Peripheral oxygen saturation was lower at 12 , 24 , and 48 hours during ropivacaine/fentanyl infusion than in patients receiving ropivacaine alone ( 12 h : 91 % + / - 2 % vs. 95 % + / - 2 % , p < 0.006 ; 24 h : 93 % + / - 1 % vs. 96 % + / - 2 % , p = 0.003 ; 48 h : 92 % + / - 1.8 % vs. 96 % + / - 1 % , p = 0.004 ) .
