Background and Goal of Study: Fluid administration may cause iatrogenic haemodilution that may eventually lead to avoidable blood transfusions [1]. We examined the effects of incremental fluid loading aimed at increasing the cardiac output (CO) on non-invasive (SpHb) and laboratory determined (BHb) haemoglobin levels. 
Materials and Methods: After informed consent, 40 adult patients undergoing major gastrointestinal or vascular surgery were included. Oxygen saturation (SpO2) and SpHb were continuously measured by a Radical-7 Pulse CO-Oximeter (Masimo Inc.). BHb and PaO2 were intermittently measured (ABL800 Radiometer). CO and stroke volume (SV) were continuously measured using a minimally invasive uncalibrated CO monitoring system (Vigileo, Edwards). Oxygen delivery (DO2) was calculated as CO x ((BHbx1.38xSpO2) + (PaO2x0.0031)). Baseline values were recorded after induction of anaesthesia (T0) and 5 min after the administration of a 250 ml colloid fluid challenge (FC) (T1). In patients whose SV increased ≥ 10% compared to T0, another FC was given and all parameters recorded 5 minutes after its completion (T2). The same protocol was repeated at T2 and T3 values were obtained. Student’s paired and unpaired tests, Wilcoxon signed rank test and ANOVA were used where appropriate. 

Results and Discussion: All 40 patients received one FC (T1), 32 patients received 2 FCs (T2), and 20 patients received 3 FCs (T3). Figure 1 represents the median values of SpHb, BHb, CO and DO2 and their percentiles during the study and the number of patients studied at each time point. There was a statistically significant decrease in SpHb and BHb after each FC associated with a significant increase of CO and DO2 in comparison with T0 values. Among the 20 patients who received 3 FCs and reached T3, the CO and the DO2 increased between T0-T1 and T1-T2. However, after the last FC the CO remained unchanged but the DO2 decreased significantly (T2-T3, figure 2). The SpHb and BHb decreased similarly after each FC (Figures 2 and 3). The decrease in SpHb and the BHb after the infusion of 750 ml colloids was 1.66±0.67 and 1.7±0.7 g/dL, respectively. This significant decrease in Hb values explains the observed decrease in the DO2. There was a gradual increase in the mean SV between T0-T1, T1-T2, and T2-T3. However, the DO2 remained unchanged between T0-T1, increased significantly only from T1-T2 and decreased significantly between T2 and T3. Conclusions: Fluid loading in goal-directed therapy may cause a paradoxical decrease in DO2 due to iatrogenic haemodilution. The continuous monitoring of SpHb provides real-time reflection of hemodilution. The changes observed in the SpHb trend are similar to the changes in intermittent BHb values.
References:1. Perel A. Iatrogenic hemodilution: A possible cause for avoidable blood transfusions Critical Care (2017) 21:291 

06 / Optimization of cardiac output by incremental fluid administration is associated with iatrogenic hemodilution and a paradoxical decrease in oxygen delivery