title: Performance and user evaluation of a novel capacitance-based automatic urinometer compared with a manual standard urinometer after elective cardiac surgery.
abstract: BACKGROUND
  In the intensive care setting, most physiologic parameters are monitored automatically. However, urine output (UO) is still monitored hourly by manually handled urinometers. In this study, we evaluated an automatic urinometer (AU) and compared it with a manual urinometer (MU).
  
  
  METHODS
  This prospective study was carried out in the intensive care unit of a cardiothoracic surgical clinic. In postoperative patients (n = 34) with indwelling urinary catheters and an expected stay of 24 hours or more, hourly UO samples were measured with an AU (Sippi, n = 220; Observe Medical, Gothenburg, Sweden) or an MU (UnoMeter™ 500, n = 188; Unomedical, Birkerød, Denmark) and thereafter validated by cylinder measurements. Malposition of the instrument at the time of reading excluded measurement. Data were analyzed with the Bland-Altman method. The performance of the MU was used as the minimum criterion of acceptance when the AU was evaluated. The loss of precision with the MU due to temporal deviation from fixed hourly measurements was recorded (n = 108). A questionnaire filled out by the ward staff (n = 28) was used to evaluate the ease of use of the AU compared with the MU.
  
  
  RESULTS
  Bland-Altman analysis showed a smaller mean bias for the AU (+1.9 ml) compared with the MU (+5.3 ml) (P <0.0001). There was no statistical difference in measurement precision between the two urinometers, as defined by their limits of agreement (±15.2 ml vs. ±16.6 ml, P = 0.11). The mean temporal variation with the MU was ±7.4 minutes (±12.4%), and the limits of agreement were ±23.9 minutes (±39.8%), compared with no temporal variation with the AU (P <0.0001). The ward staff considered the AU easy to learn to use and rated it higher than the MU (P <0.0001).
  
  
  CONCLUSIONS
  The AU was not inferior to the MU and was significantly better in terms of bias, temporal deviation and staff opinion, although the clinical relevance of these findings may be open to discussion.
authors.affiliation: Department of Cardiothoracic Surgery and Anesthesiology, Karolinska University Hospital, SE-17176, Stockholm, Sweden. anton.eklund@stud.ki.se.|Department of Molecular Medicine and Surgery, Karolinska Institutet, SE-17177, Stockholm, Sweden. anton.eklund@stud.ki.se.
authors.forename: Anton
authors.initials: A
authors.lastname: Eklund
authors.affiliation: Department of Cardiothoracic Surgery and Anesthesiology, Karolinska University Hospital, SE-17176, Stockholm, Sweden. martin.slettengren@karolinska.se.|Department of Molecular Medicine and Surgery, Karolinska Institutet, SE-17177, Stockholm, Sweden. martin.slettengren@karolinska.se.
authors.forename: Martin
authors.initials: M
authors.lastname: Slettengren
authors.affiliation: Department of Cardiothoracic Surgery and Anesthesiology, Karolinska University Hospital, SE-17176, Stockholm, Sweden. jan.vanderlinden@ki.se.|Department of Molecular Medicine and Surgery, Karolinska Institutet, SE-17177, Stockholm, Sweden. jan.vanderlinden@ki.se.
authors.forename: Jan
authors.initials: J
authors.lastname: van der Linden
mesh_terms: D001794:Blood Pressure / Q000502:physiology; D006348:Cardiac Surgical Procedures; D005069:Evaluation Studies as Topic; D006801:Humans; D007362:Intensive Care Units; D008991:Monitoring, Physiologic / Q000379:methods*; D011184:Postoperative Period; D011446:Prospective Studies; D014556:Urine; D014894:Weights and Measures / Q000295:instrumentation* / Q000592:standards