Hemodynamic effects of inspired carbon dioxide after the Norwood procedure

Background. Mortality in the early postoperative period after the Norwood p rocedure remains substantial. Inspired carbon dioxide (CO2) has been sugges ted to improve hemodynamic status in this setting. Inspired CO2 can be deli vered by one of two strategies, ie, with or without an accompanying increas e in minute ventilation. The hemodynamic effects of these two strategies ha ve not previously been studied in a controlled fashion. Methods. Seventeen infants (median age, 9 days; range, 4 to 49 days) underg oing Norwood procedures were prospectively enrolled in this crossover study . Patients were studied while sedated, paralyzed, and mechanically ventilat ed 1 day to 6 days after operation. The inspired oxygen fraction was kept c onstant (mean value, 0.24 +/- 0.01). Measurements were made at five time po ints: 1 = baseline; 2 = inspired CO2 with increased ventilation; 3 = baseli ne; 4 = inspired CO2 alone; and 5 = baseline. Mixed venous oxygen saturatio n was monitored using indwelling lines in the superior vena cava. Results. Inspired CO2 with increased ventilation produced a rise in mean ai rway pressure with no change in arterial CO2 tension or PH. This strategy h ad no effect on hemodynamic status or oxygen delivery. Inspired CO2 alone p roduced a rise in arterial CO2 tension and a fall in arterial pH (respirato ry acidosis). This strategy resulted in significant improvement in both var iables of systemic oxygen delivery: mixed venous oxygen saturation increase d from 48% +/- 2% to 56% +/- 2% (p < 0.05), and arteriovenous oxygen satura tion difference decreased from 3% +/- 2% to 26% +/- 2% (p < 0.05). Conclusions. Inspired CO2 after the Norwood procedure can improve oxygen de livery. This improvement occurs only if minute ventilation is kept constant . There is no improvement if minute ventilation is increased. Clinical use of inspired CO2 may be limited by the accompanying fall in pH. Differentiat ion of cerebral from total-body effects of inspired CO2 will require (C) 20 01 by The Society of Thoracic Surgeons.