N-terminal pro-brain natriuretic peptide levels during the acute phase of sepsis may be a useful indicator of higher risk of long-term impairments: some confounders to consider

Excerpt

Custodero et al. conclude that N-terminal pro-brain natriuretic peptide (NT-proBNP) levels during the acute phase of sepsis may be a useful indicator of higher risk of long-term impairments in physical function and muscle strength in sepsis survivors [1]. A letter from Jiarong et al. has challenged this assertion, pointing to the exponential increase in the plasma level of NT-proBNP with a declining glomerular filtration rate. As they have noted, it does not seem persuasive that NT-proBNP could completely predict outcomes without adjusting for the covariate of renal function. They suggest that the relationship of NT-proBNP levels during the acute phase of sepsis and physical function and muscle strength outcomes in sepsis survivors be stratified based on the renal function [2]. In keeping with this, we would like to comment further. Nearly half of critically ill patients, especially with septic shock, have or develop acute kidney injury (AKI) and 20–25% need renal replacement therapy (RRT) within the first week of their stay [3]. In the Custodero study, the two cohorts (chronic critical illness [CCI] and rapid recovery [RAP]) had a considerable difference in the incidence of septic shock (36.5% vs 16.4%), so it would stand to reason that the rate of AKI and continuous renal replacement therapy (CRRT) was much lower in the RAP cohort when compared to the CCI cohort [1]. CRRT is performed using membranes that have a cut-off value of 35–40 kDa and therefore some quantity of NT-proBNP will be eliminated [4]. Because of its low molecular weight (8.5 kDa), NT-proBNP is likely to be effectively cleared by both high- and low-flux membranes [4]. New highly adsorptive membranes (HAM) can adsorb many molecules with a molecular weight above 35 kDa and will increase this removal even further [4]. This could mislead patient prognostication by artificially decreasing NT-proBNP, but no studies have challenged this issue. Such studies should be done as there is already a long list of biomarkers in sepsis that are lacking reliability during CRRT [5]. As a consequence of the different rates of CRRT between the two cohorts, the reliability of NT-proBNP to be a useful indicator of long-term impairments in physical function and muscle strength in sepsis survivors might be questioned. …