Effect of remifentanil infusion rate on stress response to the pre-bypass phase of paediatric cardiac surgery

Abstract

Background. Opioids are used routinely to eliminate the stress response in the pre-bypass phase of paediatric cardiac surgery. Remifentanil is a unique opioid allowing a rapidly titratable effect. No data are available regarding a suitable remifentanil dose regimen for obtunding stress and cardiovascular responses to such surgery. Methods. We recruited 49 infants and children under 5 yr old who were randomized to receive one of four remifentanil infusion rates (0.25, 1.0, 2.5, or 5.0 μg kg-1 min-1). Blood samples were obtained at induction, pre-surgery, 5 min after opening the chest, and immediately pre-bypass. Whole blood glucose was measured at all time points while cortisol and neuropeptide Y (NPY) were measured in the first and last samples. Heart rate and arterial pressure were also recorded. Results. There was a significant increase in whole blood glucose 5 min after opening the chest and pre-bypass (P=0.009, P=0.002) in patients receiving remifentanil 0.25 μg kg-1 min-1, but not in those receiving higher doses. Increased remifentanil dosage was associated with reduced plasma cortisol during surgery (P<0.001). Baseline NPY showed considerable variation and there was no association between pre-bypass NPY and remifentanil dose. There was a significantly higher heart rate at the pre-bypass stage of surgery in the remifentanil 0.25 μg kg-1 min-1 group compared with higher doses (P=0.0006). Four out of five neonates with complex cardiac conditions showed severe bradycardia associated with remifentanil. Conclusions. In infants and children under 5 yr, remifentanil infusions of 1.0 μg kg-1 min-1 and greater can suppress the glucose increase and tachycardia associated with the pre-bypass phase of cardiac surgery, while 0.25 μg kg-1 min-1 does not. Remifentanil should be used with caution in neonates with complex congenital heart disease.