SURGICAL STRESS ATTENUATES REFLEX HEART-RATE RESPONSE TO HYPOTENSION

Purpose: The baroreflex-mediated increase in heart rate (HR) in respon se to acute reduction of systolic blood pressure (SBP) was studied in order to assess whether the changes in arterial baroreflex sensitivity depend on the intensity of surgical stress, and location of visceral and somatic stimulation during surgery. Methods: Patients were divided into visceral stimulation groups [upper(n = 30) and lower(n = 30) abd ominal surgery] and somatic stimulation groups [upper (n = 25) and low er(n = 25) limbs, and chest wall (n = 25) surgery]. Acute hypotension as a baroreflex depressor test was induced by prostaglandin E-1 (PGE(1 )) 10 min before surgical incision (control) and during surgical manip ulation under isoflurane-N2O anaesthesia or isoflurane-N2O-fentanyl an aesthesia. Plasma level of ACTH was measured in an additional 40 patie nts who underwent upper abdominal surgery. Results: During upper abdom inal surgery. the heart rate baroreflex sensitivity (Delta HR/Delta SB P) was depressed from -0.47 +/- 0.05 (control) to -0.01 +/- 0.04 (P < 0.05). The reflex heart rate baroreflex sensitivity remained unchanged and was similar among the remaining groups of patients. The concentra tion of ACTH increased from 12.5 +/- 1.0 (control) to 343 +/- 78.6 pg. ml(-1) (P < 0.05) with isoflurane-N2O anaesthesia but did not change w ith isoflurane-N2O-fentanyl anaesthesia during upper abdominal surgery , Conclusion: Upper abdominal surgery is associated with the most stre ssful stimulation to attenuate heart rate baroreflex sensitivity. Inte grity of the baroreflex can be preserved by adding opioids to suppleme nt inhalation anaesthesia.