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

BACKGROUND: Continuous measurement of urinary PO2 (PuO2) is being applied to indirectly monitor renal medullary PO2. However, when applied to critically ill patients with shock, its measurement may be affected by changes in FiO2 and PaO2 and potential associated O2 diffusion between urine and ureteric or bladder tissue. We aimed to investigate PuO2 measurements in septic shock patients with a fiberoptic luminescence optode inserted into the urinary catheter lumen in relation to episodes of FiO2 change. We also evaluated medullary and urinary oxygen tension values in Merino ewes at two different FiO2 levels. RESULTS: In 10 human patients, there were 32 FiO2 decreases and 31 increases in FiO2. Median pre-decrease FiO2 was 0.36 [0.30, 0.39] and median post-decrease FiO2 was 0.30 [0.23, 0.30], p = 0.006. PaO2 levels decreased from 83 mmHg [77, 94] to 72 [62, 80] mmHg, p = 0.009. However, PuO2 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 FiO2 was 0.30 [0.21, 0.30] and median post-increase FiO2 was 0.35 [0.30, 0.40], p = 0.008. PaO2 levels increased from 64 mmHg [58, 72 mmHg] to 71 mmHg [70, 100], p = 0.04. However, PuO2 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 PaO2 and the variation in PuO2 values. In 9 Merino ewes, when comparing oxygen tension levels between FiO2 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 FiO2 and PaO2 within the context of usual care did not affect PuO2. Our findings were supported by experimental data and suggest that PuO2 can be used as biomarker of medullary oxygenation irrespective of FiO2.

Urine biochemistry assessment in the sequential evaluation of renal function: Time to think outside the box.

Urine biochemistry (UB) remains a controversial tool in acute kidney injury (AKI) monitoring, being considered to be of limited value both in terms of AKI diagnosis and prognosis. However, many criticisms can be made to the studies that have established the so called "pre-renal paradigm" (used for decades as the essential physiological basis for UB assessment in AKI) as well as to more recent studies suggesting that UB has no utility in daily clinical practice. The aim of this article is to describe our hypothesis on how to interpret simple and widely recognized urine biochemical parameters from a novel perspective, propose the rationale for their sequential assessment and demonstrate their usefulness in AKI monitoring, especially in the critical care setting.

Platypnea-orthodeoxia syndrome after open prostatectomy and cystolithotomy: Coincidence or unknown pathophysiology?

A few cases of platypnea-orthodeoxia syndrome have been described in the literature, some of them after thoracic or upper abdominal surgeries. In most cases, hypoxemia in the upright or sitting position, which is the main clinical symptom for this uncommon diagnosis, is usually related to a dynamic right to left cardiac shunt induced by anatomical changes in the relative position between the inferior vena cava and the atria in the presence of a patent foramen ovale. In this case report, we describe a situation in which platypnea-orthodeoxia syndrome developed acutely before surgery but that became severely exacerbated after an open urologic surgery without a clear acute anatomical change that could be responsible for triggering the syndrome. This case might suggest that the pathophysiology of acute platypnea-orthodeoxia syndrome is not completely elucidated and that other possible triggers for acute clinical manifestation in addition to acute anatomical thoracic changes must be explored.

Electrical impedance tomography monitoring during spontaneous breathing trial: Physiological description and potential clinical utility.

BACKGROUND: Readiness for mechanical ventilation (MecV) weaning and extubation is usually assessed clinically with the use of a spontaneous breathing trial (SBT), but its accuracy is limited, and the pathophysiology of weaning failure not completely elucidated. The purpose of the present study was to describe the physiological behavior of electrical impedance tomography parameters during SBT and to propose additional variables that could be helpful in defining weaning/extubation outcome. METHODS: From December 2015 to January 2017, all subjects who remained under MecV with an orotracheal tube for more than 24 hours and who were submitted to SBT both in pressure-support ventilation (PSV) or T-tube were included in the study. Both clinical and impedance parameters were collected immediately before as well as during SBT. RESULTS: Forty-two subjects were included in the final analysis. For subjects submitted to SBT in PSV, none of the impedance parameters added significant information regarding weaning outcomes. For subjects submitted to a T-tube SBT, a significant and progressive decrease in end-expiratory lung impedance (dEELI) was observed, which was more prominent in subjects who clinically failed the SBT. These subjects had a significant rapid shallow breathing index at the end of SBT. CONCLUSIONS: dEELI was a potentially useful parameter in the evaluation of MecV weaning outcome when abrupt lung depressurization was induced during SBT in our study. The degree of dEELI decrease was probably related to the magnitude of lung derecruitment, which seems to play a key role in the MecV weaning outcome.

Urine electrolyte measurement as a "window" into renal microcirculatory stress assessment in critically ill patients.

Urine electrolyte assessment has long been used in order to understand electrolyte concentration disturbances in blood and as an easy tool for monitoring renal perfusion and structural tubular damage. In the last few years, great improvement in the pathophysiology of acute kidney injury (AKI) has occurred, and the correlation between urine biochemistry (UB) behavior and renal perfusion was frequently questioned. Many authors have suggested abandoning UB monitoring due to its unclear role in AKI monitoring. Our group has been working in this field in the critically ill population, and we believe that, although UB is indeed very useful, a different point of view regarding the interpretation of the data should be used. The aim of this review is to explain the rationale of these new concepts and make suggestions for their adequate use in daily ICU practice, especially in low-income countries where more sophisticated and expensive AKI biomarker assessments are not available.

Organizational characteristics, outcomes, and resource use in 78 Brazilian intensive care units: the ORCHESTRA study.

PURPOSE: Detailed information on organization and process of care in intensive care units (ICU) in emerging countries is scarce. Here, we investigated the impact of organizational factors on the outcomes and resource use in a large sample of Brazilian ICUs. METHODS: Retrospective cohort study of 59,693 patients (medical admissions, 67 %) admitted to 78 ICUs during 2013. We retrieved patients' data from an ICU quality registry and surveyed ICUs regarding structure, organization, staffing patterns, and process of care. We used multilevel logistic regression analysis to identify factors associated with hospital mortality. Efficient resource use was assessed by estimating standardized resource use and mortality rates adjusted for the SAPS 3 score. RESULTS: ICUs were mostly medical-surgical (79 %) and located at private hospitals (86 %). Median nurse to bed ratio was 0.20 (IQR, 0.15-0.28) and board-certified intensivists were present 24/7 in 16 (21 %) of ICUs. Multidisciplinary rounds occurred in 67 (86 %) and daily checklists were used in 36 (46 %) ICUs. Most frequent protocols focused on sepsis management and prevention of healthcare-associated infections. Hospital mortality was 14.4 %. In multivariable analysis, the number of protocols was the only organizational characteristic associated with mortality [odds ratio = 0.944 (95 % CI 0.904-0.987)]. The effects of protocols were consistent across subgroups including surgical and medical patients as well as the SAPS 3 tertiles. We also observed a significant trend toward efficient resource use as the number of protocols increased. CONCLUSIONS: In emerging countries such as Brazil, organizational factors, including the implementation of protocols, are potential targets to improve patient outcomes and resource use in ICUs.