Accuracy and correlation of bed and standing scale weights in monitoring volume status in heart failure patients

Abstract

Introduction: Accurate volume status monitoring is crucial for effective diuretic therapy in patients with acute decompensated heart failure (ADHF). While guidelines recommend daily standing body weight measurement as an indicator of volume status, bed scales are commonly used in healthcare facilities. Methods: A method-comparison design was used to compare bed and standing scale weights among adults hospitalized with ADHF at Los Angeles County–University of Southern California Medical Center between March and April 2023. Results & Conclusion: Among 51 weight pairs from 43 participants, a clinically significant mean difference of 1.42 ± 1.18 kg was observed, exceeding the recommended threshold. Inaccuracies, with 71% showing differences >0.6 kg, highlight potential fluid management errors when relying on bed scales in ADHF hospitalizations.

Article highlights

• Heart failure affects 6.5 million Americans, with acute decompensated heart failure causing over 1 million annual inpatient admissions with significant healthcare costs.

• Accurate weight measurement is essential in determining a patient’s volume status and titrating diuresis, a mainstay of therapy, in order to reduce hospitalization duration and prevent readmission.

• Guidelines recommend daily monitoring of standing body weight, though many hospitals use bed scales instead.

• This study compared weights obtained via bed and standing scales among patients hospitalized with acute decompensated heart failure.

• Bed scale weights were inaccurate compared with standing scale weights, with a mean difference of 1.42 ± 1.18 kg (95% CI: -0.894 to 3.73), exceeding the recommended threshold.

• Factors contributing to inaccuracies include inadequate bed calibration and the presence of extra items during in-bed weighing.

• Inaccuracies in bed scale weights highlight the need for reform in this current standard practice of care in order to avoid potential errors in medical management, reduce readmission, and facilitate the self-monitoring of patients’ weights at home.

Keywords: :

• acute decompensated heart failure; diuresis
• heart failure
• standing scale weight

1. Introduction

Heart failure is a common medical condition affecting nearly 6.5 million Americans [1]. Acute decompensated heart failure (ADHF) accounts for over 1 million inpatient admissions in the USA every year and results in almost $40 billion in healthcare costs [2]. Unfortunately, ADHF is the most common cause of Medicare readmissions, with a 30-day readmission rate of roughly 23% [3]. This not only impacts hospital reimbursement rates but also increases overall costs to the healthcare system. Adequate diuresis and volume status optimization are mainstays of therapy, and achieving optimal volume status prior to discharge is critical in lowering readmission rates and is associated with improved mortality [3]. Accurate in-hospital weight assessment is vital in determining volume status. Current American Heart Association guidelines recommend the measurement of standing body weight at the same time each day during hospitalization to monitor heart failure treatment [4]. However, bed scales are commonly used in hospitals instead, as standing scales require patients to be ambulatory. This is often not possible when patients are bedbound, sedated, deemed a high fall risk, or receiving medical therapy that hinders ambulation (i.e., dialysis, intra-aortic balloon pumps, Purewick urinary catheters). Limited data exist regarding the accuracy of bed scales compared with standing scales, and studies suggest large discrepancies between the two [5]. Inaccurate weight measurement may lead to medical error, unreliable volume assessment, and potentially inappropriate discharge. The utilization of standing scales in lieu of bed scales may improve patient outcomes and overall quality of care in the treatment of ADHF by providing more accurate body weight measurements through hospitalization. This is the first study to compare and quantify differences in standing and bed scales in patients hospitalized for ADHF and its derivatives.

2. Patients & methods

2.1. Study design

A method-comparison design was used to compare bed and standing scale weights. The primary exposure variable was the type of scale used (bed scale vs standing scale). The outcome variable was the weight obtained from each scale. Each patient served as their own control. Study approval was obtained from the University of Southern California Institutional Review Board before data collection.

2.2. Sample selection

Patients included were adults (age ≥18 years) admitted to Los Angeles County–University of Southern California Medical Center on days of data collection with a primary or secondary diagnosis of ADHF and its derivatives, including congestive heart failure, acute on chronic heart failure, acute systolic, diastolic or combined systolic and diastolic heart failure, and decompensated heart failure. Patients were located in prespecified inpatient units, including the Coronary Care Unit and select step-down and cardiac telemetry units where standing scales had been implemented. Eligible patients were identified via electronic medical records by filtering by unit location and selecting patients by diagnosis. Additional inclusion criteria included the ability to demonstrate capacity, medical clearance to mobilize out of bed, and physical ability to get out of bed and stand independently.

Assuming a standard deviation (SD) of 3.0 kg and employing t-distribution, the sample size was calculated to be 44 with a power of 0.8, α of 0.05, and an effect size of 0.6, using the formula (effect size = [mean_groupA – mean_groupB] / SD) (see Supplementary Tables S1 & S2). These parameters were based on data from prior studies and expert opinion that an average difference (bias) of greater than ± 0.6 kg and an SD (precision) greater than ± 3.0 kg between the in-bed and standing scale weights were considered clinically significant and large enough to lead to errors in clinical decision-making related to fluid management in this patient population [6].

2.3. Data collection

Collection occurred between March and April of 2023. Eligible participants, identified via electronic medical record, were screened for study inclusion criteria and written informed consent and Health Insurance Portability and Accountability Act authorization forms were obtained. Certified interpreters assisted in translation for communication with non-English-speaking patients.

Standard of care at our institution requires nursing staff to calibrate bed scales with a standard amount of linen (one pillow, sheet, and blanket) prior to weighing new patients. Research investigators did not repeat the calibration process. Study participants were first weighed on the bed scale (Progressa™ model, Hill-Rom, IL, USA) with the standardized amount of bed linen. Additional items on the bed such as extra linens, patient belongings, and medical equipment were removed to ensure accuracy. Standing weights were then obtained utilizing bedside standing scales (seca 876, Seca, CA, USA) with study team assistance when indicated. We aimed to compare 44 sets of measurements. Data sets were summed together between all participants.

2.4. Analysis

Each set of bed scale and standing scale weights were compared. Standard descriptive analytics were performed. The mean weight difference (bias), precision (SD), and limits of agreement (±2 SD) were calculated and graphed using the Bland–Altman method.

3. Results

A total of 43 patients participated in the study between March and April of 2023, and a total of 51 pairs of bed scale and standing scale weights were obtained. The average age was 62 ± 13 years, and 65% of patients were male; 81% were Hispanic, 11% were Black, 5% were White, and 2% were Asian (Table 1). Eight patients were weighed more than once, as they remained admitted on subsequent days of data collection. By increasing the sample size to 51, our power increased to 0.86. Standing weight values ranged from 43.4 to 117 kg, with a mean of 74.0 ± 32.2 kg (95% CI: 41.8–106). Weight differences are detailed in Table 2 and displayed on a Bland–Altman graph in Figure 1. The bias ± precision between weights was 1.42 ± 1.18 kg (95% CI: -0.894 to 3.73), exceeding the recommended bias value. In addition, 71% (n = 36) of participants’ weights differed by more than 0.6 kg between the bed and standing scale; 22% (n = 11) differed by more than 2.0 kg; and 5.9% (n = 3) differed by more than 4.0 kg (Table 2).

Table 1. Demographic data.

Patients, n	43
Age (mean ± SD)	62 ± 13
Gender
Male, n (%)	28 (65.1)
Female, n (%)	15 (34.9)
Race/ethnicity
White, n (%)	2 (4.7)
Black, n (%)	5 (11.6)
Hispanic, n (%)	35 (81.4)
Asian, n (%)	1 (2.3)

SD: Standard deviation.

Table 2. Weights for study participants.

	Mean ± SD weights (kg)	Difference between in-bed and standing weights (bias ± precision) (kg)	Number of weight differences > ± 0.6 kg	Number of weight differences > ± 2.0 kg	Number of weight differences ≥ ± 4.0 kg
Standing scale	74.0 ± 32.2	NA	NA	NA	NA
Bed weight	74.4 ± 32.5	1.42 ± 1.18	36 (71%)	11 (22%)	3 (5.9%)

NA: Not available; SD: Standard deviation.

Figure 1. Bland–Altman plot for comparison of bed and standing scale weights. The X-axis represents the average weights of each bed and the standing scale weight pair. The Y-axis represents the weight differences between each bed and the standing scale weight pair.

LOA: Limit of agreement.

4. Discussion

Weight measurement is critical in the treatment of patients admitted with ADHF. While bed scale weights were precise, they produced inaccurate weights compared with standing scale weights in our study. It is worth noting that accuracy is perhaps more important than precision in this context, as patients are often transferred to different rooms with different scales over the course of admission and medications are dosed based on these recorded weights. There are a multitude of factors that can contribute to user error when weighing patients on bed scales, such as inadequate bed calibration prior to patient admission and lack of attention to having only the standard amount of linen, clothing, and equipment in place during in-bed weight measurement. A study by Schneider et al. comparing electronic bed weighing versus daily fluid balance changes highlighted the contribution to weight accuracy of items left in the bed [7]. For patients with bed linens and/or medical equipment that could not be removed from the bed due to patient safety and/or comfort, the extra items averaged 3.5 ± 1.4 kg for each patient [7]. Findings from this study suggest that beds may not be properly calibrated prior to weighing when extra items are left on the bed, leading to inaccurate weights. Further opportunities exist for improved standardized processes of bed calibration, in-bed weighing, and nursing staff education for obtaining accurate weights.

As our study identifies inaccuracy in weights obtained via bed scales, a common practice of care, it highlights opportunities for reform that will optimize the management of patients with ADHF. Accurate weight measurement is necessary for effective diuretic titration, which is essential in reducing the duration of hospitalization and ensuring a dry weight at discharge to prevent readmission, thereby reducing patient morbidity and healthcare spending. It additionally provides valuable data for patient education to facilitate self-monitoring of their weight at home. The discharge weight of patients hospitalized with ADHF is often used as a reference point for outpatient volume monitoring, as clinical guidelines recommend such patients to be euvolemic at discharge [8]. As even a weight gain of 2 lb (0.9 kg) can be associated with decompensation and necessary readmission, an inaccurate discharge weight may interfere with outpatient volume monitoring recommendations [9]. In the era of telemedicine and remote patient monitoring, accurate weight data can be transmitted electronically to healthcare providers, allowing for real-time assessment of a patient’s condition and timely intervention without a physical visit to a healthcare facility. Accurate weight measurements contribute to research efforts and data analysis, leading to a better understanding of the factors influencing heart failure progression. This knowledge can inform the development of more effective treatment strategies and guidelines. When patients are able to ambulate independently, standing scales should be used to provide more accurate weight measurement and estimation of body volume status.

5. Limitations

This study may be limited by the particular brand of bed scales present and the specificity to this institution. Although Hillrom is one of the largest hospital bed manufacturers in the USA, future research could explore the applicability of our findings to other institutions and devices. Another limitation is presented by research investigators not repeating the bed calibration process. However, this more accurately reflects the clinical reality of how in-bed scales are calibrated in current practice. In the future, this study could be replicated by comparing bed weights before and after calibration to more directly evaluate the effect of accurate calibration. Further, the results of this study may not be generalizable to other facilities if the staff follow more standardized weighing procedures.

6. Conclusion

Bed scales are inaccurate compared with standing scales when weighing patients admitted and treated for ADHF. When available, standing scales are preferred as bed scale inaccuracies have the potential to lead to errors in medical management.

Financial disclosure

The purchase of standing scales was funded as part of a quality improvement grant from the Committee of Interns and Residents (CIR). The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Writing disclosure

No writing assistance was utilized in the production of this manuscript.

Ethical conduct of research

Eligible participants, identified via electronic medical record, were screened for study inclusion criteria and written informed consent and Health Insurance Portability and Accountability Act authorization forms were obtained. Certified interpreters assisted in translation for communication with non-English-speaking patients.

Competing interests disclosure

The authors have no competing interests or relevant affiliations with any organization or entity with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.