Advances in technology have improved the survival ofsmall, low birthweight infants. Due to their prematurity,

these infants are at significant risk of acquiring infectionduring their hospitalization. In fact, surveillance cultures haveshown infection rates of 15-20% in some neonatal intensivecare units (NICUs). Knowledge of risk factors, etiology, andsome fundamental principles of microbiology is a first step inprevention.1

Nosocomial, hospital-acquired, or late onset neonatalinfection are all terms used to describe those infections whichgenerally occur after the first week of life and are acquiredfrom the postnatal environment. Nosocomial infections aredifferentiated from early or congenital infections not only bythe timing of disease onset, but also by the commonoffending microorganisms. Nosocomial infections areacquired from direct contact (eg caregiver hands) and indirectcontact (eg contaminated objects) with organisms found inthe nursery macro-environment.1,2 So how are nosocomialinfections and the micro-environments in which sick infantsare cared for related? In order to answer this question, let’sbriefly review the history of incubator care.

THE CLOSED MICROENVIRONMENTExperts have recognized the importance of a closed micro-

environment as a means of achieving warmth for preterminfants since the late 19th century when significant decreasesin infant mortality were realized with the regular use of thistechnology.3 Large body surface area relative to mass,decreased subcutaneous fat, and limited ability to produceheat secondary to poorly developed brown fat stores,predispose the preterm infant to large heat losses if exposedto cool ambient temperatures.4 Incubators were the firstmicro-environment designed to provide the infant with athermally neutral environment. Present-day incubatorsprovide convective heat as means of achievingthermoneutrality. In theory, the thermal neutral zone isdefined by specifications of an environment in which thepreterm infant can minimize energy usage for heat productionand maximize his or her energy expenditure for growth anddevelopment. For many preterm infants though, evenmaximum convective air temperature settings approaching 39degrees C may be insufficient to maintain core bodytemperatures of 36.5 to 37 degrees C. This phenomenongenerally occurs because the heat partition through which theinfant is losing excessive heat is that of evaporation by way

of transepidermal water loss (TEWL) and it can be difficultfor convective heat to offset the evaporative losses.5

HUMIDITY AND THE CLOSED MICROENVIRONMENTSo how does one counterbalance evaporative losses? Use

of supplemental humidity is one method to be considered bythe clinician. However, just as with all therapies there arebenefits and risks. The use of high humidity in an enclosedmicro-environment offers several benefits. Among theseadvantages are reduced evaporative heat losses, decreasedinsensible water loss, improved fluid and electrolyte balance,and enhanced skin integrity. High levels of humidity can beespecially beneficial during the first few days and/or weeks oflife before skin of the very low birthweight infant matures.5

Researchers have shown that as the air temperature of theenclosed micro-environment increases, the relative humiditydecreases unless a source of humidity is provided (See Fig.1). This phenomenon happens because warmer air has anincreased capacity for water vapor. In effect, raising the airtemperature within an enclosed micro-environment without aconcomitant increase in water vapor increases the potentialfor TEWL and hence, evaporative heat loss which may bedifficult for the convective heat supply of an enclosed micro-environment to overcome. For example, let’s say that point Arepresents the temperature of a typical labor and deliverysuite at 68 degrees F, with a relative humidity of 50%. If thatbaby is sick and requires care in a 90 degrees F incubator,notice that the RH that the baby is subjected to drops to 25%. This factor may be particularly important in the case of asmall preterm infant’s first days and/or weeks of life, as theirimmature skin with little or no subcutaneous fat and stratumcorneum, yields a large surface area for evaporative heatloss. Hence, the need for humidity as a therapeuticintervention to protect against evaporative heat loss.6,7

RISKS ASSOCIATED WITH HUMIDTYThere is a concern that the thermoneutral environment

within an enclosed micro-environment coupled with highre la t ive humidi ty may pose a s igni f icant r i sk fornosocomial infect ion in low bi r thweight infants .However, in light of design modifications to currentinfant microenvironments, that data may be dated andrequire re-examination by clinicians.

American studies conducted in the 1950’s and 1960’ssuggested a high correlation between use of humidity andan increasing incidence of necrotizing pneumonia in lowbirthweight infants. Environmental studies of incubatorssuggested that water basins of nebulizing units used toprovide humidity were harbingers of gram-negative

50 neonatal INTENSIVE CARE/ Vol. 15 No. 2/ March, April 2002

Lynn Lynam is Clinical Research Manager for Ohmeda Medicaland a practicing neonatal nurse practitioner. Lara Biagottiworks as a consultant to the medical device industry.

TESTING FOR BACTERIALCOLONIZATION IN AN OHMEDA

MEDICAL GIRAFFEHUMIDIFICATION SYSTEM

Lynn Lynam, Lara Biagotti

PRODUCTS 51

microbial species or fungi . Organisms such asPseudomonas aeruginosa , Escherichia coli , Serratiamarcescens, or Candida albicans were found to colonizenot only the water basins but the internal mechanisms of theunit as well. In this location, sterilization would be almostimpossible. Furthermore, whenever a nebulization methodwas used to provide micro-environmental humidity, thepotential existed for any bacterial contaminant within thewater basin to become airborne on water droplets as thenebulizing device broke a larger water molecule intosmaller liquid particles. In addition, the manufacturers’design of these devices at the time did not involve anyactive heating of the water pool, as a method of bacterialcontrol. Thus, the correlations between infection rates andhumidity were probably real rather than artifact.8,9,10,11

ORGANISMS OF CONCERNCurrently, four organisms seem to cause most concern for

human newborns.2 Three are gram negative microbes and oneis a yeast.1,2,8 However, nosocomial infections in neonatalintensive care environments are not limited to the germs. Allgram negative organisms secrete numerous toxic exoproductsfrom their cell walls. These endotoxin are lethal compoundsthat initiate secretion of several inflammatory mediators felt tobe responsible for the pathogenesis of sepsis. Infections causedby gram negative rods can be severe and fulminant,progressing rapidly to multisystem organ failure.

Escherichia coli is the most prevalent gram negativeorganism (see Fig. 2). E. coli colonizes the lower intestinaltract soon after birth and remains the predominant fecal florathroughout life. Sepsis with E. coli may occur aftercolonization from the environment or from translocation of thebacterial across the intestinal tract. Strains of E. colicontaining the K1 antigen are among the most commonorganisms responsible for purulent meningitis. Invasions of thebloodstream by organisms that have colonized mucosalsurfaces usually precede both sepsis and/or meninigitis.12

Pseudomonas aeruginosa is a water-loving, gram negative,aerobic rod that can be found in moist areas (see Fig. 3). It isan opportunistic infection, as infection is rare in healthyindividuals. However, it is a virulent organism that infects thevulnerable host. Therefore, immune compromised newbornscontract systemic infections that occur through contaminated

equipment, aqueous solutions, and, at times, the hands ofhealth care personnel. It can infect all types of wounds,particularly burns. The underdeveloped stratum corneum ofthe preterm newborn makes them highly susceptible to thismicrobe. Pseudomonas can cause sepsis, severe conjunctivitis,necrotizing pneumonia, endocarditis, meningitis, and death. Itis also known to be resistant to multiple antibiotics.12

Serratia marcescens can cause rapidly spreading outbreaksof severe infections in neonatal intensive care units and isfrequently multiresistant to antibiotics (see Fig. 4). Outbreaksin NICUs have been attributed to contamination of variousequipment and supplies (e.g. ventilators, IV solutions, breastpumps, soap dispensers). Recently, studies have concluded thatcolonized and infected infants are the most frequent reservoirof Serratia marcescens and are potential sources of horizontaltransmission via the hands of healthcare personnel. Control ofoutbreaks requires cohorting and isolation of infected andcolonized infants with strict handwashing, gowning, andgloving procedures. Because Serratia marcescens has beenshown to survive on the hands of healthcare personnel despiteuse of a strict handwashing protocol, gloves are cruciallyimportant in preventing the spread of infection.12

Candida albicans (ovoid budding yeast) is the most frequentcause of fungal sepsis in the low birthweight preterm infant(see Fig. 5). It has become more prevalent since theintroduction of widespread antibiotic use and the threshold ofviability has been progressively challenged down to 22 to 23weeks gestation. In most infants, colonization from Candidaoccurs in utero or at the time of delivery. Other infants mayacquire fungus from caregivers during hospitalization. In fact,colonization of the skin generally precedes an opportunisticsystemic yeast infection.12

HUMIDITY AND CURRENT TECHNOLOGICALADVANCES

Humidity may have other benefits in addition to protectionagainst evaporative heat loss and stabilization of the neutralthermal environment. Other research shows that these sameenvironmental conditions also act to stabilize fluid andelectrolyte balance, and to preserve skin integrity. Optimizingthese aspects of newborn care may enhance utilization ofmetabolic substrates to promote growth and development ofthe infant.

Risks versus benefits is critical to the decision makingprocess before implementing any therapeutic intervention suchas humidity. The clinician should be guided by clear evidencethat the benefit outweighs the risk. When one considers theresearch, it is important to know that as a result of theinfectious outbreaks in the 1950s and 1960s, Ohmeda Medicalchanged its methodology of providing micro-environmentalhumidity. The main part of the Giraffe® HumidificationSystem consists of an immersion heater that sits within a bathof sterile, distilled water. The temperature of this water bathreaches a temperature of 52 degrees C to 58 degrees C whichby itself is bactericidal to most mesophilic microorganisms(that is, organisms which tend to thrive at moderatetemperatures of 20 to 45 degrees C and act as pathogens in thehuman body). However, this temperature is insufficient toprotect the infant from a potential source of infection shouldaccidental contamination of the reservoir take place.12 As anadded measure of safety, engineers designed the immersionheater so that a small aliquot of water is boiled just before thehumidity is disbursed into the air circulation within the infant

52 TESTING FOR BACTERIAL COLONIZATION IN AN OHMEDA MEDICAL GIRAFFE HUMIDIFICATION SYSTEM

FIG. 5: Candida albicans

FIG. 4: Serratia marcescens

FIG. 3: Pseudomonas aeruginosa

FIG. 2: Escherichia coli

compartment. By using this technology, sterile humidity is created and offered tothe infant in a gaseous vapor state, leaving no airborne water droplets to act asvectors of infectious microorganisms.

As with any humidification system, proper cleaning and routine changing ofwater will reduce the potential for bacterial propagation. The design of theGiraffe® humidification system allows for the reservoir to be accessed from thefront of the bed without disturbing the infant. This facilitates ease of changing thewater and cleaning of the water reservoir on a routine basis, as determined by unitpolicy. This study indicates that the Ohmeda Medical Giraffe® humidificationsystem will not promote bacterial growth.

EVIDENCE-BASED PRACTICEPurpose Due to concerns over bacterial or fungal propagation, this study was conducted toevaluate the Ohmeda Medical Giraffe Humidification System. Specifically, theproduct’s ability to provide specified levels of humidity and ease of operation andcleaning are important. However, the risk of bacterial propagation with high levels ofmicro-environmental humidity must be fully described.Equipment3 Giraffe units with Active Humidification SystemSterile, distilled waterAmerican Type Culture Collection (ATCC) microorganisms: P. aeruginosa, E.

coli, S. marcescens, C. albicansAppropriate culture mediaCalibrated thermometer ProcedureClean 3 Giraffe® units, including humidifier with Cavicide.Giraffe #1 (experimental)—humidity condition, reservoir contaminated.Giraffe #2 (control)—humidity condition, no reservoir contaminationGiraffe #3 (control)—no humidity condition, no reservoir contamination.Reconstitute freeze dried microorganism (103 to 106 cfu/ml).Fill humidifiers of Giraffe #1, #2 with 1 liter sterile, distilled water.Prewarm all 3 Giraffe units in air control mode @ 35 degrees C for 1 hour.Set humidity levels of Giraffe #1, #2 @ 65% RH for 1 hour.Record water bath temperature @ time of inoculation.Culture site(s) of all 3 beds just prior to inoculation: humidity reservoir at

immersion heater, reservoir injector seal, points of airflow at midpoint of eastand west doors, center of bed, servO2 system (6 sites, see Fig. 6).

Inoculate humidity reservoir of Giraffe #1 (time 0h) with P. aeruginosa (or E. coli,

S. marcesens, C. albicans @ sequential 1week intervals) with 10 cc of reconstitutedmicroorganism (103 to 106 cfu/ml).

Culture site(s) @ time 0h: humidity reservoir atimmersion heater, reservoir injector seal,points of airflow at midpoint of east and westdoors, center of bed, servO2 system (6 sites,see Fig. 6).

Refill humidifiers of Giraffe® #1, #2 q 12hours or prn with 1 liter sterile, distilledwater.

Record water bath temperature at time of eachculture session @ 24h, 48h, 72h, 168h.

Reculture sites @ 24h, 48h, 72h, 168h post-inoculation.

Site(s) of post-inoculation cultures: humidityreservoir at immersion heater, reservoir seal,points of airflow at midpoint of east and westdoors, center of bed, servO2 system (sites,see Fig. 6).

Each microorganism was studied separately atone-week intervals.

MethodsTo determine the role of humidity in

microbial colonization of an enclosed micro-environment. As a condition of this laboratoryresearch, a Giraffe micro-environment wascleaned with a germicidal detergent utilizing adilution of one ounce per gallon of water at thestart of the study (Cavicide, active disinfectingingredient: diisobutylphenoxyethyl dimethylbenzyl ammonium chloride). The enclosedmicro-environment was run in air control modeat 35 degrees C and actively humidified at 65%RH through a servo-controlled mechanism.Sterile, distilled water was added at the start ofthe study and as needed to the water reservoir.After reaching temperature and humidityequilibration, a known inoculum of one of fourdifferent micro-organisms (P. aeruginosa, S.marcesens, E. coli, or C. albicans) reconstitutedto 106 to 108 cfu/ml H2O was placed into thereservoir on day 0 and baseline cultures wereobtained. Bacterial cultures were taken at fivepoints including the humidification reservoirnear the immersion heater, the reservoir seal atentry to the Giraffe®, along the path of airflowat both the east and west doors, and the centerof the mattress. Semi-quantitative bacterialswabs were repeated at 24h, 48h, 72h, and168h. The testing of each micro-organism wasdone serially over a four week period.

Discussion Risks versus benefits is critical to the

decision making process before implementingany therapeutic intervention such as humidity.The clinician should be guided by clearevidence that the benefit outweighs the risk.When one considers the research, it isimportant to know that as a result of theinfectious outbreaks in the 1950’s and 1960’s,Ohmeda Medical changed its methodology of

PRODUCTS 53

providing micro-environmental humidity.It is not surprising that purposeful inoculation of the

patented Giraffe Humidification System yielded no pathwayfor conduction of infectious microorganisms into the infant’smicro-environment. No microorganisms were ever collectedfrom the patient environment during the entire course of thestudy. Microorganisms were cultured from the humidifierreservoirs at 24 hours under the Pseudomonas aeruginosaand Candida albicans conditions but at a colony count thatwas reduced to 102 cfu/ml. This suggests that the thermaldeath time to kill these two microorganisms at the water bathtemperature within the system is between 24 and 48 hours.

The results are also not surprising in light of the fact thatevery component of the system was designed to protect theinfant from potentially harmful pathogens when the infant’sown primary barrier, the skin, may be compromised due toconditions surrounding prematurity. Results of this studyshowed that the temperature of the water bath in thehumidification reservoir typically reached 52 degrees C at themost distal point from the immersion heater to 58 degrees Cbeside the device. These temperatures are probablybactericidal to most mesophilic microorganisms (that is,organisms which tend to thrive at human body temperatureand act as pathogens).12 Yet this intentional design feature isinsufficient to protect the infant from a potential source ofinfection should accidental contamination of the reservoirhappen.

As an added measure of safety, engineers designed theimmersion heater so that a small aliquot of water is boiledjust before the humidity is disbursed into the air circulationwithin the infant compartment. By using this technology,sterile humidity is created and offered to the infant in agaseous vapor state, leaving no airborne water droplets to actas vectors of infectious microorganisms.

Furthermore, some clinicians have reported that traditionalboiler type humidification systems have tubing distal to theboiler to conduct “sterile” steam from the boiler to the infantchamber. Principles of physics suggest that such tubingwould permit re-condensation of water vapor into a liquidstate, thereby acting as a possible focal point for bacterialovergrowth.

As with any humidification system, proper cleaning androutine changing of water with reduce the potential forbacterial propagation. The design of the Giraffe®Humidification System allows for the reservoir to be accessedfrom the front of the bed without disturbing the infant. Thisfacilitates ease of changing the water and cleaning of thewater reservoir on a routine basis, as determined by unitpolicy. This study indicates that the Ohmeda MedicalGiraffe® humidity system will not promote bacterial growth.

ConclusionThis study indicates that the humidity system in the

Ohmeda Medical Giraffe family of products will not promotebacterial or fungal growth. The humidification system of theGiraffe family of products can provide an adequate level ofrelative humidity which can be extremely beneficial to thelow birthweight infant. The system was found to be easy tooperate, to fill, and to clean without disturbing the infant.This means that the clinician can provide a therapy withoutconcern for an increased risk of infection to the infant whenthe reservoir is filled daily with sterile distilled water and the

bed is routinely cleaned, according to the protocol describedwithin this study. @n

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8. Reinartz JA, Pierce AK, Mays BB, and Sanford JP (1966).The potential role of inhalation therapy equipment innosocomial pulmonary infection. Journal of ClinicalInvestigation, 44, 831-839.

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54 TESTING FOR BACTERIAL COLONIZATION IN AN OHMEDA MEDICAL GIRAFFE HUMIDIFICATION SYSTEM

FIG. 7: GIRAFFE® Humidifier