TITLE: FIBRINOGEN AND ACUTE HEMODILUTION: A MATHEMATICAL ANALYSIS

AUTHORS: Kai Singbartl, MD¹, Jens Radvan, MSc², Ingo Heschel, MSc², Wolfgang Schleinzer, MD³, Guenter Singbartl, MD⁴
AFFILIATION: ¹WWU Muenster, Germany, Charlottesville, VA; ²RWTH, Aachen, Germany; ³SPZ, Nottwil, Switzerland; ⁴ENDO-Klinik, Hamburg, Germany.

INTRODUCTION: Acute hemodilution (HD) has often been accused to increase bleeding. Clear scientific evidence for this is lacking so far. In vitro studies revealed a colloid specific effect rather than a clear dilution-induced one. Overlooking these 'drug effects', we present a mathematical model (MM) for acute normovolemic hemodilution (ANH) and no preoperative hemodilution (no HD) describing the course of fibrinogen as part of blood coagulation.
METHODS: Our MM is based on exponential decline of fibrinogen concentration (Fib, in mg/dl) and hematocrit (hct) during isovolemic blood substitution (colloid, volume effect 1.0). Body weight (BW)=70kg, blood volume=70ml/kg BW and 200ml colloidal preload are assumed. ANH includes exchanging 4*500ml blood vs. colloid and retransfusing ANH blood together with colloid to maintain minimal acceptable Fib (Fib_m) or minimal acceptable hct (hct_m).
RESULTS: We validated our model by recalculating inde- pendent clinical data [1] (Tab.1). Tab.2 (initial hct=45%) gives final Fib for several minimal acceptable hct (hct_m) and different initial Fib (Fib_i) during HD (identical for ANH and no HD). Tab.3 (initial hct=45%) gives maximal allowable blood losses (MABL) with respect to Fib_m.
DISCUSSION: Our validated MM indicates that with Fib_i in the upper normal range HD does not induce 'coagulation relevant' fibrinogen depletion (FD), as for all hct_m calculated final Fib>critical Fib_m. By contrast, with Fib_i in the lower normal range severe, 'coagulation relevant' FD could occur. Also, with respect to MABL ANH appears to save fibrinogen when com- pared to no HD.

TABLE 1: Validation of MM by recalculating clinical data [1].

TABLE 2: Final Fib (mg/dl) for various Fib_i and hct_m.

TABLE 3: MABL (ml) with respect to Fib_m.

1) Br J Anaesth 1996 76:519-25.