Validation of a Real-Time Minute-to-Minute Urine Output Monitor and the Feasibility of Its Clinical Use for Patients Undergoing Cardiac Surgery

Urine output is an early and strong predictor of acute kidney injury and associated mortality: a systematic literature review of 50 clinical studies

BACKGROUND

Although the present diagnosis of acute kidney injury (AKI) involves measurement of acute increases in serum creatinine (SC) and reduced urine output (UO), measurement of UO is underutilized for diagnosis of AKI in clinical practice. The purpose of this investigation was to conduct a systematic literature review of published studies that evaluate both UO and SC in the detection of AKI to better understand incidence, healthcare resource use, and mortality in relation to these diagnostic measures and how these outcomes may vary by population subtype.

METHODS

The systematic literature review was performed following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist. Data were extracted from comparative studies focused on the diagnostic accuracy of UO and SC, relevant clinical outcomes, and resource usage. Quality and validity were assessed using the National Institute for Health and Care Excellence (NICE) single technology appraisal quality checklist for randomized controlled trials and the Newcastle-Ottawa Quality Assessment Scale for observational studies.

RESULTS

A total of 1729 publications were screened, with 50 studies eligible for inclusion. A majority of studies (76%) used the Kidney Disease: Improving Global Outcomes (KDIGO) criteria to classify AKI and focused on the comparison of UO alone versus SC alone, while few studies analyzed a diagnosis of AKI based on the presence of both UO and SC, or the presence of at least one of UO or SC indicators. Of the included studies, 33% analyzed patients treated for cardiovascular diseases and 30% analyzed patients treated in a general intensive care unit. The use of UO criteria was more often associated with increased incidence of AKI (36%), than was the application of SC criteria (21%), which was consistent across the subgroup analyses performed. Furthermore, the use of UO criteria was associated with an earlier diagnosis of AKI (2.4-46.0 h). Both diagnostic modalities accurately predicted risk of AKI-related mortality.

CONCLUSIONS

Evidence suggests that the inclusion of UO criteria provides substantial diagnostic and prognostic value to the detection of AKI.

Accuracy and availability of automated urine output monitoring in the operating room using a smart scale

PURPOSE

Urine output (UO) is an important intraoperative parameter that is not yet electronically monitored. We compared an automatic urinometer (AU) based on a smart scale with a manual urinometer (MU).

PATIENTS AND METHODS

This prospective study investigated the hourly UO of 35 preoperative patients with an indwelling urinary catheter using AU, MU, and cylinder measurements. Data were analyzed using the Bland-Altman method. A questionnaire related to the use of the AU was completed by medical staff (n=25).

RESULTS

Compared to the cylinder measurements, the differences in measurements by the AU and the MU were -6.31 ​± ​15.03 ​mL/h (p=0.018) and 20.26 ​± ​26.81 ​mL/h (p=0.001), respectively. The r values for the comparison of cylinder measurements with AU and MU values were 0.985 (p<0.001) and 0.968 (p<0.001), respectively. Bland-Altman analyses showed that cylinder measurements had better agreement with the AU measurements than with the MU measurements. Also, the medical staff reported that the use of the AU was easier to learn than the use of the MU (p<0.001).

CONCLUSIONS

Compared to the MU values, AU values were noninferior; they had significantly less bias and temporal deviation. Additionally, the medical staff reported that the use of the AU was easier to learn than the use of the MU.

Accuracy of Visual Assessment of Urimeter Bag Volumes: The Whiz Quiz

IMPORTANCE

Although visual estimate of urine output via urimeter bag is common, data on accuracy are limited.

OBJECTIVE

This study aimed to assess the accuracy of a visual estimate of urine output in standard urimeter bags by health care workers.

STUDY DESIGN

This is a prospective observational study. Perioperative health care workers were asked to visually estimate fluid volumes in 5 standard urimeter bags. Actual volumes were 50, 150, 350, 500, and 750 mL. Visual estimates were recorded. The primary outcome was accuracy, defined as estimated visual volume within 20% of actual volume. Secondary outcomes included effect of health care provider type, specialty, experience, sex, and age on accuracy.

RESULTS

A total of 159 responses were analyzed. There were 55 (35.3%) registered nurses, 19 (12.2%) certified registered nurse anesthetists, 18 (11.5%) advanced practice providers not identified as a certified registered nurse anesthetist, and 64 (41%) physicians. Mean estimated volumes (in milliliters) ± standard deviation and accuracy for the bags were as follows: (a) actual volume of 50 mL and estimated volume of 66 ± 29 mL (45% accuracy), (b) actual volume of 150 mL and estimated volume of 149 ± 43 mL (46% accuracy), (c) actual volume of 350 mL and estimated volume of 356 ± 74 mL (76% accuracy), (d) actual volume of 500 mL and estimated volume of 452 ± 77 mL (85% accuracy), and (e) actual volume of 750 mL and estimated volume of 675 ± 108 mL (85% accuracy). There was reasonable accuracy for individual volume estimates, but accuracy across all 5 urimeter bags was low: 22 of 159 (13.8%). There were no significant differences in accuracy based on health care provider type, specialty, experience, sex, or age.

CONCLUSIONS

Consistent accuracy of visual assessment of calibrated urimeter bag volumes was low and not influenced by health care provider characteristics.

Transparency, Public Reporting and a Culture of Change to Quality and Safety in Cardiac Surgery

Academic medical centers have a duty to serve as hospitals of last resort for advanced cardiac surgical care and therefore manage patients at elevated risk of post-operative morbidity and mortality. They must also meet state and professional quality targets devised to protect the public. The tension between these imperatives can be managed by a multi-dimensional quality improvement program which aims to manage risk, optimize outcomes and exclude futile operations. We here share our approach to this process, its impact on our institution and discuss pertinent issues relevant to institutions in a similar situation.

UScale: a digital device for automatic urine volume measurement and frequency volume charting

Background

Health issues relating to the lower urinary tract are an increasing burden on the health economy. Measurement of urination frequency/volume using diaries to evaluate symptoms and assess severity is established in the management of these health problems. In current practice, these frequency volume diaries are completed by voiding into a measuring jug and the completion of paper or digital charts. Despite being shown useful to diagnosis, this can be a cumbersome method of data collection, leading to issues with patient compliance. In this paper we describe the established benefits of providing clinicians accurate micturition data followed by an analysis of the problems with the current data collection method.

Methods

We introduce our prototype electronic device and accompanying method, which is designed to improve data accuracy and patient compliance, while reducing patient training requirements and clinician workload.

Results

The device hardware calibration and testing procedure is described, and two sets of initial data from assumed healthy volunteers are presented, allowing us to demonstrate the advantages of digital data in the fast calculation of diary summary statistics and their potential use to clinicians.

Conclusions

We discuss the design improvements to the UScale device, collection bag, and electronic medical records integration undertaken while validating our described method.

Factors that confound the prediction of renal medullary oxygenation and risk of acute kidney injury from measurement of bladder urine oxygen tension

AIM

Urinary oxygen tension (uPO₂ ) may provide an estimate of renal medullary PO₂ (mPO₂ ) and thus risk of acute kidney injury (AKI). We assessed the potential for variations in urine flow and arterial PO₂ (aPO₂ ) to confound these estimates.

METHODS

In 28 sheep urine flow, uPO₂ , aPO₂ and mPO₂ were measured during development of septic AKI. In 65 human patients undergoing cardiac surgery requiring cardiopulmonary bypass (CPB) uPO₂ and aPO₂ were measured continuously during CPB, and in a subset of 20 patients, urine flow was estimated every 5 minutes.

RESULTS

In conscious sheep breathing room air, uPO₂ was more closely correlated with mPO₂ than with aPO₂ or urine flow. The difference between mPO₂ and uPO₂ varied little with urine flow or aPO₂ . In patients, urine flow increased abruptly from 3.42 ± 0.29 mL min^-1 to 6.94 ± 0.26 mL min^-1 upon commencement of CPB, usually coincident with reduced uPO₂ . During hyperoxic CPB high values of uPO₂ were often observed at low urine flow. Low urinary PO₂ during CPB (<10 mm Hg at any time during CPB) was associated with greater (4.5-fold) risk of AKI. However, low urine flow during CPB was not significantly associated with risk of AKI.

CONCLUSIONS

uPO₂ provides a robust estimate of mPO₂ , but this relationship is confounded by the simultaneous presence of systemic hyperoxia and low urine flow. Urine flow increases and uPO₂ decreases during CPB. Thus, CPB is probably the best time to use uPO₂ to detect renal medullary hypoxia and risk of post-operative AKI.