As vasopressin is a small peptide, its sieving coefficient (SC) and clearance (CL) during hemofiltration may be intermediate to those for urea and beta 2 microglobulin (commonly used markers for small and middle molecular weight solutes, respectively).
A prospective, minimal risk study was undertaken of the SC and CL of vasopressin in critically-ill children during the first 2 days of hemofiltration using AN69 membrane filters and prefilter replacement fluid.
Nine patients were recruited (mean age: 11+/−8 years) during 10 courses of hemofiltration (continuous venovenous hemofiltration: 3; continuous venovenous hemodiafiltration: 7). Eight patients had multiorgan dysfunction syndrome and 4 were in shock during the study period: 2 were receiving a vasopressin infusion, and catecholamine therapy was started in 1 patient and increased in another patient. Mean prefilter (post replacement fluid), postfilter, and effluent [vasopressin] levels were 9+/−17, 11+/−17, and 9+/−16 pg/mL, respectively, while the predicted plasma [vasopressin] (corrected for prefilter replacement) was 11 pg/mL. Prefilter and predicted plasma [vasopressin] levels were low ( < 2 pg/mL) in 5 patients during 6 courses of hemofiltration. Mean SC was between 0.4 and 0.7 and the resulting mean effluent CL was between 13 and 25 mL/minute. Predicted total, corrected effluent, and adsorptive CL were 31, 15 to 26, and 5 to 16 mL/minute/1.73 m2, respectively.
The SC of vasopressin during hemofiltration of critically-ill children was similar to that for beta 2 microglobulin, while its CL was similar to that for urea, likely due to adsorption by the hemofilter.
Most critically-ill children not receiving vasopressin had low plasma levels of vasopressin: vasopressin therapy may thus be reasonable in children with vasodilatory shock early during hemofiltration. Further research is needed to clarify if and how hemofiltration alters the pharmacokinetics of vasopressin during pediatric critical illness.
John Baird, No Financial Disclosure Information; No Product/Research Disclosure Information