Cardiac output and central blood volume during hemodialysis: Methodology

Cardiovascular disease is the leading cause of mortality in patients whose lives depend on hemodialysis. We developed a method for measuring cardiac o utput (CO) and central blood volume (CBV) in hemodialyzed patients that may help to elucidate the mechanisms and consequences of cardiac disease in th is population. This report describes the technique, focusing on the main so urces of error and how they can be prevented. Three principal sources of er ror were identified: (1) access recirculation (existing or induced during i njection); (2) the second pass of the indicator through the cardiopulmonary system, exacerbated by prolonging the duration of intravenous injection; a nd (3) the transit time of the indicator through the dialysis blood lines. After the algorithms were adjusted to prevent the above errors, the reprodu cibility of CO and CBV, expressed as the absolute percent deviation from th e average of duplicates (3,488 values duplicated within 5 minutes), was 4.3 +/- 3.8% for CO and 4.1 +/- 3.8% for CBV. To determine the clinical value of routine CO and CBV measurements, morbid events (nausea, vomiting, and/or muscle cramps) were prospectively recorded in 73 randomly selected hemodia lysis patients. CO and CBV were measured near the beginning and near the en d of 98 dialysis sessions during which 28 morbid events were identified. In 10 of these sessions, where morbid events took place within 30 minutes of the measurements, CBV appeared to be a more sensitive indicator of morbid e vents than CO. We conclude that CO and CBV can be routinely and reliably me asured during hemodialysis if precautions are taken to avoid specifically i dentified sources of error. Preliminary studies suggest that these measurem ents may have significant prognostic value. (C) 1999 by the National Kidney Foundation, Inc.