Compatibilities and incompatibilities between gamma rays and ethylene oxide as consecutive sterilization methods

Abstracts

A dúvida sobre a questão da re-esterilização de artigos confeccionados com cloreto de polivinila (PVC), esterilizados em radiação gama (RG) e posteriormente em óxido de etileno (EO) persiste até os dias atuais. Por meio da revisão integrativa da literatura, este artigo analisou estudos que evidenciaram compatibilidades e incompatibilidades entre os processos de esterilização com RG e EO quando utilizados como métodos sucessivos de esterilização. Foram analisados 7 estudos. Constatou-se que há influência multifatorial na segurança do procedimento e que o método analítico da cromatografia empregado na maioria dos estudos produziu resultados controversos. Esse fato indica a necessidade da realização de novos estudos sobre o assunto, utilizando-se métodos analíticos mais sensíveis do que a cromatografia gasosa, como o teste de reatividade biológica em culturas celulares, que poderá dirimir em nosso meio a crônica dúvida da compatibilidade ou incompatibilidade de se esterilizar em EO materiais previamente gamairradiados.

Raios gama; Óxido de etileno; Esterilização

CRITICAL REVIEW

Rafael Queiroz de Souza^I; Kazuko Uchikawa Graziano^II

^IMaster's student, holder of a Grant by the Graduate Program in Adult Health Nursing at University of São Paulo School of Nursing. São Paulo, SP, Brazil. [e-mail] Professor of the Medical Surgical Nursing Department at University of São Paulo School of Nursing. São Paulo, SP, Brazil. [e-mail]

ABSTRACT

The doubt regarding the re-sterilization of articles made of polyvinyl chloride (PVC) sterilized with gamma radiation (GR) and subsequently with ethylene oxide (EO) persists to date. Through a systematic literature review, this article analyzed studies that demonstrated compatibilities and incompatibilities between the sterilization processes with GR and EO, when used as consecutive sterilization methods. Seven studies were analyzed. It was verified that there is a multifactor influence regarding the safety of the procedure and that the chromatography analytical method employed by most studies yielded controversial results. This fact indicates the need for further studies on the issue, using more sensitive analytical methods than gas chromatography, such as the biological reactivity test in cell cultures, in an attempt to clarify the chronic doubt regarding the adequacy or inadequacy of sterilizing previously gamma-irradiated materials with EtO.

Key words: Gamma rays. Ethylene oxide. Sterilization.

RESUMEN

La duda sobre la cuestión de la reesterilización de artículos confeccionados con policloruro de vinilo (PVC) esterilizados con Rayos Gamma (RG) y posteriormente en óxido de etileno (EO) persiste hasta la actualidad. A través de la revisión integradora de la literatura, este artículo analizó estudios que evidenciaron compatibilidades e incompatibilidades entre los procesos de esterilización con RG y EO, cuando se utilizan en forma sucesiva. Fueron analizados 7 estudios. Se constató que hay influencia multifactorial en la seguridad del procedimiento y que el método analítico de cromatografía empleado en la mayoría de los estudios generó resultados controversiales. Este hecho indica la necesidad de realizar nuevos estudios sobre el asunto, utilizando métodos analíticos más sensibles que la cromatografía gaseosa, tales como el test de reactividad biológica en cultivos celulares para dirimir en nuestro medio la crónica duda de la compatibilidad o incompatibilidad de esterilizar en EO materiales previamente irradiados con Rayos Gamma.

Descriptores: Rayos gamma. Óxido de etileno. Esterilización.

INTRODUCTION

In 1967 a letter sent to the British Medical Journal reported that performing re-sterilization with Ethylene Oxide (EO) of health care material made of Polyvinyl Chloride (PVC) that had previously been sterilized with Gamma Rays (GR) produced high concentrations of a toxic EO byproduct - Ethylene Chlorohydrin (ETCH)⁽¹⁾. In that letter, the authors did not mention the dosages they found, which would permit a comparison between the limits considered low or acceptable by official organizations. The report caused a series of debates among researchers.

In the years that followed, publications based exclusively on that letter recommended to not re-sterilize any previously irradiated material with EO^(2-4); thus contributing with the dissemination of the alleged incompatibility between those two methods of sterilization.

In Brazil, the controversy emerged in 1982, in a book that states the following information:

No previously gamma-irradiated PVC material should sterilized with ethylene oxide because there is a further reaction between the HCl (hydrochloric acid) residue set off by the irradiation and ethylene oxide, producing ethylene chlorohydrin, which has the same caustic properties of ethylene oxide, but is much more difficult to remove⁽⁵⁾.

That statement is supported by the reference of a study performed in 1971⁽⁶⁾; which evaluated the duration of EO retention in materials made of PVC, rubber, Teflon and Polyethylene, and the toxic level of the gas for the tissues by means of subcutaneous implants in rats. That study did not address the incompatibility between sterilization methods, so it could not have been cited as a support for the statements made by the author.

The author of another book, this one from 1987⁽⁷⁾; states that if the times recommended for the aeration of PVC material are followed, previous irradiation from GR would not contraindicate consecutive sterilization with EO. That statement was based on a primary study from 1976⁽⁸⁾; in which EO concentrations were dosed in endotracheal PVC tubes and its decrease rate over aeration time, and on a 1961 study⁽⁹⁾; which consisted in evincing the harm to plastic after EO sterilization, without any reference to the previous use of GR. Another study, from 1997⁽¹⁰⁾; presents the same statement followed by the same references.

It is observed that studies supporting the referred statement do not address the incompatibilities between sterilization methods. Therefore, they actually do not support the statements made by those authors.

In 1997, a bibliographic survey was performed on the subject and the author concluded that there were insufficient studies to solve the doubt and suggested that further experiments should be performed⁽¹¹⁾.

Nowadays, though there is no official recommendation prohibiting the procedure of re-sterilizing materials with an expired sterilization date, re-sterilization with EO is indicated for thermo-sensitive gamma-irradiated materials, despite the drawbacks of the method, such as adsorption and absorption of residual gas in the materials⁽¹²⁾. Nevertheless, studies that warn about the incompatibility of submitting materials that were previously gamma-irradiated, especially those made of PVC, to re-sterilization with EO leave doubts that must be solved.

OBJECTIVE

To perform an analysis on scientific literature that evinced the compatibilities and incompatibilities between Gamma Radiation and Ethylene Oxide as consecutive sterilization methods.

METHOD

This is an integrative literature review, using a method that permits to include both empirical and theoretical literature, of which main advantages include the possibility of combining data obtained through different study designs⁽¹³⁾.

The guiding question used in the present literature review was: Is there any incompatibility or compatibility in the re-sterilization of materials consecutively sterilized with GR and EO?

The material for the review was obtained through a search on the electronic databases: LILACS, PubMed/MEDLINE and SciELO. The following keywords were used: Gamma radiation, Ethylene Oxide and Sterilization. As a complementary strategy, a survey was performed on the archives of the following Libraries: Biblioteca da Escola de Enfermagem da Universidade de São Paulo, Biblioteca Central da Universidade Federal de São Paulo; and, also, a tree survey, which consists in searching for the references used to support the identified primary studied with the purpose of accessing the primary sources.

The survey included studies that performed experiments with the purpose to find incompatibilities or compatibilities of re-sterilizing with EO materials previously sterilized with GR.

A critical analysis of each study was performed based on the synoptic chart, which included a description of the methodological features obtained from the studies (Chart 2) and on the result synthesis chart (Chart 3).

RESULTS

With the purpose to facilitate the presentation of the results and the discussion, the selected studies were coded from E1 to E7. Chart 1 lists all studies per code, reference, and evidence.

Chart 2 lists the methodological aspects of the analyzed studies.

Chart 3 presents the synthesis of the results presented in the selected studies.

DISCUSSION

From the methodological perspective, study E1 (original 1967 letter that initiated the polemic) is fragile because there is insufficient details to make it reproducible. Therefore, its results are questionable. Furthermore, no quantitative experimental data was presented. The referred study presented a 1965 study⁽¹⁴⁾ as reference, which evinced the formation of toxic chlorohydrins in food, when fumigated with EO, due to the presence of Chlorine on its surface. There is no report on previous exposition of samples to GR: therefore, this study does not offer solid support to the statements made by the authors.

Study E2 does not present reference doses, which would permit to classify the amounts founds as significant. The dose of radiation used was not specified, neither was the concentration of the sterilizing agent, thus compromising the reproducibility of the study.

Study E3 did not include the aeration time after the re-sterilization with OE before the analyses, which is determinant for safety when using these materials. The study did, however, present in detail the composition of the PVC used, showing that it interferes on the residual concentrations of EO and its byproducts. Furthermore, it highlighted the differences of gas elimination on rigid and flexible PVC.

Study E4 presented in detail the parameters used for sterilization. One important variable controlled in the study was the interval between sterilizations. The authors concluded that it would be sensible to wait a few days for the material to recover before submitting it to re-sterilization with EO. That variable should be further investigated. Another important aspect considered in the study was the presentation of the material: rigid, flexible and powder, which was determinant for the safety of re-sterilization with EO.

Study E5 was meticulous regarding the description of the parameters used for sterilization. In addition, it was the first study that contested study E1, generating the polemic of incompatibility between sterilization methods. The result permitted that, in 1976, another study ensured that provided the recommended aeration time for PVC materials is followed, their previous irradiation does not represent a contraindication to their re-sterilization with EO⁽¹⁵⁾.

Study E6 used cell culture toxicity and residue quantification methods. Though pure EO was used for sterilization, results showed there was compatibility between sterilization methods. Though it used gas chromatography to quantify the residues of EO and its byproducts, the authors concluded the results based on cellular toxicity tests.

Study E7, opposed from the other studies, used latex and cotton as samples. Though it did not use PVC materials, this study draws our attention to the cytotoxicity of the materials used in health care even when those are not exposed to EO. This factor calls for further studies. Other characteristics that should be highlighted are the use and specification of forced aeration used to eliminate residues from EO and its byproducts, which is essential to guarantee safety when using material sterilized by this method.

Controversies exist regarding the results of studies that used gas chromatography as an analytical method. This fact may indicate that the method is questionable in terms of its sensitivity to evince the answer to the guiding questions in the studies. On the other hand, the analysis of cellular toxicity used in two studies proved to be a method that could verify cellular death at the presence of toxic substances in materials submitted to sterilization using those agents, because the samples are tested directly in live cells, thus simulating the contact of the material containing toxic residue with human subjects, as it would occur in health care practice.

CONCLUSION

The analysis of the evidence presented in the studies showed that there is no specific situation in which these procedures are totally safe, because, based on the performed experiments, the safety of the procedure could be affected my several factors, including: the type of raw-material, whether the material is flexible or rigid, conformation with the product, the addictives (stabilizers) used, besides the aeration time of the material after sterilization with EO. Nevertheless, these factors were found base on studies that used, namely, gas chromatography as the analytical method, which is currently questioned by experts.

The final statement points at the need for further studies that use analytical methods more sensitive than gas chromatography, e.g. the biological reactivity test in cellular cultures, to solve the chronic doubt that exists in our field of study, concerning the compatibility or incompatibility of sterilizing with EO materials that have been previously gamma-irradiated.

REFERENCES

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Compatibilities and incompatibilities between gamma rays and ethylene oxide as consecutive sterilization methods

Compatibilidades e incompatibilidades entre rayos gama y óxido de etileno como métodos sucesivos de esterilización

Publication Dates

• Publication in this collection
  15 Dec 2010
• Date of issue
  Dec 2010

History

• Received
  17 Feb 2009
• Accepted
  08 Mar 2010