Interactions of thyroid hormones and catecholamines in severely burned patients

A prospective study of thyroid function was performed in 20 thermally injured patients. Serum levels of free thyroxine (FT4) and free 3,5,3'-triiodothyronine (FT3) were measured in 10 patients (mean age, 34 years; mean burn size, 56%) studied during a period of clinical deterioration and in 10 patients of comparable age and burn size who were clinically stable. Both FT4 and FT3 values were significantly lower in the unstable patients, P less than .01. All FT3 values for the unstable patients, 193 +/- 14 pg/dl (mean +/- SE), were beneath the normal range for FT3, 230-669 pg/dl. Interactions of thyroid hormone and catecholamines were assessed in eight additional burned patients (mean age, 31 years, mean burn size, 57%). Plasma norepinephrine correlated negatively with serum T3 (r = -.70; P less than .01). A similar reciprocal relationship was described for plasma epinephrine and serum T3 (r = -.56; P less than .025). The reciprocal relationship described for serum T3 and plasma norepinephrine and epinephrine is consistent with that of similar observations in states of clinical hypothyroidism. In conclusion, the observations of suppression of free thyroid hormone with clinical deterioration and of a reciprocal relationship between T3 and catecholamines suggest that the critically ill burned patient may be chemically hypothyroid; this may be an adaptive response to assumption of metabolic control by the sympathetic nervous system and does not result from caloric deprivation.(ABSTRACT TRUNCATED AT 250 WORDS)