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. 2014 Apr-Jun;26(2):143-7.
doi: 10.5935/0103-507x.20140021.

Fractional excretion of potassium in the course of acute kidney injury in critically ill patients: potential monitoring tool?

[Article in English, Portuguese]
Alexandre Toledo Maciel  1 , Marcelo Park  1 , Etienne Macedo  2
Affiliations

Fractional excretion of potassium in the course of acute kidney injury in critically ill patients: potential monitoring tool?

[Article in English, Portuguese]
Alexandre Toledo Maciel et al. Rev Bras Ter Intensiva. 2014 Apr-Jun.

Abstract
in English, Portuguese

Objective: To evaluate the behavior of fractional excretion of potassium in the course of acute kidney injury in critically ill patients.

Methods: As part of a larger study in which we have evaluated blood and urinary parameters in the course of acute kidney injury, 168 patients were included. Blood and urine samples were collected daily until the removal of the urinary catheter or the initiation of renal replacement therapy. We describe the evolution of fractional excretion of potassium based on whether acute kidney injury was diagnosed, its duration (transient or persistent) and its severity (creatinine-based Acute Kidney Injury Network - AKIN stage). The diagnostic performance of fractional excretion of potassium in predicting the duration of acute kidney injury and the need for renal replacement therapy on the day of acute kidney injury diagnosis was also evaluated.

Results: Fractional excretion of potassium was significantly higher in persistent acute kidney injury compared to transient acute kidney injury on the day of acute kidney injury diagnosis (24.8 vs. 13.8%, p<0.001). Both groups had the median fractional excretion of potassium increasing in the two days preceding the acute kidney injury diagnosis. Patients without acute kidney injury had stable low fractional excretion of potassium values. The fractional excretion of potassium was fairly accurate in predicting persistent acute kidney injury (area under the curve: 0.712; 95% confidence interval: 0.614-0.811; p<0.001) on the day of acute kidney injury diagnosis. The area under the curve was 0.663 (95% confidence interval: 0.523-0.803; p=0.03) for renal replacement therapy. The fractional excretion of potassium increased with maximum AKIN stage reached, in both transient and persistent acute kidney injury.

Conclusion: Sequential fractional excretion of potassium assessment appears to be useful in critically ill patients at risk for acute kidney injury.

Objetivo: Avaliar o comportamento da fração de excreção de potássio durante a evolução da lesão renal aguda em pacientes graves.

Métodos: Foram incluídos 168 pacientes como parte de um estudo maior, no qual avaliamos parâmetros sanguíneos e urinários durante a evolução da lesão renal aguda. Foram coletadas diariamente amostras de sangue e urina até a remoção da sonda vesical ou a necessidade de terapia de substituição renal. Descrevemos a evolução da fração de excreção de potássio conforme a presença ou não de lesão renal aguda, sua duração - transitória ou persistente - e gravidade (com base no estágio Acute Kidney Injury Network - AKIN). Foi também avaliado o desempenho diagnóstico da fração de excreção de potássio no dia do diagnóstico da lesão renal aguda, para prever a sua duração e a necessidade de terapia de substituição renal.

Resultados: A fração de excreção de potássio foi significativamente maior na lesão renal aguda persistente do que na transitória no dia do diagnóstico da lesão renal aguda (24,8 versus 13,8%; p<0,001). Ambos os grupos tiveram aumento de sua fração de excreção de potássio mediana nos 2 dias que precederam o diagnóstico de lesão renal aguda. Pacientes que não desenvolveram mantiveram níveis baixos e estáveis de fração de excreção de potássio. A fração de excreção de potássio, no dia do diagnóstico de lesão renal aguda, demonstrou razoável precisão em prever lesão renal aguda persistente (área sob a curva: 0,712; intervalo de confiança de 95%: 0,614-0,811; p<0,001). A área sob a curva para terapia de substituição renal foi de 0,663 (intervalo de confiança de 95%: 0,523-0,803; p=0,03). A fração de excreção de potássio aumentou com o estágio máximo atingido do AKIN, tanto para lesão renal aguda transitória quanto para persistente.

Conclusão: A avaliação sequencial da fração de excreção de potássio parece útil em pacientes graves em risco de lesão renal aguda.

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Conflict of interest statement

Conflicts of interest: None.

Figures

Figure 1
Figure 1
Fractional excretion of potassium between 1 day before (-1) and 2 days after (2) diagnosis of acute kidney injury (0), according to AKI duration and diuretic use during the observation period. For non-AKI patients, D0 is the day of intensive care unit admission. FEK - fractional excretion of potassium; AKI - acute kidney injury; ICU - intensive care unit.
Figure 2
Figure 2
Receiver operating characteristic curves of fractional excretions on the day of acute kidney injury diagnosis in predicting persistent acute kidney injury. FENa - fractional excretion of sodium; FEK - fractional excretion of potassium; FEUr - fractional excretion of urea.
Figure 3
Figure 3
Fractional excretion of potassium on the day of maximum Acute Kidney Injury Network stage of acute kidney injury (AKINmax), according to acute kidney injury duration. * p=0.04; ** p=0.01. FEK - fractional excretion of potassium; AKI - acute kidney injury; AKIN - Acute Kidney Injury Network.
See this image and copyright information in PMC

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