Introduction Surfactant replacement therapy has reduced mortality and morbidity in preterm infants with RDS. However, no overall reduction in the incidence of cerebral periventricular hemorrage or leukomalacia has been demonstrated. Measurements of cerebral blood flow (CBF) and volume (CBV) following surfactant administration have yielded contrasting results. Data on brain cellular O2 availability, evaluated from the oxidation state of cytochrome a,a3, are lacking.

Method We have investigated the effects on cytochrome a,a3 oxidation and CBV of bolus bovine surfactant administration (100mg/kg) in 14 infants of gestational age 29 ± 0.7 wks, birth weight 1054 ± 90g, mechanically ventilated for RDS. Changes (Δ) in cerebral oxyhemoglobin [HbO2], deoxyhemoglobin [Hb], oxidized cytochrome a,a3[CytO2] and in CBV, derived from total hemoglobin were continuously detected by near-infrared spectroscopy (NIRS) (NIRO 500, Hamamatsu Photonics KK). Changes (Δ) were calculated at 1',5',15',30' and 60' after surfactant.

Results Table

Table 1
Full size table

Discussion We observed a rapid and sustained increase in CBV (not related to changes in arterial blood pressure or PCO2) and a gradual decrease in [CytO2], significant at 15', 30' and 60', which paralled the increase in [Hb]. The initial increase in [HbO2] probably indicates increased CBF of well oxygenated blood. The subsequent rise in [Hb], observed despite optimal systemic SaO2, suggests impaired venous return, possibly due to partially obstructed intrathoracic circulation, secondary to increased transmission of ventilatory pressures. Venous stasis could decrease cerebral microcirculatory flow leading to a reduction of CytO2, indicating an imbalance between oxygen delivery and cellular oxygen demand, with potentially harmful effects on the preterm brain.