The absolute mean BNP values in patients with subarachnoid hemorrhage are low compared to those in patients with decompensated CHF and many patients with severe sepsis or septic shock, whereas the median NT-proBNP values in stroke patients range between 1,618 and 4,589 pg/mL, which is higher than the recently proposed cutoff of 1,500 pg/mL as a discriminating marker for an adverse short-term outcome in patients with CHF and fits the range of levels found in patients with severe sepsis or septic shock. Therefore, in patients with sepsis who have pathologies of the CNS (eg, meningitis, brain abscess, or previous head trauma) elevated BNP or NT-proBNP levels are difficult to interpret.
Several other members of the family of natriuretic peptides have been evaluated as markers of disease severity in critically ill patients. In 14 patients with septic shock, the mean plasma ANP level was fivefold higher than that in healthy subjects. In another study including 14 patients with septic shock, inverse correlations between ANP and LVSWI (r = -0.86) and right ventricular stroke work index (r = -0.65), and a positive relationship between ANP and dopamine dose on day 1 of the ICU stay have been reported. In the study by Witthaut et al, the mean (± SD) values for ANP were found to be several fold higher than those in control subjects (septic shock patients, 82.7 ± 9.9; control subjects, 14.9 ± 1.2 pg/mL; p < 0.01). There was a good correlation between ANP and interleukin-6 (r = 0.73), whereas ANP was not significantly correlated with any hemodynamic parameter.
By analyzing the levels of the prohormone pro-ANP (using the measurement of mid-regional pro-ANP levels by a newly developed assay) in 101 consecutive critically ill patients (in 53 patients with sepsis, severe sepsis, or septic shock), Morgenthaler and associates found significantly lower median levels in survivors (194 pg/mL; range, 20 to 2,000 pg/mL) than in nonsurvivors (853 pg/mL; range, 100 to 2,000 pg/mL; p < 0.001). They calculated a pro-ANP threshold level of 530 pg/mL to predict death in the ICU. The area under the curve of the receiver operating characteristic curve with respect to outcome prediction was slightly higher for pro-ANP (0.88) than for the established APACHE II score (0.86).