Lower dose of sufentanil was associated with higher plasmatic level of cortisol in patients undergoing elective cardiac surgery at the same depth of anaesthesia: a prospective randomised pilot study. Do we overlook "stress under the surface"?

Objective monitoring of per-operative nociception remains an unanswered challenge. Anaesthetists still mostly rely on signs of activation of the sympathetic nervous system, e.g., an increase in heart rate and blood pressure. These signs can be often blurred in cardiac surgery because of medication influencing heart rate and blood pressure or by severe hemodynamic disturbances. Such conditions create the potential for incompletely checked nociception which can lead to unrecognised "under the surface" stress reaction. We decided to investigate whether patients undergoing cardiac surgery maintained at the same level of monitored depth of anaesthesia would express differences in plasmatic level of stress hormone cortisol when given a different dose of opioid sufentanil. Nineteen patients undergoing elective cardiac surgery were included in our prospective randomised trial. All patients were anaesthetised by a standardised protocol (using midazolam, propofol, sevoflurane, sufentanil and rocuronium) and were maintained within the same range of anaesthetic depth monitored by monitor Conox (qCON 30-50). Patients were randomised in two groups. Group LS (lower sufentanil), n = 9, recieved TCI (target controlled infusion) sufentanil in dose of 0.25 ng/mL, group HS (higher sufentanil), n = 10, in dose of 0.75 ng/mL. 15 minutes after sternotomy we took blood samples for analysis of plasmatic levels of cortisol. Group LS had significantly higher plasmatic cortisol levels, median 700 nm/L, than HS, median 328 nm/L (p = 0.006). We conclude that a lower dose of sufentanil was associated with higher plasmatic level of cortisol and thus more significant activation of hypothalamic-pituitary-adrenal axis stress response. We emphasise that activation of stress response can be underestimated during cardiac surgery. Our result supports the need for developing an objective monitoring method of per-operative nociception.