Is avoidance of air contact necessary for the in vitro evaluation of thrombogenicity in mechanical circulatory assist devices?

An effective in vitro protocol for the investigation of thrombogenicity can provide many advantages in the development of mechanical circulatory assis t devices. Strict avoidance of air contact with blood recently was proposed for reliable in vitro evaluation. This study was performed to confirm the necessity of avoidance of air contact for the in vitro test of thrombogenic ity in a rotary pump. Two sets of mock circuits with the same rotary blood pumps, reservoirs, and connecting tubes were made. In one system, blood cam e in contact with air while the other did not. The test blood was hepariniz ed at the dose of 1 IU per 1 ml of blood. The tests were terminated at an a ctivated coagulation time of 1.5 times the control value. The levels of hem atocrit, platelet, factors VIII and XII, fibrinogen, thromboxane B2, and pl asma-free hemoglobin were measured during the procedures. After the experim ents, the thrombi formed were observed, measured, and compared with those f ormed in in vivo circumstances. The tests were repeated 12 times. There wer e no statistically significant differences between the 2 groups in hematolo gic parameters and the amounts of thrombi formed. The thrombi observed in b oth groups showed the same pathologic findings as those formed in vivo with the exception of intermittent multiple air bubbles found in thrombi of the air-contact group. In conclusion, the effect of air contact in the in vitr o investigation of thrombogenicity was negligible while the proposed in vit ro test models of thrombogenesis in the mechanical circulatory assist devic e proved to be reliable.