Changes in thyroid hormones in surgical trauma.Arunabh, AK Sarda, MG Karmarkar
Dept of Surgery, All India Institute of Medical Science, New Delhi., India
Correspondence Address: Source of Support: None, Conflict of Interest: None PMID: 0001303410
Source of Support: None, Conflict of Interest: None
A prospective study of 20 patients who underwent elective surgery, is presented reporting the effect of surgical trauma on circulating thyroid hormone levels. Although no increase in the serum T4 levels was observed following surgery, serum T3 values were found to decrease and serum rT3 values were found to increase in the post-operative period, representing activation of an alternate pathway in the peripheral conversion of T4 to T3. Since trauma induces a hypermetabolic state due to hypersecretion of cortisol, alterations in thyroid hormone levels were concluded to represent an appropriate response in trauma to counter the effects of trauma-induced cortisol hypersecretion.
Keywords: Adult, Cholangiography, Cholecystectomy, Female, Human, Male, Postoperative Period, Prospective Studies, Thyroxine, blood,Triiodothyronine, blood,Triiodothyronine, Reverse, blood,
It is well known that most of the peripheral triiodothyronine (T3) and reverse triiodothyronine (rT3) result from the peripheral metabolism of the thyroxine (T4) secreted by the thyroid gland. Marked reciprocal changes in circulating T3 and rT3 are induced by a variety of acute and chronic illnesses and after surgery,,. Controversy exists whether concomitant changes occur in the serum levels of T4 after surgical trauma,,. The present investigation was undertaken in order to study the changes in serum levels of T4, T3 and rT3 following uncomplicated abdominal surgery.
The study was performed on 20 patients undergoing elective cholecystectomy and intra-operative cholangiogram for gallstone disease. There were 16 females and 4 males, the mean age being 34.4 years. None had any other detectable illness and all were clinically and biochemically euthyroid. The operations were all uncomplicated, and none of the patients harboured a common bile duct calculus. The average time taken per operation was 80 minutes. None required a blood transfusion. A venous sample was taken from each patient the day before the operation, 4 hirs after surgery, and later in the post-operative period on the 1st, 3rd and 5th day. After sampling, the blood was centrifuged at 4?C and the serum was stored at-20?C until analysed. Each sample was assayed for T4, T3 and rT3 by radioimmunoassay using the commercial radioirrimunoassay kits.
Statistical analysis was performed using the Student's T test.
The results are presented in [Figure:1].
The total serum T3 value fell progressively after surgical trauma reaching its nadir at 24 hrs in the post-operative period. The changes were statistically significant (p < 0.005).
The reverse T3 (rT3) levels in serum were elevated in the present study even in the pre-operative period. However, there was a significant rise in serum rT3 with a peak at 4 hrs in the post-operative period. These changes were also statistically significant (p < 0.005).
However, there was no change in the serum T4 levels in the post-operative period as compared to the pre-operative period.
The present study demonstrated that after a surgical trauma there is a pronounced decrease in serum T3 values with a concomitant rise in rT3 values, wIlile there is no significant change in serum T4 values.
Reports regarding changes in total serum T4 levels in connection with surgery are conflicting, probably because some anaesthetic agents may release T4 from the hepatic stores. In the present study, the serum T4 values remained unchanged in the post-operative period. Similar results have been reported by Kirby et al, while others have reported decreased or significantly increased values of serum T4 levels in the post-operative period.
The changes in total serum T3 and rT3 in the present study concur with earlier reports,, which also report a fall in serum T3 values and a rise in serum rT3 values in the post-operative period. This is due to the diminished peripheral conversion of T4 to T3 with a simultaneous increase in the amount of alternate metabolite (rT3) which are, in such situations, formed preferentially. The mechanism by which such conversion of T4 is diverted to rT3 remains uncertain. It has been suggested that stress induced secretion of cortisol initiates the post-operative changes in T3, since pharmacological doses of dexamethasone have been shown to decrease serum T3 levels and increase serum rT3 levels.
However, this is unlikely as shown in a study where these changes in thyroid hormone concentrations occurred in patients undergoing surgery in whom afferent neurogenic impulses were blocked during and after operation by epidural analgesia and in whom the stress-induced increase in cortisof was abolished.
The levels of serum rT3 in all patients in the present study were high even in the pre-operative period probably because all of them were suffering from a chronic ailment. It is well recognised that the serum rT3 levels are higher in patients with chronic illnesses,.
It is concluded that since the post-surgical state is hypermetabolic, probably due to the increased secretion of cortisol, the reported alterations in serum thyroid hormone levels may indicate an adaptive mechanism against further excessive catabolism and may be considered an appropriate response to stress.