Cross-infection can occur between patients using contaminated anesthetic apparatus. Methods of disinfection include use of soap and w ater rinses, alcohol sprays, and commercial cleaners. More effective techniques are often impractical. A simple method tested in this study provided adequate disinfection of the rubber goods used in the administration of gas.
Disinfection of nitrous oxide inhalation equipment John A. Yagiela, DDS, PhD Lindsay M. Hunt, DDS, PhD Dale E. Hunt, PhD
on cern ab o u t the possible role of the d en tal profession in th e tran sm issio n of infectious d is ease has fo cused atten tio n on th e p ro p e r steriliza tio n of d en tal e q u ip m en t.1 O ne in stru m e n t th at has largely escap ed co n sid eratio n is the n itro u s oxide gas m ach in e w ith its a tte n d a n t tubing, n asal hood, an d reserv o ir bag. R ecom m endations for ro u tin e clean in g of n itro u s oxide eq u ip m en t vary from spraying th e nasal hood w ith scen ted alco h o l2 to w ash in g all ru b b er goods w ith soap a n d w ater.3 It is q u estio n ab le w h e th e r th ese or o ther tech n iq u es cu rren tly in general use pro v id e adeq u ate d isin fec tion. M icrobial cross-contam ination d u rin g sed a tio n w ith n itro u s oxide has not b een co n sid ered a problem , b u t related in h alatio n devices have b een lin k ed w ith nosocom ial infections.
apparatus was unlikely and should not be consid ered as a health hazard associated w ith general anesthesia. Since that time, however, evidence has accum ulated indicating that anesthetic and other inhalation devices are potential sources for the iat rogenic transm ission of infectious disease.5,6 Mi croorganism s have been recovered from virtually every portion of the anesthetic breathing circuit.7 Results from a questionnaire to all directors of anesthetic training programs in the U nited States show ed that 70% of those institutions that studied the m icrobial status of their respective anesthetic systems obtained cultures of m icroorganism s from their equipm ent.8 Organisms that have been iso lated from anesthetic and inhalation equipm ent in clude know n pathogens, such as C andida albicans, C lostridium peifringens, Escherichia coli,
Microorganisms and anesthesia equipment
H a em o p h ilu s in flu e n za e suis, K lebsiella p n e u m o niae, M ycobacterium tuberculosis, Pseudom onas aeruginosa, S a lm o n ella m o n tived e o , Staphylococ cus aureus, Streptococcus pyogenes, and the viri-
In 1952, an annotation in the British M edical Jour nal4 stated that cross-infection from an anesthetic
JADA, V ol. 98, February 1979 ■ 191
dan s strep to co cci.9 It can b e assu m ed a prio ri th at v arious m y co p lasm a, v iru ses, a n d o th er organism s n o t ev alu ated m ay also have been p re sen t in the an e sth e tic devices.
The incidence of cross-infection from contam i nated anesthetic equipm ent is not known. Deaths have been reported on occasion, but it is probable that the source of m any fatal infections is unrecog nized. Perhaps a more accurate appraisal of the m agnitude of m icrobial cross-contam ination may be derived from investigations equating postopera tive rates of infection w ith techniques used to clean or disinfect inhalation equipm ent. In one study,10 it was found in a retrospective evaluation that the in cidence of postoperative pulm onary infection di m inished 75% after the adoption of routine sterili zation of the anesthetic circuit betw een use by pa tients.
Cross-infection and administration of nitrous oxide Potential problem s of iatrogenic m icrobial transfer faced by dentists are less than those encountered by anesthesiologists. Dental patients are generally healthier than hospitalized patients; techniques of sedation w ith nitrous oxide are less invasive than those of general anesthesia; and nitrous oxide units are probably less susceptible to contam ination than are anesthetic rebreathing circuits. Nevertheless, the possibility exists that dental practitioners using nonsterile equipm ent m ay unintentionally be facilitating the spread of infectious disease. This possibility was exam ined by giving patients nitrous oxide and oxygen for 30 m inutes.11 In nine of 21 in stances, bacteria m orphologically identical w ith organisms isolated from the nasal m ucosa of the pa tients were cultivated from the used nasal hoods. Further experim ents w ith an artificial breathing system designed to m im ic hum an respiration show ed that bacteria deposited on nasal hoods were routinely dislodged and inspired during sub sequent use. It is, of course, difficult to judge w hether m icroorganism s so inhaled seriously threaten health. A lthough im possible to rule out, it is unlikely that fatalities have ever resulted. Viral and other upper respiratory tract infections, how ever, could be iatrogenically dissem inated in this m anner. Considering the large num ber of patients who receive nitrous oxide daily, costs in terms of patient discomfort, decreased productivity, and lost wages m ight be considerable. Unquestionably, adequate disinfection of the nitrous oxide ap paratus is a desirable goal. 192 ■ JADA, V ol. 98, February 1979
Techniques for disinfection No satisfactory m ethod exists for sterilization be tw een use by patients of the rubber goods used in the adm inistration of gas. Traditional cleaning m ethods involving soap and w ater rinses, alcohol sprays or swabs, or comm ercial cleaners may pro vide some degree of disinfection, but they cannot be relied on to produce total sterility. More effec tive techniques are generally im practical. Tubing and nasal hoods are often dam aged by high tem peratures in the autoclave, and m onetary and space requirem ents for sterilization w ith ethylene oxide are prohibitive. Perhaps the best com prom ise be tw een effectiveness and practicality is to disinfect w ith a “cold” germ icidal solution. Of the prepara tions currently m arketed, alkaline glutaraldehyde appears to be the most suitable. As enum erated by Borick,12 glutaraldehyde offers several advantages over other chem ical disinfectants. The com pound does not coagulate proteins, and it rem ains active in the presence of m ucus and blood. Deterioration of rubber and plastic is not an im portant problem. Because of its low surface tension, glutaraldehyde penetrates small spaces easily and is readily re moved by rinsing w ith water. Finally, alkaline glutaraldehyde is the m ost effective germ icide in use; a ten-m inute subm ersion at room tem perature is sufficient to kill all m icroorganism s, w ith the ex ception of spores, w hich m ay require as long as ten. hours of submersion. G lutaraldehyde does have some drawbacks. It is relatively expensive and may irritate or darken skin w ith prolonged exposure. These are trivial com pared w ith the com pound’s reported effectiveness as a disinfectant.13 A study was conducted to eval uate alkaline glutaraldehyde as a disinfectant of nasal hoods and to compare it w ith cleaning tech niques that are currently used.
Materials and methods All nasal hoods used were initially cleaned by a soap and water wash, tap-w ater rinse, and subm er sion in 2% alkaline glutaraldehyde (Cidex 7*) for ten m inutes. The hoods were rerinsed in tap water to remove the disinfectant, allow ed to dry, and w rapped in sterile alum inum foil. Volunteers in the study had no nasal congestion or overt upper respi ratory tract disease. M icrobiological culture m edia were obtained from Baltimore Biological Labora tories, Cockeysville, Md. At the beginning of each experim ental session, nasal bacteria were obtained w ith sterile, cotton-
tipped applicators from volunteers. The nasal hoods were also swabbed to check for sterility. A pplicator tips were broken off aseptically and placed individually in tubes containing soybeancaesin digest m edium (SCDM), USP. Volunteers then breathed a m ixture of 33% nitrous oxide and 67% oxygen for 25 m inutes followed by 100% oxy gen for five m inutes. The air dilution valve was set in the closed position, and the rate of total gas flow was adjusted to 8 liters per m inute. On term ination of the adm inistration of gas, bacteria deposited on each nasal hood were sam pled by swabbing the right half of the interior of the hood. A m ixture of two m arker organisms, Serratia m arcescens and B acillu s stearoth erm op h ilu s, was then deposited on the side of the mask from w hich the culture had been taken. To check for contam ination of the m ask originat ing from the nitrous oxide m achine, reservoir bag, or connecting tubes, 8 liters per m inute of nitrous oxide and oxygen was passed through each of six disinfected hoods whose nasal openings were covered w ith sterile alum inum foil. After 30 m in utes, sam ples were taken from the hoods for cul ture, w ith particular attention given to swabbing the surfaces around each gas entry port and air exhalation valve. Each nasal hood that was contam inated clinically w ith a variety of bacteria and experim entally w ith the two m arker strains was then disinfected w ith one of three m ethods: a thorough soap and water wash (including a 30-second scrub w ith a bristle brush of the interior of the mask and exhalation valve) and a tap-w ater rinse; a thorough soap and water w ash, a tap-water rinse, ten-m inute subm er sion in glutaraldehyde, and a tap-w ater rinse; or an aerosol spray w ith 95% ethanol sufficient to com pletely w et the interior of the mask. In a second series of experim ents, use of the m arker strains was om itted. These hoods were disinfected w ith either glutaraldehyde (as in the second m ethod) or a comm ercial cleaner (Consan 5%+). The commercial preparation was sprayed or w iped on the hoods as directed by the m anufacturer. Ten m inutes after com pletely w etting all inside surfaces, the hoods were rinsed in tap water. After cleaning, samples from both the left and right halves of the hoods were taken as previously described. The various m icrobiological specim ens contained in the SCDM tubes were incubated aerobically at 37 C for 48 hours. Broth samples were stirred and streaked onto culture plates containing soybean-casein di gest ager (SCDA), USP, enriched w ith 5% sheep blood. The plates were incubated aerobically at 37
C for 48 hours. Gram staining procedures were then performed on each active culture for the single blind m orphological identification of isolated bac teria. Broth sam ples were also transferred to SCDA dishes (w ithout sheep blood) and SCDM tubes for identification of the m arker strains. The SCDA plates were incubated aerobically at 22 C to estab lish the presence of S m arcescens by the charac teristic developm ent of red-pigm ented colonies. B stearotherm ophilus was identified by its ability to grow in the SCDM tubes at 55 C.
Results In all 60 sessions, cultivable organism s were depos ited by volunteers onto the inside surfaces of the hoods. Bacteria isolated included a num ber of common nasal inhabitants: staphylococci, strep tococci, diplococci, tetrads, diphtheroids, and vari ous gram -positive bacilli. A lthough bacteria pre sent in the nares of the volunteers were not u n i formly transferred to nasal hoods, a close corre spondence was observed betw een the nasal flora of the volunteers and the respective isolates from the hoods. Only one instance occurred in w hich a bacterial strain cultivated from a nasal mask was not also obtained from the nasal m ucosa of the vol unteer. This organism, a gram -positive rod, was presum ed to be an air-borne contam inant. Cultures of samples from nasal hoods disinfected w ith glutaraldehyde before use were uniform ly negative for cultivable bacteria. All control hoods through w hich the nitrous oxide and oxygen m ixture was passed were also sterile w hen previously d isin fected w ith glutaraldehyde. Efficacies of the various cleaning m ethods used are show n in the Table. The superiority of subm er sion in glutaraldehyde is evident, as is the inability of the other techniques to provide adequate disin fection. The com plete eradication of B stearother-
T able ■ Comparison of methods for disinfection of nasal hoods. Cleaned hoods with cultivable bacteria____ Cleaning Nasal Serratia Bacillus method bacteriamarcescens stearothermophilus Soap and 10/10 4/10 water wash 9/10* Glutaraldehyde 0 /10 0 /10 submersion 0/20 10/10 10/10 Alcohol spray 10/10 Commercial cleaner (spray) 9/10 Commercial cleaner (swab)_______ 8/10 •Number of hoods found to be contaminated after cleaning with indicated m ethod/num ber of hoods initially contaminated with indicated bacteria.
Y agiela— Hunt— Hunt: DISINFECTION OF NITROUS OXIDE INHALATION EQUIPMENT ■ 193
m o p h ilu s by glutaraldehyde in the study was sur
prising as the organism produces spores. A lthough the presence of spores in each culture was ensured by using cultures that were 72 hours old for the bacterial source, no attem pt was m ade to m aximize either the num ber of spores or survival before de position. Hence, these results should not be con strued as evidence that a ten-m inute subm ersion in glutaraldehyde is sufficient to destroy all spores as well as vegetative forms. W ith the culture m ethods used, m any anaerobic species that presum ably con tam inated the masks could not be detected. How ever, previous studies12-13 have not docum ented any special resistance of such m icroorganism s to glutaraldehyde. Of the other m ethods used for disinfection, al cohol spray was the poorest. Not only did all hoods rem ain contam inated, but SCDM tube grow th was consistently luxuriant after only 24 hours of in cu bation; this indicated that large num bers of cultiva ble bacteria survived the treatm ent w ith alcohol. The spray and swab m ethods were generally u n satisfactory because m ucoid deposits left on masks after use were not adequately removed.
Discussion The consistency in w hich patients in this study contam inated their respective nasal hoods during 30 m inutes of adm inistration of nitrous oxide and oxygen was significantly greater than our earlier finding of a 42% bacterial inoculation rate11 ob tained w ith an identical clinical setting. In our pre vious investigation, however, hoods w ere sterilized in glutaraldehyde for ten hours before use. As pro longed contact w ith the germ icide can result in de position of an aldehyde residue on plastic goods,13 an antibacterial film may have developed that w ould have reduced recovery of cultivable bacteria. The ten-m inute treatm ent used in the current study w ould have had no such effect. The ability of a ten-m inute subm ersion in glutaraldehyde coupled w ith a soap and water w ash to provide adequate disinfection of the nasal hood was show n not only by com parison w ith other cleaning m ethods (Table] but also by the lack of grow th in all 60 cultures taken to assess the sterility of the hoods before experim entation. The evident superiority of this technique over previ ously suggested m ethods strongly recom m ends the use of glutaraldehyde for disinfection of the nasal hood betw een patients. At the Emory University School of Dentistry, after each use, the nasal mask is w ashed w ith soap 194 ■ JADA, V ol. 98, February 1979
and water, placed in Cidex 7 for ten m inutes, and rinsed liberally w ith tap w ater to remove the disin fectant solution. At the end of each week, all tub ing, reservoir bags, and hoods are stored in Cidex 7 for ten hours to effect com plete sterilization. After subm ersion in glutaraldehyde, the equipm ent is au tom atically rinsed in w arm tap w ater for an hour. This cleaning m ethod is a com prom ise. Masks treated for ten m inutes m ay contain viable sporeforming bacteria, and rinsing w ith tap water may deposit other microbes. Fortunately, these kinds of organism s are rarely associated w ith infections in the respiratory tract. A nother possible drawback of the technique is that the entire breathing apparatus is not cleaned betw een use by each patient. Should future studies identify retrograde bacterial con tam ination as a problem , routine disinfection of all rubber goods may have to be instituted. O ur results indicate, however, that the m ethod as outlined vir tually elim inates the possibility of iatrogenic cross-infection associated w ith the nitrous oxide apparatus. Because of its effectiveness and sim plic ity, the procedure can be recom m ended for inclu sion in dental practices that adm inister sedation w ith nitrous oxide.
Summary Cross-infection by contam inated equipm ent is a po tential hazard associated w ith conscious sedation w ith nitrous oxide and oxygen. NosOcomial infec tions have occasionally been linked w ith the use of unsterile inhalation devices; m icrobial contam ina tion of sterile nasal hoods routinely occurs during adm inistration of nitrous oxide; and in vitro exper im ents indicate that subsequent use of contam i nated nasal masks m ay lead to aspiration of m icro organisms. A lthough the incidence of respiratory disease after such contam ination is unknow n, it is clear that disinfection of the nitrous oxide ap paratus betw een patients is desirable. A simple cleaning m ethod involving alkaline glutaraldehyde is described that provides adequate disinfection of the rubber goods used in the adm inistration of gas. Superiority of this technique over previously rec om m ended cleaning m ethods is shown.
*Jo h n so n a n d Jo h n so n D ental P ro d u c ts Co., E ast W in d so r, NJ. tC a m b ia re Ltd., G reensboro, NY
Drs. Y agiela a n d D. H u n t are a sso c iate p ro fesso rs a n d Dr. L. H u n t is p ro fessor a n d c h a irm a n , d e p a rtm e n t of oral b io logy, W oo d ru ff M ed ic a l C en ter, E m ory U niv ersity , 1462 C lifto n Rd, NE, A tla n ta , Ga 30322. A d d re ss re q u e sts fo r re p rin ts to Dr. Y agiela.
T h is w o rk w as su p p o rte d in p a rt b y U n ite d S ta te s P u b lic H e a lth S ervice g ra n ts DE 04003 an d RR 05308 A p re lim in a ry re p o rt o f th is in v e stig a tio n w a s p re s e n te d a t th e 1978 m e e tin g o f th e In te rn a tio n a l A sso c ia tio n fo r D en tal R esearch . T h e in fo rm e d c o n se n t o f a ll h u m a n su b jec ts w h o p a rtic ip a te d in th e e x p e rim e n ta l in v e stig atio n re p o rte d o r d e sc rib e d in th is m a n u sc rip t w as o b ta in e d a fte r th e n a tu re o f th e p ro c e d u re s a n d p o ssib le d isco m fo rts a n d risk s h a d b e e n fu lly e x p la in ed .
1. C raw ford, J.J. N ew lig h t o n th e tra n s m is sib ility o f v ira l h e p a titis in d e n ta l p ra c tic e a n d its co n tro l. JADA 91(4]:829-835, 1975. 2. Langa, H. R elativ e a n alg esia in d e n ta l p ractice; in h a la tio n a n alg esia a n d se d a tio n w ith n itro u s o x id e. P h ila d e lp h ia , W. B. S a u n d e rs Co., 1968, p 125. 3. B en n ett, C.R. C o n scio u s s e d a tio n in d e n ta l p ra c tic e. St. Louis, C. V. M osby Co., 1974, p 106. 4. C legg, H ., a n d T h o m p so n , J.W. In fected a n a e s th e tic a p p a ra tu s. Br M e d ] 2:873-874, 1952. 5. W alter, C.W. C ro ss-in fectio n a n d th e a n esth e sio lo g ist. A n e sth A nalg 53(3):631-634, 1974.
6. O lds, J.W., a n d others. P se u d o m o n a s a e ru g in o sa re s p ira to ry tra c t in fe c tio n a c q u ire d fro m a c o n ta m in a te d a n e s th e sia m a c h in e. A m R ev R esp D is 105:628-632, 1972. 7. Joseph, J.M. D isease tra n s m is sio n b y in e ffic ie n tly s a n itiz e d a n e s th e tiz in g a p p a ra tu s. JAM A 149(13):1196-1198, 1952. 8. D ryden, G.E. A n e sth e sia e q u ip m e n t sterility : re p e a t o f q u e stio n n aire. A n e sth A n a lg 52:167-169, 1973. 9. T h o m as, E.T. T h e p ro b le m i n p ra c tic e. In R oberts, R.B. (ed.) In te rn a tio n a l a n esth e sio lo g y c lin ic s; in fe c tio n s a n d s te riliz a tio n p ro b le m s. B os to n , L ittle, B row n a n d Co., 1972, vo l 10, p 14. 10. A lb rech t, W .H., a n d D ryden, G.E. F iv e-y ear e x p e rie n c e w ith th e d e v e lo p m e n t of a n in d iv id u a lly c le a n a n e s th e sia system . A n e sth A nalg 53:24-28, 1974. 11. H u n t, L.M ., a n d Y agiela, J.A. B acterial c o n ta m in a tio n a n d tra n s m issio n b y n itro u s o x id e sed a tio n a p p a ra tu s. O ral S u rg 44{3):367-373, 1977. 12. B orick, P.M . C h em ical s teriliz ers (ch em o sterilizers). A dv A p p l M icrobiol 1 0 :2 9 1 -3 1 2 ,1 9 6 8 . 13. B oucher, R.M. A d v a n ce s in s te riliz a tio n te c h n iq u e s: s ta te o f th e a rt a n d re c e n t b re a k th ro u g h s. A m J H o sp P h a rm 29:661-672, 1972.
Y agiela— Hunt—Hunt: DISINFECTION OF NITROUS OXIDE INHALATION EQUIPMENT ■ 195
Disinfection of nitrous oxide inhalation equipment John A. Yagiela, DDS, PhD Lindsay M. Hunt, DDS, PhD Dale E. Hunt, PhD
on cern ab o u t the possible role of the d en tal profession in th e tran sm issio n of infectious d is ease has fo cused atten tio n on th e p ro p e r steriliza tio n of d en tal e q u ip m en t.1 O ne in stru m e n t th at has largely escap ed co n sid eratio n is the n itro u s oxide gas m ach in e w ith its a tte n d a n t tubing, n asal hood, an d reserv o ir bag. R ecom m endations for ro u tin e clean in g of n itro u s oxide eq u ip m en t vary from spraying th e nasal hood w ith scen ted alco h o l2 to w ash in g all ru b b er goods w ith soap a n d w ater.3 It is q u estio n ab le w h e th e r th ese or o ther tech n iq u es cu rren tly in general use pro v id e adeq u ate d isin fec tion. M icrobial cross-contam ination d u rin g sed a tio n w ith n itro u s oxide has not b een co n sid ered a problem , b u t related in h alatio n devices have b een lin k ed w ith nosocom ial infections.
apparatus was unlikely and should not be consid ered as a health hazard associated w ith general anesthesia. Since that time, however, evidence has accum ulated indicating that anesthetic and other inhalation devices are potential sources for the iat rogenic transm ission of infectious disease.5,6 Mi croorganism s have been recovered from virtually every portion of the anesthetic breathing circuit.7 Results from a questionnaire to all directors of anesthetic training programs in the U nited States show ed that 70% of those institutions that studied the m icrobial status of their respective anesthetic systems obtained cultures of m icroorganism s from their equipm ent.8 Organisms that have been iso lated from anesthetic and inhalation equipm ent in clude know n pathogens, such as C andida albicans, C lostridium peifringens, Escherichia coli,
Microorganisms and anesthesia equipment
H a em o p h ilu s in flu e n za e suis, K lebsiella p n e u m o niae, M ycobacterium tuberculosis, Pseudom onas aeruginosa, S a lm o n ella m o n tived e o , Staphylococ cus aureus, Streptococcus pyogenes, and the viri-
In 1952, an annotation in the British M edical Jour nal4 stated that cross-infection from an anesthetic
JADA, V ol. 98, February 1979 ■ 191
dan s strep to co cci.9 It can b e assu m ed a prio ri th at v arious m y co p lasm a, v iru ses, a n d o th er organism s n o t ev alu ated m ay also have been p re sen t in the an e sth e tic devices.
The incidence of cross-infection from contam i nated anesthetic equipm ent is not known. Deaths have been reported on occasion, but it is probable that the source of m any fatal infections is unrecog nized. Perhaps a more accurate appraisal of the m agnitude of m icrobial cross-contam ination may be derived from investigations equating postopera tive rates of infection w ith techniques used to clean or disinfect inhalation equipm ent. In one study,10 it was found in a retrospective evaluation that the in cidence of postoperative pulm onary infection di m inished 75% after the adoption of routine sterili zation of the anesthetic circuit betw een use by pa tients.
Cross-infection and administration of nitrous oxide Potential problem s of iatrogenic m icrobial transfer faced by dentists are less than those encountered by anesthesiologists. Dental patients are generally healthier than hospitalized patients; techniques of sedation w ith nitrous oxide are less invasive than those of general anesthesia; and nitrous oxide units are probably less susceptible to contam ination than are anesthetic rebreathing circuits. Nevertheless, the possibility exists that dental practitioners using nonsterile equipm ent m ay unintentionally be facilitating the spread of infectious disease. This possibility was exam ined by giving patients nitrous oxide and oxygen for 30 m inutes.11 In nine of 21 in stances, bacteria m orphologically identical w ith organisms isolated from the nasal m ucosa of the pa tients were cultivated from the used nasal hoods. Further experim ents w ith an artificial breathing system designed to m im ic hum an respiration show ed that bacteria deposited on nasal hoods were routinely dislodged and inspired during sub sequent use. It is, of course, difficult to judge w hether m icroorganism s so inhaled seriously threaten health. A lthough im possible to rule out, it is unlikely that fatalities have ever resulted. Viral and other upper respiratory tract infections, how ever, could be iatrogenically dissem inated in this m anner. Considering the large num ber of patients who receive nitrous oxide daily, costs in terms of patient discomfort, decreased productivity, and lost wages m ight be considerable. Unquestionably, adequate disinfection of the nitrous oxide ap paratus is a desirable goal. 192 ■ JADA, V ol. 98, February 1979
Techniques for disinfection No satisfactory m ethod exists for sterilization be tw een use by patients of the rubber goods used in the adm inistration of gas. Traditional cleaning m ethods involving soap and w ater rinses, alcohol sprays or swabs, or comm ercial cleaners may pro vide some degree of disinfection, but they cannot be relied on to produce total sterility. More effec tive techniques are generally im practical. Tubing and nasal hoods are often dam aged by high tem peratures in the autoclave, and m onetary and space requirem ents for sterilization w ith ethylene oxide are prohibitive. Perhaps the best com prom ise be tw een effectiveness and practicality is to disinfect w ith a “cold” germ icidal solution. Of the prepara tions currently m arketed, alkaline glutaraldehyde appears to be the most suitable. As enum erated by Borick,12 glutaraldehyde offers several advantages over other chem ical disinfectants. The com pound does not coagulate proteins, and it rem ains active in the presence of m ucus and blood. Deterioration of rubber and plastic is not an im portant problem. Because of its low surface tension, glutaraldehyde penetrates small spaces easily and is readily re moved by rinsing w ith water. Finally, alkaline glutaraldehyde is the m ost effective germ icide in use; a ten-m inute subm ersion at room tem perature is sufficient to kill all m icroorganism s, w ith the ex ception of spores, w hich m ay require as long as ten. hours of submersion. G lutaraldehyde does have some drawbacks. It is relatively expensive and may irritate or darken skin w ith prolonged exposure. These are trivial com pared w ith the com pound’s reported effectiveness as a disinfectant.13 A study was conducted to eval uate alkaline glutaraldehyde as a disinfectant of nasal hoods and to compare it w ith cleaning tech niques that are currently used.
Materials and methods All nasal hoods used were initially cleaned by a soap and water wash, tap-w ater rinse, and subm er sion in 2% alkaline glutaraldehyde (Cidex 7*) for ten m inutes. The hoods were rerinsed in tap water to remove the disinfectant, allow ed to dry, and w rapped in sterile alum inum foil. Volunteers in the study had no nasal congestion or overt upper respi ratory tract disease. M icrobiological culture m edia were obtained from Baltimore Biological Labora tories, Cockeysville, Md. At the beginning of each experim ental session, nasal bacteria were obtained w ith sterile, cotton-
tipped applicators from volunteers. The nasal hoods were also swabbed to check for sterility. A pplicator tips were broken off aseptically and placed individually in tubes containing soybeancaesin digest m edium (SCDM), USP. Volunteers then breathed a m ixture of 33% nitrous oxide and 67% oxygen for 25 m inutes followed by 100% oxy gen for five m inutes. The air dilution valve was set in the closed position, and the rate of total gas flow was adjusted to 8 liters per m inute. On term ination of the adm inistration of gas, bacteria deposited on each nasal hood were sam pled by swabbing the right half of the interior of the hood. A m ixture of two m arker organisms, Serratia m arcescens and B acillu s stearoth erm op h ilu s, was then deposited on the side of the mask from w hich the culture had been taken. To check for contam ination of the m ask originat ing from the nitrous oxide m achine, reservoir bag, or connecting tubes, 8 liters per m inute of nitrous oxide and oxygen was passed through each of six disinfected hoods whose nasal openings were covered w ith sterile alum inum foil. After 30 m in utes, sam ples were taken from the hoods for cul ture, w ith particular attention given to swabbing the surfaces around each gas entry port and air exhalation valve. Each nasal hood that was contam inated clinically w ith a variety of bacteria and experim entally w ith the two m arker strains was then disinfected w ith one of three m ethods: a thorough soap and water wash (including a 30-second scrub w ith a bristle brush of the interior of the mask and exhalation valve) and a tap-w ater rinse; a thorough soap and water w ash, a tap-water rinse, ten-m inute subm er sion in glutaraldehyde, and a tap-w ater rinse; or an aerosol spray w ith 95% ethanol sufficient to com pletely w et the interior of the mask. In a second series of experim ents, use of the m arker strains was om itted. These hoods were disinfected w ith either glutaraldehyde (as in the second m ethod) or a comm ercial cleaner (Consan 5%+). The commercial preparation was sprayed or w iped on the hoods as directed by the m anufacturer. Ten m inutes after com pletely w etting all inside surfaces, the hoods were rinsed in tap water. After cleaning, samples from both the left and right halves of the hoods were taken as previously described. The various m icrobiological specim ens contained in the SCDM tubes were incubated aerobically at 37 C for 48 hours. Broth samples were stirred and streaked onto culture plates containing soybean-casein di gest ager (SCDA), USP, enriched w ith 5% sheep blood. The plates were incubated aerobically at 37
C for 48 hours. Gram staining procedures were then performed on each active culture for the single blind m orphological identification of isolated bac teria. Broth sam ples were also transferred to SCDA dishes (w ithout sheep blood) and SCDM tubes for identification of the m arker strains. The SCDA plates were incubated aerobically at 22 C to estab lish the presence of S m arcescens by the charac teristic developm ent of red-pigm ented colonies. B stearotherm ophilus was identified by its ability to grow in the SCDM tubes at 55 C.
Results In all 60 sessions, cultivable organism s were depos ited by volunteers onto the inside surfaces of the hoods. Bacteria isolated included a num ber of common nasal inhabitants: staphylococci, strep tococci, diplococci, tetrads, diphtheroids, and vari ous gram -positive bacilli. A lthough bacteria pre sent in the nares of the volunteers were not u n i formly transferred to nasal hoods, a close corre spondence was observed betw een the nasal flora of the volunteers and the respective isolates from the hoods. Only one instance occurred in w hich a bacterial strain cultivated from a nasal mask was not also obtained from the nasal m ucosa of the vol unteer. This organism, a gram -positive rod, was presum ed to be an air-borne contam inant. Cultures of samples from nasal hoods disinfected w ith glutaraldehyde before use were uniform ly negative for cultivable bacteria. All control hoods through w hich the nitrous oxide and oxygen m ixture was passed were also sterile w hen previously d isin fected w ith glutaraldehyde. Efficacies of the various cleaning m ethods used are show n in the Table. The superiority of subm er sion in glutaraldehyde is evident, as is the inability of the other techniques to provide adequate disin fection. The com plete eradication of B stearother-
T able ■ Comparison of methods for disinfection of nasal hoods. Cleaned hoods with cultivable bacteria____ Cleaning Nasal Serratia Bacillus method bacteriamarcescens stearothermophilus Soap and 10/10 4/10 water wash 9/10* Glutaraldehyde 0 /10 0 /10 submersion 0/20 10/10 10/10 Alcohol spray 10/10 Commercial cleaner (spray) 9/10 Commercial cleaner (swab)_______ 8/10 •Number of hoods found to be contaminated after cleaning with indicated m ethod/num ber of hoods initially contaminated with indicated bacteria.
Y agiela— Hunt— Hunt: DISINFECTION OF NITROUS OXIDE INHALATION EQUIPMENT ■ 193
m o p h ilu s by glutaraldehyde in the study was sur
prising as the organism produces spores. A lthough the presence of spores in each culture was ensured by using cultures that were 72 hours old for the bacterial source, no attem pt was m ade to m aximize either the num ber of spores or survival before de position. Hence, these results should not be con strued as evidence that a ten-m inute subm ersion in glutaraldehyde is sufficient to destroy all spores as well as vegetative forms. W ith the culture m ethods used, m any anaerobic species that presum ably con tam inated the masks could not be detected. How ever, previous studies12-13 have not docum ented any special resistance of such m icroorganism s to glutaraldehyde. Of the other m ethods used for disinfection, al cohol spray was the poorest. Not only did all hoods rem ain contam inated, but SCDM tube grow th was consistently luxuriant after only 24 hours of in cu bation; this indicated that large num bers of cultiva ble bacteria survived the treatm ent w ith alcohol. The spray and swab m ethods were generally u n satisfactory because m ucoid deposits left on masks after use were not adequately removed.
Discussion The consistency in w hich patients in this study contam inated their respective nasal hoods during 30 m inutes of adm inistration of nitrous oxide and oxygen was significantly greater than our earlier finding of a 42% bacterial inoculation rate11 ob tained w ith an identical clinical setting. In our pre vious investigation, however, hoods w ere sterilized in glutaraldehyde for ten hours before use. As pro longed contact w ith the germ icide can result in de position of an aldehyde residue on plastic goods,13 an antibacterial film may have developed that w ould have reduced recovery of cultivable bacteria. The ten-m inute treatm ent used in the current study w ould have had no such effect. The ability of a ten-m inute subm ersion in glutaraldehyde coupled w ith a soap and water w ash to provide adequate disinfection of the nasal hood was show n not only by com parison w ith other cleaning m ethods (Table] but also by the lack of grow th in all 60 cultures taken to assess the sterility of the hoods before experim entation. The evident superiority of this technique over previ ously suggested m ethods strongly recom m ends the use of glutaraldehyde for disinfection of the nasal hood betw een patients. At the Emory University School of Dentistry, after each use, the nasal mask is w ashed w ith soap 194 ■ JADA, V ol. 98, February 1979
and water, placed in Cidex 7 for ten m inutes, and rinsed liberally w ith tap w ater to remove the disin fectant solution. At the end of each week, all tub ing, reservoir bags, and hoods are stored in Cidex 7 for ten hours to effect com plete sterilization. After subm ersion in glutaraldehyde, the equipm ent is au tom atically rinsed in w arm tap w ater for an hour. This cleaning m ethod is a com prom ise. Masks treated for ten m inutes m ay contain viable sporeforming bacteria, and rinsing w ith tap water may deposit other microbes. Fortunately, these kinds of organism s are rarely associated w ith infections in the respiratory tract. A nother possible drawback of the technique is that the entire breathing apparatus is not cleaned betw een use by each patient. Should future studies identify retrograde bacterial con tam ination as a problem , routine disinfection of all rubber goods may have to be instituted. O ur results indicate, however, that the m ethod as outlined vir tually elim inates the possibility of iatrogenic cross-infection associated w ith the nitrous oxide apparatus. Because of its effectiveness and sim plic ity, the procedure can be recom m ended for inclu sion in dental practices that adm inister sedation w ith nitrous oxide.
Summary Cross-infection by contam inated equipm ent is a po tential hazard associated w ith conscious sedation w ith nitrous oxide and oxygen. NosOcomial infec tions have occasionally been linked w ith the use of unsterile inhalation devices; m icrobial contam ina tion of sterile nasal hoods routinely occurs during adm inistration of nitrous oxide; and in vitro exper im ents indicate that subsequent use of contam i nated nasal masks m ay lead to aspiration of m icro organisms. A lthough the incidence of respiratory disease after such contam ination is unknow n, it is clear that disinfection of the nitrous oxide ap paratus betw een patients is desirable. A simple cleaning m ethod involving alkaline glutaraldehyde is described that provides adequate disinfection of the rubber goods used in the adm inistration of gas. Superiority of this technique over previously rec om m ended cleaning m ethods is shown.
*Jo h n so n a n d Jo h n so n D ental P ro d u c ts Co., E ast W in d so r, NJ. tC a m b ia re Ltd., G reensboro, NY
Drs. Y agiela a n d D. H u n t are a sso c iate p ro fesso rs a n d Dr. L. H u n t is p ro fessor a n d c h a irm a n , d e p a rtm e n t of oral b io logy, W oo d ru ff M ed ic a l C en ter, E m ory U niv ersity , 1462 C lifto n Rd, NE, A tla n ta , Ga 30322. A d d re ss re q u e sts fo r re p rin ts to Dr. Y agiela.
T h is w o rk w as su p p o rte d in p a rt b y U n ite d S ta te s P u b lic H e a lth S ervice g ra n ts DE 04003 an d RR 05308 A p re lim in a ry re p o rt o f th is in v e stig a tio n w a s p re s e n te d a t th e 1978 m e e tin g o f th e In te rn a tio n a l A sso c ia tio n fo r D en tal R esearch . T h e in fo rm e d c o n se n t o f a ll h u m a n su b jec ts w h o p a rtic ip a te d in th e e x p e rim e n ta l in v e stig atio n re p o rte d o r d e sc rib e d in th is m a n u sc rip t w as o b ta in e d a fte r th e n a tu re o f th e p ro c e d u re s a n d p o ssib le d isco m fo rts a n d risk s h a d b e e n fu lly e x p la in ed .
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6. O lds, J.W., a n d others. P se u d o m o n a s a e ru g in o sa re s p ira to ry tra c t in fe c tio n a c q u ire d fro m a c o n ta m in a te d a n e s th e sia m a c h in e. A m R ev R esp D is 105:628-632, 1972. 7. Joseph, J.M. D isease tra n s m is sio n b y in e ffic ie n tly s a n itiz e d a n e s th e tiz in g a p p a ra tu s. JAM A 149(13):1196-1198, 1952. 8. D ryden, G.E. A n e sth e sia e q u ip m e n t sterility : re p e a t o f q u e stio n n aire. A n e sth A n a lg 52:167-169, 1973. 9. T h o m as, E.T. T h e p ro b le m i n p ra c tic e. In R oberts, R.B. (ed.) In te rn a tio n a l a n esth e sio lo g y c lin ic s; in fe c tio n s a n d s te riliz a tio n p ro b le m s. B os to n , L ittle, B row n a n d Co., 1972, vo l 10, p 14. 10. A lb rech t, W .H., a n d D ryden, G.E. F iv e-y ear e x p e rie n c e w ith th e d e v e lo p m e n t of a n in d iv id u a lly c le a n a n e s th e sia system . A n e sth A nalg 53:24-28, 1974. 11. H u n t, L.M ., a n d Y agiela, J.A. B acterial c o n ta m in a tio n a n d tra n s m issio n b y n itro u s o x id e sed a tio n a p p a ra tu s. O ral S u rg 44{3):367-373, 1977. 12. B orick, P.M . C h em ical s teriliz ers (ch em o sterilizers). A dv A p p l M icrobiol 1 0 :2 9 1 -3 1 2 ,1 9 6 8 . 13. B oucher, R.M. A d v a n ce s in s te riliz a tio n te c h n iq u e s: s ta te o f th e a rt a n d re c e n t b re a k th ro u g h s. A m J H o sp P h a rm 29:661-672, 1972.
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