Introduction: Achievement of haemodynamic stability is a major problem in cardiac surgery. Perioperative hypertension is a frequent complication of CABG . The purpose of this study was to determine the role of preoperative autonomic nervous system (ANS) activity in the appearance of intraoperative hypertension (IHP) during CABG.
Method: The active tilt-test was performed the day before operation in 75 ASA physical status III and IV patients undergoing CABG surgery. Power spectral analysis of the short-term records (5 min) of heart rate variability has been used to study ANS during the active tilt-test. High Frequency (HF), Low Frequency (LF) in normalized unit, LF/HF and Total Power were analysed. The preoperative treatment for all patients included beta-blockade (atenolol), nitrate and ACE-inhibitors. The premedication included diazepam 10mg, trimeperidine hydrochloride 20 mg and atropine 0.3mg. Anaesthesia was induced with midazolam 0.1-0.15mg/kg, fentanyl 4-6μg/kg, ketamine 0.7mg/kg and maintained with halothane/02, pipecuronium bromide and fentanyl. We diagnosed IHP when MAP was more than 110mmHg, or/and SAP or DAP increased more than 20% from preoperative level. Statistical analysis was performed using Student's t-test.
Results: The active tilt-test has shown that 58.7% of patients (gr. 1, n = 44) had high activity of sympathetic nervous system (SNS), 18.7% (gr. 2, n = 17) had high activity of parasympathetic nervous system (PSNS) and 22.6% (gr. 3, n = 14) had a balanced type of responsive ANS. Total incidence of intraoperative hypertension (IHP) was 49% (n = 37). There were no cases of IHP in gr. 3. IHP was registered in 23 patients in gr. 1 (52.7%, P < 0.05 versus gr. 3) and in 14 patients in gr. 2 (82%, P < 0.05 versus gr. 3).
Discussion: Perioperative hypertension during CABG may be caused by high activity of SNS. Preoperative beta-blocking medications must control the increased SNS activity . However more than 80% patients need antihypertensive therapy during CABG . Our study has shown that a reduced activity of SNS not always reduces the frequency of intraoperative hypertension. It is possible that another mechanism is responsible for elevation blood pressure. This hypothesis had confirmed that the incidence IHP was registered in patients with high PSNS activity.
Conclusion: We suppose that for patients undergoing CABG, preoperative high activity of the SNS does not always determine intraoperative hypertension. Preoperative high activity PSNS may accompany intraoperative hypertension. Hypertension is a minimal probability in patients who have a balanced type of ANS response.
1 Vuylsteke A, Feneck RO, Jolin-Mellgård Å, et al. Perioperative blood pressure control: a prospective survey of patient management in cardiac surgery. J Cardiothorac Vasc Anesth
2 Wallace A, Layug B, Tateo I, et al. Prophylactic atenolol reduces postoperative myocardial ischemia. McSPI Research Group. Anesthesiology