Predictable Paco2, with two different flow settings using the Mapleson D system

Two different settings of fresh gas flow (VFG) and minute ventilation (VE) used with the coaxial Mapleson D system (Bain), were evaluated in 59 adults (ASA I-III) during controlled ventilation and different types of surgical procedures. The two flow settings (alternatives A and B) were VFG of 75 and 110 ml.min-1.kg-1 and VE of 150 and 175 ml.min-1.kg-1, aiming to generate normocapnea and mild hypocapnea, respectively. The PaCO2 obtained with alternative A was 5.5 +/- 0.5 kPa (mean +/- s.d.), with 92% of the patients within the range 4.7-6.1 kPa. With alternative B, the PaCO2 was 4.4 +/- 0.5 kPa, with 82% of the patients within the range 3.5-4.9 kPa. It is concluded that these two flow regimes are suitable for clinical use when either normocapnea or mild hypocapnea is desired.