1.1. Incidence of Adverse Events
The incidence of patients experiencing adverse events while hospitalized has proven a major problem     . Reports and research on the occurrences of adverse events shows that a great number of patients experience adverse events while receiving health care all over the world     . An international study conducted in England, Germany and the USA, with focus on medication errors, found that the prevalence of adverse event related to drugs alone ranged from 3.22% to 5.64% of the patients hospitalized in 2006  . There have been a greater media and research attention to patient safety and the effect of staffing on the occurrence of adverse events    . International media have previously described patients being exposed to adverse events with severe consequences, of which many are caused by poor staffing   . There are several studies on this topic, but with varying foci such as mortality, adverse events related to specific patient groups and specific patient diagnosis, medication errors, patient satisfaction, work environment and economic perspectives      . Evidence in this area has also previously been synthesized in literature reviews    , but no reviews have documented the direct and indirect relationship between understaffing of nurses and patient safety.
1.2. Patient Safety
The US Department of Health & Human Services defines patient safety as “the freedom of accidental or preventable injuries produced by medical care”. Patient safety measures are defined as interventions or work intended to reduce the occurrence of preventable events  . Several different bodies ensure patient safety in hospitals. Health care providers have a responsibility to perform professionally appropriate health care. Each hospital must ensure that the health care providers work under conditions that promote safe practice, for example with appropriate equipment, adequate staffing and safe routines. Additionally, both health care workers and the health care system must comply with the law, professional standards and procedures to provide safe healthcare services  .
The requirement of professional responsibility is the most central demand in the legislation when it comes to safety practice in the healthcare service. The demand of professional responsibility is according to law, a shared responsibility, were the health workers are responsible for their own actions, and the healthcare system is responsible for the environment these actions are conducted in. Further on health workers, in this case nurses are obligated to perform safe healthcare through the nature of their public authorization, which is an arrangement built on common national and international demands in the nursing education and is a requirement to legally assess nursing tasks  .
1.4. The Nurse’s Role in Patient Safety
The International Council of Nursing states that nurses carry a responsibility to perform safe practice and to obtain the knowledge to do so. They are obligated to provide holistic patient care, which include giving the patients and families accurate information and education. Nurses are expected to participate in maintaining safe working conditions and safe practice  .
1.5. Purpose of the Study
The purpose of this study is to increase the knowledge of understaffing amongst nurses in hospitals, and the possible consequences of understaffing for patient safety. More specifically the study examines understaffing as a risk factor for hospitalized patients. The following research question has guided the study: How can understaffing amongst nurses in hospitals affect patient safety?
1.6. Clarification of Terms
Understaffing is a term with numerous connotations and meanings. In the literature, understaffing is used, for instance, in reference to high patient-nurse ratios, heavy workload, large patient load, nursing hours per patient, and high bed occupancy. The common denominator of these definitions are that understaffing is a lack of personnel, in this case nurses, to conduct their required tasks. In this study, the term understaffing is defined as “a disparity between load of responsibilities/tasks and the possibility to conduct them in a professional manner”.
A nurse is in this study, defined as a person with a bachelor education in nursing, having regular contact with patients admitted to a hospital ward.
A literature review was conducted using a systematic approach as described by Bettany-Saltikov  . Methods on thematically retrieving, synthesizing and analyzing the data was conducted following the method of Dixon-Woods et al.  and Pope  . The review was reported using PRISMA guidelines and the PRISMA float diagram  .
2.1. Inclusion and Exclusion Criteria
To be included in the review, articles had to be written in English, they had to have a clear qualitative or quantitative design, and they had to have been published between1997 and 2016. Eligible studies had to be concerned with nurses with patient contact, working in hospitals, some form of understaffing (excessive workload, high patient-to-nurse ratio, number of working hours per patient) and patient safety.
2.2. Identification of Studies
The search strategy was developed in accordance with Bettany-Saltikov  methodology for literature reviews in nursing. Literature searches were conducted in the Cinahl, Medline, Isi Web of Science, Cochrane Library and Academic Search Premiere databases between early February and the end of January 2016. All databases focus on health and social science. In addition, secondary searches were made based on the reference lists of included articles, and a manual search was conducted in selected journals of specific interests such as BMC Health Services Research  . The terms used when searching the databases included understaffing, nurse, patient safety, lack of nurses, staffing levels, manning levels, downsizing, short-staffed, short-handed, inadequate staffing, insufficient staffing, workload, patient outcome, patient security, patient mortality and adverse events. Terms which disclosed understaffing (lack of nurses, staffing levels, manning levels) were combined with terms disclosing nurses (healthcare worker, RN, trained nurse) and hospital (healthcare facility, Hospital ward, medical institution) in a systematic manner which included all possible combinations of these words. (A comprehensive list of the searches done in each database can be found in Attachment 1)
2.3. Quality Assessment of Studies
All included studies were of quantitative study design, and underwent a quality assessment according to the Cochrane Quality Assessment Tool for Quantitative Studies  . This assessment tool was developed for use in public health, and is suitable for quality assessment in most areas of public health  . The quality assessment involves grading six areas in each study (selection bias, study design, confounders, blinding, data collecting methods, withdrawals and drop-outs). Each domain is given points (1 - 3 points) based on relevant questions. Based on the total ranking score, each study was graded as having strong, moderate or weak quality. Studies graded “moderate” or “strong” were included in the review. (Attachment 2 gives a full overview of the quality assessment.)
2.4. Data Extraction
We used a predesigned form for data extraction according to Dixon-Woods et al.  , describing the study design, quality, objectives, data material/partici- pants, main findings, and the location of the study. First author retracted data from all included studies under detailed supervision from the research group. Recognition of themes was made through “identification of prominent or recurrent results in the articles analyzed, to produce an account of evidence”  .
2.5. Selection of Studies
The database searches identified 2847 records. Six articles were found through secondary searches and recommendations from researchers in the field of patient safety. Of the 2609 articles screened, 2495 were excluded. The remaining 114 articles were read and evaluated in full text (see Figure 1, The PRISMA 2009 Flow diagram if article selection process). Following the full text evaluation, 43 articles were included based on the inclusion and exclusion criteria. 10 of these
Figure 1. The PRISMA 2009 Flow diagram of article selection process.
studies did not pass the quality assessment, and were excluded, resulting in a total of 33 quantitative studies being included in the current review. First author performed the searches and undertook the screening of titles and abstracts against inclusion criteria, with supervision from the research group. First researcher then undertook the read-through of selected full-text articles. Where there was question of inclusion eligibility, the research group was consulted independently to assess full-text item suitability.
The results of the included studies were analyzed through Thematic analysis which involve finding prominent or recurrent themes in included articles, and gather the themes under suitable headings  . The predesigned form was used to organize the main results of the included studies, allowing the researcher to detect patterns or recurring subjects in the literature. The recurring subjects were then organized in to sub-themes and themes.
Data represented in this study emerged from already published peer reviewed articles. Data collection did not involve human subjects, and a written informed consent has therefore not been obtained.
2.8. Availability of Data and Materials
All the data supporting the conclusions can be found in Table 1 with information on the included studies. Information on the search words, combinations and results, can be found in the supplementary file 2 Database search report.
This literature review synthesizes evidence about the effects of the understaffing of nurses on patient safety in hospitals. Thirty-three studies of moderate-to-strong quality were included, from which two main themes and four subthemes emerged.
Twenty-three studies     -  found a direct relationship between understaffing and patient safety. Eight of these studies focused on mortality in patients admitted to a hospital. Fourteen studies described how patients were directly harmed as a consequence of understaffing in the form of infections, pressure ulcers and other adverse hospital events. One study described the relationship between nurse staffing and length of hospital stays.
Six studies  -  found an indirect relationship between understaffing and patient safety, focusing on important nursing tasks that were left undone due to nurses lack of time to carry them out. Two of these studies showed how understaffing affected the administration of medication.
One study  investigated both direct and indirect consequences, and three studies    found weak or no association between understaffing and patient safety.
3.1. Study Characteristics
Of the thirty-three studies included, there are nine cohort studies, thirteen cross-sectional studies, two correlation studies, one case control study, three retrospective observational studies, two retrospective longitudinal studies and one with a four-stage sampling design. It was not possible to categorize the methods used in two of the studies. (Table 1 lists the articles and study characteristics). All of the studies investigated the relationship between understaffing of nurses working in hospitals and patient safety.
Table 1. Overview of included articles.
3.2. Thematic Analysis
The thematic analysis   generated two main themes and two subthemes concerning understaffing and consequences for patient safety.
Theme 1: Direct consequences
Twenty-three studies reported that understaffing had direct and severe consequences for patients.
1A) Patient harm
Sixteen of the twenty-three studies examined several adverse events as a direct consequence of understaffing among nurses working in hospitals                 . Several studies found that understaffing increased the patient’s risk of contracting pneumonia, urinary tract infections or other hospital-related infections            . Cho and colleagues  found that one extra hour of work by registered nurses per patient per day was associated with a 8.9% decrease in the odds of the patients getting pneumonia. Cimiotti et al.  also found a negative association between number of hours of care provided by registered nurses and the risk of bloodstream infections in infants receiving neonatal care, but only in one of the two neonatal intensive care units (NICU) investigated. The authors attribute these differences in results to variation in the hospitals’ and infants’ characteristics.
Along with hospital-related infections, the incidence of pressure wounds was also a problem that, according to the literature, increased in proportion to understaffing      . Twigg et al.  reported that surgical patients experienced significant lower pressure wounds rates in all three hospitals investigated, after those hospitals adopted a new staffing method called Nursing Hour Per Patient Day (NHPPD). This staffing method significantly increased the staffing levels. In other words, increased staffing levels led to decreased rates of pressure wounds. A lower proportion of licensed nurses working was associated with a higher incidence of pressure wounds in the hospital investigated by Unruh  . Van den Heede et al.  in contrast, did not find any significant relationship between acuity adjusted nursing hours per patient day and pressure wounds. Kovner et al.  also investigated the direct consequences of understaffing but did not find any significance between registered nurses (RNs) hour per patient per day and three types of adverse events: pulmonary compromise, urinary tract infection, and thrombosis. Other studies, however, found a significant relationship between understaffing and both thrombosis and shock/cardiac arrest    . Schreuders et al.  found an inconsistency in the relationship between understaffing and patient complications such as urinary tract infections and surgical wound infections related to patient characteristics such as age, gender and health status. The direction of the association between nurse staffing and inpatient complications was not consistent for different patient complications.
Lastly, one study found that higher night staffing reduced the prevalence of extended hospital stays  .
2B) Patient mortality
Nine studies found understaffing to affect mortality in hospitalized patients. Both surgical and medical patients were investigated          .
In one observational study from 2014 and one cross-sectional analysis from 2002 Aiken and colleagues found that after adjusting for patient and hospital characteristics, each additional patient per nurse was associated with a 7% increase in the likelihood of dying within 30 days after admission. Carthon et al.  reported similar results, finding that an increase of one patient in the nurse’s patient load increased the occurrence of deaths in hospitalized patients. They also found that older surgical patients were affected more by understaffing than other groups of patients. Older surgical patients had a poorer post-surgical course when their nurses had a heavier workload, including a higher chance of death and failed resuscitation  . One study investigated mortality in the form of failure to rescue (from an adverse health-related event), finding that understaffing had a negative effect also in this area  .
In two studies, no correlation between mortality and understaffing were found   . Amarvadi and colleagues  investigated the understaffing-mortality problem by taking a closer look at the night shift. They used the night time nurse-to-patient ratio to calculate staffing, and found no increased risk of dying in hospital whether one night nurse cared for one or two patients or for three or more. Kiekkas et al.  found that an increased workload among the nurses did affect hospital mortality, but these numbers did not reach statistical significance.
Theme 2: Indirect consequences
Six studies found understaffing to affect patient safety, not by causing the patient direct harm but by increasing the risk for direct harm later on.
2A) Poor quality of basic care.
Four studies concluded that understaffing led to poor quality of care     . Several nursing tasks, such as patient communication, skin care, oral hygiene, documentation, responding to patient alarms and mobilization were left undone, postponed or not prioritized due to lack of time, as a consequence of understaffing of nurses   . Zhu and colleagues  found that 30.39% of nurses reported that the care that they delivered was of moderate or poor quality. Duffield et al.  found in their longitudinal study that patient communication was not prioritized in as many as 39.5% of the shifts. Skin care and back rubs (24.0%) and oral hygiene (19.3%) were also frequently reported undone. Patients’ ability for self-care and patient satisfaction was also negatively associated with understaffing   .
2B) Errors in administration of medication.
Two studies focused on understaffing and medication errors   , reporting that heavy nursing workload, interruptions and being rushed increased the risk of adverse events in conjunction with the administration of medication. Several other studies found an association between understaffing and medication errors, even when this was not their focus    . These findings showed that understaffing led to missed or late doses of medication, poor pain management resulting from difficulties in administering needed pain medication, and medication errors in general   .
The results of the literature review indicate that understaffing of nurses have a negative effect on patient safety. The negative effect is reflected through various consequences for the patient’s wellbeing, health, and outcome of hospitalization. Even though the results of this study are divided into themes and subthemes, all four themes are interrelated. The literature review shows that the indirect consequences of understaffing (lack of managing important nursing task such as measuring vital signs, patient mobilization and responding to patient alarms) may cause severe and direct consequences (thrombosis, patient falls and mortality) later in the course of treatment.
A relationship between the themes can for example be seen in relation to pressure wounds; hygiene measures, skincare, and mobilization are measures intended to prevent pressure wounds  , and were not always undertaken by the nurses due to understaffing   . Pressure wounds will, according to the literature, increase the patient’s risk of contracting wound infections that prove fatal  . Further, poor quality of care may also prevent nurses from discovering other severe conditions like thrombosis, pneumonia and wound infections.
Failure to provide basic care as a consequence of understaffing affects patients in ways that might not always be apparent. Tasks that do not seem as important as other tasks are constantly postponed or left undone, placing the patient at risk of severe harm.
As previously stated, the results of the studies reviewed here indicate that understaffing affects patient safety in numerous negative ways. However, several other aspects must be taken in consideration before formulating conclusions.
Many of the studies of mortality were conducted in intensive care units (ICU)     . Considering that a patient admitted to an ICU in most cases will be in an acute phase of the disease  , will mean they are in greater risk of any adverse event regardless of staffing. At the same time, these patients may be more vulnerable to lack of surveillance, medication errors, and lack of basic care as described in Theme 2-Indirect consequences. Hence, these patients might actually be more affected by staffing levels than others.
Several of the studies describe surgical patients in conjunction with both patient mortality and patient harm    . Surgical procedures are associated with certain risks like pneumonia, infections, pressure ulcers, and even mortality. These are adverse events described in Theme 1―Direct consequences, that may occur regardless of understaffing  . Since these studies are limited to surgical patients, this needs to be considered when interpreting the results. The same applies to studies of elderly patients, who are also at an increased risk of being affected by adverse events of both Theme 1―Direct consequences, and Theme 2-Indirect consequences. As Carthon et al.  argue studies of the elderly are valuable in this setting, having found that elderly patients are even more affected by understaffing than other patient groups.
Furthermore, the data used in most of the included studies were based singularly on administrative data (hospital statistics, discharge data, staffing data) and/or surveys. This type of data brings a few challenges. There will always be a chance of underreporting of adverse events, which may lead to unreliable results   . ICD Codes (international identification of disease) are in most health facilities used to register diseases and health issues  . Errors in these coding’s, or lack of accuracy in coding, may affect the results, especially if the errors are systematic  . In some cases patient characteristics may be limited because of lack of clinical information in administrative databases   . The same is true for staffing characteristics  . On the other hand, this type of data material will provide a great deal of information and include a larger sample of patient and nurses, which is important to create a wide picture of the problem understaffing and patient safety.
Another important aspect is that most of the studies are conducted in high income countries all over the world. There is one study from Brazil  and two studies from Taiwan   which are countries that are borderline in form of developed and developing countries. This must be taken in consideration when reading the results. Even though the remaining studies were conducted in high income countries such as USA, Australia, UK, and Belgium it is important to keep in mind that staffing levels, hospital characteristics, and nurse characteristics will vary. Nurses’ responsibilities may also differ, and therefore workload may differ in both quantity and type, which may make direct comparisons of the result of these studies difficult.
Lastly, the health personnel in this study include Registered Nurses (RNs), even though some of the studies also included data regarding other health personnel, the results of this study do not consider the effect of other health personnel on patient safety. It is known that for example nursing assistants and licensed practical nurses (LPN) are huge contributors to the basic care given in hospital wards. Further, there are also research results showing that wards with low RN-rates in the skill mix compared with other groups such as LPNs has less fortune outcomes when it comes to adverse events   . Another factor included in some of the understaffing research, which have not been included in this study, is work environment, which has also shown to affect patient safety   .
Kane and colleagues systematic literature review from 2007  also showed an association between understaffing of nurses and several adverse events (mortality and nurse sensitive patient outcomes). This study included factors such as the effect of LPNs, nurses’ experience, education and staffing policy. Other literature reviews have concentrated on specific adverse advents such as medication errors  , mortality  or healthcare associated infections  or special settings like critical or intensive care   . The effect poor quality care such as absence of skincare, mobilization or oral hygiene (indirect consequences) may have on patient outcomes in form of direct consequences (infections, pressure wounds, mortality) have not been explored in previous literature reviews.
As showed, there may be characteristics about the patient, the hospital, and the ward, that affect the results of the studies included in our literature review. Understaffing may be one of the contributing factors that affect patient safety, but other factors may most likely also be contributing
There are possible limitations in our literature review and several confounders need to be addressed when reviewing the results. Manual searches could have been conducted in other additional journals, by using citation tracking, and by assessing unpublished literature to increase chances of finding further relevant items. To test for additional findings, we tested new search terms and search words, without identifying new items meeting our inclusion criteria. The study was conducted according to strict methodological guidelines for literature reviews  and we believe that the majority of publications of relevance for our topic and research question are identified, although relevant publications could be missed by traditional database searches due to not being indexed in such a way as to allow identification within the parameters of such a search  .
Secondly we excluded studies of other health facilities than hospitals, and other health personnel than nurses, and also publications on discharge outcomes, in accordance with the exclusion criteria. This may have led to the loss of valuable information about understaffing and patient safety.
Thirdly, the thematic analysis method used in this review is more commonly used in studies with singularly qualitative designs, or with mixed methods  . Yet, early in the search process, this method proved to be the right one, as the themes emerged from the data. Meta-analysis, and so-called pooling of data―more commonly used in reviews of quantitative data―could not be used because of the wide range of results and study designs  .
Finally, some general risks of bias will always be present in literature reviews. Studies with valuable results, but not written in English, are excluded because of the exclusion criteria  . Furthermore, if the method of identifying relevant studies is not sensitive enough, there is always a risk of relevant studies being overlooked  . Bias may also occur during data retraction, if the same data is not retracted from each study  . Dixon-Woods et al.  mention some weaknesses with the use of thematic analysis. There can be a lack of transparency in the decisions made during the analysis process. To compensate, we have described the process in detail, showed examples in the tables to illustrate the findings, and demonstrated how the research group collaborated during the review process.
The literature review documents that understaffing of nurses can affect patient safety negatively in both direct―(pressure wounds, infections, mortality) and indirect ways (poor documentation, failure to mobilize patients, lack of proper surveillance). The type of ward, hospital, patient group, and country in the included studies vary, but all studies show that too few nurses at the hospital wards give too little time to perform important nursing tasks, which may have consequences of varying degrees of severity for the patient. The current results show that numerous characteristics and factors (e.g. type of hospital, ward, and patient characteristics) are important when investigating the relationship between understaffing and patient safety. All of these characteristics and factors must be considered when reading the results of this and other studies. More research on the topic is needed, as the articles included in this study mention the lack of research, especially in the Nordic countries. Lastly, no clear and direct causal relationship between understaffing and patient safety is found, but the findings leads us to the conclusion that understaffing of nurses constitutes a risk factor for hospitalized patients and could be one threat to patient safety.
Availability of Data and Materials
All the data supporting the conclusions can be found in Table 1 with information on the included studies. Information on the search words, combinations and results, can be found in the supplementary file Database search report.
The results of this systematic review emerged from analysis of data extracted from already published peer reviewed articles. The study does not involve any data collection involving human subjects and does not require any consent or ethical approval.
All members of the research group participated in the conception and design of the study as well as in analysis and interpretation of data. The first researcher undertook acquisition of data and the drafting of the manuscript. All authors were involved in critically revising the manuscript for important intellectual content and all read and approved the final manuscript.
Attachment 1: Database Search Report
2) Lack of nurses
3) Staffing levels
4) Under manning
5) Manning levels
9) Inadequate in number of workers
10) Inadequate staffing
11) Insufficient number of personnel
14) Health worker
15) RN (registered nurse)
17) Trained nurse
18) Patient safety
21) Patient security
22) Patient mortality
25) Health care facilities
26) Hospital ward
27) Medical institution
Searches done in Chinal 04.02.14-
*Search word 4 (undermanning) didn’t give any results in any combinations. **Search word 5 (Manning levels) didn’t give any results in any combinations. ***Search word 6 (Downsizing) didn’t give any results in any combinations. ****Search word 8 (short-handed) didn’t give any results in any combinations.
Searches done in Medline―15.02.14
Searches done in ISI Web of science 31.03.14-
*Reduced the result to 7 hits, by checking of nursing and excluding case report, meeting and editorial. **Reduced the result to 280 hits, by checking of English, nursing and excluding Editorial, meeting and case report. ***Reduced the result to 34 hits by checking of nursing and English. ****Reduced the result to 36 hits by checking of nursing and English and excluding case report. *****Reduced the result to 5 by checking of nursing, English an exclude newsletter, editorial, reference material and case report.
Searches done in Cohrane library 29.04.14-
Searches done in Academic search premiere 31.04.14-
Searches done in Chinal December 2015-February 2016 (Year 2014-2015)
Attachment 2: Quality Assessment of Included Studies
Fulltext Quality Assesement tool for quantitative studies: http://www.ephpp.ca/PDF/Quality%20Assessment%20Tool_2010_2.pdf
Fulltext Quality Assessment tool for quantitative studies dictionary: http://www.ephpp.ca/PDF/QADictionary_dec2009.pdf