Nurse-to-Patient Ratio and Healthcare Quality: Evidence Review

Introduction

It would be hard to understate the importance of a low nurse-to-patient ratio (NPR) for patient and staff safety, as well as quality of care. While a number of nursing factors can influence these outcomes — including nursing education, experience, skills mix, contact time, frequency of interactions, and type of inpatient unit — the NPR has been the focus of considerable interest in part because it can be easily quantified (Sidani, Manojlovich, & Covel, 2010). This review examines the empirical evidence for the importance of NPR in determining patient and staff safety, as well as quality of care. Research articles obtained from the Library of Medicine are reviewed in detail and compared to the findings of more recent studies. This approach is intended to establish a historical foundation for the topic and then use it to elaborate on the different variables that influence the predictive value of the NPR.

Patient Safety

When the Institute of Medicine (2000) published its report on patient safety, To Err is Human, the American public woke up to the hidden reality that hospitals can be bad for patient health. The authors estimated that between 44,000 and 98,000 people died each year as a result of medical errors — more deaths than those caused by vehicle accidents, breast cancer, or AIDS.

In the aftermath of the Institute of Medicine report, Aiken and colleagues (2002) published a large study in the Journal of the American Medical Association revealing NPR to be a significant contributor to medical errors. The study included 168 Pennsylvania general hospitals encompassing 232,342 patients and 10,184 nurses. NPRs were broken down into the following groups: 1:4 or fewer (11.9%), 1:5 (38.1%), 1:6 (24.4%), 1:7 (17.3%), and 1:8 or greater (8.3%). Based on discharge abstracts, 23.2% of patients experienced a major complication that emerged after hospital admission and another 2.0% died within a month. All patients were admitted for surgery: orthopedic (51.2%), gastrointestinal (36.4%), and other (12.4%).

The main factors investigated by Aiken and colleagues (2002) were the relationship between NPR and nurse burnout and patient adverse events. Their data revealed that for every additional patient in the NPR, nurses were 23% and 15% more likely to report feeling burned out and dissatisfied with their job, respectively. Every one-patient increase in NPR also raised the risk of patient death by 7%. To put this in perspective, increasing the NPR from 4:1 to 8:1 would result in 18.2 and 5.0 excess deaths per 1,000 patients with and without complications, respectively. While the study had some limitations — including a hospital selection bias and the inclusion of only a few confounding factors — the large, representative sample created a high degree of confidence in the findings.

In support of these findings, a number of studies have investigated the same issue in the years since the Pennsylvania hospital study was published. However, none have conducted a controlled study of an intentional change in staffing levels. To work around these limitations, researchers have taken advantage of below-target staffing levels to examine whether they tended to increase adverse outcomes for patients within the same hospital. By doing so, variables such as differences in organizational attitudes, the quality of nursing staff, and other confounders could be minimized or eliminated.

This approach was taken by Needleman and colleagues (2011) at a major medical center, where they examined almost 200,000 records for adult patient admissions to assess whether units operating with below-target staffing levels experienced increased patient mortality. They controlled for a number of confounding factors, such as day versus night shift and type of unit, and deliberately selected a well-respected, high-quality tertiary care hospital with a low NPR. This allowed them to determine whether subtle changes in nurse staffing levels negatively affected patient safety. They also controlled for the impact that patient turnover would have on nursing load and patient mortality.

Staffing levels were generally found to be near target levels for most units, but 16% were more than 8 hours below target, including over 19% of ICUs (Needleman et al., 2011). Differences between daytime and nighttime staffing were limited to step-down and general care units, with higher staffing levels during the daytime. After adjusting for selected confounding factors, the authors found that the risk of death increased significantly [Hazard Ratio (HR) = 1.02, 95% CI, 1.01–1.03, p < 0.001] when staffing levels dropped more than 8 hours below target, or when a shift experienced high patient turnover (HR = 1.04, 95% CI, 1.03–1.10, p < 0.001). Both results are consistent with the theory that any factors increasing nursing workloads tend to have a negative impact on patient safety, including NPR.

The study by Needleman and colleagues (2011) demonstrated how patient safety can be degraded when NPR fails to meet target goals even in a high-quality hospital, and revealed that more subtle changes in nurse workload can still have a significant negative impact on patient mortality rates. This implies that NPR functions as a healthcare quality indicator because it has a dramatic effect on nurse workload.

One important dimension of this issue is the ratio of nursing training and expertise: a higher percentage of well-trained and experienced nurses tends to reduce negative patient outcomes. This implies that nursing assistants cannot compensate for a lack of registered nurses (RNs) and licensed practical nurses (LPNs). A longitudinal and cross-sectional study in Australia examined the effect of RN:LPN:nursing assistant (NA) ratios in randomly selected medical, surgical, ICU, and emergency units in 19 hospitals (Duffield et al., 2011). The percentage of RNs ranged from a low of 45% to a high of 100%. Nursing workload and demand were calculated such that a score of 100 indicated a balance; approximately 25% of units had scores of 100 or less, meaning that nursing workload exceeded recommended levels in 75% of all units, with the highest score reaching 250. NPRs varied from 1:6 to 1:10, with the RN-to-patient ratio averaging around 1:8.

The longitudinal arm of the study revealed that over the 5-year study period, units with a higher percentage of RNs — including clinical nursing specialists — had lower rates of patient adverse events (Duffield et al., 2011). The three patient outcomes significantly associated with a low RN-to-patient ratio were bedsores, pneumonia, and sepsis (p ≤ 0.01). Other factors that significantly and negatively influenced patient outcomes included patient turnover rates, the use of temporary rather than permanent nursing staff, threats of physical violence, and patient acuity. All of these factors effectively reduce nurse staffing levels by increasing workload. These findings reveal that the importance of NPR to patient safety depends on more than simply having a nurse present — the skill level of that nurse also matters.

A similar study was conducted by Patrician and colleagues (2011a) across 13 U.S. military hospitals. They found that the percentage of RNs made a difference to patient safety — measured in terms of falls, falls with injury, and medical errors — but in a nuanced way. The analysis was broken down by unit type: medical-surgical, step-down, and critical care. Each 10% increase in RN percentage reduced falls in medical-surgical and critical care units by 30% and 36%, respectively. The training and experience of the RN also mattered: each 10% decrease in civilian RN presence increased the chance of a fall by 33–48% and the chance of a medical error by up to 67%. The other RNs on staff were military, contractor, and reservist personnel. The reason civilian nurses provided a significant advantage to patient safety was their average experience level of 14 years, compared to 5 years for military nurses. A lower NPR reduced both falls and falls with injury, and most falls occurred during night shifts. Reduced medical errors were associated with more RNs and civilian RNs per shift, a lower NPR, and night-shift assignment.

Patrician and colleagues (2011a) acknowledge several weaknesses in their study, including a reliance on incident reports, which many researchers consider an invalid measure because incidents tend to be underreported out of fear of reprisal and litigation. Additional weaknesses include a failure to adjust for differences in the individual risk of falling and medical errors across patients, though the authors argue that dividing the data by unit type produced an equivalent effect.

References

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