We measured the apparent blood clearance and pulmonary extraction rati
o of remifentanil in 10 adult patients undergoing elective myocardial
revascularization for the first time with hypothermic cardiopulmonary
bypass (CPB). Patients received continuous infusions of remifentanil 1
.0, 1.5 or 2.0 mu g . kg(-1). min(-1). After surgery, remifentanil was
infused at 1.0 mu g . kg(-1). min(-1) in all patients. Remifentanil c
oncentrations were measured in pulmonary and radial artery blood by ga
s chromatography with high resolution mass spectrometry before and aft
er CPB and 165 min (60 SD) after surgery. Cardiac output was measured
by thermodilution at the time of blood sampling. The mean pulmonary ex
traction ratio of remifentanil was 5.7% (13.1% SD), which was not sign
ificantly different from zero. However, pulmonary extraction ratio was
related inversely to the pulmonary artery hydrogen ion concentration
and directly to the percent of nonionized form of the base in the pulm
onary artery. Remifentanil concentrations in pulmonary and radial arte
ry blood were related directly to infusion rate, but not to duration o
f infusion. There was no evidence of accumulation or sequestration. Me
an apparent blood remifentanil clearance was 2.03 L/min (0.35 SD) and,
in contrast to remifentanil pulmonary extraction ratio, was related d
irectly to cardiac index and oxygen delivery. Increased tissue perfusi
on increased blood remifentanil clearance. We found predictable blood
remifentanil levels with no evidence of accumulation or pulmonary extr
action.