Defining oliguria during cardiopulmonary bypass and its relationship with cardiac surgery–associated acute kidney injury

Abstract

Background. While urine flow rate 0.5 ml kg À1 h À1 is believed to define oliguria during cardiopulmonary bypass (CPB), it is

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

“…3 In prior studies we identified that both excursions of mean arterial pressure (MAP) below the threshold of cerebral autoregulation and low urine flow rate during cardiopulmonary bypass (CPB) were identified risk factors for postoperative AKI. 4,5 Our results suggest that close monitoring of urine flow rate might allow for individualizing MAP targets during CPB to ensure optimal renal perfusion. This practice would differ from current standards of care where urine output is imprecisely measured at arbitrary time epochs (e.g., hourly, etc).…”

“…5 When urine flow was < 1.5 ml·kg −1 ·hr −1 , every 0.5 ml/kg/h increase in urine flow rate reduced the risk for AKI by 30%. We found that urine flow rate < 0.5 ml·kg −1 ·hr −1 occurred in only 5.8% of the nearly 30% of patients with AKI suggesting that oliguria based definitions for AKI may be imprecise for the intraoperative setting.…”

“…We found that urine flow rate < 0.5 ml·kg −1 ·hr −1 occurred in only 5.8% of the nearly 30% of patients with AKI suggesting that oliguria based definitions for AKI may be imprecise for the intraoperative setting. 5,9 Other devices for measurement of urine output are available ( Accuryn , Potrero Medical, San Francisco, CA; Criticore , Bard, Murray Hill, NJ; Renalguard , Renalguard Solutions Inc., Milford, MA; Output Medical, Chicago, IL). However, unlike our device, they do not integrate with one-piece closed urinary catheter systems most commonly used in surgical patients.…”

“…Urine bag weight from the scale is streamed via RS232 protocol to a laptop running ICM+ software (Cambridge, UK) used in our cerebral autoregulation studies. 4,5 A threshold filter with alpha of 20 was applied to the highest and lowest 10% of measurements from the previous 10 seconds to exclude outliers resulting from mechanical interference by clinical personnel. The mean value of the remaining measurements, along with six previous 10-second mean values are used to calculate the average urine flow rate.…”

“…The latter urine flow rate was deemed to be a “high flow rate” in our previous study. 5 For the first simulation, 25 randomized flows equivalent to 0.72 to 2.52 ml·kg −1 ·hr −1 for a 70 kg patient were evaluated over 75 minutes. The system outputs a value every 10 seconds, resulting in 451 measurements used to compare percent difference between infused and measured volumes.…”