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Nonthyroidal illness syndrome in off-pump coronary artery bypass grafting
Alfredo Giuseppe Cerillo1, Laura Sabatino, Stefano Bevilacqua
1Unità Operativa di Cardiochirurgia Adulti, Ospedale G. Pasquinucci, Massa, Italy. cerillo@ifc.cnr.it
Insights
Off-pump coronary artery bypass (OPCAB) surgery induces a nonthyroidal illness syndrome (NTIS) similar to cardiopulmonary bypass (CPB). This suggests NTIS is a general stress response, not solely triggered by CPB in cardiac surgery patients.
Area of Science:
- Endocrinology
- Cardiovascular Surgery
- Metabolic Research
Background:
- Cardiopulmonary bypass (CPB) is a known cause of nonthyroidal illness syndrome (NTIS).
- Off-pump coronary artery bypass (OPCAB) is considered less invasive than traditional coronary artery bypass grafting (CABG) with CPB.
- Thyroid metabolism changes during major surgery are not fully understood.
Purpose of the Study:
- To prospectively evaluate and compare thyroid hormone metabolism in patients undergoing OPCAB versus CABG with CPB.
- To determine if OPCAB surgery elicits a similar NTIS response compared to CPB.
- To investigate the role of stress in the development of NTIS after cardiac surgery.
Main Methods:
- Prospective analysis of thyroid hormones (free T3, free T4, TSH, reverse T3) in 20 CABG patients (9 CPB, 11 OPCAB).
- Serial blood sampling from admission through 144 hours postoperatively.
- Hormone concentrations measured using established assays.
Main Results:
- Free T3 levels significantly decreased in both groups, reaching a nadir at 12 hours postoperatively, with no significant difference between CPB and OPCAB.
- Free T4 levels varied significantly but remained within the normal range for both groups.
- Reverse T3 levels significantly increased in both groups, peaking at 24 hours postoperatively.
Conclusions:
- Off-pump coronary artery bypass (OPCAB) induces a nonthyroidal illness syndrome (NTIS) comparable to that seen with cardiopulmonary bypass (CPB).
- The observed NTIS is likely due to the inhibition of T4 to T3 conversion, indicating a nonspecific stress response.
- CPB should not be solely implicated as the trigger for NTIS in cardiac surgical patients.
Background:
Cardiopulmonary bypass (CPB) is an established cause of nonthyroidal illness syndrome (NTIS). Off-pump coronary artery bypass (OPCAB) has been reported to be less invasive than coronary artery bypass grafting (CABG) with CPB. We prospectively evaluated thyroid metabolism in OPCAB patients.
Methods:
We analyzed free thyroid hormones (FT3 and FT4), thyroid-stimulating hormone (TSH), and reverse T3 (rT3) in 20 consecutive patients undergoing CABG surgery. Nine patients underwent CABG with CPB, and 11 underwent OPCAB. Blood samples were taken on admission, on the day of surgery (7:30 AM), after sternotomy, at the end of the operation, and at 2, 6, 12, 24, 36, 48, 72, 96, 120, and 144 hours postoperatively. The concentrations of FT3, FT4, and TSH were determined on each sample. Reverse T3 concentration was measured in 10 patients up to 48 hours and at 144 hours postoperatively.
Results:
Baseline, operative, and postoperative variables were similar in the two groups. FT3 concentration dropped significantly (p < 0.0001), reaching its lowest value 12 hours postoperatively. There were no significant differences between CPB and OPCAB patients. FT4 varied significantly in both groups (p < 0.0001), but remained in the normal range. TSH variation was not significant. rT3 concentration rose significantly (p = 0.0002) in both groups, peaking 24 hours after surgery. CONCLUSIONS. OPCAB induces a NTIS similar to that observed after CPB, probably due to the inhibition of T4 conversion to T3. This finding suggests that NTIS is a nonspecific response to stress. CPB should not be considered as the sole trigger of NTIS in cardiac surgical patients.