Physicochemical analysis of blood and urine in the course of acute kidney injury in critically ill patients: a prospective, observational study

Abstract

BackgroundSequential physicochemical alterations in blood and urine in the course of acute kidney injury (AKI) development have not been previously described. We aimed to describe these alterations in parallel to traditional renal and acid–base parameters.MethodsOne hundred and sixty eight consecutive critically ill patients with no previous kidney disease, who had an indwelling urinary catheter at ICU admission and who remained with the catheter for at least two days without dialysis were included. A sample of blood and spot urine were collected simultaneously, once daily, until catheter removal or dialysis requirement. Traditional acid–base and renal parameters were sequentially evaluated in parallel to blood and urinary physicochemical parameters. Patients were classified during this period as having or not AKI and, for patients with AKI, duration (transient or persistent) and severity (creatinine-based AKIN stage) were evaluated.ResultsOne hundred and thirteen patients (67.3%) had AKI: 92 at ICU admission and 21 during the observation period. AKI development was characterized in blood by increased values of phosphate and unmeasured anions (SIG), decreased albumin, and in urine by decreased values of sodium (NaU), chloride (ClU) as well as high urinary strong ion difference (SIDu). These alterations began to occur before AKI diagnosis, and they reverted in transient AKI but remained in persistent AKI. NaU, ClU and albumin decreased, and phosphate, SIG and SIDu increased with AKI severity progression. NaU and ClU values increased again when AKIN stage 3 was reached.ConclusionsSimultaneous physicochemical analysis of blood and urine revealed standardized alterations that characterize AKI development in critically ill patients. These alterations paralleled AKI duration and severity. Future studies should consider including sequential evaluation of urine biochemistry as part of the armamentarium for AKI diagnosis and management.

Simple blood and urinary parameters measured at ICU admission may sign for AKI development in the early postoperative period: a retrospective, exploratory study

“…Unfortunately, we don't have the data regarding intra-operative fluid management and the types of fluids used. Although fluctuations in urinary values are expected in a 24-h period, we believe, based on recent publications, 5,13,19 that a single spot urine biochemistry assessment per day, usually at the same hour (together with the routine blood exams) is useful and quite more practical than in a 24-h urine sample.…”

“…We have previously suggested that some of these parameters may be useful in the early AKI diagnosis. 5,13,14 However, in these studies, most AKI diagnoses were made at ICU admission, limiting the data available at the days preceding AKI. In the present study, we have found that a minority of the patients had AKI diagnosed at ICU admission (D0), which is not surprising in a population composed mainly by elective surgical patients.…”

“…In another complementary study, 6 we have suggested that increases in the fractional excretion of potassium (FEK) may be surrogates of decreases in glomerular filtration rate (GFR) and also precede increases in sCr. Of note, in these previous studies, 5,6 most of the patients had a medical reason for ICU admission. Surgical patients, however, are expected to have a more precise and homogeneous moment that AKI is usually triggered, which is the surgical procedure itself.…”

“…We have recently described the differences in the sequential behavior of blood physicochemical parameters and urinary biochemistry of critically ill patients who had or had not developed AKI. 5 In that study, AKI development was characterized by increases in the strong ion gap (SIG) and serum phosphate besides decreases in urinary sodium (NaU), chloride (ClU) and increases in urinary strong ion difference (SIDu), alterations which preceded increases in serum creatinine (sCr) and decreases in urine output. In another complementary study, 6 we have suggested that increases in the fractional excretion of potassium (FEK) may be surrogates of decreases in glomerular filtration rate (GFR) and also precede increases in sCr.…”

Influência das alterações bioquímicas urinárias e séricas sobre o índice de resistividade renal em pacientes críticos e evolução durante injúria renal aguda

“…Nesse contexto, tem-se observado a avaliação dos eletrólitos urinários para esse propósito, com estudos clínicos demonstrando um padrão específico na fase precoce da injúria renal aguda, como a diminuição na excreção urinária de sódio e cloreto (13). Adicionalmente, índices derivativos dos eletrólitos urinários, como a fração de excreção urinária de sódio e ureia, também tem sido utilizados como ferramentas potenciais para distinguir a injuria renal aguda entre estrutural e funcional, com potencial impacto na sua duração (14,15).…”