Four Cases of Radical Hysterectomy with Acute Normovolemic Hemodilution Despite Low Preoperative Hematocrit Values

Abstract

Acute preoperative normovolemic hemodilution (ANH) is not recommended in patients with preoperative anemia and hematocrit (Hct) values <33% (1–3). However, as the following four cases will demonstrate, a low preoperative Hct value does not necessarily imply a small preoperative red cell volume (RCV). Methods The study was approved by the institutional ethics committee at our institution with all patients giving their written, informed consent. Four patients from a continuing study with preoperative diagnosis of carcinoma of the cervix are presented. They had a preoperative Hct of <33%, were ASA physical status I or II, were without cardiovascular, pulmonary, or hormonal dysfunctions, and were scheduled for radical hysterectomy. They fasted for 10 h, and neither preoperative bowel cleansing nor any preoperative infusions were administered before measurement. After the induction of general anesthesia and insertion of central and arterial catheters, baseline measurements of plasma volume (PV), Hct, and RCV were performed. (For measuring procedures, see below.) These baseline measurements showed that all four patients had low preoperative Hct values because of extraordinarily large PVs rather than small RCVs. Therefore, ANH to a target Hct of 20% was performed. A median of 1,300 mL of blood was removed and simultaneously replaced by 1,550 mL of colloid (5% albumin solution or 6% hydroxyethylstarch). After completion of ANH and a steady-state interval of 30 min without any further infusions, simultaneous measurements of PV, Hct, and RCV were performed. After these measurements, the surgical procedure began. The intraoperative transfusion trigger for beginning retransfusion was a Hct of 16%. After having reached this Hct value, the fraction of inspired oxygen was switched from 0.5 to 1.0. All autologous blood was retransfused in every patient late in surgery when major blood loss had ceased. Postoperative measurements of PV, Hct, and RCV were performed immediately after closure of the abdominal wall during a period of stable anesthesia without obvious blood loss. Preoperative PV and Hct measurements before ANH and postoperative measurements were performed in duplicate in a time interval of 30 min without any infusions. Determination of PV This method is referred to as “whole blood method” for PV determination and gives reproducible results immediately in the operating theater within 10 min (mean difference and variation coefficient between double measurements: 0.3% and 6.2%, respectively) (4,5). After having constructed a calibration curve (measuring 2 times 10 mL of patient’s blood having two known indocyanine green concentrations; Paesel, Frankfurt AM, Germany), indocyanine green, in a dose of 0.25 mg/kg of body weight, were injected into the central venous catheter as a bolus over 5 s. From the second to the fifth minute after the injection, blood was withdrawn continuously from the arterial catheter by means of a calibrated pump. Optical density of the blood (corrected for blank) was read in a densitometer at 800 and 900 nm. The blood density at injection time (which gives the initial distribution volume) was derived by monoexponential extrapolation of the density curve. Determination of RCV This method of using autologous red cells stained with sodium fluorescein and their determination by flow cytometry was recently described in detail (6,7). In brief, 20 mL of the patient’s blood was labeled with 50 mg of sodium fluorescein per measurement and injected into a peripheral vein. After injection samples were drawn from the arterial catheter at 4, 6, and 8 min, stored on ice, and analyzed by flow cytometry (Becton Dickinson, Heidelberg, Germany). In our laboratory, mean difference and variation coefficient for RCV double measurements were 0.6% and 3.1%, respectively (6). Hct was determined by centrifugation (12,000/min; 4 min) without correction for plasma trapping. Results Patient data, preoperative (before and after ANH) and postoperative variables, are shown in Table 1. During ANH, median preoperative blood volume (BV = PV + RCV) of 4767 mL decreased slightly to 4589 mL. After a median calculated surgical blood loss of 1761 mL (for calculation see Appendix, Equations 1 and 2) and a median crystalloid and colloid supply of 6975 and 1550 mL, respectively, BV increased slightly to 4643 mL. None of the four patients perioperatively received allogeneic red cell concentrates. The largest amount of red blood cells saved, which was 148 mL (for calculation see Appendix, Equations 3–6), means that nearly one unit of red cells (containing about 180 mL of red cells) was saved at maximum.Table 1: Patient Data and Measured Variables Shown Separately for the Measuring Points Before Acute Normovolemic Hemodilution (ANH), after ANH, and PostoperativeDiscussion Normal values for PV and RCV are 1395 ± 349 (8) and 845 ± 110 mL/m2 (6), respectively. Without any infusions or hormonal dysfunctions, the four patients had a preoperative PV of (median) 156% (143%–158%) in relation to normal values. The comparison with 15 patients also scheduled for radical hysterectomy (control values) who had a preoperative PV of 1514 ± 143 mL/m2 and RCV of 707 ± 79 mL/m2 (9) demonstrates that, with (median) 2171 mL/m2, the four patients had a very large PV and, with (median) 723 mL/m2, a typical preoperative RCV. Consequently the four patients’ low preoperative Hcts were caused by large PVs and not by extraordinarily low RCVs. A slight deficit in RCV and a very large PV resulted in a high preoperative BV (130% in relation to normal values). This combination allowed us to perform preoperative ANH with a relevant saving of red cells. Without transfusing allogeneic red cell concentrates, postoperative Hct values were still approximately 20%, despite a median blood loss of nearly 40% of preoperative BV. The theoretical model shows that surgical loss of red cells could be reduced by 30% by means of ANH. However, this saving of red cells was only possible in these four patients because they had only a slight preoperative deficit of RCV. In other words, if low preoperative Hct is combined with normal PV and reduced RCV, ANH cannot be efficient. We conclude that a large preoperative PV can mimic anemia. The reason for this constellation is unknown, but it is not caused by artificial infusions or a hormone dysfunction. Preoperative ANH can be performed in these patients with relevant saving of red blood cells.