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Factors that confound the prediction of renal medullary oxygenation and risk of acute kidney injury from measurement of bladder urine oxygen tension
Author(s) -
Ngo Jennifer P.,
Lankadeva Yugeesh R.,
Zhu Michael Z. L.,
Martin Andrew,
Kanki Monica,
Cochrane Andrew D.,
Smith Julian A.,
Thrift Amanda G.,
May Clive N.,
Evans Roger G.
Publication year - 2019
Publication title -
acta physiologica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.591
H-Index - 116
eISSN - 1748-1716
pISSN - 1748-1708
DOI - 10.1111/apha.13294
Subject(s) - acute kidney injury , urine , medicine , urinary system , kidney , oxygenation , cardiology , anesthesia , urology
Aim Urinary oxygen tension (uPO 2 ) may provide an estimate of renal medullary PO 2 (mPO 2 ) and thus risk of acute kidney injury (AKI). We assessed the potential for variations in urine flow and arterial PO 2 (aPO 2 ) to confound these estimates. Methods In 28 sheep urine flow, uPO 2 , aPO 2 and mPO 2 were measured during development of septic AKI. In 65 human patients undergoing cardiac surgery requiring cardiopulmonary bypass (CPB) uPO 2 and aPO 2 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, uPO 2 was more closely correlated with mPO 2 than with aPO 2 or urine flow. The difference between mPO 2 and uPO 2 varied little with urine flow or aPO 2 . 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 uPO 2 . During hyperoxic CPB high values of uPO 2 were often observed at low urine flow. Low urinary PO 2 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 uPO 2 provides a robust estimate of mPO 2 , but this relationship is confounded by the simultaneous presence of systemic hyperoxia and low urine flow. Urine flow increases and uPO 2 decreases during CPB. Thus, CPB is probably the best time to use uPO 2 to detect renal medullary hypoxia and risk of post‐operative AKI.