OBJECTIVE: Cardiopulmonary bypass (CPB) is associated with thyroid hormone 
changes consistent with euthyroid sick syndrome. Similar changes have been 
observed after general surgical operations. Thyroid hormone changes and their 
association with global oxygen consumption were studied in low-risk patients 
undergoing coronary artery bypass grafting (CABG) with and without CPB.
METHODS: Fifty-two patients undergoing primary CABG by the same surgeon were 
randomised into either on-pump (ONCAB, n=26) or off-pump (OPCAB, n=26) groups. 
Thyroid-stimulating hormone (TSH), free thyroxine (fT4) and free 
triiodothyronine (fT3) levels were measured at sequential time-points using 
chemiluminescence assays. Global oxygen consumption was measured at sequential 
time-points using a continuous cardiac output Swan-Ganz catheter.
RESULTS: In both groups TSH and fT4 remained within normal range throughout the 
study. There was a similar and progressive decline in fT3 levels with no 
significant difference between the groups over time (p=0.42). Mean fT3 levels at 
24h were below the normal range and significantly lower than baseline values 
(ONCAB, 3.3+/-0.69 pmol/L vs 5.1+/-0.41 pmol/L, p<0.001; OPCAB, 3.3+/-0.51 
pmol/L vs 5.0+/-0.46 pmol/L, p<0.001). There was a significant inverse 
relationship between fT3 levels and global oxygen consumption.
CONCLUSIONS: Off-pump surgery is associated with thyroid hormone changes similar 
to conventional surgical revascularisation. The data suggest that further 
studies into T3 administration during OPCAB may be warranted.