Reducing stress responses in the pre-bypass phase of open heart surgery ininfants and young children: a comparison of different fentanyl doses

High-dose opioids are advocated for paediatric cardiac surgery to suppress stress responses but they can produce unwanted side effects. There are no d ata on the dose-dependent effects of opioids on the stress response on whic h to base rational opioid administration. We conducted a dose ranging study on 40 children less than 4 yr undergoing elective open heart surgery using one of five fentanyl doses: 2, 25, 50, 100 or 150 mu g kg(-1) before surge ry. The standardized anaesthetic also included pancuronium and isoflurane. Blood samples were taken at induction, before incision, after sternotomy, i mmediately before, and at the end of cardiopulmonary bypass. Patients in th e 2 mu g kg(-1) group had significant rises in pre-bypass glucose (P<0.01), pre- and post-bypass cortisol (P<0.01), and pre- and post-bypass norepinep hrine (P<0.01). No significant rise occurred in glucose, cortisol and catec holamines in any of the higher dosage groups. Patients in the 2 mu g kg(-1) group had significantly higher mean systolic blood pressure (P<0.02) and h eart rate (P<0.04). A balanced anaesthetic containing fentanyl 25-50 mu g k g(-1) is sufficient to obtund haemodynamic and stress responses to the pre- bypass phase of surgery. Higher doses of fentanyl (100 and 150 mu g kg(-1)) offer little advantage over 50 mu g kg(-1), and can necessitate interventi on to prevent hypotension.