The threshold for intra-operative urine output (UO) for which the risk of acute kidney injury (AKI) increases is unclear.
This is a retrospective cohort study to investigate the relationship between intra-operative urine output during major abdominal surgery and the development of postoperative AKI .
To identify an optimal threshold for predicting the differential risk of AKI.
Single-centre retrospective cohort study.
Conducted in Kyoto University Hospital.
Teaching hospital in Japan with 1121 beds.
- Patients aged 18 or older undergoing major abdominal surgery under general anaesthesia
- March 2008 to April 2015
Major abdominal surgery included liver, colorectal, gastric, pancreatic, or oesophageal resection by either laparotomy or a laparoscopic approach
Data on study participants were collected from the electronic database and the electronic medical record system.
Data collected was done according to uniform criteria to prevent variability.
The type of surgery was categorized into six groups (liver, colorectal, gastric, pancreatic, oesophageal, and complex)
For each patient, the average intraoperative UO per hour was calculated by dividing the total intraoperative UO by the duration of operating room stay and by the measured body weight.
The primary outcome was AKI as determined by change in serum creatinine (SCr) according to the Kidney Disease: Improving Global Outcomes (KDIGO) definition (increase in SCr of 26.5 mmol/litre within 48h or 1.5 times baseline within 7 days after surgery). The most recent SCr measured before the surgery was used as the baseline value.
Patients who developed AKI had a higher AKI risk index, had more blood loss, and were more likely to receive intraoperative vasopressor infusion.
Intraoperative UO in patients with AKI was lower than in those without
Using the minimum P-value approach, multivariable analysis demonstrated that the ideal threshold of intraoperative UO was 0.3 ml kg/hr
An intraoperative UO of <0.3 ml kg 1 h 1 occurred in 11.3% of patients.
These patients had a higher AKI risk index, were more likely to undergo laparoscopic surgery, and had less blood loss and lower net fluid balance
The incidences of AKI were 10.2% and 5.9% in patients with an intraoperative UO of <0.3 and >0.3 ml kg 1 h 1, respectively
Information on clinical risk factors of AKI was not prospectively collected; instead, it was retrieved from the electronic database and the electronic medical record system.
Thus, the effects of certain risk factors might have been biased.
The design of the study means that we are unable to ascertain whether intraoperative management targeting the urine flow rate at or above 0.3 ml kg/hr will reduce the risk of AKI. Future randomiaed trials are needed to address this hypothesis.
The duration of oliguria not clearly determined.
The study included patients undergoing major abdominal surgery, so it is unclear whether findings can be extrapolated to patients undergoing other operations.
Summary by Dr Osato Osagie