99mTc-DTPA clearance in preterm lambs. Effect of surfactant therapy and ventilation.

Surfactant therapy and high-frequency oscillatory ventilation (HFO) may minimize damage to the pulmonary epithelium of surfactant-deficient newborns. Using pulmonary clearance of insufflated, aerosolized 99mTc-DTPA (molecular weight 492) as an index of lung epithelial permeability, 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, delivered by cesarean section at 129 to 133 days of gestation, were studied: (1) HFO + S, (2) CMV + S, (3) HFO, and (4) CMV. 99mTc-DTPA clearance was assessed at 2, 4, and 5.5 h after birth. Surfactant treatment improved oxygenation and lung pressure-volume relationships, with oxygenation best maintained by the combination of HFO + S. All groups had similar biexponential clearance curves at the three time points, however, and there was no significant difference in the mean rates of clearance (k) between the four groups at 2 h (k = 6.03 +/- 0.60 [SEM], 7.04 +/- 1.46, 5.67 +/- 0.91, and 7.23 +/- 0.97 %/min for Groups 1, 2, 3, and 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 permeability to a small radiolabeled molecule in preterm lambs.