J Neurosurg 47:861-863, 1977
Experiences with sterilization of the operating microscope THEODORE KURZE, M.D., MICHAEL L. J. APUZZO, M.D., MARTIN a . WEISS, M.D., AND JAMES S. HEIDEN, M.D.
Department of Surgery, Division of Neurosurgery, University of Southern California School of Medicine, Los Angeles, California o,' Experiments were conducted to assess the feasibility of both paraformaldehyde and ethylene oxide gas sterilization of the operating microscope. From these experiments and practical experience, it is concluded that ethylene oxide sterilization of the operating microscope is a feasible and desirable alternative to cumbersome draping techniques. KEY WORDS surgical microscope 9 sterilization 9 paraformaldehyde 9 ethylene oxide 9
T
HERE is little doubt that the presence of the surgical microscope in the operating room compounds the complexities of this environment, not the least of which is the preservation of sterile techniques. It is generally believed that the instrument will not withstand sterilization, and laborious and somewhat cumbersome draping techniques are used. Based on these considerations, we have been interested in alternative techniques for preparation of the instrument for surgical utilization. Approximately 5 years ago, it was learned that some surgeons had been sterilizing their microscopes with formalin gas, using paraformaldehyde, 3,B a white powder polymer of formaldehyde, as a source. The techniques consisted o f enclosing the microscope assembled on its stand and a quantity of paraformaldehyde in a sealed polyethylene bag for 48 hours at r o o m temperature. However, no data on the effectiveness of this technique could be found beyond statements that there were no problems with wound infection. We, therefore, conducted the following experiments.
J. Neurosurg. / Volume 47 / December, 1977
9 gas sterilization
Experiments and Results
Group 1 Experiments The O P M - I * microscope was cleaned with Betadine, and two test surfaces were designated on the instrument. One was inoculated with Staphylococcus aureus, the other with Pseudomonas aeruginosa. The instrument was sealed in a polyethylene bag for 40 hours at room temperature. The bag was opened, and smears from the designated surfaces were plated. Abundant growth from both test surfaces was observed. The same experiment was repeated with 10 gm of paraformaldehyde in the bottom of a sealed bag. After 48 hours, the bag was opened. The weight of the paraformaldehyde was unchanged, and there was only a weak odor of formalin gas. Once again, cultures of the test surfaces revealed substantial amounts of bacteria. The experiment was repeated eight times. Evidence of significant bacterial *OPM-I microscope manufactured by Carl Zeiss, Inc., 444 Fifth Avenue, New York, New York. 861
T. Kurze, M. L. J. Apuzzo, M. H. Weiss and J. S. Heiden TABLE 1 Ethylene oxide mixtures devoid of fluorinated hydrocarbons
Mixtures*
Manufacturer
107o ethylene oxide Union Carbide Corp. Linde Division, New York, N.Y. 90 ~o carbon dioxide Oxyfume Sterilant-20 207o ethylene oxide Union Carbide Corp. Linde Division, New York, N.Y. 80 Yocarbon dioxide 20 ~o ethylene oxide Castle Ritter Pfaudler Corp. Steroxide-20 Rochester, N.Y. 80 ~o carbon dioxide Carboxide
Container Weight (lb) Gross Wt.
Net Wt.
Tare Wt.
145 193 145 193 193
30 60 30 60 60
115 133 115 133 133
*All mixtures available in metal cylinders. growth was evident in all cases. It was noted that a variable intensity of formalin odor with p a r a f o r m a l d e h y d e was obtained from different sources. In a n o t h e r experiment, 3 gm of paraformaldehyde was completely sublimated by heat with all of the resultant gas sealed in a polyethylene bag with the microscope for 24 hours. When the bag was opened, a strong odor of formalin gas was apparent; and a fine powder covered the microscope. However, in this case as in others, significant bacterial growth was noted. In view of the international agreement to avoid contamination of extraterrestial bodies, it seemed that some assistance could be obtained from the experience of the space program. We discovered extensive literature on the technique of sterilization of electronic gadgetry by both ethylene oxide and formalin gas and could discover no hypothetical medical reasons to suggest that the operating microscope would be damaged by this technique7 ,5 Therefore, a second group of experiments was carried out. Group 2 Experiments An O P M - I microscope in good operating condition was wrapped in a polyethylene bag, placed in a cardboard container, and subjected to ethylene oxide gas sterilization daily for 30 days. The instrument was removed from the container and thoroughly inspected by executives of the Zeiss Corporation, who had no knowledge of the preparation of the unit. It was found that the instrument was in excellent condition. At this time, a series of experiments similar to those conducted in Group 1 demonstrated 862
that the ethylene oxide technique was bactericidal for all c o m m o n bacterial pathogens and Bacillus subtilis. Recommended Sterilization Technique We have now been sterilizing two of our operating microscopes in regular use for over 36 months, and there has been no visible sign of instrument deterioration after more than 700 procedures. The following technique for sterilization has been employed: 4 1) The microscope is disassembled to reduce its bulk and weight for easy handling. 2) It is placed in a polyethylene bag in a cardboard box. 3) The box is placed in a medium-sized hospital A m s c o t sterilizer, and exposed to an ethylene oxide CO2 mixture at 130 ~ F (54.4 ~ C) with a humidity of 50% for 41/2 hours. 4) The unit is aerated for 8 hours. On one occasion in over 700 sterilization procedures, apparent lens hazing was noted. Examination of the instrument by representatives of the Zeiss Corporation disclosed an element of white dust over the lens prisms which we have attributed to a failure of observance of the proper aeration cycle. Strict adherence to the schedule as noted has resulted in no further occurrences of this problem. While the incidence of wound infection is at best only an indirect index of the reliability of the technique, it should be noted that there has been no increase in infection since we have employed this technique. A f o u t 30 months ago, we began sterilizing tAmsco sterilizer manufactured by American Sterilizer Co., Erie, Pennsylvania. J. Neurosurg. / Volume 4 7 / December, 1977
Ethylene oxide sterilization of operating microscope TABLE 2 Ethylene oxide mixtures containingfluorinated hydrocarbons Container Weight Mixtures Cry-Oxcide Benvicide
Pennoxide
Manufacturer
Gross Wt.
11 7o ethylene oxide Ben Venue Laboratories 79 7o trichloromonofluoromethane Bedford,Ohio 10 ~o dichlorodifluoromethane 11 ~o ethylene oxide The Matheson Co. 54 ~o trichloromonofluoromethane East Rutherford, N.J. 35 % dichlorodifluoromethane 12 ~o ethylene oxide 88 ~o dichlorodifluoromethane
Steroxide-12 12 7o ethylene oxide 88 7o dichlorodifluoromethane
20-Oz
Castle Ritter Pfaudler Corp. Rochester, N.Y.
Discussion The previous reports 7 that ethylene oxide damages lens cement and mountings are probably due to the use of Freon (trichlormonofluoromethane). However, we have not attempted to prove this and have confined our experiences to ethylene oxide CO2 compounds. Therefore, we recommend that only those ethylene oxide mixtures that are devoid of fluorinated hydrocarbons (Table 1) be employed in the sterilization process and that those compounds that contain fluorinated hydrocarbons (Table 2) be avoided. The use of formalin emitted from paraformaldehyde as a method of sterilization was not shown effective by our experiments. There are two possible explanations for this. We cultured "nonsterile" shelf-clean instruments in our operating room, and found that they were all sterile. It is therefore possible that if satisfactory results have been found with this technique they are due not to the effectiveness of the formalin sterilization but to the fact that the instruments were sterile before they were put in formalin. Another more likely possibility is that the paraformaldehyde polymer available to us was not an effective source of gas. J. Neurosurg. / Volume 47 / December, 1977
Tare Wt.
disposable cans
Pennsylvania Engineering Co. Philadelphia, Pa.
our television camera with the same technique without difficulty, de Andrade 1 has recommended ethylene oxide sterilization of cameras and color film without danger to either. We have confirmed that his statements are valid.
Net Wt.
metal cylinder (lb) 43 16 27 235 100 135 381 270 111 metal cylinder (lb) 39 25 14 180 140 40 20- & 36-oz disposable cans
It is evident on the basis of these experiments and our practical experience in over 3 years of application of this method, that ethylene oxide gas sterilization of the operating m i c r o s c o p e is a feasible and desirable alternative to cumbersome draping techniques that have been employed until nOW.
References 1. de Andrade JR: Photography in the operating room: the camera as a sterile instrument. Surg Team 2:26, 1973 2. Hoffman RK: Ethylene and sterilization rates and protective influences. COSPAR Technique Manual, Series No. 4. 1968, p 75 3. Hosobuchi Y: Personal communication, 1974 4. Kereluk K, Lloyd RS: Ethylene oxide sterilization. A current review of principles and practices. J Hosp Res 7:7-75, 1969 5. Phillips CR: Gaseous sterilization. NASA Special Publication SP-108 (Spacecraft Sterilization Technology), 1966, p 231 6. Tulis J J: Formaldehyde gas as a sterilant, in Phillips GB, Miller WS (eds): Industrial Sterilization. Durham, NC: Duke University Press, 1973, pp 209-238 7. Zeiss Corporation: Personal communication, 1965
Address reprint requests to: Theodore Kurze, M.D., Department of Neurosurgery, University of Southern California, School of Medicine, 1200 North State Street, Suite 5046, Los Angeles, California 90033. 863
Experiences with sterilization of the operating microscope THEODORE KURZE, M.D., MICHAEL L. J. APUZZO, M.D., MARTIN a . WEISS, M.D., AND JAMES S. HEIDEN, M.D.
Department of Surgery, Division of Neurosurgery, University of Southern California School of Medicine, Los Angeles, California o,' Experiments were conducted to assess the feasibility of both paraformaldehyde and ethylene oxide gas sterilization of the operating microscope. From these experiments and practical experience, it is concluded that ethylene oxide sterilization of the operating microscope is a feasible and desirable alternative to cumbersome draping techniques. KEY WORDS surgical microscope 9 sterilization 9 paraformaldehyde 9 ethylene oxide 9
T
HERE is little doubt that the presence of the surgical microscope in the operating room compounds the complexities of this environment, not the least of which is the preservation of sterile techniques. It is generally believed that the instrument will not withstand sterilization, and laborious and somewhat cumbersome draping techniques are used. Based on these considerations, we have been interested in alternative techniques for preparation of the instrument for surgical utilization. Approximately 5 years ago, it was learned that some surgeons had been sterilizing their microscopes with formalin gas, using paraformaldehyde, 3,B a white powder polymer of formaldehyde, as a source. The techniques consisted o f enclosing the microscope assembled on its stand and a quantity of paraformaldehyde in a sealed polyethylene bag for 48 hours at r o o m temperature. However, no data on the effectiveness of this technique could be found beyond statements that there were no problems with wound infection. We, therefore, conducted the following experiments.
J. Neurosurg. / Volume 47 / December, 1977
9 gas sterilization
Experiments and Results
Group 1 Experiments The O P M - I * microscope was cleaned with Betadine, and two test surfaces were designated on the instrument. One was inoculated with Staphylococcus aureus, the other with Pseudomonas aeruginosa. The instrument was sealed in a polyethylene bag for 40 hours at room temperature. The bag was opened, and smears from the designated surfaces were plated. Abundant growth from both test surfaces was observed. The same experiment was repeated with 10 gm of paraformaldehyde in the bottom of a sealed bag. After 48 hours, the bag was opened. The weight of the paraformaldehyde was unchanged, and there was only a weak odor of formalin gas. Once again, cultures of the test surfaces revealed substantial amounts of bacteria. The experiment was repeated eight times. Evidence of significant bacterial *OPM-I microscope manufactured by Carl Zeiss, Inc., 444 Fifth Avenue, New York, New York. 861
T. Kurze, M. L. J. Apuzzo, M. H. Weiss and J. S. Heiden TABLE 1 Ethylene oxide mixtures devoid of fluorinated hydrocarbons
Mixtures*
Manufacturer
107o ethylene oxide Union Carbide Corp. Linde Division, New York, N.Y. 90 ~o carbon dioxide Oxyfume Sterilant-20 207o ethylene oxide Union Carbide Corp. Linde Division, New York, N.Y. 80 Yocarbon dioxide 20 ~o ethylene oxide Castle Ritter Pfaudler Corp. Steroxide-20 Rochester, N.Y. 80 ~o carbon dioxide Carboxide
Container Weight (lb) Gross Wt.
Net Wt.
Tare Wt.
145 193 145 193 193
30 60 30 60 60
115 133 115 133 133
*All mixtures available in metal cylinders. growth was evident in all cases. It was noted that a variable intensity of formalin odor with p a r a f o r m a l d e h y d e was obtained from different sources. In a n o t h e r experiment, 3 gm of paraformaldehyde was completely sublimated by heat with all of the resultant gas sealed in a polyethylene bag with the microscope for 24 hours. When the bag was opened, a strong odor of formalin gas was apparent; and a fine powder covered the microscope. However, in this case as in others, significant bacterial growth was noted. In view of the international agreement to avoid contamination of extraterrestial bodies, it seemed that some assistance could be obtained from the experience of the space program. We discovered extensive literature on the technique of sterilization of electronic gadgetry by both ethylene oxide and formalin gas and could discover no hypothetical medical reasons to suggest that the operating microscope would be damaged by this technique7 ,5 Therefore, a second group of experiments was carried out. Group 2 Experiments An O P M - I microscope in good operating condition was wrapped in a polyethylene bag, placed in a cardboard container, and subjected to ethylene oxide gas sterilization daily for 30 days. The instrument was removed from the container and thoroughly inspected by executives of the Zeiss Corporation, who had no knowledge of the preparation of the unit. It was found that the instrument was in excellent condition. At this time, a series of experiments similar to those conducted in Group 1 demonstrated 862
that the ethylene oxide technique was bactericidal for all c o m m o n bacterial pathogens and Bacillus subtilis. Recommended Sterilization Technique We have now been sterilizing two of our operating microscopes in regular use for over 36 months, and there has been no visible sign of instrument deterioration after more than 700 procedures. The following technique for sterilization has been employed: 4 1) The microscope is disassembled to reduce its bulk and weight for easy handling. 2) It is placed in a polyethylene bag in a cardboard box. 3) The box is placed in a medium-sized hospital A m s c o t sterilizer, and exposed to an ethylene oxide CO2 mixture at 130 ~ F (54.4 ~ C) with a humidity of 50% for 41/2 hours. 4) The unit is aerated for 8 hours. On one occasion in over 700 sterilization procedures, apparent lens hazing was noted. Examination of the instrument by representatives of the Zeiss Corporation disclosed an element of white dust over the lens prisms which we have attributed to a failure of observance of the proper aeration cycle. Strict adherence to the schedule as noted has resulted in no further occurrences of this problem. While the incidence of wound infection is at best only an indirect index of the reliability of the technique, it should be noted that there has been no increase in infection since we have employed this technique. A f o u t 30 months ago, we began sterilizing tAmsco sterilizer manufactured by American Sterilizer Co., Erie, Pennsylvania. J. Neurosurg. / Volume 4 7 / December, 1977
Ethylene oxide sterilization of operating microscope TABLE 2 Ethylene oxide mixtures containingfluorinated hydrocarbons Container Weight Mixtures Cry-Oxcide Benvicide
Pennoxide
Manufacturer
Gross Wt.
11 7o ethylene oxide Ben Venue Laboratories 79 7o trichloromonofluoromethane Bedford,Ohio 10 ~o dichlorodifluoromethane 11 ~o ethylene oxide The Matheson Co. 54 ~o trichloromonofluoromethane East Rutherford, N.J. 35 % dichlorodifluoromethane 12 ~o ethylene oxide 88 ~o dichlorodifluoromethane
Steroxide-12 12 7o ethylene oxide 88 7o dichlorodifluoromethane
20-Oz
Castle Ritter Pfaudler Corp. Rochester, N.Y.
Discussion The previous reports 7 that ethylene oxide damages lens cement and mountings are probably due to the use of Freon (trichlormonofluoromethane). However, we have not attempted to prove this and have confined our experiences to ethylene oxide CO2 compounds. Therefore, we recommend that only those ethylene oxide mixtures that are devoid of fluorinated hydrocarbons (Table 1) be employed in the sterilization process and that those compounds that contain fluorinated hydrocarbons (Table 2) be avoided. The use of formalin emitted from paraformaldehyde as a method of sterilization was not shown effective by our experiments. There are two possible explanations for this. We cultured "nonsterile" shelf-clean instruments in our operating room, and found that they were all sterile. It is therefore possible that if satisfactory results have been found with this technique they are due not to the effectiveness of the formalin sterilization but to the fact that the instruments were sterile before they were put in formalin. Another more likely possibility is that the paraformaldehyde polymer available to us was not an effective source of gas. J. Neurosurg. / Volume 47 / December, 1977
Tare Wt.
disposable cans
Pennsylvania Engineering Co. Philadelphia, Pa.
our television camera with the same technique without difficulty, de Andrade 1 has recommended ethylene oxide sterilization of cameras and color film without danger to either. We have confirmed that his statements are valid.
Net Wt.
metal cylinder (lb) 43 16 27 235 100 135 381 270 111 metal cylinder (lb) 39 25 14 180 140 40 20- & 36-oz disposable cans
It is evident on the basis of these experiments and our practical experience in over 3 years of application of this method, that ethylene oxide gas sterilization of the operating m i c r o s c o p e is a feasible and desirable alternative to cumbersome draping techniques that have been employed until nOW.
References 1. de Andrade JR: Photography in the operating room: the camera as a sterile instrument. Surg Team 2:26, 1973 2. Hoffman RK: Ethylene and sterilization rates and protective influences. COSPAR Technique Manual, Series No. 4. 1968, p 75 3. Hosobuchi Y: Personal communication, 1974 4. Kereluk K, Lloyd RS: Ethylene oxide sterilization. A current review of principles and practices. J Hosp Res 7:7-75, 1969 5. Phillips CR: Gaseous sterilization. NASA Special Publication SP-108 (Spacecraft Sterilization Technology), 1966, p 231 6. Tulis J J: Formaldehyde gas as a sterilant, in Phillips GB, Miller WS (eds): Industrial Sterilization. Durham, NC: Duke University Press, 1973, pp 209-238 7. Zeiss Corporation: Personal communication, 1965
Address reprint requests to: Theodore Kurze, M.D., Department of Neurosurgery, University of Southern California, School of Medicine, 1200 North State Street, Suite 5046, Los Angeles, California 90033. 863
