Introduction
Organ and body tissue transplantation is an effective treatment for certain end-stage organ diseases, such as the liver, heart and lungs, which enhances the quality of life of patients (1,2). The need for organ transplantation has increased dramatically within the past 200 years. According to the statistics reported by the Organ Procurement and Transplantation Network (OPTN), more than 120,000 individuals are in the waiting lists of transplantation in the care centers across the world. This number increases by one individual per minute, 21 of whom die every day (3,4).
Nurses play a key role in recognizing the potential organs for transplantation, obtaining the consent of families for organ transplantation, general training of the families, and performing effective nursing care (5). Today, nursing care in special units has been mainly focused on organ transplantation, which has changes the role of nurses as well (6). According to the literature, involvement of nurses in the process of organ transplantation is the most positive and rewarding part of this profession. Attitudes strongly affect various aspects of organ and tissue transplantation (7). In addition to general awareness, level of knowledge and attitudes of healthcare providers are of paramount importance in effective care (8). This is due to the key role of healthcare providers in different processes of organ and tissue donation, from recognizing the potential donor to the isolation of the donated organs and tissues. Among the other influential factors in the process of decision-making and participation of healthcare staff in organ donation are the accurate diagnosis of brain death, organ maintenance, and observance of the rules and regulations (9).
Fostering a positive attitude toward organ and tissue donation and declaring its effectiveness in the survival of patients and preventing disabilities could result in the motivation and positive work atmosphere among healthcare providers, thereby increasing the number of organ donors. Undoubtedly, this leads to better outcomes of the transplantation process and future planning in this regard (10).
In some cases, organ and tissue transplantation is the only option to save the life of a patient. Given the importance of nursing care in the process of organ transplantation and considering the results of the previous studies, an important issue to be addressed is the extent to which the level of knowledge and attitude in nurses affects the organ donation process, as well as the influential factors in this regard.
Several surveys have been conducted to evaluate the knowledge and attitude of nurses toward organ donation, endorsing the role of these healthcare professionals in the related decision-making and carrying out the process. In addition, considering the direct association between the positive attitudes of healthcare teams, especially nurses, and the level of consent on organ donation, the knowledge and attitude of nurses have been the most imperative subjects in this regard. Nevertheless, no definite conclusions have been drawn to address the stated issue.
The present study aimed to review the current literature on the knowledge and attitude of nurses toward organ donation and transplantation.

Methods
A systematic review was conducted to investigate the knowledge level and attitude of nurses toward the process of organ donation based on PRISMA guidelines for systematic reviews (11,12). In the first step, the research question was developed and formulized. After formulating the question and before beginning the study, any potential bias was removed by determining the inclusion and exclusion criteria of the study.
Inclusion criteria were as follows: 1) data obtained from case studies, abstracts, or full-text articles; 2) study populations of ICU nurses (undergraduate or graduate); 3) articles published in English and 4) studies investigating the awareness and attitude of nurses toward organ donation. Exclusion criteria were review studies and letters to editor. After excluding 22,000 documents due to being repetitive in different sites, 500 articles due to inappropriate design, 450 articles due to considering other healthcare professionals than nurses, 15 non-English articles, 10 studies conducted on nursing students, and four qualitative studies, the remaining documents were collected and reviewed (Figure 1).

Literature review was initiated via searching in databases such as Web of Science, ProQuest, Medscape, MedlinePlus, Ovid, SID, MagIran, PubMed, Google Scholar, and ScienceDirect duting 1990-2015 using keywords such as nurses, organ donation knowledge and attitude, nurse or nurses, knowledge, nurses’ knowledge or nursing knowledge, attitude, nurses’ attitude or nursing attitude, organ donation or organ donation process, transplant or transplantation, organ transplantation or tissue transplantation, and brain death by AND/OR operators in the title or abstract and alone or in combinations. Moreover, literature search was resumed in the references of the selected articles (Table 1).

In total, 70,000 relevant articles were identified in Google search, including 50,000 articles in Google Scholar, 141 articles in PubMed, 905 articles in ScienceDirect, 1,900 articles in ProQuest, 39 articles in Medscape, three papers in MedlinePlus, two papers in Ovid, and 10 articles in MagIran. From 123,000 potential articles, 100,000 cases were excluded due to the irrelevant content.

The primary search targeted the articles that were published in English during 1990-2015 on the research subject using the mentioned keywords. In addition, the reference lists of the selected papers were searched, and we also searched for unpublished studies through the available libraries of congresses and seminars, as well as the titles of research projects and those available in university websites via Scopus and IRANDOC. Additionally, we visited the the Cochrane Central Register of Controlled Trials and the Iranian Registry for Clinical Trials (IRCT) for relevant documents.
Required data were collected using a form that had been previously prepared by two of the researchers. Studies with similar titles and varied subjects were also excluded.
To evaluate each article, data abstractions were completed based on the RRISMA guidelines. Accordingly, two reviewers initially examined the titles of the selected articles independently based on the provided abstracts and eliminated the irrelevant studies from further evaluation.
Relevant studies were selected based on the inclusion criteria of the study. Following that, the documents were independently examined and recorded by two reviewers. Moreover, quality of the selected studies was assessed using CONSORT (randomized clinical trials) and Oxford (analytical and descriptive studies). Finally, 21 articles were selected and approved for further evaluation.
Data extraction was performed after selecting the relevant documents. Extracted data from the papers were determined based on the survey questions in the data extraction form before the beginning of the study, including the names of the authors, titles, study objectives, location of the research, time of the study, type of the study, number and characteristics of the samples, and the final results. In the case of any arguments between the two reviewers, the disagreement would be resolved by a third reviewer.

Result
In total, 21 articles focusing on the attitude and knowledge of ICU nurses toward organ donation and the related factors were reviewed in the present study. Considering the differences in the findings of the selected studies, five articles generally claimed that the attitudes and knowledge of nurses toward the issue in question vary in different countries, while attitude and awareness in these healthcare professionals are affected by several factors (Table 1).
According to the findings, some of the main influential factors in this regard were the prior experience of care provision for an organ donation patient, education level, willingness, acceptance and participation in the process of organ donation, willingness toward explaining the brain death of a patient to the others, contact with the families of dead patients, receiving specific training on the criteria of brain death diagnosis, and positive attitudes of the others toward the process of organ donation (13-18). In contrast, some studies were indicative of the lack of knowledge in nurses in this regard, which could be attributed to the lack of training on the organ donation process, inefficiency in the diagnosis of brain death based on the standard criteria, and cognitive chaos toward the organ donation process and brain death (5,9,13-17).
In some of the selected articles, nurses were reported to have a positive attitude toward organ donation. These studies were mostly conducted in countries such as Israel, India, the United States, Poland, Turkey, China, and Spain. According to the findings, some of the main influential factors in the positive attitude of nurses toward organ donation were the standard guidelines for the diagnosis of brain death in hospitals, guidelines for the ethical codes in hospitals, training programs for brain death and organ donation, self-confidence of nurses in facing the families of dead patients, enhancing the quality of life of patients, reducing medical expenses and psychological pressures of the families, prior experience of organ donation, higher education level and being married, religious beliefs, acceptance of brain death and the organ donation process, and personal willingness for organ donation (1,13-21).
On the other hand, other studies denoted the most important influential factors in the negative attitude of nurses toward organ donation to be the lack of training programs for determining the criteria of brain death and organ donation process, psychological factors (e.g., fear of organ incision), viewpoints of the patients’ families, pain, uncertainty that brain death might not be an actual death, physical factors, burring and autopsy, reluctance to be part of the organ donation process and accepting it as a nursing duty, personal unwillingness to donate their own (or their family members’) organs, lack of consent from the family of patients for organ donation, contradictory ideas about organ donation and transplantation, becoming sympathetically stressed, and becoming emotional when the donor is a close relative (5,11-18).
With respect to the effect of training on attitude, findings of the selected studies indicated that in the first years of clinical nursing practice, nurses with positive attitudes believe that the existing protocol used to explain brain death and give awareness to the families of organ donors could result in positive attitudes in this regard. Furthermore, most nurses confirmed the lack of adequate training and experience in supporting the families of dead patients (5).

Discussion
The present study aimed to review the current literature on the level of knowledge and attitudes of ICU nurses toward organ donation and the related factors. Considering the critical role of ICU nurses in the process of organ donation (recognizing the potential donors, supporting and approaching the families of dead patients), their attitude and knowledge is of paramount importance in the process of organ donation. Although the selected articles revealed that nurses have a positive attitude toward organ donation in general (1,13-21), special training programs are required to improve their level of awareness. Adequate knowledge could effectively change the attitudes and improve the performance of nurses (13).
Training is considered to be the most important factor in changing the attitudes and performance of nurses toward organ donation. Using standard guidelines and scheduled training programs in nursing schools or offering related courses could also increase the awareness in nurses, thereby reinforcing their performance. According to the results of the present review, positive attitude and adequate knowledge of nurses could affect the attitude of the families of patients toward organ donation as well (4,8).
An important issue to be taken into account is that nurses may be involved with at least one element in the organ donation process (e.g., recognizing the potential donor and notifying the transplantation coordinator). Therefore, positive attitude of these healthcare professionals could remarkably affect notifying the transplantation coordinator, supporting the families of dead patients, and encouraging other individuals to participate in the process. Moreover, positive attitude helps nurses to control their negative feelings while explaining the organ donation process of a dead patient to the family, which paves the way for obtaining the consent of the families by establishing a connection (1,2).
According to some studies, nurses engaged in internal medicine wards or emergency sections are the main individuals who are responsible for recognizing potential donors. However, negative attitudes have been reported on behalf of these healthcare providers (13). Additionally, it has been confirmed that inexperienced healthcare personnel tend to have negative attitudes toward their experienced peers mostly due to the lack of exposure to brain death patients in nursing schools, which is of great importance regarding the outcomes of the organ donation process (14).
Studies have confirmed that the attitudes, beliefs, and behaviors of individuals are influenced by the cultural background, social norms, and religious beliefs. For instance, in South Korea and Turkey, people believe that corpus should be intact for burying, and therefore, they are likely to resist organ donation (9,15).
It has been endorsed that organ donors consider training to be more important than the care process, and the attitudes of individuals is known to enhance through proper training. Fostering a positive attitude in line with effective training is of paramount importance, especially for the healthcare providers who are involved in the care stage of the process. Given the importance of positive attitude in the organ donation process, some studies have accentuated that such positivism could be obtained by clarifying the concept of brain death. In addition, since participation in this process may be an active decision concerning the attitudes of the individuals toward brain death, negative attitudes may lower participation (16,17).
According to the reviewed articles in the current research, awareness and knowledge are important factors in organ donation, which are largely influenced by social norms and religious beliefs. In this regard, awareness should be applied to create positive attitudes in the individuals who participate in the process of organ donation. Furthermore, extensive clinical knowledge is required on organ donation, and the communication skills of ICU nurses should also be reinforced through proper training programs (18). Adequate knowledge enables nurses to confidently communicate with the families of dead patients, and awareness could change their attitude and performance during this critical process.
One of the limitations of the current research was that some of the reviewed studies were conducted using qualitative methods, which were excluded despite their reliability and evidential consistency.

Conclusion
To the best of our knowledge, this is the first systematic review conducted in Iran to investigate the attitude and knowledge of ICU nurses toward the process of organ donation. Although several studies support the key role of nurses in the process of organ transplantation, further investigation is required in order to confirm this role. In this regard, proper training and standard guidelines are essential to helping nurses fulfill their duties. Nurses are irreplaceable members of healthcare teams; however, they mostly lack the necessary knowledge and awareness in the organ donation process. Therefore, it is recommended that evidence-based activities be carried out in order to enhance the nursing performance and contribute to the process of organ donation positively.

Implications for Nursing and Healthcare Policy
Positive attitude and knowledge of nurses could affect the viewpoint of the families of patients toward organ donation. Given the importance of nurses’ awareness and attitude toward the organ donation process in different countries and considering the influential factors in this regard, it is suggested that interventions be conducted to enhance the awareness and attitude of nurses toward the organ donation process.

Acknowledgements
Hereby, we extend our gratitude to the authorities of Torbat Heydariyeh University of Medical Sciences, authorities of the School of Nursing and Midwifery, and the other participants for assiting us in this research project.

Conflict of Interest
The authors declare no conflict of interest.