Discordance between estimated and measured changes in plasma volume among patients with acute heart failure

Abstract

Aims In acute heart failure (AHF), changes of venous haemoglobin (Hb) concentrations, haematocrit (Hct), and estimated plasma volume (ePV) have been proposed as surrogates of decongestion. These estimates are based on the theoretical assumptions that changes of Hb concentrations and Hct are driven by the intravascular volume status and that the intravascular Hb pool remains stable. The objective of this study was to assess the relationship of changes of measured plasma volume (mPV) with changes of Hb, Hct, and ePV in AHF. Methods and results We studied 36 AHF patients, who received two sequential assessments of mPV, measured red cell volume (mRCV) and measured total blood volume (mTBV) (48 h apart), during the course of diuretic therapy using a novel visible fluorescent injectate (VFI) technique based on the indicator dilution principle. Changes of ePV were calculated based on the Kaplan–Hakim or Strauss formula. AHF patients receiving diuretics (median intravenous furosemide equivalent 160 mg/48 h) displayed a wide range of changes of mPV (−25.4% to +37.0%). Changes in mPV were not significantly correlated with changes of Hb concentration [Pearson's r (r) = −0.241, P = 0.157], Hct (r = −0.307, P = 0.069), ePVKaplan–Hakim (r = 0.228, P = 0.182), or ePVStrauss (r = 0.237, P = 0.163). In contrast to theoretical assumptions, changes of mTBV were poorly correlated with changes of Hb concentrations and some patients displayed unanticipated variability of mRCV, suggesting an unstable intravascular red cell pool. Conclusions Changes of Hb or Hct were not reflective of directly measured changes of intravascular volume status in AHF patients. Basing clinical assessment of decongestion on changes of Hb or Hct may misguide clinical decision‐making on an individual patient level.

Critical Analysis of the Effects of SGLT2 Inhibitors on Renal Tubular Sodium, Water and Chloride Homeostasis and Their Role in Influencing Heart Failure Outcomes

“…Even if there were no erythropoiesis, estimation of plasma volume by the Strauss formula can be distorted by shifts in the distribution of red blood cells from intravascular pools, as is commonly seen during the clinical course of patients with acutely decompensated heart failure. [86][87][88]93 Even if measured accurately, decreases in plasma volume do not reliably reflect intravascular or total body decongestion. Diuretics may have little effect on or even increase plasma volume in heart failure, if they mobilize fluid from the interstitial space.…”

“…Diuretics may have little effect on or even increase plasma volume in heart failure, if they mobilize fluid from the interstitial space. 89,[93][94][95] Furthermore, any expansion of red blood cell mass triggers an adaptive reduction in plasma volume, because if plasma volume were to remain constant, erythrocytosis would result in intolerable hypervolemia. This principle explains why physiological or pharmacologically induced increases in hematocrit (regardless of cause) lead to decreases in plasma volume.…”

Letter to the editor regarding ‘Discordance between estimated and measured changes in plasma volume among patients with acute heart failure’

“…We read with interest the recent article on the discordance between measured and estimated plasma volume (ePV) in patients with heart failure. 1 The study evaluated 36 patients with acute heart failure (AHF) by using a novel method for measured plasma volume (mPV) and comparing this with two existing formulas for ePV, the Strauss and the Kaplan--Hakim formulas, which are based on haemoglobin (Hb) and haematocrit (Hct) levels. The authors found that changes in mPV correlated moderately well with the Kaplan-Hakim formula (r = 0.75), and also with the Strauss formula in a subgroup of 19 patients with a stable measured red cell volume (mRCV) (r = 0.78).…”

“…7). 1 We would inquire as to why these patients weren't excluded and if the results would differ if they had been. Another question concerns the Kaplan-Hakim formula.…”

Response to Letter to the editor regarding ‘Discordance between estimated and measured changes in plasma volume among patients with acute heart failure’

“…We thank Begos et al . 1 for their interest in our work 2 and would like to respond to their comments and questions regarding our study. The study considered 36 patients with acute heart failure and assessed the relationships of changes in measured plasma volume (mPV), using the FAST Biomedical Technology technique, and changes in estimates of plasma volume (ePV), using haemoglobin and haematocrit‐based Strauss and Kaplan–Hakim equations during 48 h of decongestive therapy.…”