LETTERS TO THE EDITOR: Letters & Announcements
To the Editor:
We have read with interest the study of Nuttall and colleagues in which they tried to optimize the dosing of aprotinin by weight-adjustment (1). Weight-adjustment, however, neglects the prime-volume of the cardiopulmonary bypass (CPB) system as well as the pump prime dose. Given a normal adult (65 kg body weight) the only difference between the 250 KIU/mL group in Nuttall’s study and the “Full-Dose” group is the pump prime load (88 mg vs. 280 mg). Furthermore, an 88-mg pump prime load results in a far lower concentration than the 4.4 mg/kg bolus given intravenously. Besides the pump prime load, the volume of the CPB system is of special interest, especially in pediatric cardiac surgery where the volume of the CPB system is several fold higher than the circulating blood volume. The smaller the patient the greater is this discrepancy, leading to aprotinin plasma levels that are ineffective in terms of blood loss reduction in pediatric patients (2).
Given these considerations, it may be more appropriate to base the aprotinin dose on the estimated circulating blood volume during bypass (CBVbypass = patient’s estimated blood volume + CPB prime-volume), rather than simply basing it on the patient’s body weight. By multiplying CBVbypass with the desired concentration of aprotinin in plasma and the hematocrit (see formula below), the needed amount of aprotinin can easily be calculated, no matter whether it is an adult patient or a pediatric patient:MATH
This initial loading dose is then to be followed by a maintanance infusion as described by Nuttall and colleagues (1).
While in the study of Nuttall et al. the measured plasma concentrations were up to some 70% higher than the desired aprotinin plasma levels (1), dosing aprotinin according to the above-mentioned formula would prevent this happening.
H. Van Aken
1. Nuttall GA, Fass DN, Oyen LJ, et al. A study of a weight-adjusted aprotinin dosing schedule during cardiac surgery. Anesth Analg 2002; 94: 283–9.
2. Moessinger H, Dietrich W. Activation of hemostasis during cardiopulmonary bypass and pediatric aprotinin dosage. Ann Thorac Surg 1998; 65: S45–51.