The haemodynamic effects of crystalloid and colloid volume resuscitation on primary, derived and efficiency variables in post-CABG patients

Abstract

Background: Recent studies in haemodynamic management have focused on fluid management and assessed its effects in terms of increase in cardiac output based on fluid challenges or variations in pulse pressure caused by cyclical positive pressure ventilation. The theoretical scope may be characterised as Starling-oriented. This approach ignores the actual events of right-sided excitation and left-sided response which is consistently described in a Guyton-oriented model of the cardiovascular system.

Aim: Based on data from a previous study, we aim to elucidate the primary response to crystalloid and colloid fluids in terms of cardiac output, mean blood pressure and right atrial pressure as well as derived and efficiency variables defined in terms of Guyton venous return physiology.

Method: Re-analyses of previously published data.

Results: Cardiac output invariably increased on infusion of crystalloid and colloid solutions, whereas static and dynamic efficiency measures declined in spite of increasing pressure gradient for venous return.

Discussion: We argue that primary as well as derived and efficiency measures should be reported and discussed when haemodynamic studies are reported involving fluid administrations.

Keywords: Cardiovascular; Fluid therapy; Haemodynamics; Methods; Models; Physiology; Utilisation.

Fig. 1

Two situations of venous return curves intersecting with cardiac function curve after fluid resuscitation. CO is on y-axis and CVP is on x-axis. In the first situation, marked with subscripts 1 and 2, a volume bolus increases P_msa from P_msa1 to P_msa2 and CVP from CVP₁ to CVP₂. The increase in return pressure (Δ (P_msa − CVP)) is large. Compare this favourable situation with the situation marked with subscripts 3 and 4: an identical increase in P_msa generates a larger increase in CVP and thus a smaller Δ (P_msa − CVP). Relating Δ (P_msa − CVP) to ΔP_msa (E_vol) in the first instance yields a larger figure (app. 0.8) than in the second case (app. 0.25), indicating a better outcome of fluid resuscitation. This is formalised in Eq. (7). Heart efficiency, E_h, declines from app. 0.5–0.6 in the first instance to 0.39–0.36 in the second

Fig. 2

Concordant cardiac function curve (filled circle), volume efficiency (filled square) and power efficiency (filled diamond) as P_msa is increased stepwise by 2 mmHg. Power efficiency has been scaled by a factor 10 for visibility

Fig. 3

Fluid retention after one, two and three 20 min periods in the crystalloid (Cr, full square) and colloid (Co, full circle) group

Fig. 4

Temporal variation in primary variables MAP, CVP and CO during crystalloid and colloid resuscitation. Analysed as ANOVA with Tukey’s multiple comparisons. In all but one case (MAP), there were significant changes between time points in crystalloid MAP (decrease from t²⁰ to t⁴⁰) and CO (increase control to t²⁰ and t⁴⁰) and decrease t²⁰ and t⁴⁰ to t⁶⁰). In the colloid series, increases from control to t²⁰, t⁴⁰ and t⁶⁰ were seen in all three variables. The figures show mean ± SD

Fig. 5

P_msa, (P_msa − CVP) and power during crystalloid and colloid resuscitation. P_msa increased in both series and remained elevated for the time course of 60 min. The pressure gradient (P_msa − CVP) stayed elevated in the colloid series, but deteriorated from t²⁰ onwards in the crystalloid series. Power increased significantly in both series but only stayed elevated in the colloid series

Fig. 6

E_h did not change in the crystalloid series but decreased significantly in the colloid series indicating that the hearts were not able to convert the potential energy of P_msa into kinetic energy of MAP and CO but instead caused an increase in CVP, cp. Figure 2. Volume and power efficiency did not change significantly from control to timed stations. Power efficiency was close to zero in crystalloid series and approached ½ W/mmHg increase in P_msa. The differences between crystalloid and colloid were significant in C vs t²⁰ (p = 0.0003), C vs t⁴⁰ (p = 0.0145) and C vs t⁶⁰ (p = 0.005)

Fig. 7

The compliances calculated from change in P_msa from baseline to t²⁰, t⁴⁰ and t⁶⁰, and volume infused differed significantly between crystalloid and colloid (p = < 0.0001, 0.0013 and 0.0034) at identical time points. Crystalloid, full square; colloid, full circle