TC-99M-DTPA CLEARANCE IN PRETERM LAMBS - EFFECT OF SURFACTANT THERAPYAND VENTILATION

Surfactant therapy and high-frequency oscillatory ventilation (HFO) ma y minimize damage to the pulmonary epithelium of surfactant-deficient newborns. Using pulmonary clearance of insufflated, aerosolized Tc-99m -DTPA (molecular weight 492) as an index of lung epithelial permeabili ty, we examined the effects of 300 mg bovine lipid extract surfactant (S) administered at birth to preterm lambs ventilated by either HFO or conventional mechanical ventilation (CMV). Four groups of lambs, deli vered by cesarean section at 129 to 133 days of gestation, were studie d: (1) HFO + S, (2) CMV + S, (3) HFO, and (4) CMV Tc-99m-DTPA clearanc e was assessed at 2, 4, and 5.5 h after birth. Surfactant treatment im proved oxygenation and lung pressure-volume relationships, with oxygen ation best maintained by the combination of HFO + S. All groups had si milar biexponential clearance curves at the three time points, however , and there was no significant difference in the mean rates of clearan ce (k) between the four groups at 2 h (k = 6.03 +/- 0. 60 [SEM], 7.04 +/- 1.46, 5.67 +/- 0.91, and 723 +/- 0.97 %/min for Groups 1, 2, 3, an d 4, respectively), 4 h (k = 6.95 +/- 0.77, 5.60 +/- 0.51, 6.39 +/- 0. 64, and 6.78 +/- 1.71 %/min), and 5.5 h (k = 7.43 +/- 0.78, 6.08 +/- 0 .80, 7.86 +/- 0.90, and 7.95 +/- 0.66 %/min). These data suggest that neither surfactant nor HFO significantly alters pulmonary epithelial p ermeability to a small radiolabeled molecule in preterm lambs.