Comparison of endtidal CO2 and arterial blood gas analysis in paediatric patients undergoing controlled ventilation with a laryngeal mask or a face mask

Endtidal CO2 (PECO2) and arterial blood gas tensions were compared between laryngeal mask (LMA) and face mask (FM) ventilation in paediatric outpatien ts. Following premedication with midazolam, anaesthesia was induced with ei ther thiopentone or isoflurane and atracurium. Anaesthesia was maintained w ith N2O, O-2 and isoflurane. Manually controlled ventilation was applied wi th a nonrebreathing system. Both PECO2 and arterial blood gas tensions were measured at 5 and 15 min after skin incision. The mean PaCO2 values in the LMA group were 36.6 +/- 7.4 and 37.5 +/- 6.4 mmHg and PaCO2 -PECO2 were 1. 8 +/- 2.4 and 2.5 +/- 3.3 mmHg, respectively. The mean PaCO2 values in the FM group were 41.3 +/- 8.1 and 43.4 +/- 8.9 mmHg; and PaCO2 -PECO2 were 5.3 +/- 3.6 and 8.8 +/- 7.0 mmHg, respectively. These values were lower in the LMA group (P< 0.05). We have concluded that monitoring of PECO2 is more re liable for estimating blood gas values during controlled ventilation with a LMA than a face mask.