The Importance of Accurate Measurements When Treating the Critically Ill

By Mary Pat Eble | May 21, 2018

With more than 5.7 million patients admitted to U.S. intensive care units (ICUs) each year, accurate and timely monitoring of the five critical vital signs most closely tied to outcomes is key to patient care. Most studies summarize these five as:

1. Core body temperature (CBT)
2. Heart rate (HR)
3. Blood pressure (BP) specifically mean atrial blood pressure (MAP)
4. Respiratory rate (RR),
5. Hourly urine output (UO).

Hourly urine output is the key physiological measure that guides fluid therapy for critically ill patients, but until now has often been overlooked or not accurately recorded. A recent study published in CHEST showed only 26 percent of ICU patients received UO monitoring at least every three hours. This is a concern for critically ill patients as many decisions depend on accurate assessment of the hemodynamic status. In the study, intensive monitoring of UO was associated with improved detection of AKI and reduced 30-day mortality in patients experiencing AKI, as well as less fluid overload for all patients.¹

When determining whether and how to treat a critically ill patient, nurses and physicians look at trends within all five of the critical vital signs. When the HR or BP is questioned, nurses and physicians will do a ‘reality’ check, because one does not want to intervene and treat a rapid heart rate or hypotension unless these are real events.

The same is true for urine output measurements. One doesn’t want to treat oliguria, the production of abnormally small amounts of urine, if the patient’s urine is simply backed up in the tubing and bladder due to airlock or dependent loops. Yet, oliguria is a commonly observed symptom in critically ill patients and puts patients in a high risk category for further worsening renal function and acute kidney injury. When a patient presents with oliguria, it’s imperative to know if the oliguria is real or false. So, then, why don’t hourly UO measurements receive the same scrutiny and demand for accuracy as the other vital signs?

As Gregory J. Schears stated at the 2018 Society of Critical Care Medicine Congress. “Urine output has been an illusive vital sign, critical to the understanding of hemodynamics, renal function and fluid management, yet difficult to accurately obtain and report on a continuous basis. That deficit will now change and open new opportunities for earlier diagnosis, interventions, injury prevention and better overall patient care.”

The Introduction of Accuryn®

An innovative new technology, the Accuryn critical care monitor, can change this and pave the way for improved patient care. Accuryn, transforms the traditional indwelling urinary catheter (IUC) into a next-generation diagnostic tool for precise, real-time measurement of intra-abdominal pressure (IAP), urine output (UO) and core body temperature to help guide care – all at the push of a button.

IUCs are pre-connected to a urine meter drainbag to enable the nurse to monitor hourly UO. As one of the only vital signs still measured manually, hourly urine output measurements are subject to much human variability that can affect the accuracy of this critical measurement. As one example of this, measurements are dependent on when the nurse emptied the meter: was it 10 minutes before the hour or 10 minutes after the hour when the UO was recorded?

Furthermore, because of airlocks that occur in the tubing with gravity systems, the amount of urine in the drainbag when the nurse takes the measurement may not necessarily represent the amount of urine made by the patient. Rather, the aforementioned CHEST study shows an average of 96ml of urine is retained in the bladder in ICU patients due to airlocks. Nurses need to ‘milk’ (raise and lower for a number of minutes) the tubing to break these airlocks, which adds human variability to the measurement process, as well as time pressure while caring for the patient.

If the airlock is not taken care of prior to measurement, the data may show false oliguria – what appears to be low production of urine by the patient may actually be an inability of the patient’s urine to get to the drainbag for measurement. Clinicians may treat this false oliguria with unnecessary fluids. Fluids are one of the most commonly used therapies in critically ill patients and represent the cornerstone of hemodynamic management in intensive care units. Liberal administration of fluids may lead to a positive fluid balance which is independently associated with a poor outcome. It’s important to note that of the 80 percent of critically ill patients who receive liberal fluids, 18 percent are in response to oliguria.

Some catheters have vents either on the tubing, within the drain bag, or both to help facilitate a passive drain-line clearance; passively providing air exchange within the closed drainage system to aide in the prevention of airlock and the resultant false oliguria. But these systems are still limited by gravity and dependent loops and still often require tubing to be ‘milked.’

New technology is long overdue to move hourly UO into the 21st century. Accuryn is the world’s most advanced critical care monitor partly because it takes a highly accurate hourly UO measurement using active drain-line clearance technology which eliminates human variables and ensures the urine produced by the patient actually arrives in the drainage bag and is appropriately recorded for the hour. False oliguria is no longer a possibility. Neither are airlock or dependent loops, because the urine is actively moved through the drainage tubing via the active technology. As a result, urine output measurements are exceedingly accurate, all the time. And they are automatically recorded and time stamped on the hour, saving time and enabling clinicians to spend more time with their patients.

As Dr. Schears puts it, “This is the Holy Grail.”

Medline will be exhibiting the Accuryn critical care monitor at the American Association of Critical Care Nurses National Teaching Institute and Critical Care Exhibition in Boston, Mass. To learn more, visit the Medline booth or go to


1. Intensive Monitoring of Urine Output is Associated with Increased Detection of Acute Kidney Injury and Improved Outcomes. Intensive Care Med. 2015; 41(9): 1529–1537. Published online 2015 Jul 11. doi: 10.1007/s00134-015-3850-x
Fluid challenges in intensive care: the FENICE study
A global inception cohort study
Maurizio Cecconi, Christoph Hofer, Jean-Louis Teboul, Ville Pettila, Erika Wilkman, Zsolt Molnar, Giorgio Della Rocca,Cesar Aldecoa, Antonio Artigas, Sameer Jog, Michael Sander, Claudia Spies, Jean-Yves Lefrant, Daniel De Backer,and on behalf of the FENICE Investigators and the ESICM Trial Group

Categories: Expert Views, Healthcare Segment News

Mary Pat Eble

Clinical Nurse Educator

Mary Pat Eble, MSN, RN, has more than 38 years of critical care nurse experience. As a Clinical Product Specialist and a Clinical Nurse Educator for the Urology Division of Medline, Eble is uniquely positioned to educate nurses. She has published and presented white papers and posters at the Seattle Nursing Research Council, International Society of Burn Injuries, and the American Burn Association. Eble is a 2012 DAISY Foundation awardee and March of Dimes Nurse of the Year Nominee. She was a member of the Washington State Nurses Association Board and Seattle Area Pharmaceutical Representative Council, and chair of the first Sustainability Nursing Committee at Harborview Medical Center/University of Washington in Seattle, Washington.

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