Fluid overload at start of continuous renal replacement therapy is associated with poorer clinical condition and outcome: a prospective observational study on the combined use of bioimpedance vector analysis and serum N-terminal pro-B-type natriuretic peptide measurement

It is unclear whether the fluid status, as determined by bioimpedance vector analysis (BIVA) combined with serum N-terminal pro-B-type natriuretic peptides (NT-pro-BNP) measurement, is associated with treatment outcome among patients receiving continuous renal replacement therapy (CRRT). Our objective was to answer this question.

Patients who were in the intensive care units of a university teaching hospital and who required CRRT were screened for enrollment. For the enrolled patients, BIVA and serum NT-pro BNP measurement were performed just before the start of CRRT and 3 days afterward. According to the BIVA and NT-pro BNP measurement results, the patients were divided into four groups according to fluid status type: type 1, both normal; type 2, normal BIVA results and abnormal NT-pro BNP levels; type 3, abnormal BIVA results and normal NT-pro BNP levels; and type 4, both abnormal. The associations between fluid status and outcome were analyzed.

Eighty-nine patients were enrolled, 58 were males, and the mean age was 49.0 ± 17.2 years. The mean score of Acute Physiology and Chronic Health Evaluation II (APACHE II) was 18.8 ± 8.6. The fluid status before CRRT start was as follows: type 1, 21.3% (19 out of 89); type 2, 16.9% (15 out of 89); type 3, 11.2% (10 out of 89); and type 4, 50.6% (45 out of 89). There were significant differences between fluid status types before starting CRRT on baseline values for APACHE II scores, serum creatinine, hemoglobin, platelet count, urine volume, and incidences of oliguria and acute kidney injury (P <0.05). There were significant differences between patients with different fluid status before CRRT start on hospital mortality—type 1, 26.3% (5 out of 19); type 2, 33.3% (5 out of 15); type 3, 40% (4 out of 10); and type 4, 64.4% (29 out of 45) (P = 0.019)—as well as renal function recovery rates: type 1, 57.1% (4 out of 7); type 2, 67.7% (6 out of 9); type 3, 50% (3 out of 6); and type 4, 23.7% (9 out of 38) (P = 0.051).

Fluid status abnormalities were common among patients receiving CRRT. Different types of fluid status distinguished by BIVA combined with serum NT-pro BNP measurements corresponded to different clinical conditions and treatment outcomes, which implies a value of this method for evaluation of fluid status among patients receiving CRRT.