Clinical Application Of Bioimpedance Analysis Combined With N-terminal Pro-B-type Natriuretic Peptide Measurement For Volume Evaluation In Critically Ill Patients Receiving Continuous Renal Replacement Therapy

Objective:Two useful methods for volume evaluation in critically ill patients, bioimpedance analysis (BIA) and N-terminal pro-B-type natriuretic peptide (NT-pro-BNP), theoretically have their limitation when used singly. Through a prospective observational study, we investigated the role of combined using BIA and NT-pro-BNP in evaluation of volume status of critically ill patients receiving continuous renal replacement therapy (CRRT) and the relationship between volume status and patients’ outcome.Methods:Critically ill patients in ICU requiring CRRT were screened for enrollment. After enrollment, BIA, and blood NT-pro BNP measurement were performed at the initiation of CRRT and 3 days later. Clinical status, lab tests results, as well as discharge survival status and renal function status were recorded.Results:Eighty-nine patients(58 males) were enrolled in the research, with an average age 49.0 ± 17.2 years old, and mean APACHE II score 18.8 ± 8.6. The mean duration of CRRT was 8.0±8.2 day(1-45 day). Among them,15 patients (16.9%) were dead and 4 transferred to other hospitals within 3 days after the initiation of CRRT, and finally 70 patients finished 2 times data collection. Of 89 patients,43 were dead at hospital (48.3%). Among 60 with acute kidney injury (AKI, 67.4%),22 (36.7%) recovered renal function.a) Comparison of the two volume parameters between the survival group and dead group:reactance and NT-pro BNPAccording to the discharge survival status, the patients were divided into the survival group (n=46) and the dead group (n=43). In the two groups, the average age was 44.0±15.8 and 54.3±17.2 years old(P=0.004), the APACHE Ⅱ score was 14.4±7.1 and 23.6±7.3 (P< 0.001),respectively. Compared with the dead group, significantly higher values were found in the survival group for resistance values (-0.99±1.62 vs.-1.86±1.73, p=0.015) and reactance values (-1.61±1.24 vs.-2.17±1.56, p= 0.063) when measured by BIA (currency frequency 50kHz) before CRRT; while a significant lower level of blood NT-pro BNP [173.6 (51.0-857.4) vs.349.0 (151-2707) p mol/1, p= 0.007] before CRRT was found in the survival group. The logarithm of NT-pro BNP values shows a negative correlation with resistance values (r=-0.451, p<0.001).b) The relationship between patients’ outcomes and fluid status evaluated by combination of BIA and NT-pro BNP According to the test results of BIA and NT-pro BNP,89 patients were divided into four groups:Group1, normal BIA and normal NT-pro BNP level (19 cases, 21.3%); Group2, normal BIA and higher than normal NT-pro BNP level (15 cases, 16.9%); Group3, higher than normal BIA and normal NT-pro BNP level (10 cases,11.2%); Group4, higher than normal BIA and NT-pro BNP level (45 cases, 50.6%). From group 1 to group 4, a trend of worse volume status existed, accompanied with a worse clinical conditions as evaluated by APACHE Ⅱ score(in 1-4 groups:13.6,17.1,15.5 and 22.2, p=0.001). The incidence of AKI, and the percentage of patients with urine output less than 500ml/day were significantly different between groups (p=0.001, and 0.002), as well as serum creatinine level (P=0.004), blood hemoglobin level (P=0.022) and platelets count (p=0.005). Significant difference between 4 groups was also found in discharge mortality (1-4 group:23.6%,33.3%,40% and 64.4%, p=0.019), and renal function recovery rate (1-4 group:57.1%,67.7%,50% and 23.7%, p=0.047). In 70 patients with the 3th day measurement, the changes of BIA values and blood NT-pro BNP level were analyzed. A trend toward lower discharge mortality was found in patients with improvement of volume parameters such as BIA and NT-pro BNP level (P>0.05). For the patients with both higher than normal values of BIA and NT-pro BNP before CRRT, no mortality benefit was found although with improvement of the two volume parameters.Summary of the results:Both BIA and NT-pro BNP were significantly different between the survivors and the dead. Patients with different volume status as evaluated by combined BIA and NT-pro BNP have significantly different discharge mortality and renal function recovery rate. The patients with both parameters higher than normal had the worst outcomes and no benefit was found in them although the two parameters improved by interventions.