Effect of preanesthetic medication on carbon dioxide tension in children with congenital heart disease

Abstract

Hypercarbia during the postoperative period following repair of congenital heart defects in children has been associated with acute pulmonary hypertension. Because decreases in respiratory rate (RR) and digital pulse oximetry (SPO 2) have been observed after preanesthetic medication of similar children, it is possible that hypercarbia and pulmonary hypertension may be unappreciated risks in premedicated children during the preoperative period. As the first step in addressing this question, changes in transcutaneous and end-tidal PCO 2 (PtcCO 2 and PetCO 2) were examined after preanesthetic medication of children prior to cardiac surgery. Forty-four children were randomly assigned to receive either intramuscular morphine, 0.2 mg/kg, and scopolamine, 0.01 mg/kg, or oral midazolam, 0.75 mg/kg, 1 hour before anesthetic induction. PtcCO 2, PetCO 2, SPO 2, RR, and sedation score were monitored. Significant sedation occurred after both premedication regimens. Following morphine/scopolamine, PtcCO 2 increased from 36 ± 4 (mean ± SD) to 43 ± 6 mmHg ( P < 0.01), PetCO 2 increased from 35 ± 3 to 40 ± 5 mmHg ( P < 0.01), SPO 2 decreased from 93 ± 2 to 91 ± 4% ( P < 0.01), and RR decreased from 30 ± 10 to 24 ± 7 breaths/minute ( P < 0.01). After midazolam, PtcCO 2 increased from 35 ± 4 to 40 ± 6 mmHg ( P < 0.01), PetCO 2 increased from 34 ± 5 to 39 ± 3 mmHg ( P < 0.01), SPO 2 decreased from 93 ± 6 to 90 ± 7% ( ) , and RR decreased from 33 ± 13 to 30 ± 13 breaths/minute ( P < 0.01). Clinically significant increases in PtcCO 2 (>45 mmHg) occurred in nine patients, including five with pulmonary hypertension. Clinically significant decreases in SPO 2 (<90% in acyanotic patients; decrease of >5 absolute % in cyanotic patients) occurred in eight patients, including six with pulmonary hypertension. Although the data were obtained by noninvasive techniques, they suggest that hypercarbia following premedication may pose a risk to children with congenital heart disease and pulmonary hypertension.