Protecting Renal Blood Flow in the Intensive Care Unit

Abstract

Acute renal failure (ARF) in the intensive care unit (ICU) represents a different spectrum of disease compared to ARF occurring outside the ICU. As much as 95% of ARF in the ICU is secondary to acute tubular necrosis (ATN). Incidence and mortality rates for ARF in and outside the ICU are quite different [1–3]. For example, the incidence of ARF is about 5% outside the ICU and mortality rates are usually < 30%. However, in the ICU, the incidence can be as high as 15% with a mortality rate between 50% and 90%. Severe ARF (defined as requiring dialysis) rarely occurs in isolation, and most often occurs in association with multiple organ failure (MOF) [4]. Ischemia, principally of the renal medulla, is estimated to contribute to 85% of cases of ARF [5], and multiple causes of medullary ischemia have been identified [6]. Most ARF occurs with multiple insults. Common conditions causing or exacerbating medullary ischemia are shown in Table 1. Thus, it seems reasonable that preserving renal blood flow (RBF) should be seen as an imperative for the intensivist. Unfortunately, this goal is easier to espouse than to achieve, and increasing RBF may not always be beneficial.