Abstract
A growing fraction of the clinical duties of Nephrologists is undertaken inside intensive care units. While assessing patients with acute renal failure in the context of circulatory collapse, which are also edematous and/or with impaired gas exchanges, the Nephrologist must decide between two opposing therapies: 1) remove volume with the aid of dialysis or diuretics to improve the edematous state; 2) volume expand to improve hemodynamics. To minimize the odds of making incorrect choices, the Nephrologist must be familiar with the tools available for determining the adequacy of volume status and for invasive hemodynamic monitoring in the critically ill patient. In this manuscript, we will briefly review the physiology of extra cellular fluid volume regulation and then tackle the issue of volume status assessment, based on clinical and hemodynamic criteria.
Highlights
Due to the high incidence of acute renal failure (ARF) in critically ill patients, a growing fraction of the clinical activities of nephrologists occurs in intensive care units (ICUs)
The degree of indecision is so high that the nephrologist is called to start dialysis aiming at removing volume of a shocked patient, who is being actively expanded with crystalloid solutions by the intensivist. - “I will continue to expand because the patient is shocked, but I need you to dialyze the patient and remove fluid to improve gas exchanges.”
There are several limitations to the use of those techniques: 1) the patients need to be in the volume-controlled mode of mechanical ventilation, deeply sedated or paralyzed; 2) the technique has not been tested in patients ventilated with low tidal volume and high positive end-expiratory pressure (PEEP); 3) situations that increase the intraabdominal pressure make their use impossible; and 4) no validation in patients with cardiac arrhythmias or severe cardiopulmonary disease
Summary
Due to the high incidence of acute renal failure (ARF) in critically ill patients, a growing fraction of the clinical activities of nephrologists occurs in intensive care units (ICUs). Baroreceptors in the aortic arch, carotid sinus, and kidneys EIVV expansion: pressure natriuresis, ANF secretion EIVV depletion: catecholamine and ADH secretion, RAAS activation Sodium excretion or retention History, clinical examination, simple complementary tests, invasive hemodynamic assessment. A hypovolemic patient should have low urinary sodium (usually < 20 mEq/L) Frequently true, this may not CLINICAL DATA THAT MAY HELP DETERMINING BLOOD VOLUME. A patient with congestive heart failure (CHF), who has edema and pulmonary edema, needs a diuretic, even when his urinary sodium is < 20 mEq/L, because, in that case, sodium renal retention represents a response to the poor cardiac performance in perfusing tissues and baroreceptors (a reduction in EIVV). A literature review from 1966 to 1988 has shown that, considering the Swan-Ganz catheter gold standard, the sensitivity of the clinical assessment to detect hypervolemia in clinical patients was 73%; in ICU patients, that sensitivity was only 40%.1 the careful physician needs to have expertise in different hemodynamic assessment methodologies applicable to critical patients and to integrate to his rationale a wide range of information to establish a more precise diagnosis of the volemic status and, to define the most adequate therapeutic approach
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