Can chronic volume overload be recognized and prevented in hemodialysis patients? The pitfalls of the clinical examination in assessing volume status.

The twin goals of renal replacement therapy are to restore sodium and water homeostasis and to remove uremic toxins. Urea is the usual (although surrogate) marker of uremic toxin, and our current standard of defining adequacy of dialysis hinges upon the monthly measurement of volume-normalized urea clearance · time product (Kt ⁄V). Sadly, similar standards to define adequacy of sodium homeostasis, arguably the most potent uremic toxin, are not present. As a result hypovolemia and hypervolemia are common among patients with end-stage renal disease and the concept of dry-weight has taken a backstage in the everyday practice of dialysis. Unfortunately, there exists no consensus on how the dry-weight should be clinically defined. Now over four decades old, the earliest definition of dry-weight relied on blood pressure during dialysis. Thomson et al. (1) stated that achieving dry-weight will result in ‘‘reduction of blood pressure to hypotensive levels during ultrafiltration and unassociated with other obvious causes.’’ Henderson also defined dry-weight in relation to intradialytic blood pressure stating that dry-weight is ‘‘the weight obtained at the conclusion of a regular dialysis treatment below which the patient more often than not will become symptomatic and go into shock’’ (2). Finally, Charra departed from prior definitions of dry-weight and used interdialytic blood pressure in defining dry-weight as, ‘‘that body weight at the end of dialysis at which the patient can remain normotensive until the next dialysis despite the retention of salt water (saline),’’ and ideally without the use of antihypertensive medications (3). In sharp contrast from the clinical definitions based on blood pressure recording during dialysis or between dialysis sessions, Levin proposed a definition of dry-weight defined by continuous calf bioimpedance analysis during dialysis. ‘‘Dry weight is defined as a flattening of the R0(baseline impedance) ⁄ Rt(instantaneous impedance) curve for at least 20 minutes in the presence of ongoing ultrafiltration’’ (4). Determination of dry-weight as we define this latent variable is an iterative process, not only incorporating many of the aspects of earlier definitions but also introducing into our definition how the patient feels. We define a patient’s dry-weight as the lowest tolerated postdialysis weight achieved via gradual change in postdialysis weight at which there are minimal signs or symptoms of either hypovolemia or hypervolemia. Therefore, the patient at dry-weight should have symptomatic hypotension or cramps in only a minority of dialysis treatments and yet the patient should remain normotensive in the interdialytic period. The frequency of intradialytic symptoms which denote dry-weight cannot be determined by an arbitrary cut-off but should be decided by the informed patient. We recognize that not all patients will get normotensive when we reduce dry-weight. Nor will all patients experience reduction in intradialytic symptoms when we increase their dry-weight. Thus, the determination of a patient’s volume status depends on a thorough clinical assessment that includes a history and physical examination and is a gradual process. Thus, reducing postdialysis weight by 3 kg may make most patients symptomatic. Yet, reducing postdialysis weight gradually by 0.2–0.3 kg per treatment may allow incremental removal of small amounts of excess fluid. But this individual decision making in the absence of gold standards will vary between physicians andmay vary even in the judgment of the physician from one visit to the next. The purpose of this review is to outline some of the potential pitfalls of the clinical examination in assessing volume status in hemodialysis patients.