Anaesthetic requirement and stress hormone responses in patients undergoing lumbar spine surgery: anterior vs. posterior approach

Background: The intensity of nociceptive stimuli reflects the severity of tissue injury. The anaesthetic requirement and stress hormonal responses were determined to learn whether they differ according to different surgical approaches (anterior vs. posterior) during the spinal surgery.
Methods: Patients undergoing lumbar spine surgery without neurological deficits were divided into two groups: one having posterior ( n =13) and the other having anterior fusion ( n =13). The end-tidal sevoflurane concentrations (ET_SEVO) required to maintain the bispectral index score at 40–50 were determined. Mean arterial pressure (MAP), heart rate (HR), central venous pressure (CVP), serum osmolality and plasma concentrations of catecholamines, cortisol and vasopressin (AVP) were measured.
Results: There were no differences in MAP, HR, CVP and serum osmolality between the groups. ET_SEVO was higher in the anterior than in the posterior group ( P <0.05). The plasma concentrations of norepinephrine and cortisol increased in both groups during the surgery, whereas those of epinephrine remained unchanged. AVP concentrations increased during the surgery in the anterior group, and remained unaltered in the posterior group. The anterior group needed more analgesics ( P <0.01) during the first 1 h after the operation.
Conclusions: The anterior approach required a deeper level of anaesthesia while undergoing spinal surgery and more use of post-operative analgesics than the posterior approach. It was also associated with a more pronounced AVP release during the surgery.