Intravascular volumes evaluated by a carbon monoxide rebreathing method in patients undergoing chronic hemodialysis

Abstract

Introduction: Treatment of fluid overload and anemia remains a challenge in patients undergoing hemodialysis. Hypervolemia can be evaluated using a carbon monoxide (CO) rebreathing method by which blood volume (BV), plasma volume (PV), and red blood cell volumes (RBCV) can be determined. We hypothesized that recurrent hypervolemia would cause hemoglobin (Hb) levels to be in the anemic range without a concurrent reduction in RBCV in patients undergoing hemodialysis.Methods: BV, PV, and RBCV were determined by a CO rebreathing test in 19 patients with type 2 diabetes undergoing chronic hemodialysis. The tests were performed 20 minutes before initiating dialysis, and the measured intravascular volumes were compared with predicted normal intravascular volumes according to Nadler's equation. Before initiating dialysis, Hb and blood pressure were measured, and edema severity was graded.Findings: Measured BV was higher in 17 out of the 19 patients with a median of 71.1 (62.4--76.9) mL/kg and higher than the predicted BV of 58.3 (53.5-59.9) mL/kg (P < 0.001). The measured PV was found to be higher in all patients. RBCV was measured as 25.2 (23.4-28.2) mL/kg with a predicted volume of 25.9 (22.4-26.7) mL/kg (P = 0.56). Eighteen patients were anemic as determined by Hb concentrations (defined as Hb < 13 g/dL for men and <12 g/dL for women), and nine were anemic according to RBCV. Discussion:The CO rebreathing test is a new approach to measuring intravascular volumes in hemodialysis patients. Compared with predicted intravascular volumes, the predialysis BV was expanded in the majority with elevated PV as the main cause. No overall difference in RBCV was found between the measured and predicted volumes. According to predialysis Hb levels, all but one patient was anemic, but according to the measured RBCV, only nine were in the anemic range, indicating dilution of Hb.

Dynamics of vascular refilling in extended nocturnal hemodialysis

“…A refilling fraction of 74% ± 9% was also identified using a mathematical model, 6 and it was 74% in an experimental study 5 . Alvarez Nadal et al found a refilling fraction of 76% ± 13%, 13 whereas Bomholt et al measured a refilling fraction of 69% using the carbon monoxide rebreathing method to estimate absolute blood volume 21 . Already in 1986, Fauchald determined a ratio between refilling rate and UF rate of 75% 19 …”

“…5 Alvarez Nadal et al found a refilling fraction of 76% AE 13%, 13 whereas Bomholt et al measured a refilling fraction of 69% using the carbon monoxide rebreathing method to estimate absolute blood volume. 21 Already in 1986, Fauchald determined a ratio between refilling rate and UF rate of 75%. 19 In summary, cumulative refilling fraction seems to reach a constant level of about 70%-75% under the condition of stable dialysis.…”

An improved method to estimate absolute blood volume based on dialysate dilution

“…1,7 Data of specific absolute BV in chronic hemodialysis patients are rare. Only a few experimental studies with small numbers of patients are available with other methods (carbon rebreathing method: 62-77 mL/kg, 19 patients 16 ; indocyanine green dilution: 61 ± 10 mL/kg, 9 patients 17 ; radioisotope method: 75 mL/ kg, 10 patients, 18 and 81 mL/kg, 7 patients 19 ). Our measurements after 1 hour were in the range of those studies.…”

Validation of a clinically applicable device for fast and accurate quantification of blood volume

“…For instance, a decrease or increase in hemoglobin concentration (i.e., anemia and polycythemia vera, respectively) may result from alterations in RBCV and PV independently or in combination. The etiology of anemia, which is commonly assumed caused by low RBCV, is indeed frequently related to expanded PV while RBCV are well within normal range 1,2 . Accordingly, anemia as diagnosed by hemoglobin concentration and peripheral hematocrit is overestimated in ~50% of patients 3,4 .…”

“…The CO‐rebreathing procedure specifically quantifies total hemoglobin mass 11 but also RBCV, PV, and BV when including hematocrit and hemoglobin concentration or MCHC 11,12 . Despite that the CO‐rebreathing method has been used extensively in physiology studies for more than 100 years, 13 it is only recently that various patient trials have emerged 1,2,7,14–16 . Since the CO‐rebreathing method is considered both reliable, simple, and fast, its implementation into clinical workflow has been advocated for as early as in 1993 14,15,17,18 .…”