極小未熟児における網膜症の発生・進行と動脈血二酸化炭素分圧に関する研究（Ⅲ）

Statistical study on the partial pressure of arterial blood carbon dioxide as a risk factor in retinopathy of prematurity (Ⅲ)

　出生体重1,500g以下の極小未熟児84例を対象とし，未熟児網膜症（ROP）の危険因子に対する動脈血二酸化炭素分圧（PaCO₂）等のガス分析値の重要性の程度を決定するために，統計学的検討を行った。まずガス分析値の他に，一般に危険因子と考えられている他の項目も含めて，全25項目とROP重症度との相関分析を行った。その結果，動脈血酸素分圧（PaO₂）最低値およびPaCO2最高値と各々有意な相関関係があった。次に我々が考案したROP重症度指数を目的変数とし，上記危険因子を説明変数とした重回帰分析を行った。この解析では，少数例のもつデータが過大評価されることのないようにⅠ型のみを対象とし，さらに最重要因子である出生体重，在胎週数以外の危険因子を明らかにするために上記2者を除く検討を行った。その結果，PaCO₂最高値とPaCO₂最低値との比が選択された。すなわち，PaCO₂はその高値と共に低値もまたROPの進展に関与することが明らかになった。

Eighty-four premature infants with a birthweight of 1,500 g or less were statistically analized in order to clarify the relation between severity of retinopathy of prematurity (ROP) and arterial blood gas levels, and partial pressure of arterial blood carbon dioxide (PaCO₂) level in particular. First, we conducted a correlation analysis and found that both the minimum of partial pressure of arterial blood oxygen (Pa0₂) and the maximum of PaCO₂ were significantly correlated with the sever-ity of ROP. Secondly, multiple-regression analysis was performed with a dependent variable of theseverity index designed by us and all or most in-dependent variables selected among 25 possible risk factors. The subjects used in this study were only infants with type Ⅰ ROP, since infants with type Ⅱ or intermediate type ROP might be overestimated because of high values calculated by our severity index. Further, birthweight and gestational age were excluded from independent variables in favor of other important risk factors they masked. As a result, the ratio between the maximum and mini-mum PaCO₂ levels was selected with a stepwise forward selection method. Thus, we speculate that a low PaCO₂ level may also be a risk factor as well as a high PaCO₂ level.