NUMBER AND ACTIVATION OF CIRCULATING POLYMORPHONUCLEAR LEUKOCYTES ANDPLATELETS ARE ASSOCIATED WITH NEONATAL RESPIRATORY-DISTRESS SYNDROME SEVERITY

Objective. To determine whether number and activation of circulating p olymorphonuclear leukocytes (PMNs) and platelets are associated with d isease severity in neonatal respiratory distress syndrome (RDS). Desig n. Prospective study. Setting. Tertiary neonatal intensive care unit. Patients. Preterm infants with, severe (n = 18) or mild tee moderate ( n = 18) RDS who were consecutively admitted. Interventions. FMN and pl atelet counts and plasma concentrations of elastase-alpha(1)-proteinas e inhibitor (E-alpha(1)-PI) and thromboxane B-2 (TxB(2)) were recorded each day during the first 5 days of life. E-alpha(1)-PI-to PMN and Tx B(2)-to-platelet ratios were calculated to correct for the influence o f the PMN and platelet count on elastase and thromboxane release. Resu lts. From day 2, the severe RDS group had lower median PMN counts (1.5 vs 4.5 x 10(9)/L), lower mean platelet counts (136 vs 230 x 10(9)/L), and more elastase and thromboxane release, indicated by higher median E-alpha(1)-PI-to-PMN (39.2 vs 13.0 ng/10(6) PMNs on day 2) and TxB(2) -to-platelet (2.61 vs 0.52 pg/10(6) platelets on day 3) ratios than th e mild-to-moderate group. Lower PMN and platelet counts and higher ela stase and thromboxane release were correlated with birth asphyxia (low er 5-minute Apgar scores and umbilical arterial PH values), higher res piratory requirements (fraction of inspired oxygen and peak inspirator y pressure), and decreased values for continuous measures of RDS sever ity (ventilatory efficiency index and PaO2-to-alveolar oxygen tension ratio). Conclusion. Decreased PMN and platelet counts and increased el astase and thromboxane release are correlated with increased RDS sever ity. Birth asphyxia (hypoxia and acidosis) and tissue injury caused by high-pressure ventilation and hyperoxia may promote this activation p rocess.