Effects of changes in inspired oxygen fraction on urinary oxygen tension measurements

• Published in: Intensive care medicine experimental 2022-12, Vol.10 (1), p.52-52, Article 52
• Main Authors: Osawa, Eduardo A., Cutuli, Salvatore L., Yanase, Fumitaka, Iguchi, Naoya, Bitker, Laurent, Maciel, Alexandre T., Lankadeva, Yugeesh R., May, Clive N., Evans, Roger G., Eastwood, Glenn M., Bellomo, Rinaldo
• Format: Article
• Language: English
• Subjects: Bladder; Catheters; Critical Care Medicine; Inspired oxygen fraction; Intensive; Intensive care; Life Sciences; Medicine; Medicine & Public Health; Oxygen saturation; Sepsis; Septic shock; Urinalysis; Urinary oxygen tension; Urinary oxygenation
• ISSN: 2197-425X; 2197-425X
• DOI: 10.1186/s40635-022-00479-y

Background Continuous measurement of urinary PO 2 (PuO 2 ) is being applied to indirectly monitor renal medullary PO 2 . However, when applied to critically ill patients with shock, its measurement may be affected by changes in FiO 2 and PaO 2 and potential associated O 2 diffusion between urine and ureteric or bladder tissue. We aimed to investigate PuO 2 measurements in septic shock patients with a fiberoptic luminescence optode inserted into the urinary catheter lumen in relation to episodes of FiO 2 change. We also evaluated medullary and urinary oxygen tension values in Merino ewes at two different FiO 2 levels. Results In 10 human patients, there were 32 FiO 2 decreases and 31 increases in FiO 2 . Median pre-decrease FiO 2 was 0.36 [0.30, 0.39] and median post-decrease FiO 2 was 0.30 [0.23, 0.30], p  = 0.006. PaO 2 levels decreased from 83 mmHg [77, 94] to 72 [62, 80] mmHg, p  = 0.009. However, PuO 2 was 23.2 mmHg [20.5, 29.0] before and 24.2 mmHg [20.6, 26.3] after the intervention ( p  = 0.56). The median pre-increase FiO 2 was 0.30 [0.21, 0.30] and median post-increase FiO 2 was 0.35 [0.30, 0.40], p  = 0.008. PaO 2 levels increased from 64 mmHg [58, 72 mmHg] to 71 mmHg [70, 100], p  = 0.04. However, PuO 2 was 25.0 mmHg [IQR: 20.7, 26.8] before and 24.3 mmHg [IQR: 20.7, 26.3] after the intervention ( p  = 0.65). A mixed linear regression model showed a weak correlation between the variation in PaO 2 and the variation in PuO 2 values. In 9 Merino ewes, when comparing oxygen tension levels between FiO 2 of 0.21 and 0.40, medullary values did not differ (25.1 ± 13.4 mmHg vs. 27.9 ± 15.4 mmHg, respectively, p  = 0.6766) and this was similar to urinary oxygen values (27.1 ± 6.17 mmHg vs. 29.7 ± 4.41 mmHg, respectively, p  = 0.3192). Conclusions Changes in FiO 2 and PaO 2 within the context of usual care did not affect PuO 2 . Our findings were supported by experimental data and suggest that PuO 2 can be used as biomarker of medullary oxygenation irrespective of FiO 2 .