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Invited Critique
March 1, 2008

B-Type Natriuretic Peptide: A Biomarker for the Diagnosis and Risk Stratification of Patients With Septic Shock—Invited Critique

Arch Surg. 2008;143(3):246. doi:10.1001/archsurg.2007.70

Kandil and colleagues purport a role for BNP level as a useful marker of ventricular function and mortality in sepsis. There were no demographic data provided for the groups, specifically age and the underlying disease. Also, the absence of any BNP data between days 1 and 21 precludes potential useful information about BNP activity in response to therapy. These investigators state that patients without renal and heart failure may benefit from measurement of BNP levels but do not present any supporting data, only concepts. They also state that BNP level determination may help with risk stratification, which is suspect because there was no significant difference between the control subjects and patients with early sepsis (100 ± 9.4 vs 120 ± 11.2 pg/mL). They further stated that BNP level may serve as “a valuable measure for determining reduced left ventricular function in patients with septic shock”; again, with no supporting data. Besides, there are much better tools for assessing left ventricular function (eg, thermistor-tipped, flow-directed pulmonary artery catheters and transesophageal echocardiography or even transthoracic echocardiography) because BNP level provides no quantitative data. The authors gave no information about the availability of this test in most hospitals: Is it a routine test, or a research study that must be sent to a reference laboratory? What does it cost, and will insurance companies pay for it? Elevation of BNP level in septic shock may well be just a measure of deteriorating myocardial function during end-stage sepsis after weeks of significant tachycardia and pressors, when the heart can no longer compensate. I was surprised to see a resurrection of an ancient term, myocardial depressant substance, which we used (and discarded) many years ago to explain observations we did not understand. In my view, their goal of determining a role for BNP in sepsis was not achieved, and their observations most likely represent a “true-true but unrelated” association between the two. As presented, they can say only that if BNP levels remain high, death is imminent; there is little one can do with such information except withhold treatment, which is not an option in this context.