Pre-treatment with hyperoxia before coronary artery bypass grafting - effects on myocardial injury and inflammatory response.
BACKGROUND
In experimental studies, exposure to hyperoxia for a limited time before ischaemia induces a low-grade systemic oxidative stress and evokes an (ischaemic) preconditioning-like effect of the myocardium. We hypothesised that hyperoxia before cardioplegia could protect the myocardium against necrosis and stunning caused by ischaemia-reperfusion.


METHODS
Forty patients undergoing coronary artery bypass grafting were randomly exposed to an oxygen fraction of 0.4 or > 0.96 in inspired air on an average of 120 min before cardioplegia. Blood for troponin I, creatine kinase-MB, lactate, glutathione and interleukin-6 was sampled from arterial and coronary sinus cannulae during 20 min of reperfusion. Additional arterial samples were drawn 60 min after declamping and in the first post-operative morning. The cardiac index and right and left ventricular stroke work indices were measured before sternotomy and up to 12 h post-operatively.


RESULTS
Troponin I, creatine kinase-MB and lactate did not differ between the groups. Hyperoxic pre-treatment had no impact on the post-operative haemodynamic indices measured with the thermodilution pulmonary artery catheter. More oxidised glutathione was released in the hyperoxia group in the first minute of reperfusion (P = 0.015). Hyperoxic pre-treatment abolished the myocardial release of interleukin-6 during 20 min of reperfusion (P = 0.021 vs. controls). In the first post-operative morning, interleukin-6 was higher in the hyperoxia group [127.0 (86.0-140.0) vs. 85.2 pg/ml (66.6-94.5 pg/ml); P = 0.016].


CONCLUSIONS
Exposure to >96% oxygen before cardioplegia did not attenuate ischaemia-reperfusion injury of the heart in patients undergoing coronary artery bypass grafting. The only potentially beneficial effect observed was the decreased transmyocardial release of interleukin-6.
Karu
I
I
North Estonia Regional Hospital, Clinic of Anaesthesiology, Tallinn; Institute of Biochemistry, University of Tartu, Tartu, Estonia. inga@mini.li.tt.ee
Loit
R
R
Zilmer
K
K
Kairane
C
C
Paapstel
A
A
Zilmer
M
M
Starkopf
J
J
D001026:Coronary Artery Bypass; D003402:Creatine Kinase / Q000097:blood; D005260:Female; D006439:Hemodynamics; D006801:Humans; D018496:Hyperoxia / Q000097:blood / Q000601:surgery*; D007249:Inflammation / Q000097:blood / Q000601:surgery; D015850:Interleukin-6 / Q000097:blood; D007527:Isoenzymes / Q000097:blood; D019344:Lactic Acid / Q000097:blood; D008297:Male; D008875:Middle Aged; D015428:Myocardial Reperfusion Injury / Q000097:blood / Q000601:surgery*; D018384:Oxidative Stress; D019210:Troponin I / Q000097:blood
D015850:Interleukin-6; D007527:Isoenzymes; D019210:Troponin I; D019344:Lactic Acid; D003402:Creatine Kinase