for
any costs related to three common hospitalacquired infections
 Catheter-associated infections
 Infections in the blood due to central vascular
lines
 Infection in the chest incision after open-heart
surgery
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Types of Infections
 Primary infection
 Initial infection caused by one pathogen
 Secondary infection
 Caused by a second, different pathogen
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Types of Infections
 Localized infection
 Infection in one area of the body
 Systemtic infection
 Spreads from the one area of the body to other
areas
 Septicemia
 Microorganisms present and multiplying in the
blood
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Primary Defenses Against Infection
 Skin—intact
 Mucous membranes
 Sticky—trap invading pathogens
 Respiratory—GU
 Gastrointestinal system
 Saliva—enzymes Normal flora Hydrochloric acid
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Secondary Defenses
Against Infection
 Inflammatory process
 Elevated temperature—hostile
 Complement cascade—specialized proteins
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Tertiary Defenses Against Infection
 B and T cells
 Lymphocytes found in lymph tissue (spleen,
thymus, lymph nodes and tonsils) and circulating
in the blood
 Signal phagocytes to destroy invaders
 Have major role in antigen-antibody response
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Factors Affecting Body Defenses
Against Infection
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Age
Chemical exposure
Chronic illness
Lack of exercise
Lack of rest
Increased stress
Nonintact skin
Poor nutrition
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Preventing Infection
 Do not become a mode of transmission
 Prevent infection from
 Patient-to-patient
 Nurse-to-patient
 Patient-to-nurse
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Techniques Performed in Medical
Asepsis
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Hand hygiene
Maintaining a clean patient environment
Using standard precautions
Using transmission-based precautions when
necessary
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Preventing Infection
 Most effective way to break the chain of
infection
 HAND HYGIENE!!!!!
 Handwashing
 Hand sanitizer
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Surgical Asepsis/Sterile Technique
 Surgical asepsis
 Maintaining a sterile environment such as that
found in operating rooms
 Sterile technique
 Performing procedures in such a way that no
pathogens will enter the patient’s body when
inserting tubes or giving injections
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
True/False Question
A nurse uses surgical asepsis when performing
hand hygiene.
A. True
B. False
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Answer
B. False
Rationale: The term medical asepsis refers to
practices performed to prevent the spread of
infection. These practices, or techniques,
include performing hand hygiene, maintaining
a clean patient environment, using standard
precautions, and using transmission-based
precautions when necessary.
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
When to Wash Your Hands
 After touching blood, body fluids, secretions,
excretions, or contaminated items
 After using the restroom
 Any time your hands are visibly dirty
 After caring for a patient infected with a spore
forming organism
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
When to Wash Your Hands or Use
Hand Sanitizer
 Immediately after removing gloves
 Upon entering a patient’s room
 Between caring for two patients in the same
room
 When arriving on the nursing unit
 After returning to the nursing unit from break
or meals
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Guidelines for Health Care Workers
 Guidelines for preventing infection
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Limit jewelry—watch and wedding ring
Only natural nails—tips < ¼ inch
Nail polish must be well kept—no chipping
Hand lotion—no oils
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Handwashing
 Prefer not to use bar soap
 Turn on water
 Adjust to comfortable temperature
 Wet hands under running water
 Careful not to touch the dirty sink
 Obtain a quarter size amount of soap in palm
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Handwashing
 Work into a lather
 Using friction
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Rub palms together
Place one hand on top of the other and rub
Interlace fingers
Perform on both hands
 Friction helps dislodge soil & microorganisms
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Handwashing
 Rub fingernails against the palm of the
opposite hand
 Work the lather around and under the nails
 Lather around each wrist
 Handwashing is recommended for at least 20
seconds—length of time to sing “happy
birthday” twice
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Handwashing
 Rinse hands with fingers pointed downward
 Allows water to urn from the cleanest area
downward
 Avoid touching the sink
 Dry hands with paper towel
 Use a clean paper towel to turn off faucet
 DROP paper towel in trash without touching
waste recepticle
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Hand Sanitizer
 First—is it appropriate to use a hand sanitizer
 Obtain the manufacturers recommended
amount of sanitizer in the palm of hand
 Rub hands together so sanitizer covers all
surfaces of hands and fingers
 Continue rubbing hands together, interlacing
fingers until hands are dry
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Maintaining a Clean Environment
and Equipment
 Clean up spills as soon as occur—Safety and
potential breeding ground
 Remove uneaten food from room
 Offer handwashing to confined patients
 Disinfect overbed table or ………………….
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Disinfection
 Will remove most pathogens
 Not some viruses or spore-forming bacteria
 Must be sterilized
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Clean Environment and Equipment
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Disposable equipment—single patient use
Reuseable equipment—must be disinfected
Disinfect according to facility policy
Dried blood—some viruses can survive for
days to week or more
 Clean equipment and then send to central
supply
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Standard Precautions
 Group of safety measures performed to
prevent the transmission of pathogens found
in the blood and body fluids
 Includes performing hand hygiene, wearing
appropriate protective equipment if exposure
is possible, and using cough etiquette
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Protective Equipment Used With
Standard Precautions
 Gloves*
 Gown*
 Mask*
 Eye protection*
 Face shield*
 Puncture-resistant sharps container
*When risk of contact with blood or body fluids is
present
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Standard Precautions
 Used with ALL patients—regardless of
diagnosis
 Protect health care worker
 Protects patients
 Discuss Table 14-2
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Standard Precautions
 View video on proper application and removal
of PPE
 Discuss Box 14-3 Signs and Symptoms of Latex
Reactions
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Transmission-Based Precautions
 Prevents the spread of known infection to
patients or health-care staff
 Used when a patient has a communicable
illness spread through contact, respiratory
droplets, or through the air
 Gowns, gloves, masks, eye protection, and
possibly head covers are used for protection
as appropriate
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Transmission-Based Precautions
 Contact—Direct and Indirect Contact
 Use for excessive wound drainage, fecal
incontinence, and infection with multidrugresistant organisms
 Droplet
 Use when in close contact with respiratory or
mucous membrane secretions
 Airborne
 Use with pathogens spread by air currents
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Contact Isolation
 Most common path of transmission is by
direct contact
 One person directly to another—usually hands
 Indirect contact—microorganisms from
someone contaminate an object (BP cuff) then
cuff is used on a susceptible host
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Contact Isolation
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Wash hands
Gloves
Gown
Upon entering room
Wear gloves to touch patient and contents of
room
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Droplet Isolation
 Illness transmitted from respiratory system
 Through small droplets—coughing, sneezing,
talking
 Droplets then inhaled or swallowed by
another person
 3 feet distance from patient if not wearing PPE
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Droplet Isolation
 Not ideal but can share room with another
patient not on droplet isolation—but must be
3’ apart and pull curtain
 Proper PPE
 Mask
 Gloves
 Gown
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Droplet Isolation
 Patient teaching
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Teach and encourage proper cough etiquette
Cough/sneeze into a tissue
Discard tissue properly
Hand hygiene
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Airborne Isolation
 Infectious particles so small and lightweight
float on air
 Catch an air current
 Airborne infection isolation room—previously
negative pressure room
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Airborne Isolation
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N95 respirator mask
Custom fit
Gloves
Gown
Copyright © 2011 F.A. Davis
Fundamentals of Nursing Care: Concepts, Connections, & Skills
Caring for Patients in Isolation
 Spend time talking with the patient while you are in
the room
 Ask the patient if you can bring him or her anything
to pass the time, such as newspapers or magazines
 Avoid expressing distaste regarding the patient’s
diagnosis or having to enter an isolation room
 Remember that the patient is a person first, and that
the diagnosis is secondary to his or her human needs
Copyright © 2011 F.A. Davis