Benefits of Acuity-Based Nurse Staffing

In today’s healthcare environment, nurses’ roles within the care team are becoming increasingly more important as value-based care models tie hospital reimbursement to patient outcomes.

This has led many healthcare organizations to seek strategies for enhancing nurse care delivery.

In the past, many nurse leaders hypothesized that nurse staffing was one factor that could impact the quality of nurse care delivery, and subsequently, patient outcomes.

Today, researchers have confirmed this hypothesis through the first nurse staffing study leveraging unit-by-unit and shift-by-shift data to examine the relationships between staffing and patient outcomes.

The study, “Nurse Staffing and Patient Outcomes: Bridging Research into Evidenced-Based Practice,” found significant relationships between staffing and nurse-sensitive outcomes on more than half the units studied.

More specifically, data showed that patient falls are almost one and one-half times more likely and medication errors are two times more likely to occur when nurse staff levels deviate from the recommended staffing based on patient acuity.

In addition to staffing levels, the researchers also correlated several staff and patient characteristics to negative outcomes.


Conducted in 2011, the six-month study examined data acquired from nursing shifts in 49 inpatient units within nine large, general or teaching hospitals.

Instead of looking at aggregated staffing data with patient volume as a control, the researchers decided to use data collected daily from an acuity-based solution that recommends nurse staffing based on care requirements per patient. This approach enabled a more accurate evaluation of recommended versus actual staffing levels before, during and after an incident.

Additionally, because researchers collected data on a daily basis – as opposed to monthly or quarterly – they were able to look for correlations between staffing and nurse-sensitive patient outcomes that may have not been apparent in summarized data.


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Following data collection, researchers analyzed the data to find relationship between staffing patterns and medication errors, falls and hospital-associated pressure ulcers (HAPU).

Findings for each of these areas included:

1. Findings: Medication Errors

Researchers found a correlation between nurse staffing and the incidence of medication errors.


The days with the units operating with lower registered nurse (RN) hours per workload (HPW) than the level recommended by an acuity system reported more medication errors than those days staffed according to the acuity system’s HPW recommendations.

In fact, on the days where the units were operating below recommended staffing levels, patients were twice as likely to receive the wrong medication, the wrong dosage, another patient’s medication, medication via the wrong route or medication at the wrong time.

A closer look at one surgical unit’s medication errors showed that on days when the hospital staffed:

• Under the level recommended by the acuity system, the likelihood of a medication error was 13 %

• Close (within 5% of target) to the level recommended by the system, the incidence rate was 2%

• Greater than the level recommended by the system, medication errors dropped to 1.8%

In addition to staffing variances, researchers found the patient’s length of time in the unit also affected the medication error rate.

For example, in the first 24 hours of the patient’s admission to a unit, the likelihood of a medication error was 1.95%. This risk dropped to 0.87% when the patient had been in the unit between 24 and 72 hours, and dropped even further – to 0.79% – once a patient had been in the unit more than 72 hours. This was likely due in part to the potential for errors in properly reconciling medications on patient admission or transfer and nurse unfamiliarity with new patients.

These findings can greatly help nurse leaders looking to leverage staffing strategies to reduce the chance of medical error. By identifying when medication errors are most likely to occur, nursing managers can educate staff, enhance resources at the start of a patient’s admission or transfer to a unit and evaluate processes that can be improved to reduce errors.

2. Findings: Patient Falls


In addition to medication errors, researchers also discovered a link between nurse staffing and patient falls. The study evaluated patient falls occurring on each unit (with and without injury) and compared the occurrences to the acuity-based nurse staffing levels for all caregivers – RNs, LPNs and UAPs. Researchers found nurse staffing levels significantly affected the incidence of patient falls. More specifically, on days when hospitals staffed:

• Significantly less than the level the acuity system recommended, the likelihood of a fall occurring was 6.7 % (less than 95% of recommended staffing hours)

• Close to the level the acuity system recommended, the likelihood of a fall was 1.2%

• Above the acuity system’s recommendation, no falls were reported

Researchers also found that a higher:

• Utilization of agency and float pool nurses correlated with higher fall rates

• Percentage of BSN staff correlated with lower fall rates

• Amount of staff with one or more years of experience on the unit or in the specialty correlated with lower fall rates

• Percentage of overtime hours on the unit correlated to higher fall rates. While use of overtime hours may not be directly related to patient falls, higher use of overtime hours may point to underlying unit staffing issues that may make the unit more susceptible to patient falls.

Patient falls potentially result in longer lengths of stay as well as patient injury. This data enables nursing managers to identify specific staffing patterns that increase the risk of patient falls, thus making it possible for managers to staff appropriately. To mitigate fall risk, nurse managers should set core staffing patterns to match workload demands and provide additional management and oversight to support the unit when the use of agency nurses, inexperienced and overtime staff is necessitated.


Prevention of Medical Errors

Healthcare providers must work effectively in collaborative teams to improve patient safety.

3. Findings: Hospital-Associated Pressure Ulcers

Although the study of HAPU rates proved more difficult due to timing the onset of pressure ulcers and the multiple staffing environments faced by patients with inter-unit transfers, the researchers found some relationship with staffing. Increased HAPU rates were observed on units that staffed with fewer RNs than recommended by the acuity system suggesting that adequate RN staffing may help lower incidence of pressure ulcers.

The impact of RNs on HAPU rates contradicts some earlier studies that suggested higher use of unlicensed caregivers (UAPs) could lower pressure ulcer rates. While higher acuity units (ICUs & step downs) tend to have higher HAPU rates and use fewer UAPs than lower acuity general units, the relationship between HAPU rates and UAP staffing disappears when controls for patient acuity were employed.

4. Findings: Ongoing Understaffing

One of the more dramatic discoveries was the cumulative effect of understaffing. While a medication error was 12.5% more likely to occur and a patient fall was 6.1%. more likely to occur on the first day a unit was understaffed, these percentages increased for both incidences with each consecutive day a unit continued to be understaffed [chart].

Moreover, when a unit was understaffed for six consecutive days, the likelihood of a medication error increased to 56.4%and the likelihood of a fall occurring increased to 30.6 percent. While probability functions predict an increasing likelihood of an event occurring over consecutive trials (days), the occurrence of medication errors was beyond what was predicted by probabilities.

This suggests a cumulative effect of understaffing that created an environment more prone to negative outcomes. Based on this data, nurse managers should regularly evaluate workload demands on a shift-by-shift basis and adjust staffing in a timely manner to ensure understaffing does not contribute to negative patient outcomes.


Effectively Engaging Your Nursing Staff

High nurse retention rates enjoyed by employers during the Great Recession may quickly evaporate as the economy recovers.


Staffing a nursing unit to provide excellent clinical care as well as a safe environment for all patients is both an art and a science. While data at a macro level – number of patients on the unit-allows managers to assign numbers of patients to available nurses, information about the nuances of patient acuity and complexity of care improves staffing assignments.

The study demonstrates that effective staffing goes beyond numbers of staff members; it must also address factors such as patient acuity, skill level, amount of overtime and familiarity of staff with the individual unit’s specialty. This means nurse managers should use shift-by-shift staffing data on a daily basis to appropriately staff based on patient acuity and move staff resources to other areas of need to manage the use of agency or overtime staff.

By examining detailed patterns and levels of staffing, based on workload as opposed to number of patients, nurse leaders can staff units at levels that enhance nursing’s ability to provide optimal clinical care and affect outcomes positively.

Ken Colbert, MS, is senior research analyst at QuadraMed Corporation. For more information about “Nurse Staffing and Patient Outcomes: Bridging Research into Evidenced-Based Practice,” contact Colbert at [email protected].

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