Measuring dobutamine (Db) clearance during continuous hemofiltration (CHF)

Extrarenal purification modifies the pharmacocinetics of many molecules, including the cardiotonics, which are frequently administered in conjunction with these techniques. The objective of this study was to measure Db clearance during CHF in ICU patients.

Patients and methods

15 measurements were taken in 5 consecutive ICU patients (age: 75.4 ± 7 years, SAPS: 17.6 ± 6.6) under Db (posology (D): 16.5 ± 5 (μg/kg/min) and CHF (pump: Gambro AK10, hemofilter AN69S Hospal). Samples were taken from plasma afferent to the filter (Ca), the efferent plasma (Ce) and the ultrafiltrate (Cuf). Db clearance was assessed using HPLC with electrochemical detection in 18% acetonitrile. Clearances were calculated: instantaneous Cl (iCl = mass of Db extract/Ca) and total body Cl (tbCl = D/Ca) as well as the transmittance coefficient-spectrum (TCS = Cuf/Ca).

Results

1) There was no correlation between the Db concentrations and the administered dose. 2) Average Db purification was 30% for CHF. 3) The iCl was 78 ± 52 ml, non correlated to the Cuf. 4) Average tbCl was 150 ± 160 ml/min, and 93.3% of the tbCl were over 40 ml/min. There was a negative polynomial correlation between tbCl and Ca (P < 0.01). 5) The TCS was 0.45 ± 0.28, irrespective of the posology, not influenced by coprescription of dopamine.

Conclusion

During CHF, Db purification is significant and transmembrane filtration is not the only involved mechanism. A non-linear elimination of the Db, implicating various factors, remains to be proved.