Epidural versus intravenous fentanyl for reducing hormonal, metabolic, and physiologic responses after thoracotomy

Previous attempts to prevent all the unwanted postoperative responses to major surgery with an epidural hydrophilic opioid, morphine, have not succeeded. The authors' hypothesis was that the lipophilic opioid fentanyl, infused epidurally close to the spinal-cord opioid receptors corresponding to the dermatome of the surgical incision, gives equal pain relief but attenuates postoperative hormonal and metabolic responses more effectively than does systemic fentanyl.

Forty patients were randomly assigned to receive either fentanyl epidurally and saline intravenously, or fentanyl intravenously and saline epidurally, in a double-blind fashion for the first 20 h after thoracotomy. For each patient, the fentanyl infusion was titrated to the rate required for pain relief (pain score < 3, maximum 10). Postoperative changes in blood pressure, heart rate, rectal temperature, and blood concentrations of adrenocorticotrophic hormone, beta-endorphin immunoreactivity, cortisol, growth hormone, prolactin, glucose, and leukocytes were assessed.

Patients reported similar median pain scores, but the epidural group required about 40% less fentanyl than the intravenous group. Four hours postoperatively, the beta-endorphin immunoreactivity concentrations were less in the epidural than in the intravenous group. Plasma cortisol increased in a similar manner in both groups within 4 h of surgery, but the increase persisted to the next morning only in patients receiving intravenous fentanyl. Adrenocorticotropin, growth hormone, and prolactin responses were similar in both groups. The postoperative hyperglycemic response, leukocytosis, and blood pressure were greater, and mean rectal temperature was lower, in the intravenous than in the epidural fentanyl group.

The authors' results indicate that some aspects of the hormonal response to surgery are blocked more completely with epidural than with intravenous fentanyl. Adequate pain relief with epidural fentanyl, with a smaller mean dose, led to a smaller increase of some hormonal, metabolic, and physiologic responses after thoracotomy than in association with the adequate pain relief provided by intravenous fentanyl.