Presented at the Neonatal Society 2002 Autumn Meeting.
Jackson A1, Lyon A1, Elton R2
1 Simpson Centre for Reproductive Health, Royal Infirmary, Little France, Edinburgh EH16 4SU
2 Statistician, 5 Winton Rd, Edinburgh
Introduction: In our unit the incidence of significant (stage 3) ROP in survivors <30 weeks’ gestation has fallen from 10% in the mid 1990’s to 5% in 2000-2001. Cunningham et al, from this unit, published data showing that babies with threshold ROP had increased transcutaneous oxygen variability in the first 2 weeks of life (1). The same group subsequently developed a rat model in which ROP was induced by varying the oxygen levels in a manner similar to that found in the preterm infant (2). The aim of this study was to repeat the work of Cunningham to test whether the fall in the incidence of significant ROP was associated with a reduction in oxygen variability in the first week of life.
Methods: The methodology used by Cunningham was repeated. All babies <32 weeks or <1250g birthweight from January 2000, with complete transcutaneous data for at least the first week of life, were included. They were divided into 2 groups, ROP (stage 3 in either eye) and no ROP (less than stage 3). Artefact was removed visually from traces of one minute averaged TcPO2values. Data were then grouped into sequential six hour blocks and the standard deviation of the TcPO2 calculated for each period. The mean of these standard deviations was then calculated for the whole week for the 2 groups and compared with the original data of Cunningham et al using students t test.
Results: When comparing the babies without significant ROP, there was significantly less variability in the present day babies compared with the controls of Cunningham et al (n=18, SD=1.02 vs n=38, SD=1.12, p=0.034). This is despite the babies in the present study having lower mean birthweights (902g v 981g) and earlier gestations (26 v 27 weeks). There was no significant difference between present day cases (n=5, SD=1.12) and those in the original study (n=31, SD=1.19, p=0.44). In the 2000/2001 group there was no significant difference in oxygen variability in cases and controls (n=5, SD 1.12 vs n=18, SD=1.02) but this may represent small numbers and a type II error.
Conclusions: There has been a significant reduction in oxygen variability amongst babies less than 32 weeks’ gestation compared with the original study and this has been associated with a reduction in the incidence of threshold ROP. This study supports the hypothesis that the reduction in incidence of ROP is accompanied by a reduction TcPO2 variability.
References
1. Cunningham S, Fleck BW, Elton RA, McIntosh N. Transcutaneous oxygen levels in retinopathy of prematurity. Lancet 1995;346:1464-1465
2. McColm JR, Cunningham S, Sedowofia SK, Wade J, Fleck BW. Induction of retinopathy in newborn rats using a clinically relevant oxygen profile. Early Hum Dev 2000;58:75-76.