Propofol attenuates myocardial lipid peroxidation during coronary artery bypass grafting surgery{dagger}

M. M. Sayin*,1, O. Özatamer1, R. Tasöz2, K. Kilinç3 and N. Ünal1

1 Department of Anaesthesiology and Intensive Care, 2 Department of Cardiovascular and Thoracic Surgery, Ankara University Faculty of Medicine and 3 Department of Biochemistry, Hacettepe University Faculty of Medicine, Ankara, Turkey*Corresponding author

{dagger}Presented at the Annual Congress of European Society of Anaesthesiologists, April 1998.

Accepted for publication: March 5, 2002


    Abstract
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 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
Background. Propofol can scavenge free radicals because it has a chemical structure similar to antioxidants.

Methods. We examined if free radical scavenging occurs with propofol during CABG operations. We studied 24 patients undergoing CABG surgery for triple vessel disease, randomized into two groups. After induction of anaesthesia with fentanyl 10 µg kg–1 and midazolam 0.1 mg kg–1, patients in the fentanyl group (n=14) received fentanyl infusion 10–30 µg kg–1 h–1 and patients in the propofol group (n=10) received propofol infusion 3–6 mg kg–1 h–1 for maintenance of anaesthesia. Atrial tissue biopsies were taken during cannulation for bypass, 45 min after cross-clamp insertion, 5 min after unclamping, and in the decannulation period. Lipid peroxidation was assessed by measurement of thiobarbituric acid reactive substances (TBARS) in the atrial tissue samples.

Results. Lipid peroxidation in the propofol group was less than in the fentanyl group (P<0.05) in all sampling periods. Lipid peroxidation in the fentanyl group increased significantly during cardiopulmonary bypass (CPB) (P<0.05), but no increase was found in the propofol group (P>0.05).

Conclusion. In clinical doses, propofol strongly attenuates lipid peroxidation during CABG surgery.

Br J Anaesth 2002; 89: 242–6

Keywords: anaesthetics i.v., propofol; heart, coronary artery bypass; metabolism, lipid


    Introduction
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 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
Reintroduction of molecular oxygen into previously ischaemic tissue can further damage partially injured cells, an event known as ‘reperfusion injury’. Oxygen supply leads to the formation of free oxygen radicals which react with polyunsaturated fatty acids of cell membranes forming lipid peroxides and hydroperoxides through a chain of reactions resulting in decreased membrane fluidity, increased membrane permeability, and finally disruption of the membranes.1 Cross-clamping of the aorta and removal of the cross-clamp leads to ischaemic injury and then to reperfusion injury in the myocardial tissue. Myocardial cell injury can cause post-ischaemic dysfunction, myocardial stunning, reperfusion arrhythmias, and necrosis.26

As well as factors such as myocardial protection and the quality of anastomosis, prevention of reperfusion injury could allow safer weaning from cardiopulmonary bypass (CPB) and preserve stable haemodynamic conditions after surgery. The anaesthetic agents used may protect the myocardium against reperfusion injury.

Propofol resembles phenol-based anti-oxidants in chemical structure. It is a scavenger of free oxygen radicals in vitro,7 in vivo in animals,8 9 in man,10 and on human cellular models during CPB.11 The in vivo effects of propofol on human myocardial muscle have not been studied during CABG, so we investigated the effect of propofol infusion during the CABG operations on the concentration of end products of lipid peroxidation (malondialdehyde (MDA)) levels in human myocardial muscle.


    Methods
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 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
After approval of the ethics committee and with informed consent, we studied 24 patients with triple vessel coronary artery disease about to have CABG surgery. We excluded patients with atrial fibrillation, an ejection fraction less than 0.45, history of allergy to propofol or its preservatives, and other chronic diseases such as diabetes or chronic obstructive lung disease.

In all patients, anaesthesia was induced with fentanyl 10 µg kg–1 and midazolam 0.1 mg kg–1, and muscle relaxation for tracheal intubation was facilitated with pancuronium 0.08 mg kg–1. After cannulation of the right internal jugular vein and left radial artery, a pulmonary catheter was placed. Thereafter, patients were randomly allocated into two using computer generated random numbers: fentanyl group (n=14) and propofol group (n=10). Anaesthesia was maintained with fentanyl 10– 30 µg kg–1 h–1 in the fentanyl group and propofol 3–6 mg kg–1 h–1 in the propofol group. All patients received midazolam 0.1 mg kg–1 hourly and pancuronium 0.04 mg kg–1 every 45 min. The lungs were mechanically ventilated with 8 ml kg–1 of 50% oxygen in air, except during total bypass when they were insufflated with the same gas mixture. Patients received anaesthetic drugs until they were transferred to the ICU. If indicated, dopamine 2–5 µg kg–1 h–1 was used.

A standard pump priming solution was used in each patient. The pump flow was kept constant at 2.4 litre min–1m–2 during the partial bypass and during the hypothermic total bypass (rectal temperature was 29– 30°C) the pump flow was 2 litre min–1 m–2. After application of the cross-clamp, St Thomas Cardioplegic Solution (Plegisol®) at +4°C was infused into the coronary arteries from a retrograde cannula, initially a volume of 1 litre and then 500 ml every 30 min.

Right atrial myocardial tissue samples were taken at the following times: during cannulation, 45 min after insertion of cross-clamp when the rectal temperature was 29°C, 5 min after unclamping, and at the end of decannulation procedure. At least 0.2 g of atrial myocardial tissue was taken from the right atrial tissue below the superior vena cava (SVC) cannulation suture where the circulation was intact, and then the suture of the venous canula was renewed below the biopsy area. For each sample, the same procedure was used to avoid sampling the possible partially ischaemic tissue created by the sutures of SVC canula. The atrial tissue samples were then immediately frozen at –70°C and kept frozen until analysis. At each sampling time, arterial pressure, heart rate, arterial blood gases, haemoglobin concentration, and cardiac output were recorded, and arterial oxygen content and cardiac index were calculated.

End products of lipid peroxidation in MDA levels in the samples were detected by the method described by Michara and Uchiyama.12 Frozen tissues were immediately weighed and homogenized in 10 volumes of ice-cold phosphate buffer (50 mmol litre–1, pH 7.4) using a glass–glass homogenizer (B. Brown, Germany). The homogenate (0.5 ml) was mixed with 3 ml of 1% H3PO4. After addition of 1 ml of TBA reagent (0.67%) the tubes were heated in boiling water for 45 min. The colour formed was extracted into 4 ml of n-butanol. After centrifugation, the colour intensity of the butanol layer was measured at 532 nm using a Shimadzu UV-120-02 model spectrophotometer. Tetra methoxypropane was used as the standard and concentrations of thiobarbituric acid reactive substances (TBARS) were calculated as nanomoles of MDA per gram of wet tissue.

The results were analysed by ANOVA for repeated measures test with Bonferroni t-procedure. The groups were also compared with the Mann–Whitney U test and the comparisons within the groups were analysed with Wilcoxon matched pairs test. In all comparisons P<0.05 was considered statistically significant.


    Results
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 Methods
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The characteristics of the two groups were similar in age, surface area, extracorporeal circulation time, total bypass time, and the duration of reperfusion (Table 1). Mean arterial pressure, arterial oxygen content, and cardiac index for the groups were not significantly different (Fig. 1AC). The MDA concentrations (mean (SD)) during cannulation, cross-clamp, unclamping, and decannulation periods in the fentanyl group were 45.6 (7.9), 63.6 (15.9), 74.5 (14.9), and 72.8 (16) nmol (g wet tissue)–1 and in the propofol group were 34.4 (7.2), 38.9 (18.2), 43.9 (16.8), and 43.8 (13.6) nmol (g wet tissue)–1, respectively. The differences between the two study groups were significant at each time of sampling (P<0.05) (Fig. 2).


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Table 1 Characteristics of the study groups (mean (SD or range))
 


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Fig 1 Mean arterial pressure. Arterial oxygen content, and cardiac index in both groups during sampling periods.

 


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Fig 2 Changes in the lipid peroxidation during sampling periods. *P<0.05 (statistical difference between the groups); {dagger}P<0.05 (statistical difference within the group, when compared with cannulation); {ddagger}P<0.05 (statistical difference within the group, when compared with cross-clamp).

 
Comparisons in each group revealed a progressive statistically significant increase in lipid peroxidation products compared with the cannulation period in the fentanyl group but no difference in the propofol group for each sampling period (Fig. 2). Lipid peroxidation levels during the unclamping and decannulation periods were greater than in the cross-clamp period in the fentanyl group (P<0.05).


    Discussion
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 Introduction
 Methods
 Results
 Discussion
 References
 
Propofol stucturally resembles phenol-based anti-oxidants such as butyrated hydroxytoulene and {alpha}-tocopherol and it can act as a scavenger of free radicals. Murphy and co-workers7 showed that each molecule of propofol inhibited two molecules of oxygen radicals in vitro. Some investigators claim that this effect is evident only at supramaximal blood levels of propofol, and has no clinical significance.13 However, Murphy and colleagues14 15 found that even at the anaesthetic blood concentrations, propofol inhibited the peroxidation of lipids, in proportion to the blood concentration of propofol. Propofol can attenuate lipid peroxidation on human skeletal muscle10 and can increase the antioxidant capacity of erythrocytes (RBC) during CPB11 but human myocardial muscle has not been studied during CPB.

MDA is one of several low-molecular-weight end products formed by decomposition of primary and secondary lipid peroxidation products. Many sophisticated assays are available for measurement of lipid peroxides.16 However, the TBARS assay remains a test that provides a global measure of lipoperoxidation.17 Coghlan and co-workers used the TBARS method to measure myocardial free radical generation in coronary sinus blood.18 It has been used in myocardial tissue of the cats by Maulik and co-workers,19 rats,20 and other animals. This method of determination of MDA is a widely accepted and an easy way of assessing free radical insult to tissues.10 21 22

We investigated the effect of maintenance of anaesthesia with propofol on atrial myocardial tissue lipid peroxidation, compared with a fentanyl infusion, during CABG operations. We chose fentanyl as a control substance rather than other i.v. anaesthetics such as thiopentone or barbiturates because the minimal antioxidant action of these anaesthetic agents might be a source of confusion.23 24 Fentanyl, as far as we know, does not have antioxidant effects.25 26 Opioids are also preferred by many anaesthesiologists for cardiac anaesthesia because of their non-cardiac depressant properties. Infusion of propofol 3–6 mg kg–1 h–1 caused a significant reduction in the atrial tissue lipid peroxidation when compared with the fentanyl group.

Ytreus and co-workers1 suggested that lipid peroxidation normally occurs in the myocardial tissue in low levels even without ischaemia and reperfusion injury. We also found some degree of lipid peroxidation in the fentanyl group during the cannulation period, but the propofol infusion, started after induction of anaesthesia, significantly attenuated the lipid peroxidation levels in the propofol group. This difference is unlikely to be caused by haemodynamic, technical, and methodological differences between the groups, but can only be attributed to the propofol infusion. We could not obtain a pre-operative control value in our study as other authors have. Our results resemble those of Ytrehus and co-workers,1 where propofol infusion significantly attenuated pre-exising lipid peroxidation.

During ischaemia, the cross-clamp period, lipid peroxidation levels in the myocardium tended to increase. Ferrari and co-workers27 proposed that, during ischaemia, free radicals are still formed because of the residual molecular oxygen. Free radical generation was found in other studies,28 and an experimental study by Hegstad and colleagues29 found that lipid peroxides could accumulate during ischaemia. Our results support these findings, during the period of ischaemia during CPB in the fentanyl group, and propofol infusion prevented this increase. This suggests that free radical injury to the myocardial tissue could relatively be controlled by propofol infusion.

At the cross-clamp removal sampling time, when reperfusion injury was added to the injury of ischaemia, we observed a further statistically significant increase in lipid peroxidation. According to the electron spin resonance spectroscopy studies of Garlick and Baker and colleagues,30 31 a large amount of free radicals are produced during the first few minutes of post-ischaemic reperfusion. These reactive oxygen species cause lipid peroxidation of the cellular and intracellular membranes. We observed an increase in lipid peroxidation products in the fentanyl group of our study, but in the propofol group no statistically significant increases in the lipid peroxidation, relative to the cannulation or the cross-clamp periods, were observed.

The sample at decannulation was the last time that a biopsy could be obtained without interfering with the integrity of the heart. In the fentanyl group lipid peroxidation was still greater than the propofol group. A burst of oxygen radical generation occurs during the early phase of reperfusion,27 32 33 but reperfusion injury continues for some hours after unclamping.28 Others have chosen different times after reperfusion for sampling.34 35 We sampled both in the early stage after unclamping and in the late reperfusion stage, which was equal to the cross-clamp duration. Our findings support those of the previous studies, that reperfusion injury continued for some period after ischaemia,28 and propofol relatively decreased this injury.

Kahraman and co-workers10 used propofol in order to inhibit tourniquet-induced ischaemia and reperfusion injury, which reduced lipid peroxidation in muscle tissue. Hans and co-workers36 examined the effect of TIVA with propofol in 18 neurosurgical patients assigned for cerebrospinal fluid shunting and found out that propofol increased the capacity of plasma to inhibit lipid peroxidation. Ansley and co-workers11 showed that propofol at 3–6 mg kg–1 h–1 enhanced the antioxidant capacity of red blood cells. This is the first clinical study examining the antioxidant effects of propofol on myocardial muscle tissue during CABG operations. Our results support the results of Kahraman, Hans, and Ansley.10 11 36

Although the changes in lipid peroxidation did not relate to haemodynamic changes, it is inappropriate to link peroxidation to the outcome of the groups, because post-operative measurements were not made. Our study was designed to investigate the biochemical in vivo effects of propofol on free radical injury during CPB. The effects of reduced free radical injury by propofol on clinical outcome should be the subject of a further clinical study.

We conclude that propofol effectively attenuates lipid peroxidation and could be used in an anaesthetic drug regimen during CABG if ischaemia and reperfusion injury is of concern.


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 Introduction
 Methods
 Results
 Discussion
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